Adding upstream version 110.0.1.upstream/110.0.1upstream

Signed-off-by: Daniel Baumann <daniel.baumann@progress-linux.org>

176 files changed, 24783 insertions, 0 deletions

diff --git a/third_party/rust/futures-util/src/abortable.rs b/third_party/rust/futures-util/src/abortable.rs
new file mode 100644
index 0000000000..e0afd47218
--- /dev/null
+++ b/third_party/rust/futures-util/src/abortable.rs
@@ -0,0 +1,185 @@
+use crate::task::AtomicWaker;
+use alloc::sync::Arc;
+use core::fmt;
+use core::pin::Pin;
+use core::sync::atomic::{AtomicBool, Ordering};
+use futures_core::future::Future;
+use futures_core::task::{Context, Poll};
+use futures_core::Stream;
+use pin_project_lite::pin_project;
+
+pin_project! {
+    /// A future/stream which can be remotely short-circuited using an `AbortHandle`.
+    #[derive(Debug, Clone)]
+    #[must_use = "futures/streams do nothing unless you poll them"]
+    pub struct Abortable<T> {
+        #[pin]
+        task: T,
+        inner: Arc<AbortInner>,
+    }
+}
+
+impl<T> Abortable<T> {
+    /// Creates a new `Abortable` future/stream using an existing `AbortRegistration`.
+    /// `AbortRegistration`s can be acquired through `AbortHandle::new`.
+    ///
+    /// When `abort` is called on the handle tied to `reg` or if `abort` has
+    /// already been called, the future/stream will complete immediately without making
+    /// any further progress.
+    ///
+    /// # Examples:
+    ///
+    /// Usage with futures:
+    ///
+    /// ```
+    /// # futures::executor::block_on(async {
+    /// use futures::future::{Abortable, AbortHandle, Aborted};
+    ///
+    /// let (abort_handle, abort_registration) = AbortHandle::new_pair();
+    /// let future = Abortable::new(async { 2 }, abort_registration);
+    /// abort_handle.abort();
+    /// assert_eq!(future.await, Err(Aborted));
+    /// # });
+    /// ```
+    ///
+    /// Usage with streams:
+    ///
+    /// ```
+    /// # futures::executor::block_on(async {
+    /// # use futures::future::{Abortable, AbortHandle};
+    /// # use futures::stream::{self, StreamExt};
+    ///
+    /// let (abort_handle, abort_registration) = AbortHandle::new_pair();
+    /// let mut stream = Abortable::new(stream::iter(vec![1, 2, 3]), abort_registration);
+    /// abort_handle.abort();
+    /// assert_eq!(stream.next().await, None);
+    /// # });
+    /// ```
+    pub fn new(task: T, reg: AbortRegistration) -> Self {
+        Self { task, inner: reg.inner }
+    }
+
+    /// Checks whether the task has been aborted. Note that all this
+    /// method indicates is whether [`AbortHandle::abort`] was *called*.
+    /// This means that it will return `true` even if:
+    /// * `abort` was called after the task had completed.
+    /// * `abort` was called while the task was being polled - the task may still be running and
+    /// will not be stopped until `poll` returns.
+    pub fn is_aborted(&self) -> bool {
+        self.inner.aborted.load(Ordering::Relaxed)
+    }
+}
+
+/// A registration handle for an `Abortable` task.
+/// Values of this type can be acquired from `AbortHandle::new` and are used
+/// in calls to `Abortable::new`.
+#[derive(Debug)]
+pub struct AbortRegistration {
+    pub(crate) inner: Arc<AbortInner>,
+}
+
+/// A handle to an `Abortable` task.
+#[derive(Debug, Clone)]
+pub struct AbortHandle {
+    inner: Arc<AbortInner>,
+}
+
+impl AbortHandle {
+    /// Creates an (`AbortHandle`, `AbortRegistration`) pair which can be used
+    /// to abort a running future or stream.
+    ///
+    /// This function is usually paired with a call to [`Abortable::new`].
+    pub fn new_pair() -> (Self, AbortRegistration) {
+        let inner =
+            Arc::new(AbortInner { waker: AtomicWaker::new(), aborted: AtomicBool::new(false) });
+
+        (Self { inner: inner.clone() }, AbortRegistration { inner })
+    }
+}
+
+// Inner type storing the waker to awaken and a bool indicating that it
+// should be aborted.
+#[derive(Debug)]
+pub(crate) struct AbortInner {
+    pub(crate) waker: AtomicWaker,
+    pub(crate) aborted: AtomicBool,
+}
+
+/// Indicator that the `Abortable` task was aborted.
+#[derive(Copy, Clone, Debug, Eq, PartialEq)]
+pub struct Aborted;
+
+impl fmt::Display for Aborted {
+    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
+        write!(f, "`Abortable` future has been aborted")
+    }
+}
+
+#[cfg(feature = "std")]
+impl std::error::Error for Aborted {}
+
+impl<T> Abortable<T> {
+    fn try_poll<I>(
+        mut self: Pin<&mut Self>,
+        cx: &mut Context<'_>,
+        poll: impl Fn(Pin<&mut T>, &mut Context<'_>) -> Poll<I>,
+    ) -> Poll<Result<I, Aborted>> {
+        // Check if the task has been aborted
+        if self.is_aborted() {
+            return Poll::Ready(Err(Aborted));
+        }
+
+        // attempt to complete the task
+        if let Poll::Ready(x) = poll(self.as_mut().project().task, cx) {
+            return Poll::Ready(Ok(x));
+        }
+
+        // Register to receive a wakeup if the task is aborted in the future
+        self.inner.waker.register(cx.waker());
+
+        // Check to see if the task was aborted between the first check and
+        // registration.
+        // Checking with `is_aborted` which uses `Relaxed` is sufficient because
+        // `register` introduces an `AcqRel` barrier.
+        if self.is_aborted() {
+            return Poll::Ready(Err(Aborted));
+        }
+
+        Poll::Pending
+    }
+}
+
+impl<Fut> Future for Abortable<Fut>
+where
+    Fut: Future,
+{
+    type Output = Result<Fut::Output, Aborted>;
+
+    fn poll(self: Pin<&mut Self>, cx: &mut Context<'_>) -> Poll<Self::Output> {
+        self.try_poll(cx, |fut, cx| fut.poll(cx))
+    }
+}
+
+impl<St> Stream for Abortable<St>
+where
+    St: Stream,
+{
+    type Item = St::Item;
+
+    fn poll_next(self: Pin<&mut Self>, cx: &mut Context<'_>) -> Poll<Option<Self::Item>> {
+        self.try_poll(cx, |stream, cx| stream.poll_next(cx)).map(Result::ok).map(Option::flatten)
+    }
+}
+
+impl AbortHandle {
+    /// Abort the `Abortable` stream/future associated with this handle.
+    ///
+    /// Notifies the Abortable task associated with this handle that it
+    /// should abort. Note that if the task is currently being polled on
+    /// another thread, it will not immediately stop running. Instead, it will
+    /// continue to run until its poll method returns.
+    pub fn abort(&self) {
+        self.inner.aborted.store(true, Ordering::Relaxed);
+        self.inner.waker.wake();
+    }
+}
diff --git a/third_party/rust/futures-util/src/async_await/join_mod.rs b/third_party/rust/futures-util/src/async_await/join_mod.rs
new file mode 100644
index 0000000000..28f3b232e7
--- /dev/null
+++ b/third_party/rust/futures-util/src/async_await/join_mod.rs
@@ -0,0 +1,110 @@
+//! The `join` macro.
+
+macro_rules! document_join_macro {
+    ($join:item $try_join:item) => {
+        /// Polls multiple futures simultaneously, returning a tuple
+        /// of all results once complete.
+        ///
+        /// While `join!(a, b)` is similar to `(a.await, b.await)`,
+        /// `join!` polls both futures concurrently and therefore is more efficient.
+        ///
+        /// This macro is only usable inside of async functions, closures, and blocks.
+        /// It is also gated behind the `async-await` feature of this library, which is
+        /// activated by default.
+        ///
+        /// # Examples
+        ///
+        /// ```
+        /// # futures::executor::block_on(async {
+        /// use futures::join;
+        ///
+        /// let a = async { 1 };
+        /// let b = async { 2 };
+        /// assert_eq!(join!(a, b), (1, 2));
+        ///
+        /// // `join!` is variadic, so you can pass any number of futures
+        /// let c = async { 3 };
+        /// let d = async { 4 };
+        /// let e = async { 5 };
+        /// assert_eq!(join!(c, d, e), (3, 4, 5));
+        /// # });
+        /// ```
+        $join
+
+        /// Polls multiple futures simultaneously, resolving to a [`Result`] containing
+        /// either a tuple of the successful outputs or an error.
+        ///
+        /// `try_join!` is similar to [`join!`], but completes immediately if any of
+        /// the futures return an error.
+        ///
+        /// This macro is only usable inside of async functions, closures, and blocks.
+        /// It is also gated behind the `async-await` feature of this library, which is
+        /// activated by default.
+        ///
+        /// # Examples
+        ///
+        /// When used on multiple futures that return `Ok`, `try_join!` will return
+        /// `Ok` of a tuple of the values:
+        ///
+        /// ```
+        /// # futures::executor::block_on(async {
+        /// use futures::try_join;
+        ///
+        /// let a = async { Ok::<i32, i32>(1) };
+        /// let b = async { Ok::<i32, i32>(2) };
+        /// assert_eq!(try_join!(a, b), Ok((1, 2)));
+        ///
+        /// // `try_join!` is variadic, so you can pass any number of futures
+        /// let c = async { Ok::<i32, i32>(3) };
+        /// let d = async { Ok::<i32, i32>(4) };
+        /// let e = async { Ok::<i32, i32>(5) };
+        /// assert_eq!(try_join!(c, d, e), Ok((3, 4, 5)));
+        /// # });
+        /// ```
+        ///
+        /// If one of the futures resolves to an error, `try_join!` will return
+        /// that error:
+        ///
+        /// ```
+        /// # futures::executor::block_on(async {
+        /// use futures::try_join;
+        ///
+        /// let a = async { Ok::<i32, i32>(1) };
+        /// let b = async { Err::<u64, i32>(2) };
+        ///
+        /// assert_eq!(try_join!(a, b), Err(2));
+        /// # });
+        /// ```
+        $try_join
+    }
+}
+
+#[allow(unreachable_pub)]
+#[doc(hidden)]
+pub use futures_macro::join_internal;
+
+#[allow(unreachable_pub)]
+#[doc(hidden)]
+pub use futures_macro::try_join_internal;
+
+document_join_macro! {
+    #[macro_export]
+    macro_rules! join {
+        ($($tokens:tt)*) => {{
+            use $crate::__private as __futures_crate;
+            $crate::join_internal! {
+                $( $tokens )*
+            }
+        }}
+    }
+
+    #[macro_export]
+    macro_rules! try_join {
+        ($($tokens:tt)*) => {{
+            use $crate::__private as __futures_crate;
+            $crate::try_join_internal! {
+                $( $tokens )*
+            }
+        }}
+    }
+}
diff --git a/third_party/rust/futures-util/src/async_await/mod.rs b/third_party/rust/futures-util/src/async_await/mod.rs
new file mode 100644
index 0000000000..7276da227a
--- /dev/null
+++ b/third_party/rust/futures-util/src/async_await/mod.rs
@@ -0,0 +1,58 @@
+//! Await
+//!
+//! This module contains a number of functions and combinators for working
+//! with `async`/`await` code.
+
+use futures_core::future::{FusedFuture, Future};
+use futures_core::stream::{FusedStream, Stream};
+
+#[macro_use]
+mod poll;
+#[allow(unreachable_pub)] // https://github.com/rust-lang/rust/issues/64762
+pub use self::poll::*;
+
+#[macro_use]
+mod pending;
+#[allow(unreachable_pub)] // https://github.com/rust-lang/rust/issues/64762
+pub use self::pending::*;
+
+// Primary export is a macro
+#[cfg(feature = "async-await-macro")]
+mod join_mod;
+#[allow(unreachable_pub)] // https://github.com/rust-lang/rust/issues/64762
+#[cfg(feature = "async-await-macro")]
+pub use self::join_mod::*;
+
+// Primary export is a macro
+#[cfg(feature = "async-await-macro")]
+mod select_mod;
+#[allow(unreachable_pub)] // https://github.com/rust-lang/rust/issues/64762
+#[cfg(feature = "async-await-macro")]
+pub use self::select_mod::*;
+
+// Primary export is a macro
+#[cfg(feature = "async-await-macro")]
+mod stream_select_mod;
+#[allow(unreachable_pub)] // https://github.com/rust-lang/rust/issues/64762
+#[cfg(feature = "async-await-macro")]
+pub use self::stream_select_mod::*;
+
+#[cfg(feature = "std")]
+#[cfg(feature = "async-await-macro")]
+mod random;
+#[allow(unreachable_pub)] // https://github.com/rust-lang/rust/issues/64762
+#[cfg(feature = "std")]
+#[cfg(feature = "async-await-macro")]
+pub use self::random::*;
+
+#[doc(hidden)]
+#[inline(always)]
+pub fn assert_unpin<T: Unpin>(_: &T) {}
+
+#[doc(hidden)]
+#[inline(always)]
+pub fn assert_fused_future<T: Future + FusedFuture>(_: &T) {}
+
+#[doc(hidden)]
+#[inline(always)]
+pub fn assert_fused_stream<T: Stream + FusedStream>(_: &T) {}
diff --git a/third_party/rust/futures-util/src/async_await/pending.rs b/third_party/rust/futures-util/src/async_await/pending.rs
new file mode 100644
index 0000000000..5d7a431811
--- /dev/null
+++ b/third_party/rust/futures-util/src/async_await/pending.rs
@@ -0,0 +1,43 @@
+use core::pin::Pin;
+use futures_core::future::Future;
+use futures_core::task::{Context, Poll};
+
+/// A macro which yields to the event loop once.
+///
+/// This is equivalent to returning [`Poll::Pending`](futures_core::task::Poll)
+/// from a [`Future::poll`](futures_core::future::Future::poll) implementation.
+/// Similarly, when using this macro, it must be ensured that [`wake`](std::task::Waker::wake)
+/// is called somewhere when further progress can be made.
+///
+/// This macro is only usable inside of async functions, closures, and blocks.
+/// It is also gated behind the `async-await` feature of this library, which is
+/// activated by default.
+#[macro_export]
+macro_rules! pending {
+    () => {
+        $crate::__private::async_await::pending_once().await
+    };
+}
+
+#[doc(hidden)]
+pub fn pending_once() -> PendingOnce {
+    PendingOnce { is_ready: false }
+}
+
+#[allow(missing_debug_implementations)]
+#[doc(hidden)]
+pub struct PendingOnce {
+    is_ready: bool,
+}
+
+impl Future for PendingOnce {
+    type Output = ();
+    fn poll(mut self: Pin<&mut Self>, _: &mut Context<'_>) -> Poll<Self::Output> {
+        if self.is_ready {
+            Poll::Ready(())
+        } else {
+            self.is_ready = true;
+            Poll::Pending
+        }
+    }
+}
diff --git a/third_party/rust/futures-util/src/async_await/poll.rs b/third_party/rust/futures-util/src/async_await/poll.rs
new file mode 100644
index 0000000000..b62f45a943
--- /dev/null
+++ b/third_party/rust/futures-util/src/async_await/poll.rs
@@ -0,0 +1,39 @@
+use crate::future::FutureExt;
+use core::pin::Pin;
+use futures_core::future::Future;
+use futures_core::task::{Context, Poll};
+
+/// A macro which returns the result of polling a future once within the
+/// current `async` context.
+///
+/// This macro is only usable inside of `async` functions, closures, and blocks.
+/// It is also gated behind the `async-await` feature of this library, which is
+/// activated by default.
+///
+/// If you need the result of polling a [`Stream`](crate::stream::Stream),
+/// you can use this macro with the [`next`](crate::stream::StreamExt::next) method:
+/// `poll!(stream.next())`.
+#[macro_export]
+macro_rules! poll {
+    ($x:expr $(,)?) => {
+        $crate::__private::async_await::poll($x).await
+    };
+}
+
+#[doc(hidden)]
+pub fn poll<F: Future + Unpin>(future: F) -> PollOnce<F> {
+    PollOnce { future }
+}
+
+#[allow(missing_debug_implementations)]
+#[doc(hidden)]
+pub struct PollOnce<F: Future + Unpin> {
+    future: F,
+}
+
+impl<F: Future + Unpin> Future for PollOnce<F> {
+    type Output = Poll<F::Output>;
+    fn poll(mut self: Pin<&mut Self>, cx: &mut Context<'_>) -> Poll<Self::Output> {
+        Poll::Ready(self.future.poll_unpin(cx))
+    }
+}
diff --git a/third_party/rust/futures-util/src/async_await/random.rs b/third_party/rust/futures-util/src/async_await/random.rs
new file mode 100644
index 0000000000..4f8c7254b4
--- /dev/null
+++ b/third_party/rust/futures-util/src/async_await/random.rs
@@ -0,0 +1,54 @@
+use std::{
+    cell::Cell,
+    collections::hash_map::DefaultHasher,
+    hash::Hasher,
+    num::Wrapping,
+    sync::atomic::{AtomicUsize, Ordering},
+};
+
+// Based on [Fisher–Yates shuffle].
+//
+// [Fisher–Yates shuffle]: https://en.wikipedia.org/wiki/Fisher–Yates_shuffle
+#[doc(hidden)]
+pub fn shuffle<T>(slice: &mut [T]) {
+    for i in (1..slice.len()).rev() {
+        slice.swap(i, gen_index(i + 1));
+    }
+}
+
+/// Return a value from `0..n`.
+fn gen_index(n: usize) -> usize {
+    (random() % n as u64) as usize
+}
+
+/// Pseudorandom number generator based on [xorshift*].
+///
+/// [xorshift*]: https://en.wikipedia.org/wiki/Xorshift#xorshift*
+fn random() -> u64 {
+    thread_local! {
+        static RNG: Cell<Wrapping<u64>> = Cell::new(Wrapping(prng_seed()));
+    }
+
+    fn prng_seed() -> u64 {
+        static COUNTER: AtomicUsize = AtomicUsize::new(0);
+
+        // Any non-zero seed will do
+        let mut seed = 0;
+        while seed == 0 {
+            let mut hasher = DefaultHasher::new();
+            hasher.write_usize(COUNTER.fetch_add(1, Ordering::Relaxed));
+            seed = hasher.finish();
+        }
+        seed
+    }
+
+    RNG.with(|rng| {
+        let mut x = rng.get();
+        debug_assert_ne!(x.0, 0);
+        x ^= x >> 12;
+        x ^= x << 25;
+        x ^= x >> 27;
+        rng.set(x);
+        x.0.wrapping_mul(0x2545_f491_4f6c_dd1d)
+    })
+}
diff --git a/third_party/rust/futures-util/src/async_await/select_mod.rs b/third_party/rust/futures-util/src/async_await/select_mod.rs
new file mode 100644
index 0000000000..1d13067d38
--- /dev/null
+++ b/third_party/rust/futures-util/src/async_await/select_mod.rs
@@ -0,0 +1,336 @@
+//! The `select` macro.
+
+macro_rules! document_select_macro {
+    // This branch is required for `futures 0.3.1`, from before select_biased was introduced
+    ($select:item) => {
+        /// Polls multiple futures and streams simultaneously, executing the branch
+        /// for the future that finishes first. If multiple futures are ready,
+        /// one will be pseudo-randomly selected at runtime. Futures directly
+        /// passed to `select!` must be `Unpin` and implement `FusedFuture`.
+        ///
+        /// If an expression which yields a `Future` is passed to `select!`
+        /// (e.g. an `async fn` call) instead of a `Future` by name the `Unpin`
+        /// requirement is relaxed, since the macro will pin the resulting `Future`
+        /// on the stack. However the `Future` returned by the expression must
+        /// still implement `FusedFuture`.
+        ///
+        /// Futures and streams which are not already fused can be fused using the
+        /// `.fuse()` method. Note, though, that fusing a future or stream directly
+        /// in the call to `select!` will not be enough to prevent it from being
+        /// polled after completion if the `select!` call is in a loop, so when
+        /// `select!`ing in a loop, users should take care to `fuse()` outside of
+        /// the loop.
+        ///
+        /// `select!` can be used as an expression and will return the return
+        /// value of the selected branch. For this reason the return type of every
+        /// branch in a `select!` must be the same.
+        ///
+        /// This macro is only usable inside of async functions, closures, and blocks.
+        /// It is also gated behind the `async-await` feature of this library, which is
+        /// activated by default.
+        ///
+        /// # Examples
+        ///
+        /// ```
+        /// # futures::executor::block_on(async {
+        /// use futures::future;
+        /// use futures::select;
+        /// let mut a = future::ready(4);
+        /// let mut b = future::pending::<()>();
+        ///
+        /// let res = select! {
+        ///     a_res = a => a_res + 1,
+        ///     _ = b => 0,
+        /// };
+        /// assert_eq!(res, 5);
+        /// # });
+        /// ```
+        ///
+        /// ```
+        /// # futures::executor::block_on(async {
+        /// use futures::future;
+        /// use futures::stream::{self, StreamExt};
+        /// use futures::select;
+        /// let mut st = stream::iter(vec![2]).fuse();
+        /// let mut fut = future::pending::<()>();
+        ///
+        /// select! {
+        ///     x = st.next() => assert_eq!(Some(2), x),
+        ///     _ = fut => panic!(),
+        /// };
+        /// # });
+        /// ```
+        ///
+        /// As described earlier, `select` can directly select on expressions
+        /// which return `Future`s - even if those do not implement `Unpin`:
+        ///
+        /// ```
+        /// # futures::executor::block_on(async {
+        /// use futures::future::FutureExt;
+        /// use futures::select;
+        ///
+        /// // Calling the following async fn returns a Future which does not
+        /// // implement Unpin
+        /// async fn async_identity_fn(arg: usize) -> usize {
+        ///     arg
+        /// }
+        ///
+        /// let res = select! {
+        ///     a_res = async_identity_fn(62).fuse() => a_res + 1,
+        ///     b_res = async_identity_fn(13).fuse() => b_res,
+        /// };
+        /// assert!(res == 63 || res == 13);
+        /// # });
+        /// ```
+        ///
+        /// If a similar async function is called outside of `select` to produce
+        /// a `Future`, the `Future` must be pinned in order to be able to pass
+        /// it to `select`. This can be achieved via `Box::pin` for pinning a
+        /// `Future` on the heap or the `pin_mut!` macro for pinning a `Future`
+        /// on the stack.
+        ///
+        /// ```
+        /// # futures::executor::block_on(async {
+        /// use futures::future::FutureExt;
+        /// use futures::select;
+        /// use futures::pin_mut;
+        ///
+        /// // Calling the following async fn returns a Future which does not
+        /// // implement Unpin
+        /// async fn async_identity_fn(arg: usize) -> usize {
+        ///     arg
+        /// }
+        ///
+        /// let fut_1 = async_identity_fn(1).fuse();
+        /// let fut_2 = async_identity_fn(2).fuse();
+        /// let mut fut_1 = Box::pin(fut_1); // Pins the Future on the heap
+        /// pin_mut!(fut_2); // Pins the Future on the stack
+        ///
+        /// let res = select! {
+        ///     a_res = fut_1 => a_res,
+        ///     b_res = fut_2 => b_res,
+        /// };
+        /// assert!(res == 1 || res == 2);
+        /// # });
+        /// ```
+        ///
+        /// `select` also accepts a `complete` branch and a `default` branch.
+        /// `complete` will run if all futures and streams have already been
+        /// exhausted. `default` will run if no futures or streams are
+        /// immediately ready. `complete` takes priority over `default` in
+        /// the case where all futures have completed.
+        /// A motivating use-case for passing `Future`s by name as well as for
+        /// `complete` blocks is to call `select!` in a loop, which is
+        /// demonstrated in the following example:
+        ///
+        /// ```
+        /// # futures::executor::block_on(async {
+        /// use futures::future;
+        /// use futures::select;
+        /// let mut a_fut = future::ready(4);
+        /// let mut b_fut = future::ready(6);
+        /// let mut total = 0;
+        ///
+        /// loop {
+        ///     select! {
+        ///         a = a_fut => total += a,
+        ///         b = b_fut => total += b,
+        ///         complete => break,
+        ///         default => panic!(), // never runs (futures run first, then complete)
+        ///     };
+        /// }
+        /// assert_eq!(total, 10);
+        /// # });
+        /// ```
+        ///
+        /// Note that the futures that have been matched over can still be mutated
+        /// from inside the `select!` block's branches. This can be used to implement
+        /// more complex behavior such as timer resets or writing into the head of
+        /// a stream.
+        $select
+    };
+
+    ($select:item $select_biased:item) => {
+        document_select_macro!($select);
+
+        /// Polls multiple futures and streams simultaneously, executing the branch
+        /// for the future that finishes first. Unlike [`select!`], if multiple futures are ready,
+        /// one will be selected in order of declaration. Futures directly
+        /// passed to `select_biased!` must be `Unpin` and implement `FusedFuture`.
+        ///
+        /// If an expression which yields a `Future` is passed to `select_biased!`
+        /// (e.g. an `async fn` call) instead of a `Future` by name the `Unpin`
+        /// requirement is relaxed, since the macro will pin the resulting `Future`
+        /// on the stack. However the `Future` returned by the expression must
+        /// still implement `FusedFuture`.
+        ///
+        /// Futures and streams which are not already fused can be fused using the
+        /// `.fuse()` method. Note, though, that fusing a future or stream directly
+        /// in the call to `select_biased!` will not be enough to prevent it from being
+        /// polled after completion if the `select_biased!` call is in a loop, so when
+        /// `select_biased!`ing in a loop, users should take care to `fuse()` outside of
+        /// the loop.
+        ///
+        /// `select_biased!` can be used as an expression and will return the return
+        /// value of the selected branch. For this reason the return type of every
+        /// branch in a `select_biased!` must be the same.
+        ///
+        /// This macro is only usable inside of async functions, closures, and blocks.
+        /// It is also gated behind the `async-await` feature of this library, which is
+        /// activated by default.
+        ///
+        /// # Examples
+        ///
+        /// ```
+        /// # futures::executor::block_on(async {
+        /// use futures::future;
+        /// use futures::select_biased;
+        /// let mut a = future::ready(4);
+        /// let mut b = future::pending::<()>();
+        ///
+        /// let res = select_biased! {
+        ///     a_res = a => a_res + 1,
+        ///     _ = b => 0,
+        /// };
+        /// assert_eq!(res, 5);
+        /// # });
+        /// ```
+        ///
+        /// ```
+        /// # futures::executor::block_on(async {
+        /// use futures::future;
+        /// use futures::stream::{self, StreamExt};
+        /// use futures::select_biased;
+        /// let mut st = stream::iter(vec![2]).fuse();
+        /// let mut fut = future::pending::<()>();
+        ///
+        /// select_biased! {
+        ///     x = st.next() => assert_eq!(Some(2), x),
+        ///     _ = fut => panic!(),
+        /// };
+        /// # });
+        /// ```
+        ///
+        /// As described earlier, `select_biased` can directly select on expressions
+        /// which return `Future`s - even if those do not implement `Unpin`:
+        ///
+        /// ```
+        /// # futures::executor::block_on(async {
+        /// use futures::future::FutureExt;
+        /// use futures::select_biased;
+        ///
+        /// // Calling the following async fn returns a Future which does not
+        /// // implement Unpin
+        /// async fn async_identity_fn(arg: usize) -> usize {
+        ///     arg
+        /// }
+        ///
+        /// let res = select_biased! {
+        ///     a_res = async_identity_fn(62).fuse() => a_res + 1,
+        ///     b_res = async_identity_fn(13).fuse() => b_res,
+        /// };
+        /// assert!(res == 63 || res == 12);
+        /// # });
+        /// ```
+        ///
+        /// If a similar async function is called outside of `select_biased` to produce
+        /// a `Future`, the `Future` must be pinned in order to be able to pass
+        /// it to `select_biased`. This can be achieved via `Box::pin` for pinning a
+        /// `Future` on the heap or the `pin_mut!` macro for pinning a `Future`
+        /// on the stack.
+        ///
+        /// ```
+        /// # futures::executor::block_on(async {
+        /// use futures::future::FutureExt;
+        /// use futures::select_biased;
+        /// use futures::pin_mut;
+        ///
+        /// // Calling the following async fn returns a Future which does not
+        /// // implement Unpin
+        /// async fn async_identity_fn(arg: usize) -> usize {
+        ///     arg
+        /// }
+        ///
+        /// let fut_1 = async_identity_fn(1).fuse();
+        /// let fut_2 = async_identity_fn(2).fuse();
+        /// let mut fut_1 = Box::pin(fut_1); // Pins the Future on the heap
+        /// pin_mut!(fut_2); // Pins the Future on the stack
+        ///
+        /// let res = select_biased! {
+        ///     a_res = fut_1 => a_res,
+        ///     b_res = fut_2 => b_res,
+        /// };
+        /// assert!(res == 1 || res == 2);
+        /// # });
+        /// ```
+        ///
+        /// `select_biased` also accepts a `complete` branch and a `default` branch.
+        /// `complete` will run if all futures and streams have already been
+        /// exhausted. `default` will run if no futures or streams are
+        /// immediately ready. `complete` takes priority over `default` in
+        /// the case where all futures have completed.
+        /// A motivating use-case for passing `Future`s by name as well as for
+        /// `complete` blocks is to call `select_biased!` in a loop, which is
+        /// demonstrated in the following example:
+        ///
+        /// ```
+        /// # futures::executor::block_on(async {
+        /// use futures::future;
+        /// use futures::select_biased;
+        /// let mut a_fut = future::ready(4);
+        /// let mut b_fut = future::ready(6);
+        /// let mut total = 0;
+        ///
+        /// loop {
+        ///     select_biased! {
+        ///         a = a_fut => total += a,
+        ///         b = b_fut => total += b,
+        ///         complete => break,
+        ///         default => panic!(), // never runs (futures run first, then complete)
+        ///     };
+        /// }
+        /// assert_eq!(total, 10);
+        /// # });
+        /// ```
+        ///
+        /// Note that the futures that have been matched over can still be mutated
+        /// from inside the `select_biased!` block's branches. This can be used to implement
+        /// more complex behavior such as timer resets or writing into the head of
+        /// a stream.
+        ///
+        /// [`select!`]: macro.select.html
+        $select_biased
+    };
+}
+
+#[cfg(feature = "std")]
+#[allow(unreachable_pub)]
+#[doc(hidden)]
+pub use futures_macro::select_internal;
+
+#[allow(unreachable_pub)]
+#[doc(hidden)]
+pub use futures_macro::select_biased_internal;
+
+document_select_macro! {
+    #[cfg(feature = "std")]
+    #[macro_export]
+    macro_rules! select {
+        ($($tokens:tt)*) => {{
+            use $crate::__private as __futures_crate;
+            $crate::select_internal! {
+                $( $tokens )*
+            }
+        }}
+    }
+
+    #[macro_export]
+    macro_rules! select_biased {
+        ($($tokens:tt)*) => {{
+            use $crate::__private as __futures_crate;
+            $crate::select_biased_internal! {
+                $( $tokens )*
+            }
+        }}
+    }
+}
diff --git a/third_party/rust/futures-util/src/async_await/stream_select_mod.rs b/third_party/rust/futures-util/src/async_await/stream_select_mod.rs
new file mode 100644
index 0000000000..1c8002fff3
--- /dev/null
+++ b/third_party/rust/futures-util/src/async_await/stream_select_mod.rs
@@ -0,0 +1,40 @@
+//! The `stream_select` macro.
+
+#[cfg(feature = "std")]
+#[allow(unreachable_pub)]
+#[doc(hidden)]
+pub use futures_macro::stream_select_internal;
+
+/// Combines several streams, all producing the same `Item` type, into one stream.
+/// This is similar to `select_all` but does not require the streams to all be the same type.
+/// It also keeps the streams inline, and does not require `Box<dyn Stream>`s to be allocated.
+/// Streams passed to this macro must be `Unpin`.
+///
+/// If multiple streams are ready, one will be pseudo randomly selected at runtime.
+///
+/// # Examples
+///
+/// ```
+/// # futures::executor::block_on(async {
+/// use futures::{stream, StreamExt, stream_select};
+/// let endless_ints = |i| stream::iter(vec![i].into_iter().cycle()).fuse();
+///
+/// let mut endless_numbers = stream_select!(endless_ints(1i32), endless_ints(2), endless_ints(3));
+/// match endless_numbers.next().await {
+///     Some(1) => println!("Got a 1"),
+///     Some(2) => println!("Got a 2"),
+///     Some(3) => println!("Got a 3"),
+///     _ => unreachable!(),
+/// }
+/// # });
+/// ```
+#[cfg(feature = "std")]
+#[macro_export]
+macro_rules! stream_select {
+    ($($tokens:tt)*) => {{
+        use $crate::__private as __futures_crate;
+        $crate::stream_select_internal! {
+            $( $tokens )*
+        }
+    }}
+}
diff --git a/third_party/rust/futures-util/src/compat/compat01as03.rs b/third_party/rust/futures-util/src/compat/compat01as03.rs
new file mode 100644
index 0000000000..36de1da98d
--- /dev/null
+++ b/third_party/rust/futures-util/src/compat/compat01as03.rs
@@ -0,0 +1,454 @@
+use futures_01::executor::{
+    spawn as spawn01, Notify as Notify01, NotifyHandle as NotifyHandle01, Spawn as Spawn01,
+    UnsafeNotify as UnsafeNotify01,
+};
+use futures_01::{Async as Async01, Future as Future01, Stream as Stream01};
+#[cfg(feature = "sink")]
+use futures_01::{AsyncSink as AsyncSink01, Sink as Sink01};
+use futures_core::{future::Future as Future03, stream::Stream as Stream03, task as task03};
+#[cfg(feature = "sink")]
+use futures_sink::Sink as Sink03;
+use std::pin::Pin;
+use std::task::Context;
+
+#[cfg(feature = "io-compat")]
+#[cfg_attr(docsrs, doc(cfg(feature = "io-compat")))]
+#[allow(unreachable_pub)] // https://github.com/rust-lang/rust/issues/57411
+pub use io::{AsyncRead01CompatExt, AsyncWrite01CompatExt};
+
+/// Converts a futures 0.1 Future, Stream, AsyncRead, or AsyncWrite
+/// object to a futures 0.3-compatible version,
+#[derive(Debug)]
+#[must_use = "futures do nothing unless you `.await` or poll them"]
+pub struct Compat01As03<T> {
+    pub(crate) inner: Spawn01<T>,
+}
+
+impl<T> Unpin for Compat01As03<T> {}
+
+impl<T> Compat01As03<T> {
+    /// Wraps a futures 0.1 Future, Stream, AsyncRead, or AsyncWrite
+    /// object in a futures 0.3-compatible wrapper.
+    pub fn new(object: T) -> Self {
+        Self { inner: spawn01(object) }
+    }
+
+    fn in_notify<R>(&mut self, cx: &mut Context<'_>, f: impl FnOnce(&mut T) -> R) -> R {
+        let notify = &WakerToHandle(cx.waker());
+        self.inner.poll_fn_notify(notify, 0, f)
+    }
+
+    /// Get a reference to 0.1 Future, Stream, AsyncRead, or AsyncWrite object contained within.
+    pub fn get_ref(&self) -> &T {
+        self.inner.get_ref()
+    }
+
+    /// Get a mutable reference to 0.1 Future, Stream, AsyncRead or AsyncWrite object contained
+    /// within.
+    pub fn get_mut(&mut self) -> &mut T {
+        self.inner.get_mut()
+    }
+
+    /// Consume this wrapper to return the underlying 0.1 Future, Stream, AsyncRead, or
+    /// AsyncWrite object.
+    pub fn into_inner(self) -> T {
+        self.inner.into_inner()
+    }
+}
+
+/// Extension trait for futures 0.1 [`Future`](futures_01::future::Future)
+pub trait Future01CompatExt: Future01 {
+    /// Converts a futures 0.1
+    /// [`Future<Item = T, Error = E>`](futures_01::future::Future)
+    /// into a futures 0.3
+    /// [`Future<Output = Result<T, E>>`](futures_core::future::Future).
+    ///
+    /// ```
+    /// # if cfg!(miri) { return; } // https://github.com/rust-lang/futures-rs/issues/2514
+    /// # futures::executor::block_on(async {
+    /// # // TODO: These should be all using `futures::compat`, but that runs up against Cargo
+    /// # // feature issues
+    /// use futures_util::compat::Future01CompatExt;
+    ///
+    /// let future = futures_01::future::ok::<u32, ()>(1);
+    /// assert_eq!(future.compat().await, Ok(1));
+    /// # });
+    /// ```
+    fn compat(self) -> Compat01As03<Self>
+    where
+        Self: Sized,
+    {
+        Compat01As03::new(self)
+    }
+}
+impl<Fut: Future01> Future01CompatExt for Fut {}
+
+/// Extension trait for futures 0.1 [`Stream`](futures_01::stream::Stream)
+pub trait Stream01CompatExt: Stream01 {
+    /// Converts a futures 0.1
+    /// [`Stream<Item = T, Error = E>`](futures_01::stream::Stream)
+    /// into a futures 0.3
+    /// [`Stream<Item = Result<T, E>>`](futures_core::stream::Stream).
+    ///
+    /// ```
+    /// # if cfg!(miri) { return; } // https://github.com/rust-lang/futures-rs/issues/2514
+    /// # futures::executor::block_on(async {
+    /// use futures::stream::StreamExt;
+    /// use futures_util::compat::Stream01CompatExt;
+    ///
+    /// let stream = futures_01::stream::once::<u32, ()>(Ok(1));
+    /// let mut stream = stream.compat();
+    /// assert_eq!(stream.next().await, Some(Ok(1)));
+    /// assert_eq!(stream.next().await, None);
+    /// # });
+    /// ```
+    fn compat(self) -> Compat01As03<Self>
+    where
+        Self: Sized,
+    {
+        Compat01As03::new(self)
+    }
+}
+impl<St: Stream01> Stream01CompatExt for St {}
+
+/// Extension trait for futures 0.1 [`Sink`](futures_01::sink::Sink)
+#[cfg(feature = "sink")]
+#[cfg_attr(docsrs, doc(cfg(feature = "sink")))]
+pub trait Sink01CompatExt: Sink01 {
+    /// Converts a futures 0.1
+    /// [`Sink<SinkItem = T, SinkError = E>`](futures_01::sink::Sink)
+    /// into a futures 0.3
+    /// [`Sink<T, Error = E>`](futures_sink::Sink).
+    ///
+    /// ```
+    /// # if cfg!(miri) { return; } // https://github.com/rust-lang/futures-rs/issues/2514
+    /// # futures::executor::block_on(async {
+    /// use futures::{sink::SinkExt, stream::StreamExt};
+    /// use futures_util::compat::{Stream01CompatExt, Sink01CompatExt};
+    ///
+    /// let (tx, rx) = futures_01::unsync::mpsc::channel(1);
+    /// let (mut tx, mut rx) = (tx.sink_compat(), rx.compat());
+    ///
+    /// tx.send(1).await.unwrap();
+    /// drop(tx);
+    /// assert_eq!(rx.next().await, Some(Ok(1)));
+    /// assert_eq!(rx.next().await, None);
+    /// # });
+    /// ```
+    fn sink_compat(self) -> Compat01As03Sink<Self, Self::SinkItem>
+    where
+        Self: Sized,
+    {
+        Compat01As03Sink::new(self)
+    }
+}
+#[cfg(feature = "sink")]
+impl<Si: Sink01> Sink01CompatExt for Si {}
+
+fn poll_01_to_03<T, E>(x: Result<Async01<T>, E>) -> task03::Poll<Result<T, E>> {
+    match x? {
+        Async01::Ready(t) => task03::Poll::Ready(Ok(t)),
+        Async01::NotReady => task03::Poll::Pending,
+    }
+}
+
+impl<Fut: Future01> Future03 for Compat01As03<Fut> {
+    type Output = Result<Fut::Item, Fut::Error>;
+
+    fn poll(mut self: Pin<&mut Self>, cx: &mut Context<'_>) -> task03::Poll<Self::Output> {
+        poll_01_to_03(self.in_notify(cx, Future01::poll))
+    }
+}
+
+impl<St: Stream01> Stream03 for Compat01As03<St> {
+    type Item = Result<St::Item, St::Error>;
+
+    fn poll_next(
+        mut self: Pin<&mut Self>,
+        cx: &mut Context<'_>,
+    ) -> task03::Poll<Option<Self::Item>> {
+        match self.in_notify(cx, Stream01::poll)? {
+            Async01::Ready(Some(t)) => task03::Poll::Ready(Some(Ok(t))),
+            Async01::Ready(None) => task03::Poll::Ready(None),
+            Async01::NotReady => task03::Poll::Pending,
+        }
+    }
+}
+
+/// Converts a futures 0.1 Sink object to a futures 0.3-compatible version
+#[cfg(feature = "sink")]
+#[cfg_attr(docsrs, doc(cfg(feature = "sink")))]
+#[derive(Debug)]
+#[must_use = "sinks do nothing unless polled"]
+pub struct Compat01As03Sink<S, SinkItem> {
+    pub(crate) inner: Spawn01<S>,
+    pub(crate) buffer: Option<SinkItem>,
+    pub(crate) close_started: bool,
+}
+
+#[cfg(feature = "sink")]
+impl<S, SinkItem> Unpin for Compat01As03Sink<S, SinkItem> {}
+
+#[cfg(feature = "sink")]
+impl<S, SinkItem> Compat01As03Sink<S, SinkItem> {
+    /// Wraps a futures 0.1 Sink object in a futures 0.3-compatible wrapper.
+    pub fn new(inner: S) -> Self {
+        Self { inner: spawn01(inner), buffer: None, close_started: false }
+    }
+
+    fn in_notify<R>(&mut self, cx: &mut Context<'_>, f: impl FnOnce(&mut S) -> R) -> R {
+        let notify = &WakerToHandle(cx.waker());
+        self.inner.poll_fn_notify(notify, 0, f)
+    }
+
+    /// Get a reference to 0.1 Sink object contained within.
+    pub fn get_ref(&self) -> &S {
+        self.inner.get_ref()
+    }
+
+    /// Get a mutable reference to 0.1 Sink contained within.
+    pub fn get_mut(&mut self) -> &mut S {
+        self.inner.get_mut()
+    }
+
+    /// Consume this wrapper to return the underlying 0.1 Sink.
+    pub fn into_inner(self) -> S {
+        self.inner.into_inner()
+    }
+}
+
+#[cfg(feature = "sink")]
+impl<S, SinkItem> Stream03 for Compat01As03Sink<S, SinkItem>
+where
+    S: Stream01,
+{
+    type Item = Result<S::Item, S::Error>;
+
+    fn poll_next(
+        mut self: Pin<&mut Self>,
+        cx: &mut Context<'_>,
+    ) -> task03::Poll<Option<Self::Item>> {
+        match self.in_notify(cx, Stream01::poll)? {
+            Async01::Ready(Some(t)) => task03::Poll::Ready(Some(Ok(t))),
+            Async01::Ready(None) => task03::Poll::Ready(None),
+            Async01::NotReady => task03::Poll::Pending,
+        }
+    }
+}
+
+#[cfg(feature = "sink")]
+impl<S, SinkItem> Sink03<SinkItem> for Compat01As03Sink<S, SinkItem>
+where
+    S: Sink01<SinkItem = SinkItem>,
+{
+    type Error = S::SinkError;
+
+    fn start_send(mut self: Pin<&mut Self>, item: SinkItem) -> Result<(), Self::Error> {
+        debug_assert!(self.buffer.is_none());
+        self.buffer = Some(item);
+        Ok(())
+    }
+
+    fn poll_ready(
+        mut self: Pin<&mut Self>,
+        cx: &mut Context<'_>,
+    ) -> task03::Poll<Result<(), Self::Error>> {
+        match self.buffer.take() {
+            Some(item) => match self.in_notify(cx, |f| f.start_send(item))? {
+                AsyncSink01::Ready => task03::Poll::Ready(Ok(())),
+                AsyncSink01::NotReady(i) => {
+                    self.buffer = Some(i);
+                    task03::Poll::Pending
+                }
+            },
+            None => task03::Poll::Ready(Ok(())),
+        }
+    }
+
+    fn poll_flush(
+        mut self: Pin<&mut Self>,
+        cx: &mut Context<'_>,
+    ) -> task03::Poll<Result<(), Self::Error>> {
+        let item = self.buffer.take();
+        match self.in_notify(cx, |f| match item {
+            Some(i) => match f.start_send(i)? {
+                AsyncSink01::Ready => f.poll_complete().map(|i| (i, None)),
+                AsyncSink01::NotReady(t) => Ok((Async01::NotReady, Some(t))),
+            },
+            None => f.poll_complete().map(|i| (i, None)),
+        })? {
+            (Async01::Ready(_), _) => task03::Poll::Ready(Ok(())),
+            (Async01::NotReady, item) => {
+                self.buffer = item;
+                task03::Poll::Pending
+            }
+        }
+    }
+
+    fn poll_close(
+        mut self: Pin<&mut Self>,
+        cx: &mut Context<'_>,
+    ) -> task03::Poll<Result<(), Self::Error>> {
+        let item = self.buffer.take();
+        let close_started = self.close_started;
+
+        let result = self.in_notify(cx, |f| {
+            if !close_started {
+                if let Some(item) = item {
+                    if let AsyncSink01::NotReady(item) = f.start_send(item)? {
+                        return Ok((Async01::NotReady, Some(item), false));
+                    }
+                }
+
+                if let Async01::NotReady = f.poll_complete()? {
+                    return Ok((Async01::NotReady, None, false));
+                }
+            }
+
+            Ok((<S as Sink01>::close(f)?, None, true))
+        });
+
+        match result? {
+            (Async01::Ready(_), _, _) => task03::Poll::Ready(Ok(())),
+            (Async01::NotReady, item, close_started) => {
+                self.buffer = item;
+                self.close_started = close_started;
+                task03::Poll::Pending
+            }
+        }
+    }
+}
+
+struct NotifyWaker(task03::Waker);
+
+#[allow(missing_debug_implementations)] // false positive: this is private type
+#[derive(Clone)]
+struct WakerToHandle<'a>(&'a task03::Waker);
+
+impl From<WakerToHandle<'_>> for NotifyHandle01 {
+    fn from(handle: WakerToHandle<'_>) -> Self {
+        let ptr = Box::new(NotifyWaker(handle.0.clone()));
+
+        unsafe { Self::new(Box::into_raw(ptr)) }
+    }
+}
+
+impl Notify01 for NotifyWaker {
+    fn notify(&self, _: usize) {
+        self.0.wake_by_ref();
+    }
+}
+
+unsafe impl UnsafeNotify01 for NotifyWaker {
+    unsafe fn clone_raw(&self) -> NotifyHandle01 {
+        WakerToHandle(&self.0).into()
+    }
+
+    unsafe fn drop_raw(&self) {
+        let ptr: *const dyn UnsafeNotify01 = self;
+        drop(Box::from_raw(ptr as *mut dyn UnsafeNotify01));
+    }
+}
+
+#[cfg(feature = "io-compat")]
+#[cfg_attr(docsrs, doc(cfg(feature = "io-compat")))]
+mod io {
+    use super::*;
+    use futures_io::{AsyncRead as AsyncRead03, AsyncWrite as AsyncWrite03};
+    use std::io::Error;
+    use tokio_io::{AsyncRead as AsyncRead01, AsyncWrite as AsyncWrite01};
+
+    /// Extension trait for tokio-io [`AsyncRead`](tokio_io::AsyncRead)
+    #[cfg_attr(docsrs, doc(cfg(feature = "io-compat")))]
+    pub trait AsyncRead01CompatExt: AsyncRead01 {
+        /// Converts a tokio-io [`AsyncRead`](tokio_io::AsyncRead) into a futures-io 0.3
+        /// [`AsyncRead`](futures_io::AsyncRead).
+        ///
+        /// ```
+        /// # if cfg!(miri) { return; } // https://github.com/rust-lang/futures-rs/issues/2514
+        /// # futures::executor::block_on(async {
+        /// use futures::io::AsyncReadExt;
+        /// use futures_util::compat::AsyncRead01CompatExt;
+        ///
+        /// let input = b"Hello World!";
+        /// let reader /* : impl tokio_io::AsyncRead */ = std::io::Cursor::new(input);
+        /// let mut reader /* : impl futures::io::AsyncRead + Unpin */ = reader.compat();
+        ///
+        /// let mut output = Vec::with_capacity(12);
+        /// reader.read_to_end(&mut output).await.unwrap();
+        /// assert_eq!(output, input);
+        /// # });
+        /// ```
+        fn compat(self) -> Compat01As03<Self>
+        where
+            Self: Sized,
+        {
+            Compat01As03::new(self)
+        }
+    }
+    impl<R: AsyncRead01> AsyncRead01CompatExt for R {}
+
+    /// Extension trait for tokio-io [`AsyncWrite`](tokio_io::AsyncWrite)
+    #[cfg_attr(docsrs, doc(cfg(feature = "io-compat")))]
+    pub trait AsyncWrite01CompatExt: AsyncWrite01 {
+        /// Converts a tokio-io [`AsyncWrite`](tokio_io::AsyncWrite) into a futures-io 0.3
+        /// [`AsyncWrite`](futures_io::AsyncWrite).
+        ///
+        /// ```
+        /// # if cfg!(miri) { return; } // https://github.com/rust-lang/futures-rs/issues/2514
+        /// # futures::executor::block_on(async {
+        /// use futures::io::AsyncWriteExt;
+        /// use futures_util::compat::AsyncWrite01CompatExt;
+        ///
+        /// let input = b"Hello World!";
+        /// let mut cursor = std::io::Cursor::new(Vec::with_capacity(12));
+        ///
+        /// let mut writer = (&mut cursor).compat();
+        /// writer.write_all(input).await.unwrap();
+        ///
+        /// assert_eq!(cursor.into_inner(), input);
+        /// # });
+        /// ```
+        fn compat(self) -> Compat01As03<Self>
+        where
+            Self: Sized,
+        {
+            Compat01As03::new(self)
+        }
+    }
+    impl<W: AsyncWrite01> AsyncWrite01CompatExt for W {}
+
+    impl<R: AsyncRead01> AsyncRead03 for Compat01As03<R> {
+        fn poll_read(
+            mut self: Pin<&mut Self>,
+            cx: &mut Context<'_>,
+            buf: &mut [u8],
+        ) -> task03::Poll<Result<usize, Error>> {
+            poll_01_to_03(self.in_notify(cx, |x| x.poll_read(buf)))
+        }
+    }
+
+    impl<W: AsyncWrite01> AsyncWrite03 for Compat01As03<W> {
+        fn poll_write(
+            mut self: Pin<&mut Self>,
+            cx: &mut Context<'_>,
+            buf: &[u8],
+        ) -> task03::Poll<Result<usize, Error>> {
+            poll_01_to_03(self.in_notify(cx, |x| x.poll_write(buf)))
+        }
+
+        fn poll_flush(
+            mut self: Pin<&mut Self>,
+            cx: &mut Context<'_>,
+        ) -> task03::Poll<Result<(), Error>> {
+            poll_01_to_03(self.in_notify(cx, AsyncWrite01::poll_flush))
+        }
+
+        fn poll_close(
+            mut self: Pin<&mut Self>,
+            cx: &mut Context<'_>,
+        ) -> task03::Poll<Result<(), Error>> {
+            poll_01_to_03(self.in_notify(cx, AsyncWrite01::shutdown))
+        }
+    }
+}
diff --git a/third_party/rust/futures-util/src/compat/compat03as01.rs b/third_party/rust/futures-util/src/compat/compat03as01.rs
new file mode 100644
index 0000000000..5d3a6e920b
--- /dev/null
+++ b/third_party/rust/futures-util/src/compat/compat03as01.rs
@@ -0,0 +1,265 @@
+use crate::task::{self as task03, ArcWake as ArcWake03, WakerRef};
+use futures_01::{
+    task as task01, Async as Async01, Future as Future01, Poll as Poll01, Stream as Stream01,
+};
+#[cfg(feature = "sink")]
+use futures_01::{AsyncSink as AsyncSink01, Sink as Sink01, StartSend as StartSend01};
+use futures_core::{
+    future::TryFuture as TryFuture03,
+    stream::TryStream as TryStream03,
+    task::{RawWaker, RawWakerVTable},
+};
+#[cfg(feature = "sink")]
+use futures_sink::Sink as Sink03;
+#[cfg(feature = "sink")]
+use std::marker::PhantomData;
+use std::{mem, pin::Pin, sync::Arc, task::Context};
+
+/// Converts a futures 0.3 [`TryFuture`](futures_core::future::TryFuture) or
+/// [`TryStream`](futures_core::stream::TryStream) into a futures 0.1
+/// [`Future`](futures_01::future::Future) or
+/// [`Stream`](futures_01::stream::Stream).
+#[derive(Debug, Clone, Copy)]
+#[must_use = "futures do nothing unless you `.await` or poll them"]
+pub struct Compat<T> {
+    pub(crate) inner: T,
+}
+
+/// Converts a futures 0.3 [`Sink`](futures_sink::Sink) into a futures 0.1
+/// [`Sink`](futures_01::sink::Sink).
+#[cfg(feature = "sink")]
+#[cfg_attr(docsrs, doc(cfg(feature = "sink")))]
+#[derive(Debug)]
+#[must_use = "sinks do nothing unless polled"]
+pub struct CompatSink<T, Item> {
+    inner: T,
+    _phantom: PhantomData<fn(Item)>,
+}
+
+impl<T> Compat<T> {
+    /// Creates a new [`Compat`].
+    ///
+    /// For types which implement appropriate futures `0.3`
+    /// traits, the result will be a type which implements
+    /// the corresponding futures 0.1 type.
+    pub fn new(inner: T) -> Self {
+        Self { inner }
+    }
+
+    /// Get a reference to 0.3 Future, Stream, AsyncRead, or AsyncWrite object
+    /// contained within.
+    pub fn get_ref(&self) -> &T {
+        &self.inner
+    }
+
+    /// Get a mutable reference to 0.3 Future, Stream, AsyncRead, or AsyncWrite object
+    /// contained within.
+    pub fn get_mut(&mut self) -> &mut T {
+        &mut self.inner
+    }
+
+    /// Returns the inner item.
+    pub fn into_inner(self) -> T {
+        self.inner
+    }
+}
+
+#[cfg(feature = "sink")]
+impl<T, Item> CompatSink<T, Item> {
+    /// Creates a new [`CompatSink`].
+    pub fn new(inner: T) -> Self {
+        Self { inner, _phantom: PhantomData }
+    }
+
+    /// Get a reference to 0.3 Sink contained within.
+    pub fn get_ref(&self) -> &T {
+        &self.inner
+    }
+
+    /// Get a mutable reference to 0.3 Sink contained within.
+    pub fn get_mut(&mut self) -> &mut T {
+        &mut self.inner
+    }
+
+    /// Returns the inner item.
+    pub fn into_inner(self) -> T {
+        self.inner
+    }
+}
+
+fn poll_03_to_01<T, E>(x: task03::Poll<Result<T, E>>) -> Result<Async01<T>, E> {
+    match x? {
+        task03::Poll::Ready(t) => Ok(Async01::Ready(t)),
+        task03::Poll::Pending => Ok(Async01::NotReady),
+    }
+}
+
+impl<Fut> Future01 for Compat<Fut>
+where
+    Fut: TryFuture03 + Unpin,
+{
+    type Item = Fut::Ok;
+    type Error = Fut::Error;
+
+    fn poll(&mut self) -> Poll01<Self::Item, Self::Error> {
+        with_context(self, |inner, cx| poll_03_to_01(inner.try_poll(cx)))
+    }
+}
+
+impl<St> Stream01 for Compat<St>
+where
+    St: TryStream03 + Unpin,
+{
+    type Item = St::Ok;
+    type Error = St::Error;
+
+    fn poll(&mut self) -> Poll01<Option<Self::Item>, Self::Error> {
+        with_context(self, |inner, cx| match inner.try_poll_next(cx)? {
+            task03::Poll::Ready(None) => Ok(Async01::Ready(None)),
+            task03::Poll::Ready(Some(t)) => Ok(Async01::Ready(Some(t))),
+            task03::Poll::Pending => Ok(Async01::NotReady),
+        })
+    }
+}
+
+#[cfg(feature = "sink")]
+impl<T, Item> Sink01 for CompatSink<T, Item>
+where
+    T: Sink03<Item> + Unpin,
+{
+    type SinkItem = Item;
+    type SinkError = T::Error;
+
+    fn start_send(&mut self, item: Self::SinkItem) -> StartSend01<Self::SinkItem, Self::SinkError> {
+        with_sink_context(self, |mut inner, cx| match inner.as_mut().poll_ready(cx)? {
+            task03::Poll::Ready(()) => inner.start_send(item).map(|()| AsyncSink01::Ready),
+            task03::Poll::Pending => Ok(AsyncSink01::NotReady(item)),
+        })
+    }
+
+    fn poll_complete(&mut self) -> Poll01<(), Self::SinkError> {
+        with_sink_context(self, |inner, cx| poll_03_to_01(inner.poll_flush(cx)))
+    }
+
+    fn close(&mut self) -> Poll01<(), Self::SinkError> {
+        with_sink_context(self, |inner, cx| poll_03_to_01(inner.poll_close(cx)))
+    }
+}
+
+#[derive(Clone)]
+struct Current(task01::Task);
+
+impl Current {
+    fn new() -> Self {
+        Self(task01::current())
+    }
+
+    fn as_waker(&self) -> WakerRef<'_> {
+        unsafe fn ptr_to_current<'a>(ptr: *const ()) -> &'a Current {
+            &*(ptr as *const Current)
+        }
+        fn current_to_ptr(current: &Current) -> *const () {
+            current as *const Current as *const ()
+        }
+
+        unsafe fn clone(ptr: *const ()) -> RawWaker {
+            // Lazily create the `Arc` only when the waker is actually cloned.
+            // FIXME: remove `transmute` when a `Waker` -> `RawWaker` conversion
+            // function is landed in `core`.
+            mem::transmute::<task03::Waker, RawWaker>(task03::waker(Arc::new(
+                ptr_to_current(ptr).clone(),
+            )))
+        }
+        unsafe fn drop(_: *const ()) {}
+        unsafe fn wake(ptr: *const ()) {
+            ptr_to_current(ptr).0.notify()
+        }
+
+        let ptr = current_to_ptr(self);
+        let vtable = &RawWakerVTable::new(clone, wake, wake, drop);
+        WakerRef::new_unowned(std::mem::ManuallyDrop::new(unsafe {
+            task03::Waker::from_raw(RawWaker::new(ptr, vtable))
+        }))
+    }
+}
+
+impl ArcWake03 for Current {
+    fn wake_by_ref(arc_self: &Arc<Self>) {
+        arc_self.0.notify();
+    }
+}
+
+fn with_context<T, R, F>(compat: &mut Compat<T>, f: F) -> R
+where
+    T: Unpin,
+    F: FnOnce(Pin<&mut T>, &mut Context<'_>) -> R,
+{
+    let current = Current::new();
+    let waker = current.as_waker();
+    let mut cx = Context::from_waker(&waker);
+    f(Pin::new(&mut compat.inner), &mut cx)
+}
+
+#[cfg(feature = "sink")]
+fn with_sink_context<T, Item, R, F>(compat: &mut CompatSink<T, Item>, f: F) -> R
+where
+    T: Unpin,
+    F: FnOnce(Pin<&mut T>, &mut Context<'_>) -> R,
+{
+    let current = Current::new();
+    let waker = current.as_waker();
+    let mut cx = Context::from_waker(&waker);
+    f(Pin::new(&mut compat.inner), &mut cx)
+}
+
+#[cfg(feature = "io-compat")]
+#[cfg_attr(docsrs, doc(cfg(feature = "io-compat")))]
+mod io {
+    use super::*;
+    use futures_io::{AsyncRead as AsyncRead03, AsyncWrite as AsyncWrite03};
+    use tokio_io::{AsyncRead as AsyncRead01, AsyncWrite as AsyncWrite01};
+
+    fn poll_03_to_io<T>(x: task03::Poll<Result<T, std::io::Error>>) -> Result<T, std::io::Error> {
+        match x {
+            task03::Poll::Ready(Ok(t)) => Ok(t),
+            task03::Poll::Pending => Err(std::io::ErrorKind::WouldBlock.into()),
+            task03::Poll::Ready(Err(e)) => Err(e),
+        }
+    }
+
+    impl<R: AsyncRead03 + Unpin> std::io::Read for Compat<R> {
+        fn read(&mut self, buf: &mut [u8]) -> std::io::Result<usize> {
+            let current = Current::new();
+            let waker = current.as_waker();
+            let mut cx = Context::from_waker(&waker);
+            poll_03_to_io(Pin::new(&mut self.inner).poll_read(&mut cx, buf))
+        }
+    }
+
+    impl<R: AsyncRead03 + Unpin> AsyncRead01 for Compat<R> {}
+
+    impl<W: AsyncWrite03 + Unpin> std::io::Write for Compat<W> {
+        fn write(&mut self, buf: &[u8]) -> std::io::Result<usize> {
+            let current = Current::new();
+            let waker = current.as_waker();
+            let mut cx = Context::from_waker(&waker);
+            poll_03_to_io(Pin::new(&mut self.inner).poll_write(&mut cx, buf))
+        }
+
+        fn flush(&mut self) -> std::io::Result<()> {
+            let current = Current::new();
+            let waker = current.as_waker();
+            let mut cx = Context::from_waker(&waker);
+            poll_03_to_io(Pin::new(&mut self.inner).poll_flush(&mut cx))
+        }
+    }
+
+    impl<W: AsyncWrite03 + Unpin> AsyncWrite01 for Compat<W> {
+        fn shutdown(&mut self) -> std::io::Result<Async01<()>> {
+            let current = Current::new();
+            let waker = current.as_waker();
+            let mut cx = Context::from_waker(&waker);
+            poll_03_to_01(Pin::new(&mut self.inner).poll_close(&mut cx))
+        }
+    }
+}
diff --git a/third_party/rust/futures-util/src/compat/executor.rs b/third_party/rust/futures-util/src/compat/executor.rs
new file mode 100644
index 0000000000..ea0c67a0ae
--- /dev/null
+++ b/third_party/rust/futures-util/src/compat/executor.rs
@@ -0,0 +1,86 @@
+use super::{Compat, Future01CompatExt};
+use crate::{
+    future::{FutureExt, TryFutureExt, UnitError},
+    task::SpawnExt,
+};
+use futures_01::future::{ExecuteError as ExecuteError01, Executor as Executor01};
+use futures_01::Future as Future01;
+use futures_task::{FutureObj, Spawn as Spawn03, SpawnError as SpawnError03};
+
+/// A future that can run on a futures 0.1
+/// [`Executor`](futures_01::future::Executor).
+pub type Executor01Future = Compat<UnitError<FutureObj<'static, ()>>>;
+
+/// Extension trait for futures 0.1 [`Executor`](futures_01::future::Executor).
+pub trait Executor01CompatExt: Executor01<Executor01Future> + Clone + Send + 'static {
+    /// Converts a futures 0.1 [`Executor`](futures_01::future::Executor) into a
+    /// futures 0.3 [`Spawn`](futures_task::Spawn).
+    ///
+    /// ```
+    /// # if cfg!(miri) { return; } // Miri does not support epoll
+    /// use futures::task::SpawnExt;
+    /// use futures::future::{FutureExt, TryFutureExt};
+    /// use futures_util::compat::Executor01CompatExt;
+    /// use tokio::executor::DefaultExecutor;
+    ///
+    /// # let (tx, rx) = futures::channel::oneshot::channel();
+    ///
+    /// let spawner = DefaultExecutor::current().compat();
+    /// let future03 = async move {
+    ///     println!("Running on the pool");
+    ///     spawner.spawn(async {
+    ///         println!("Spawned!");
+    ///         # tx.send(42).unwrap();
+    ///     }).unwrap();
+    /// };
+    ///
+    /// let future01 = future03.unit_error().boxed().compat();
+    ///
+    /// tokio::run(future01);
+    /// # futures::executor::block_on(rx).unwrap();
+    /// ```
+    fn compat(self) -> Executor01As03<Self>
+    where
+        Self: Sized;
+}
+
+impl<Ex> Executor01CompatExt for Ex
+where
+    Ex: Executor01<Executor01Future> + Clone + Send + 'static,
+{
+    fn compat(self) -> Executor01As03<Self> {
+        Executor01As03 { executor01: self }
+    }
+}
+
+/// Converts a futures 0.1 [`Executor`](futures_01::future::Executor) into a
+/// futures 0.3 [`Spawn`](futures_task::Spawn).
+#[derive(Debug, Clone)]
+pub struct Executor01As03<Ex> {
+    executor01: Ex,
+}
+
+impl<Ex> Spawn03 for Executor01As03<Ex>
+where
+    Ex: Executor01<Executor01Future> + Clone + Send + 'static,
+{
+    fn spawn_obj(&self, future: FutureObj<'static, ()>) -> Result<(), SpawnError03> {
+        let future = future.unit_error().compat();
+
+        self.executor01.execute(future).map_err(|_| SpawnError03::shutdown())
+    }
+}
+
+#[allow(single_use_lifetimes)] // https://github.com/rust-lang/rust/issues/55058
+impl<Sp, Fut> Executor01<Fut> for Compat<Sp>
+where
+    for<'a> &'a Sp: Spawn03,
+    Fut: Future01<Item = (), Error = ()> + Send + 'static,
+{
+    fn execute(&self, future: Fut) -> Result<(), ExecuteError01<Fut>> {
+        (&self.inner)
+            .spawn(future.compat().map(|_| ()))
+            .expect("unable to spawn future from Compat executor");
+        Ok(())
+    }
+}
diff --git a/third_party/rust/futures-util/src/compat/mod.rs b/third_party/rust/futures-util/src/compat/mod.rs
new file mode 100644
index 0000000000..4812803eb6
--- /dev/null
+++ b/third_party/rust/futures-util/src/compat/mod.rs
@@ -0,0 +1,22 @@
+//! Interop between `futures` 0.1 and 0.3.
+//!
+//! This module is only available when the `compat` feature of this
+//! library is activated.
+
+mod executor;
+pub use self::executor::{Executor01As03, Executor01CompatExt, Executor01Future};
+
+mod compat01as03;
+#[cfg(feature = "io-compat")]
+#[cfg_attr(docsrs, doc(cfg(feature = "io-compat")))]
+pub use self::compat01as03::{AsyncRead01CompatExt, AsyncWrite01CompatExt};
+pub use self::compat01as03::{Compat01As03, Future01CompatExt, Stream01CompatExt};
+#[cfg(feature = "sink")]
+#[cfg_attr(docsrs, doc(cfg(feature = "sink")))]
+pub use self::compat01as03::{Compat01As03Sink, Sink01CompatExt};
+
+mod compat03as01;
+pub use self::compat03as01::Compat;
+#[cfg(feature = "sink")]
+#[cfg_attr(docsrs, doc(cfg(feature = "sink")))]
+pub use self::compat03as01::CompatSink;
diff --git a/third_party/rust/futures-util/src/fns.rs b/third_party/rust/futures-util/src/fns.rs
new file mode 100644
index 0000000000..37ee03e6df
--- /dev/null
+++ b/third_party/rust/futures-util/src/fns.rs
@@ -0,0 +1,372 @@
+use core::fmt::{self, Debug};
+use core::marker::PhantomData;
+
+pub trait FnOnce1<A> {
+    type Output;
+    fn call_once(self, arg: A) -> Self::Output;
+}
+
+impl<T, A, R> FnOnce1<A> for T
+where
+    T: FnOnce(A) -> R,
+{
+    type Output = R;
+    fn call_once(self, arg: A) -> R {
+        self(arg)
+    }
+}
+
+pub trait FnMut1<A>: FnOnce1<A> {
+    fn call_mut(&mut self, arg: A) -> Self::Output;
+}
+
+impl<T, A, R> FnMut1<A> for T
+where
+    T: FnMut(A) -> R,
+{
+    fn call_mut(&mut self, arg: A) -> R {
+        self(arg)
+    }
+}
+
+// Not used, but present for completeness
+#[allow(unreachable_pub)]
+pub trait Fn1<A>: FnMut1<A> {
+    fn call(&self, arg: A) -> Self::Output;
+}
+
+impl<T, A, R> Fn1<A> for T
+where
+    T: Fn(A) -> R,
+{
+    fn call(&self, arg: A) -> R {
+        self(arg)
+    }
+}
+
+macro_rules! trivial_fn_impls {
+    ($name:ident <$($arg:ident),*> $t:ty = $debug:literal) => {
+        impl<$($arg),*> Copy for $t {}
+        impl<$($arg),*> Clone for $t {
+            fn clone(&self) -> Self { *self }
+        }
+        impl<$($arg),*> Debug for $t {
+            fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
+                f.write_str($debug)
+            }
+        }
+        impl<$($arg,)* A> FnMut1<A> for $t where Self: FnOnce1<A> {
+            fn call_mut(&mut self, arg: A) -> Self::Output {
+                self.call_once(arg)
+            }
+        }
+        impl<$($arg,)* A> Fn1<A> for $t where Self: FnOnce1<A> {
+            fn call(&self, arg: A) -> Self::Output {
+                self.call_once(arg)
+            }
+        }
+        pub(crate) fn $name<$($arg),*>() -> $t {
+            Default::default()
+        }
+    }
+}
+
+pub struct OkFn<E>(PhantomData<fn(E)>);
+
+impl<E> Default for OkFn<E> {
+    fn default() -> Self {
+        Self(PhantomData)
+    }
+}
+
+impl<A, E> FnOnce1<A> for OkFn<E> {
+    type Output = Result<A, E>;
+    fn call_once(self, arg: A) -> Self::Output {
+        Ok(arg)
+    }
+}
+
+trivial_fn_impls!(ok_fn <T> OkFn<T> = "Ok");
+
+#[derive(Debug, Copy, Clone, Default)]
+pub struct ChainFn<F, G>(F, G);
+
+impl<F, G, A> FnOnce1<A> for ChainFn<F, G>
+where
+    F: FnOnce1<A>,
+    G: FnOnce1<F::Output>,
+{
+    type Output = G::Output;
+    fn call_once(self, arg: A) -> Self::Output {
+        self.1.call_once(self.0.call_once(arg))
+    }
+}
+impl<F, G, A> FnMut1<A> for ChainFn<F, G>
+where
+    F: FnMut1<A>,
+    G: FnMut1<F::Output>,
+{
+    fn call_mut(&mut self, arg: A) -> Self::Output {
+        self.1.call_mut(self.0.call_mut(arg))
+    }
+}
+impl<F, G, A> Fn1<A> for ChainFn<F, G>
+where
+    F: Fn1<A>,
+    G: Fn1<F::Output>,
+{
+    fn call(&self, arg: A) -> Self::Output {
+        self.1.call(self.0.call(arg))
+    }
+}
+pub(crate) fn chain_fn<F, G>(f: F, g: G) -> ChainFn<F, G> {
+    ChainFn(f, g)
+}
+
+#[derive(Default)]
+pub struct MergeResultFn;
+
+impl<T> FnOnce1<Result<T, T>> for MergeResultFn {
+    type Output = T;
+    fn call_once(self, arg: Result<T, T>) -> Self::Output {
+        match arg {
+            Ok(x) => x,
+            Err(x) => x,
+        }
+    }
+}
+trivial_fn_impls!(merge_result_fn <> MergeResultFn = "merge_result");
+
+#[derive(Debug, Copy, Clone, Default)]
+pub struct InspectFn<F>(F);
+
+#[allow(single_use_lifetimes)] // https://github.com/rust-lang/rust/issues/55058
+impl<F, A> FnOnce1<A> for InspectFn<F>
+where
+    F: for<'a> FnOnce1<&'a A, Output = ()>,
+{
+    type Output = A;
+    fn call_once(self, arg: A) -> Self::Output {
+        self.0.call_once(&arg);
+        arg
+    }
+}
+#[allow(single_use_lifetimes)] // https://github.com/rust-lang/rust/issues/55058
+impl<F, A> FnMut1<A> for InspectFn<F>
+where
+    F: for<'a> FnMut1<&'a A, Output = ()>,
+{
+    fn call_mut(&mut self, arg: A) -> Self::Output {
+        self.0.call_mut(&arg);
+        arg
+    }
+}
+#[allow(single_use_lifetimes)] // https://github.com/rust-lang/rust/issues/55058
+impl<F, A> Fn1<A> for InspectFn<F>
+where
+    F: for<'a> Fn1<&'a A, Output = ()>,
+{
+    fn call(&self, arg: A) -> Self::Output {
+        self.0.call(&arg);
+        arg
+    }
+}
+pub(crate) fn inspect_fn<F>(f: F) -> InspectFn<F> {
+    InspectFn(f)
+}
+
+#[derive(Debug, Copy, Clone, Default)]
+pub struct MapOkFn<F>(F);
+
+impl<F, T, E> FnOnce1<Result<T, E>> for MapOkFn<F>
+where
+    F: FnOnce1<T>,
+{
+    type Output = Result<F::Output, E>;
+    fn call_once(self, arg: Result<T, E>) -> Self::Output {
+        arg.map(|x| self.0.call_once(x))
+    }
+}
+impl<F, T, E> FnMut1<Result<T, E>> for MapOkFn<F>
+where
+    F: FnMut1<T>,
+{
+    fn call_mut(&mut self, arg: Result<T, E>) -> Self::Output {
+        arg.map(|x| self.0.call_mut(x))
+    }
+}
+impl<F, T, E> Fn1<Result<T, E>> for MapOkFn<F>
+where
+    F: Fn1<T>,
+{
+    fn call(&self, arg: Result<T, E>) -> Self::Output {
+        arg.map(|x| self.0.call(x))
+    }
+}
+pub(crate) fn map_ok_fn<F>(f: F) -> MapOkFn<F> {
+    MapOkFn(f)
+}
+
+#[derive(Debug, Copy, Clone, Default)]
+pub struct MapErrFn<F>(F);
+
+impl<F, T, E> FnOnce1<Result<T, E>> for MapErrFn<F>
+where
+    F: FnOnce1<E>,
+{
+    type Output = Result<T, F::Output>;
+    fn call_once(self, arg: Result<T, E>) -> Self::Output {
+        arg.map_err(|x| self.0.call_once(x))
+    }
+}
+impl<F, T, E> FnMut1<Result<T, E>> for MapErrFn<F>
+where
+    F: FnMut1<E>,
+{
+    fn call_mut(&mut self, arg: Result<T, E>) -> Self::Output {
+        arg.map_err(|x| self.0.call_mut(x))
+    }
+}
+impl<F, T, E> Fn1<Result<T, E>> for MapErrFn<F>
+where
+    F: Fn1<E>,
+{
+    fn call(&self, arg: Result<T, E>) -> Self::Output {
+        arg.map_err(|x| self.0.call(x))
+    }
+}
+pub(crate) fn map_err_fn<F>(f: F) -> MapErrFn<F> {
+    MapErrFn(f)
+}
+
+#[derive(Debug, Copy, Clone)]
+pub struct InspectOkFn<F>(F);
+
+impl<'a, F, T, E> FnOnce1<&'a Result<T, E>> for InspectOkFn<F>
+where
+    F: FnOnce1<&'a T, Output = ()>,
+{
+    type Output = ();
+    fn call_once(self, arg: &'a Result<T, E>) -> Self::Output {
+        if let Ok(x) = arg {
+            self.0.call_once(x)
+        }
+    }
+}
+impl<'a, F, T, E> FnMut1<&'a Result<T, E>> for InspectOkFn<F>
+where
+    F: FnMut1<&'a T, Output = ()>,
+{
+    fn call_mut(&mut self, arg: &'a Result<T, E>) -> Self::Output {
+        if let Ok(x) = arg {
+            self.0.call_mut(x)
+        }
+    }
+}
+impl<'a, F, T, E> Fn1<&'a Result<T, E>> for InspectOkFn<F>
+where
+    F: Fn1<&'a T, Output = ()>,
+{
+    fn call(&self, arg: &'a Result<T, E>) -> Self::Output {
+        if let Ok(x) = arg {
+            self.0.call(x)
+        }
+    }
+}
+pub(crate) fn inspect_ok_fn<F>(f: F) -> InspectOkFn<F> {
+    InspectOkFn(f)
+}
+
+#[derive(Debug, Copy, Clone)]
+pub struct InspectErrFn<F>(F);
+
+impl<'a, F, T, E> FnOnce1<&'a Result<T, E>> for InspectErrFn<F>
+where
+    F: FnOnce1<&'a E, Output = ()>,
+{
+    type Output = ();
+    fn call_once(self, arg: &'a Result<T, E>) -> Self::Output {
+        if let Err(x) = arg {
+            self.0.call_once(x)
+        }
+    }
+}
+impl<'a, F, T, E> FnMut1<&'a Result<T, E>> for InspectErrFn<F>
+where
+    F: FnMut1<&'a E, Output = ()>,
+{
+    fn call_mut(&mut self, arg: &'a Result<T, E>) -> Self::Output {
+        if let Err(x) = arg {
+            self.0.call_mut(x)
+        }
+    }
+}
+impl<'a, F, T, E> Fn1<&'a Result<T, E>> for InspectErrFn<F>
+where
+    F: Fn1<&'a E, Output = ()>,
+{
+    fn call(&self, arg: &'a Result<T, E>) -> Self::Output {
+        if let Err(x) = arg {
+            self.0.call(x)
+        }
+    }
+}
+pub(crate) fn inspect_err_fn<F>(f: F) -> InspectErrFn<F> {
+    InspectErrFn(f)
+}
+
+pub(crate) type MapOkOrElseFn<F, G> = ChainFn<MapOkFn<F>, ChainFn<MapErrFn<G>, MergeResultFn>>;
+pub(crate) fn map_ok_or_else_fn<F, G>(f: F, g: G) -> MapOkOrElseFn<F, G> {
+    chain_fn(map_ok_fn(f), chain_fn(map_err_fn(g), merge_result_fn()))
+}
+
+#[derive(Debug, Copy, Clone, Default)]
+pub struct UnwrapOrElseFn<F>(F);
+
+impl<F, T, E> FnOnce1<Result<T, E>> for UnwrapOrElseFn<F>
+where
+    F: FnOnce1<E, Output = T>,
+{
+    type Output = T;
+    fn call_once(self, arg: Result<T, E>) -> Self::Output {
+        arg.unwrap_or_else(|x| self.0.call_once(x))
+    }
+}
+impl<F, T, E> FnMut1<Result<T, E>> for UnwrapOrElseFn<F>
+where
+    F: FnMut1<E, Output = T>,
+{
+    fn call_mut(&mut self, arg: Result<T, E>) -> Self::Output {
+        arg.unwrap_or_else(|x| self.0.call_mut(x))
+    }
+}
+impl<F, T, E> Fn1<Result<T, E>> for UnwrapOrElseFn<F>
+where
+    F: Fn1<E, Output = T>,
+{
+    fn call(&self, arg: Result<T, E>) -> Self::Output {
+        arg.unwrap_or_else(|x| self.0.call(x))
+    }
+}
+pub(crate) fn unwrap_or_else_fn<F>(f: F) -> UnwrapOrElseFn<F> {
+    UnwrapOrElseFn(f)
+}
+
+pub struct IntoFn<T>(PhantomData<fn() -> T>);
+
+impl<T> Default for IntoFn<T> {
+    fn default() -> Self {
+        Self(PhantomData)
+    }
+}
+impl<A, T> FnOnce1<A> for IntoFn<T>
+where
+    A: Into<T>,
+{
+    type Output = T;
+    fn call_once(self, arg: A) -> Self::Output {
+        arg.into()
+    }
+}
+
+trivial_fn_impls!(into_fn <T> IntoFn<T> = "Into::into");
diff --git a/third_party/rust/futures-util/src/future/abortable.rs b/third_party/rust/futures-util/src/future/abortable.rs
new file mode 100644
index 0000000000..d017ab7340
--- /dev/null
+++ b/third_party/rust/futures-util/src/future/abortable.rs
@@ -0,0 +1,19 @@
+use super::assert_future;
+use crate::future::{AbortHandle, Abortable, Aborted};
+use futures_core::future::Future;
+
+/// Creates a new `Abortable` future and an `AbortHandle` which can be used to stop it.
+///
+/// This function is a convenient (but less flexible) alternative to calling
+/// `AbortHandle::new` and `Abortable::new` manually.
+///
+/// This function is only available when the `std` or `alloc` feature of this
+/// library is activated, and it is activated by default.
+pub fn abortable<Fut>(future: Fut) -> (Abortable<Fut>, AbortHandle)
+where
+    Fut: Future,
+{
+    let (handle, reg) = AbortHandle::new_pair();
+    let abortable = assert_future::<Result<Fut::Output, Aborted>, _>(Abortable::new(future, reg));
+    (abortable, handle)
+}
diff --git a/third_party/rust/futures-util/src/future/either.rs b/third_party/rust/futures-util/src/future/either.rs
new file mode 100644
index 0000000000..9602de7a42
--- /dev/null
+++ b/third_party/rust/futures-util/src/future/either.rs
@@ -0,0 +1,297 @@
+use core::pin::Pin;
+use core::task::{Context, Poll};
+use futures_core::future::{FusedFuture, Future};
+use futures_core::stream::{FusedStream, Stream};
+#[cfg(feature = "sink")]
+use futures_sink::Sink;
+
+/// Combines two different futures, streams, or sinks having the same associated types into a single type.
+///
+/// This is useful when conditionally choosing between two distinct future types:
+///
+/// ```rust
+/// use futures::future::Either;
+///
+/// # futures::executor::block_on(async {
+/// let cond = true;
+///
+/// let fut = if cond {
+///     Either::Left(async move { 12 })
+/// } else {
+///     Either::Right(async move { 44 })
+/// };
+///
+/// assert_eq!(fut.await, 12);
+/// # })
+/// ```
+#[derive(Debug, Clone)]
+pub enum Either<A, B> {
+    /// First branch of the type
+    Left(/* #[pin] */ A),
+    /// Second branch of the type
+    Right(/* #[pin] */ B),
+}
+
+impl<A, B> Either<A, B> {
+    fn project(self: Pin<&mut Self>) -> Either<Pin<&mut A>, Pin<&mut B>> {
+        unsafe {
+            match self.get_unchecked_mut() {
+                Either::Left(a) => Either::Left(Pin::new_unchecked(a)),
+                Either::Right(b) => Either::Right(Pin::new_unchecked(b)),
+            }
+        }
+    }
+}
+
+impl<A, B, T> Either<(T, A), (T, B)> {
+    /// Factor out a homogeneous type from an either of pairs.
+    ///
+    /// Here, the homogeneous type is the first element of the pairs.
+    pub fn factor_first(self) -> (T, Either<A, B>) {
+        match self {
+            Either::Left((x, a)) => (x, Either::Left(a)),
+            Either::Right((x, b)) => (x, Either::Right(b)),
+        }
+    }
+}
+
+impl<A, B, T> Either<(A, T), (B, T)> {
+    /// Factor out a homogeneous type from an either of pairs.
+    ///
+    /// Here, the homogeneous type is the second element of the pairs.
+    pub fn factor_second(self) -> (Either<A, B>, T) {
+        match self {
+            Either::Left((a, x)) => (Either::Left(a), x),
+            Either::Right((b, x)) => (Either::Right(b), x),
+        }
+    }
+}
+
+impl<T> Either<T, T> {
+    /// Extract the value of an either over two equivalent types.
+    pub fn into_inner(self) -> T {
+        match self {
+            Either::Left(x) => x,
+            Either::Right(x) => x,
+        }
+    }
+}
+
+impl<A, B> Future for Either<A, B>
+where
+    A: Future,
+    B: Future<Output = A::Output>,
+{
+    type Output = A::Output;
+
+    fn poll(self: Pin<&mut Self>, cx: &mut Context<'_>) -> Poll<Self::Output> {
+        match self.project() {
+            Either::Left(x) => x.poll(cx),
+            Either::Right(x) => x.poll(cx),
+        }
+    }
+}
+
+impl<A, B> FusedFuture for Either<A, B>
+where
+    A: FusedFuture,
+    B: FusedFuture<Output = A::Output>,
+{
+    fn is_terminated(&self) -> bool {
+        match self {
+            Either::Left(x) => x.is_terminated(),
+            Either::Right(x) => x.is_terminated(),
+        }
+    }
+}
+
+impl<A, B> Stream for Either<A, B>
+where
+    A: Stream,
+    B: Stream<Item = A::Item>,
+{
+    type Item = A::Item;
+
+    fn poll_next(self: Pin<&mut Self>, cx: &mut Context<'_>) -> Poll<Option<Self::Item>> {
+        match self.project() {
+            Either::Left(x) => x.poll_next(cx),
+            Either::Right(x) => x.poll_next(cx),
+        }
+    }
+
+    fn size_hint(&self) -> (usize, Option<usize>) {
+        match self {
+            Either::Left(x) => x.size_hint(),
+            Either::Right(x) => x.size_hint(),
+        }
+    }
+}
+
+impl<A, B> FusedStream for Either<A, B>
+where
+    A: FusedStream,
+    B: FusedStream<Item = A::Item>,
+{
+    fn is_terminated(&self) -> bool {
+        match self {
+            Either::Left(x) => x.is_terminated(),
+            Either::Right(x) => x.is_terminated(),
+        }
+    }
+}
+
+#[cfg(feature = "sink")]
+impl<A, B, Item> Sink<Item> for Either<A, B>
+where
+    A: Sink<Item>,
+    B: Sink<Item, Error = A::Error>,
+{
+    type Error = A::Error;
+
+    fn poll_ready(self: Pin<&mut Self>, cx: &mut Context<'_>) -> Poll<Result<(), Self::Error>> {
+        match self.project() {
+            Either::Left(x) => x.poll_ready(cx),
+            Either::Right(x) => x.poll_ready(cx),
+        }
+    }
+
+    fn start_send(self: Pin<&mut Self>, item: Item) -> Result<(), Self::Error> {
+        match self.project() {
+            Either::Left(x) => x.start_send(item),
+            Either::Right(x) => x.start_send(item),
+        }
+    }
+
+    fn poll_flush(self: Pin<&mut Self>, cx: &mut Context<'_>) -> Poll<Result<(), Self::Error>> {
+        match self.project() {
+            Either::Left(x) => x.poll_flush(cx),
+            Either::Right(x) => x.poll_flush(cx),
+        }
+    }
+
+    fn poll_close(self: Pin<&mut Self>, cx: &mut Context<'_>) -> Poll<Result<(), Self::Error>> {
+        match self.project() {
+            Either::Left(x) => x.poll_close(cx),
+            Either::Right(x) => x.poll_close(cx),
+        }
+    }
+}
+
+#[cfg(feature = "io")]
+#[cfg(feature = "std")]
+mod if_std {
+    use super::*;
+
+    use core::pin::Pin;
+    use core::task::{Context, Poll};
+    use futures_io::{
+        AsyncBufRead, AsyncRead, AsyncSeek, AsyncWrite, IoSlice, IoSliceMut, Result, SeekFrom,
+    };
+
+    impl<A, B> AsyncRead for Either<A, B>
+    where
+        A: AsyncRead,
+        B: AsyncRead,
+    {
+        fn poll_read(
+            self: Pin<&mut Self>,
+            cx: &mut Context<'_>,
+            buf: &mut [u8],
+        ) -> Poll<Result<usize>> {
+            match self.project() {
+                Either::Left(x) => x.poll_read(cx, buf),
+                Either::Right(x) => x.poll_read(cx, buf),
+            }
+        }
+
+        fn poll_read_vectored(
+            self: Pin<&mut Self>,
+            cx: &mut Context<'_>,
+            bufs: &mut [IoSliceMut<'_>],
+        ) -> Poll<Result<usize>> {
+            match self.project() {
+                Either::Left(x) => x.poll_read_vectored(cx, bufs),
+                Either::Right(x) => x.poll_read_vectored(cx, bufs),
+            }
+        }
+    }
+
+    impl<A, B> AsyncWrite for Either<A, B>
+    where
+        A: AsyncWrite,
+        B: AsyncWrite,
+    {
+        fn poll_write(
+            self: Pin<&mut Self>,
+            cx: &mut Context<'_>,
+            buf: &[u8],
+        ) -> Poll<Result<usize>> {
+            match self.project() {
+                Either::Left(x) => x.poll_write(cx, buf),
+                Either::Right(x) => x.poll_write(cx, buf),
+            }
+        }
+
+        fn poll_write_vectored(
+            self: Pin<&mut Self>,
+            cx: &mut Context<'_>,
+            bufs: &[IoSlice<'_>],
+        ) -> Poll<Result<usize>> {
+            match self.project() {
+                Either::Left(x) => x.poll_write_vectored(cx, bufs),
+                Either::Right(x) => x.poll_write_vectored(cx, bufs),
+            }
+        }
+
+        fn poll_flush(self: Pin<&mut Self>, cx: &mut Context<'_>) -> Poll<Result<()>> {
+            match self.project() {
+                Either::Left(x) => x.poll_flush(cx),
+                Either::Right(x) => x.poll_flush(cx),
+            }
+        }
+
+        fn poll_close(self: Pin<&mut Self>, cx: &mut Context<'_>) -> Poll<Result<()>> {
+            match self.project() {
+                Either::Left(x) => x.poll_close(cx),
+                Either::Right(x) => x.poll_close(cx),
+            }
+        }
+    }
+
+    impl<A, B> AsyncSeek for Either<A, B>
+    where
+        A: AsyncSeek,
+        B: AsyncSeek,
+    {
+        fn poll_seek(
+            self: Pin<&mut Self>,
+            cx: &mut Context<'_>,
+            pos: SeekFrom,
+        ) -> Poll<Result<u64>> {
+            match self.project() {
+                Either::Left(x) => x.poll_seek(cx, pos),
+                Either::Right(x) => x.poll_seek(cx, pos),
+            }
+        }
+    }
+
+    impl<A, B> AsyncBufRead for Either<A, B>
+    where
+        A: AsyncBufRead,
+        B: AsyncBufRead,
+    {
+        fn poll_fill_buf(self: Pin<&mut Self>, cx: &mut Context<'_>) -> Poll<Result<&[u8]>> {
+            match self.project() {
+                Either::Left(x) => x.poll_fill_buf(cx),
+                Either::Right(x) => x.poll_fill_buf(cx),
+            }
+        }
+
+        fn consume(self: Pin<&mut Self>, amt: usize) {
+            match self.project() {
+                Either::Left(x) => x.consume(amt),
+                Either::Right(x) => x.consume(amt),
+            }
+        }
+    }
+}
diff --git a/third_party/rust/futures-util/src/future/future/catch_unwind.rs b/third_party/rust/futures-util/src/future/future/catch_unwind.rs
new file mode 100644
index 0000000000..0e09d6eeb0
--- /dev/null
+++ b/third_party/rust/futures-util/src/future/future/catch_unwind.rs
@@ -0,0 +1,38 @@
+use core::any::Any;
+use core::pin::Pin;
+use std::panic::{catch_unwind, AssertUnwindSafe, UnwindSafe};
+
+use futures_core::future::Future;
+use futures_core::task::{Context, Poll};
+use pin_project_lite::pin_project;
+
+pin_project! {
+    /// Future for the [`catch_unwind`](super::FutureExt::catch_unwind) method.
+    #[derive(Debug)]
+    #[must_use = "futures do nothing unless you `.await` or poll them"]
+    pub struct CatchUnwind<Fut> {
+        #[pin]
+        future: Fut,
+    }
+}
+
+impl<Fut> CatchUnwind<Fut>
+where
+    Fut: Future + UnwindSafe,
+{
+    pub(super) fn new(future: Fut) -> Self {
+        Self { future }
+    }
+}
+
+impl<Fut> Future for CatchUnwind<Fut>
+where
+    Fut: Future + UnwindSafe,
+{
+    type Output = Result<Fut::Output, Box<dyn Any + Send>>;
+
+    fn poll(self: Pin<&mut Self>, cx: &mut Context<'_>) -> Poll<Self::Output> {
+        let f = self.project().future;
+        catch_unwind(AssertUnwindSafe(|| f.poll(cx)))?.map(Ok)
+    }
+}
diff --git a/third_party/rust/futures-util/src/future/future/flatten.rs b/third_party/rust/futures-util/src/future/future/flatten.rs
new file mode 100644
index 0000000000..bd767af344
--- /dev/null
+++ b/third_party/rust/futures-util/src/future/future/flatten.rs
@@ -0,0 +1,153 @@
+use core::pin::Pin;
+use futures_core::future::{FusedFuture, Future};
+use futures_core::ready;
+use futures_core::stream::{FusedStream, Stream};
+use futures_core::task::{Context, Poll};
+#[cfg(feature = "sink")]
+use futures_sink::Sink;
+use pin_project_lite::pin_project;
+
+pin_project! {
+    #[project = FlattenProj]
+    #[derive(Debug)]
+    pub enum Flatten<Fut1, Fut2> {
+        First { #[pin] f: Fut1 },
+        Second { #[pin] f: Fut2 },
+        Empty,
+    }
+}
+
+impl<Fut1, Fut2> Flatten<Fut1, Fut2> {
+    pub(crate) fn new(future: Fut1) -> Self {
+        Self::First { f: future }
+    }
+}
+
+impl<Fut> FusedFuture for Flatten<Fut, Fut::Output>
+where
+    Fut: Future,
+    Fut::Output: Future,
+{
+    fn is_terminated(&self) -> bool {
+        match self {
+            Self::Empty => true,
+            _ => false,
+        }
+    }
+}
+
+impl<Fut> Future for Flatten<Fut, Fut::Output>
+where
+    Fut: Future,
+    Fut::Output: Future,
+{
+    type Output = <Fut::Output as Future>::Output;
+
+    fn poll(mut self: Pin<&mut Self>, cx: &mut Context<'_>) -> Poll<Self::Output> {
+        Poll::Ready(loop {
+            match self.as_mut().project() {
+                FlattenProj::First { f } => {
+                    let f = ready!(f.poll(cx));
+                    self.set(Self::Second { f });
+                }
+                FlattenProj::Second { f } => {
+                    let output = ready!(f.poll(cx));
+                    self.set(Self::Empty);
+                    break output;
+                }
+                FlattenProj::Empty => panic!("Flatten polled after completion"),
+            }
+        })
+    }
+}
+
+impl<Fut> FusedStream for Flatten<Fut, Fut::Output>
+where
+    Fut: Future,
+    Fut::Output: Stream,
+{
+    fn is_terminated(&self) -> bool {
+        match self {
+            Self::Empty => true,
+            _ => false,
+        }
+    }
+}
+
+impl<Fut> Stream for Flatten<Fut, Fut::Output>
+where
+    Fut: Future,
+    Fut::Output: Stream,
+{
+    type Item = <Fut::Output as Stream>::Item;
+
+    fn poll_next(mut self: Pin<&mut Self>, cx: &mut Context<'_>) -> Poll<Option<Self::Item>> {
+        Poll::Ready(loop {
+            match self.as_mut().project() {
+                FlattenProj::First { f } => {
+                    let f = ready!(f.poll(cx));
+                    self.set(Self::Second { f });
+                }
+                FlattenProj::Second { f } => {
+                    let output = ready!(f.poll_next(cx));
+                    if output.is_none() {
+                        self.set(Self::Empty);
+                    }
+                    break output;
+                }
+                FlattenProj::Empty => break None,
+            }
+        })
+    }
+}
+
+#[cfg(feature = "sink")]
+impl<Fut, Item> Sink<Item> for Flatten<Fut, Fut::Output>
+where
+    Fut: Future,
+    Fut::Output: Sink<Item>,
+{
+    type Error = <Fut::Output as Sink<Item>>::Error;
+
+    fn poll_ready(mut self: Pin<&mut Self>, cx: &mut Context<'_>) -> Poll<Result<(), Self::Error>> {
+        Poll::Ready(loop {
+            match self.as_mut().project() {
+                FlattenProj::First { f } => {
+                    let f = ready!(f.poll(cx));
+                    self.set(Self::Second { f });
+                }
+                FlattenProj::Second { f } => {
+                    break ready!(f.poll_ready(cx));
+                }
+                FlattenProj::Empty => panic!("poll_ready called after eof"),
+            }
+        })
+    }
+
+    fn start_send(self: Pin<&mut Self>, item: Item) -> Result<(), Self::Error> {
+        match self.project() {
+            FlattenProj::First { .. } => panic!("poll_ready not called first"),
+            FlattenProj::Second { f } => f.start_send(item),
+            FlattenProj::Empty => panic!("start_send called after eof"),
+        }
+    }
+
+    fn poll_flush(self: Pin<&mut Self>, cx: &mut Context<'_>) -> Poll<Result<(), Self::Error>> {
+        match self.project() {
+            FlattenProj::First { .. } => Poll::Ready(Ok(())),
+            FlattenProj::Second { f } => f.poll_flush(cx),
+            FlattenProj::Empty => panic!("poll_flush called after eof"),
+        }
+    }
+
+    fn poll_close(mut self: Pin<&mut Self>, cx: &mut Context<'_>) -> Poll<Result<(), Self::Error>> {
+        let res = match self.as_mut().project() {
+            FlattenProj::Second { f } => f.poll_close(cx),
+            _ => Poll::Ready(Ok(())),
+        };
+        if res.is_ready() {
+            self.set(Self::Empty);
+        }
+        res
+    }
+}
diff --git a/third_party/rust/futures-util/src/future/future/fuse.rs b/third_party/rust/futures-util/src/future/future/fuse.rs
new file mode 100644
index 0000000000..597aec1a40
--- /dev/null
+++ b/third_party/rust/futures-util/src/future/future/fuse.rs
@@ -0,0 +1,93 @@
+use core::pin::Pin;
+use futures_core::future::{FusedFuture, Future};
+use futures_core::ready;
+use futures_core::task::{Context, Poll};
+use pin_project_lite::pin_project;
+
+pin_project! {
+    /// Future for the [`fuse`](super::FutureExt::fuse) method.
+    #[derive(Debug)]
+    #[must_use = "futures do nothing unless you `.await` or poll them"]
+    pub struct Fuse<Fut> {
+        #[pin]
+        inner: Option<Fut>,
+    }
+}
+
+impl<Fut> Fuse<Fut> {
+    pub(super) fn new(f: Fut) -> Self {
+        Self { inner: Some(f) }
+    }
+}
+
+impl<Fut: Future> Fuse<Fut> {
+    /// Creates a new `Fuse`-wrapped future which is already terminated.
+    ///
+    /// This can be useful in combination with looping and the `select!`
+    /// macro, which bypasses terminated futures.
+    ///
+    /// # Examples
+    ///
+    /// ```
+    /// # futures::executor::block_on(async {
+    /// use futures::channel::mpsc;
+    /// use futures::future::{Fuse, FusedFuture, FutureExt};
+    /// use futures::select;
+    /// use futures::stream::StreamExt;
+    /// use futures::pin_mut;
+    ///
+    /// let (sender, mut stream) = mpsc::unbounded();
+    ///
+    /// // Send a few messages into the stream
+    /// sender.unbounded_send(()).unwrap();
+    /// sender.unbounded_send(()).unwrap();
+    /// drop(sender);
+    ///
+    /// // Use `Fuse::terminated()` to create an already-terminated future
+    /// // which may be instantiated later.
+    /// let foo_printer = Fuse::terminated();
+    /// pin_mut!(foo_printer);
+    ///
+    /// loop {
+    ///     select! {
+    ///         _ = foo_printer => {},
+    ///         () = stream.select_next_some() => {
+    ///             if !foo_printer.is_terminated() {
+    ///                 println!("Foo is already being printed!");
+    ///             } else {
+    ///                 foo_printer.set(async {
+    ///                     // do some other async operations
+    ///                     println!("Printing foo from `foo_printer` future");
+    ///                 }.fuse());
+    ///             }
+    ///         },
+    ///         complete => break, // `foo_printer` is terminated and the stream is done
+    ///     }
+    /// }
+    /// # });
+    /// ```
+    pub fn terminated() -> Self {
+        Self { inner: None }
+    }
+}
+
+impl<Fut: Future> FusedFuture for Fuse<Fut> {
+    fn is_terminated(&self) -> bool {
+        self.inner.is_none()
+    }
+}
+
+impl<Fut: Future> Future for Fuse<Fut> {
+    type Output = Fut::Output;
+
+    fn poll(mut self: Pin<&mut Self>, cx: &mut Context<'_>) -> Poll<Fut::Output> {
+        Poll::Ready(match self.as_mut().project().inner.as_pin_mut() {
+            Some(fut) => {
+                let output = ready!(fut.poll(cx));
+                self.project().inner.set(None);
+                output
+            }
+            None => return Poll::Pending,
+        })
+    }
+}
diff --git a/third_party/rust/futures-util/src/future/future/map.rs b/third_party/rust/futures-util/src/future/future/map.rs
new file mode 100644
index 0000000000..7471aba000
--- /dev/null
+++ b/third_party/rust/futures-util/src/future/future/map.rs
@@ -0,0 +1,66 @@
+use core::pin::Pin;
+use futures_core::future::{FusedFuture, Future};
+use futures_core::ready;
+use futures_core::task::{Context, Poll};
+use pin_project_lite::pin_project;
+
+use crate::fns::FnOnce1;
+
+pin_project! {
+    /// Internal Map future
+    #[project = MapProj]
+    #[project_replace = MapProjReplace]
+    #[derive(Debug)]
+    #[must_use = "futures do nothing unless you `.await` or poll them"]
+    pub enum Map<Fut, F> {
+        Incomplete {
+            #[pin]
+            future: Fut,
+            f: F,
+        },
+        Complete,
+    }
+}
+
+impl<Fut, F> Map<Fut, F> {
+    /// Creates a new Map.
+    pub(crate) fn new(future: Fut, f: F) -> Self {
+        Self::Incomplete { future, f }
+    }
+}
+
+impl<Fut, F, T> FusedFuture for Map<Fut, F>
+where
+    Fut: Future,
+    F: FnOnce1<Fut::Output, Output = T>,
+{
+    fn is_terminated(&self) -> bool {
+        match self {
+            Self::Incomplete { .. } => false,
+            Self::Complete => true,
+        }
+    }
+}
+
+impl<Fut, F, T> Future for Map<Fut, F>
+where
+    Fut: Future,
+    F: FnOnce1<Fut::Output, Output = T>,
+{
+    type Output = T;
+
+    fn poll(mut self: Pin<&mut Self>, cx: &mut Context<'_>) -> Poll<T> {
+        match self.as_mut().project() {
+            MapProj::Incomplete { future, .. } => {
+                let output = ready!(future.poll(cx));
+                match self.project_replace(Map::Complete) {
+                    MapProjReplace::Incomplete { f, .. } => Poll::Ready(f.call_once(output)),
+                    MapProjReplace::Complete => unreachable!(),
+                }
+            }
+            MapProj::Complete => {
+                panic!("Map must not be polled after it returned `Poll::Ready`")
+            }
+        }
+    }
+}
diff --git a/third_party/rust/futures-util/src/future/future/mod.rs b/third_party/rust/futures-util/src/future/future/mod.rs
new file mode 100644
index 0000000000..c11d108207
--- /dev/null
+++ b/third_party/rust/futures-util/src/future/future/mod.rs
@@ -0,0 +1,610 @@
+//! Futures
+//!
+//! This module contains a number of functions for working with `Future`s,
+//! including the `FutureExt` trait which adds methods to `Future` types.
+
+#[cfg(feature = "alloc")]
+use alloc::boxed::Box;
+use core::pin::Pin;
+
+use crate::fns::{inspect_fn, into_fn, ok_fn, InspectFn, IntoFn, OkFn};
+use crate::future::{assert_future, Either};
+use crate::never::Never;
+use crate::stream::assert_stream;
+#[cfg(feature = "alloc")]
+use futures_core::future::{BoxFuture, LocalBoxFuture};
+use futures_core::{
+    future::Future,
+    stream::Stream,
+    task::{Context, Poll},
+};
+use pin_utils::pin_mut;
+
+// Combinators
+
+mod flatten;
+mod fuse;
+mod map;
+
+delegate_all!(
+    /// Future for the [`flatten`](super::FutureExt::flatten) method.
+    Flatten<F>(
+        flatten::Flatten<F, <F as Future>::Output>
+    ): Debug + Future + FusedFuture + New[|x: F| flatten::Flatten::new(x)]
+    where F: Future
+);
+
+delegate_all!(
+    /// Stream for the [`flatten_stream`](FutureExt::flatten_stream) method.
+    FlattenStream<F>(
+        flatten::Flatten<F, <F as Future>::Output>
+    ): Debug + Sink + Stream + FusedStream + New[|x: F| flatten::Flatten::new(x)]
+    where F: Future
+);
+
+#[allow(unreachable_pub)] // https://github.com/rust-lang/rust/issues/57411
+pub use fuse::Fuse;
+
+delegate_all!(
+    /// Future for the [`map`](super::FutureExt::map) method.
+    Map<Fut, F>(
+        map::Map<Fut, F>
+    ): Debug + Future + FusedFuture + New[|x: Fut, f: F| map::Map::new(x, f)]
+);
+
+delegate_all!(
+    /// Stream for the [`into_stream`](FutureExt::into_stream) method.
+    IntoStream<F>(
+        crate::stream::Once<F>
+    ): Debug + Stream + FusedStream + New[|x: F| crate::stream::Once::new(x)]
+);
+
+delegate_all!(
+    /// Future for the [`map_into`](FutureExt::map_into) combinator.
+    MapInto<Fut, T>(
+        Map<Fut, IntoFn<T>>
+    ): Debug + Future + FusedFuture + New[|x: Fut| Map::new(x, into_fn())]
+);
+
+delegate_all!(
+    /// Future for the [`then`](FutureExt::then) method.
+    Then<Fut1, Fut2, F>(
+        flatten::Flatten<Map<Fut1, F>, Fut2>
+    ): Debug + Future + FusedFuture + New[|x: Fut1, y: F| flatten::Flatten::new(Map::new(x, y))]
+);
+
+delegate_all!(
+    /// Future for the [`inspect`](FutureExt::inspect) method.
+    Inspect<Fut, F>(
+        map::Map<Fut, InspectFn<F>>
+    ): Debug + Future + FusedFuture + New[|x: Fut, f: F| map::Map::new(x, inspect_fn(f))]
+);
+
+delegate_all!(
+    /// Future for the [`never_error`](super::FutureExt::never_error) combinator.
+    NeverError<Fut>(
+        Map<Fut, OkFn<Never>>
+    ): Debug + Future + FusedFuture + New[|x: Fut| Map::new(x, ok_fn())]
+);
+
+delegate_all!(
+    /// Future for the [`unit_error`](super::FutureExt::unit_error) combinator.
+    UnitError<Fut>(
+        Map<Fut, OkFn<()>>
+    ): Debug + Future + FusedFuture + New[|x: Fut| Map::new(x, ok_fn())]
+);
+
+#[cfg(feature = "std")]
+mod catch_unwind;
+#[cfg(feature = "std")]
+#[allow(unreachable_pub)] // https://github.com/rust-lang/rust/issues/57411
+pub use self::catch_unwind::CatchUnwind;
+
+#[cfg(feature = "channel")]
+#[cfg_attr(docsrs, doc(cfg(feature = "channel")))]
+#[cfg(feature = "std")]
+mod remote_handle;
+#[cfg(feature = "channel")]
+#[cfg_attr(docsrs, doc(cfg(feature = "channel")))]
+#[cfg(feature = "std")]
+#[allow(unreachable_pub)] // https://github.com/rust-lang/rust/issues/57411
+pub use self::remote_handle::{Remote, RemoteHandle};
+
+#[cfg(feature = "std")]
+mod shared;
+#[cfg(feature = "std")]
+#[allow(unreachable_pub)] // https://github.com/rust-lang/rust/issues/57411
+pub use self::shared::{Shared, WeakShared};
+
+impl<T: ?Sized> FutureExt for T where T: Future {}
+
+/// An extension trait for `Future`s that provides a variety of convenient
+/// adapters.
+pub trait FutureExt: Future {
+    /// Map this future's output to a different type, returning a new future of
+    /// the resulting type.
+    ///
+    /// This function is similar to the `Option::map` or `Iterator::map` where
+    /// it will change the type of the underlying future. This is useful to
+    /// chain along a computation once a future has been resolved.
+    ///
+    /// Note that this function consumes the receiving future and returns a
+    /// wrapped version of it, similar to the existing `map` methods in the
+    /// standard library.
+    ///
+    /// # Examples
+    ///
+    /// ```
+    /// # futures::executor::block_on(async {
+    /// use futures::future::FutureExt;
+    ///
+    /// let future = async { 1 };
+    /// let new_future = future.map(|x| x + 3);
+    /// assert_eq!(new_future.await, 4);
+    /// # });
+    /// ```
+    fn map<U, F>(self, f: F) -> Map<Self, F>
+    where
+        F: FnOnce(Self::Output) -> U,
+        Self: Sized,
+    {
+        assert_future::<U, _>(Map::new(self, f))
+    }
+
+    /// Map this future's output to a different type, returning a new future of
+    /// the resulting type.
+    ///
+    /// This function is equivalent to calling `map(Into::into)` but allows naming
+    /// the return type.
+    fn map_into<U>(self) -> MapInto<Self, U>
+    where
+        Self::Output: Into<U>,
+        Self: Sized,
+    {
+        assert_future::<U, _>(MapInto::new(self))
+    }
+
+    /// Chain on a computation for when a future finished, passing the result of
+    /// the future to the provided closure `f`.
+    ///
+    /// The returned value of the closure must implement the `Future` trait
+    /// and can represent some more work to be done before the composed future
+    /// is finished.
+    ///
+    /// The closure `f` is only run *after* successful completion of the `self`
+    /// future.
+    ///
+    /// Note that this function consumes the receiving future and returns a
+    /// wrapped version of it.
+    ///
+    /// # Examples
+    ///
+    /// ```
+    /// # futures::executor::block_on(async {
+    /// use futures::future::FutureExt;
+    ///
+    /// let future_of_1 = async { 1 };
+    /// let future_of_4 = future_of_1.then(|x| async move { x + 3 });
+    /// assert_eq!(future_of_4.await, 4);
+    /// # });
+    /// ```
+    fn then<Fut, F>(self, f: F) -> Then<Self, Fut, F>
+    where
+        F: FnOnce(Self::Output) -> Fut,
+        Fut: Future,
+        Self: Sized,
+    {
+        assert_future::<Fut::Output, _>(Then::new(self, f))
+    }
+
+    /// Wrap this future in an `Either` future, making it the left-hand variant
+    /// of that `Either`.
+    ///
+    /// This can be used in combination with the `right_future` method to write `if`
+    /// statements that evaluate to different futures in different branches.
+    ///
+    /// # Examples
+    ///
+    /// ```
+    /// # futures::executor::block_on(async {
+    /// use futures::future::FutureExt;
+    ///
+    /// let x = 6;
+    /// let future = if x < 10 {
+    ///     async { true }.left_future()
+    /// } else {
+    ///     async { false }.right_future()
+    /// };
+    ///
+    /// assert_eq!(future.await, true);
+    /// # });
+    /// ```
+    fn left_future<B>(self) -> Either<Self, B>
+    where
+        B: Future<Output = Self::Output>,
+        Self: Sized,
+    {
+        assert_future::<Self::Output, _>(Either::Left(self))
+    }
+
+    /// Wrap this future in an `Either` future, making it the right-hand variant
+    /// of that `Either`.
+    ///
+    /// This can be used in combination with the `left_future` method to write `if`
+    /// statements that evaluate to different futures in different branches.
+    ///
+    /// # Examples
+    ///
+    /// ```
+    /// # futures::executor::block_on(async {
+    /// use futures::future::FutureExt;
+    ///
+    /// let x = 6;
+    /// let future = if x > 10 {
+    ///     async { true }.left_future()
+    /// } else {
+    ///     async { false }.right_future()
+    /// };
+    ///
+    /// assert_eq!(future.await, false);
+    /// # });
+    /// ```
+    fn right_future<A>(self) -> Either<A, Self>
+    where
+        A: Future<Output = Self::Output>,
+        Self: Sized,
+    {
+        assert_future::<Self::Output, _>(Either::Right(self))
+    }
+
+    /// Convert this future into a single element stream.
+    ///
+    /// The returned stream contains single success if this future resolves to
+    /// success or single error if this future resolves into error.
+    ///
+    /// # Examples
+    ///
+    /// ```
+    /// # futures::executor::block_on(async {
+    /// use futures::future::FutureExt;
+    /// use futures::stream::StreamExt;
+    ///
+    /// let future = async { 17 };
+    /// let stream = future.into_stream();
+    /// let collected: Vec<_> = stream.collect().await;
+    /// assert_eq!(collected, vec![17]);
+    /// # });
+    /// ```
+    fn into_stream(self) -> IntoStream<Self>
+    where
+        Self: Sized,
+    {
+        assert_stream::<Self::Output, _>(IntoStream::new(self))
+    }
+
+    /// Flatten the execution of this future when the output of this
+    /// future is itself another future.
+    ///
+    /// This can be useful when combining futures together to flatten the
+    /// computation out the final result.
+    ///
+    /// This method is roughly equivalent to `self.then(|x| x)`.
+    ///
+    /// Note that this function consumes the receiving future and returns a
+    /// wrapped version of it.
+    ///
+    /// # Examples
+    ///
+    /// ```
+    /// # futures::executor::block_on(async {
+    /// use futures::future::FutureExt;
+    ///
+    /// let nested_future = async { async { 1 } };
+    /// let future = nested_future.flatten();
+    /// assert_eq!(future.await, 1);
+    /// # });
+    /// ```
+    fn flatten(self) -> Flatten<Self>
+    where
+        Self::Output: Future,
+        Self: Sized,
+    {
+        let f = Flatten::new(self);
+        assert_future::<<<Self as Future>::Output as Future>::Output, _>(f)
+    }
+
+    /// Flatten the execution of this future when the successful result of this
+    /// future is a stream.
+    ///
+    /// This can be useful when stream initialization is deferred, and it is
+    /// convenient to work with that stream as if stream was available at the
+    /// call site.
+    ///
+    /// Note that this function consumes this future and returns a wrapped
+    /// version of it.
+    ///
+    /// # Examples
+    ///
+    /// ```
+    /// # futures::executor::block_on(async {
+    /// use futures::future::FutureExt;
+    /// use futures::stream::{self, StreamExt};
+    ///
+    /// let stream_items = vec![17, 18, 19];
+    /// let future_of_a_stream = async { stream::iter(stream_items) };
+    ///
+    /// let stream = future_of_a_stream.flatten_stream();
+    /// let list: Vec<_> = stream.collect().await;
+    /// assert_eq!(list, vec![17, 18, 19]);
+    /// # });
+    /// ```
+    fn flatten_stream(self) -> FlattenStream<Self>
+    where
+        Self::Output: Stream,
+        Self: Sized,
+    {
+        assert_stream::<<Self::Output as Stream>::Item, _>(FlattenStream::new(self))
+    }
+
+    /// Fuse a future such that `poll` will never again be called once it has
+    /// completed. This method can be used to turn any `Future` into a
+    /// `FusedFuture`.
+    ///
+    /// Normally, once a future has returned `Poll::Ready` from `poll`,
+    /// any further calls could exhibit bad behavior such as blocking
+    /// forever, panicking, never returning, etc. If it is known that `poll`
+    /// may be called too often then this method can be used to ensure that it
+    /// has defined semantics.
+    ///
+    /// If a `fuse`d future is `poll`ed after having returned `Poll::Ready`
+    /// previously, it will return `Poll::Pending`, from `poll` again (and will
+    /// continue to do so for all future calls to `poll`).
+    ///
+    /// This combinator will drop the underlying future as soon as it has been
+    /// completed to ensure resources are reclaimed as soon as possible.
+    fn fuse(self) -> Fuse<Self>
+    where
+        Self: Sized,
+    {
+        let f = Fuse::new(self);
+        assert_future::<Self::Output, _>(f)
+    }
+
+    /// Do something with the output of a future before passing it on.
+    ///
+    /// When using futures, you'll often chain several of them together.  While
+    /// working on such code, you might want to check out what's happening at
+    /// various parts in the pipeline, without consuming the intermediate
+    /// value. To do that, insert a call to `inspect`.
+    ///
+    /// # Examples
+    ///
+    /// ```
+    /// # futures::executor::block_on(async {
+    /// use futures::future::FutureExt;
+    ///
+    /// let future = async { 1 };
+    /// let new_future = future.inspect(|&x| println!("about to resolve: {}", x));
+    /// assert_eq!(new_future.await, 1);
+    /// # });
+    /// ```
+    fn inspect<F>(self, f: F) -> Inspect<Self, F>
+    where
+        F: FnOnce(&Self::Output),
+        Self: Sized,
+    {
+        assert_future::<Self::Output, _>(Inspect::new(self, f))
+    }
+
+    /// Catches unwinding panics while polling the future.
+    ///
+    /// In general, panics within a future can propagate all the way out to the
+    /// task level. This combinator makes it possible to halt unwinding within
+    /// the future itself. It's most commonly used within task executors. It's
+    /// not recommended to use this for error handling.
+    ///
+    /// Note that this method requires the `UnwindSafe` bound from the standard
+    /// library. This isn't always applied automatically, and the standard
+    /// library provides an `AssertUnwindSafe` wrapper type to apply it
+    /// after-the fact. To assist using this method, the `Future` trait is also
+    /// implemented for `AssertUnwindSafe<F>` where `F` implements `Future`.
+    ///
+    /// This method is only available when the `std` feature of this
+    /// library is activated, and it is activated by default.
+    ///
+    /// # Examples
+    ///
+    /// ```
+    /// # futures::executor::block_on(async {
+    /// use futures::future::{self, FutureExt, Ready};
+    ///
+    /// let future = future::ready(2);
+    /// assert!(future.catch_unwind().await.is_ok());
+    ///
+    /// let future = future::lazy(|_| -> Ready<i32> {
+    ///     unimplemented!()
+    /// });
+    /// assert!(future.catch_unwind().await.is_err());
+    /// # });
+    /// ```
+    #[cfg(feature = "std")]
+    fn catch_unwind(self) -> CatchUnwind<Self>
+    where
+        Self: Sized + ::std::panic::UnwindSafe,
+    {
+        assert_future::<Result<Self::Output, Box<dyn std::any::Any + Send>>, _>(CatchUnwind::new(
+            self,
+        ))
+    }
+
+    /// Create a cloneable handle to this future where all handles will resolve
+    /// to the same result.
+    ///
+    /// The `shared` combinator method provides a method to convert any future
+    /// into a cloneable future. It enables a future to be polled by multiple
+    /// threads.
+    ///
+    /// This method is only available when the `std` feature of this
+    /// library is activated, and it is activated by default.
+    ///
+    /// # Examples
+    ///
+    /// ```
+    /// # futures::executor::block_on(async {
+    /// use futures::future::FutureExt;
+    ///
+    /// let future = async { 6 };
+    /// let shared1 = future.shared();
+    /// let shared2 = shared1.clone();
+    ///
+    /// assert_eq!(6, shared1.await);
+    /// assert_eq!(6, shared2.await);
+    /// # });
+    /// ```
+    ///
+    /// ```
+    /// // Note, unlike most examples this is written in the context of a
+    /// // synchronous function to better illustrate the cross-thread aspect of
+    /// // the `shared` combinator.
+    ///
+    /// # futures::executor::block_on(async {
+    /// use futures::future::FutureExt;
+    /// use futures::executor::block_on;
+    /// use std::thread;
+    ///
+    /// let future = async { 6 };
+    /// let shared1 = future.shared();
+    /// let shared2 = shared1.clone();
+    /// let join_handle = thread::spawn(move || {
+    ///     assert_eq!(6, block_on(shared2));
+    /// });
+    /// assert_eq!(6, shared1.await);
+    /// join_handle.join().unwrap();
+    /// # });
+    /// ```
+    #[cfg(feature = "std")]
+    fn shared(self) -> Shared<Self>
+    where
+        Self: Sized,
+        Self::Output: Clone,
+    {
+        assert_future::<Self::Output, _>(Shared::new(self))
+    }
+
+    /// Turn this future into a future that yields `()` on completion and sends
+    /// its output to another future on a separate task.
+    ///
+    /// This can be used with spawning executors to easily retrieve the result
+    /// of a future executing on a separate task or thread.
+    ///
+    /// This method is only available when the `std` feature of this
+    /// library is activated, and it is activated by default.
+    #[cfg(feature = "channel")]
+    #[cfg_attr(docsrs, doc(cfg(feature = "channel")))]
+    #[cfg(feature = "std")]
+    fn remote_handle(self) -> (Remote<Self>, RemoteHandle<Self::Output>)
+    where
+        Self: Sized,
+    {
+        let (wrapped, handle) = remote_handle::remote_handle(self);
+        (assert_future::<(), _>(wrapped), handle)
+    }
+
+    /// Wrap the future in a Box, pinning it.
+    ///
+    /// This method is only available when the `std` or `alloc` feature of this
+    /// library is activated, and it is activated by default.
+    #[cfg(feature = "alloc")]
+    fn boxed<'a>(self) -> BoxFuture<'a, Self::Output>
+    where
+        Self: Sized + Send + 'a,
+    {
+        assert_future::<Self::Output, _>(Box::pin(self))
+    }
+
+    /// Wrap the future in a Box, pinning it.
+    ///
+    /// Similar to `boxed`, but without the `Send` requirement.
+    ///
+    /// This method is only available when the `std` or `alloc` feature of this
+    /// library is activated, and it is activated by default.
+    #[cfg(feature = "alloc")]
+    fn boxed_local<'a>(self) -> LocalBoxFuture<'a, Self::Output>
+    where
+        Self: Sized + 'a,
+    {
+        assert_future::<Self::Output, _>(Box::pin(self))
+    }
+
+    /// Turns a [`Future<Output = T>`](Future) into a
+    /// [`TryFuture<Ok = T, Error = ()`>](futures_core::future::TryFuture).
+    fn unit_error(self) -> UnitError<Self>
+    where
+        Self: Sized,
+    {
+        assert_future::<Result<Self::Output, ()>, _>(UnitError::new(self))
+    }
+
+    /// Turns a [`Future<Output = T>`](Future) into a
+    /// [`TryFuture<Ok = T, Error = Never`>](futures_core::future::TryFuture).
+    fn never_error(self) -> NeverError<Self>
+    where
+        Self: Sized,
+    {
+        assert_future::<Result<Self::Output, Never>, _>(NeverError::new(self))
+    }
+
+    /// A convenience for calling `Future::poll` on `Unpin` future types.
+    fn poll_unpin(&mut self, cx: &mut Context<'_>) -> Poll<Self::Output>
+    where
+        Self: Unpin,
+    {
+        Pin::new(self).poll(cx)
+    }
+
+    /// Evaluates and consumes the future, returning the resulting output if
+    /// the future is ready after the first call to `Future::poll`.
+    ///
+    /// If `poll` instead returns `Poll::Pending`, `None` is returned.
+    ///
+    /// This method is useful in cases where immediacy is more important than
+    /// waiting for a result. It is also convenient for quickly obtaining
+    /// the value of a future that is known to always resolve immediately.
+    ///
+    /// # Examples
+    ///
+    /// ```
+    /// # use futures::prelude::*;
+    /// use futures::{future::ready, future::pending};
+    /// let future_ready = ready("foobar");
+    /// let future_pending = pending::<&'static str>();
+    ///
+    /// assert_eq!(future_ready.now_or_never(), Some("foobar"));
+    /// assert_eq!(future_pending.now_or_never(), None);
+    /// ```
+    ///
+    /// In cases where it is absolutely known that a future should always
+    /// resolve immediately and never return `Poll::Pending`, this method can
+    /// be combined with `expect()`:
+    ///
+    /// ```
+    /// # use futures::{prelude::*, future::ready};
+    /// let future_ready = ready("foobar");
+    ///
+    /// assert_eq!(future_ready.now_or_never().expect("Future not ready"), "foobar");
+    /// ```
+    fn now_or_never(self) -> Option<Self::Output>
+    where
+        Self: Sized,
+    {
+        let noop_waker = crate::task::noop_waker();
+        let mut cx = Context::from_waker(&noop_waker);
+
+        let this = self;
+        pin_mut!(this);
+        match this.poll(&mut cx) {
+            Poll::Ready(x) => Some(x),
+            _ => None,
+        }
+    }
+}
diff --git a/third_party/rust/futures-util/src/future/future/remote_handle.rs b/third_party/rust/futures-util/src/future/future/remote_handle.rs
new file mode 100644
index 0000000000..1358902cab
--- /dev/null
+++ b/third_party/rust/futures-util/src/future/future/remote_handle.rs
@@ -0,0 +1,126 @@
+use {
+    crate::future::{CatchUnwind, FutureExt},
+    futures_channel::oneshot::{self, Receiver, Sender},
+    futures_core::{
+        future::Future,
+        ready,
+        task::{Context, Poll},
+    },
+    pin_project_lite::pin_project,
+    std::{
+        any::Any,
+        fmt,
+        panic::{self, AssertUnwindSafe},
+        pin::Pin,
+        sync::{
+            atomic::{AtomicBool, Ordering},
+            Arc,
+        },
+        thread,
+    },
+};
+
+/// The handle to a remote future returned by
+/// [`remote_handle`](crate::future::FutureExt::remote_handle). When you drop this,
+/// the remote future will be woken up to be dropped by the executor.
+///
+/// ## Unwind safety
+///
+/// When the remote future panics, [Remote] will catch the unwind and transfer it to
+/// the thread where `RemoteHandle` is being awaited. This is good for the common
+/// case where [Remote] is spawned on a threadpool. It is unlikely that other code
+/// in the executor working thread shares mutable data with the spawned future and we
+/// preserve the executor from losing its working threads.
+///
+/// If you run the future locally and send the handle of to be awaited elsewhere, you
+/// must be careful with regard to unwind safety because the thread in which the future
+/// is polled will keep running after the panic and the thread running the [RemoteHandle]
+/// will unwind.
+#[must_use = "dropping a remote handle cancels the underlying future"]
+#[derive(Debug)]
+#[cfg_attr(docsrs, doc(cfg(feature = "channel")))]
+pub struct RemoteHandle<T> {
+    rx: Receiver<thread::Result<T>>,
+    keep_running: Arc<AtomicBool>,
+}
+
+impl<T> RemoteHandle<T> {
+    /// Drops this handle *without* canceling the underlying future.
+    ///
+    /// This method can be used if you want to drop the handle, but let the
+    /// execution continue.
+    pub fn forget(self) {
+        self.keep_running.store(true, Ordering::SeqCst);
+    }
+}
+
+impl<T: 'static> Future for RemoteHandle<T> {
+    type Output = T;
+
+    fn poll(mut self: Pin<&mut Self>, cx: &mut Context<'_>) -> Poll<T> {
+        match ready!(self.rx.poll_unpin(cx)) {
+            Ok(Ok(output)) => Poll::Ready(output),
+            // the remote future panicked.
+            Ok(Err(e)) => panic::resume_unwind(e),
+            // The oneshot sender was dropped.
+            Err(e) => panic::resume_unwind(Box::new(e)),
+        }
+    }
+}
+
+type SendMsg<Fut> = Result<<Fut as Future>::Output, Box<(dyn Any + Send + 'static)>>;
+
+pin_project! {
+    /// A future which sends its output to the corresponding `RemoteHandle`.
+    /// Created by [`remote_handle`](crate::future::FutureExt::remote_handle).
+    #[must_use = "futures do nothing unless you `.await` or poll them"]
+    #[cfg_attr(docsrs, doc(cfg(feature = "channel")))]
+    pub struct Remote<Fut: Future> {
+        tx: Option<Sender<SendMsg<Fut>>>,
+        keep_running: Arc<AtomicBool>,
+        #[pin]
+        future: CatchUnwind<AssertUnwindSafe<Fut>>,
+    }
+}
+
+impl<Fut: Future + fmt::Debug> fmt::Debug for Remote<Fut> {
+    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
+        f.debug_tuple("Remote").field(&self.future).finish()
+    }
+}
+
+impl<Fut: Future> Future for Remote<Fut> {
+    type Output = ();
+
+    fn poll(self: Pin<&mut Self>, cx: &mut Context<'_>) -> Poll<()> {
+        let this = self.project();
+
+        if this.tx.as_mut().unwrap().poll_canceled(cx).is_ready()
+            && !this.keep_running.load(Ordering::SeqCst)
+        {
+            // Cancelled, bail out
+            return Poll::Ready(());
+        }
+
+        let output = ready!(this.future.poll(cx));
+
+        // if the receiving end has gone away then that's ok, we just ignore the
+        // send error here.
+        drop(this.tx.take().unwrap().send(output));
+        Poll::Ready(())
+    }
+}
+
+pub(super) fn remote_handle<Fut: Future>(future: Fut) -> (Remote<Fut>, RemoteHandle<Fut::Output>) {
+    let (tx, rx) = oneshot::channel();
+    let keep_running = Arc::new(AtomicBool::new(false));
+
+    // Unwind Safety: See the docs for RemoteHandle.
+    let wrapped = Remote {
+        future: AssertUnwindSafe(future).catch_unwind(),
+        tx: Some(tx),
+        keep_running: keep_running.clone(),
+    };
+
+    (wrapped, RemoteHandle { rx, keep_running })
+}
diff --git a/third_party/rust/futures-util/src/future/future/shared.rs b/third_party/rust/futures-util/src/future/future/shared.rs
new file mode 100644
index 0000000000..985931564b
--- /dev/null
+++ b/third_party/rust/futures-util/src/future/future/shared.rs
@@ -0,0 +1,375 @@
+use crate::task::{waker_ref, ArcWake};
+use futures_core::future::{FusedFuture, Future};
+use futures_core::task::{Context, Poll, Waker};
+use slab::Slab;
+use std::cell::UnsafeCell;
+use std::fmt;
+use std::pin::Pin;
+use std::sync::atomic::AtomicUsize;
+use std::sync::atomic::Ordering::{Acquire, SeqCst};
+use std::sync::{Arc, Mutex, Weak};
+
+/// Future for the [`shared`](super::FutureExt::shared) method.
+#[must_use = "futures do nothing unless you `.await` or poll them"]
+pub struct Shared<Fut: Future> {
+    inner: Option<Arc<Inner<Fut>>>,
+    waker_key: usize,
+}
+
+struct Inner<Fut: Future> {
+    future_or_output: UnsafeCell<FutureOrOutput<Fut>>,
+    notifier: Arc<Notifier>,
+}
+
+struct Notifier {
+    state: AtomicUsize,
+    wakers: Mutex<Option<Slab<Option<Waker>>>>,
+}
+
+/// A weak reference to a [`Shared`] that can be upgraded much like an `Arc`.
+pub struct WeakShared<Fut: Future>(Weak<Inner<Fut>>);
+
+impl<Fut: Future> Clone for WeakShared<Fut> {
+    fn clone(&self) -> Self {
+        Self(self.0.clone())
+    }
+}
+
+// The future itself is polled behind the `Arc`, so it won't be moved
+// when `Shared` is moved.
+impl<Fut: Future> Unpin for Shared<Fut> {}
+
+impl<Fut: Future> fmt::Debug for Shared<Fut> {
+    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
+        f.debug_struct("Shared")
+            .field("inner", &self.inner)
+            .field("waker_key", &self.waker_key)
+            .finish()
+    }
+}
+
+impl<Fut: Future> fmt::Debug for Inner<Fut> {
+    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
+        f.debug_struct("Inner").finish()
+    }
+}
+
+impl<Fut: Future> fmt::Debug for WeakShared<Fut> {
+    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
+        f.debug_struct("WeakShared").finish()
+    }
+}
+
+enum FutureOrOutput<Fut: Future> {
+    Future(Fut),
+    Output(Fut::Output),
+}
+
+unsafe impl<Fut> Send for Inner<Fut>
+where
+    Fut: Future + Send,
+    Fut::Output: Send + Sync,
+{
+}
+
+unsafe impl<Fut> Sync for Inner<Fut>
+where
+    Fut: Future + Send,
+    Fut::Output: Send + Sync,
+{
+}
+
+const IDLE: usize = 0;
+const POLLING: usize = 1;
+const COMPLETE: usize = 2;
+const POISONED: usize = 3;
+
+const NULL_WAKER_KEY: usize = usize::max_value();
+
+impl<Fut: Future> Shared<Fut> {
+    pub(super) fn new(future: Fut) -> Self {
+        let inner = Inner {
+            future_or_output: UnsafeCell::new(FutureOrOutput::Future(future)),
+            notifier: Arc::new(Notifier {
+                state: AtomicUsize::new(IDLE),
+                wakers: Mutex::new(Some(Slab::new())),
+            }),
+        };
+
+        Self { inner: Some(Arc::new(inner)), waker_key: NULL_WAKER_KEY }
+    }
+}
+
+impl<Fut> Shared<Fut>
+where
+    Fut: Future,
+    Fut::Output: Clone,
+{
+    /// Returns [`Some`] containing a reference to this [`Shared`]'s output if
+    /// it has already been computed by a clone or [`None`] if it hasn't been
+    /// computed yet or this [`Shared`] already returned its output from
+    /// [`poll`](Future::poll).
+    pub fn peek(&self) -> Option<&Fut::Output> {
+        if let Some(inner) = self.inner.as_ref() {
+            match inner.notifier.state.load(SeqCst) {
+                COMPLETE => unsafe { return Some(inner.output()) },
+                POISONED => panic!("inner future panicked during poll"),
+                _ => {}
+            }
+        }
+        None
+    }
+
+    /// Creates a new [`WeakShared`] for this [`Shared`].
+    ///
+    /// Returns [`None`] if it has already been polled to completion.
+    pub fn downgrade(&self) -> Option<WeakShared<Fut>> {
+        if let Some(inner) = self.inner.as_ref() {
+            return Some(WeakShared(Arc::downgrade(inner)));
+        }
+        None
+    }
+
+    /// Gets the number of strong pointers to this allocation.
+    ///
+    /// Returns [`None`] if it has already been polled to completion.
+    ///
+    /// # Safety
+    ///
+    /// This method by itself is safe, but using it correctly requires extra care. Another thread
+    /// can change the strong count at any time, including potentially between calling this method
+    /// and acting on the result.
+    pub fn strong_count(&self) -> Option<usize> {
+        self.inner.as_ref().map(|arc| Arc::strong_count(arc))
+    }
+
+    /// Gets the number of weak pointers to this allocation.
+    ///
+    /// Returns [`None`] if it has already been polled to completion.
+    ///
+    /// # Safety
+    ///
+    /// This method by itself is safe, but using it correctly requires extra care. Another thread
+    /// can change the weak count at any time, including potentially between calling this method
+    /// and acting on the result.
+    pub fn weak_count(&self) -> Option<usize> {
+        self.inner.as_ref().map(|arc| Arc::weak_count(arc))
+    }
+}
+
+impl<Fut> Inner<Fut>
+where
+    Fut: Future,
+    Fut::Output: Clone,
+{
+    /// Safety: callers must first ensure that `self.inner.state`
+    /// is `COMPLETE`
+    unsafe fn output(&self) -> &Fut::Output {
+        match &*self.future_or_output.get() {
+            FutureOrOutput::Output(ref item) => item,
+            FutureOrOutput::Future(_) => unreachable!(),
+        }
+    }
+    /// Registers the current task to receive a wakeup when we are awoken.
+    fn record_waker(&self, waker_key: &mut usize, cx: &mut Context<'_>) {
+        let mut wakers_guard = self.notifier.wakers.lock().unwrap();
+
+        let wakers = match wakers_guard.as_mut() {
+            Some(wakers) => wakers,
+            None => return,
+        };
+
+        let new_waker = cx.waker();
+
+        if *waker_key == NULL_WAKER_KEY {
+            *waker_key = wakers.insert(Some(new_waker.clone()));
+        } else {
+            match wakers[*waker_key] {
+                Some(ref old_waker) if new_waker.will_wake(old_waker) => {}
+                // Could use clone_from here, but Waker doesn't specialize it.
+                ref mut slot => *slot = Some(new_waker.clone()),
+            }
+        }
+        debug_assert!(*waker_key != NULL_WAKER_KEY);
+    }
+
+    /// Safety: callers must first ensure that `inner.state`
+    /// is `COMPLETE`
+    unsafe fn take_or_clone_output(self: Arc<Self>) -> Fut::Output {
+        match Arc::try_unwrap(self) {
+            Ok(inner) => match inner.future_or_output.into_inner() {
+                FutureOrOutput::Output(item) => item,
+                FutureOrOutput::Future(_) => unreachable!(),
+            },
+            Err(inner) => inner.output().clone(),
+        }
+    }
+}
+
+impl<Fut> FusedFuture for Shared<Fut>
+where
+    Fut: Future,
+    Fut::Output: Clone,
+{
+    fn is_terminated(&self) -> bool {
+        self.inner.is_none()
+    }
+}
+
+impl<Fut> Future for Shared<Fut>
+where
+    Fut: Future,
+    Fut::Output: Clone,
+{
+    type Output = Fut::Output;
+
+    fn poll(mut self: Pin<&mut Self>, cx: &mut Context<'_>) -> Poll<Self::Output> {
+        let this = &mut *self;
+
+        let inner = this.inner.take().expect("Shared future polled again after completion");
+
+        // Fast path for when the wrapped future has already completed
+        if inner.notifier.state.load(Acquire) == COMPLETE {
+            // Safety: We're in the COMPLETE state
+            return unsafe { Poll::Ready(inner.take_or_clone_output()) };
+        }
+
+        inner.record_waker(&mut this.waker_key, cx);
+
+        match inner
+            .notifier
+            .state
+            .compare_exchange(IDLE, POLLING, SeqCst, SeqCst)
+            .unwrap_or_else(|x| x)
+        {
+            IDLE => {
+                // Lock acquired, fall through
+            }
+            POLLING => {
+                // Another task is currently polling, at this point we just want
+                // to ensure that the waker for this task is registered
+                this.inner = Some(inner);
+                return Poll::Pending;
+            }
+            COMPLETE => {
+                // Safety: We're in the COMPLETE state
+                return unsafe { Poll::Ready(inner.take_or_clone_output()) };
+            }
+            POISONED => panic!("inner future panicked during poll"),
+            _ => unreachable!(),
+        }
+
+        let waker = waker_ref(&inner.notifier);
+        let mut cx = Context::from_waker(&waker);
+
+        struct Reset<'a> {
+            state: &'a AtomicUsize,
+            did_not_panic: bool,
+        }
+
+        impl Drop for Reset<'_> {
+            fn drop(&mut self) {
+                if !self.did_not_panic {
+                    self.state.store(POISONED, SeqCst);
+                }
+            }
+        }
+
+        let mut reset = Reset { state: &inner.notifier.state, did_not_panic: false };
+
+        let output = {
+            let future = unsafe {
+                match &mut *inner.future_or_output.get() {
+                    FutureOrOutput::Future(fut) => Pin::new_unchecked(fut),
+                    _ => unreachable!(),
+                }
+            };
+
+            let poll_result = future.poll(&mut cx);
+            reset.did_not_panic = true;
+
+            match poll_result {
+                Poll::Pending => {
+                    if inner.notifier.state.compare_exchange(POLLING, IDLE, SeqCst, SeqCst).is_ok()
+                    {
+                        // Success
+                        drop(reset);
+                        this.inner = Some(inner);
+                        return Poll::Pending;
+                    } else {
+                        unreachable!()
+                    }
+                }
+                Poll::Ready(output) => output,
+            }
+        };
+
+        unsafe {
+            *inner.future_or_output.get() = FutureOrOutput::Output(output);
+        }
+
+        inner.notifier.state.store(COMPLETE, SeqCst);
+
+        // Wake all tasks and drop the slab
+        let mut wakers_guard = inner.notifier.wakers.lock().unwrap();
+        let mut wakers = wakers_guard.take().unwrap();
+        for waker in wakers.drain().flatten() {
+            waker.wake();
+        }
+
+        drop(reset); // Make borrow checker happy
+        drop(wakers_guard);
+
+        // Safety: We're in the COMPLETE state
+        unsafe { Poll::Ready(inner.take_or_clone_output()) }
+    }
+}
+
+impl<Fut> Clone for Shared<Fut>
+where
+    Fut: Future,
+{
+    fn clone(&self) -> Self {
+        Self { inner: self.inner.clone(), waker_key: NULL_WAKER_KEY }
+    }
+}
+
+impl<Fut> Drop for Shared<Fut>
+where
+    Fut: Future,
+{
+    fn drop(&mut self) {
+        if self.waker_key != NULL_WAKER_KEY {
+            if let Some(ref inner) = self.inner {
+                if let Ok(mut wakers) = inner.notifier.wakers.lock() {
+                    if let Some(wakers) = wakers.as_mut() {
+                        wakers.remove(self.waker_key);
+                    }
+                }
+            }
+        }
+    }
+}
+
+impl ArcWake for Notifier {
+    fn wake_by_ref(arc_self: &Arc<Self>) {
+        let wakers = &mut *arc_self.wakers.lock().unwrap();
+        if let Some(wakers) = wakers.as_mut() {
+            for (_key, opt_waker) in wakers {
+                if let Some(waker) = opt_waker.take() {
+                    waker.wake();
+                }
+            }
+        }
+    }
+}
+
+impl<Fut: Future> WeakShared<Fut> {
+    /// Attempts to upgrade this [`WeakShared`] into a [`Shared`].
+    ///
+    /// Returns [`None`] if all clones of the [`Shared`] have been dropped or polled
+    /// to completion.
+    pub fn upgrade(&self) -> Option<Shared<Fut>> {
+        Some(Shared { inner: Some(self.0.upgrade()?), waker_key: NULL_WAKER_KEY })
+    }
+}
diff --git a/third_party/rust/futures-util/src/future/join.rs b/third_party/rust/futures-util/src/future/join.rs
new file mode 100644
index 0000000000..740ffbc988
--- /dev/null
+++ b/third_party/rust/futures-util/src/future/join.rs
@@ -0,0 +1,217 @@
+#![allow(non_snake_case)]
+
+use super::assert_future;
+use crate::future::{maybe_done, MaybeDone};
+use core::fmt;
+use core::pin::Pin;
+use futures_core::future::{FusedFuture, Future};
+use futures_core::task::{Context, Poll};
+use pin_project_lite::pin_project;
+
+macro_rules! generate {
+    ($(
+        $(#[$doc:meta])*
+        ($Join:ident, <$($Fut:ident),*>),
+    )*) => ($(
+        pin_project! {
+            $(#[$doc])*
+            #[must_use = "futures do nothing unless you `.await` or poll them"]
+            pub struct $Join<$($Fut: Future),*> {
+                $(#[pin] $Fut: MaybeDone<$Fut>,)*
+            }
+        }
+
+        impl<$($Fut),*> fmt::Debug for $Join<$($Fut),*>
+        where
+            $(
+                $Fut: Future + fmt::Debug,
+                $Fut::Output: fmt::Debug,
+            )*
+        {
+            fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
+                f.debug_struct(stringify!($Join))
+                    $(.field(stringify!($Fut), &self.$Fut))*
+                    .finish()
+            }
+        }
+
+        impl<$($Fut: Future),*> $Join<$($Fut),*> {
+            fn new($($Fut: $Fut),*) -> Self {
+                Self {
+                    $($Fut: maybe_done($Fut)),*
+                }
+            }
+        }
+
+        impl<$($Fut: Future),*> Future for $Join<$($Fut),*> {
+            type Output = ($($Fut::Output),*);
+
+            fn poll(
+                self: Pin<&mut Self>, cx: &mut Context<'_>
+            ) -> Poll<Self::Output> {
+                let mut all_done = true;
+                let mut futures = self.project();
+                $(
+                    all_done &= futures.$Fut.as_mut().poll(cx).is_ready();
+                )*
+
+                if all_done {
+                    Poll::Ready(($(futures.$Fut.take_output().unwrap()), *))
+                } else {
+                    Poll::Pending
+                }
+            }
+        }
+
+        impl<$($Fut: FusedFuture),*> FusedFuture for $Join<$($Fut),*> {
+            fn is_terminated(&self) -> bool {
+                $(
+                    self.$Fut.is_terminated()
+                ) && *
+            }
+        }
+    )*)
+}
+
+generate! {
+    /// Future for the [`join`](join()) function.
+    (Join, <Fut1, Fut2>),
+
+    /// Future for the [`join3`] function.
+    (Join3, <Fut1, Fut2, Fut3>),
+
+    /// Future for the [`join4`] function.
+    (Join4, <Fut1, Fut2, Fut3, Fut4>),
+
+    /// Future for the [`join5`] function.
+    (Join5, <Fut1, Fut2, Fut3, Fut4, Fut5>),
+}
+
+/// Joins the result of two futures, waiting for them both to complete.
+///
+/// This function will return a new future which awaits both futures to
+/// complete. The returned future will finish with a tuple of both results.
+///
+/// Note that this function consumes the passed futures and returns a
+/// wrapped version of it.
+///
+/// # Examples
+///
+/// ```
+/// # futures::executor::block_on(async {
+/// use futures::future;
+///
+/// let a = async { 1 };
+/// let b = async { 2 };
+/// let pair = future::join(a, b);
+///
+/// assert_eq!(pair.await, (1, 2));
+/// # });
+/// ```
+pub fn join<Fut1, Fut2>(future1: Fut1, future2: Fut2) -> Join<Fut1, Fut2>
+where
+    Fut1: Future,
+    Fut2: Future,
+{
+    let f = Join::new(future1, future2);
+    assert_future::<(Fut1::Output, Fut2::Output), _>(f)
+}
+
+/// Same as [`join`](join()), but with more futures.
+///
+/// # Examples
+///
+/// ```
+/// # futures::executor::block_on(async {
+/// use futures::future;
+///
+/// let a = async { 1 };
+/// let b = async { 2 };
+/// let c = async { 3 };
+/// let tuple = future::join3(a, b, c);
+///
+/// assert_eq!(tuple.await, (1, 2, 3));
+/// # });
+/// ```
+pub fn join3<Fut1, Fut2, Fut3>(
+    future1: Fut1,
+    future2: Fut2,
+    future3: Fut3,
+) -> Join3<Fut1, Fut2, Fut3>
+where
+    Fut1: Future,
+    Fut2: Future,
+    Fut3: Future,
+{
+    let f = Join3::new(future1, future2, future3);
+    assert_future::<(Fut1::Output, Fut2::Output, Fut3::Output), _>(f)
+}
+
+/// Same as [`join`](join()), but with more futures.
+///
+/// # Examples
+///
+/// ```
+/// # futures::executor::block_on(async {
+/// use futures::future;
+///
+/// let a = async { 1 };
+/// let b = async { 2 };
+/// let c = async { 3 };
+/// let d = async { 4 };
+/// let tuple = future::join4(a, b, c, d);
+///
+/// assert_eq!(tuple.await, (1, 2, 3, 4));
+/// # });
+/// ```
+pub fn join4<Fut1, Fut2, Fut3, Fut4>(
+    future1: Fut1,
+    future2: Fut2,
+    future3: Fut3,
+    future4: Fut4,
+) -> Join4<Fut1, Fut2, Fut3, Fut4>
+where
+    Fut1: Future,
+    Fut2: Future,
+    Fut3: Future,
+    Fut4: Future,
+{
+    let f = Join4::new(future1, future2, future3, future4);
+    assert_future::<(Fut1::Output, Fut2::Output, Fut3::Output, Fut4::Output), _>(f)
+}
+
+/// Same as [`join`](join()), but with more futures.
+///
+/// # Examples
+///
+/// ```
+/// # futures::executor::block_on(async {
+/// use futures::future;
+///
+/// let a = async { 1 };
+/// let b = async { 2 };
+/// let c = async { 3 };
+/// let d = async { 4 };
+/// let e = async { 5 };
+/// let tuple = future::join5(a, b, c, d, e);
+///
+/// assert_eq!(tuple.await, (1, 2, 3, 4, 5));
+/// # });
+/// ```
+pub fn join5<Fut1, Fut2, Fut3, Fut4, Fut5>(
+    future1: Fut1,
+    future2: Fut2,
+    future3: Fut3,
+    future4: Fut4,
+    future5: Fut5,
+) -> Join5<Fut1, Fut2, Fut3, Fut4, Fut5>
+where
+    Fut1: Future,
+    Fut2: Future,
+    Fut3: Future,
+    Fut4: Future,
+    Fut5: Future,
+{
+    let f = Join5::new(future1, future2, future3, future4, future5);
+    assert_future::<(Fut1::Output, Fut2::Output, Fut3::Output, Fut4::Output, Fut5::Output), _>(f)
+}
diff --git a/third_party/rust/futures-util/src/future/join_all.rs b/third_party/rust/futures-util/src/future/join_all.rs
new file mode 100644
index 0000000000..7dc159ba07
--- /dev/null
+++ b/third_party/rust/futures-util/src/future/join_all.rs
@@ -0,0 +1,166 @@
+//! Definition of the `JoinAll` combinator, waiting for all of a list of futures
+//! to finish.
+
+use alloc::boxed::Box;
+use alloc::vec::Vec;
+use core::fmt;
+use core::future::Future;
+use core::iter::FromIterator;
+use core::mem;
+use core::pin::Pin;
+use core::task::{Context, Poll};
+
+use super::{assert_future, MaybeDone};
+
+#[cfg(not(futures_no_atomic_cas))]
+use crate::stream::{Collect, FuturesOrdered, StreamExt};
+
+pub(crate) fn iter_pin_mut<T>(slice: Pin<&mut [T]>) -> impl Iterator<Item = Pin<&mut T>> {
+    // Safety: `std` _could_ make this unsound if it were to decide Pin's
+    // invariants aren't required to transmit through slices. Otherwise this has
+    // the same safety as a normal field pin projection.
+    unsafe { slice.get_unchecked_mut() }.iter_mut().map(|t| unsafe { Pin::new_unchecked(t) })
+}
+
+#[must_use = "futures do nothing unless you `.await` or poll them"]
+/// Future for the [`join_all`] function.
+pub struct JoinAll<F>
+where
+    F: Future,
+{
+    kind: JoinAllKind<F>,
+}
+
+#[cfg(not(futures_no_atomic_cas))]
+pub(crate) const SMALL: usize = 30;
+
+enum JoinAllKind<F>
+where
+    F: Future,
+{
+    Small {
+        elems: Pin<Box<[MaybeDone<F>]>>,
+    },
+    #[cfg(not(futures_no_atomic_cas))]
+    Big {
+        fut: Collect<FuturesOrdered<F>, Vec<F::Output>>,
+    },
+}
+
+impl<F> fmt::Debug for JoinAll<F>
+where
+    F: Future + fmt::Debug,
+    F::Output: fmt::Debug,
+{
+    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
+        match self.kind {
+            JoinAllKind::Small { ref elems } => {
+                f.debug_struct("JoinAll").field("elems", elems).finish()
+            }
+            #[cfg(not(futures_no_atomic_cas))]
+            JoinAllKind::Big { ref fut, .. } => fmt::Debug::fmt(fut, f),
+        }
+    }
+}
+
+/// Creates a future which represents a collection of the outputs of the futures
+/// given.
+///
+/// The returned future will drive execution for all of its underlying futures,
+/// collecting the results into a destination `Vec<T>` in the same order as they
+/// were provided.
+///
+/// This function is only available when the `std` or `alloc` feature of this
+/// library is activated, and it is activated by default.
+///
+/// # See Also
+///
+/// `join_all` will switch to the more powerful [`FuturesOrdered`] for performance
+/// reasons if the number of futures is large. You may want to look into using it or
+/// it's counterpart [`FuturesUnordered`][crate::stream::FuturesUnordered] directly.
+///
+/// Some examples for additional functionality provided by these are:
+///
+///  * Adding new futures to the set even after it has been started.
+///
+///  * Only polling the specific futures that have been woken. In cases where
+///    you have a lot of futures this will result in much more efficient polling.
+///
+/// # Examples
+///
+/// ```
+/// # futures::executor::block_on(async {
+/// use futures::future::join_all;
+///
+/// async fn foo(i: u32) -> u32 { i }
+///
+/// let futures = vec![foo(1), foo(2), foo(3)];
+///
+/// assert_eq!(join_all(futures).await, [1, 2, 3]);
+/// # });
+/// ```
+pub fn join_all<I>(iter: I) -> JoinAll<I::Item>
+where
+    I: IntoIterator,
+    I::Item: Future,
+{
+    let iter = iter.into_iter();
+
+    #[cfg(futures_no_atomic_cas)]
+    {
+        let kind =
+            JoinAllKind::Small { elems: iter.map(MaybeDone::Future).collect::<Box<[_]>>().into() };
+
+        assert_future::<Vec<<I::Item as Future>::Output>, _>(JoinAll { kind })
+    }
+
+    #[cfg(not(futures_no_atomic_cas))]
+    {
+        let kind = match iter.size_hint().1 {
+            Some(max) if max <= SMALL => JoinAllKind::Small {
+                elems: iter.map(MaybeDone::Future).collect::<Box<[_]>>().into(),
+            },
+            _ => JoinAllKind::Big { fut: iter.collect::<FuturesOrdered<_>>().collect() },
+        };
+
+        assert_future::<Vec<<I::Item as Future>::Output>, _>(JoinAll { kind })
+    }
+}
+
+impl<F> Future for JoinAll<F>
+where
+    F: Future,
+{
+    type Output = Vec<F::Output>;
+
+    fn poll(mut self: Pin<&mut Self>, cx: &mut Context<'_>) -> Poll<Self::Output> {
+        match &mut self.kind {
+            JoinAllKind::Small { elems } => {
+                let mut all_done = true;
+
+                for elem in iter_pin_mut(elems.as_mut()) {
+                    if elem.poll(cx).is_pending() {
+                        all_done = false;
+                    }
+                }
+
+                if all_done {
+                    let mut elems = mem::replace(elems, Box::pin([]));
+                    let result =
+                        iter_pin_mut(elems.as_mut()).map(|e| e.take_output().unwrap()).collect();
+                    Poll::Ready(result)
+                } else {
+                    Poll::Pending
+                }
+            }
+            #[cfg(not(futures_no_atomic_cas))]
+            JoinAllKind::Big { fut } => Pin::new(fut).poll(cx),
+        }
+    }
+}
+
+impl<F: Future> FromIterator<F> for JoinAll<F> {
+    fn from_iter<T: IntoIterator<Item = F>>(iter: T) -> Self {
+        join_all(iter)
+    }
+}
diff --git a/third_party/rust/futures-util/src/future/lazy.rs b/third_party/rust/futures-util/src/future/lazy.rs
new file mode 100644
index 0000000000..e9a8cf2fa9
--- /dev/null
+++ b/third_party/rust/futures-util/src/future/lazy.rs
@@ -0,0 +1,60 @@
+use super::assert_future;
+use core::pin::Pin;
+use futures_core::future::{FusedFuture, Future};
+use futures_core::task::{Context, Poll};
+
+/// Future for the [`lazy`] function.
+#[derive(Debug)]
+#[must_use = "futures do nothing unless you `.await` or poll them"]
+pub struct Lazy<F> {
+    f: Option<F>,
+}
+
+// safe because we never generate `Pin<&mut F>`
+impl<F> Unpin for Lazy<F> {}
+
+/// Creates a new future that allows delayed execution of a closure.
+///
+/// The provided closure is only run once the future is polled.
+///
+/// # Examples
+///
+/// ```
+/// # futures::executor::block_on(async {
+/// use futures::future;
+///
+/// let a = future::lazy(|_| 1);
+/// assert_eq!(a.await, 1);
+///
+/// let b = future::lazy(|_| -> i32 {
+///     panic!("oh no!")
+/// });
+/// drop(b); // closure is never run
+/// # });
+/// ```
+pub fn lazy<F, R>(f: F) -> Lazy<F>
+where
+    F: FnOnce(&mut Context<'_>) -> R,
+{
+    assert_future::<R, _>(Lazy { f: Some(f) })
+}
+
+impl<F, R> FusedFuture for Lazy<F>
+where
+    F: FnOnce(&mut Context<'_>) -> R,
+{
+    fn is_terminated(&self) -> bool {
+        self.f.is_none()
+    }
+}
+
+impl<F, R> Future for Lazy<F>
+where
+    F: FnOnce(&mut Context<'_>) -> R,
+{
+    type Output = R;
+
+    fn poll(mut self: Pin<&mut Self>, cx: &mut Context<'_>) -> Poll<R> {
+        Poll::Ready((self.f.take().expect("Lazy polled after completion"))(cx))
+    }
+}
diff --git a/third_party/rust/futures-util/src/future/maybe_done.rs b/third_party/rust/futures-util/src/future/maybe_done.rs
new file mode 100644
index 0000000000..26e6c27588
--- /dev/null
+++ b/third_party/rust/futures-util/src/future/maybe_done.rs
@@ -0,0 +1,104 @@
+//! Definition of the MaybeDone combinator
+
+use super::assert_future;
+use core::mem;
+use core::pin::Pin;
+use futures_core::future::{FusedFuture, Future};
+use futures_core::ready;
+use futures_core::task::{Context, Poll};
+
+/// A future that may have completed.
+///
+/// This is created by the [`maybe_done()`] function.
+#[derive(Debug)]
+pub enum MaybeDone<Fut: Future> {
+    /// A not-yet-completed future
+    Future(/* #[pin] */ Fut),
+    /// The output of the completed future
+    Done(Fut::Output),
+    /// The empty variant after the result of a [`MaybeDone`] has been
+    /// taken using the [`take_output`](MaybeDone::take_output) method.
+    Gone,
+}
+
+impl<Fut: Future + Unpin> Unpin for MaybeDone<Fut> {}
+
+/// Wraps a future into a `MaybeDone`
+///
+/// # Examples
+///
+/// ```
+/// # futures::executor::block_on(async {
+/// use futures::future;
+/// use futures::pin_mut;
+///
+/// let future = future::maybe_done(async { 5 });
+/// pin_mut!(future);
+/// assert_eq!(future.as_mut().take_output(), None);
+/// let () = future.as_mut().await;
+/// assert_eq!(future.as_mut().take_output(), Some(5));
+/// assert_eq!(future.as_mut().take_output(), None);
+/// # });
+/// ```
+pub fn maybe_done<Fut: Future>(future: Fut) -> MaybeDone<Fut> {
+    assert_future::<(), _>(MaybeDone::Future(future))
+}
+
+impl<Fut: Future> MaybeDone<Fut> {
+    /// Returns an [`Option`] containing a mutable reference to the output of the future.
+    /// The output of this method will be [`Some`] if and only if the inner
+    /// future has been completed and [`take_output`](MaybeDone::take_output)
+    /// has not yet been called.
+    #[inline]
+    pub fn output_mut(self: Pin<&mut Self>) -> Option<&mut Fut::Output> {
+        unsafe {
+            match self.get_unchecked_mut() {
+                MaybeDone::Done(res) => Some(res),
+                _ => None,
+            }
+        }
+    }
+
+    /// Attempt to take the output of a `MaybeDone` without driving it
+    /// towards completion.
+    #[inline]
+    pub fn take_output(self: Pin<&mut Self>) -> Option<Fut::Output> {
+        match &*self {
+            Self::Done(_) => {}
+            Self::Future(_) | Self::Gone => return None,
+        }
+        unsafe {
+            match mem::replace(self.get_unchecked_mut(), Self::Gone) {
+                MaybeDone::Done(output) => Some(output),
+                _ => unreachable!(),
+            }
+        }
+    }
+}
+
+impl<Fut: Future> FusedFuture for MaybeDone<Fut> {
+    fn is_terminated(&self) -> bool {
+        match self {
+            Self::Future(_) => false,
+            Self::Done(_) | Self::Gone => true,
+        }
+    }
+}
+
+impl<Fut: Future> Future for MaybeDone<Fut> {
+    type Output = ();
+
+    fn poll(mut self: Pin<&mut Self>, cx: &mut Context<'_>) -> Poll<Self::Output> {
+        unsafe {
+            match self.as_mut().get_unchecked_mut() {
+                MaybeDone::Future(f) => {
+                    let res = ready!(Pin::new_unchecked(f).poll(cx));
+                    self.set(Self::Done(res));
+                }
+                MaybeDone::Done(_) => {}
+                MaybeDone::Gone => panic!("MaybeDone polled after value taken"),
+            }
+        }
+        Poll::Ready(())
+    }
+}
diff --git a/third_party/rust/futures-util/src/future/mod.rs b/third_party/rust/futures-util/src/future/mod.rs
new file mode 100644
index 0000000000..374e36512f
--- /dev/null
+++ b/third_party/rust/futures-util/src/future/mod.rs
@@ -0,0 +1,131 @@
+//! Asynchronous values.
+//!
+//! This module contains:
+//!
+//! - The [`Future`] trait.
+//! - The [`FutureExt`] and [`TryFutureExt`] trait, which provides adapters for
+//!   chaining and composing futures.
+//! - Top-level future combinators like [`lazy`](lazy()) which creates a future
+//!   from a closure that defines its return value, and [`ready`](ready()),
+//!   which constructs a future with an immediate defined value.
+
+#[doc(no_inline)]
+pub use core::future::Future;
+
+#[cfg(feature = "alloc")]
+pub use futures_core::future::{BoxFuture, LocalBoxFuture};
+pub use futures_core::future::{FusedFuture, TryFuture};
+pub use futures_task::{FutureObj, LocalFutureObj, UnsafeFutureObj};
+
+// Extension traits and combinators
+#[allow(clippy::module_inception)]
+mod future;
+pub use self::future::{
+    Flatten, Fuse, FutureExt, Inspect, IntoStream, Map, MapInto, NeverError, Then, UnitError,
+};
+
+#[deprecated(note = "This is now an alias for [Flatten](Flatten)")]
+pub use self::future::FlattenStream;
+
+#[cfg(feature = "std")]
+pub use self::future::CatchUnwind;
+
+#[cfg(feature = "channel")]
+#[cfg_attr(docsrs, doc(cfg(feature = "channel")))]
+#[cfg(feature = "std")]
+pub use self::future::{Remote, RemoteHandle};
+
+#[cfg(feature = "std")]
+pub use self::future::{Shared, WeakShared};
+
+mod try_future;
+pub use self::try_future::{
+    AndThen, ErrInto, InspectErr, InspectOk, IntoFuture, MapErr, MapOk, MapOkOrElse, OkInto,
+    OrElse, TryFlatten, TryFlattenStream, TryFutureExt, UnwrapOrElse,
+};
+
+#[cfg(feature = "sink")]
+#[cfg_attr(docsrs, doc(cfg(feature = "sink")))]
+pub use self::try_future::FlattenSink;
+
+// Primitive futures
+
+mod lazy;
+pub use self::lazy::{lazy, Lazy};
+
+mod pending;
+pub use self::pending::{pending, Pending};
+
+mod maybe_done;
+pub use self::maybe_done::{maybe_done, MaybeDone};
+
+mod try_maybe_done;
+pub use self::try_maybe_done::{try_maybe_done, TryMaybeDone};
+
+mod option;
+pub use self::option::OptionFuture;
+
+mod poll_fn;
+pub use self::poll_fn::{poll_fn, PollFn};
+
+mod poll_immediate;
+pub use self::poll_immediate::{poll_immediate, PollImmediate};
+
+mod ready;
+pub use self::ready::{err, ok, ready, Ready};
+
+mod join;
+pub use self::join::{join, join3, join4, join5, Join, Join3, Join4, Join5};
+
+#[cfg(feature = "alloc")]
+mod join_all;
+#[cfg(feature = "alloc")]
+pub use self::join_all::{join_all, JoinAll};
+
+mod select;
+pub use self::select::{select, Select};
+
+#[cfg(feature = "alloc")]
+mod select_all;
+#[cfg(feature = "alloc")]
+pub use self::select_all::{select_all, SelectAll};
+
+mod try_join;
+pub use self::try_join::{
+    try_join, try_join3, try_join4, try_join5, TryJoin, TryJoin3, TryJoin4, TryJoin5,
+};
+
+#[cfg(feature = "alloc")]
+mod try_join_all;
+#[cfg(feature = "alloc")]
+pub use self::try_join_all::{try_join_all, TryJoinAll};
+
+mod try_select;
+pub use self::try_select::{try_select, TrySelect};
+
+#[cfg(feature = "alloc")]
+mod select_ok;
+#[cfg(feature = "alloc")]
+pub use self::select_ok::{select_ok, SelectOk};
+
+mod either;
+pub use self::either::Either;
+
+#[cfg(not(futures_no_atomic_cas))]
+#[cfg(feature = "alloc")]
+mod abortable;
+#[cfg(not(futures_no_atomic_cas))]
+#[cfg(feature = "alloc")]
+pub use crate::abortable::{AbortHandle, AbortRegistration, Abortable, Aborted};
+#[cfg(not(futures_no_atomic_cas))]
+#[cfg(feature = "alloc")]
+pub use abortable::abortable;
+
+// Just a helper function to ensure the futures we're returning all have the
+// right implementations.
+pub(crate) fn assert_future<T, F>(future: F) -> F
+where
+    F: Future<Output = T>,
+{
+    future
+}
diff --git a/third_party/rust/futures-util/src/future/option.rs b/third_party/rust/futures-util/src/future/option.rs
new file mode 100644
index 0000000000..0bc377758a
--- /dev/null
+++ b/third_party/rust/futures-util/src/future/option.rs
@@ -0,0 +1,64 @@
+//! Definition of the `Option` (optional step) combinator
+
+use core::pin::Pin;
+use futures_core::future::{FusedFuture, Future};
+use futures_core::task::{Context, Poll};
+use pin_project_lite::pin_project;
+
+pin_project! {
+    /// A future representing a value which may or may not be present.
+    ///
+    /// Created by the [`From`] implementation for [`Option`](std::option::Option).
+    ///
+    /// # Examples
+    ///
+    /// ```
+    /// # futures::executor::block_on(async {
+    /// use futures::future::OptionFuture;
+    ///
+    /// let mut a: OptionFuture<_> = Some(async { 123 }).into();
+    /// assert_eq!(a.await, Some(123));
+    ///
+    /// a = None.into();
+    /// assert_eq!(a.await, None);
+    /// # });
+    /// ```
+    #[derive(Debug, Clone)]
+    #[must_use = "futures do nothing unless you `.await` or poll them"]
+    pub struct OptionFuture<F> {
+        #[pin]
+        inner: Option<F>,
+    }
+}
+
+impl<F> Default for OptionFuture<F> {
+    fn default() -> Self {
+        Self { inner: None }
+    }
+}
+
+impl<F: Future> Future for OptionFuture<F> {
+    type Output = Option<F::Output>;
+
+    fn poll(self: Pin<&mut Self>, cx: &mut Context<'_>) -> Poll<Self::Output> {
+        match self.project().inner.as_pin_mut() {
+            Some(x) => x.poll(cx).map(Some),
+            None => Poll::Ready(None),
+        }
+    }
+}
+
+impl<F: FusedFuture> FusedFuture for OptionFuture<F> {
+    fn is_terminated(&self) -> bool {
+        match &self.inner {
+            Some(x) => x.is_terminated(),
+            None => true,
+        }
+    }
+}
+
+impl<T> From<Option<T>> for OptionFuture<T> {
+    fn from(option: Option<T>) -> Self {
+        Self { inner: option }
+    }
+}
diff --git a/third_party/rust/futures-util/src/future/pending.rs b/third_party/rust/futures-util/src/future/pending.rs
new file mode 100644
index 0000000000..b8e28686e1
--- /dev/null
+++ b/third_party/rust/futures-util/src/future/pending.rs
@@ -0,0 +1,55 @@
+use super::assert_future;
+use core::marker;
+use core::pin::Pin;
+use futures_core::future::{FusedFuture, Future};
+use futures_core::task::{Context, Poll};
+
+/// Future for the [`pending()`] function.
+#[derive(Debug)]
+#[must_use = "futures do nothing unless you `.await` or poll them"]
+pub struct Pending<T> {
+    _data: marker::PhantomData<T>,
+}
+
+impl<T> FusedFuture for Pending<T> {
+    fn is_terminated(&self) -> bool {
+        true
+    }
+}
+
+/// Creates a future which never resolves, representing a computation that never
+/// finishes.
+///
+/// The returned future will forever return [`Poll::Pending`].
+///
+/// # Examples
+///
+/// ```ignore
+/// # futures::executor::block_on(async {
+/// use futures::future;
+///
+/// let future = future::pending();
+/// let () = future.await;
+/// unreachable!();
+/// # });
+/// ```
+#[cfg_attr(docsrs, doc(alias = "never"))]
+pub fn pending<T>() -> Pending<T> {
+    assert_future::<T, _>(Pending { _data: marker::PhantomData })
+}
+
+impl<T> Future for Pending<T> {
+    type Output = T;
+
+    fn poll(self: Pin<&mut Self>, _: &mut Context<'_>) -> Poll<T> {
+        Poll::Pending
+    }
+}
+
+impl<T> Unpin for Pending<T> {}
+
+impl<T> Clone for Pending<T> {
+    fn clone(&self) -> Self {
+        pending()
+    }
+}
diff --git a/third_party/rust/futures-util/src/future/poll_fn.rs b/third_party/rust/futures-util/src/future/poll_fn.rs
new file mode 100644
index 0000000000..19311570b5
--- /dev/null
+++ b/third_party/rust/futures-util/src/future/poll_fn.rs
@@ -0,0 +1,58 @@
+//! Definition of the `PollFn` adapter combinator
+
+use super::assert_future;
+use core::fmt;
+use core::pin::Pin;
+use futures_core::future::Future;
+use futures_core::task::{Context, Poll};
+
+/// Future for the [`poll_fn`] function.
+#[must_use = "futures do nothing unless you `.await` or poll them"]
+pub struct PollFn<F> {
+    f: F,
+}
+
+impl<F> Unpin for PollFn<F> {}
+
+/// Creates a new future wrapping around a function returning [`Poll`].
+///
+/// Polling the returned future delegates to the wrapped function.
+///
+/// # Examples
+///
+/// ```
+/// # futures::executor::block_on(async {
+/// use futures::future::poll_fn;
+/// use futures::task::{Context, Poll};
+///
+/// fn read_line(_cx: &mut Context<'_>) -> Poll<String> {
+///     Poll::Ready("Hello, World!".into())
+/// }
+///
+/// let read_future = poll_fn(read_line);
+/// assert_eq!(read_future.await, "Hello, World!".to_owned());
+/// # });
+/// ```
+pub fn poll_fn<T, F>(f: F) -> PollFn<F>
+where
+    F: FnMut(&mut Context<'_>) -> Poll<T>,
+{
+    assert_future::<T, _>(PollFn { f })
+}
+
+impl<F> fmt::Debug for PollFn<F> {
+    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
+        f.debug_struct("PollFn").finish()
+    }
+}
+
+impl<T, F> Future for PollFn<F>
+where
+    F: FnMut(&mut Context<'_>) -> Poll<T>,
+{
+    type Output = T;
+
+    fn poll(mut self: Pin<&mut Self>, cx: &mut Context<'_>) -> Poll<T> {
+        (&mut self.f)(cx)
+    }
+}
diff --git a/third_party/rust/futures-util/src/future/poll_immediate.rs b/third_party/rust/futures-util/src/future/poll_immediate.rs
new file mode 100644
index 0000000000..5ae555c73e
--- /dev/null
+++ b/third_party/rust/futures-util/src/future/poll_immediate.rs
@@ -0,0 +1,126 @@
+use super::assert_future;
+use core::pin::Pin;
+use futures_core::task::{Context, Poll};
+use futures_core::{FusedFuture, Future, Stream};
+use pin_project_lite::pin_project;
+
+pin_project! {
+    /// Future for the [`poll_immediate`](poll_immediate()) function.
+    ///
+    /// It will never return [Poll::Pending](core::task::Poll::Pending)
+    #[derive(Debug, Clone)]
+    #[must_use = "futures do nothing unless you `.await` or poll them"]
+    pub struct PollImmediate<T> {
+        #[pin]
+        future: Option<T>
+    }
+}
+
+impl<T, F> Future for PollImmediate<F>
+where
+    F: Future<Output = T>,
+{
+    type Output = Option<T>;
+
+    #[inline]
+    fn poll(self: Pin<&mut Self>, cx: &mut Context<'_>) -> Poll<Option<T>> {
+        let mut this = self.project();
+        let inner =
+            this.future.as_mut().as_pin_mut().expect("PollImmediate polled after completion");
+        match inner.poll(cx) {
+            Poll::Ready(t) => {
+                this.future.set(None);
+                Poll::Ready(Some(t))
+            }
+            Poll::Pending => Poll::Ready(None),
+        }
+    }
+}
+
+impl<T: Future> FusedFuture for PollImmediate<T> {
+    fn is_terminated(&self) -> bool {
+        self.future.is_none()
+    }
+}
+
+/// A [Stream](crate::stream::Stream) implementation that can be polled repeatedly until the future is done.
+/// The stream will never return [Poll::Pending](core::task::Poll::Pending)
+/// so polling it in a tight loop is worse than using a blocking synchronous function.
+/// ```
+/// # futures::executor::block_on(async {
+/// use futures::task::Poll;
+/// use futures::{StreamExt, future, pin_mut};
+/// use future::FusedFuture;
+///
+/// let f = async { 1_u32 };
+/// pin_mut!(f);
+/// let mut r = future::poll_immediate(f);
+/// assert_eq!(r.next().await, Some(Poll::Ready(1)));
+///
+/// let f = async {futures::pending!(); 42_u8};
+/// pin_mut!(f);
+/// let mut p = future::poll_immediate(f);
+/// assert_eq!(p.next().await, Some(Poll::Pending));
+/// assert!(!p.is_terminated());
+/// assert_eq!(p.next().await, Some(Poll::Ready(42)));
+/// assert!(p.is_terminated());
+/// assert_eq!(p.next().await, None);
+/// # });
+/// ```
+impl<T, F> Stream for PollImmediate<F>
+where
+    F: Future<Output = T>,
+{
+    type Item = Poll<T>;
+
+    fn poll_next(self: Pin<&mut Self>, cx: &mut Context<'_>) -> Poll<Option<Self::Item>> {
+        let mut this = self.project();
+        match this.future.as_mut().as_pin_mut() {
+            // inner is gone, so we can signal that the stream is closed.
+            None => Poll::Ready(None),
+            Some(fut) => Poll::Ready(Some(fut.poll(cx).map(|t| {
+                this.future.set(None);
+                t
+            }))),
+        }
+    }
+}
+
+/// Creates a future that is immediately ready with an Option of a value.
+/// Specifically this means that [poll](core::future::Future::poll()) always returns [Poll::Ready](core::task::Poll::Ready).
+///
+/// # Caution
+///
+/// When consuming the future by this function, note the following:
+///
+/// - This function does not guarantee that the future will run to completion, so it is generally incompatible with passing the non-cancellation-safe future by value.
+/// - Even if the future is cancellation-safe, creating and dropping new futures frequently may lead to performance problems.
+///
+/// # Examples
+///
+/// ```
+/// # futures::executor::block_on(async {
+/// use futures::future;
+///
+/// let r = future::poll_immediate(async { 1_u32 });
+/// assert_eq!(r.await, Some(1));
+///
+/// let p = future::poll_immediate(future::pending::<i32>());
+/// assert_eq!(p.await, None);
+/// # });
+/// ```
+///
+/// ### Reusing a future
+///
+/// ```
+/// # futures::executor::block_on(async {
+/// use futures::{future, pin_mut};
+/// let f = async {futures::pending!(); 42_u8};
+/// pin_mut!(f);
+/// assert_eq!(None, future::poll_immediate(&mut f).await);
+/// assert_eq!(42, f.await);
+/// # });
+/// ```
+pub fn poll_immediate<F: Future>(f: F) -> PollImmediate<F> {
+    assert_future::<Option<F::Output>, PollImmediate<F>>(PollImmediate { future: Some(f) })
+}
diff --git a/third_party/rust/futures-util/src/future/ready.rs b/third_party/rust/futures-util/src/future/ready.rs
new file mode 100644
index 0000000000..e3d791b3cf
--- /dev/null
+++ b/third_party/rust/futures-util/src/future/ready.rs
@@ -0,0 +1,82 @@
+use super::assert_future;
+use core::pin::Pin;
+use futures_core::future::{FusedFuture, Future};
+use futures_core::task::{Context, Poll};
+
+/// Future for the [`ready`](ready()) function.
+#[derive(Debug, Clone)]
+#[must_use = "futures do nothing unless you `.await` or poll them"]
+pub struct Ready<T>(Option<T>);
+
+impl<T> Ready<T> {
+    /// Unwraps the value from this immediately ready future.
+    #[inline]
+    pub fn into_inner(mut self) -> T {
+        self.0.take().unwrap()
+    }
+}
+
+impl<T> Unpin for Ready<T> {}
+
+impl<T> FusedFuture for Ready<T> {
+    fn is_terminated(&self) -> bool {
+        self.0.is_none()
+    }
+}
+
+impl<T> Future for Ready<T> {
+    type Output = T;
+
+    #[inline]
+    fn poll(mut self: Pin<&mut Self>, _cx: &mut Context<'_>) -> Poll<T> {
+        Poll::Ready(self.0.take().expect("Ready polled after completion"))
+    }
+}
+
+/// Creates a future that is immediately ready with a value.
+///
+/// # Examples
+///
+/// ```
+/// # futures::executor::block_on(async {
+/// use futures::future;
+///
+/// let a = future::ready(1);
+/// assert_eq!(a.await, 1);
+/// # });
+/// ```
+pub fn ready<T>(t: T) -> Ready<T> {
+    assert_future::<T, _>(Ready(Some(t)))
+}
+
+/// Create a future that is immediately ready with a success value.
+///
+/// # Examples
+///
+/// ```
+/// # futures::executor::block_on(async {
+/// use futures::future;
+///
+/// let a = future::ok::<i32, i32>(1);
+/// assert_eq!(a.await, Ok(1));
+/// # });
+/// ```
+pub fn ok<T, E>(t: T) -> Ready<Result<T, E>> {
+    Ready(Some(Ok(t)))
+}
+
+/// Create a future that is immediately ready with an error value.
+///
+/// # Examples
+///
+/// ```
+/// # futures::executor::block_on(async {
+/// use futures::future;
+///
+/// let a = future::err::<i32, i32>(1);
+/// assert_eq!(a.await, Err(1));
+/// # });
+/// ```
+pub fn err<T, E>(err: E) -> Ready<Result<T, E>> {
+    Ready(Some(Err(err)))
+}
diff --git a/third_party/rust/futures-util/src/future/select.rs b/third_party/rust/futures-util/src/future/select.rs
new file mode 100644
index 0000000000..e693a30b00
--- /dev/null
+++ b/third_party/rust/futures-util/src/future/select.rs
@@ -0,0 +1,125 @@
+use super::assert_future;
+use crate::future::{Either, FutureExt};
+use core::pin::Pin;
+use futures_core::future::{FusedFuture, Future};
+use futures_core::task::{Context, Poll};
+
+/// Future for the [`select()`] function.
+#[must_use = "futures do nothing unless you `.await` or poll them"]
+#[derive(Debug)]
+pub struct Select<A, B> {
+    inner: Option<(A, B)>,
+}
+
+impl<A: Unpin, B: Unpin> Unpin for Select<A, B> {}
+
+/// Waits for either one of two differently-typed futures to complete.
+///
+/// This function will return a new future which awaits for either one of both
+/// futures to complete. The returned future will finish with both the value
+/// resolved and a future representing the completion of the other work.
+///
+/// Note that this function consumes the receiving futures and returns a
+/// wrapped version of them.
+///
+/// Also note that if both this and the second future have the same
+/// output type you can use the `Either::factor_first` method to
+/// conveniently extract out the value at the end.
+///
+/// # Examples
+///
+/// A simple example
+///
+/// ```
+/// # futures::executor::block_on(async {
+/// use futures::{
+///     pin_mut,
+///     future::Either,
+///     future::self,
+/// };
+///
+/// // These two futures have different types even though their outputs have the same type.
+/// let future1 = async {
+///     future::pending::<()>().await; // will never finish
+///     1
+/// };
+/// let future2 = async {
+///     future::ready(2).await
+/// };
+///
+/// // 'select' requires Future + Unpin bounds
+/// pin_mut!(future1);
+/// pin_mut!(future2);
+///
+/// let value = match future::select(future1, future2).await {
+///     Either::Left((value1, _)) => value1,  // `value1` is resolved from `future1`
+///                                           // `_` represents `future2`
+///     Either::Right((value2, _)) => value2, // `value2` is resolved from `future2`
+///                                           // `_` represents `future1`
+/// };
+///
+/// assert!(value == 2);
+/// # });
+/// ```
+///
+/// A more complex example
+///
+/// ```
+/// use futures::future::{self, Either, Future, FutureExt};
+///
+/// // A poor-man's join implemented on top of select
+///
+/// fn join<A, B>(a: A, b: B) -> impl Future<Output=(A::Output, B::Output)>
+///     where A: Future + Unpin,
+///           B: Future + Unpin,
+/// {
+///     future::select(a, b).then(|either| {
+///         match either {
+///             Either::Left((x, b)) => b.map(move |y| (x, y)).left_future(),
+///             Either::Right((y, a)) => a.map(move |x| (x, y)).right_future(),
+///         }
+///     })
+/// }
+/// ```
+pub fn select<A, B>(future1: A, future2: B) -> Select<A, B>
+where
+    A: Future + Unpin,
+    B: Future + Unpin,
+{
+    assert_future::<Either<(A::Output, B), (B::Output, A)>, _>(Select {
+        inner: Some((future1, future2)),
+    })
+}
+
+impl<A, B> Future for Select<A, B>
+where
+    A: Future + Unpin,
+    B: Future + Unpin,
+{
+    type Output = Either<(A::Output, B), (B::Output, A)>;
+
+    fn poll(mut self: Pin<&mut Self>, cx: &mut Context<'_>) -> Poll<Self::Output> {
+        let (mut a, mut b) = self.inner.take().expect("cannot poll Select twice");
+
+        if let Poll::Ready(val) = a.poll_unpin(cx) {
+            return Poll::Ready(Either::Left((val, b)));
+        }
+
+        if let Poll::Ready(val) = b.poll_unpin(cx) {
+            return Poll::Ready(Either::Right((val, a)));
+        }
+
+        self.inner = Some((a, b));
+        Poll::Pending
+    }
+}
+
+impl<A, B> FusedFuture for Select<A, B>
+where
+    A: Future + Unpin,
+    B: Future + Unpin,
+{
+    fn is_terminated(&self) -> bool {
+        self.inner.is_none()
+    }
+}
diff --git a/third_party/rust/futures-util/src/future/select_all.rs b/third_party/rust/futures-util/src/future/select_all.rs
new file mode 100644
index 0000000000..07d65cae79
--- /dev/null
+++ b/third_party/rust/futures-util/src/future/select_all.rs
@@ -0,0 +1,74 @@
+use super::assert_future;
+use crate::future::FutureExt;
+use alloc::vec::Vec;
+use core::iter::FromIterator;
+use core::mem;
+use core::pin::Pin;
+use futures_core::future::Future;
+use futures_core::task::{Context, Poll};
+
+/// Future for the [`select_all`] function.
+#[derive(Debug)]
+#[must_use = "futures do nothing unless you `.await` or poll them"]
+pub struct SelectAll<Fut> {
+    inner: Vec<Fut>,
+}
+
+impl<Fut: Unpin> Unpin for SelectAll<Fut> {}
+
+/// Creates a new future which will select over a list of futures.
+///
+/// The returned future will wait for any future within `iter` to be ready. Upon
+/// completion the item resolved will be returned, along with the index of the
+/// future that was ready and the list of all the remaining futures.
+///
+/// There are no guarantees provided on the order of the list with the remaining
+/// futures. They might be swapped around, reversed, or completely random.
+///
+/// This function is only available when the `std` or `alloc` feature of this
+/// library is activated, and it is activated by default.
+///
+/// # Panics
+///
+/// This function will panic if the iterator specified contains no items.
+pub fn select_all<I>(iter: I) -> SelectAll<I::Item>
+where
+    I: IntoIterator,
+    I::Item: Future + Unpin,
+{
+    let ret = SelectAll { inner: iter.into_iter().collect() };
+    assert!(!ret.inner.is_empty());
+    assert_future::<(<I::Item as Future>::Output, usize, Vec<I::Item>), _>(ret)
+}
+
+impl<Fut> SelectAll<Fut> {
+    /// Consumes this combinator, returning the underlying futures.
+    pub fn into_inner(self) -> Vec<Fut> {
+        self.inner
+    }
+}
+
+impl<Fut: Future + Unpin> Future for SelectAll<Fut> {
+    type Output = (Fut::Output, usize, Vec<Fut>);
+
+    fn poll(mut self: Pin<&mut Self>, cx: &mut Context<'_>) -> Poll<Self::Output> {
+        let item = self.inner.iter_mut().enumerate().find_map(|(i, f)| match f.poll_unpin(cx) {
+            Poll::Pending => None,
+            Poll::Ready(e) => Some((i, e)),
+        });
+        match item {
+            Some((idx, res)) => {
+                let _ = self.inner.swap_remove(idx);
+                let rest = mem::take(&mut self.inner);
+                Poll::Ready((res, idx, rest))
+            }
+            None => Poll::Pending,
+        }
+    }
+}
+
+impl<Fut: Future + Unpin> FromIterator<Fut> for SelectAll<Fut> {
+    fn from_iter<T: IntoIterator<Item = Fut>>(iter: T) -> Self {
+        select_all(iter)
+    }
+}
diff --git a/third_party/rust/futures-util/src/future/select_ok.rs b/third_party/rust/futures-util/src/future/select_ok.rs
new file mode 100644
index 0000000000..5d5579930b
--- /dev/null
+++ b/third_party/rust/futures-util/src/future/select_ok.rs
@@ -0,0 +1,85 @@
+use super::assert_future;
+use crate::future::TryFutureExt;
+use alloc::vec::Vec;
+use core::iter::FromIterator;
+use core::mem;
+use core::pin::Pin;
+use futures_core::future::{Future, TryFuture};
+use futures_core::task::{Context, Poll};
+
+/// Future for the [`select_ok`] function.
+#[derive(Debug)]
+#[must_use = "futures do nothing unless you `.await` or poll them"]
+pub struct SelectOk<Fut> {
+    inner: Vec<Fut>,
+}
+
+impl<Fut: Unpin> Unpin for SelectOk<Fut> {}
+
+/// Creates a new future which will select the first successful future over a list of futures.
+///
+/// The returned future will wait for any future within `iter` to be ready and Ok. Unlike
+/// `select_all`, this will only return the first successful completion, or the last
+/// failure. This is useful in contexts where any success is desired and failures
+/// are ignored, unless all the futures fail.
+///
+///  This function is only available when the `std` or `alloc` feature of this
+/// library is activated, and it is activated by default.
+///
+/// # Panics
+///
+/// This function will panic if the iterator specified contains no items.
+pub fn select_ok<I>(iter: I) -> SelectOk<I::Item>
+where
+    I: IntoIterator,
+    I::Item: TryFuture + Unpin,
+{
+    let ret = SelectOk { inner: iter.into_iter().collect() };
+    assert!(!ret.inner.is_empty(), "iterator provided to select_ok was empty");
+    assert_future::<
+        Result<(<I::Item as TryFuture>::Ok, Vec<I::Item>), <I::Item as TryFuture>::Error>,
+        _,
+    >(ret)
+}
+
+impl<Fut: TryFuture + Unpin> Future for SelectOk<Fut> {
+    type Output = Result<(Fut::Ok, Vec<Fut>), Fut::Error>;
+
+    fn poll(mut self: Pin<&mut Self>, cx: &mut Context<'_>) -> Poll<Self::Output> {
+        // loop until we've either exhausted all errors, a success was hit, or nothing is ready
+        loop {
+            let item =
+                self.inner.iter_mut().enumerate().find_map(|(i, f)| match f.try_poll_unpin(cx) {
+                    Poll::Pending => None,
+                    Poll::Ready(e) => Some((i, e)),
+                });
+            match item {
+                Some((idx, res)) => {
+                    // always remove Ok or Err, if it's not the last Err continue looping
+                    drop(self.inner.remove(idx));
+                    match res {
+                        Ok(e) => {
+                            let rest = mem::take(&mut self.inner);
+                            return Poll::Ready(Ok((e, rest)));
+                        }
+                        Err(e) => {
+                            if self.inner.is_empty() {
+                                return Poll::Ready(Err(e));
+                            }
+                        }
+                    }
+                }
+                None => {
+                    // based on the filter above, nothing is ready, return
+                    return Poll::Pending;
+                }
+            }
+        }
+    }
+}
+
+impl<Fut: TryFuture + Unpin> FromIterator<Fut> for SelectOk<Fut> {
+    fn from_iter<T: IntoIterator<Item = Fut>>(iter: T) -> Self {
+        select_ok(iter)
+    }
+}
diff --git a/third_party/rust/futures-util/src/future/try_future/into_future.rs b/third_party/rust/futures-util/src/future/try_future/into_future.rs
new file mode 100644
index 0000000000..9f093d0e2e
--- /dev/null
+++ b/third_party/rust/futures-util/src/future/try_future/into_future.rs
@@ -0,0 +1,36 @@
+use core::pin::Pin;
+use futures_core::future::{FusedFuture, Future, TryFuture};
+use futures_core::task::{Context, Poll};
+use pin_project_lite::pin_project;
+
+pin_project! {
+    /// Future for the [`into_future`](super::TryFutureExt::into_future) method.
+    #[derive(Debug)]
+    #[must_use = "futures do nothing unless you `.await` or poll them"]
+    pub struct IntoFuture<Fut> {
+        #[pin]
+        future: Fut,
+    }
+}
+
+impl<Fut> IntoFuture<Fut> {
+    #[inline]
+    pub(crate) fn new(future: Fut) -> Self {
+        Self { future }
+    }
+}
+
+impl<Fut: TryFuture + FusedFuture> FusedFuture for IntoFuture<Fut> {
+    fn is_terminated(&self) -> bool {
+        self.future.is_terminated()
+    }
+}
+
+impl<Fut: TryFuture> Future for IntoFuture<Fut> {
+    type Output = Result<Fut::Ok, Fut::Error>;
+
+    #[inline]
+    fn poll(self: Pin<&mut Self>, cx: &mut Context<'_>) -> Poll<Self::Output> {
+        self.project().future.try_poll(cx)
+    }
+}
diff --git a/third_party/rust/futures-util/src/future/try_future/mod.rs b/third_party/rust/futures-util/src/future/try_future/mod.rs
new file mode 100644
index 0000000000..e5bc700714
--- /dev/null
+++ b/third_party/rust/futures-util/src/future/try_future/mod.rs
@@ -0,0 +1,625 @@
+//! Futures
+//!
+//! This module contains a number of functions for working with `Future`s,
+//! including the `FutureExt` trait which adds methods to `Future` types.
+
+#[cfg(feature = "compat")]
+use crate::compat::Compat;
+use core::pin::Pin;
+use futures_core::{
+    future::TryFuture,
+    stream::TryStream,
+    task::{Context, Poll},
+};
+#[cfg(feature = "sink")]
+use futures_sink::Sink;
+
+use crate::fns::{
+    inspect_err_fn, inspect_ok_fn, into_fn, map_err_fn, map_ok_fn, map_ok_or_else_fn,
+    unwrap_or_else_fn, InspectErrFn, InspectOkFn, IntoFn, MapErrFn, MapOkFn, MapOkOrElseFn,
+    UnwrapOrElseFn,
+};
+use crate::future::{assert_future, Inspect, Map};
+use crate::stream::assert_stream;
+
+// Combinators
+mod into_future;
+mod try_flatten;
+mod try_flatten_err;
+
+delegate_all!(
+    /// Future for the [`try_flatten`](TryFutureExt::try_flatten) method.
+    TryFlatten<Fut1, Fut2>(
+        try_flatten::TryFlatten<Fut1, Fut2>
+    ): Debug + Future + FusedFuture + New[|x: Fut1| try_flatten::TryFlatten::new(x)]
+);
+
+delegate_all!(
+    /// Future for the [`try_flatten_err`](TryFutureExt::try_flatten_err) method.
+    TryFlattenErr<Fut1, Fut2>(
+        try_flatten_err::TryFlattenErr<Fut1, Fut2>
+    ): Debug + Future + FusedFuture + New[|x: Fut1| try_flatten_err::TryFlattenErr::new(x)]
+);
+
+delegate_all!(
+    /// Future for the [`try_flatten_stream`](TryFutureExt::try_flatten_stream) method.
+    TryFlattenStream<Fut>(
+        try_flatten::TryFlatten<Fut, Fut::Ok>
+    ): Debug + Sink + Stream + FusedStream + New[|x: Fut| try_flatten::TryFlatten::new(x)]
+    where Fut: TryFuture
+);
+
+#[cfg(feature = "sink")]
+delegate_all!(
+    /// Sink for the [`flatten_sink`](TryFutureExt::flatten_sink) method.
+    #[cfg_attr(docsrs, doc(cfg(feature = "sink")))]
+    FlattenSink<Fut, Si>(
+        try_flatten::TryFlatten<Fut, Si>
+    ): Debug + Sink + Stream + FusedStream + New[|x: Fut| try_flatten::TryFlatten::new(x)]
+);
+
+delegate_all!(
+    /// Future for the [`and_then`](TryFutureExt::and_then) method.
+    AndThen<Fut1, Fut2, F>(
+        TryFlatten<MapOk<Fut1, F>, Fut2>
+    ): Debug + Future + FusedFuture + New[|x: Fut1, f: F| TryFlatten::new(MapOk::new(x, f))]
+);
+
+delegate_all!(
+    /// Future for the [`or_else`](TryFutureExt::or_else) method.
+    OrElse<Fut1, Fut2, F>(
+        TryFlattenErr<MapErr<Fut1, F>, Fut2>
+    ): Debug + Future + FusedFuture + New[|x: Fut1, f: F| TryFlattenErr::new(MapErr::new(x, f))]
+);
+
+delegate_all!(
+    /// Future for the [`err_into`](TryFutureExt::err_into) method.
+    ErrInto<Fut, E>(
+        MapErr<Fut, IntoFn<E>>
+    ): Debug + Future + FusedFuture + New[|x: Fut| MapErr::new(x, into_fn())]
+);
+
+delegate_all!(
+    /// Future for the [`ok_into`](TryFutureExt::ok_into) method.
+    OkInto<Fut, E>(
+        MapOk<Fut, IntoFn<E>>
+    ): Debug + Future + FusedFuture + New[|x: Fut| MapOk::new(x, into_fn())]
+);
+
+delegate_all!(
+    /// Future for the [`inspect_ok`](super::TryFutureExt::inspect_ok) method.
+    InspectOk<Fut, F>(
+        Inspect<IntoFuture<Fut>, InspectOkFn<F>>
+    ): Debug + Future + FusedFuture + New[|x: Fut, f: F| Inspect::new(IntoFuture::new(x), inspect_ok_fn(f))]
+);
+
+delegate_all!(
+    /// Future for the [`inspect_err`](super::TryFutureExt::inspect_err) method.
+    InspectErr<Fut, F>(
+        Inspect<IntoFuture<Fut>, InspectErrFn<F>>
+    ): Debug + Future + FusedFuture + New[|x: Fut, f: F| Inspect::new(IntoFuture::new(x), inspect_err_fn(f))]
+);
+
+#[allow(unreachable_pub)] // https://github.com/rust-lang/rust/issues/57411
+pub use self::into_future::IntoFuture;
+
+delegate_all!(
+    /// Future for the [`map_ok`](TryFutureExt::map_ok) method.
+    MapOk<Fut, F>(
+        Map<IntoFuture<Fut>, MapOkFn<F>>
+    ): Debug + Future + FusedFuture + New[|x: Fut, f: F| Map::new(IntoFuture::new(x), map_ok_fn(f))]
+);
+
+delegate_all!(
+    /// Future for the [`map_err`](TryFutureExt::map_err) method.
+    MapErr<Fut, F>(
+        Map<IntoFuture<Fut>, MapErrFn<F>>
+    ): Debug + Future + FusedFuture + New[|x: Fut, f: F| Map::new(IntoFuture::new(x), map_err_fn(f))]
+);
+
+delegate_all!(
+    /// Future for the [`map_ok_or_else`](TryFutureExt::map_ok_or_else) method.
+    MapOkOrElse<Fut, F, G>(
+        Map<IntoFuture<Fut>, MapOkOrElseFn<F, G>>
+    ): Debug + Future + FusedFuture + New[|x: Fut, f: F, g: G| Map::new(IntoFuture::new(x), map_ok_or_else_fn(f, g))]
+);
+
+delegate_all!(
+    /// Future for the [`unwrap_or_else`](TryFutureExt::unwrap_or_else) method.
+    UnwrapOrElse<Fut, F>(
+        Map<IntoFuture<Fut>, UnwrapOrElseFn<F>>
+    ): Debug + Future + FusedFuture + New[|x: Fut, f: F| Map::new(IntoFuture::new(x), unwrap_or_else_fn(f))]
+);
+
+impl<Fut: ?Sized + TryFuture> TryFutureExt for Fut {}
+
+/// Adapters specific to [`Result`]-returning futures
+pub trait TryFutureExt: TryFuture {
+    /// Flattens the execution of this future when the successful result of this
+    /// future is a [`Sink`].
+    ///
+    /// This can be useful when sink initialization is deferred, and it is
+    /// convenient to work with that sink as if the sink was available at the
+    /// call site.
+    ///
+    /// Note that this function consumes this future and returns a wrapped
+    /// version of it.
+    ///
+    /// # Examples
+    ///
+    /// ```
+    /// use futures::future::{Future, TryFutureExt};
+    /// use futures::sink::Sink;
+    /// # use futures::channel::mpsc::{self, SendError};
+    /// # type T = i32;
+    /// # type E = SendError;
+    ///
+    /// fn make_sink_async() -> impl Future<Output = Result<
+    ///     impl Sink<T, Error = E>,
+    ///     E,
+    /// >> { // ... }
+    /// # let (tx, _rx) = mpsc::unbounded::<i32>();
+    /// # futures::future::ready(Ok(tx))
+    /// # }
+    /// fn take_sink(sink: impl Sink<T, Error = E>) { /* ... */ }
+    ///
+    /// let fut = make_sink_async();
+    /// take_sink(fut.flatten_sink())
+    /// ```
+    #[cfg(feature = "sink")]
+    #[cfg_attr(docsrs, doc(cfg(feature = "sink")))]
+    fn flatten_sink<Item>(self) -> FlattenSink<Self, Self::Ok>
+    where
+        Self::Ok: Sink<Item, Error = Self::Error>,
+        Self: Sized,
+    {
+        crate::sink::assert_sink::<Item, Self::Error, _>(FlattenSink::new(self))
+    }
+
+    /// Maps this future's success value to a different value.
+    ///
+    /// This method can be used to change the [`Ok`](TryFuture::Ok) type of the
+    /// future into a different type. It is similar to the [`Result::map`]
+    /// method. You can use this method to chain along a computation once the
+    /// future has been resolved.
+    ///
+    /// The provided closure `f` will only be called if this future is resolved
+    /// to an [`Ok`]. If it resolves to an [`Err`], panics, or is dropped, then
+    /// the provided closure will never be invoked.
+    ///
+    /// Note that this method consumes the future it is called on and returns a
+    /// wrapped version of it.
+    ///
+    /// # Examples
+    ///
+    /// ```
+    /// use futures::future::TryFutureExt;
+    ///
+    /// # futures::executor::block_on(async {
+    /// let future = async { Ok::<i32, i32>(1) };
+    /// let future = future.map_ok(|x| x + 3);
+    /// assert_eq!(future.await, Ok(4));
+    /// # });
+    /// ```
+    ///
+    /// Calling [`map_ok`](TryFutureExt::map_ok) on an errored future has no
+    /// effect:
+    ///
+    /// ```
+    /// use futures::future::TryFutureExt;
+    ///
+    /// # futures::executor::block_on(async {
+    /// let future = async { Err::<i32, i32>(1) };
+    /// let future = future.map_ok(|x| x + 3);
+    /// assert_eq!(future.await, Err(1));
+    /// # });
+    /// ```
+    fn map_ok<T, F>(self, f: F) -> MapOk<Self, F>
+    where
+        F: FnOnce(Self::Ok) -> T,
+        Self: Sized,
+    {
+        assert_future::<Result<T, Self::Error>, _>(MapOk::new(self, f))
+    }
+
+    /// Maps this future's success value to a different value, and permits for error handling resulting in the same type.
+    ///
+    /// This method can be used to coalesce your [`Ok`](TryFuture::Ok) type and [`Error`](TryFuture::Error) into another type,
+    /// where that type is the same for both outcomes.
+    ///
+    /// The provided closure `f` will only be called if this future is resolved
+    /// to an [`Ok`]. If it resolves to an [`Err`], panics, or is dropped, then
+    /// the provided closure will never be invoked.
+    ///
+    /// The provided closure `e` will only be called if this future is resolved
+    /// to an [`Err`]. If it resolves to an [`Ok`], panics, or is dropped, then
+    /// the provided closure will never be invoked.
+    ///
+    /// Note that this method consumes the future it is called on and returns a
+    /// wrapped version of it.
+    ///
+    /// # Examples
+    ///
+    /// ```
+    /// use futures::future::TryFutureExt;
+    ///
+    /// # futures::executor::block_on(async {
+    /// let future = async { Ok::<i32, i32>(5) };
+    /// let future = future.map_ok_or_else(|x| x * 2, |x| x + 3);
+    /// assert_eq!(future.await, 8);
+    ///
+    /// let future = async { Err::<i32, i32>(5) };
+    /// let future = future.map_ok_or_else(|x| x * 2, |x| x + 3);
+    /// assert_eq!(future.await, 10);
+    /// # });
+    /// ```
+    ///
+    fn map_ok_or_else<T, E, F>(self, e: E, f: F) -> MapOkOrElse<Self, F, E>
+    where
+        F: FnOnce(Self::Ok) -> T,
+        E: FnOnce(Self::Error) -> T,
+        Self: Sized,
+    {
+        assert_future::<T, _>(MapOkOrElse::new(self, f, e))
+    }
+
+    /// Maps this future's error value to a different value.
+    ///
+    /// This method can be used to change the [`Error`](TryFuture::Error) type
+    /// of the future into a different type. It is similar to the
+    /// [`Result::map_err`] method. You can use this method for example to
+    /// ensure that futures have the same [`Error`](TryFuture::Error) type when
+    /// using [`select!`] or [`join!`].
+    ///
+    /// The provided closure `f` will only be called if this future is resolved
+    /// to an [`Err`]. If it resolves to an [`Ok`], panics, or is dropped, then
+    /// the provided closure will never be invoked.
+    ///
+    /// Note that this method consumes the future it is called on and returns a
+    /// wrapped version of it.
+    ///
+    /// # Examples
+    ///
+    /// ```
+    /// use futures::future::TryFutureExt;
+    ///
+    /// # futures::executor::block_on(async {
+    /// let future = async { Err::<i32, i32>(1) };
+    /// let future = future.map_err(|x| x + 3);
+    /// assert_eq!(future.await, Err(4));
+    /// # });
+    /// ```
+    ///
+    /// Calling [`map_err`](TryFutureExt::map_err) on a successful future has
+    /// no effect:
+    ///
+    /// ```
+    /// use futures::future::TryFutureExt;
+    ///
+    /// # futures::executor::block_on(async {
+    /// let future = async { Ok::<i32, i32>(1) };
+    /// let future = future.map_err(|x| x + 3);
+    /// assert_eq!(future.await, Ok(1));
+    /// # });
+    /// ```
+    ///
+    /// [`join!`]: crate::join
+    /// [`select!`]: crate::select
+    fn map_err<E, F>(self, f: F) -> MapErr<Self, F>
+    where
+        F: FnOnce(Self::Error) -> E,
+        Self: Sized,
+    {
+        assert_future::<Result<Self::Ok, E>, _>(MapErr::new(self, f))
+    }
+
+    /// Maps this future's [`Error`](TryFuture::Error) to a new error type
+    /// using the [`Into`](std::convert::Into) trait.
+    ///
+    /// This method does for futures what the `?`-operator does for
+    /// [`Result`]: It lets the compiler infer the type of the resulting
+    /// error. Just as [`map_err`](TryFutureExt::map_err), this is useful for
+    /// example to ensure that futures have the same [`Error`](TryFuture::Error)
+    /// type when using [`select!`] or [`join!`].
+    ///
+    /// Note that this method consumes the future it is called on and returns a
+    /// wrapped version of it.
+    ///
+    /// # Examples
+    ///
+    /// ```
+    /// use futures::future::TryFutureExt;
+    ///
+    /// # futures::executor::block_on(async {
+    /// let future_err_u8 = async { Err::<(), u8>(1) };
+    /// let future_err_i32 = future_err_u8.err_into::<i32>();
+    /// # });
+    /// ```
+    ///
+    /// [`join!`]: crate::join
+    /// [`select!`]: crate::select
+    fn err_into<E>(self) -> ErrInto<Self, E>
+    where
+        Self: Sized,
+        Self::Error: Into<E>,
+    {
+        assert_future::<Result<Self::Ok, E>, _>(ErrInto::new(self))
+    }
+
+    /// Maps this future's [`Ok`](TryFuture::Ok) to a new type
+    /// using the [`Into`](std::convert::Into) trait.
+    fn ok_into<U>(self) -> OkInto<Self, U>
+    where
+        Self: Sized,
+        Self::Ok: Into<U>,
+    {
+        assert_future::<Result<U, Self::Error>, _>(OkInto::new(self))
+    }
+
+    /// Executes another future after this one resolves successfully. The
+    /// success value is passed to a closure to create this subsequent future.
+    ///
+    /// The provided closure `f` will only be called if this future is resolved
+    /// to an [`Ok`]. If this future resolves to an [`Err`], panics, or is
+    /// dropped, then the provided closure will never be invoked. The
+    /// [`Error`](TryFuture::Error) type of this future and the future
+    /// returned by `f` have to match.
+    ///
+    /// Note that this method consumes the future it is called on and returns a
+    /// wrapped version of it.
+    ///
+    /// # Examples
+    ///
+    /// ```
+    /// use futures::future::TryFutureExt;
+    ///
+    /// # futures::executor::block_on(async {
+    /// let future = async { Ok::<i32, i32>(1) };
+    /// let future = future.and_then(|x| async move { Ok::<i32, i32>(x + 3) });
+    /// assert_eq!(future.await, Ok(4));
+    /// # });
+    /// ```
+    ///
+    /// Calling [`and_then`](TryFutureExt::and_then) on an errored future has no
+    /// effect:
+    ///
+    /// ```
+    /// use futures::future::TryFutureExt;
+    ///
+    /// # futures::executor::block_on(async {
+    /// let future = async { Err::<i32, i32>(1) };
+    /// let future = future.and_then(|x| async move { Err::<i32, i32>(x + 3) });
+    /// assert_eq!(future.await, Err(1));
+    /// # });
+    /// ```
+    fn and_then<Fut, F>(self, f: F) -> AndThen<Self, Fut, F>
+    where
+        F: FnOnce(Self::Ok) -> Fut,
+        Fut: TryFuture<Error = Self::Error>,
+        Self: Sized,
+    {
+        assert_future::<Result<Fut::Ok, Fut::Error>, _>(AndThen::new(self, f))
+    }
+
+    /// Executes another future if this one resolves to an error. The
+    /// error value is passed to a closure to create this subsequent future.
+    ///
+    /// The provided closure `f` will only be called if this future is resolved
+    /// to an [`Err`]. If this future resolves to an [`Ok`], panics, or is
+    /// dropped, then the provided closure will never be invoked. The
+    /// [`Ok`](TryFuture::Ok) type of this future and the future returned by `f`
+    /// have to match.
+    ///
+    /// Note that this method consumes the future it is called on and returns a
+    /// wrapped version of it.
+    ///
+    /// # Examples
+    ///
+    /// ```
+    /// use futures::future::TryFutureExt;
+    ///
+    /// # futures::executor::block_on(async {
+    /// let future = async { Err::<i32, i32>(1) };
+    /// let future = future.or_else(|x| async move { Err::<i32, i32>(x + 3) });
+    /// assert_eq!(future.await, Err(4));
+    /// # });
+    /// ```
+    ///
+    /// Calling [`or_else`](TryFutureExt::or_else) on a successful future has
+    /// no effect:
+    ///
+    /// ```
+    /// use futures::future::TryFutureExt;
+    ///
+    /// # futures::executor::block_on(async {
+    /// let future = async { Ok::<i32, i32>(1) };
+    /// let future = future.or_else(|x| async move { Ok::<i32, i32>(x + 3) });
+    /// assert_eq!(future.await, Ok(1));
+    /// # });
+    /// ```
+    fn or_else<Fut, F>(self, f: F) -> OrElse<Self, Fut, F>
+    where
+        F: FnOnce(Self::Error) -> Fut,
+        Fut: TryFuture<Ok = Self::Ok>,
+        Self: Sized,
+    {
+        assert_future::<Result<Fut::Ok, Fut::Error>, _>(OrElse::new(self, f))
+    }
+
+    /// Do something with the success value of a future before passing it on.
+    ///
+    /// When using futures, you'll often chain several of them together.  While
+    /// working on such code, you might want to check out what's happening at
+    /// various parts in the pipeline, without consuming the intermediate
+    /// value. To do that, insert a call to `inspect_ok`.
+    ///
+    /// # Examples
+    ///
+    /// ```
+    /// # futures::executor::block_on(async {
+    /// use futures::future::TryFutureExt;
+    ///
+    /// let future = async { Ok::<_, ()>(1) };
+    /// let new_future = future.inspect_ok(|&x| println!("about to resolve: {}", x));
+    /// assert_eq!(new_future.await, Ok(1));
+    /// # });
+    /// ```
+    fn inspect_ok<F>(self, f: F) -> InspectOk<Self, F>
+    where
+        F: FnOnce(&Self::Ok),
+        Self: Sized,
+    {
+        assert_future::<Result<Self::Ok, Self::Error>, _>(InspectOk::new(self, f))
+    }
+
+    /// Do something with the error value of a future before passing it on.
+    ///
+    /// When using futures, you'll often chain several of them together.  While
+    /// working on such code, you might want to check out what's happening at
+    /// various parts in the pipeline, without consuming the intermediate
+    /// value. To do that, insert a call to `inspect_err`.
+    ///
+    /// # Examples
+    ///
+    /// ```
+    /// # futures::executor::block_on(async {
+    /// use futures::future::TryFutureExt;
+    ///
+    /// let future = async { Err::<(), _>(1) };
+    /// let new_future = future.inspect_err(|&x| println!("about to error: {}", x));
+    /// assert_eq!(new_future.await, Err(1));
+    /// # });
+    /// ```
+    fn inspect_err<F>(self, f: F) -> InspectErr<Self, F>
+    where
+        F: FnOnce(&Self::Error),
+        Self: Sized,
+    {
+        assert_future::<Result<Self::Ok, Self::Error>, _>(InspectErr::new(self, f))
+    }
+
+    /// Flatten the execution of this future when the successful result of this
+    /// future is another future.
+    ///
+    /// This is equivalent to `future.and_then(|x| x)`.
+    fn try_flatten(self) -> TryFlatten<Self, Self::Ok>
+    where
+        Self::Ok: TryFuture<Error = Self::Error>,
+        Self: Sized,
+    {
+        assert_future::<Result<<Self::Ok as TryFuture>::Ok, Self::Error>, _>(TryFlatten::new(self))
+    }
+
+    /// Flatten the execution of this future when the successful result of this
+    /// future is a stream.
+    ///
+    /// This can be useful when stream initialization is deferred, and it is
+    /// convenient to work with that stream as if stream was available at the
+    /// call site.
+    ///
+    /// Note that this function consumes this future and returns a wrapped
+    /// version of it.
+    ///
+    /// # Examples
+    ///
+    /// ```
+    /// # futures::executor::block_on(async {
+    /// use futures::future::TryFutureExt;
+    /// use futures::stream::{self, TryStreamExt};
+    ///
+    /// let stream_items = vec![17, 18, 19].into_iter().map(Ok);
+    /// let future_of_a_stream = async { Ok::<_, ()>(stream::iter(stream_items)) };
+    ///
+    /// let stream = future_of_a_stream.try_flatten_stream();
+    /// let list = stream.try_collect::<Vec<_>>().await;
+    /// assert_eq!(list, Ok(vec![17, 18, 19]));
+    /// # });
+    /// ```
+    fn try_flatten_stream(self) -> TryFlattenStream<Self>
+    where
+        Self::Ok: TryStream<Error = Self::Error>,
+        Self: Sized,
+    {
+        assert_stream::<Result<<Self::Ok as TryStream>::Ok, Self::Error>, _>(TryFlattenStream::new(
+            self,
+        ))
+    }
+
+    /// Unwraps this future's output, producing a future with this future's
+    /// [`Ok`](TryFuture::Ok) type as its
+    /// [`Output`](std::future::Future::Output) type.
+    ///
+    /// If this future is resolved successfully, the returned future will
+    /// contain the original future's success value as output. Otherwise, the
+    /// closure `f` is called with the error value to produce an alternate
+    /// success value.
+    ///
+    /// This method is similar to the [`Result::unwrap_or_else`] method.
+    ///
+    /// # Examples
+    ///
+    /// ```
+    /// use futures::future::TryFutureExt;
+    ///
+    /// # futures::executor::block_on(async {
+    /// let future = async { Err::<(), &str>("Boom!") };
+    /// let future = future.unwrap_or_else(|_| ());
+    /// assert_eq!(future.await, ());
+    /// # });
+    /// ```
+    fn unwrap_or_else<F>(self, f: F) -> UnwrapOrElse<Self, F>
+    where
+        Self: Sized,
+        F: FnOnce(Self::Error) -> Self::Ok,
+    {
+        assert_future::<Self::Ok, _>(UnwrapOrElse::new(self, f))
+    }
+
+    /// Wraps a [`TryFuture`] into a future compatible with libraries using
+    /// futures 0.1 future definitions. Requires the `compat` feature to enable.
+    #[cfg(feature = "compat")]
+    #[cfg_attr(docsrs, doc(cfg(feature = "compat")))]
+    fn compat(self) -> Compat<Self>
+    where
+        Self: Sized + Unpin,
+    {
+        Compat::new(self)
+    }
+
+    /// Wraps a [`TryFuture`] into a type that implements
+    /// [`Future`](std::future::Future).
+    ///
+    /// [`TryFuture`]s currently do not implement the
+    /// [`Future`](std::future::Future) trait due to limitations of the
+    /// compiler.
+    ///
+    /// # Examples
+    ///
+    /// ```
+    /// use futures::future::{Future, TryFuture, TryFutureExt};
+    ///
+    /// # type T = i32;
+    /// # type E = ();
+    /// fn make_try_future() -> impl TryFuture<Ok = T, Error = E> { // ... }
+    /// # async { Ok::<i32, ()>(1) }
+    /// # }
+    /// fn take_future(future: impl Future<Output = Result<T, E>>) { /* ... */ }
+    ///
+    /// take_future(make_try_future().into_future());
+    /// ```
+    fn into_future(self) -> IntoFuture<Self>
+    where
+        Self: Sized,
+    {
+        assert_future::<Result<Self::Ok, Self::Error>, _>(IntoFuture::new(self))
+    }
+
+    /// A convenience method for calling [`TryFuture::try_poll`] on [`Unpin`]
+    /// future types.
+    fn try_poll_unpin(&mut self, cx: &mut Context<'_>) -> Poll<Result<Self::Ok, Self::Error>>
+    where
+        Self: Unpin,
+    {
+        Pin::new(self).try_poll(cx)
+    }
+}
diff --git a/third_party/rust/futures-util/src/future/try_future/try_flatten.rs b/third_party/rust/futures-util/src/future/try_future/try_flatten.rs
new file mode 100644
index 0000000000..1ce4559ac2
--- /dev/null
+++ b/third_party/rust/futures-util/src/future/try_future/try_flatten.rs
@@ -0,0 +1,162 @@
+use core::pin::Pin;
+use futures_core::future::{FusedFuture, Future, TryFuture};
+use futures_core::ready;
+use futures_core::stream::{FusedStream, Stream, TryStream};
+use futures_core::task::{Context, Poll};
+#[cfg(feature = "sink")]
+use futures_sink::Sink;
+use pin_project_lite::pin_project;
+
+pin_project! {
+    #[project = TryFlattenProj]
+    #[derive(Debug)]
+    pub enum TryFlatten<Fut1, Fut2> {
+        First { #[pin] f: Fut1 },
+        Second { #[pin] f: Fut2 },
+        Empty,
+    }
+}
+
+impl<Fut1, Fut2> TryFlatten<Fut1, Fut2> {
+    pub(crate) fn new(future: Fut1) -> Self {
+        Self::First { f: future }
+    }
+}
+
+impl<Fut> FusedFuture for TryFlatten<Fut, Fut::Ok>
+where
+    Fut: TryFuture,
+    Fut::Ok: TryFuture<Error = Fut::Error>,
+{
+    fn is_terminated(&self) -> bool {
+        match self {
+            Self::Empty => true,
+            _ => false,
+        }
+    }
+}
+
+impl<Fut> Future for TryFlatten<Fut, Fut::Ok>
+where
+    Fut: TryFuture,
+    Fut::Ok: TryFuture<Error = Fut::Error>,
+{
+    type Output = Result<<Fut::Ok as TryFuture>::Ok, Fut::Error>;
+
+    fn poll(mut self: Pin<&mut Self>, cx: &mut Context<'_>) -> Poll<Self::Output> {
+        Poll::Ready(loop {
+            match self.as_mut().project() {
+                TryFlattenProj::First { f } => match ready!(f.try_poll(cx)) {
+                    Ok(f) => self.set(Self::Second { f }),
+                    Err(e) => {
+                        self.set(Self::Empty);
+                        break Err(e);
+                    }
+                },
+                TryFlattenProj::Second { f } => {
+                    let output = ready!(f.try_poll(cx));
+                    self.set(Self::Empty);
+                    break output;
+                }
+                TryFlattenProj::Empty => panic!("TryFlatten polled after completion"),
+            }
+        })
+    }
+}
+
+impl<Fut> FusedStream for TryFlatten<Fut, Fut::Ok>
+where
+    Fut: TryFuture,
+    Fut::Ok: TryStream<Error = Fut::Error>,
+{
+    fn is_terminated(&self) -> bool {
+        match self {
+            Self::Empty => true,
+            _ => false,
+        }
+    }
+}
+
+impl<Fut> Stream for TryFlatten<Fut, Fut::Ok>
+where
+    Fut: TryFuture,
+    Fut::Ok: TryStream<Error = Fut::Error>,
+{
+    type Item = Result<<Fut::Ok as TryStream>::Ok, Fut::Error>;
+
+    fn poll_next(mut self: Pin<&mut Self>, cx: &mut Context<'_>) -> Poll<Option<Self::Item>> {
+        Poll::Ready(loop {
+            match self.as_mut().project() {
+                TryFlattenProj::First { f } => match ready!(f.try_poll(cx)) {
+                    Ok(f) => self.set(Self::Second { f }),
+                    Err(e) => {
+                        self.set(Self::Empty);
+                        break Some(Err(e));
+                    }
+                },
+                TryFlattenProj::Second { f } => {
+                    let output = ready!(f.try_poll_next(cx));
+                    if output.is_none() {
+                        self.set(Self::Empty);
+                    }
+                    break output;
+                }
+                TryFlattenProj::Empty => break None,
+            }
+        })
+    }
+}
+
+#[cfg(feature = "sink")]
+impl<Fut, Item> Sink<Item> for TryFlatten<Fut, Fut::Ok>
+where
+    Fut: TryFuture,
+    Fut::Ok: Sink<Item, Error = Fut::Error>,
+{
+    type Error = Fut::Error;
+
+    fn poll_ready(mut self: Pin<&mut Self>, cx: &mut Context<'_>) -> Poll<Result<(), Self::Error>> {
+        Poll::Ready(loop {
+            match self.as_mut().project() {
+                TryFlattenProj::First { f } => match ready!(f.try_poll(cx)) {
+                    Ok(f) => self.set(Self::Second { f }),
+                    Err(e) => {
+                        self.set(Self::Empty);
+                        break Err(e);
+                    }
+                },
+                TryFlattenProj::Second { f } => {
+                    break ready!(f.poll_ready(cx));
+                }
+                TryFlattenProj::Empty => panic!("poll_ready called after eof"),
+            }
+        })
+    }
+
+    fn start_send(self: Pin<&mut Self>, item: Item) -> Result<(), Self::Error> {
+        match self.project() {
+            TryFlattenProj::First { .. } => panic!("poll_ready not called first"),
+            TryFlattenProj::Second { f } => f.start_send(item),
+            TryFlattenProj::Empty => panic!("start_send called after eof"),
+        }
+    }
+
+    fn poll_flush(self: Pin<&mut Self>, cx: &mut Context<'_>) -> Poll<Result<(), Self::Error>> {
+        match self.project() {
+            TryFlattenProj::First { .. } => Poll::Ready(Ok(())),
+            TryFlattenProj::Second { f } => f.poll_flush(cx),
+            TryFlattenProj::Empty => panic!("poll_flush called after eof"),
+        }
+    }
+
+    fn poll_close(mut self: Pin<&mut Self>, cx: &mut Context<'_>) -> Poll<Result<(), Self::Error>> {
+        let res = match self.as_mut().project() {
+            TryFlattenProj::Second { f } => f.poll_close(cx),
+            _ => Poll::Ready(Ok(())),
+        };
+        if res.is_ready() {
+            self.set(Self::Empty);
+        }
+        res
+    }
+}
diff --git a/third_party/rust/futures-util/src/future/try_future/try_flatten_err.rs b/third_party/rust/futures-util/src/future/try_future/try_flatten_err.rs
new file mode 100644
index 0000000000..39b7d9f5f6
--- /dev/null
+++ b/third_party/rust/futures-util/src/future/try_future/try_flatten_err.rs
@@ -0,0 +1,62 @@
+use core::pin::Pin;
+use futures_core::future::{FusedFuture, Future, TryFuture};
+use futures_core::ready;
+use futures_core::task::{Context, Poll};
+use pin_project_lite::pin_project;
+
+pin_project! {
+    #[project = TryFlattenErrProj]
+    #[derive(Debug)]
+    pub enum TryFlattenErr<Fut1, Fut2> {
+        First { #[pin] f: Fut1 },
+        Second { #[pin] f: Fut2 },
+        Empty,
+    }
+}
+
+impl<Fut1, Fut2> TryFlattenErr<Fut1, Fut2> {
+    pub(crate) fn new(future: Fut1) -> Self {
+        Self::First { f: future }
+    }
+}
+
+impl<Fut> FusedFuture for TryFlattenErr<Fut, Fut::Error>
+where
+    Fut: TryFuture,
+    Fut::Error: TryFuture<Ok = Fut::Ok>,
+{
+    fn is_terminated(&self) -> bool {
+        match self {
+            Self::Empty => true,
+            _ => false,
+        }
+    }
+}
+
+impl<Fut> Future for TryFlattenErr<Fut, Fut::Error>
+where
+    Fut: TryFuture,
+    Fut::Error: TryFuture<Ok = Fut::Ok>,
+{
+    type Output = Result<Fut::Ok, <Fut::Error as TryFuture>::Error>;
+
+    fn poll(mut self: Pin<&mut Self>, cx: &mut Context<'_>) -> Poll<Self::Output> {
+        Poll::Ready(loop {
+            match self.as_mut().project() {
+                TryFlattenErrProj::First { f } => match ready!(f.try_poll(cx)) {
+                    Err(f) => self.set(Self::Second { f }),
+                    Ok(e) => {
+                        self.set(Self::Empty);
+                        break Ok(e);
+                    }
+                },
+                TryFlattenErrProj::Second { f } => {
+                    let output = ready!(f.try_poll(cx));
+                    self.set(Self::Empty);
+                    break output;
+                }
+                TryFlattenErrProj::Empty => panic!("TryFlattenErr polled after completion"),
+            }
+        })
+    }
+}
diff --git a/third_party/rust/futures-util/src/future/try_join.rs b/third_party/rust/futures-util/src/future/try_join.rs
new file mode 100644
index 0000000000..6af1f0ccbf
--- /dev/null
+++ b/third_party/rust/futures-util/src/future/try_join.rs
@@ -0,0 +1,256 @@
+#![allow(non_snake_case)]
+
+use crate::future::{assert_future, try_maybe_done, TryMaybeDone};
+use core::fmt;
+use core::pin::Pin;
+use futures_core::future::{Future, TryFuture};
+use futures_core::task::{Context, Poll};
+use pin_project_lite::pin_project;
+
+macro_rules! generate {
+    ($(
+        $(#[$doc:meta])*
+        ($Join:ident, <Fut1, $($Fut:ident),*>),
+    )*) => ($(
+        pin_project! {
+            $(#[$doc])*
+            #[must_use = "futures do nothing unless you `.await` or poll them"]
+            pub struct $Join<Fut1: TryFuture, $($Fut: TryFuture),*> {
+                #[pin] Fut1: TryMaybeDone<Fut1>,
+                $(#[pin] $Fut: TryMaybeDone<$Fut>,)*
+            }
+        }
+
+        impl<Fut1, $($Fut),*> fmt::Debug for $Join<Fut1, $($Fut),*>
+        where
+            Fut1: TryFuture + fmt::Debug,
+            Fut1::Ok: fmt::Debug,
+            Fut1::Error: fmt::Debug,
+            $(
+                $Fut: TryFuture + fmt::Debug,
+                $Fut::Ok: fmt::Debug,
+                $Fut::Error: fmt::Debug,
+            )*
+        {
+            fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
+                f.debug_struct(stringify!($Join))
+                    .field("Fut1", &self.Fut1)
+                    $(.field(stringify!($Fut), &self.$Fut))*
+                    .finish()
+            }
+        }
+
+        impl<Fut1, $($Fut),*> $Join<Fut1, $($Fut),*>
+        where
+            Fut1: TryFuture,
+            $(
+                $Fut: TryFuture<Error=Fut1::Error>
+            ),*
+        {
+            fn new(Fut1: Fut1, $($Fut: $Fut),*) -> Self {
+                Self {
+                    Fut1: try_maybe_done(Fut1),
+                    $($Fut: try_maybe_done($Fut)),*
+                }
+            }
+        }
+
+        impl<Fut1, $($Fut),*> Future for $Join<Fut1, $($Fut),*>
+        where
+            Fut1: TryFuture,
+            $(
+                $Fut: TryFuture<Error=Fut1::Error>
+            ),*
+        {
+            type Output = Result<(Fut1::Ok, $($Fut::Ok),*), Fut1::Error>;
+
+            fn poll(
+                self: Pin<&mut Self>, cx: &mut Context<'_>
+            ) -> Poll<Self::Output> {
+                let mut all_done = true;
+                let mut futures = self.project();
+                all_done &= futures.Fut1.as_mut().poll(cx)?.is_ready();
+                $(
+                    all_done &= futures.$Fut.as_mut().poll(cx)?.is_ready();
+                )*
+
+                if all_done {
+                    Poll::Ready(Ok((
+                        futures.Fut1.take_output().unwrap(),
+                        $(
+                            futures.$Fut.take_output().unwrap()
+                        ),*
+                    )))
+                } else {
+                    Poll::Pending
+                }
+            }
+        }
+    )*)
+}
+
+generate! {
+    /// Future for the [`try_join`](try_join()) function.
+    (TryJoin, <Fut1, Fut2>),
+
+    /// Future for the [`try_join3`] function.
+    (TryJoin3, <Fut1, Fut2, Fut3>),
+
+    /// Future for the [`try_join4`] function.
+    (TryJoin4, <Fut1, Fut2, Fut3, Fut4>),
+
+    /// Future for the [`try_join5`] function.
+    (TryJoin5, <Fut1, Fut2, Fut3, Fut4, Fut5>),
+}
+
+/// Joins the result of two futures, waiting for them both to complete or
+/// for one to produce an error.
+///
+/// This function will return a new future which awaits both futures to
+/// complete. If successful, the returned future will finish with a tuple of
+/// both results. If unsuccessful, it will complete with the first error
+/// encountered.
+///
+/// Note that this function consumes the passed futures and returns a
+/// wrapped version of it.
+///
+/// # Examples
+///
+/// When used on multiple futures that return [`Ok`], `try_join` will return
+/// [`Ok`] of a tuple of the values:
+///
+/// ```
+/// # futures::executor::block_on(async {
+/// use futures::future;
+///
+/// let a = future::ready(Ok::<i32, i32>(1));
+/// let b = future::ready(Ok::<i32, i32>(2));
+/// let pair = future::try_join(a, b);
+///
+/// assert_eq!(pair.await, Ok((1, 2)));
+/// # });
+/// ```
+///
+/// If one of the futures resolves to an error, `try_join` will return
+/// that error:
+///
+/// ```
+/// # futures::executor::block_on(async {
+/// use futures::future;
+///
+/// let a = future::ready(Ok::<i32, i32>(1));
+/// let b = future::ready(Err::<i32, i32>(2));
+/// let pair = future::try_join(a, b);
+///
+/// assert_eq!(pair.await, Err(2));
+/// # });
+/// ```
+pub fn try_join<Fut1, Fut2>(future1: Fut1, future2: Fut2) -> TryJoin<Fut1, Fut2>
+where
+    Fut1: TryFuture,
+    Fut2: TryFuture<Error = Fut1::Error>,
+{
+    assert_future::<Result<(Fut1::Ok, Fut2::Ok), Fut1::Error>, _>(TryJoin::new(future1, future2))
+}
+
+/// Same as [`try_join`](try_join()), but with more futures.
+///
+/// # Examples
+///
+/// ```
+/// # futures::executor::block_on(async {
+/// use futures::future;
+///
+/// let a = future::ready(Ok::<i32, i32>(1));
+/// let b = future::ready(Ok::<i32, i32>(2));
+/// let c = future::ready(Ok::<i32, i32>(3));
+/// let tuple = future::try_join3(a, b, c);
+///
+/// assert_eq!(tuple.await, Ok((1, 2, 3)));
+/// # });
+/// ```
+pub fn try_join3<Fut1, Fut2, Fut3>(
+    future1: Fut1,
+    future2: Fut2,
+    future3: Fut3,
+) -> TryJoin3<Fut1, Fut2, Fut3>
+where
+    Fut1: TryFuture,
+    Fut2: TryFuture<Error = Fut1::Error>,
+    Fut3: TryFuture<Error = Fut1::Error>,
+{
+    assert_future::<Result<(Fut1::Ok, Fut2::Ok, Fut3::Ok), Fut1::Error>, _>(TryJoin3::new(
+        future1, future2, future3,
+    ))
+}
+
+/// Same as [`try_join`](try_join()), but with more futures.
+///
+/// # Examples
+///
+/// ```
+/// # futures::executor::block_on(async {
+/// use futures::future;
+///
+/// let a = future::ready(Ok::<i32, i32>(1));
+/// let b = future::ready(Ok::<i32, i32>(2));
+/// let c = future::ready(Ok::<i32, i32>(3));
+/// let d = future::ready(Ok::<i32, i32>(4));
+/// let tuple = future::try_join4(a, b, c, d);
+///
+/// assert_eq!(tuple.await, Ok((1, 2, 3, 4)));
+/// # });
+/// ```
+pub fn try_join4<Fut1, Fut2, Fut3, Fut4>(
+    future1: Fut1,
+    future2: Fut2,
+    future3: Fut3,
+    future4: Fut4,
+) -> TryJoin4<Fut1, Fut2, Fut3, Fut4>
+where
+    Fut1: TryFuture,
+    Fut2: TryFuture<Error = Fut1::Error>,
+    Fut3: TryFuture<Error = Fut1::Error>,
+    Fut4: TryFuture<Error = Fut1::Error>,
+{
+    assert_future::<Result<(Fut1::Ok, Fut2::Ok, Fut3::Ok, Fut4::Ok), Fut1::Error>, _>(
+        TryJoin4::new(future1, future2, future3, future4),
+    )
+}
+
+/// Same as [`try_join`](try_join()), but with more futures.
+///
+/// # Examples
+///
+/// ```
+/// # futures::executor::block_on(async {
+/// use futures::future;
+///
+/// let a = future::ready(Ok::<i32, i32>(1));
+/// let b = future::ready(Ok::<i32, i32>(2));
+/// let c = future::ready(Ok::<i32, i32>(3));
+/// let d = future::ready(Ok::<i32, i32>(4));
+/// let e = future::ready(Ok::<i32, i32>(5));
+/// let tuple = future::try_join5(a, b, c, d, e);
+///
+/// assert_eq!(tuple.await, Ok((1, 2, 3, 4, 5)));
+/// # });
+/// ```
+pub fn try_join5<Fut1, Fut2, Fut3, Fut4, Fut5>(
+    future1: Fut1,
+    future2: Fut2,
+    future3: Fut3,
+    future4: Fut4,
+    future5: Fut5,
+) -> TryJoin5<Fut1, Fut2, Fut3, Fut4, Fut5>
+where
+    Fut1: TryFuture,
+    Fut2: TryFuture<Error = Fut1::Error>,
+    Fut3: TryFuture<Error = Fut1::Error>,
+    Fut4: TryFuture<Error = Fut1::Error>,
+    Fut5: TryFuture<Error = Fut1::Error>,
+{
+    assert_future::<Result<(Fut1::Ok, Fut2::Ok, Fut3::Ok, Fut4::Ok, Fut5::Ok), Fut1::Error>, _>(
+        TryJoin5::new(future1, future2, future3, future4, future5),
+    )
+}
diff --git a/third_party/rust/futures-util/src/future/try_join_all.rs b/third_party/rust/futures-util/src/future/try_join_all.rs
new file mode 100644
index 0000000000..25fcfcb6c2
--- /dev/null
+++ b/third_party/rust/futures-util/src/future/try_join_all.rs
@@ -0,0 +1,186 @@
+//! Definition of the `TryJoinAll` combinator, waiting for all of a list of
+//! futures to finish with either success or error.
+
+use alloc::boxed::Box;
+use alloc::vec::Vec;
+use core::fmt;
+use core::future::Future;
+use core::iter::FromIterator;
+use core::mem;
+use core::pin::Pin;
+use core::task::{Context, Poll};
+
+use super::{assert_future, join_all, IntoFuture, TryFuture, TryMaybeDone};
+
+#[cfg(not(futures_no_atomic_cas))]
+use crate::stream::{FuturesOrdered, TryCollect, TryStreamExt};
+use crate::TryFutureExt;
+
+enum FinalState<E = ()> {
+    Pending,
+    AllDone,
+    Error(E),
+}
+
+/// Future for the [`try_join_all`] function.
+#[must_use = "futures do nothing unless you `.await` or poll them"]
+pub struct TryJoinAll<F>
+where
+    F: TryFuture,
+{
+    kind: TryJoinAllKind<F>,
+}
+
+enum TryJoinAllKind<F>
+where
+    F: TryFuture,
+{
+    Small {
+        elems: Pin<Box<[TryMaybeDone<IntoFuture<F>>]>>,
+    },
+    #[cfg(not(futures_no_atomic_cas))]
+    Big {
+        fut: TryCollect<FuturesOrdered<IntoFuture<F>>, Vec<F::Ok>>,
+    },
+}
+
+impl<F> fmt::Debug for TryJoinAll<F>
+where
+    F: TryFuture + fmt::Debug,
+    F::Ok: fmt::Debug,
+    F::Error: fmt::Debug,
+    F::Output: fmt::Debug,
+{
+    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
+        match self.kind {
+            TryJoinAllKind::Small { ref elems } => {
+                f.debug_struct("TryJoinAll").field("elems", elems).finish()
+            }
+            #[cfg(not(futures_no_atomic_cas))]
+            TryJoinAllKind::Big { ref fut, .. } => fmt::Debug::fmt(fut, f),
+        }
+    }
+}
+
+/// Creates a future which represents either a collection of the results of the
+/// futures given or an error.
+///
+/// The returned future will drive execution for all of its underlying futures,
+/// collecting the results into a destination `Vec<T>` in the same order as they
+/// were provided.
+///
+/// If any future returns an error then all other futures will be canceled and
+/// an error will be returned immediately. If all futures complete successfully,
+/// however, then the returned future will succeed with a `Vec` of all the
+/// successful results.
+///
+/// This function is only available when the `std` or `alloc` feature of this
+/// library is activated, and it is activated by default.
+///
+/// # Examples
+///
+/// ```
+/// # futures::executor::block_on(async {
+/// use futures::future::{self, try_join_all};
+///
+/// let futures = vec![
+///     future::ok::<u32, u32>(1),
+///     future::ok::<u32, u32>(2),
+///     future::ok::<u32, u32>(3),
+/// ];
+///
+/// assert_eq!(try_join_all(futures).await, Ok(vec![1, 2, 3]));
+///
+/// let futures = vec![
+///     future::ok::<u32, u32>(1),
+///     future::err::<u32, u32>(2),
+///     future::ok::<u32, u32>(3),
+/// ];
+///
+/// assert_eq!(try_join_all(futures).await, Err(2));
+/// # });
+/// ```
+pub fn try_join_all<I>(iter: I) -> TryJoinAll<I::Item>
+where
+    I: IntoIterator,
+    I::Item: TryFuture,
+{
+    let iter = iter.into_iter().map(TryFutureExt::into_future);
+
+    #[cfg(futures_no_atomic_cas)]
+    {
+        let kind = TryJoinAllKind::Small {
+            elems: iter.map(TryMaybeDone::Future).collect::<Box<[_]>>().into(),
+        };
+
+        assert_future::<Result<Vec<<I::Item as TryFuture>::Ok>, <I::Item as TryFuture>::Error>, _>(
+            TryJoinAll { kind },
+        )
+    }
+
+    #[cfg(not(futures_no_atomic_cas))]
+    {
+        let kind = match iter.size_hint().1 {
+            Some(max) if max <= join_all::SMALL => TryJoinAllKind::Small {
+                elems: iter.map(TryMaybeDone::Future).collect::<Box<[_]>>().into(),
+            },
+            _ => TryJoinAllKind::Big { fut: iter.collect::<FuturesOrdered<_>>().try_collect() },
+        };
+
+        assert_future::<Result<Vec<<I::Item as TryFuture>::Ok>, <I::Item as TryFuture>::Error>, _>(
+            TryJoinAll { kind },
+        )
+    }
+}
+
+impl<F> Future for TryJoinAll<F>
+where
+    F: TryFuture,
+{
+    type Output = Result<Vec<F::Ok>, F::Error>;
+
+    fn poll(mut self: Pin<&mut Self>, cx: &mut Context<'_>) -> Poll<Self::Output> {
+        match &mut self.kind {
+            TryJoinAllKind::Small { elems } => {
+                let mut state = FinalState::AllDone;
+
+                for elem in join_all::iter_pin_mut(elems.as_mut()) {
+                    match elem.try_poll(cx) {
+                        Poll::Pending => state = FinalState::Pending,
+                        Poll::Ready(Ok(())) => {}
+                        Poll::Ready(Err(e)) => {
+                            state = FinalState::Error(e);
+                            break;
+                        }
+                    }
+                }
+
+                match state {
+                    FinalState::Pending => Poll::Pending,
+                    FinalState::AllDone => {
+                        let mut elems = mem::replace(elems, Box::pin([]));
+                        let results = join_all::iter_pin_mut(elems.as_mut())
+                            .map(|e| e.take_output().unwrap())
+                            .collect();
+                        Poll::Ready(Ok(results))
+                    }
+                    FinalState::Error(e) => {
+                        let _ = mem::replace(elems, Box::pin([]));
+                        Poll::Ready(Err(e))
+                    }
+                }
+            }
+            #[cfg(not(futures_no_atomic_cas))]
+            TryJoinAllKind::Big { fut } => Pin::new(fut).poll(cx),
+        }
+    }
+}
+
+impl<F> FromIterator<F> for TryJoinAll<F>
+where
+    F: TryFuture,
+{
+    fn from_iter<T: IntoIterator<Item = F>>(iter: T) -> Self {
+        try_join_all(iter)
+    }
+}
diff --git a/third_party/rust/futures-util/src/future/try_maybe_done.rs b/third_party/rust/futures-util/src/future/try_maybe_done.rs
new file mode 100644
index 0000000000..24044d2c27
--- /dev/null
+++ b/third_party/rust/futures-util/src/future/try_maybe_done.rs
@@ -0,0 +1,92 @@
+//! Definition of the TryMaybeDone combinator
+
+use super::assert_future;
+use core::mem;
+use core::pin::Pin;
+use futures_core::future::{FusedFuture, Future, TryFuture};
+use futures_core::ready;
+use futures_core::task::{Context, Poll};
+
+/// A future that may have completed with an error.
+///
+/// This is created by the [`try_maybe_done()`] function.
+#[derive(Debug)]
+pub enum TryMaybeDone<Fut: TryFuture> {
+    /// A not-yet-completed future
+    Future(/* #[pin] */ Fut),
+    /// The output of the completed future
+    Done(Fut::Ok),
+    /// The empty variant after the result of a [`TryMaybeDone`] has been
+    /// taken using the [`take_output`](TryMaybeDone::take_output) method,
+    /// or if the future returned an error.
+    Gone,
+}
+
+impl<Fut: TryFuture + Unpin> Unpin for TryMaybeDone<Fut> {}
+
+/// Wraps a future into a `TryMaybeDone`
+pub fn try_maybe_done<Fut: TryFuture>(future: Fut) -> TryMaybeDone<Fut> {
+    assert_future::<Result<(), Fut::Error>, _>(TryMaybeDone::Future(future))
+}
+
+impl<Fut: TryFuture> TryMaybeDone<Fut> {
+    /// Returns an [`Option`] containing a mutable reference to the output of the future.
+    /// The output of this method will be [`Some`] if and only if the inner
+    /// future has completed successfully and [`take_output`](TryMaybeDone::take_output)
+    /// has not yet been called.
+    #[inline]
+    pub fn output_mut(self: Pin<&mut Self>) -> Option<&mut Fut::Ok> {
+        unsafe {
+            match self.get_unchecked_mut() {
+                TryMaybeDone::Done(res) => Some(res),
+                _ => None,
+            }
+        }
+    }
+
+    /// Attempt to take the output of a `TryMaybeDone` without driving it
+    /// towards completion.
+    #[inline]
+    pub fn take_output(self: Pin<&mut Self>) -> Option<Fut::Ok> {
+        match &*self {
+            Self::Done(_) => {}
+            Self::Future(_) | Self::Gone => return None,
+        }
+        unsafe {
+            match mem::replace(self.get_unchecked_mut(), Self::Gone) {
+                TryMaybeDone::Done(output) => Some(output),
+                _ => unreachable!(),
+            }
+        }
+    }
+}
+
+impl<Fut: TryFuture> FusedFuture for TryMaybeDone<Fut> {
+    fn is_terminated(&self) -> bool {
+        match self {
+            Self::Future(_) => false,
+            Self::Done(_) | Self::Gone => true,
+        }
+    }
+}
+
+impl<Fut: TryFuture> Future for TryMaybeDone<Fut> {
+    type Output = Result<(), Fut::Error>;
+
+    fn poll(mut self: Pin<&mut Self>, cx: &mut Context<'_>) -> Poll<Self::Output> {
+        unsafe {
+            match self.as_mut().get_unchecked_mut() {
+                TryMaybeDone::Future(f) => match ready!(Pin::new_unchecked(f).try_poll(cx)) {
+                    Ok(res) => self.set(Self::Done(res)),
+                    Err(e) => {
+                        self.set(Self::Gone);
+                        return Poll::Ready(Err(e));
+                    }
+                },
+                TryMaybeDone::Done(_) => {}
+                TryMaybeDone::Gone => panic!("TryMaybeDone polled after value taken"),
+            }
+        }
+        Poll::Ready(Ok(()))
+    }
+}
diff --git a/third_party/rust/futures-util/src/future/try_select.rs b/third_party/rust/futures-util/src/future/try_select.rs
new file mode 100644
index 0000000000..4d0b7ff135
--- /dev/null
+++ b/third_party/rust/futures-util/src/future/try_select.rs
@@ -0,0 +1,84 @@
+use crate::future::{Either, TryFutureExt};
+use core::pin::Pin;
+use futures_core::future::{Future, TryFuture};
+use futures_core::task::{Context, Poll};
+
+/// Future for the [`try_select()`] function.
+#[must_use = "futures do nothing unless you `.await` or poll them"]
+#[derive(Debug)]
+pub struct TrySelect<A, B> {
+    inner: Option<(A, B)>,
+}
+
+impl<A: Unpin, B: Unpin> Unpin for TrySelect<A, B> {}
+
+/// Waits for either one of two differently-typed futures to complete.
+///
+/// This function will return a new future which awaits for either one of both
+/// futures to complete. The returned future will finish with both the value
+/// resolved and a future representing the completion of the other work.
+///
+/// Note that this function consumes the receiving futures and returns a
+/// wrapped version of them.
+///
+/// Also note that if both this and the second future have the same
+/// success/error type you can use the `Either::factor_first` method to
+/// conveniently extract out the value at the end.
+///
+/// # Examples
+///
+/// ```
+/// use futures::future::{self, Either, Future, FutureExt, TryFuture, TryFutureExt};
+///
+/// // A poor-man's try_join implemented on top of select
+///
+/// fn try_join<A, B, E>(a: A, b: B) -> impl TryFuture<Ok=(A::Ok, B::Ok), Error=E>
+///      where A: TryFuture<Error = E> + Unpin + 'static,
+///            B: TryFuture<Error = E> + Unpin + 'static,
+///            E: 'static,
+/// {
+///     future::try_select(a, b).then(|res| -> Box<dyn Future<Output = Result<_, _>> + Unpin> {
+///         match res {
+///             Ok(Either::Left((x, b))) => Box::new(b.map_ok(move |y| (x, y))),
+///             Ok(Either::Right((y, a))) => Box::new(a.map_ok(move |x| (x, y))),
+///             Err(Either::Left((e, _))) => Box::new(future::err(e)),
+///             Err(Either::Right((e, _))) => Box::new(future::err(e)),
+///         }
+///     })
+/// }
+/// ```
+pub fn try_select<A, B>(future1: A, future2: B) -> TrySelect<A, B>
+where
+    A: TryFuture + Unpin,
+    B: TryFuture + Unpin,
+{
+    super::assert_future::<
+        Result<Either<(A::Ok, B), (B::Ok, A)>, Either<(A::Error, B), (B::Error, A)>>,
+        _,
+    >(TrySelect { inner: Some((future1, future2)) })
+}
+
+impl<A: Unpin, B: Unpin> Future for TrySelect<A, B>
+where
+    A: TryFuture,
+    B: TryFuture,
+{
+    #[allow(clippy::type_complexity)]
+    type Output = Result<Either<(A::Ok, B), (B::Ok, A)>, Either<(A::Error, B), (B::Error, A)>>;
+
+    fn poll(mut self: Pin<&mut Self>, cx: &mut Context<'_>) -> Poll<Self::Output> {
+        let (mut a, mut b) = self.inner.take().expect("cannot poll Select twice");
+        match a.try_poll_unpin(cx) {
+            Poll::Ready(Err(x)) => Poll::Ready(Err(Either::Left((x, b)))),
+            Poll::Ready(Ok(x)) => Poll::Ready(Ok(Either::Left((x, b)))),
+            Poll::Pending => match b.try_poll_unpin(cx) {
+                Poll::Ready(Err(x)) => Poll::Ready(Err(Either::Right((x, a)))),
+                Poll::Ready(Ok(x)) => Poll::Ready(Ok(Either::Right((x, a)))),
+                Poll::Pending => {
+                    self.inner = Some((a, b));
+                    Poll::Pending
+                }
+            },
+        }
+    }
+}
diff --git a/third_party/rust/futures-util/src/io/allow_std.rs b/third_party/rust/futures-util/src/io/allow_std.rs
new file mode 100644
index 0000000000..ec30ee31e5
--- /dev/null
+++ b/third_party/rust/futures-util/src/io/allow_std.rs
@@ -0,0 +1,200 @@
+use futures_core::task::{Context, Poll};
+use futures_io::{AsyncBufRead, AsyncRead, AsyncSeek, AsyncWrite, IoSlice, IoSliceMut, SeekFrom};
+use std::pin::Pin;
+use std::{fmt, io};
+
+/// A simple wrapper type which allows types which implement only
+/// implement `std::io::Read` or `std::io::Write`
+/// to be used in contexts which expect an `AsyncRead` or `AsyncWrite`.
+///
+/// If these types issue an error with the kind `io::ErrorKind::WouldBlock`,
+/// it is expected that they will notify the current task on readiness.
+/// Synchronous `std` types should not issue errors of this kind and
+/// are safe to use in this context. However, using these types with
+/// `AllowStdIo` will cause the event loop to block, so they should be used
+/// with care.
+#[derive(Debug, Copy, Clone, Eq, PartialEq, Ord, PartialOrd, Hash)]
+pub struct AllowStdIo<T>(T);
+
+impl<T> Unpin for AllowStdIo<T> {}
+
+macro_rules! try_with_interrupt {
+    ($e:expr) => {
+        loop {
+            match $e {
+                Ok(e) => {
+                    break e;
+                }
+                Err(ref e) if e.kind() == ::std::io::ErrorKind::Interrupted => {
+                    continue;
+                }
+                Err(e) => {
+                    return Poll::Ready(Err(e));
+                }
+            }
+        }
+    };
+}
+
+impl<T> AllowStdIo<T> {
+    /// Creates a new `AllowStdIo` from an existing IO object.
+    pub fn new(io: T) -> Self {
+        Self(io)
+    }
+
+    /// Returns a reference to the contained IO object.
+    pub fn get_ref(&self) -> &T {
+        &self.0
+    }
+
+    /// Returns a mutable reference to the contained IO object.
+    pub fn get_mut(&mut self) -> &mut T {
+        &mut self.0
+    }
+
+    /// Consumes self and returns the contained IO object.
+    pub fn into_inner(self) -> T {
+        self.0
+    }
+}
+
+impl<T> io::Write for AllowStdIo<T>
+where
+    T: io::Write,
+{
+    fn write(&mut self, buf: &[u8]) -> io::Result<usize> {
+        self.0.write(buf)
+    }
+    fn write_vectored(&mut self, bufs: &[IoSlice<'_>]) -> io::Result<usize> {
+        self.0.write_vectored(bufs)
+    }
+    fn flush(&mut self) -> io::Result<()> {
+        self.0.flush()
+    }
+    fn write_all(&mut self, buf: &[u8]) -> io::Result<()> {
+        self.0.write_all(buf)
+    }
+    fn write_fmt(&mut self, fmt: fmt::Arguments<'_>) -> io::Result<()> {
+        self.0.write_fmt(fmt)
+    }
+}
+
+impl<T> AsyncWrite for AllowStdIo<T>
+where
+    T: io::Write,
+{
+    fn poll_write(
+        mut self: Pin<&mut Self>,
+        _: &mut Context<'_>,
+        buf: &[u8],
+    ) -> Poll<io::Result<usize>> {
+        Poll::Ready(Ok(try_with_interrupt!(self.0.write(buf))))
+    }
+
+    fn poll_write_vectored(
+        mut self: Pin<&mut Self>,
+        _: &mut Context<'_>,
+        bufs: &[IoSlice<'_>],
+    ) -> Poll<io::Result<usize>> {
+        Poll::Ready(Ok(try_with_interrupt!(self.0.write_vectored(bufs))))
+    }
+
+    fn poll_flush(mut self: Pin<&mut Self>, _: &mut Context<'_>) -> Poll<io::Result<()>> {
+        try_with_interrupt!(self.0.flush());
+        Poll::Ready(Ok(()))
+    }
+
+    fn poll_close(self: Pin<&mut Self>, cx: &mut Context<'_>) -> Poll<io::Result<()>> {
+        self.poll_flush(cx)
+    }
+}
+
+impl<T> io::Read for AllowStdIo<T>
+where
+    T: io::Read,
+{
+    fn read(&mut self, buf: &mut [u8]) -> io::Result<usize> {
+        self.0.read(buf)
+    }
+    fn read_vectored(&mut self, bufs: &mut [IoSliceMut<'_>]) -> io::Result<usize> {
+        self.0.read_vectored(bufs)
+    }
+    fn read_to_end(&mut self, buf: &mut Vec<u8>) -> io::Result<usize> {
+        self.0.read_to_end(buf)
+    }
+    fn read_to_string(&mut self, buf: &mut String) -> io::Result<usize> {
+        self.0.read_to_string(buf)
+    }
+    fn read_exact(&mut self, buf: &mut [u8]) -> io::Result<()> {
+        self.0.read_exact(buf)
+    }
+}
+
+impl<T> AsyncRead for AllowStdIo<T>
+where
+    T: io::Read,
+{
+    fn poll_read(
+        mut self: Pin<&mut Self>,
+        _: &mut Context<'_>,
+        buf: &mut [u8],
+    ) -> Poll<io::Result<usize>> {
+        Poll::Ready(Ok(try_with_interrupt!(self.0.read(buf))))
+    }
+
+    fn poll_read_vectored(
+        mut self: Pin<&mut Self>,
+        _: &mut Context<'_>,
+        bufs: &mut [IoSliceMut<'_>],
+    ) -> Poll<io::Result<usize>> {
+        Poll::Ready(Ok(try_with_interrupt!(self.0.read_vectored(bufs))))
+    }
+}
+
+impl<T> io::Seek for AllowStdIo<T>
+where
+    T: io::Seek,
+{
+    fn seek(&mut self, pos: SeekFrom) -> io::Result<u64> {
+        self.0.seek(pos)
+    }
+}
+
+impl<T> AsyncSeek for AllowStdIo<T>
+where
+    T: io::Seek,
+{
+    fn poll_seek(
+        mut self: Pin<&mut Self>,
+        _: &mut Context<'_>,
+        pos: SeekFrom,
+    ) -> Poll<io::Result<u64>> {
+        Poll::Ready(Ok(try_with_interrupt!(self.0.seek(pos))))
+    }
+}
+
+impl<T> io::BufRead for AllowStdIo<T>
+where
+    T: io::BufRead,
+{
+    fn fill_buf(&mut self) -> io::Result<&[u8]> {
+        self.0.fill_buf()
+    }
+    fn consume(&mut self, amt: usize) {
+        self.0.consume(amt)
+    }
+}
+
+impl<T> AsyncBufRead for AllowStdIo<T>
+where
+    T: io::BufRead,
+{
+    fn poll_fill_buf(mut self: Pin<&mut Self>, _: &mut Context<'_>) -> Poll<io::Result<&[u8]>> {
+        let this: *mut Self = &mut *self as *mut _;
+        Poll::Ready(Ok(try_with_interrupt!(unsafe { &mut *this }.0.fill_buf())))
+    }
+
+    fn consume(mut self: Pin<&mut Self>, amt: usize) {
+        self.0.consume(amt)
+    }
+}
diff --git a/third_party/rust/futures-util/src/io/buf_reader.rs b/third_party/rust/futures-util/src/io/buf_reader.rs
new file mode 100644
index 0000000000..0334a9f081
--- /dev/null
+++ b/third_party/rust/futures-util/src/io/buf_reader.rs
@@ -0,0 +1,263 @@
+use super::DEFAULT_BUF_SIZE;
+use futures_core::future::Future;
+use futures_core::ready;
+use futures_core::task::{Context, Poll};
+use futures_io::{AsyncBufRead, AsyncRead, AsyncSeek, AsyncWrite, IoSliceMut, SeekFrom};
+use pin_project_lite::pin_project;
+use std::io::{self, Read};
+use std::pin::Pin;
+use std::{cmp, fmt};
+
+pin_project! {
+    /// The `BufReader` struct adds buffering to any reader.
+    ///
+    /// It can be excessively inefficient to work directly with a [`AsyncRead`]
+    /// instance. A `BufReader` performs large, infrequent reads on the underlying
+    /// [`AsyncRead`] and maintains an in-memory buffer of the results.
+    ///
+    /// `BufReader` can improve the speed of programs that make *small* and
+    /// *repeated* read calls to the same file or network socket. It does not
+    /// help when reading very large amounts at once, or reading just one or a few
+    /// times. It also provides no advantage when reading from a source that is
+    /// already in memory, like a `Vec<u8>`.
+    ///
+    /// When the `BufReader` is dropped, the contents of its buffer will be
+    /// discarded. Creating multiple instances of a `BufReader` on the same
+    /// stream can cause data loss.
+    ///
+    /// [`AsyncRead`]: futures_io::AsyncRead
+    ///
+    // TODO: Examples
+    pub struct BufReader<R> {
+        #[pin]
+        inner: R,
+        buffer: Box<[u8]>,
+        pos: usize,
+        cap: usize,
+    }
+}
+
+impl<R: AsyncRead> BufReader<R> {
+    /// Creates a new `BufReader` with a default buffer capacity. The default is currently 8 KB,
+    /// but may change in the future.
+    pub fn new(inner: R) -> Self {
+        Self::with_capacity(DEFAULT_BUF_SIZE, inner)
+    }
+
+    /// Creates a new `BufReader` with the specified buffer capacity.
+    pub fn with_capacity(capacity: usize, inner: R) -> Self {
+        unsafe {
+            let mut buffer = Vec::with_capacity(capacity);
+            buffer.set_len(capacity);
+            super::initialize(&inner, &mut buffer);
+            Self { inner, buffer: buffer.into_boxed_slice(), pos: 0, cap: 0 }
+        }
+    }
+
+    delegate_access_inner!(inner, R, ());
+
+    /// Returns a reference to the internally buffered data.
+    ///
+    /// Unlike `fill_buf`, this will not attempt to fill the buffer if it is empty.
+    pub fn buffer(&self) -> &[u8] {
+        &self.buffer[self.pos..self.cap]
+    }
+
+    /// Invalidates all data in the internal buffer.
+    #[inline]
+    fn discard_buffer(self: Pin<&mut Self>) {
+        let this = self.project();
+        *this.pos = 0;
+        *this.cap = 0;
+    }
+}
+
+impl<R: AsyncRead + AsyncSeek> BufReader<R> {
+    /// Seeks relative to the current position. If the new position lies within the buffer,
+    /// the buffer will not be flushed, allowing for more efficient seeks.
+    /// This method does not return the location of the underlying reader, so the caller
+    /// must track this information themselves if it is required.
+    pub fn seek_relative(self: Pin<&mut Self>, offset: i64) -> SeeKRelative<'_, R> {
+        SeeKRelative { inner: self, offset, first: true }
+    }
+
+    /// Attempts to seek relative to the current position. If the new position lies within the buffer,
+    /// the buffer will not be flushed, allowing for more efficient seeks.
+    /// This method does not return the location of the underlying reader, so the caller
+    /// must track this information themselves if it is required.
+    pub fn poll_seek_relative(
+        self: Pin<&mut Self>,
+        cx: &mut Context<'_>,
+        offset: i64,
+    ) -> Poll<io::Result<()>> {
+        let pos = self.pos as u64;
+        if offset < 0 {
+            if let Some(new_pos) = pos.checked_sub((-offset) as u64) {
+                *self.project().pos = new_pos as usize;
+                return Poll::Ready(Ok(()));
+            }
+        } else if let Some(new_pos) = pos.checked_add(offset as u64) {
+            if new_pos <= self.cap as u64 {
+                *self.project().pos = new_pos as usize;
+                return Poll::Ready(Ok(()));
+            }
+        }
+        self.poll_seek(cx, SeekFrom::Current(offset)).map(|res| res.map(|_| ()))
+    }
+}
+
+impl<R: AsyncRead> AsyncRead for BufReader<R> {
+    fn poll_read(
+        mut self: Pin<&mut Self>,
+        cx: &mut Context<'_>,
+        buf: &mut [u8],
+    ) -> Poll<io::Result<usize>> {
+        // If we don't have any buffered data and we're doing a massive read
+        // (larger than our internal buffer), bypass our internal buffer
+        // entirely.
+        if self.pos == self.cap && buf.len() >= self.buffer.len() {
+            let res = ready!(self.as_mut().project().inner.poll_read(cx, buf));
+            self.discard_buffer();
+            return Poll::Ready(res);
+        }
+        let mut rem = ready!(self.as_mut().poll_fill_buf(cx))?;
+        let nread = rem.read(buf)?;
+        self.consume(nread);
+        Poll::Ready(Ok(nread))
+    }
+
+    fn poll_read_vectored(
+        mut self: Pin<&mut Self>,
+        cx: &mut Context<'_>,
+        bufs: &mut [IoSliceMut<'_>],
+    ) -> Poll<io::Result<usize>> {
+        let total_len = bufs.iter().map(|b| b.len()).sum::<usize>();
+        if self.pos == self.cap && total_len >= self.buffer.len() {
+            let res = ready!(self.as_mut().project().inner.poll_read_vectored(cx, bufs));
+            self.discard_buffer();
+            return Poll::Ready(res);
+        }
+        let mut rem = ready!(self.as_mut().poll_fill_buf(cx))?;
+        let nread = rem.read_vectored(bufs)?;
+        self.consume(nread);
+        Poll::Ready(Ok(nread))
+    }
+}
+
+impl<R: AsyncRead> AsyncBufRead for BufReader<R> {
+    fn poll_fill_buf(self: Pin<&mut Self>, cx: &mut Context<'_>) -> Poll<io::Result<&[u8]>> {
+        let this = self.project();
+
+        // If we've reached the end of our internal buffer then we need to fetch
+        // some more data from the underlying reader.
+        // Branch using `>=` instead of the more correct `==`
+        // to tell the compiler that the pos..cap slice is always valid.
+        if *this.pos >= *this.cap {
+            debug_assert!(*this.pos == *this.cap);
+            *this.cap = ready!(this.inner.poll_read(cx, this.buffer))?;
+            *this.pos = 0;
+        }
+        Poll::Ready(Ok(&this.buffer[*this.pos..*this.cap]))
+    }
+
+    fn consume(self: Pin<&mut Self>, amt: usize) {
+        *self.project().pos = cmp::min(self.pos + amt, self.cap);
+    }
+}
+
+impl<R: AsyncWrite> AsyncWrite for BufReader<R> {
+    delegate_async_write!(inner);
+}
+
+impl<R: fmt::Debug> fmt::Debug for BufReader<R> {
+    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
+        f.debug_struct("BufReader")
+            .field("reader", &self.inner)
+            .field("buffer", &format_args!("{}/{}", self.cap - self.pos, self.buffer.len()))
+            .finish()
+    }
+}
+
+impl<R: AsyncRead + AsyncSeek> AsyncSeek for BufReader<R> {
+    /// Seek to an offset, in bytes, in the underlying reader.
+    ///
+    /// The position used for seeking with `SeekFrom::Current(_)` is the
+    /// position the underlying reader would be at if the `BufReader` had no
+    /// internal buffer.
+    ///
+    /// Seeking always discards the internal buffer, even if the seek position
+    /// would otherwise fall within it. This guarantees that calling
+    /// `.into_inner()` immediately after a seek yields the underlying reader
+    /// at the same position.
+    ///
+    /// To seek without discarding the internal buffer, use
+    /// [`BufReader::seek_relative`](BufReader::seek_relative) or
+    /// [`BufReader::poll_seek_relative`](BufReader::poll_seek_relative).
+    ///
+    /// See [`AsyncSeek`](futures_io::AsyncSeek) for more details.
+    ///
+    /// Note: In the edge case where you're seeking with `SeekFrom::Current(n)`
+    /// where `n` minus the internal buffer length overflows an `i64`, two
+    /// seeks will be performed instead of one. If the second seek returns
+    /// `Err`, the underlying reader will be left at the same position it would
+    /// have if you called `seek` with `SeekFrom::Current(0)`.
+    fn poll_seek(
+        mut self: Pin<&mut Self>,
+        cx: &mut Context<'_>,
+        pos: SeekFrom,
+    ) -> Poll<io::Result<u64>> {
+        let result: u64;
+        if let SeekFrom::Current(n) = pos {
+            let remainder = (self.cap - self.pos) as i64;
+            // it should be safe to assume that remainder fits within an i64 as the alternative
+            // means we managed to allocate 8 exbibytes and that's absurd.
+            // But it's not out of the realm of possibility for some weird underlying reader to
+            // support seeking by i64::min_value() so we need to handle underflow when subtracting
+            // remainder.
+            if let Some(offset) = n.checked_sub(remainder) {
+                result =
+                    ready!(self.as_mut().project().inner.poll_seek(cx, SeekFrom::Current(offset)))?;
+            } else {
+                // seek backwards by our remainder, and then by the offset
+                ready!(self.as_mut().project().inner.poll_seek(cx, SeekFrom::Current(-remainder)))?;
+                self.as_mut().discard_buffer();
+                result = ready!(self.as_mut().project().inner.poll_seek(cx, SeekFrom::Current(n)))?;
+            }
+        } else {
+            // Seeking with Start/End doesn't care about our buffer length.
+            result = ready!(self.as_mut().project().inner.poll_seek(cx, pos))?;
+        }
+        self.discard_buffer();
+        Poll::Ready(Ok(result))
+    }
+}
+
+/// Future for the [`BufReader::seek_relative`](self::BufReader::seek_relative) method.
+#[derive(Debug)]
+#[must_use = "futures do nothing unless polled"]
+pub struct SeeKRelative<'a, R> {
+    inner: Pin<&'a mut BufReader<R>>,
+    offset: i64,
+    first: bool,
+}
+
+impl<R> Future for SeeKRelative<'_, R>
+where
+    R: AsyncRead + AsyncSeek,
+{
+    type Output = io::Result<()>;
+
+    fn poll(mut self: Pin<&mut Self>, cx: &mut Context<'_>) -> Poll<Self::Output> {
+        let offset = self.offset;
+        if self.first {
+            self.first = false;
+            self.inner.as_mut().poll_seek_relative(cx, offset)
+        } else {
+            self.inner
+                .as_mut()
+                .as_mut()
+                .poll_seek(cx, SeekFrom::Current(offset))
+                .map(|res| res.map(|_| ()))
+        }
+    }
+}
diff --git a/third_party/rust/futures-util/src/io/buf_writer.rs b/third_party/rust/futures-util/src/io/buf_writer.rs
new file mode 100644
index 0000000000..cb74863ad0
--- /dev/null
+++ b/third_party/rust/futures-util/src/io/buf_writer.rs
@@ -0,0 +1,224 @@
+use super::DEFAULT_BUF_SIZE;
+use futures_core::ready;
+use futures_core::task::{Context, Poll};
+use futures_io::{AsyncBufRead, AsyncRead, AsyncSeek, AsyncWrite, IoSlice, SeekFrom};
+use pin_project_lite::pin_project;
+use std::fmt;
+use std::io::{self, Write};
+use std::pin::Pin;
+use std::ptr;
+
+pin_project! {
+    /// Wraps a writer and buffers its output.
+    ///
+    /// It can be excessively inefficient to work directly with something that
+    /// implements [`AsyncWrite`]. A `BufWriter` keeps an in-memory buffer of data and
+    /// writes it to an underlying writer in large, infrequent batches.
+    ///
+    /// `BufWriter` can improve the speed of programs that make *small* and
+    /// *repeated* write calls to the same file or network socket. It does not
+    /// help when writing very large amounts at once, or writing just one or a few
+    /// times. It also provides no advantage when writing to a destination that is
+    /// in memory, like a `Vec<u8>`.
+    ///
+    /// When the `BufWriter` is dropped, the contents of its buffer will be
+    /// discarded. Creating multiple instances of a `BufWriter` on the same
+    /// stream can cause data loss. If you need to write out the contents of its
+    /// buffer, you must manually call flush before the writer is dropped.
+    ///
+    /// [`AsyncWrite`]: futures_io::AsyncWrite
+    /// [`flush`]: super::AsyncWriteExt::flush
+    ///
+    // TODO: Examples
+    pub struct BufWriter<W> {
+        #[pin]
+        inner: W,
+        buf: Vec<u8>,
+        written: usize,
+    }
+}
+
+impl<W: AsyncWrite> BufWriter<W> {
+    /// Creates a new `BufWriter` with a default buffer capacity. The default is currently 8 KB,
+    /// but may change in the future.
+    pub fn new(inner: W) -> Self {
+        Self::with_capacity(DEFAULT_BUF_SIZE, inner)
+    }
+
+    /// Creates a new `BufWriter` with the specified buffer capacity.
+    pub fn with_capacity(cap: usize, inner: W) -> Self {
+        Self { inner, buf: Vec::with_capacity(cap), written: 0 }
+    }
+
+    pub(super) fn flush_buf(self: Pin<&mut Self>, cx: &mut Context<'_>) -> Poll<io::Result<()>> {
+        let mut this = self.project();
+
+        let len = this.buf.len();
+        let mut ret = Ok(());
+        while *this.written < len {
+            match ready!(this.inner.as_mut().poll_write(cx, &this.buf[*this.written..])) {
+                Ok(0) => {
+                    ret = Err(io::Error::new(
+                        io::ErrorKind::WriteZero,
+                        "failed to write the buffered data",
+                    ));
+                    break;
+                }
+                Ok(n) => *this.written += n,
+                Err(e) => {
+                    ret = Err(e);
+                    break;
+                }
+            }
+        }
+        if *this.written > 0 {
+            this.buf.drain(..*this.written);
+        }
+        *this.written = 0;
+        Poll::Ready(ret)
+    }
+
+    delegate_access_inner!(inner, W, ());
+
+    /// Returns a reference to the internally buffered data.
+    pub fn buffer(&self) -> &[u8] {
+        &self.buf
+    }
+
+    /// Capacity of `buf`. how many chars can be held in buffer
+    pub(super) fn capacity(&self) -> usize {
+        self.buf.capacity()
+    }
+
+    /// Remaining number of bytes to reach `buf` 's capacity
+    #[inline]
+    pub(super) fn spare_capacity(&self) -> usize {
+        self.buf.capacity() - self.buf.len()
+    }
+
+    /// Write a byte slice directly into buffer
+    ///
+    /// Will truncate the number of bytes written to `spare_capacity()` so you want to
+    /// calculate the size of your slice to avoid losing bytes
+    ///
+    /// Based on `std::io::BufWriter`
+    pub(super) fn write_to_buf(self: Pin<&mut Self>, buf: &[u8]) -> usize {
+        let available = self.spare_capacity();
+        let amt_to_buffer = available.min(buf.len());
+
+        // SAFETY: `amt_to_buffer` is <= buffer's spare capacity by construction.
+        unsafe {
+            self.write_to_buffer_unchecked(&buf[..amt_to_buffer]);
+        }
+
+        amt_to_buffer
+    }
+
+    /// Write byte slice directly into `self.buf`
+    ///
+    /// Based on `std::io::BufWriter`
+    #[inline]
+    unsafe fn write_to_buffer_unchecked(self: Pin<&mut Self>, buf: &[u8]) {
+        debug_assert!(buf.len() <= self.spare_capacity());
+        let this = self.project();
+        let old_len = this.buf.len();
+        let buf_len = buf.len();
+        let src = buf.as_ptr();
+        let dst = this.buf.as_mut_ptr().add(old_len);
+        ptr::copy_nonoverlapping(src, dst, buf_len);
+        this.buf.set_len(old_len + buf_len);
+    }
+
+    /// Write directly using `inner`, bypassing buffering
+    pub(super) fn inner_poll_write(
+        self: Pin<&mut Self>,
+        cx: &mut Context<'_>,
+        buf: &[u8],
+    ) -> Poll<io::Result<usize>> {
+        self.project().inner.poll_write(cx, buf)
+    }
+
+    /// Write directly using `inner`, bypassing buffering
+    pub(super) fn inner_poll_write_vectored(
+        self: Pin<&mut Self>,
+        cx: &mut Context<'_>,
+        bufs: &[IoSlice<'_>],
+    ) -> Poll<io::Result<usize>> {
+        self.project().inner.poll_write_vectored(cx, bufs)
+    }
+}
+
+impl<W: AsyncWrite> AsyncWrite for BufWriter<W> {
+    fn poll_write(
+        mut self: Pin<&mut Self>,
+        cx: &mut Context<'_>,
+        buf: &[u8],
+    ) -> Poll<io::Result<usize>> {
+        if self.buf.len() + buf.len() > self.buf.capacity() {
+            ready!(self.as_mut().flush_buf(cx))?;
+        }
+        if buf.len() >= self.buf.capacity() {
+            self.project().inner.poll_write(cx, buf)
+        } else {
+            Poll::Ready(self.project().buf.write(buf))
+        }
+    }
+
+    fn poll_write_vectored(
+        mut self: Pin<&mut Self>,
+        cx: &mut Context<'_>,
+        bufs: &[IoSlice<'_>],
+    ) -> Poll<io::Result<usize>> {
+        let total_len = bufs.iter().map(|b| b.len()).sum::<usize>();
+        if self.buf.len() + total_len > self.buf.capacity() {
+            ready!(self.as_mut().flush_buf(cx))?;
+        }
+        if total_len >= self.buf.capacity() {
+            self.project().inner.poll_write_vectored(cx, bufs)
+        } else {
+            Poll::Ready(self.project().buf.write_vectored(bufs))
+        }
+    }
+
+    fn poll_flush(mut self: Pin<&mut Self>, cx: &mut Context<'_>) -> Poll<io::Result<()>> {
+        ready!(self.as_mut().flush_buf(cx))?;
+        self.project().inner.poll_flush(cx)
+    }
+
+    fn poll_close(mut self: Pin<&mut Self>, cx: &mut Context<'_>) -> Poll<io::Result<()>> {
+        ready!(self.as_mut().flush_buf(cx))?;
+        self.project().inner.poll_close(cx)
+    }
+}
+
+impl<W: AsyncRead> AsyncRead for BufWriter<W> {
+    delegate_async_read!(inner);
+}
+
+impl<W: AsyncBufRead> AsyncBufRead for BufWriter<W> {
+    delegate_async_buf_read!(inner);
+}
+
+impl<W: fmt::Debug> fmt::Debug for BufWriter<W> {
+    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
+        f.debug_struct("BufWriter")
+            .field("writer", &self.inner)
+            .field("buffer", &format_args!("{}/{}", self.buf.len(), self.buf.capacity()))
+            .field("written", &self.written)
+            .finish()
+    }
+}
+
+impl<W: AsyncWrite + AsyncSeek> AsyncSeek for BufWriter<W> {
+    /// Seek to the offset, in bytes, in the underlying writer.
+    ///
+    /// Seeking always writes out the internal buffer before seeking.
+    fn poll_seek(
+        mut self: Pin<&mut Self>,
+        cx: &mut Context<'_>,
+        pos: SeekFrom,
+    ) -> Poll<io::Result<u64>> {
+        ready!(self.as_mut().flush_buf(cx))?;
+        self.project().inner.poll_seek(cx, pos)
+    }
+}
diff --git a/third_party/rust/futures-util/src/io/chain.rs b/third_party/rust/futures-util/src/io/chain.rs
new file mode 100644
index 0000000000..728a3d2dc0
--- /dev/null
+++ b/third_party/rust/futures-util/src/io/chain.rs
@@ -0,0 +1,142 @@
+use futures_core::ready;
+use futures_core::task::{Context, Poll};
+use futures_io::{AsyncBufRead, AsyncRead, IoSliceMut};
+use pin_project_lite::pin_project;
+use std::fmt;
+use std::io;
+use std::pin::Pin;
+
+pin_project! {
+    /// Reader for the [`chain`](super::AsyncReadExt::chain) method.
+    #[must_use = "readers do nothing unless polled"]
+    pub struct Chain<T, U> {
+        #[pin]
+        first: T,
+        #[pin]
+        second: U,
+        done_first: bool,
+    }
+}
+
+impl<T, U> Chain<T, U>
+where
+    T: AsyncRead,
+    U: AsyncRead,
+{
+    pub(super) fn new(first: T, second: U) -> Self {
+        Self { first, second, done_first: false }
+    }
+
+    /// Gets references to the underlying readers in this `Chain`.
+    pub fn get_ref(&self) -> (&T, &U) {
+        (&self.first, &self.second)
+    }
+
+    /// Gets mutable references to the underlying readers in this `Chain`.
+    ///
+    /// Care should be taken to avoid modifying the internal I/O state of the
+    /// underlying readers as doing so may corrupt the internal state of this
+    /// `Chain`.
+    pub fn get_mut(&mut self) -> (&mut T, &mut U) {
+        (&mut self.first, &mut self.second)
+    }
+
+    /// Gets pinned mutable references to the underlying readers in this `Chain`.
+    ///
+    /// Care should be taken to avoid modifying the internal I/O state of the
+    /// underlying readers as doing so may corrupt the internal state of this
+    /// `Chain`.
+    pub fn get_pin_mut(self: Pin<&mut Self>) -> (Pin<&mut T>, Pin<&mut U>) {
+        let this = self.project();
+        (this.first, this.second)
+    }
+
+    /// Consumes the `Chain`, returning the wrapped readers.
+    pub fn into_inner(self) -> (T, U) {
+        (self.first, self.second)
+    }
+}
+
+impl<T, U> fmt::Debug for Chain<T, U>
+where
+    T: fmt::Debug,
+    U: fmt::Debug,
+{
+    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
+        f.debug_struct("Chain")
+            .field("t", &self.first)
+            .field("u", &self.second)
+            .field("done_first", &self.done_first)
+            .finish()
+    }
+}
+
+impl<T, U> AsyncRead for Chain<T, U>
+where
+    T: AsyncRead,
+    U: AsyncRead,
+{
+    fn poll_read(
+        self: Pin<&mut Self>,
+        cx: &mut Context<'_>,
+        buf: &mut [u8],
+    ) -> Poll<io::Result<usize>> {
+        let this = self.project();
+
+        if !*this.done_first {
+            match ready!(this.first.poll_read(cx, buf)?) {
+                0 if !buf.is_empty() => *this.done_first = true,
+                n => return Poll::Ready(Ok(n)),
+            }
+        }
+        this.second.poll_read(cx, buf)
+    }
+
+    fn poll_read_vectored(
+        self: Pin<&mut Self>,
+        cx: &mut Context<'_>,
+        bufs: &mut [IoSliceMut<'_>],
+    ) -> Poll<io::Result<usize>> {
+        let this = self.project();
+
+        if !*this.done_first {
+            let n = ready!(this.first.poll_read_vectored(cx, bufs)?);
+            if n == 0 && bufs.iter().any(|b| !b.is_empty()) {
+                *this.done_first = true
+            } else {
+                return Poll::Ready(Ok(n));
+            }
+        }
+        this.second.poll_read_vectored(cx, bufs)
+    }
+}
+
+impl<T, U> AsyncBufRead for Chain<T, U>
+where
+    T: AsyncBufRead,
+    U: AsyncBufRead,
+{
+    fn poll_fill_buf(self: Pin<&mut Self>, cx: &mut Context<'_>) -> Poll<io::Result<&[u8]>> {
+        let this = self.project();
+
+        if !*this.done_first {
+            match ready!(this.first.poll_fill_buf(cx)?) {
+                buf if buf.is_empty() => {
+                    *this.done_first = true;
+                }
+                buf => return Poll::Ready(Ok(buf)),
+            }
+        }
+        this.second.poll_fill_buf(cx)
+    }
+
+    fn consume(self: Pin<&mut Self>, amt: usize) {
+        let this = self.project();
+
+        if !*this.done_first {
+            this.first.consume(amt)
+        } else {
+            this.second.consume(amt)
+        }
+    }
+}
diff --git a/third_party/rust/futures-util/src/io/close.rs b/third_party/rust/futures-util/src/io/close.rs
new file mode 100644
index 0000000000..b94459279a
--- /dev/null
+++ b/third_party/rust/futures-util/src/io/close.rs
@@ -0,0 +1,28 @@
+use futures_core::future::Future;
+use futures_core::task::{Context, Poll};
+use futures_io::AsyncWrite;
+use std::io;
+use std::pin::Pin;
+
+/// Future for the [`close`](super::AsyncWriteExt::close) method.
+#[derive(Debug)]
+#[must_use = "futures do nothing unless you `.await` or poll them"]
+pub struct Close<'a, W: ?Sized> {
+    writer: &'a mut W,
+}
+
+impl<W: ?Sized + Unpin> Unpin for Close<'_, W> {}
+
+impl<'a, W: AsyncWrite + ?Sized + Unpin> Close<'a, W> {
+    pub(super) fn new(writer: &'a mut W) -> Self {
+        Self { writer }
+    }
+}
+
+impl<W: AsyncWrite + ?Sized + Unpin> Future for Close<'_, W> {
+    type Output = io::Result<()>;
+
+    fn poll(mut self: Pin<&mut Self>, cx: &mut Context<'_>) -> Poll<Self::Output> {
+        Pin::new(&mut *self.writer).poll_close(cx)
+    }
+}
diff --git a/third_party/rust/futures-util/src/io/copy.rs b/third_party/rust/futures-util/src/io/copy.rs
new file mode 100644
index 0000000000..c80add271b
--- /dev/null
+++ b/third_party/rust/futures-util/src/io/copy.rs
@@ -0,0 +1,58 @@
+use super::{copy_buf, BufReader, CopyBuf};
+use futures_core::future::Future;
+use futures_core::task::{Context, Poll};
+use futures_io::{AsyncRead, AsyncWrite};
+use pin_project_lite::pin_project;
+use std::io;
+use std::pin::Pin;
+
+/// Creates a future which copies all the bytes from one object to another.
+///
+/// The returned future will copy all the bytes read from this `AsyncRead` into the
+/// `writer` specified. This future will only complete once the `reader` has hit
+/// EOF and all bytes have been written to and flushed from the `writer`
+/// provided.
+///
+/// On success the number of bytes is returned.
+///
+/// # Examples
+///
+/// ```
+/// # futures::executor::block_on(async {
+/// use futures::io::{self, AsyncWriteExt, Cursor};
+///
+/// let reader = Cursor::new([1, 2, 3, 4]);
+/// let mut writer = Cursor::new(vec![0u8; 5]);
+///
+/// let bytes = io::copy(reader, &mut writer).await?;
+/// writer.close().await?;
+///
+/// assert_eq!(bytes, 4);
+/// assert_eq!(writer.into_inner(), [1, 2, 3, 4, 0]);
+/// # Ok::<(), Box<dyn std::error::Error>>(()) }).unwrap();
+/// ```
+pub fn copy<R, W>(reader: R, writer: &mut W) -> Copy<'_, R, W>
+where
+    R: AsyncRead,
+    W: AsyncWrite + Unpin + ?Sized,
+{
+    Copy { inner: copy_buf(BufReader::new(reader), writer) }
+}
+
+pin_project! {
+    /// Future for the [`copy()`] function.
+    #[derive(Debug)]
+    #[must_use = "futures do nothing unless you `.await` or poll them"]
+    pub struct Copy<'a, R, W: ?Sized> {
+        #[pin]
+        inner: CopyBuf<'a, BufReader<R>, W>,
+    }
+}
+
+impl<R: AsyncRead, W: AsyncWrite + Unpin + ?Sized> Future for Copy<'_, R, W> {
+    type Output = io::Result<u64>;
+
+    fn poll(self: Pin<&mut Self>, cx: &mut Context<'_>) -> Poll<Self::Output> {
+        self.project().inner.poll(cx)
+    }
+}
diff --git a/third_party/rust/futures-util/src/io/copy_buf.rs b/third_party/rust/futures-util/src/io/copy_buf.rs
new file mode 100644
index 0000000000..50f7abdca9
--- /dev/null
+++ b/third_party/rust/futures-util/src/io/copy_buf.rs
@@ -0,0 +1,78 @@
+use futures_core::future::Future;
+use futures_core::ready;
+use futures_core::task::{Context, Poll};
+use futures_io::{AsyncBufRead, AsyncWrite};
+use pin_project_lite::pin_project;
+use std::io;
+use std::pin::Pin;
+
+/// Creates a future which copies all the bytes from one object to another.
+///
+/// The returned future will copy all the bytes read from this `AsyncBufRead` into the
+/// `writer` specified. This future will only complete once the `reader` has hit
+/// EOF and all bytes have been written to and flushed from the `writer`
+/// provided.
+///
+/// On success the number of bytes is returned.
+///
+/// # Examples
+///
+/// ```
+/// # futures::executor::block_on(async {
+/// use futures::io::{self, AsyncWriteExt, Cursor};
+///
+/// let reader = Cursor::new([1, 2, 3, 4]);
+/// let mut writer = Cursor::new(vec![0u8; 5]);
+///
+/// let bytes = io::copy_buf(reader, &mut writer).await?;
+/// writer.close().await?;
+///
+/// assert_eq!(bytes, 4);
+/// assert_eq!(writer.into_inner(), [1, 2, 3, 4, 0]);
+/// # Ok::<(), Box<dyn std::error::Error>>(()) }).unwrap();
+/// ```
+pub fn copy_buf<R, W>(reader: R, writer: &mut W) -> CopyBuf<'_, R, W>
+where
+    R: AsyncBufRead,
+    W: AsyncWrite + Unpin + ?Sized,
+{
+    CopyBuf { reader, writer, amt: 0 }
+}
+
+pin_project! {
+    /// Future for the [`copy_buf()`] function.
+    #[derive(Debug)]
+    #[must_use = "futures do nothing unless you `.await` or poll them"]
+    pub struct CopyBuf<'a, R, W: ?Sized> {
+        #[pin]
+        reader: R,
+        writer: &'a mut W,
+        amt: u64,
+    }
+}
+
+impl<R, W> Future for CopyBuf<'_, R, W>
+where
+    R: AsyncBufRead,
+    W: AsyncWrite + Unpin + ?Sized,
+{
+    type Output = io::Result<u64>;
+
+    fn poll(self: Pin<&mut Self>, cx: &mut Context<'_>) -> Poll<Self::Output> {
+        let mut this = self.project();
+        loop {
+            let buffer = ready!(this.reader.as_mut().poll_fill_buf(cx))?;
+            if buffer.is_empty() {
+                ready!(Pin::new(&mut this.writer).poll_flush(cx))?;
+                return Poll::Ready(Ok(*this.amt));
+            }
+
+            let i = ready!(Pin::new(&mut this.writer).poll_write(cx, buffer))?;
+            if i == 0 {
+                return Poll::Ready(Err(io::ErrorKind::WriteZero.into()));
+            }
+            *this.amt += i as u64;
+            this.reader.as_mut().consume(i);
+        }
+    }
+}
diff --git a/third_party/rust/futures-util/src/io/copy_buf_abortable.rs b/third_party/rust/futures-util/src/io/copy_buf_abortable.rs
new file mode 100644
index 0000000000..fdbc4a5f00
--- /dev/null
+++ b/third_party/rust/futures-util/src/io/copy_buf_abortable.rs
@@ -0,0 +1,124 @@
+use crate::abortable::{AbortHandle, AbortInner, Aborted};
+use futures_core::future::Future;
+use futures_core::task::{Context, Poll};
+use futures_io::{AsyncBufRead, AsyncWrite};
+use pin_project_lite::pin_project;
+use std::io;
+use std::pin::Pin;
+use std::sync::atomic::Ordering;
+use std::sync::Arc;
+
+/// Creates a future which copies all the bytes from one object to another, with its `AbortHandle`.
+///
+/// The returned future will copy all the bytes read from this `AsyncBufRead` into the
+/// `writer` specified. This future will only complete once abort has been requested or the `reader` has hit
+/// EOF and all bytes have been written to and flushed from the `writer`
+/// provided.
+///
+/// On success the number of bytes is returned. If aborted, `Aborted` is returned. Otherwise, the underlying error is returned.
+///
+/// # Examples
+///
+/// ```
+/// # futures::executor::block_on(async {
+/// use futures::io::{self, AsyncWriteExt, Cursor};
+/// use futures::future::Aborted;
+///
+/// let reader = Cursor::new([1, 2, 3, 4]);
+/// let mut writer = Cursor::new(vec![0u8; 5]);
+///
+/// let (fut, abort_handle) = io::copy_buf_abortable(reader, &mut writer);
+/// let bytes = fut.await;
+/// abort_handle.abort();
+/// writer.close().await.unwrap();
+/// match bytes {
+///     Ok(Ok(n)) => {
+///         assert_eq!(n, 4);
+///         assert_eq!(writer.into_inner(), [1, 2, 3, 4, 0]);
+///         Ok(n)
+///     },
+///     Ok(Err(a)) => {
+///         Err::<u64, Aborted>(a)
+///     }
+///     Err(e) => panic!("{}", e)
+/// }
+/// #  }).unwrap();
+/// ```
+pub fn copy_buf_abortable<R, W>(
+    reader: R,
+    writer: &mut W,
+) -> (CopyBufAbortable<'_, R, W>, AbortHandle)
+where
+    R: AsyncBufRead,
+    W: AsyncWrite + Unpin + ?Sized,
+{
+    let (handle, reg) = AbortHandle::new_pair();
+    (CopyBufAbortable { reader, writer, amt: 0, inner: reg.inner }, handle)
+}
+
+pin_project! {
+    /// Future for the [`copy_buf()`] function.
+    #[derive(Debug)]
+    #[must_use = "futures do nothing unless you `.await` or poll them"]
+    pub struct CopyBufAbortable<'a, R, W: ?Sized> {
+        #[pin]
+        reader: R,
+        writer: &'a mut W,
+        amt: u64,
+        inner: Arc<AbortInner>
+    }
+}
+
+macro_rules! ready_or_break {
+    ($e:expr $(,)?) => {
+        match $e {
+            $crate::task::Poll::Ready(t) => t,
+            $crate::task::Poll::Pending => break,
+        }
+    };
+}
+
+impl<R, W> Future for CopyBufAbortable<'_, R, W>
+where
+    R: AsyncBufRead,
+    W: AsyncWrite + Unpin + Sized,
+{
+    type Output = Result<Result<u64, Aborted>, io::Error>;
+
+    fn poll(self: Pin<&mut Self>, cx: &mut Context<'_>) -> Poll<Self::Output> {
+        let mut this = self.project();
+        loop {
+            // Check if the task has been aborted
+            if this.inner.aborted.load(Ordering::Relaxed) {
+                return Poll::Ready(Ok(Err(Aborted)));
+            }
+
+            // Read some bytes from the reader, and if we have reached EOF, return total bytes read
+            let buffer = ready_or_break!(this.reader.as_mut().poll_fill_buf(cx))?;
+            if buffer.is_empty() {
+                ready_or_break!(Pin::new(&mut this.writer).poll_flush(cx))?;
+                return Poll::Ready(Ok(Ok(*this.amt)));
+            }
+
+            // Pass the buffer to the writer, and update the amount written
+            let i = ready_or_break!(Pin::new(&mut this.writer).poll_write(cx, buffer))?;
+            if i == 0 {
+                return Poll::Ready(Err(io::ErrorKind::WriteZero.into()));
+            }
+            *this.amt += i as u64;
+            this.reader.as_mut().consume(i);
+        }
+        // Schedule the task to be woken up again.
+        // Never called unless Poll::Pending is returned from io objects.
+        this.inner.waker.register(cx.waker());
+
+        // Check to see if the task was aborted between the first check and
+        // registration.
+        // Checking with  `Relaxed` is sufficient because
+        // `register` introduces an `AcqRel` barrier.
+        if this.inner.aborted.load(Ordering::Relaxed) {
+            return Poll::Ready(Ok(Err(Aborted)));
+        }
+        Poll::Pending
+    }
+}
diff --git a/third_party/rust/futures-util/src/io/cursor.rs b/third_party/rust/futures-util/src/io/cursor.rs
new file mode 100644
index 0000000000..b6fb3724c7
--- /dev/null
+++ b/third_party/rust/futures-util/src/io/cursor.rs
@@ -0,0 +1,240 @@
+use futures_core::task::{Context, Poll};
+#[cfg(feature = "read_initializer")]
+use futures_io::Initializer;
+use futures_io::{AsyncBufRead, AsyncRead, AsyncSeek, AsyncWrite, IoSlice, IoSliceMut, SeekFrom};
+use std::io;
+use std::pin::Pin;
+
+/// A `Cursor` wraps an in-memory buffer and provides it with a
+/// [`AsyncSeek`] implementation.
+///
+/// `Cursor`s are used with in-memory buffers, anything implementing
+/// `AsRef<[u8]>`, to allow them to implement [`AsyncRead`] and/or [`AsyncWrite`],
+/// allowing these buffers to be used anywhere you might use a reader or writer
+/// that does actual I/O.
+///
+/// This library implements some I/O traits on various types which
+/// are commonly used as a buffer, like `Cursor<`[`Vec`]`<u8>>` and
+/// `Cursor<`[`&[u8]`][bytes]`>`.
+///
+/// [`AsyncSeek`]: trait.AsyncSeek.html
+/// [`AsyncRead`]: trait.AsyncRead.html
+/// [`AsyncWrite`]: trait.AsyncWrite.html
+/// [bytes]: https://doc.rust-lang.org/std/primitive.slice.html
+#[derive(Clone, Debug, Default)]
+pub struct Cursor<T> {
+    inner: io::Cursor<T>,
+}
+
+impl<T> Cursor<T> {
+    /// Creates a new cursor wrapping the provided underlying in-memory buffer.
+    ///
+    /// Cursor initial position is `0` even if underlying buffer (e.g., `Vec`)
+    /// is not empty. So writing to cursor starts with overwriting `Vec`
+    /// content, not with appending to it.
+    ///
+    /// # Examples
+    ///
+    /// ```
+    /// use futures::io::Cursor;
+    ///
+    /// let buff = Cursor::new(Vec::new());
+    /// # fn force_inference(_: &Cursor<Vec<u8>>) {}
+    /// # force_inference(&buff);
+    /// ```
+    pub fn new(inner: T) -> Self {
+        Self { inner: io::Cursor::new(inner) }
+    }
+
+    /// Consumes this cursor, returning the underlying value.
+    ///
+    /// # Examples
+    ///
+    /// ```
+    /// use futures::io::Cursor;
+    ///
+    /// let buff = Cursor::new(Vec::new());
+    /// # fn force_inference(_: &Cursor<Vec<u8>>) {}
+    /// # force_inference(&buff);
+    ///
+    /// let vec = buff.into_inner();
+    /// ```
+    pub fn into_inner(self) -> T {
+        self.inner.into_inner()
+    }
+
+    /// Gets a reference to the underlying value in this cursor.
+    ///
+    /// # Examples
+    ///
+    /// ```
+    /// use futures::io::Cursor;
+    ///
+    /// let buff = Cursor::new(Vec::new());
+    /// # fn force_inference(_: &Cursor<Vec<u8>>) {}
+    /// # force_inference(&buff);
+    ///
+    /// let reference = buff.get_ref();
+    /// ```
+    pub fn get_ref(&self) -> &T {
+        self.inner.get_ref()
+    }
+
+    /// Gets a mutable reference to the underlying value in this cursor.
+    ///
+    /// Care should be taken to avoid modifying the internal I/O state of the
+    /// underlying value as it may corrupt this cursor's position.
+    ///
+    /// # Examples
+    ///
+    /// ```
+    /// use futures::io::Cursor;
+    ///
+    /// let mut buff = Cursor::new(Vec::new());
+    /// # fn force_inference(_: &Cursor<Vec<u8>>) {}
+    /// # force_inference(&buff);
+    ///
+    /// let reference = buff.get_mut();
+    /// ```
+    pub fn get_mut(&mut self) -> &mut T {
+        self.inner.get_mut()
+    }
+
+    /// Returns the current position of this cursor.
+    ///
+    /// # Examples
+    ///
+    /// ```
+    /// # futures::executor::block_on(async {
+    /// use futures::io::{AsyncSeekExt, Cursor, SeekFrom};
+    ///
+    /// let mut buff = Cursor::new(vec![1, 2, 3, 4, 5]);
+    ///
+    /// assert_eq!(buff.position(), 0);
+    ///
+    /// buff.seek(SeekFrom::Current(2)).await?;
+    /// assert_eq!(buff.position(), 2);
+    ///
+    /// buff.seek(SeekFrom::Current(-1)).await?;
+    /// assert_eq!(buff.position(), 1);
+    /// # Ok::<(), Box<dyn std::error::Error>>(()) }).unwrap();
+    /// ```
+    pub fn position(&self) -> u64 {
+        self.inner.position()
+    }
+
+    /// Sets the position of this cursor.
+    ///
+    /// # Examples
+    ///
+    /// ```
+    /// use futures::io::Cursor;
+    ///
+    /// let mut buff = Cursor::new(vec![1, 2, 3, 4, 5]);
+    ///
+    /// assert_eq!(buff.position(), 0);
+    ///
+    /// buff.set_position(2);
+    /// assert_eq!(buff.position(), 2);
+    ///
+    /// buff.set_position(4);
+    /// assert_eq!(buff.position(), 4);
+    /// ```
+    pub fn set_position(&mut self, pos: u64) {
+        self.inner.set_position(pos)
+    }
+}
+
+impl<T> AsyncSeek for Cursor<T>
+where
+    T: AsRef<[u8]> + Unpin,
+{
+    fn poll_seek(
+        mut self: Pin<&mut Self>,
+        _: &mut Context<'_>,
+        pos: SeekFrom,
+    ) -> Poll<io::Result<u64>> {
+        Poll::Ready(io::Seek::seek(&mut self.inner, pos))
+    }
+}
+
+impl<T: AsRef<[u8]> + Unpin> AsyncRead for Cursor<T> {
+    #[cfg(feature = "read_initializer")]
+    #[inline]
+    unsafe fn initializer(&self) -> Initializer {
+        io::Read::initializer(&self.inner)
+    }
+
+    fn poll_read(
+        mut self: Pin<&mut Self>,
+        _cx: &mut Context<'_>,
+        buf: &mut [u8],
+    ) -> Poll<io::Result<usize>> {
+        Poll::Ready(io::Read::read(&mut self.inner, buf))
+    }
+
+    fn poll_read_vectored(
+        mut self: Pin<&mut Self>,
+        _: &mut Context<'_>,
+        bufs: &mut [IoSliceMut<'_>],
+    ) -> Poll<io::Result<usize>> {
+        Poll::Ready(io::Read::read_vectored(&mut self.inner, bufs))
+    }
+}
+
+impl<T> AsyncBufRead for Cursor<T>
+where
+    T: AsRef<[u8]> + Unpin,
+{
+    fn poll_fill_buf(self: Pin<&mut Self>, _: &mut Context<'_>) -> Poll<io::Result<&[u8]>> {
+        Poll::Ready(io::BufRead::fill_buf(&mut self.get_mut().inner))
+    }
+
+    fn consume(mut self: Pin<&mut Self>, amt: usize) {
+        io::BufRead::consume(&mut self.inner, amt)
+    }
+}
+
+macro_rules! delegate_async_write_to_stdio {
+    () => {
+        fn poll_write(
+            mut self: Pin<&mut Self>,
+            _: &mut Context<'_>,
+            buf: &[u8],
+        ) -> Poll<io::Result<usize>> {
+            Poll::Ready(io::Write::write(&mut self.inner, buf))
+        }
+
+        fn poll_write_vectored(
+            mut self: Pin<&mut Self>,
+            _: &mut Context<'_>,
+            bufs: &[IoSlice<'_>],
+        ) -> Poll<io::Result<usize>> {
+            Poll::Ready(io::Write::write_vectored(&mut self.inner, bufs))
+        }
+
+        fn poll_flush(mut self: Pin<&mut Self>, _: &mut Context<'_>) -> Poll<io::Result<()>> {
+            Poll::Ready(io::Write::flush(&mut self.inner))
+        }
+
+        fn poll_close(self: Pin<&mut Self>, cx: &mut Context<'_>) -> Poll<io::Result<()>> {
+            self.poll_flush(cx)
+        }
+    };
+}
+
+impl AsyncWrite for Cursor<&mut [u8]> {
+    delegate_async_write_to_stdio!();
+}
+
+impl AsyncWrite for Cursor<&mut Vec<u8>> {
+    delegate_async_write_to_stdio!();
+}
+
+impl AsyncWrite for Cursor<Vec<u8>> {
+    delegate_async_write_to_stdio!();
+}
+
+impl AsyncWrite for Cursor<Box<[u8]>> {
+    delegate_async_write_to_stdio!();
+}
diff --git a/third_party/rust/futures-util/src/io/empty.rs b/third_party/rust/futures-util/src/io/empty.rs
new file mode 100644
index 0000000000..02f6103f54
--- /dev/null
+++ b/third_party/rust/futures-util/src/io/empty.rs
@@ -0,0 +1,59 @@
+use futures_core::task::{Context, Poll};
+use futures_io::{AsyncBufRead, AsyncRead};
+use std::fmt;
+use std::io;
+use std::pin::Pin;
+
+/// Reader for the [`empty()`] function.
+#[must_use = "readers do nothing unless polled"]
+pub struct Empty {
+    _priv: (),
+}
+
+/// Constructs a new handle to an empty reader.
+///
+/// All reads from the returned reader will return `Poll::Ready(Ok(0))`.
+///
+/// # Examples
+///
+/// A slightly sad example of not reading anything into a buffer:
+///
+/// ```
+/// # futures::executor::block_on(async {
+/// use futures::io::{self, AsyncReadExt};
+///
+/// let mut buffer = String::new();
+/// let mut reader = io::empty();
+/// reader.read_to_string(&mut buffer).await?;
+/// assert!(buffer.is_empty());
+/// # Ok::<(), Box<dyn std::error::Error>>(()) }).unwrap();
+/// ```
+pub fn empty() -> Empty {
+    Empty { _priv: () }
+}
+
+impl AsyncRead for Empty {
+    #[inline]
+    fn poll_read(
+        self: Pin<&mut Self>,
+        _: &mut Context<'_>,
+        _: &mut [u8],
+    ) -> Poll<io::Result<usize>> {
+        Poll::Ready(Ok(0))
+    }
+}
+
+impl AsyncBufRead for Empty {
+    #[inline]
+    fn poll_fill_buf(self: Pin<&mut Self>, _: &mut Context<'_>) -> Poll<io::Result<&[u8]>> {
+        Poll::Ready(Ok(&[]))
+    }
+    #[inline]
+    fn consume(self: Pin<&mut Self>, _: usize) {}
+}
+
+impl fmt::Debug for Empty {
+    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
+        f.pad("Empty { .. }")
+    }
+}
diff --git a/third_party/rust/futures-util/src/io/fill_buf.rs b/third_party/rust/futures-util/src/io/fill_buf.rs
new file mode 100644
index 0000000000..a1484c0322
--- /dev/null
+++ b/third_party/rust/futures-util/src/io/fill_buf.rs
@@ -0,0 +1,51 @@
+use futures_core::future::Future;
+use futures_core::task::{Context, Poll};
+use futures_io::AsyncBufRead;
+use std::io;
+use std::pin::Pin;
+
+/// Future for the [`fill_buf`](super::AsyncBufReadExt::fill_buf) method.
+#[derive(Debug)]
+#[must_use = "futures do nothing unless you `.await` or poll them"]
+pub struct FillBuf<'a, R: ?Sized> {
+    reader: Option<&'a mut R>,
+}
+
+impl<R: ?Sized> Unpin for FillBuf<'_, R> {}
+
+impl<'a, R: AsyncBufRead + ?Sized + Unpin> FillBuf<'a, R> {
+    pub(super) fn new(reader: &'a mut R) -> Self {
+        Self { reader: Some(reader) }
+    }
+}
+
+impl<'a, R> Future for FillBuf<'a, R>
+where
+    R: AsyncBufRead + ?Sized + Unpin,
+{
+    type Output = io::Result<&'a [u8]>;
+
+    fn poll(mut self: Pin<&mut Self>, cx: &mut Context<'_>) -> Poll<Self::Output> {
+        let this = &mut *self;
+        let reader = this.reader.take().expect("Polled FillBuf after completion");
+
+        match Pin::new(&mut *reader).poll_fill_buf(cx) {
+            // With polonius it is possible to remove this inner match and just have the correct
+            // lifetime of the reference inferred based on which branch is taken
+            Poll::Ready(Ok(_)) => match Pin::new(reader).poll_fill_buf(cx) {
+                Poll::Ready(Ok(slice)) => Poll::Ready(Ok(slice)),
+                Poll::Ready(Err(err)) => {
+                    unreachable!("reader indicated readiness but then returned an error: {:?}", err)
+                }
+                Poll::Pending => {
+                    unreachable!("reader indicated readiness but then returned pending")
+                }
+            },
+            Poll::Ready(Err(err)) => Poll::Ready(Err(err)),
+            Poll::Pending => {
+                this.reader = Some(reader);
+                Poll::Pending
+            }
+        }
+    }
+}
diff --git a/third_party/rust/futures-util/src/io/flush.rs b/third_party/rust/futures-util/src/io/flush.rs
new file mode 100644
index 0000000000..b75d14c5d3
--- /dev/null
+++ b/third_party/rust/futures-util/src/io/flush.rs
@@ -0,0 +1,31 @@
+use futures_core::future::Future;
+use futures_core::task::{Context, Poll};
+use futures_io::AsyncWrite;
+use std::io;
+use std::pin::Pin;
+
+/// Future for the [`flush`](super::AsyncWriteExt::flush) method.
+#[derive(Debug)]
+#[must_use = "futures do nothing unless you `.await` or poll them"]
+pub struct Flush<'a, W: ?Sized> {
+    writer: &'a mut W,
+}
+
+impl<W: ?Sized + Unpin> Unpin for Flush<'_, W> {}
+
+impl<'a, W: AsyncWrite + ?Sized + Unpin> Flush<'a, W> {
+    pub(super) fn new(writer: &'a mut W) -> Self {
+        Self { writer }
+    }
+}
+
+impl<W> Future for Flush<'_, W>
+where
+    W: AsyncWrite + ?Sized + Unpin,
+{
+    type Output = io::Result<()>;
+
+    fn poll(mut self: Pin<&mut Self>, cx: &mut Context<'_>) -> Poll<Self::Output> {
+        Pin::new(&mut *self.writer).poll_flush(cx)
+    }
+}
diff --git a/third_party/rust/futures-util/src/io/into_sink.rs b/third_party/rust/futures-util/src/io/into_sink.rs
new file mode 100644
index 0000000000..6a41ee2269
--- /dev/null
+++ b/third_party/rust/futures-util/src/io/into_sink.rs
@@ -0,0 +1,82 @@
+use futures_core::ready;
+use futures_core::task::{Context, Poll};
+use futures_io::AsyncWrite;
+use futures_sink::Sink;
+use pin_project_lite::pin_project;
+use std::io;
+use std::pin::Pin;
+
+#[derive(Debug)]
+struct Block<Item> {
+    offset: usize,
+    bytes: Item,
+}
+
+pin_project! {
+    /// Sink for the [`into_sink`](super::AsyncWriteExt::into_sink) method.
+    #[must_use = "sinks do nothing unless polled"]
+    #[derive(Debug)]
+    #[cfg_attr(docsrs, doc(cfg(feature = "sink")))]
+    pub struct IntoSink<W, Item> {
+        #[pin]
+        writer: W,
+        // An outstanding block for us to push into the underlying writer, along with an offset of how
+        // far into this block we have written already.
+        buffer: Option<Block<Item>>,
+    }
+}
+
+impl<W: AsyncWrite, Item: AsRef<[u8]>> IntoSink<W, Item> {
+    pub(super) fn new(writer: W) -> Self {
+        Self { writer, buffer: None }
+    }
+
+    /// If we have an outstanding block in `buffer` attempt to push it into the writer, does _not_
+    /// flush the writer after it succeeds in pushing the block into it.
+    fn poll_flush_buffer(
+        self: Pin<&mut Self>,
+        cx: &mut Context<'_>,
+    ) -> Poll<Result<(), io::Error>> {
+        let mut this = self.project();
+
+        if let Some(buffer) = this.buffer {
+            loop {
+                let bytes = buffer.bytes.as_ref();
+                let written = ready!(this.writer.as_mut().poll_write(cx, &bytes[buffer.offset..]))?;
+                buffer.offset += written;
+                if buffer.offset == bytes.len() {
+                    break;
+                }
+            }
+        }
+        *this.buffer = None;
+        Poll::Ready(Ok(()))
+    }
+}
+
+impl<W: AsyncWrite, Item: AsRef<[u8]>> Sink<Item> for IntoSink<W, Item> {
+    type Error = io::Error;
+
+    fn poll_ready(self: Pin<&mut Self>, cx: &mut Context<'_>) -> Poll<Result<(), Self::Error>> {
+        ready!(self.poll_flush_buffer(cx))?;
+        Poll::Ready(Ok(()))
+    }
+
+    fn start_send(self: Pin<&mut Self>, item: Item) -> Result<(), Self::Error> {
+        debug_assert!(self.buffer.is_none());
+        *self.project().buffer = Some(Block { offset: 0, bytes: item });
+        Ok(())
+    }
+
+    fn poll_flush(mut self: Pin<&mut Self>, cx: &mut Context<'_>) -> Poll<Result<(), Self::Error>> {
+        ready!(self.as_mut().poll_flush_buffer(cx))?;
+        ready!(self.project().writer.poll_flush(cx))?;
+        Poll::Ready(Ok(()))
+    }
+
+    fn poll_close(mut self: Pin<&mut Self>, cx: &mut Context<'_>) -> Poll<Result<(), Self::Error>> {
+        ready!(self.as_mut().poll_flush_buffer(cx))?;
+        ready!(self.project().writer.poll_close(cx))?;
+        Poll::Ready(Ok(()))
+    }
+}
diff --git a/third_party/rust/futures-util/src/io/line_writer.rs b/third_party/rust/futures-util/src/io/line_writer.rs
new file mode 100644
index 0000000000..71cd668325
--- /dev/null
+++ b/third_party/rust/futures-util/src/io/line_writer.rs
@@ -0,0 +1,155 @@
+use super::buf_writer::BufWriter;
+use futures_core::ready;
+use futures_core::task::{Context, Poll};
+use futures_io::AsyncWrite;
+use futures_io::IoSlice;
+use pin_project_lite::pin_project;
+use std::io;
+use std::pin::Pin;
+
+pin_project! {
+/// Wrap a writer, like [`BufWriter`] does, but prioritizes buffering lines
+///
+/// This was written based on `std::io::LineWriter` which goes into further details
+/// explaining the code.
+///
+/// Buffering is actually done using `BufWriter`. This class will leverage `BufWriter`
+/// to write on-each-line.
+#[derive(Debug)]
+pub struct LineWriter<W: AsyncWrite> {
+    #[pin]
+    buf_writer: BufWriter<W>,
+}
+}
+
+impl<W: AsyncWrite> LineWriter<W> {
+    /// Create a new `LineWriter` with default buffer capacity. The default is currently 1KB
+    /// which was taken from `std::io::LineWriter`
+    pub fn new(inner: W) -> LineWriter<W> {
+        LineWriter::with_capacity(1024, inner)
+    }
+
+    /// Creates a new `LineWriter` with the specified buffer capacity.
+    pub fn with_capacity(capacity: usize, inner: W) -> LineWriter<W> {
+        LineWriter { buf_writer: BufWriter::with_capacity(capacity, inner) }
+    }
+
+    /// Flush `buf_writer` if last char is "new line"
+    fn flush_if_completed_line(self: Pin<&mut Self>, cx: &mut Context<'_>) -> Poll<io::Result<()>> {
+        let this = self.project();
+        match this.buf_writer.buffer().last().copied() {
+            Some(b'\n') => this.buf_writer.flush_buf(cx),
+            _ => Poll::Ready(Ok(())),
+        }
+    }
+
+    /// Returns a reference to `buf_writer`'s internally buffered data.
+    pub fn buffer(&self) -> &[u8] {
+        self.buf_writer.buffer()
+    }
+
+    /// Acquires a reference to the underlying sink or stream that this combinator is
+    /// pulling from.
+    pub fn get_ref(&self) -> &W {
+        self.buf_writer.get_ref()
+    }
+}
+
+impl<W: AsyncWrite> AsyncWrite for LineWriter<W> {
+    fn poll_write(
+        mut self: Pin<&mut Self>,
+        cx: &mut Context<'_>,
+        buf: &[u8],
+    ) -> Poll<io::Result<usize>> {
+        let mut this = self.as_mut().project();
+        let newline_index = match memchr::memrchr(b'\n', buf) {
+            None => {
+                ready!(self.as_mut().flush_if_completed_line(cx)?);
+                return self.project().buf_writer.poll_write(cx, buf);
+            }
+            Some(newline_index) => newline_index + 1,
+        };
+
+        ready!(this.buf_writer.as_mut().poll_flush(cx)?);
+
+        let lines = &buf[..newline_index];
+
+        let flushed = { ready!(this.buf_writer.as_mut().inner_poll_write(cx, lines))? };
+
+        if flushed == 0 {
+            return Poll::Ready(Ok(0));
+        }
+
+        let tail = if flushed >= newline_index {
+            &buf[flushed..]
+        } else if newline_index - flushed <= this.buf_writer.capacity() {
+            &buf[flushed..newline_index]
+        } else {
+            let scan_area = &buf[flushed..];
+            let scan_area = &scan_area[..this.buf_writer.capacity()];
+            match memchr::memrchr(b'\n', scan_area) {
+                Some(newline_index) => &scan_area[..newline_index + 1],
+                None => scan_area,
+            }
+        };
+
+        let buffered = this.buf_writer.as_mut().write_to_buf(tail);
+        Poll::Ready(Ok(flushed + buffered))
+    }
+
+    fn poll_write_vectored(
+        mut self: Pin<&mut Self>,
+        cx: &mut Context<'_>,
+        bufs: &[IoSlice<'_>],
+    ) -> Poll<io::Result<usize>> {
+        let mut this = self.as_mut().project();
+        // `is_write_vectored()` is handled in original code, but not in this crate
+        // see https://github.com/rust-lang/rust/issues/70436
+
+        let last_newline_buf_idx = bufs
+            .iter()
+            .enumerate()
+            .rev()
+            .find_map(|(i, buf)| memchr::memchr(b'\n', buf).map(|_| i));
+        let last_newline_buf_idx = match last_newline_buf_idx {
+            None => {
+                ready!(self.as_mut().flush_if_completed_line(cx)?);
+                return self.project().buf_writer.poll_write_vectored(cx, bufs);
+            }
+            Some(i) => i,
+        };
+
+        ready!(this.buf_writer.as_mut().poll_flush(cx)?);
+
+        let (lines, tail) = bufs.split_at(last_newline_buf_idx + 1);
+
+        let flushed = { ready!(this.buf_writer.as_mut().inner_poll_write_vectored(cx, lines))? };
+        if flushed == 0 {
+            return Poll::Ready(Ok(0));
+        }
+
+        let lines_len = lines.iter().map(|buf| buf.len()).sum();
+        if flushed < lines_len {
+            return Poll::Ready(Ok(flushed));
+        }
+
+        let buffered: usize = tail
+            .iter()
+            .filter(|buf| !buf.is_empty())
+            .map(|buf| this.buf_writer.as_mut().write_to_buf(buf))
+            .take_while(|&n| n > 0)
+            .sum();
+
+        Poll::Ready(Ok(flushed + buffered))
+    }
+
+    /// Forward to `buf_writer` 's `BufWriter::poll_flush()`
+    fn poll_flush(mut self: Pin<&mut Self>, cx: &mut Context<'_>) -> Poll<io::Result<()>> {
+        self.as_mut().project().buf_writer.poll_flush(cx)
+    }
+
+    /// Forward to `buf_writer` 's `BufWriter::poll_close()`
+    fn poll_close(mut self: Pin<&mut Self>, cx: &mut Context<'_>) -> Poll<io::Result<()>> {
+        self.as_mut().project().buf_writer.poll_close(cx)
+    }
+}
diff --git a/third_party/rust/futures-util/src/io/lines.rs b/third_party/rust/futures-util/src/io/lines.rs
new file mode 100644
index 0000000000..b5561bfa7d
--- /dev/null
+++ b/third_party/rust/futures-util/src/io/lines.rs
@@ -0,0 +1,47 @@
+use super::read_line::read_line_internal;
+use futures_core::ready;
+use futures_core::stream::Stream;
+use futures_core::task::{Context, Poll};
+use futures_io::AsyncBufRead;
+use pin_project_lite::pin_project;
+use std::io;
+use std::mem;
+use std::pin::Pin;
+
+pin_project! {
+    /// Stream for the [`lines`](super::AsyncBufReadExt::lines) method.
+    #[derive(Debug)]
+    #[must_use = "streams do nothing unless polled"]
+    pub struct Lines<R> {
+        #[pin]
+        reader: R,
+        buf: String,
+        bytes: Vec<u8>,
+        read: usize,
+    }
+}
+
+impl<R: AsyncBufRead> Lines<R> {
+    pub(super) fn new(reader: R) -> Self {
+        Self { reader, buf: String::new(), bytes: Vec::new(), read: 0 }
+    }
+}
+
+impl<R: AsyncBufRead> Stream for Lines<R> {
+    type Item = io::Result<String>;
+
+    fn poll_next(self: Pin<&mut Self>, cx: &mut Context<'_>) -> Poll<Option<Self::Item>> {
+        let this = self.project();
+        let n = ready!(read_line_internal(this.reader, cx, this.buf, this.bytes, this.read))?;
+        if n == 0 && this.buf.is_empty() {
+            return Poll::Ready(None);
+        }
+        if this.buf.ends_with('\n') {
+            this.buf.pop();
+            if this.buf.ends_with('\r') {
+                this.buf.pop();
+            }
+        }
+        Poll::Ready(Some(Ok(mem::take(this.buf))))
+    }
+}
diff --git a/third_party/rust/futures-util/src/io/mod.rs b/third_party/rust/futures-util/src/io/mod.rs
new file mode 100644
index 0000000000..8ce3ad644b
--- /dev/null
+++ b/third_party/rust/futures-util/src/io/mod.rs
@@ -0,0 +1,841 @@
+//! Asynchronous I/O.
+//!
+//! This module is the asynchronous version of `std::io`. It defines four
+//! traits, [`AsyncRead`], [`AsyncWrite`], [`AsyncSeek`], and [`AsyncBufRead`],
+//! which mirror the `Read`, `Write`, `Seek`, and `BufRead` traits of the
+//! standard library. However, these traits integrate with the asynchronous
+//! task system, so that if an I/O object isn't ready for reading (or writing),
+//! the thread is not blocked, and instead the current task is queued to be
+//! woken when I/O is ready.
+//!
+//! In addition, the [`AsyncReadExt`], [`AsyncWriteExt`], [`AsyncSeekExt`], and
+//! [`AsyncBufReadExt`] extension traits offer a variety of useful combinators
+//! for operating with asynchronous I/O objects, including ways to work with
+//! them using futures, streams and sinks.
+//!
+//! This module is only available when the `std` feature of this
+//! library is activated, and it is activated by default.
+
+#[cfg(feature = "io-compat")]
+#[cfg_attr(docsrs, doc(cfg(feature = "io-compat")))]
+use crate::compat::Compat;
+use crate::future::assert_future;
+use crate::stream::assert_stream;
+use std::{pin::Pin, ptr};
+
+// Re-export some types from `std::io` so that users don't have to deal
+// with conflicts when `use`ing `futures::io` and `std::io`.
+#[doc(no_inline)]
+pub use std::io::{Error, ErrorKind, IoSlice, IoSliceMut, Result, SeekFrom};
+
+pub use futures_io::{AsyncBufRead, AsyncRead, AsyncSeek, AsyncWrite};
+
+// used by `BufReader` and `BufWriter`
+// https://github.com/rust-lang/rust/blob/master/src/libstd/sys_common/io.rs#L1
+const DEFAULT_BUF_SIZE: usize = 8 * 1024;
+
+/// Initializes a buffer if necessary.
+///
+/// A buffer is currently always initialized.
+#[inline]
+unsafe fn initialize<R: AsyncRead>(_reader: &R, buf: &mut [u8]) {
+    ptr::write_bytes(buf.as_mut_ptr(), 0, buf.len())
+}
+
+mod allow_std;
+pub use self::allow_std::AllowStdIo;
+
+mod buf_reader;
+pub use self::buf_reader::{BufReader, SeeKRelative};
+
+mod buf_writer;
+pub use self::buf_writer::BufWriter;
+
+mod line_writer;
+pub use self::line_writer::LineWriter;
+
+mod chain;
+pub use self::chain::Chain;
+
+mod close;
+pub use self::close::Close;
+
+mod copy;
+pub use self::copy::{copy, Copy};
+
+mod copy_buf;
+pub use self::copy_buf::{copy_buf, CopyBuf};
+
+mod copy_buf_abortable;
+pub use self::copy_buf_abortable::{copy_buf_abortable, CopyBufAbortable};
+
+mod cursor;
+pub use self::cursor::Cursor;
+
+mod empty;
+pub use self::empty::{empty, Empty};
+
+mod fill_buf;
+pub use self::fill_buf::FillBuf;
+
+mod flush;
+pub use self::flush::Flush;
+
+#[cfg(feature = "sink")]
+#[cfg_attr(docsrs, doc(cfg(feature = "sink")))]
+mod into_sink;
+#[cfg(feature = "sink")]
+#[cfg_attr(docsrs, doc(cfg(feature = "sink")))]
+pub use self::into_sink::IntoSink;
+
+mod lines;
+pub use self::lines::Lines;
+
+mod read;
+pub use self::read::Read;
+
+mod read_vectored;
+pub use self::read_vectored::ReadVectored;
+
+mod read_exact;
+pub use self::read_exact::ReadExact;
+
+mod read_line;
+pub use self::read_line::ReadLine;
+
+mod read_to_end;
+pub use self::read_to_end::ReadToEnd;
+
+mod read_to_string;
+pub use self::read_to_string::ReadToString;
+
+mod read_until;
+pub use self::read_until::ReadUntil;
+
+mod repeat;
+pub use self::repeat::{repeat, Repeat};
+
+mod seek;
+pub use self::seek::Seek;
+
+mod sink;
+pub use self::sink::{sink, Sink};
+
+mod split;
+pub use self::split::{ReadHalf, ReuniteError, WriteHalf};
+
+mod take;
+pub use self::take::Take;
+
+mod window;
+pub use self::window::Window;
+
+mod write;
+pub use self::write::Write;
+
+mod write_vectored;
+pub use self::write_vectored::WriteVectored;
+
+mod write_all;
+pub use self::write_all::WriteAll;
+
+#[cfg(feature = "write-all-vectored")]
+mod write_all_vectored;
+#[cfg(feature = "write-all-vectored")]
+pub use self::write_all_vectored::WriteAllVectored;
+
+/// An extension trait which adds utility methods to `AsyncRead` types.
+pub trait AsyncReadExt: AsyncRead {
+    /// Creates an adaptor which will chain this stream with another.
+    ///
+    /// The returned `AsyncRead` instance will first read all bytes from this object
+    /// until EOF is encountered. Afterwards the output is equivalent to the
+    /// output of `next`.
+    ///
+    /// # Examples
+    ///
+    /// ```
+    /// # futures::executor::block_on(async {
+    /// use futures::io::{AsyncReadExt, Cursor};
+    ///
+    /// let reader1 = Cursor::new([1, 2, 3, 4]);
+    /// let reader2 = Cursor::new([5, 6, 7, 8]);
+    ///
+    /// let mut reader = reader1.chain(reader2);
+    /// let mut buffer = Vec::new();
+    ///
+    /// // read the value into a Vec.
+    /// reader.read_to_end(&mut buffer).await?;
+    /// assert_eq!(buffer, [1, 2, 3, 4, 5, 6, 7, 8]);
+    /// # Ok::<(), Box<dyn std::error::Error>>(()) }).unwrap();
+    /// ```
+    fn chain<R>(self, next: R) -> Chain<Self, R>
+    where
+        Self: Sized,
+        R: AsyncRead,
+    {
+        assert_read(Chain::new(self, next))
+    }
+
+    /// Tries to read some bytes directly into the given `buf` in asynchronous
+    /// manner, returning a future type.
+    ///
+    /// The returned future will resolve to the number of bytes read once the read
+    /// operation is completed.
+    ///
+    /// # Examples
+    ///
+    /// ```
+    /// # futures::executor::block_on(async {
+    /// use futures::io::{AsyncReadExt, Cursor};
+    ///
+    /// let mut reader = Cursor::new([1, 2, 3, 4]);
+    /// let mut output = [0u8; 5];
+    ///
+    /// let bytes = reader.read(&mut output[..]).await?;
+    ///
+    /// // This is only guaranteed to be 4 because `&[u8]` is a synchronous
+    /// // reader. In a real system you could get anywhere from 1 to
+    /// // `output.len()` bytes in a single read.
+    /// assert_eq!(bytes, 4);
+    /// assert_eq!(output, [1, 2, 3, 4, 0]);
+    /// # Ok::<(), Box<dyn std::error::Error>>(()) }).unwrap();
+    /// ```
+    fn read<'a>(&'a mut self, buf: &'a mut [u8]) -> Read<'a, Self>
+    where
+        Self: Unpin,
+    {
+        assert_future::<Result<usize>, _>(Read::new(self, buf))
+    }
+
+    /// Creates a future which will read from the `AsyncRead` into `bufs` using vectored
+    /// IO operations.
+    ///
+    /// The returned future will resolve to the number of bytes read once the read
+    /// operation is completed.
+    fn read_vectored<'a>(&'a mut self, bufs: &'a mut [IoSliceMut<'a>]) -> ReadVectored<'a, Self>
+    where
+        Self: Unpin,
+    {
+        assert_future::<Result<usize>, _>(ReadVectored::new(self, bufs))
+    }
+
+    /// Creates a future which will read exactly enough bytes to fill `buf`,
+    /// returning an error if end of file (EOF) is hit sooner.
+    ///
+    /// The returned future will resolve once the read operation is completed.
+    ///
+    /// In the case of an error the buffer and the object will be discarded, with
+    /// the error yielded.
+    ///
+    /// # Examples
+    ///
+    /// ```
+    /// # futures::executor::block_on(async {
+    /// use futures::io::{AsyncReadExt, Cursor};
+    ///
+    /// let mut reader = Cursor::new([1, 2, 3, 4]);
+    /// let mut output = [0u8; 4];
+    ///
+    /// reader.read_exact(&mut output).await?;
+    ///
+    /// assert_eq!(output, [1, 2, 3, 4]);
+    /// # Ok::<(), Box<dyn std::error::Error>>(()) }).unwrap();
+    /// ```
+    ///
+    /// ## EOF is hit before `buf` is filled
+    ///
+    /// ```
+    /// # futures::executor::block_on(async {
+    /// use futures::io::{self, AsyncReadExt, Cursor};
+    ///
+    /// let mut reader = Cursor::new([1, 2, 3, 4]);
+    /// let mut output = [0u8; 5];
+    ///
+    /// let result = reader.read_exact(&mut output).await;
+    ///
+    /// assert_eq!(result.unwrap_err().kind(), io::ErrorKind::UnexpectedEof);
+    /// # });
+    /// ```
+    fn read_exact<'a>(&'a mut self, buf: &'a mut [u8]) -> ReadExact<'a, Self>
+    where
+        Self: Unpin,
+    {
+        assert_future::<Result<()>, _>(ReadExact::new(self, buf))
+    }
+
+    /// Creates a future which will read all the bytes from this `AsyncRead`.
+    ///
+    /// On success the total number of bytes read is returned.
+    ///
+    /// # Examples
+    ///
+    /// ```
+    /// # futures::executor::block_on(async {
+    /// use futures::io::{AsyncReadExt, Cursor};
+    ///
+    /// let mut reader = Cursor::new([1, 2, 3, 4]);
+    /// let mut output = Vec::with_capacity(4);
+    ///
+    /// let bytes = reader.read_to_end(&mut output).await?;
+    ///
+    /// assert_eq!(bytes, 4);
+    /// assert_eq!(output, vec![1, 2, 3, 4]);
+    /// # Ok::<(), Box<dyn std::error::Error>>(()) }).unwrap();
+    /// ```
+    fn read_to_end<'a>(&'a mut self, buf: &'a mut Vec<u8>) -> ReadToEnd<'a, Self>
+    where
+        Self: Unpin,
+    {
+        assert_future::<Result<usize>, _>(ReadToEnd::new(self, buf))
+    }
+
+    /// Creates a future which will read all the bytes from this `AsyncRead`.
+    ///
+    /// On success the total number of bytes read is returned.
+    ///
+    /// # Examples
+    ///
+    /// ```
+    /// # futures::executor::block_on(async {
+    /// use futures::io::{AsyncReadExt, Cursor};
+    ///
+    /// let mut reader = Cursor::new(&b"1234"[..]);
+    /// let mut buffer = String::with_capacity(4);
+    ///
+    /// let bytes = reader.read_to_string(&mut buffer).await?;
+    ///
+    /// assert_eq!(bytes, 4);
+    /// assert_eq!(buffer, String::from("1234"));
+    /// # Ok::<(), Box<dyn std::error::Error>>(()) }).unwrap();
+    /// ```
+    fn read_to_string<'a>(&'a mut self, buf: &'a mut String) -> ReadToString<'a, Self>
+    where
+        Self: Unpin,
+    {
+        assert_future::<Result<usize>, _>(ReadToString::new(self, buf))
+    }
+
+    /// Helper method for splitting this read/write object into two halves.
+    ///
+    /// The two halves returned implement the `AsyncRead` and `AsyncWrite`
+    /// traits, respectively.
+    ///
+    /// # Examples
+    ///
+    /// ```
+    /// # futures::executor::block_on(async {
+    /// use futures::io::{self, AsyncReadExt, Cursor};
+    ///
+    /// // Note that for `Cursor` the read and write halves share a single
+    /// // seek position. This may or may not be true for other types that
+    /// // implement both `AsyncRead` and `AsyncWrite`.
+    ///
+    /// let reader = Cursor::new([1, 2, 3, 4]);
+    /// let mut buffer = Cursor::new(vec![0, 0, 0, 0, 5, 6, 7, 8]);
+    /// let mut writer = Cursor::new(vec![0u8; 5]);
+    ///
+    /// {
+    ///     let (buffer_reader, mut buffer_writer) = (&mut buffer).split();
+    ///     io::copy(reader, &mut buffer_writer).await?;
+    ///     io::copy(buffer_reader, &mut writer).await?;
+    /// }
+    ///
+    /// assert_eq!(buffer.into_inner(), [1, 2, 3, 4, 5, 6, 7, 8]);
+    /// assert_eq!(writer.into_inner(), [5, 6, 7, 8, 0]);
+    /// # Ok::<(), Box<dyn std::error::Error>>(()) }).unwrap();
+    /// ```
+    fn split(self) -> (ReadHalf<Self>, WriteHalf<Self>)
+    where
+        Self: AsyncWrite + Sized,
+    {
+        let (r, w) = split::split(self);
+        (assert_read(r), assert_write(w))
+    }
+
+    /// Creates an AsyncRead adapter which will read at most `limit` bytes
+    /// from the underlying reader.
+    ///
+    /// # Examples
+    ///
+    /// ```
+    /// # futures::executor::block_on(async {
+    /// use futures::io::{AsyncReadExt, Cursor};
+    ///
+    /// let reader = Cursor::new(&b"12345678"[..]);
+    /// let mut buffer = [0; 5];
+    ///
+    /// let mut take = reader.take(4);
+    /// let n = take.read(&mut buffer).await?;
+    ///
+    /// assert_eq!(n, 4);
+    /// assert_eq!(&buffer, b"1234\0");
+    /// # Ok::<(), Box<dyn std::error::Error>>(()) }).unwrap();
+    /// ```
+    fn take(self, limit: u64) -> Take<Self>
+    where
+        Self: Sized,
+    {
+        assert_read(Take::new(self, limit))
+    }
+
+    /// Wraps an [`AsyncRead`] in a compatibility wrapper that allows it to be
+    /// used as a futures 0.1 / tokio-io 0.1 `AsyncRead`. If the wrapped type
+    /// implements [`AsyncWrite`] as well, the result will also implement the
+    /// futures 0.1 / tokio 0.1 `AsyncWrite` trait.
+    ///
+    /// Requires the `io-compat` feature to enable.
+    #[cfg(feature = "io-compat")]
+    #[cfg_attr(docsrs, doc(cfg(feature = "io-compat")))]
+    fn compat(self) -> Compat<Self>
+    where
+        Self: Sized + Unpin,
+    {
+        Compat::new(self)
+    }
+}
+
+impl<R: AsyncRead + ?Sized> AsyncReadExt for R {}
+
+/// An extension trait which adds utility methods to `AsyncWrite` types.
+pub trait AsyncWriteExt: AsyncWrite {
+    /// Creates a future which will entirely flush this `AsyncWrite`.
+    ///
+    /// # Examples
+    ///
+    /// ```
+    /// # futures::executor::block_on(async {
+    /// use futures::io::{AllowStdIo, AsyncWriteExt};
+    /// use std::io::{BufWriter, Cursor};
+    ///
+    /// let mut output = vec![0u8; 5];
+    ///
+    /// {
+    ///     let writer = Cursor::new(&mut output);
+    ///     let mut buffered = AllowStdIo::new(BufWriter::new(writer));
+    ///     buffered.write_all(&[1, 2]).await?;
+    ///     buffered.write_all(&[3, 4]).await?;
+    ///     buffered.flush().await?;
+    /// }
+    ///
+    /// assert_eq!(output, [1, 2, 3, 4, 0]);
+    /// # Ok::<(), Box<dyn std::error::Error>>(()) }).unwrap();
+    /// ```
+    fn flush(&mut self) -> Flush<'_, Self>
+    where
+        Self: Unpin,
+    {
+        assert_future::<Result<()>, _>(Flush::new(self))
+    }
+
+    /// Creates a future which will entirely close this `AsyncWrite`.
+    fn close(&mut self) -> Close<'_, Self>
+    where
+        Self: Unpin,
+    {
+        assert_future::<Result<()>, _>(Close::new(self))
+    }
+
+    /// Creates a future which will write bytes from `buf` into the object.
+    ///
+    /// The returned future will resolve to the number of bytes written once the write
+    /// operation is completed.
+    fn write<'a>(&'a mut self, buf: &'a [u8]) -> Write<'a, Self>
+    where
+        Self: Unpin,
+    {
+        assert_future::<Result<usize>, _>(Write::new(self, buf))
+    }
+
+    /// Creates a future which will write bytes from `bufs` into the object using vectored
+    /// IO operations.
+    ///
+    /// The returned future will resolve to the number of bytes written once the write
+    /// operation is completed.
+    fn write_vectored<'a>(&'a mut self, bufs: &'a [IoSlice<'a>]) -> WriteVectored<'a, Self>
+    where
+        Self: Unpin,
+    {
+        assert_future::<Result<usize>, _>(WriteVectored::new(self, bufs))
+    }
+
+    /// Write data into this object.
+    ///
+    /// Creates a future that will write the entire contents of the buffer `buf` into
+    /// this `AsyncWrite`.
+    ///
+    /// The returned future will not complete until all the data has been written.
+    ///
+    /// # Examples
+    ///
+    /// ```
+    /// # futures::executor::block_on(async {
+    /// use futures::io::{AsyncWriteExt, Cursor};
+    ///
+    /// let mut writer = Cursor::new(vec![0u8; 5]);
+    ///
+    /// writer.write_all(&[1, 2, 3, 4]).await?;
+    ///
+    /// assert_eq!(writer.into_inner(), [1, 2, 3, 4, 0]);
+    /// # Ok::<(), Box<dyn std::error::Error>>(()) }).unwrap();
+    /// ```
+    fn write_all<'a>(&'a mut self, buf: &'a [u8]) -> WriteAll<'a, Self>
+    where
+        Self: Unpin,
+    {
+        assert_future::<Result<()>, _>(WriteAll::new(self, buf))
+    }
+
+    /// Attempts to write multiple buffers into this writer.
+    ///
+    /// Creates a future that will write the entire contents of `bufs` into this
+    /// `AsyncWrite` using [vectored writes].
+    ///
+    /// The returned future will not complete until all the data has been
+    /// written.
+    ///
+    /// [vectored writes]: std::io::Write::write_vectored
+    ///
+    /// # Notes
+    ///
+    /// Unlike `io::Write::write_vectored`, this takes a *mutable* reference to
+    /// a slice of `IoSlice`s, not an immutable one. That's because we need to
+    /// modify the slice to keep track of the bytes already written.
+    ///
+    /// Once this futures returns, the contents of `bufs` are unspecified, as
+    /// this depends on how many calls to `write_vectored` were necessary. It is
+    /// best to understand this function as taking ownership of `bufs` and to
+    /// not use `bufs` afterwards. The underlying buffers, to which the
+    /// `IoSlice`s point (but not the `IoSlice`s themselves), are unchanged and
+    /// can be reused.
+    ///
+    /// # Examples
+    ///
+    /// ```
+    /// # futures::executor::block_on(async {
+    /// use futures::io::AsyncWriteExt;
+    /// use futures_util::io::Cursor;
+    /// use std::io::IoSlice;
+    ///
+    /// let mut writer = Cursor::new(Vec::new());
+    /// let bufs = &mut [
+    ///     IoSlice::new(&[1]),
+    ///     IoSlice::new(&[2, 3]),
+    ///     IoSlice::new(&[4, 5, 6]),
+    /// ];
+    ///
+    /// writer.write_all_vectored(bufs).await?;
+    /// // Note: the contents of `bufs` is now unspecified, see the Notes section.
+    ///
+    /// assert_eq!(writer.into_inner(), &[1, 2, 3, 4, 5, 6]);
+    /// # Ok::<(), Box<dyn std::error::Error>>(()) }).unwrap();
+    /// ```
+    #[cfg(feature = "write-all-vectored")]
+    fn write_all_vectored<'a>(
+        &'a mut self,
+        bufs: &'a mut [IoSlice<'a>],
+    ) -> WriteAllVectored<'a, Self>
+    where
+        Self: Unpin,
+    {
+        assert_future::<Result<()>, _>(WriteAllVectored::new(self, bufs))
+    }
+
+    /// Wraps an [`AsyncWrite`] in a compatibility wrapper that allows it to be
+    /// used as a futures 0.1 / tokio-io 0.1 `AsyncWrite`.
+    /// Requires the `io-compat` feature to enable.
+    #[cfg(feature = "io-compat")]
+    #[cfg_attr(docsrs, doc(cfg(feature = "io-compat")))]
+    fn compat_write(self) -> Compat<Self>
+    where
+        Self: Sized + Unpin,
+    {
+        Compat::new(self)
+    }
+
+    /// Allow using an [`AsyncWrite`] as a [`Sink`](futures_sink::Sink)`<Item: AsRef<[u8]>>`.
+    ///
+    /// This adapter produces a sink that will write each value passed to it
+    /// into the underlying writer.
+    ///
+    /// Note that this function consumes the given writer, returning a wrapped
+    /// version.
+    ///
+    /// # Examples
+    ///
+    /// ```
+    /// # futures::executor::block_on(async {
+    /// use futures::io::AsyncWriteExt;
+    /// use futures::stream::{self, StreamExt};
+    ///
+    /// let stream = stream::iter(vec![Ok([1, 2, 3]), Ok([4, 5, 6])]);
+    ///
+    /// let mut writer = vec![];
+    ///
+    /// stream.forward((&mut writer).into_sink()).await?;
+    ///
+    /// assert_eq!(writer, vec![1, 2, 3, 4, 5, 6]);
+    /// # Ok::<(), Box<dyn std::error::Error>>(())
+    /// # })?;
+    /// # Ok::<(), Box<dyn std::error::Error>>(())
+    /// ```
+    #[cfg(feature = "sink")]
+    #[cfg_attr(docsrs, doc(cfg(feature = "sink")))]
+    fn into_sink<Item: AsRef<[u8]>>(self) -> IntoSink<Self, Item>
+    where
+        Self: Sized,
+    {
+        crate::sink::assert_sink::<Item, Error, _>(IntoSink::new(self))
+    }
+}
+
+impl<W: AsyncWrite + ?Sized> AsyncWriteExt for W {}
+
+/// An extension trait which adds utility methods to `AsyncSeek` types.
+pub trait AsyncSeekExt: AsyncSeek {
+    /// Creates a future which will seek an IO object, and then yield the
+    /// new position in the object and the object itself.
+    ///
+    /// In the case of an error the buffer and the object will be discarded, with
+    /// the error yielded.
+    fn seek(&mut self, pos: SeekFrom) -> Seek<'_, Self>
+    where
+        Self: Unpin,
+    {
+        assert_future::<Result<u64>, _>(Seek::new(self, pos))
+    }
+
+    /// Creates a future which will return the current seek position from the
+    /// start of the stream.
+    ///
+    /// This is equivalent to `self.seek(SeekFrom::Current(0))`.
+    fn stream_position(&mut self) -> Seek<'_, Self>
+    where
+        Self: Unpin,
+    {
+        self.seek(SeekFrom::Current(0))
+    }
+}
+
+impl<S: AsyncSeek + ?Sized> AsyncSeekExt for S {}
+
+/// An extension trait which adds utility methods to `AsyncBufRead` types.
+pub trait AsyncBufReadExt: AsyncBufRead {
+    /// Creates a future which will wait for a non-empty buffer to be available from this I/O
+    /// object or EOF to be reached.
+    ///
+    /// This method is the async equivalent to [`BufRead::fill_buf`](std::io::BufRead::fill_buf).
+    ///
+    /// ```rust
+    /// # futures::executor::block_on(async {
+    /// use futures::{io::AsyncBufReadExt as _, stream::{iter, TryStreamExt as _}};
+    ///
+    /// let mut stream = iter(vec![Ok(vec![1, 2, 3]), Ok(vec![4, 5, 6])]).into_async_read();
+    ///
+    /// assert_eq!(stream.fill_buf().await?, vec![1, 2, 3]);
+    /// stream.consume_unpin(2);
+    ///
+    /// assert_eq!(stream.fill_buf().await?, vec![3]);
+    /// stream.consume_unpin(1);
+    ///
+    /// assert_eq!(stream.fill_buf().await?, vec![4, 5, 6]);
+    /// stream.consume_unpin(3);
+    ///
+    /// assert_eq!(stream.fill_buf().await?, vec![]);
+    /// # Ok::<(), Box<dyn std::error::Error>>(()) }).unwrap();
+    /// ```
+    fn fill_buf(&mut self) -> FillBuf<'_, Self>
+    where
+        Self: Unpin,
+    {
+        assert_future::<Result<&[u8]>, _>(FillBuf::new(self))
+    }
+
+    /// A convenience for calling [`AsyncBufRead::consume`] on [`Unpin`] IO types.
+    ///
+    /// ```rust
+    /// # futures::executor::block_on(async {
+    /// use futures::{io::AsyncBufReadExt as _, stream::{iter, TryStreamExt as _}};
+    ///
+    /// let mut stream = iter(vec![Ok(vec![1, 2, 3])]).into_async_read();
+    ///
+    /// assert_eq!(stream.fill_buf().await?, vec![1, 2, 3]);
+    /// stream.consume_unpin(2);
+    ///
+    /// assert_eq!(stream.fill_buf().await?, vec![3]);
+    /// stream.consume_unpin(1);
+    ///
+    /// assert_eq!(stream.fill_buf().await?, vec![]);
+    /// # Ok::<(), Box<dyn std::error::Error>>(()) }).unwrap();
+    /// ```
+    fn consume_unpin(&mut self, amt: usize)
+    where
+        Self: Unpin,
+    {
+        Pin::new(self).consume(amt)
+    }
+
+    /// Creates a future which will read all the bytes associated with this I/O
+    /// object into `buf` until the delimiter `byte` or EOF is reached.
+    /// This method is the async equivalent to [`BufRead::read_until`](std::io::BufRead::read_until).
+    ///
+    /// This function will read bytes from the underlying stream until the
+    /// delimiter or EOF is found. Once found, all bytes up to, and including,
+    /// the delimiter (if found) will be appended to `buf`.
+    ///
+    /// The returned future will resolve to the number of bytes read once the read
+    /// operation is completed.
+    ///
+    /// In the case of an error the buffer and the object will be discarded, with
+    /// the error yielded.
+    ///
+    /// # Examples
+    ///
+    /// ```
+    /// # futures::executor::block_on(async {
+    /// use futures::io::{AsyncBufReadExt, Cursor};
+    ///
+    /// let mut cursor = Cursor::new(b"lorem-ipsum");
+    /// let mut buf = vec![];
+    ///
+    /// // cursor is at 'l'
+    /// let num_bytes = cursor.read_until(b'-', &mut buf).await?;
+    /// assert_eq!(num_bytes, 6);
+    /// assert_eq!(buf, b"lorem-");
+    /// buf.clear();
+    ///
+    /// // cursor is at 'i'
+    /// let num_bytes = cursor.read_until(b'-', &mut buf).await?;
+    /// assert_eq!(num_bytes, 5);
+    /// assert_eq!(buf, b"ipsum");
+    /// buf.clear();
+    ///
+    /// // cursor is at EOF
+    /// let num_bytes = cursor.read_until(b'-', &mut buf).await?;
+    /// assert_eq!(num_bytes, 0);
+    /// assert_eq!(buf, b"");
+    /// # Ok::<(), Box<dyn std::error::Error>>(()) }).unwrap();
+    /// ```
+    fn read_until<'a>(&'a mut self, byte: u8, buf: &'a mut Vec<u8>) -> ReadUntil<'a, Self>
+    where
+        Self: Unpin,
+    {
+        assert_future::<Result<usize>, _>(ReadUntil::new(self, byte, buf))
+    }
+
+    /// Creates a future which will read all the bytes associated with this I/O
+    /// object into `buf` until a newline (the 0xA byte) or EOF is reached,
+    /// This method is the async equivalent to [`BufRead::read_line`](std::io::BufRead::read_line).
+    ///
+    /// This function will read bytes from the underlying stream until the
+    /// newline delimiter (the 0xA byte) or EOF is found. Once found, all bytes
+    /// up to, and including, the delimiter (if found) will be appended to
+    /// `buf`.
+    ///
+    /// The returned future will resolve to the number of bytes read once the read
+    /// operation is completed.
+    ///
+    /// In the case of an error the buffer and the object will be discarded, with
+    /// the error yielded.
+    ///
+    /// # Errors
+    ///
+    /// This function has the same error semantics as [`read_until`] and will
+    /// also return an error if the read bytes are not valid UTF-8. If an I/O
+    /// error is encountered then `buf` may contain some bytes already read in
+    /// the event that all data read so far was valid UTF-8.
+    ///
+    /// [`read_until`]: AsyncBufReadExt::read_until
+    ///
+    /// # Examples
+    ///
+    /// ```
+    /// # futures::executor::block_on(async {
+    /// use futures::io::{AsyncBufReadExt, Cursor};
+    ///
+    /// let mut cursor = Cursor::new(b"foo\nbar");
+    /// let mut buf = String::new();
+    ///
+    /// // cursor is at 'f'
+    /// let num_bytes = cursor.read_line(&mut buf).await?;
+    /// assert_eq!(num_bytes, 4);
+    /// assert_eq!(buf, "foo\n");
+    /// buf.clear();
+    ///
+    /// // cursor is at 'b'
+    /// let num_bytes = cursor.read_line(&mut buf).await?;
+    /// assert_eq!(num_bytes, 3);
+    /// assert_eq!(buf, "bar");
+    /// buf.clear();
+    ///
+    /// // cursor is at EOF
+    /// let num_bytes = cursor.read_line(&mut buf).await?;
+    /// assert_eq!(num_bytes, 0);
+    /// assert_eq!(buf, "");
+    /// # Ok::<(), Box<dyn std::error::Error>>(()) }).unwrap();
+    /// ```
+    fn read_line<'a>(&'a mut self, buf: &'a mut String) -> ReadLine<'a, Self>
+    where
+        Self: Unpin,
+    {
+        assert_future::<Result<usize>, _>(ReadLine::new(self, buf))
+    }
+
+    /// Returns a stream over the lines of this reader.
+    /// This method is the async equivalent to [`BufRead::lines`](std::io::BufRead::lines).
+    ///
+    /// The stream returned from this function will yield instances of
+    /// [`io::Result`]`<`[`String`]`>`. Each string returned will *not* have a newline
+    /// byte (the 0xA byte) or CRLF (0xD, 0xA bytes) at the end.
+    ///
+    /// [`io::Result`]: std::io::Result
+    /// [`String`]: String
+    ///
+    /// # Errors
+    ///
+    /// Each line of the stream has the same error semantics as [`AsyncBufReadExt::read_line`].
+    ///
+    /// [`AsyncBufReadExt::read_line`]: AsyncBufReadExt::read_line
+    ///
+    /// # Examples
+    ///
+    /// ```
+    /// # futures::executor::block_on(async {
+    /// use futures::io::{AsyncBufReadExt, Cursor};
+    /// use futures::stream::StreamExt;
+    ///
+    /// let cursor = Cursor::new(b"lorem\nipsum\r\ndolor");
+    ///
+    /// let mut lines_stream = cursor.lines().map(|l| l.unwrap());
+    /// assert_eq!(lines_stream.next().await, Some(String::from("lorem")));
+    /// assert_eq!(lines_stream.next().await, Some(String::from("ipsum")));
+    /// assert_eq!(lines_stream.next().await, Some(String::from("dolor")));
+    /// assert_eq!(lines_stream.next().await, None);
+    /// # Ok::<(), Box<dyn std::error::Error>>(()) }).unwrap();
+    /// ```
+    fn lines(self) -> Lines<Self>
+    where
+        Self: Sized,
+    {
+        assert_stream::<Result<String>, _>(Lines::new(self))
+    }
+}
+
+impl<R: AsyncBufRead + ?Sized> AsyncBufReadExt for R {}
+
+// Just a helper function to ensure the reader we're returning all have the
+// right implementations.
+pub(crate) fn assert_read<R>(reader: R) -> R
+where
+    R: AsyncRead,
+{
+    reader
+}
+// Just a helper function to ensure the writer we're returning all have the
+// right implementations.
+pub(crate) fn assert_write<W>(writer: W) -> W
+where
+    W: AsyncWrite,
+{
+    writer
+}
diff --git a/third_party/rust/futures-util/src/io/read.rs b/third_party/rust/futures-util/src/io/read.rs
new file mode 100644
index 0000000000..677ba818d9
--- /dev/null
+++ b/third_party/rust/futures-util/src/io/read.rs
@@ -0,0 +1,30 @@
+use crate::io::AsyncRead;
+use futures_core::future::Future;
+use futures_core::task::{Context, Poll};
+use std::io;
+use std::pin::Pin;
+
+/// Future for the [`read`](super::AsyncReadExt::read) method.
+#[derive(Debug)]
+#[must_use = "futures do nothing unless you `.await` or poll them"]
+pub struct Read<'a, R: ?Sized> {
+    reader: &'a mut R,
+    buf: &'a mut [u8],
+}
+
+impl<R: ?Sized + Unpin> Unpin for Read<'_, R> {}
+
+impl<'a, R: AsyncRead + ?Sized + Unpin> Read<'a, R> {
+    pub(super) fn new(reader: &'a mut R, buf: &'a mut [u8]) -> Self {
+        Self { reader, buf }
+    }
+}
+
+impl<R: AsyncRead + ?Sized + Unpin> Future for Read<'_, R> {
+    type Output = io::Result<usize>;
+
+    fn poll(mut self: Pin<&mut Self>, cx: &mut Context<'_>) -> Poll<Self::Output> {
+        let this = &mut *self;
+        Pin::new(&mut this.reader).poll_read(cx, this.buf)
+    }
+}
diff --git a/third_party/rust/futures-util/src/io/read_exact.rs b/third_party/rust/futures-util/src/io/read_exact.rs
new file mode 100644
index 0000000000..cd0b20e597
--- /dev/null
+++ b/third_party/rust/futures-util/src/io/read_exact.rs
@@ -0,0 +1,42 @@
+use crate::io::AsyncRead;
+use futures_core::future::Future;
+use futures_core::ready;
+use futures_core::task::{Context, Poll};
+use std::io;
+use std::mem;
+use std::pin::Pin;
+
+/// Future for the [`read_exact`](super::AsyncReadExt::read_exact) method.
+#[derive(Debug)]
+#[must_use = "futures do nothing unless you `.await` or poll them"]
+pub struct ReadExact<'a, R: ?Sized> {
+    reader: &'a mut R,
+    buf: &'a mut [u8],
+}
+
+impl<R: ?Sized + Unpin> Unpin for ReadExact<'_, R> {}
+
+impl<'a, R: AsyncRead + ?Sized + Unpin> ReadExact<'a, R> {
+    pub(super) fn new(reader: &'a mut R, buf: &'a mut [u8]) -> Self {
+        Self { reader, buf }
+    }
+}
+
+impl<R: AsyncRead + ?Sized + Unpin> Future for ReadExact<'_, R> {
+    type Output = io::Result<()>;
+
+    fn poll(mut self: Pin<&mut Self>, cx: &mut Context<'_>) -> Poll<Self::Output> {
+        let this = &mut *self;
+        while !this.buf.is_empty() {
+            let n = ready!(Pin::new(&mut this.reader).poll_read(cx, this.buf))?;
+            {
+                let (_, rest) = mem::take(&mut this.buf).split_at_mut(n);
+                this.buf = rest;
+            }
+            if n == 0 {
+                return Poll::Ready(Err(io::ErrorKind::UnexpectedEof.into()));
+            }
+        }
+        Poll::Ready(Ok(()))
+    }
+}
diff --git a/third_party/rust/futures-util/src/io/read_line.rs b/third_party/rust/futures-util/src/io/read_line.rs
new file mode 100644
index 0000000000..e1b8fc9455
--- /dev/null
+++ b/third_party/rust/futures-util/src/io/read_line.rs
@@ -0,0 +1,57 @@
+use super::read_until::read_until_internal;
+use futures_core::future::Future;
+use futures_core::ready;
+use futures_core::task::{Context, Poll};
+use futures_io::AsyncBufRead;
+use std::io;
+use std::mem;
+use std::pin::Pin;
+use std::str;
+
+/// Future for the [`read_line`](super::AsyncBufReadExt::read_line) method.
+#[derive(Debug)]
+#[must_use = "futures do nothing unless you `.await` or poll them"]
+pub struct ReadLine<'a, R: ?Sized> {
+    reader: &'a mut R,
+    buf: &'a mut String,
+    bytes: Vec<u8>,
+    read: usize,
+}
+
+impl<R: ?Sized + Unpin> Unpin for ReadLine<'_, R> {}
+
+impl<'a, R: AsyncBufRead + ?Sized + Unpin> ReadLine<'a, R> {
+    pub(super) fn new(reader: &'a mut R, buf: &'a mut String) -> Self {
+        Self { reader, bytes: mem::take(buf).into_bytes(), buf, read: 0 }
+    }
+}
+
+pub(super) fn read_line_internal<R: AsyncBufRead + ?Sized>(
+    reader: Pin<&mut R>,
+    cx: &mut Context<'_>,
+    buf: &mut String,
+    bytes: &mut Vec<u8>,
+    read: &mut usize,
+) -> Poll<io::Result<usize>> {
+    let ret = ready!(read_until_internal(reader, cx, b'\n', bytes, read));
+    if str::from_utf8(bytes).is_err() {
+        Poll::Ready(ret.and_then(|_| {
+            Err(io::Error::new(io::ErrorKind::InvalidData, "stream did not contain valid UTF-8"))
+        }))
+    } else {
+        debug_assert!(buf.is_empty());
+        debug_assert_eq!(*read, 0);
+        // Safety: `bytes` is a valid UTF-8 because `str::from_utf8` returned `Ok`.
+        mem::swap(unsafe { buf.as_mut_vec() }, bytes);
+        Poll::Ready(ret)
+    }
+}
+
+impl<R: AsyncBufRead + ?Sized + Unpin> Future for ReadLine<'_, R> {
+    type Output = io::Result<usize>;
+
+    fn poll(mut self: Pin<&mut Self>, cx: &mut Context<'_>) -> Poll<Self::Output> {
+        let Self { reader, buf, bytes, read } = &mut *self;
+        read_line_internal(Pin::new(reader), cx, buf, bytes, read)
+    }
+}
diff --git a/third_party/rust/futures-util/src/io/read_to_end.rs b/third_party/rust/futures-util/src/io/read_to_end.rs
new file mode 100644
index 0000000000..919d7d13c7
--- /dev/null
+++ b/third_party/rust/futures-util/src/io/read_to_end.rs
@@ -0,0 +1,91 @@
+use futures_core::future::Future;
+use futures_core::ready;
+use futures_core::task::{Context, Poll};
+use futures_io::AsyncRead;
+use std::io;
+use std::pin::Pin;
+use std::vec::Vec;
+
+/// Future for the [`read_to_end`](super::AsyncReadExt::read_to_end) method.
+#[derive(Debug)]
+#[must_use = "futures do nothing unless you `.await` or poll them"]
+pub struct ReadToEnd<'a, R: ?Sized> {
+    reader: &'a mut R,
+    buf: &'a mut Vec<u8>,
+    start_len: usize,
+}
+
+impl<R: ?Sized + Unpin> Unpin for ReadToEnd<'_, R> {}
+
+impl<'a, R: AsyncRead + ?Sized + Unpin> ReadToEnd<'a, R> {
+    pub(super) fn new(reader: &'a mut R, buf: &'a mut Vec<u8>) -> Self {
+        let start_len = buf.len();
+        Self { reader, buf, start_len }
+    }
+}
+
+struct Guard<'a> {
+    buf: &'a mut Vec<u8>,
+    len: usize,
+}
+
+impl Drop for Guard<'_> {
+    fn drop(&mut self) {
+        unsafe {
+            self.buf.set_len(self.len);
+        }
+    }
+}
+
+// This uses an adaptive system to extend the vector when it fills. We want to
+// avoid paying to allocate and zero a huge chunk of memory if the reader only
+// has 4 bytes while still making large reads if the reader does have a ton
+// of data to return. Simply tacking on an extra DEFAULT_BUF_SIZE space every
+// time is 4,500 times (!) slower than this if the reader has a very small
+// amount of data to return.
+//
+// Because we're extending the buffer with uninitialized data for trusted
+// readers, we need to make sure to truncate that if any of this panics.
+pub(super) fn read_to_end_internal<R: AsyncRead + ?Sized>(
+    mut rd: Pin<&mut R>,
+    cx: &mut Context<'_>,
+    buf: &mut Vec<u8>,
+    start_len: usize,
+) -> Poll<io::Result<usize>> {
+    let mut g = Guard { len: buf.len(), buf };
+    loop {
+        if g.len == g.buf.len() {
+            unsafe {
+                g.buf.reserve(32);
+                let capacity = g.buf.capacity();
+                g.buf.set_len(capacity);
+                super::initialize(&rd, &mut g.buf[g.len..]);
+            }
+        }
+
+        let buf = &mut g.buf[g.len..];
+        match ready!(rd.as_mut().poll_read(cx, buf)) {
+            Ok(0) => return Poll::Ready(Ok(g.len - start_len)),
+            Ok(n) => {
+                // We can't allow bogus values from read. If it is too large, the returned vec could have its length
+                // set past its capacity, or if it overflows the vec could be shortened which could create an invalid
+                // string if this is called via read_to_string.
+                assert!(n <= buf.len());
+                g.len += n;
+            }
+            Err(e) => return Poll::Ready(Err(e)),
+        }
+    }
+}
+
+impl<A> Future for ReadToEnd<'_, A>
+where
+    A: AsyncRead + ?Sized + Unpin,
+{
+    type Output = io::Result<usize>;
+
+    fn poll(mut self: Pin<&mut Self>, cx: &mut Context<'_>) -> Poll<Self::Output> {
+        let this = &mut *self;
+        read_to_end_internal(Pin::new(&mut this.reader), cx, this.buf, this.start_len)
+    }
+}
diff --git a/third_party/rust/futures-util/src/io/read_to_string.rs b/third_party/rust/futures-util/src/io/read_to_string.rs
new file mode 100644
index 0000000000..c175396d81
--- /dev/null
+++ b/third_party/rust/futures-util/src/io/read_to_string.rs
@@ -0,0 +1,59 @@
+use super::read_to_end::read_to_end_internal;
+use futures_core::future::Future;
+use futures_core::ready;
+use futures_core::task::{Context, Poll};
+use futures_io::AsyncRead;
+use std::pin::Pin;
+use std::vec::Vec;
+use std::{io, mem, str};
+
+/// Future for the [`read_to_string`](super::AsyncReadExt::read_to_string) method.
+#[derive(Debug)]
+#[must_use = "futures do nothing unless you `.await` or poll them"]
+pub struct ReadToString<'a, R: ?Sized> {
+    reader: &'a mut R,
+    buf: &'a mut String,
+    bytes: Vec<u8>,
+    start_len: usize,
+}
+
+impl<R: ?Sized + Unpin> Unpin for ReadToString<'_, R> {}
+
+impl<'a, R: AsyncRead + ?Sized + Unpin> ReadToString<'a, R> {
+    pub(super) fn new(reader: &'a mut R, buf: &'a mut String) -> Self {
+        let start_len = buf.len();
+        Self { reader, bytes: mem::take(buf).into_bytes(), buf, start_len }
+    }
+}
+
+fn read_to_string_internal<R: AsyncRead + ?Sized>(
+    reader: Pin<&mut R>,
+    cx: &mut Context<'_>,
+    buf: &mut String,
+    bytes: &mut Vec<u8>,
+    start_len: usize,
+) -> Poll<io::Result<usize>> {
+    let ret = ready!(read_to_end_internal(reader, cx, bytes, start_len));
+    if str::from_utf8(bytes).is_err() {
+        Poll::Ready(ret.and_then(|_| {
+            Err(io::Error::new(io::ErrorKind::InvalidData, "stream did not contain valid UTF-8"))
+        }))
+    } else {
+        debug_assert!(buf.is_empty());
+        // Safety: `bytes` is a valid UTF-8 because `str::from_utf8` returned `Ok`.
+        mem::swap(unsafe { buf.as_mut_vec() }, bytes);
+        Poll::Ready(ret)
+    }
+}
+
+impl<A> Future for ReadToString<'_, A>
+where
+    A: AsyncRead + ?Sized + Unpin,
+{
+    type Output = io::Result<usize>;
+
+    fn poll(mut self: Pin<&mut Self>, cx: &mut Context<'_>) -> Poll<Self::Output> {
+        let Self { reader, buf, bytes, start_len } = &mut *self;
+        read_to_string_internal(Pin::new(reader), cx, buf, bytes, *start_len)
+    }
+}
diff --git a/third_party/rust/futures-util/src/io/read_until.rs b/third_party/rust/futures-util/src/io/read_until.rs
new file mode 100644
index 0000000000..72b59eab13
--- /dev/null
+++ b/third_party/rust/futures-util/src/io/read_until.rs
@@ -0,0 +1,60 @@
+use futures_core::future::Future;
+use futures_core::ready;
+use futures_core::task::{Context, Poll};
+use futures_io::AsyncBufRead;
+use std::io;
+use std::mem;
+use std::pin::Pin;
+
+/// Future for the [`read_until`](super::AsyncBufReadExt::read_until) method.
+#[derive(Debug)]
+#[must_use = "futures do nothing unless you `.await` or poll them"]
+pub struct ReadUntil<'a, R: ?Sized> {
+    reader: &'a mut R,
+    byte: u8,
+    buf: &'a mut Vec<u8>,
+    read: usize,
+}
+
+impl<R: ?Sized + Unpin> Unpin for ReadUntil<'_, R> {}
+
+impl<'a, R: AsyncBufRead + ?Sized + Unpin> ReadUntil<'a, R> {
+    pub(super) fn new(reader: &'a mut R, byte: u8, buf: &'a mut Vec<u8>) -> Self {
+        Self { reader, byte, buf, read: 0 }
+    }
+}
+
+pub(super) fn read_until_internal<R: AsyncBufRead + ?Sized>(
+    mut reader: Pin<&mut R>,
+    cx: &mut Context<'_>,
+    byte: u8,
+    buf: &mut Vec<u8>,
+    read: &mut usize,
+) -> Poll<io::Result<usize>> {
+    loop {
+        let (done, used) = {
+            let available = ready!(reader.as_mut().poll_fill_buf(cx))?;
+            if let Some(i) = memchr::memchr(byte, available) {
+                buf.extend_from_slice(&available[..=i]);
+                (true, i + 1)
+            } else {
+                buf.extend_from_slice(available);
+                (false, available.len())
+            }
+        };
+        reader.as_mut().consume(used);
+        *read += used;
+        if done || used == 0 {
+            return Poll::Ready(Ok(mem::replace(read, 0)));
+        }
+    }
+}
+
+impl<R: AsyncBufRead + ?Sized + Unpin> Future for ReadUntil<'_, R> {
+    type Output = io::Result<usize>;
+
+    fn poll(mut self: Pin<&mut Self>, cx: &mut Context<'_>) -> Poll<Self::Output> {
+        let Self { reader, byte, buf, read } = &mut *self;
+        read_until_internal(Pin::new(reader), cx, *byte, buf, read)
+    }
+}
diff --git a/third_party/rust/futures-util/src/io/read_vectored.rs b/third_party/rust/futures-util/src/io/read_vectored.rs
new file mode 100644
index 0000000000..4e22df57e9
--- /dev/null
+++ b/third_party/rust/futures-util/src/io/read_vectored.rs
@@ -0,0 +1,30 @@
+use crate::io::AsyncRead;
+use futures_core::future::Future;
+use futures_core::task::{Context, Poll};
+use std::io::{self, IoSliceMut};
+use std::pin::Pin;
+
+/// Future for the [`read_vectored`](super::AsyncReadExt::read_vectored) method.
+#[derive(Debug)]
+#[must_use = "futures do nothing unless you `.await` or poll them"]
+pub struct ReadVectored<'a, R: ?Sized> {
+    reader: &'a mut R,
+    bufs: &'a mut [IoSliceMut<'a>],
+}
+
+impl<R: ?Sized + Unpin> Unpin for ReadVectored<'_, R> {}
+
+impl<'a, R: AsyncRead + ?Sized + Unpin> ReadVectored<'a, R> {
+    pub(super) fn new(reader: &'a mut R, bufs: &'a mut [IoSliceMut<'a>]) -> Self {
+        Self { reader, bufs }
+    }
+}
+
+impl<R: AsyncRead + ?Sized + Unpin> Future for ReadVectored<'_, R> {
+    type Output = io::Result<usize>;
+
+    fn poll(mut self: Pin<&mut Self>, cx: &mut Context<'_>) -> Poll<Self::Output> {
+        let this = &mut *self;
+        Pin::new(&mut this.reader).poll_read_vectored(cx, this.bufs)
+    }
+}
diff --git a/third_party/rust/futures-util/src/io/repeat.rs b/third_party/rust/futures-util/src/io/repeat.rs
new file mode 100644
index 0000000000..2828bf0114
--- /dev/null
+++ b/third_party/rust/futures-util/src/io/repeat.rs
@@ -0,0 +1,66 @@
+use futures_core::ready;
+use futures_core::task::{Context, Poll};
+use futures_io::{AsyncRead, IoSliceMut};
+use std::fmt;
+use std::io;
+use std::pin::Pin;
+
+/// Reader for the [`repeat()`] function.
+#[must_use = "readers do nothing unless polled"]
+pub struct Repeat {
+    byte: u8,
+}
+
+/// Creates an instance of a reader that infinitely repeats one byte.
+///
+/// All reads from this reader will succeed by filling the specified buffer with
+/// the given byte.
+///
+/// # Examples
+///
+/// ```
+/// # futures::executor::block_on(async {
+/// use futures::io::{self, AsyncReadExt};
+///
+/// let mut buffer = [0; 3];
+/// let mut reader = io::repeat(0b101);
+/// reader.read_exact(&mut buffer).await.unwrap();
+/// assert_eq!(buffer, [0b101, 0b101, 0b101]);
+/// # Ok::<(), Box<dyn std::error::Error>>(()) }).unwrap();
+/// ```
+pub fn repeat(byte: u8) -> Repeat {
+    Repeat { byte }
+}
+
+impl AsyncRead for Repeat {
+    #[inline]
+    fn poll_read(
+        self: Pin<&mut Self>,
+        _: &mut Context<'_>,
+        buf: &mut [u8],
+    ) -> Poll<io::Result<usize>> {
+        for slot in &mut *buf {
+            *slot = self.byte;
+        }
+        Poll::Ready(Ok(buf.len()))
+    }
+
+    #[inline]
+    fn poll_read_vectored(
+        mut self: Pin<&mut Self>,
+        cx: &mut Context<'_>,
+        bufs: &mut [IoSliceMut<'_>],
+    ) -> Poll<io::Result<usize>> {
+        let mut nwritten = 0;
+        for buf in bufs {
+            nwritten += ready!(self.as_mut().poll_read(cx, buf))?;
+        }
+        Poll::Ready(Ok(nwritten))
+    }
+}
+
+impl fmt::Debug for Repeat {
+    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
+        f.pad("Repeat { .. }")
+    }
+}
diff --git a/third_party/rust/futures-util/src/io/seek.rs b/third_party/rust/futures-util/src/io/seek.rs
new file mode 100644
index 0000000000..0aa2371393
--- /dev/null
+++ b/third_party/rust/futures-util/src/io/seek.rs
@@ -0,0 +1,30 @@
+use crate::io::{AsyncSeek, SeekFrom};
+use futures_core::future::Future;
+use futures_core::task::{Context, Poll};
+use std::io;
+use std::pin::Pin;
+
+/// Future for the [`seek`](crate::io::AsyncSeekExt::seek) method.
+#[derive(Debug)]
+#[must_use = "futures do nothing unless you `.await` or poll them"]
+pub struct Seek<'a, S: ?Sized> {
+    seek: &'a mut S,
+    pos: SeekFrom,
+}
+
+impl<S: ?Sized + Unpin> Unpin for Seek<'_, S> {}
+
+impl<'a, S: AsyncSeek + ?Sized + Unpin> Seek<'a, S> {
+    pub(super) fn new(seek: &'a mut S, pos: SeekFrom) -> Self {
+        Self { seek, pos }
+    }
+}
+
+impl<S: AsyncSeek + ?Sized + Unpin> Future for Seek<'_, S> {
+    type Output = io::Result<u64>;
+
+    fn poll(mut self: Pin<&mut Self>, cx: &mut Context<'_>) -> Poll<Self::Output> {
+        let this = &mut *self;
+        Pin::new(&mut this.seek).poll_seek(cx, this.pos)
+    }
+}
diff --git a/third_party/rust/futures-util/src/io/sink.rs b/third_party/rust/futures-util/src/io/sink.rs
new file mode 100644
index 0000000000..4a32ca7041
--- /dev/null
+++ b/third_party/rust/futures-util/src/io/sink.rs
@@ -0,0 +1,67 @@
+use futures_core::task::{Context, Poll};
+use futures_io::{AsyncWrite, IoSlice};
+use std::fmt;
+use std::io;
+use std::pin::Pin;
+
+/// Writer for the [`sink()`] function.
+#[must_use = "writers do nothing unless polled"]
+pub struct Sink {
+    _priv: (),
+}
+
+/// Creates an instance of a writer which will successfully consume all data.
+///
+/// All calls to `poll_write` on the returned instance will return `Poll::Ready(Ok(buf.len()))`
+/// and the contents of the buffer will not be inspected.
+///
+/// # Examples
+///
+/// ```rust
+/// # futures::executor::block_on(async {
+/// use futures::io::{self, AsyncWriteExt};
+///
+/// let buffer = vec![1, 2, 3, 5, 8];
+/// let mut writer = io::sink();
+/// let num_bytes = writer.write(&buffer).await?;
+/// assert_eq!(num_bytes, 5);
+/// # Ok::<(), Box<dyn std::error::Error>>(()) }).unwrap();
+/// ```
+pub fn sink() -> Sink {
+    Sink { _priv: () }
+}
+
+impl AsyncWrite for Sink {
+    #[inline]
+    fn poll_write(
+        self: Pin<&mut Self>,
+        _: &mut Context<'_>,
+        buf: &[u8],
+    ) -> Poll<io::Result<usize>> {
+        Poll::Ready(Ok(buf.len()))
+    }
+
+    #[inline]
+    fn poll_write_vectored(
+        self: Pin<&mut Self>,
+        _: &mut Context<'_>,
+        bufs: &[IoSlice<'_>],
+    ) -> Poll<io::Result<usize>> {
+        Poll::Ready(Ok(bufs.iter().map(|b| b.len()).sum()))
+    }
+
+    #[inline]
+    fn poll_flush(self: Pin<&mut Self>, _: &mut Context<'_>) -> Poll<io::Result<()>> {
+        Poll::Ready(Ok(()))
+    }
+    #[inline]
+    fn poll_close(self: Pin<&mut Self>, _: &mut Context<'_>) -> Poll<io::Result<()>> {
+        Poll::Ready(Ok(()))
+    }
+}
+
+impl fmt::Debug for Sink {
+    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
+        f.pad("Sink { .. }")
+    }
+}
diff --git a/third_party/rust/futures-util/src/io/split.rs b/third_party/rust/futures-util/src/io/split.rs
new file mode 100644
index 0000000000..3f1b9af456
--- /dev/null
+++ b/third_party/rust/futures-util/src/io/split.rs
@@ -0,0 +1,115 @@
+use crate::lock::BiLock;
+use core::fmt;
+use futures_core::ready;
+use futures_core::task::{Context, Poll};
+use futures_io::{AsyncRead, AsyncWrite, IoSlice, IoSliceMut};
+use std::io;
+use std::pin::Pin;
+
+/// The readable half of an object returned from `AsyncRead::split`.
+#[derive(Debug)]
+pub struct ReadHalf<T> {
+    handle: BiLock<T>,
+}
+
+/// The writable half of an object returned from `AsyncRead::split`.
+#[derive(Debug)]
+pub struct WriteHalf<T> {
+    handle: BiLock<T>,
+}
+
+fn lock_and_then<T, U, E, F>(lock: &BiLock<T>, cx: &mut Context<'_>, f: F) -> Poll<Result<U, E>>
+where
+    F: FnOnce(Pin<&mut T>, &mut Context<'_>) -> Poll<Result<U, E>>,
+{
+    let mut l = ready!(lock.poll_lock(cx));
+    f(l.as_pin_mut(), cx)
+}
+
+pub(super) fn split<T: AsyncRead + AsyncWrite>(t: T) -> (ReadHalf<T>, WriteHalf<T>) {
+    let (a, b) = BiLock::new(t);
+    (ReadHalf { handle: a }, WriteHalf { handle: b })
+}
+
+impl<T: Unpin> ReadHalf<T> {
+    /// Attempts to put the two "halves" of a split `AsyncRead + AsyncWrite` back
+    /// together. Succeeds only if the `ReadHalf<T>` and `WriteHalf<T>` are
+    /// a matching pair originating from the same call to `AsyncReadExt::split`.
+    pub fn reunite(self, other: WriteHalf<T>) -> Result<T, ReuniteError<T>> {
+        self.handle
+            .reunite(other.handle)
+            .map_err(|err| ReuniteError(ReadHalf { handle: err.0 }, WriteHalf { handle: err.1 }))
+    }
+}
+
+impl<T: Unpin> WriteHalf<T> {
+    /// Attempts to put the two "halves" of a split `AsyncRead + AsyncWrite` back
+    /// together. Succeeds only if the `ReadHalf<T>` and `WriteHalf<T>` are
+    /// a matching pair originating from the same call to `AsyncReadExt::split`.
+    pub fn reunite(self, other: ReadHalf<T>) -> Result<T, ReuniteError<T>> {
+        other.reunite(self)
+    }
+}
+
+impl<R: AsyncRead> AsyncRead for ReadHalf<R> {
+    fn poll_read(
+        self: Pin<&mut Self>,
+        cx: &mut Context<'_>,
+        buf: &mut [u8],
+    ) -> Poll<io::Result<usize>> {
+        lock_and_then(&self.handle, cx, |l, cx| l.poll_read(cx, buf))
+    }
+
+    fn poll_read_vectored(
+        self: Pin<&mut Self>,
+        cx: &mut Context<'_>,
+        bufs: &mut [IoSliceMut<'_>],
+    ) -> Poll<io::Result<usize>> {
+        lock_and_then(&self.handle, cx, |l, cx| l.poll_read_vectored(cx, bufs))
+    }
+}
+
+impl<W: AsyncWrite> AsyncWrite for WriteHalf<W> {
+    fn poll_write(
+        self: Pin<&mut Self>,
+        cx: &mut Context<'_>,
+        buf: &[u8],
+    ) -> Poll<io::Result<usize>> {
+        lock_and_then(&self.handle, cx, |l, cx| l.poll_write(cx, buf))
+    }
+
+    fn poll_write_vectored(
+        self: Pin<&mut Self>,
+        cx: &mut Context<'_>,
+        bufs: &[IoSlice<'_>],
+    ) -> Poll<io::Result<usize>> {
+        lock_and_then(&self.handle, cx, |l, cx| l.poll_write_vectored(cx, bufs))
+    }
+
+    fn poll_flush(self: Pin<&mut Self>, cx: &mut Context<'_>) -> Poll<io::Result<()>> {
+        lock_and_then(&self.handle, cx, |l, cx| l.poll_flush(cx))
+    }
+
+    fn poll_close(self: Pin<&mut Self>, cx: &mut Context<'_>) -> Poll<io::Result<()>> {
+        lock_and_then(&self.handle, cx, |l, cx| l.poll_close(cx))
+    }
+}
+
+/// Error indicating a `ReadHalf<T>` and `WriteHalf<T>` were not two halves
+/// of a `AsyncRead + AsyncWrite`, and thus could not be `reunite`d.
+pub struct ReuniteError<T>(pub ReadHalf<T>, pub WriteHalf<T>);
+
+impl<T> fmt::Debug for ReuniteError<T> {
+    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
+        f.debug_tuple("ReuniteError").field(&"...").finish()
+    }
+}
+
+impl<T> fmt::Display for ReuniteError<T> {
+    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
+        write!(f, "tried to reunite a ReadHalf and WriteHalf that don't form a pair")
+    }
+}
+
+#[cfg(feature = "std")]
+impl<T: core::any::Any> std::error::Error for ReuniteError<T> {}
diff --git a/third_party/rust/futures-util/src/io/take.rs b/third_party/rust/futures-util/src/io/take.rs
new file mode 100644
index 0000000000..2c494804d9
--- /dev/null
+++ b/third_party/rust/futures-util/src/io/take.rs
@@ -0,0 +1,125 @@
+use futures_core::ready;
+use futures_core::task::{Context, Poll};
+use futures_io::{AsyncBufRead, AsyncRead};
+use pin_project_lite::pin_project;
+use std::pin::Pin;
+use std::{cmp, io};
+
+pin_project! {
+    /// Reader for the [`take`](super::AsyncReadExt::take) method.
+    #[derive(Debug)]
+    #[must_use = "readers do nothing unless you `.await` or poll them"]
+    pub struct Take<R> {
+        #[pin]
+        inner: R,
+        limit: u64,
+    }
+}
+
+impl<R: AsyncRead> Take<R> {
+    pub(super) fn new(inner: R, limit: u64) -> Self {
+        Self { inner, limit }
+    }
+
+    /// Returns the remaining number of bytes that can be
+    /// read before this instance will return EOF.
+    ///
+    /// # Note
+    ///
+    /// This instance may reach `EOF` after reading fewer bytes than indicated by
+    /// this method if the underlying [`AsyncRead`] instance reaches EOF.
+    ///
+    /// # Examples
+    ///
+    /// ```
+    /// # futures::executor::block_on(async {
+    /// use futures::io::{AsyncReadExt, Cursor};
+    ///
+    /// let reader = Cursor::new(&b"12345678"[..]);
+    /// let mut buffer = [0; 2];
+    ///
+    /// let mut take = reader.take(4);
+    /// let n = take.read(&mut buffer).await?;
+    ///
+    /// assert_eq!(take.limit(), 2);
+    /// # Ok::<(), Box<dyn std::error::Error>>(()) }).unwrap();
+    /// ```
+    pub fn limit(&self) -> u64 {
+        self.limit
+    }
+
+    /// Sets the number of bytes that can be read before this instance will
+    /// return EOF. This is the same as constructing a new `Take` instance, so
+    /// the amount of bytes read and the previous limit value don't matter when
+    /// calling this method.
+    ///
+    /// # Examples
+    ///
+    /// ```
+    /// # futures::executor::block_on(async {
+    /// use futures::io::{AsyncReadExt, Cursor};
+    ///
+    /// let reader = Cursor::new(&b"12345678"[..]);
+    /// let mut buffer = [0; 4];
+    ///
+    /// let mut take = reader.take(4);
+    /// let n = take.read(&mut buffer).await?;
+    ///
+    /// assert_eq!(n, 4);
+    /// assert_eq!(take.limit(), 0);
+    ///
+    /// take.set_limit(10);
+    /// let n = take.read(&mut buffer).await?;
+    /// assert_eq!(n, 4);
+    ///
+    /// # Ok::<(), Box<dyn std::error::Error>>(()) }).unwrap();
+    /// ```
+    pub fn set_limit(&mut self, limit: u64) {
+        self.limit = limit
+    }
+
+    delegate_access_inner!(inner, R, ());
+}
+
+impl<R: AsyncRead> AsyncRead for Take<R> {
+    fn poll_read(
+        self: Pin<&mut Self>,
+        cx: &mut Context<'_>,
+        buf: &mut [u8],
+    ) -> Poll<Result<usize, io::Error>> {
+        let this = self.project();
+
+        if *this.limit == 0 {
+            return Poll::Ready(Ok(0));
+        }
+
+        let max = cmp::min(buf.len() as u64, *this.limit) as usize;
+        let n = ready!(this.inner.poll_read(cx, &mut buf[..max]))?;
+        *this.limit -= n as u64;
+        Poll::Ready(Ok(n))
+    }
+}
+
+impl<R: AsyncBufRead> AsyncBufRead for Take<R> {
+    fn poll_fill_buf(self: Pin<&mut Self>, cx: &mut Context<'_>) -> Poll<io::Result<&[u8]>> {
+        let this = self.project();
+
+        // Don't call into inner reader at all at EOF because it may still block
+        if *this.limit == 0 {
+            return Poll::Ready(Ok(&[]));
+        }
+
+        let buf = ready!(this.inner.poll_fill_buf(cx)?);
+        let cap = cmp::min(buf.len() as u64, *this.limit) as usize;
+        Poll::Ready(Ok(&buf[..cap]))
+    }
+
+    fn consume(self: Pin<&mut Self>, amt: usize) {
+        let this = self.project();
+
+        // Don't let callers reset the limit by passing an overlarge value
+        let amt = cmp::min(amt as u64, *this.limit) as usize;
+        *this.limit -= amt as u64;
+        this.inner.consume(amt);
+    }
+}
diff --git a/third_party/rust/futures-util/src/io/window.rs b/third_party/rust/futures-util/src/io/window.rs
new file mode 100644
index 0000000000..77b7267c69
--- /dev/null
+++ b/third_party/rust/futures-util/src/io/window.rs
@@ -0,0 +1,104 @@
+use std::ops::{Bound, Range, RangeBounds};
+
+/// A owned window around an underlying buffer.
+///
+/// Normally slices work great for considering sub-portions of a buffer, but
+/// unfortunately a slice is a *borrowed* type in Rust which has an associated
+/// lifetime. When working with future and async I/O these lifetimes are not
+/// always appropriate, and are sometimes difficult to store in tasks. This
+/// type strives to fill this gap by providing an "owned slice" around an
+/// underlying buffer of bytes.
+///
+/// A `Window<T>` wraps an underlying buffer, `T`, and has configurable
+/// start/end indexes to alter the behavior of the `AsRef<[u8]>` implementation
+/// that this type carries.
+///
+/// This type can be particularly useful when working with the `write_all`
+/// combinator in this crate. Data can be sliced via `Window`, consumed by
+/// `write_all`, and then earned back once the write operation finishes through
+/// the `into_inner` method on this type.
+#[derive(Debug)]
+pub struct Window<T> {
+    inner: T,
+    range: Range<usize>,
+}
+
+impl<T: AsRef<[u8]>> Window<T> {
+    /// Creates a new window around the buffer `t` defaulting to the entire
+    /// slice.
+    ///
+    /// Further methods can be called on the returned `Window<T>` to alter the
+    /// window into the data provided.
+    pub fn new(t: T) -> Self {
+        Self { range: 0..t.as_ref().len(), inner: t }
+    }
+
+    /// Gets a shared reference to the underlying buffer inside of this
+    /// `Window`.
+    pub fn get_ref(&self) -> &T {
+        &self.inner
+    }
+
+    /// Gets a mutable reference to the underlying buffer inside of this
+    /// `Window`.
+    pub fn get_mut(&mut self) -> &mut T {
+        &mut self.inner
+    }
+
+    /// Consumes this `Window`, returning the underlying buffer.
+    pub fn into_inner(self) -> T {
+        self.inner
+    }
+
+    /// Returns the starting index of this window into the underlying buffer
+    /// `T`.
+    pub fn start(&self) -> usize {
+        self.range.start
+    }
+
+    /// Returns the end index of this window into the underlying buffer
+    /// `T`.
+    pub fn end(&self) -> usize {
+        self.range.end
+    }
+
+    /// Changes the range of this window to the range specified.
+    ///
+    /// # Panics
+    ///
+    /// This method will panic if `range` is out of bounds for the underlying
+    /// slice or if [`start_bound()`] of `range` comes after the [`end_bound()`].
+    ///
+    /// [`start_bound()`]: std::ops::RangeBounds::start_bound
+    /// [`end_bound()`]: std::ops::RangeBounds::end_bound
+    pub fn set<R: RangeBounds<usize>>(&mut self, range: R) {
+        let start = match range.start_bound() {
+            Bound::Included(n) => *n,
+            Bound::Excluded(n) => *n + 1,
+            Bound::Unbounded => 0,
+        };
+        let end = match range.end_bound() {
+            Bound::Included(n) => *n + 1,
+            Bound::Excluded(n) => *n,
+            Bound::Unbounded => self.inner.as_ref().len(),
+        };
+
+        assert!(end <= self.inner.as_ref().len());
+        assert!(start <= end);
+
+        self.range.start = start;
+        self.range.end = end;
+    }
+}
+
+impl<T: AsRef<[u8]>> AsRef<[u8]> for Window<T> {
+    fn as_ref(&self) -> &[u8] {
+        &self.inner.as_ref()[self.range.start..self.range.end]
+    }
+}
+
+impl<T: AsMut<[u8]>> AsMut<[u8]> for Window<T> {
+    fn as_mut(&mut self) -> &mut [u8] {
+        &mut self.inner.as_mut()[self.range.start..self.range.end]
+    }
+}
diff --git a/third_party/rust/futures-util/src/io/write.rs b/third_party/rust/futures-util/src/io/write.rs
new file mode 100644
index 0000000000..c47ef9e2eb
--- /dev/null
+++ b/third_party/rust/futures-util/src/io/write.rs
@@ -0,0 +1,30 @@
+use crate::io::AsyncWrite;
+use futures_core::future::Future;
+use futures_core::task::{Context, Poll};
+use std::io;
+use std::pin::Pin;
+
+/// Future for the [`write`](super::AsyncWriteExt::write) method.
+#[derive(Debug)]
+#[must_use = "futures do nothing unless you `.await` or poll them"]
+pub struct Write<'a, W: ?Sized> {
+    writer: &'a mut W,
+    buf: &'a [u8],
+}
+
+impl<W: ?Sized + Unpin> Unpin for Write<'_, W> {}
+
+impl<'a, W: AsyncWrite + ?Sized + Unpin> Write<'a, W> {
+    pub(super) fn new(writer: &'a mut W, buf: &'a [u8]) -> Self {
+        Self { writer, buf }
+    }
+}
+
+impl<W: AsyncWrite + ?Sized + Unpin> Future for Write<'_, W> {
+    type Output = io::Result<usize>;
+
+    fn poll(mut self: Pin<&mut Self>, cx: &mut Context<'_>) -> Poll<Self::Output> {
+        let this = &mut *self;
+        Pin::new(&mut this.writer).poll_write(cx, this.buf)
+    }
+}
diff --git a/third_party/rust/futures-util/src/io/write_all.rs b/third_party/rust/futures-util/src/io/write_all.rs
new file mode 100644
index 0000000000..08c025f94d
--- /dev/null
+++ b/third_party/rust/futures-util/src/io/write_all.rs
@@ -0,0 +1,43 @@
+use futures_core::future::Future;
+use futures_core::ready;
+use futures_core::task::{Context, Poll};
+use futures_io::AsyncWrite;
+use std::io;
+use std::mem;
+use std::pin::Pin;
+
+/// Future for the [`write_all`](super::AsyncWriteExt::write_all) method.
+#[derive(Debug)]
+#[must_use = "futures do nothing unless you `.await` or poll them"]
+pub struct WriteAll<'a, W: ?Sized> {
+    writer: &'a mut W,
+    buf: &'a [u8],
+}
+
+impl<W: ?Sized + Unpin> Unpin for WriteAll<'_, W> {}
+
+impl<'a, W: AsyncWrite + ?Sized + Unpin> WriteAll<'a, W> {
+    pub(super) fn new(writer: &'a mut W, buf: &'a [u8]) -> Self {
+        Self { writer, buf }
+    }
+}
+
+impl<W: AsyncWrite + ?Sized + Unpin> Future for WriteAll<'_, W> {
+    type Output = io::Result<()>;
+
+    fn poll(mut self: Pin<&mut Self>, cx: &mut Context<'_>) -> Poll<io::Result<()>> {
+        let this = &mut *self;
+        while !this.buf.is_empty() {
+            let n = ready!(Pin::new(&mut this.writer).poll_write(cx, this.buf))?;
+            {
+                let (_, rest) = mem::take(&mut this.buf).split_at(n);
+                this.buf = rest;
+            }
+            if n == 0 {
+                return Poll::Ready(Err(io::ErrorKind::WriteZero.into()));
+            }
+        }
+
+        Poll::Ready(Ok(()))
+    }
+}
diff --git a/third_party/rust/futures-util/src/io/write_all_vectored.rs b/third_party/rust/futures-util/src/io/write_all_vectored.rs
new file mode 100644
index 0000000000..a8fc4c641c
--- /dev/null
+++ b/third_party/rust/futures-util/src/io/write_all_vectored.rs
@@ -0,0 +1,193 @@
+use futures_core::future::Future;
+use futures_core::ready;
+use futures_core::task::{Context, Poll};
+use futures_io::AsyncWrite;
+use futures_io::IoSlice;
+use std::io;
+use std::pin::Pin;
+
+/// Future for the
+/// [`write_all_vectored`](super::AsyncWriteExt::write_all_vectored) method.
+#[derive(Debug)]
+#[must_use = "futures do nothing unless you `.await` or poll them"]
+pub struct WriteAllVectored<'a, W: ?Sized + Unpin> {
+    writer: &'a mut W,
+    bufs: &'a mut [IoSlice<'a>],
+}
+
+impl<W: ?Sized + Unpin> Unpin for WriteAllVectored<'_, W> {}
+
+impl<'a, W: AsyncWrite + ?Sized + Unpin> WriteAllVectored<'a, W> {
+    pub(super) fn new(writer: &'a mut W, mut bufs: &'a mut [IoSlice<'a>]) -> Self {
+        IoSlice::advance_slices(&mut bufs, 0);
+        Self { writer, bufs }
+    }
+}
+
+impl<W: AsyncWrite + ?Sized + Unpin> Future for WriteAllVectored<'_, W> {
+    type Output = io::Result<()>;
+
+    fn poll(mut self: Pin<&mut Self>, cx: &mut Context<'_>) -> Poll<io::Result<()>> {
+        let this = &mut *self;
+        while !this.bufs.is_empty() {
+            let n = ready!(Pin::new(&mut this.writer).poll_write_vectored(cx, this.bufs))?;
+            if n == 0 {
+                return Poll::Ready(Err(io::ErrorKind::WriteZero.into()));
+            } else {
+                IoSlice::advance_slices(&mut this.bufs, n);
+            }
+        }
+
+        Poll::Ready(Ok(()))
+    }
+}
+
+#[cfg(test)]
+mod tests {
+    use std::cmp::min;
+    use std::future::Future;
+    use std::io;
+    use std::pin::Pin;
+    use std::task::{Context, Poll};
+
+    use crate::io::{AsyncWrite, AsyncWriteExt, IoSlice};
+    use crate::task::noop_waker;
+
+    /// Create a new writer that reads from at most `n_bufs` and reads
+    /// `per_call` bytes (in total) per call to write.
+    fn test_writer(n_bufs: usize, per_call: usize) -> TestWriter {
+        TestWriter { n_bufs, per_call, written: Vec::new() }
+    }
+
+    // TODO: maybe move this the future-test crate?
+    struct TestWriter {
+        n_bufs: usize,
+        per_call: usize,
+        written: Vec<u8>,
+    }
+
+    impl AsyncWrite for TestWriter {
+        fn poll_write(
+            self: Pin<&mut Self>,
+            cx: &mut Context<'_>,
+            buf: &[u8],
+        ) -> Poll<io::Result<usize>> {
+            self.poll_write_vectored(cx, &[IoSlice::new(buf)])
+        }
+
+        fn poll_write_vectored(
+            mut self: Pin<&mut Self>,
+            _cx: &mut Context<'_>,
+            bufs: &[IoSlice<'_>],
+        ) -> Poll<io::Result<usize>> {
+            let mut left = self.per_call;
+            let mut written = 0;
+            for buf in bufs.iter().take(self.n_bufs) {
+                let n = min(left, buf.len());
+                self.written.extend_from_slice(&buf[0..n]);
+                left -= n;
+                written += n;
+            }
+            Poll::Ready(Ok(written))
+        }
+
+        fn poll_flush(self: Pin<&mut Self>, _cx: &mut Context<'_>) -> Poll<io::Result<()>> {
+            Poll::Ready(Ok(()))
+        }
+
+        fn poll_close(self: Pin<&mut Self>, _cx: &mut Context<'_>) -> Poll<io::Result<()>> {
+            Poll::Ready(Ok(()))
+        }
+    }
+
+    // TODO: maybe move this the future-test crate?
+    macro_rules! assert_poll_ok {
+        ($e:expr, $expected:expr) => {
+            let expected = $expected;
+            match $e {
+                Poll::Ready(Ok(ok)) if ok == expected => {}
+                got => {
+                    panic!("unexpected result, got: {:?}, wanted: Ready(Ok({:?}))", got, expected)
+                }
+            }
+        };
+    }
+
+    #[test]
+    fn test_writer_read_from_one_buf() {
+        let waker = noop_waker();
+        let mut cx = Context::from_waker(&waker);
+
+        let mut dst = test_writer(1, 2);
+        let mut dst = Pin::new(&mut dst);
+
+        assert_poll_ok!(dst.as_mut().poll_write(&mut cx, &[]), 0);
+        assert_poll_ok!(dst.as_mut().poll_write_vectored(&mut cx, &[]), 0);
+
+        // Read at most 2 bytes.
+        assert_poll_ok!(dst.as_mut().poll_write(&mut cx, &[1, 1, 1]), 2);
+        let bufs = &[IoSlice::new(&[2, 2, 2])];
+        assert_poll_ok!(dst.as_mut().poll_write_vectored(&mut cx, bufs), 2);
+
+        // Only read from first buf.
+        let bufs = &[IoSlice::new(&[3]), IoSlice::new(&[4, 4])];
+        assert_poll_ok!(dst.as_mut().poll_write_vectored(&mut cx, bufs), 1);
+
+        assert_eq!(dst.written, &[1, 1, 2, 2, 3]);
+    }
+
+    #[test]
+    fn test_writer_read_from_multiple_bufs() {
+        let waker = noop_waker();
+        let mut cx = Context::from_waker(&waker);
+
+        let mut dst = test_writer(3, 3);
+        let mut dst = Pin::new(&mut dst);
+
+        // Read at most 3 bytes from two buffers.
+        let bufs = &[IoSlice::new(&[1]), IoSlice::new(&[2, 2, 2])];
+        assert_poll_ok!(dst.as_mut().poll_write_vectored(&mut cx, bufs), 3);
+
+        // Read at most 3 bytes from three buffers.
+        let bufs = &[IoSlice::new(&[3]), IoSlice::new(&[4]), IoSlice::new(&[5, 5])];
+        assert_poll_ok!(dst.as_mut().poll_write_vectored(&mut cx, bufs), 3);
+
+        assert_eq!(dst.written, &[1, 2, 2, 3, 4, 5]);
+    }
+
+    #[test]
+    fn test_write_all_vectored() {
+        let waker = noop_waker();
+        let mut cx = Context::from_waker(&waker);
+
+        #[rustfmt::skip] // Becomes unreadable otherwise.
+        let tests: Vec<(_, &'static [u8])> = vec![
+            (vec![], &[]),
+            (vec![IoSlice::new(&[]), IoSlice::new(&[])], &[]),
+            (vec![IoSlice::new(&[1])], &[1]),
+            (vec![IoSlice::new(&[1, 2])], &[1, 2]),
+            (vec![IoSlice::new(&[1, 2, 3])], &[1, 2, 3]),
+            (vec![IoSlice::new(&[1, 2, 3, 4])], &[1, 2, 3, 4]),
+            (vec![IoSlice::new(&[1, 2, 3, 4, 5])], &[1, 2, 3, 4, 5]),
+            (vec![IoSlice::new(&[1]), IoSlice::new(&[2])], &[1, 2]),
+            (vec![IoSlice::new(&[1, 1]), IoSlice::new(&[2, 2])], &[1, 1, 2, 2]),
+            (vec![IoSlice::new(&[1, 1, 1]), IoSlice::new(&[2, 2, 2])], &[1, 1, 1, 2, 2, 2]),
+            (vec![IoSlice::new(&[1, 1, 1, 1]), IoSlice::new(&[2, 2, 2, 2])], &[1, 1, 1, 1, 2, 2, 2, 2]),
+            (vec![IoSlice::new(&[1]), IoSlice::new(&[2]), IoSlice::new(&[3])], &[1, 2, 3]),
+            (vec![IoSlice::new(&[1, 1]), IoSlice::new(&[2, 2]), IoSlice::new(&[3, 3])], &[1, 1, 2, 2, 3, 3]),
+            (vec![IoSlice::new(&[1, 1, 1]), IoSlice::new(&[2, 2, 2]), IoSlice::new(&[3, 3, 3])], &[1, 1, 1, 2, 2, 2, 3, 3, 3]),
+        ];
+
+        for (mut input, wanted) in tests {
+            let mut dst = test_writer(2, 2);
+            {
+                let mut future = dst.write_all_vectored(&mut *input);
+                match Pin::new(&mut future).poll(&mut cx) {
+                    Poll::Ready(Ok(())) => {}
+                    other => panic!("unexpected result polling future: {:?}", other),
+                }
+            }
+            assert_eq!(&*dst.written, &*wanted);
+        }
+    }
+}
diff --git a/third_party/rust/futures-util/src/io/write_vectored.rs b/third_party/rust/futures-util/src/io/write_vectored.rs
new file mode 100644
index 0000000000..14a01d7302
--- /dev/null
+++ b/third_party/rust/futures-util/src/io/write_vectored.rs
@@ -0,0 +1,30 @@
+use crate::io::AsyncWrite;
+use futures_core::future::Future;
+use futures_core::task::{Context, Poll};
+use std::io::{self, IoSlice};
+use std::pin::Pin;
+
+/// Future for the [`write_vectored`](super::AsyncWriteExt::write_vectored) method.
+#[derive(Debug)]
+#[must_use = "futures do nothing unless you `.await` or poll them"]
+pub struct WriteVectored<'a, W: ?Sized> {
+    writer: &'a mut W,
+    bufs: &'a [IoSlice<'a>],
+}
+
+impl<W: ?Sized + Unpin> Unpin for WriteVectored<'_, W> {}
+
+impl<'a, W: AsyncWrite + ?Sized + Unpin> WriteVectored<'a, W> {
+    pub(super) fn new(writer: &'a mut W, bufs: &'a [IoSlice<'a>]) -> Self {
+        Self { writer, bufs }
+    }
+}
+
+impl<W: AsyncWrite + ?Sized + Unpin> Future for WriteVectored<'_, W> {
+    type Output = io::Result<usize>;
+
+    fn poll(mut self: Pin<&mut Self>, cx: &mut Context<'_>) -> Poll<Self::Output> {
+        let this = &mut *self;
+        Pin::new(&mut this.writer).poll_write_vectored(cx, this.bufs)
+    }
+}
diff --git a/third_party/rust/futures-util/src/lib.rs b/third_party/rust/futures-util/src/lib.rs
new file mode 100644
index 0000000000..9a10c93c9a
--- /dev/null
+++ b/third_party/rust/futures-util/src/lib.rs
@@ -0,0 +1,337 @@
+//! Combinators and utilities for working with `Future`s, `Stream`s, `Sink`s,
+//! and the `AsyncRead` and `AsyncWrite` traits.
+
+#![cfg_attr(feature = "write-all-vectored", feature(io_slice_advance))]
+#![cfg_attr(not(feature = "std"), no_std)]
+#![warn(
+    missing_debug_implementations,
+    missing_docs,
+    rust_2018_idioms,
+    single_use_lifetimes,
+    unreachable_pub
+)]
+#![doc(test(
+    no_crate_inject,
+    attr(
+        deny(warnings, rust_2018_idioms, single_use_lifetimes),
+        allow(dead_code, unused_assignments, unused_variables)
+    )
+))]
+#![cfg_attr(docsrs, feature(doc_cfg))]
+
+#[cfg(all(feature = "bilock", not(feature = "unstable")))]
+compile_error!("The `bilock` feature requires the `unstable` feature as an explicit opt-in to unstable features");
+
+#[cfg(feature = "alloc")]
+extern crate alloc;
+
+// Macro re-exports
+pub use futures_core::ready;
+pub use pin_utils::pin_mut;
+
+#[cfg(feature = "async-await")]
+#[macro_use]
+mod async_await;
+#[cfg(feature = "async-await")]
+#[doc(hidden)]
+pub use self::async_await::*;
+
+// Not public API.
+#[cfg(feature = "async-await")]
+#[doc(hidden)]
+pub mod __private {
+    pub use crate::*;
+    pub use core::{
+        option::Option::{self, None, Some},
+        pin::Pin,
+        result::Result::{Err, Ok},
+    };
+
+    pub mod async_await {
+        pub use crate::async_await::*;
+    }
+}
+
+#[cfg(feature = "sink")]
+macro_rules! delegate_sink {
+    ($field:ident, $item:ty) => {
+        fn poll_ready(
+            self: core::pin::Pin<&mut Self>,
+            cx: &mut core::task::Context<'_>,
+        ) -> core::task::Poll<Result<(), Self::Error>> {
+            self.project().$field.poll_ready(cx)
+        }
+
+        fn start_send(self: core::pin::Pin<&mut Self>, item: $item) -> Result<(), Self::Error> {
+            self.project().$field.start_send(item)
+        }
+
+        fn poll_flush(
+            self: core::pin::Pin<&mut Self>,
+            cx: &mut core::task::Context<'_>,
+        ) -> core::task::Poll<Result<(), Self::Error>> {
+            self.project().$field.poll_flush(cx)
+        }
+
+        fn poll_close(
+            self: core::pin::Pin<&mut Self>,
+            cx: &mut core::task::Context<'_>,
+        ) -> core::task::Poll<Result<(), Self::Error>> {
+            self.project().$field.poll_close(cx)
+        }
+    };
+}
+
+macro_rules! delegate_future {
+    ($field:ident) => {
+        fn poll(
+            self: core::pin::Pin<&mut Self>,
+            cx: &mut core::task::Context<'_>,
+        ) -> core::task::Poll<Self::Output> {
+            self.project().$field.poll(cx)
+        }
+    };
+}
+
+macro_rules! delegate_stream {
+    ($field:ident) => {
+        fn poll_next(
+            self: core::pin::Pin<&mut Self>,
+            cx: &mut core::task::Context<'_>,
+        ) -> core::task::Poll<Option<Self::Item>> {
+            self.project().$field.poll_next(cx)
+        }
+        fn size_hint(&self) -> (usize, Option<usize>) {
+            self.$field.size_hint()
+        }
+    };
+}
+
+#[cfg(feature = "io")]
+#[cfg(feature = "std")]
+macro_rules! delegate_async_write {
+    ($field:ident) => {
+        fn poll_write(
+            self: core::pin::Pin<&mut Self>,
+            cx: &mut core::task::Context<'_>,
+            buf: &[u8],
+        ) -> core::task::Poll<std::io::Result<usize>> {
+            self.project().$field.poll_write(cx, buf)
+        }
+        fn poll_write_vectored(
+            self: core::pin::Pin<&mut Self>,
+            cx: &mut core::task::Context<'_>,
+            bufs: &[std::io::IoSlice<'_>],
+        ) -> core::task::Poll<std::io::Result<usize>> {
+            self.project().$field.poll_write_vectored(cx, bufs)
+        }
+        fn poll_flush(
+            self: core::pin::Pin<&mut Self>,
+            cx: &mut core::task::Context<'_>,
+        ) -> core::task::Poll<std::io::Result<()>> {
+            self.project().$field.poll_flush(cx)
+        }
+        fn poll_close(
+            self: core::pin::Pin<&mut Self>,
+            cx: &mut core::task::Context<'_>,
+        ) -> core::task::Poll<std::io::Result<()>> {
+            self.project().$field.poll_close(cx)
+        }
+    };
+}
+
+#[cfg(feature = "io")]
+#[cfg(feature = "std")]
+macro_rules! delegate_async_read {
+    ($field:ident) => {
+        fn poll_read(
+            self: core::pin::Pin<&mut Self>,
+            cx: &mut core::task::Context<'_>,
+            buf: &mut [u8],
+        ) -> core::task::Poll<std::io::Result<usize>> {
+            self.project().$field.poll_read(cx, buf)
+        }
+
+        fn poll_read_vectored(
+            self: core::pin::Pin<&mut Self>,
+            cx: &mut core::task::Context<'_>,
+            bufs: &mut [std::io::IoSliceMut<'_>],
+        ) -> core::task::Poll<std::io::Result<usize>> {
+            self.project().$field.poll_read_vectored(cx, bufs)
+        }
+    };
+}
+
+#[cfg(feature = "io")]
+#[cfg(feature = "std")]
+macro_rules! delegate_async_buf_read {
+    ($field:ident) => {
+        fn poll_fill_buf(
+            self: core::pin::Pin<&mut Self>,
+            cx: &mut core::task::Context<'_>,
+        ) -> core::task::Poll<std::io::Result<&[u8]>> {
+            self.project().$field.poll_fill_buf(cx)
+        }
+
+        fn consume(self: core::pin::Pin<&mut Self>, amt: usize) {
+            self.project().$field.consume(amt)
+        }
+    };
+}
+
+macro_rules! delegate_access_inner {
+    ($field:ident, $inner:ty, ($($ind:tt)*)) => {
+        /// Acquires a reference to the underlying sink or stream that this combinator is
+        /// pulling from.
+        pub fn get_ref(&self) -> &$inner {
+            (&self.$field) $($ind get_ref())*
+        }
+
+        /// Acquires a mutable reference to the underlying sink or stream that this
+        /// combinator is pulling from.
+        ///
+        /// Note that care must be taken to avoid tampering with the state of the
+        /// sink or stream which may otherwise confuse this combinator.
+        pub fn get_mut(&mut self) -> &mut $inner {
+            (&mut self.$field) $($ind get_mut())*
+        }
+
+        /// Acquires a pinned mutable reference to the underlying sink or stream that this
+        /// combinator is pulling from.
+        ///
+        /// Note that care must be taken to avoid tampering with the state of the
+        /// sink or stream which may otherwise confuse this combinator.
+        pub fn get_pin_mut(self: core::pin::Pin<&mut Self>) -> core::pin::Pin<&mut $inner> {
+            self.project().$field $($ind get_pin_mut())*
+        }
+
+        /// Consumes this combinator, returning the underlying sink or stream.
+        ///
+        /// Note that this may discard intermediate state of this combinator, so
+        /// care should be taken to avoid losing resources when this is called.
+        pub fn into_inner(self) -> $inner {
+            self.$field $($ind into_inner())*
+        }
+    }
+}
+
+macro_rules! delegate_all {
+    (@trait Future $name:ident < $($arg:ident),* > ($t:ty) $(where $($bound:tt)*)*) => {
+        impl<$($arg),*> futures_core::future::Future for $name<$($arg),*> where $t: futures_core::future::Future $(, $($bound)*)* {
+            type Output = <$t as futures_core::future::Future>::Output;
+
+            delegate_future!(inner);
+        }
+    };
+    (@trait FusedFuture $name:ident < $($arg:ident),* > ($t:ty) $(where $($bound:tt)*)*) => {
+        impl<$($arg),*> futures_core::future::FusedFuture for $name<$($arg),*> where $t: futures_core::future::FusedFuture $(, $($bound)*)* {
+            fn is_terminated(&self) -> bool {
+                self.inner.is_terminated()
+            }
+        }
+    };
+    (@trait Stream $name:ident < $($arg:ident),* > ($t:ty) $(where $($bound:tt)*)*) => {
+        impl<$($arg),*> futures_core::stream::Stream for $name<$($arg),*> where $t: futures_core::stream::Stream $(, $($bound)*)* {
+            type Item = <$t as futures_core::stream::Stream>::Item;
+
+            delegate_stream!(inner);
+        }
+    };
+    (@trait FusedStream $name:ident < $($arg:ident),* > ($t:ty) $(where $($bound:tt)*)*) => {
+        impl<$($arg),*> futures_core::stream::FusedStream for $name<$($arg),*> where $t: futures_core::stream::FusedStream $(, $($bound)*)* {
+            fn is_terminated(&self) -> bool {
+                self.inner.is_terminated()
+            }
+        }
+    };
+    (@trait Sink $name:ident < $($arg:ident),* > ($t:ty) $(where $($bound:tt)*)*) => {
+        #[cfg(feature = "sink")]
+        impl<_Item, $($arg),*> futures_sink::Sink<_Item> for $name<$($arg),*> where $t: futures_sink::Sink<_Item> $(, $($bound)*)* {
+            type Error = <$t as futures_sink::Sink<_Item>>::Error;
+
+            delegate_sink!(inner, _Item);
+        }
+    };
+    (@trait Debug $name:ident < $($arg:ident),* > ($t:ty) $(where $($bound:tt)*)*) => {
+        impl<$($arg),*> core::fmt::Debug for $name<$($arg),*> where $t: core::fmt::Debug $(, $($bound)*)* {
+            fn fmt(&self, f: &mut core::fmt::Formatter<'_>) -> core::fmt::Result {
+                core::fmt::Debug::fmt(&self.inner, f)
+            }
+        }
+    };
+    (@trait AccessInner[$inner:ty, ($($ind:tt)*)] $name:ident < $($arg:ident),* > ($t:ty) $(where $($bound:tt)*)*) => {
+        impl<$($arg),*> $name<$($arg),*> $(where $($bound)*)* {
+            delegate_access_inner!(inner, $inner, ($($ind)*));
+        }
+    };
+    (@trait New[|$($param:ident: $paramt:ty),*| $cons:expr] $name:ident < $($arg:ident),* > ($t:ty) $(where $($bound:tt)*)*) => {
+        impl<$($arg),*> $name<$($arg),*> $(where $($bound)*)* {
+            pub(crate) fn new($($param: $paramt),*) -> Self {
+                Self { inner: $cons }
+            }
+        }
+    };
+    ($(#[$attr:meta])* $name:ident<$($arg:ident),*>($t:ty) : $ftrait:ident $([$($targs:tt)*])* $({$($item:tt)*})* $(where $($bound:tt)*)*) => {
+        pin_project_lite::pin_project! {
+            #[must_use = "futures/streams/sinks do nothing unless you `.await` or poll them"]
+            $(#[$attr])*
+            pub struct $name< $($arg),* > $(where $($bound)*)* { #[pin] inner: $t }
+        }
+
+        impl<$($arg),*> $name< $($arg),* > $(where $($bound)*)* {
+            $($($item)*)*
+        }
+
+        delegate_all!(@trait $ftrait $([$($targs)*])* $name<$($arg),*>($t) $(where $($bound)*)*);
+    };
+    ($(#[$attr:meta])* $name:ident<$($arg:ident),*>($t:ty) : $ftrait:ident $([$($ftargs:tt)*])* + $strait:ident $([$($stargs:tt)*])* $(+ $trait:ident $([$($targs:tt)*])*)* $({$($item:tt)*})* $(where $($bound:tt)*)*) => {
+        delegate_all!($(#[$attr])* $name<$($arg),*>($t) : $strait $([$($stargs)*])* $(+ $trait $([$($targs)*])*)* $({$($item)*})* $(where $($bound)*)*);
+
+        delegate_all!(@trait $ftrait $([$($ftargs)*])* $name<$($arg),*>($t) $(where $($bound)*)*);
+    };
+}
+
+pub mod future;
+#[doc(no_inline)]
+pub use crate::future::{Future, FutureExt, TryFuture, TryFutureExt};
+
+pub mod stream;
+#[doc(no_inline)]
+pub use crate::stream::{Stream, StreamExt, TryStream, TryStreamExt};
+
+#[cfg(feature = "sink")]
+#[cfg_attr(docsrs, doc(cfg(feature = "sink")))]
+pub mod sink;
+#[cfg(feature = "sink")]
+#[doc(no_inline)]
+pub use crate::sink::{Sink, SinkExt};
+
+pub mod task;
+
+pub mod never;
+
+#[cfg(feature = "compat")]
+#[cfg_attr(docsrs, doc(cfg(feature = "compat")))]
+pub mod compat;
+
+#[cfg(feature = "io")]
+#[cfg_attr(docsrs, doc(cfg(feature = "io")))]
+#[cfg(feature = "std")]
+pub mod io;
+#[cfg(feature = "io")]
+#[cfg(feature = "std")]
+#[doc(no_inline)]
+pub use crate::io::{
+    AsyncBufRead, AsyncBufReadExt, AsyncRead, AsyncReadExt, AsyncSeek, AsyncSeekExt, AsyncWrite,
+    AsyncWriteExt,
+};
+
+#[cfg(feature = "alloc")]
+pub mod lock;
+
+#[cfg(not(futures_no_atomic_cas))]
+#[cfg(feature = "alloc")]
+mod abortable;
+
+mod fns;
+mod unfold_state;
diff --git a/third_party/rust/futures-util/src/lock/bilock.rs b/third_party/rust/futures-util/src/lock/bilock.rs
new file mode 100644
index 0000000000..2174079c83
--- /dev/null
+++ b/third_party/rust/futures-util/src/lock/bilock.rs
@@ -0,0 +1,279 @@
+//! Futures-powered synchronization primitives.
+
+use alloc::boxed::Box;
+use alloc::sync::Arc;
+use core::cell::UnsafeCell;
+use core::fmt;
+use core::ops::{Deref, DerefMut};
+use core::pin::Pin;
+use core::sync::atomic::AtomicUsize;
+use core::sync::atomic::Ordering::SeqCst;
+#[cfg(feature = "bilock")]
+use futures_core::future::Future;
+use futures_core::task::{Context, Poll, Waker};
+
+/// A type of futures-powered synchronization primitive which is a mutex between
+/// two possible owners.
+///
+/// This primitive is not as generic as a full-blown mutex but is sufficient for
+/// many use cases where there are only two possible owners of a resource. The
+/// implementation of `BiLock` can be more optimized for just the two possible
+/// owners.
+///
+/// Note that it's possible to use this lock through a poll-style interface with
+/// the `poll_lock` method but you can also use it as a future with the `lock`
+/// method that consumes a `BiLock` and returns a future that will resolve when
+/// it's locked.
+///
+/// A `BiLock` is typically used for "split" operations where data which serves
+/// two purposes wants to be split into two to be worked with separately. For
+/// example a TCP stream could be both a reader and a writer or a framing layer
+/// could be both a stream and a sink for messages. A `BiLock` enables splitting
+/// these two and then using each independently in a futures-powered fashion.
+///
+/// This type is only available when the `bilock` feature of this
+/// library is activated.
+#[derive(Debug)]
+#[cfg_attr(docsrs, doc(cfg(feature = "bilock")))]
+pub struct BiLock<T> {
+    arc: Arc<Inner<T>>,
+}
+
+#[derive(Debug)]
+struct Inner<T> {
+    state: AtomicUsize,
+    value: Option<UnsafeCell<T>>,
+}
+
+unsafe impl<T: Send> Send for Inner<T> {}
+unsafe impl<T: Send> Sync for Inner<T> {}
+
+impl<T> BiLock<T> {
+    /// Creates a new `BiLock` protecting the provided data.
+    ///
+    /// Two handles to the lock are returned, and these are the only two handles
+    /// that will ever be available to the lock. These can then be sent to separate
+    /// tasks to be managed there.
+    ///
+    /// The data behind the bilock is considered to be pinned, which allows `Pin`
+    /// references to locked data. However, this means that the locked value
+    /// will only be available through `Pin<&mut T>` (not `&mut T`) unless `T` is `Unpin`.
+    /// Similarly, reuniting the lock and extracting the inner value is only
+    /// possible when `T` is `Unpin`.
+    pub fn new(t: T) -> (Self, Self) {
+        let arc = Arc::new(Inner { state: AtomicUsize::new(0), value: Some(UnsafeCell::new(t)) });
+
+        (Self { arc: arc.clone() }, Self { arc })
+    }
+
+    /// Attempt to acquire this lock, returning `Pending` if it can't be
+    /// acquired.
+    ///
+    /// This function will acquire the lock in a nonblocking fashion, returning
+    /// immediately if the lock is already held. If the lock is successfully
+    /// acquired then `Poll::Ready` is returned with a value that represents
+    /// the locked value (and can be used to access the protected data). The
+    /// lock is unlocked when the returned `BiLockGuard` is dropped.
+    ///
+    /// If the lock is already held then this function will return
+    /// `Poll::Pending`. In this case the current task will also be scheduled
+    /// to receive a notification when the lock would otherwise become
+    /// available.
+    ///
+    /// # Panics
+    ///
+    /// This function will panic if called outside the context of a future's
+    /// task.
+    pub fn poll_lock(&self, cx: &mut Context<'_>) -> Poll<BiLockGuard<'_, T>> {
+        let mut waker = None;
+        loop {
+            match self.arc.state.swap(1, SeqCst) {
+                // Woohoo, we grabbed the lock!
+                0 => return Poll::Ready(BiLockGuard { bilock: self }),
+
+                // Oops, someone else has locked the lock
+                1 => {}
+
+                // A task was previously blocked on this lock, likely our task,
+                // so we need to update that task.
+                n => unsafe {
+                    let mut prev = Box::from_raw(n as *mut Waker);
+                    *prev = cx.waker().clone();
+                    waker = Some(prev);
+                },
+            }
+
+            // type ascription for safety's sake!
+            let me: Box<Waker> = waker.take().unwrap_or_else(|| Box::new(cx.waker().clone()));
+            let me = Box::into_raw(me) as usize;
+
+            match self.arc.state.compare_exchange(1, me, SeqCst, SeqCst) {
+                // The lock is still locked, but we've now parked ourselves, so
+                // just report that we're scheduled to receive a notification.
+                Ok(_) => return Poll::Pending,
+
+                // Oops, looks like the lock was unlocked after our swap above
+                // and before the compare_exchange. Deallocate what we just
+                // allocated and go through the loop again.
+                Err(0) => unsafe {
+                    waker = Some(Box::from_raw(me as *mut Waker));
+                },
+
+                // The top of this loop set the previous state to 1, so if we
+                // failed the CAS above then it's because the previous value was
+                // *not* zero or one. This indicates that a task was blocked,
+                // but we're trying to acquire the lock and there's only one
+                // other reference of the lock, so it should be impossible for
+                // that task to ever block itself.
+                Err(n) => panic!("invalid state: {}", n),
+            }
+        }
+    }
+
+    /// Perform a "blocking lock" of this lock, consuming this lock handle and
+    /// returning a future to the acquired lock.
+    ///
+    /// This function consumes the `BiLock<T>` and returns a sentinel future,
+    /// `BiLockAcquire<T>`. The returned future will resolve to
+    /// `BiLockAcquired<T>` which represents a locked lock similarly to
+    /// `BiLockGuard<T>`.
+    ///
+    /// Note that the returned future will never resolve to an error.
+    #[cfg(feature = "bilock")]
+    #[cfg_attr(docsrs, doc(cfg(feature = "bilock")))]
+    pub fn lock(&self) -> BiLockAcquire<'_, T> {
+        BiLockAcquire { bilock: self }
+    }
+
+    /// Attempts to put the two "halves" of a `BiLock<T>` back together and
+    /// recover the original value. Succeeds only if the two `BiLock<T>`s
+    /// originated from the same call to `BiLock::new`.
+    pub fn reunite(self, other: Self) -> Result<T, ReuniteError<T>>
+    where
+        T: Unpin,
+    {
+        if Arc::ptr_eq(&self.arc, &other.arc) {
+            drop(other);
+            let inner = Arc::try_unwrap(self.arc)
+                .ok()
+                .expect("futures: try_unwrap failed in BiLock<T>::reunite");
+            Ok(unsafe { inner.into_value() })
+        } else {
+            Err(ReuniteError(self, other))
+        }
+    }
+
+    fn unlock(&self) {
+        match self.arc.state.swap(0, SeqCst) {
+            // we've locked the lock, shouldn't be possible for us to see an
+            // unlocked lock.
+            0 => panic!("invalid unlocked state"),
+
+            // Ok, no one else tried to get the lock, we're done.
+            1 => {}
+
+            // Another task has parked themselves on this lock, let's wake them
+            // up as its now their turn.
+            n => unsafe {
+                Box::from_raw(n as *mut Waker).wake();
+            },
+        }
+    }
+}
+
+impl<T: Unpin> Inner<T> {
+    unsafe fn into_value(mut self) -> T {
+        self.value.take().unwrap().into_inner()
+    }
+}
+
+impl<T> Drop for Inner<T> {
+    fn drop(&mut self) {
+        assert_eq!(self.state.load(SeqCst), 0);
+    }
+}
+
+/// Error indicating two `BiLock<T>`s were not two halves of a whole, and
+/// thus could not be `reunite`d.
+#[cfg_attr(docsrs, doc(cfg(feature = "bilock")))]
+pub struct ReuniteError<T>(pub BiLock<T>, pub BiLock<T>);
+
+impl<T> fmt::Debug for ReuniteError<T> {
+    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
+        f.debug_tuple("ReuniteError").field(&"...").finish()
+    }
+}
+
+impl<T> fmt::Display for ReuniteError<T> {
+    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
+        write!(f, "tried to reunite two BiLocks that don't form a pair")
+    }
+}
+
+#[cfg(feature = "std")]
+impl<T: core::any::Any> std::error::Error for ReuniteError<T> {}
+
+/// Returned RAII guard from the `poll_lock` method.
+///
+/// This structure acts as a sentinel to the data in the `BiLock<T>` itself,
+/// implementing `Deref` and `DerefMut` to `T`. When dropped, the lock will be
+/// unlocked.
+#[derive(Debug)]
+#[cfg_attr(docsrs, doc(cfg(feature = "bilock")))]
+pub struct BiLockGuard<'a, T> {
+    bilock: &'a BiLock<T>,
+}
+
+// We allow parallel access to T via Deref, so Sync bound is also needed here.
+unsafe impl<T: Send + Sync> Sync for BiLockGuard<'_, T> {}
+
+impl<T> Deref for BiLockGuard<'_, T> {
+    type Target = T;
+    fn deref(&self) -> &T {
+        unsafe { &*self.bilock.arc.value.as_ref().unwrap().get() }
+    }
+}
+
+impl<T: Unpin> DerefMut for BiLockGuard<'_, T> {
+    fn deref_mut(&mut self) -> &mut T {
+        unsafe { &mut *self.bilock.arc.value.as_ref().unwrap().get() }
+    }
+}
+
+impl<T> BiLockGuard<'_, T> {
+    /// Get a mutable pinned reference to the locked value.
+    pub fn as_pin_mut(&mut self) -> Pin<&mut T> {
+        // Safety: we never allow moving a !Unpin value out of a bilock, nor
+        // allow mutable access to it
+        unsafe { Pin::new_unchecked(&mut *self.bilock.arc.value.as_ref().unwrap().get()) }
+    }
+}
+
+impl<T> Drop for BiLockGuard<'_, T> {
+    fn drop(&mut self) {
+        self.bilock.unlock();
+    }
+}
+
+/// Future returned by `BiLock::lock` which will resolve when the lock is
+/// acquired.
+#[cfg(feature = "bilock")]
+#[cfg_attr(docsrs, doc(cfg(feature = "bilock")))]
+#[must_use = "futures do nothing unless you `.await` or poll them"]
+#[derive(Debug)]
+pub struct BiLockAcquire<'a, T> {
+    bilock: &'a BiLock<T>,
+}
+
+// Pinning is never projected to fields
+#[cfg(feature = "bilock")]
+impl<T> Unpin for BiLockAcquire<'_, T> {}
+
+#[cfg(feature = "bilock")]
+impl<'a, T> Future for BiLockAcquire<'a, T> {
+    type Output = BiLockGuard<'a, T>;
+
+    fn poll(self: Pin<&mut Self>, cx: &mut Context<'_>) -> Poll<Self::Output> {
+        self.bilock.poll_lock(cx)
+    }
+}
diff --git a/third_party/rust/futures-util/src/lock/mod.rs b/third_party/rust/futures-util/src/lock/mod.rs
new file mode 100644
index 0000000000..0be72717c8
--- /dev/null
+++ b/third_party/rust/futures-util/src/lock/mod.rs
@@ -0,0 +1,27 @@
+//! Futures-powered synchronization primitives.
+//!
+//! This module is only available when the `std` or `alloc` feature of this
+//! library is activated, and it is activated by default.
+
+#[cfg(not(futures_no_atomic_cas))]
+#[cfg(any(feature = "sink", feature = "io"))]
+#[cfg(not(feature = "bilock"))]
+pub(crate) use self::bilock::BiLock;
+#[cfg(not(futures_no_atomic_cas))]
+#[cfg(feature = "bilock")]
+#[cfg_attr(docsrs, doc(cfg(feature = "bilock")))]
+pub use self::bilock::{BiLock, BiLockAcquire, BiLockGuard, ReuniteError};
+#[cfg(not(futures_no_atomic_cas))]
+#[cfg(feature = "std")]
+pub use self::mutex::{
+    MappedMutexGuard, Mutex, MutexGuard, MutexLockFuture, OwnedMutexGuard, OwnedMutexLockFuture,
+};
+
+#[cfg(not(futures_no_atomic_cas))]
+#[cfg(any(feature = "bilock", feature = "sink", feature = "io"))]
+#[cfg_attr(docsrs, doc(cfg(feature = "bilock")))]
+#[cfg_attr(not(feature = "bilock"), allow(unreachable_pub))]
+mod bilock;
+#[cfg(not(futures_no_atomic_cas))]
+#[cfg(feature = "std")]
+mod mutex;
diff --git a/third_party/rust/futures-util/src/lock/mutex.rs b/third_party/rust/futures-util/src/lock/mutex.rs
new file mode 100644
index 0000000000..335ad14273
--- /dev/null
+++ b/third_party/rust/futures-util/src/lock/mutex.rs
@@ -0,0 +1,551 @@
+use std::cell::UnsafeCell;
+use std::marker::PhantomData;
+use std::ops::{Deref, DerefMut};
+use std::pin::Pin;
+use std::sync::atomic::{AtomicUsize, Ordering};
+use std::sync::{Arc, Mutex as StdMutex};
+use std::{fmt, mem};
+
+use slab::Slab;
+
+use futures_core::future::{FusedFuture, Future};
+use futures_core::task::{Context, Poll, Waker};
+
+/// A futures-aware mutex.
+///
+/// # Fairness
+///
+/// This mutex provides no fairness guarantees. Tasks may not acquire the mutex
+/// in the order that they requested the lock, and it's possible for a single task
+/// which repeatedly takes the lock to starve other tasks, which may be left waiting
+/// indefinitely.
+pub struct Mutex<T: ?Sized> {
+    state: AtomicUsize,
+    waiters: StdMutex<Slab<Waiter>>,
+    value: UnsafeCell<T>,
+}
+
+impl<T: ?Sized> fmt::Debug for Mutex<T> {
+    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
+        let state = self.state.load(Ordering::SeqCst);
+        f.debug_struct("Mutex")
+            .field("is_locked", &((state & IS_LOCKED) != 0))
+            .field("has_waiters", &((state & HAS_WAITERS) != 0))
+            .finish()
+    }
+}
+
+impl<T> From<T> for Mutex<T> {
+    fn from(t: T) -> Self {
+        Self::new(t)
+    }
+}
+
+impl<T: Default> Default for Mutex<T> {
+    fn default() -> Self {
+        Self::new(Default::default())
+    }
+}
+
+enum Waiter {
+    Waiting(Waker),
+    Woken,
+}
+
+impl Waiter {
+    fn register(&mut self, waker: &Waker) {
+        match self {
+            Self::Waiting(w) if waker.will_wake(w) => {}
+            _ => *self = Self::Waiting(waker.clone()),
+        }
+    }
+
+    fn wake(&mut self) {
+        match mem::replace(self, Self::Woken) {
+            Self::Waiting(waker) => waker.wake(),
+            Self::Woken => {}
+        }
+    }
+}
+
+const IS_LOCKED: usize = 1 << 0;
+const HAS_WAITERS: usize = 1 << 1;
+
+impl<T> Mutex<T> {
+    /// Creates a new futures-aware mutex.
+    pub fn new(t: T) -> Self {
+        Self {
+            state: AtomicUsize::new(0),
+            waiters: StdMutex::new(Slab::new()),
+            value: UnsafeCell::new(t),
+        }
+    }
+
+    /// Consumes this mutex, returning the underlying data.
+    ///
+    /// # Examples
+    ///
+    /// ```
+    /// use futures::lock::Mutex;
+    ///
+    /// let mutex = Mutex::new(0);
+    /// assert_eq!(mutex.into_inner(), 0);
+    /// ```
+    pub fn into_inner(self) -> T {
+        self.value.into_inner()
+    }
+}
+
+impl<T: ?Sized> Mutex<T> {
+    /// Attempt to acquire the lock immediately.
+    ///
+    /// If the lock is currently held, this will return `None`.
+    pub fn try_lock(&self) -> Option<MutexGuard<'_, T>> {
+        let old_state = self.state.fetch_or(IS_LOCKED, Ordering::Acquire);
+        if (old_state & IS_LOCKED) == 0 {
+            Some(MutexGuard { mutex: self })
+        } else {
+            None
+        }
+    }
+
+    /// Attempt to acquire the lock immediately.
+    ///
+    /// If the lock is currently held, this will return `None`.
+    pub fn try_lock_owned(self: &Arc<Self>) -> Option<OwnedMutexGuard<T>> {
+        let old_state = self.state.fetch_or(IS_LOCKED, Ordering::Acquire);
+        if (old_state & IS_LOCKED) == 0 {
+            Some(OwnedMutexGuard { mutex: self.clone() })
+        } else {
+            None
+        }
+    }
+
+    /// Acquire the lock asynchronously.
+    ///
+    /// This method returns a future that will resolve once the lock has been
+    /// successfully acquired.
+    pub fn lock(&self) -> MutexLockFuture<'_, T> {
+        MutexLockFuture { mutex: Some(self), wait_key: WAIT_KEY_NONE }
+    }
+
+    /// Acquire the lock asynchronously.
+    ///
+    /// This method returns a future that will resolve once the lock has been
+    /// successfully acquired.
+    pub fn lock_owned(self: Arc<Self>) -> OwnedMutexLockFuture<T> {
+        OwnedMutexLockFuture { mutex: Some(self), wait_key: WAIT_KEY_NONE }
+    }
+
+    /// Returns a mutable reference to the underlying data.
+    ///
+    /// Since this call borrows the `Mutex` mutably, no actual locking needs to
+    /// take place -- the mutable borrow statically guarantees no locks exist.
+    ///
+    /// # Examples
+    ///
+    /// ```
+    /// # futures::executor::block_on(async {
+    /// use futures::lock::Mutex;
+    ///
+    /// let mut mutex = Mutex::new(0);
+    /// *mutex.get_mut() = 10;
+    /// assert_eq!(*mutex.lock().await, 10);
+    /// # });
+    /// ```
+    pub fn get_mut(&mut self) -> &mut T {
+        // We know statically that there are no other references to `self`, so
+        // there's no need to lock the inner mutex.
+        unsafe { &mut *self.value.get() }
+    }
+
+    fn remove_waker(&self, wait_key: usize, wake_another: bool) {
+        if wait_key != WAIT_KEY_NONE {
+            let mut waiters = self.waiters.lock().unwrap();
+            match waiters.remove(wait_key) {
+                Waiter::Waiting(_) => {}
+                Waiter::Woken => {
+                    // We were awoken, but then dropped before we could
+                    // wake up to acquire the lock. Wake up another
+                    // waiter.
+                    if wake_another {
+                        if let Some((_i, waiter)) = waiters.iter_mut().next() {
+                            waiter.wake();
+                        }
+                    }
+                }
+            }
+            if waiters.is_empty() {
+                self.state.fetch_and(!HAS_WAITERS, Ordering::Relaxed); // released by mutex unlock
+            }
+        }
+    }
+
+    // Unlocks the mutex. Called by MutexGuard and MappedMutexGuard when they are
+    // dropped.
+    fn unlock(&self) {
+        let old_state = self.state.fetch_and(!IS_LOCKED, Ordering::AcqRel);
+        if (old_state & HAS_WAITERS) != 0 {
+            let mut waiters = self.waiters.lock().unwrap();
+            if let Some((_i, waiter)) = waiters.iter_mut().next() {
+                waiter.wake();
+            }
+        }
+    }
+}
+
+// Sentinel for when no slot in the `Slab` has been dedicated to this object.
+const WAIT_KEY_NONE: usize = usize::MAX;
+
+/// A future which resolves when the target mutex has been successfully acquired, owned version.
+pub struct OwnedMutexLockFuture<T: ?Sized> {
+    // `None` indicates that the mutex was successfully acquired.
+    mutex: Option<Arc<Mutex<T>>>,
+    wait_key: usize,
+}
+
+impl<T: ?Sized> fmt::Debug for OwnedMutexLockFuture<T> {
+    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
+        f.debug_struct("OwnedMutexLockFuture")
+            .field("was_acquired", &self.mutex.is_none())
+            .field("mutex", &self.mutex)
+            .field(
+                "wait_key",
+                &(if self.wait_key == WAIT_KEY_NONE { None } else { Some(self.wait_key) }),
+            )
+            .finish()
+    }
+}
+
+impl<T: ?Sized> FusedFuture for OwnedMutexLockFuture<T> {
+    fn is_terminated(&self) -> bool {
+        self.mutex.is_none()
+    }
+}
+
+impl<T: ?Sized> Future for OwnedMutexLockFuture<T> {
+    type Output = OwnedMutexGuard<T>;
+
+    fn poll(self: Pin<&mut Self>, cx: &mut Context<'_>) -> Poll<Self::Output> {
+        let this = self.get_mut();
+
+        let mutex = this.mutex.as_ref().expect("polled OwnedMutexLockFuture after completion");
+
+        if let Some(lock) = mutex.try_lock_owned() {
+            mutex.remove_waker(this.wait_key, false);
+            this.mutex = None;
+            return Poll::Ready(lock);
+        }
+
+        {
+            let mut waiters = mutex.waiters.lock().unwrap();
+            if this.wait_key == WAIT_KEY_NONE {
+                this.wait_key = waiters.insert(Waiter::Waiting(cx.waker().clone()));
+                if waiters.len() == 1 {
+                    mutex.state.fetch_or(HAS_WAITERS, Ordering::Relaxed); // released by mutex unlock
+                }
+            } else {
+                waiters[this.wait_key].register(cx.waker());
+            }
+        }
+
+        // Ensure that we haven't raced `MutexGuard::drop`'s unlock path by
+        // attempting to acquire the lock again.
+        if let Some(lock) = mutex.try_lock_owned() {
+            mutex.remove_waker(this.wait_key, false);
+            this.mutex = None;
+            return Poll::Ready(lock);
+        }
+
+        Poll::Pending
+    }
+}
+
+impl<T: ?Sized> Drop for OwnedMutexLockFuture<T> {
+    fn drop(&mut self) {
+        if let Some(mutex) = self.mutex.as_ref() {
+            // This future was dropped before it acquired the mutex.
+            //
+            // Remove ourselves from the map, waking up another waiter if we
+            // had been awoken to acquire the lock.
+            mutex.remove_waker(self.wait_key, true);
+        }
+    }
+}
+
+/// An RAII guard returned by the `lock_owned` and `try_lock_owned` methods.
+/// When this structure is dropped (falls out of scope), the lock will be
+/// unlocked.
+pub struct OwnedMutexGuard<T: ?Sized> {
+    mutex: Arc<Mutex<T>>,
+}
+
+impl<T: ?Sized + fmt::Debug> fmt::Debug for OwnedMutexGuard<T> {
+    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
+        f.debug_struct("OwnedMutexGuard")
+            .field("value", &&**self)
+            .field("mutex", &self.mutex)
+            .finish()
+    }
+}
+
+impl<T: ?Sized> Drop for OwnedMutexGuard<T> {
+    fn drop(&mut self) {
+        self.mutex.unlock()
+    }
+}
+
+impl<T: ?Sized> Deref for OwnedMutexGuard<T> {
+    type Target = T;
+    fn deref(&self) -> &T {
+        unsafe { &*self.mutex.value.get() }
+    }
+}
+
+impl<T: ?Sized> DerefMut for OwnedMutexGuard<T> {
+    fn deref_mut(&mut self) -> &mut T {
+        unsafe { &mut *self.mutex.value.get() }
+    }
+}
+
+/// A future which resolves when the target mutex has been successfully acquired.
+pub struct MutexLockFuture<'a, T: ?Sized> {
+    // `None` indicates that the mutex was successfully acquired.
+    mutex: Option<&'a Mutex<T>>,
+    wait_key: usize,
+}
+
+impl<T: ?Sized> fmt::Debug for MutexLockFuture<'_, T> {
+    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
+        f.debug_struct("MutexLockFuture")
+            .field("was_acquired", &self.mutex.is_none())
+            .field("mutex", &self.mutex)
+            .field(
+                "wait_key",
+                &(if self.wait_key == WAIT_KEY_NONE { None } else { Some(self.wait_key) }),
+            )
+            .finish()
+    }
+}
+
+impl<T: ?Sized> FusedFuture for MutexLockFuture<'_, T> {
+    fn is_terminated(&self) -> bool {
+        self.mutex.is_none()
+    }
+}
+
+impl<'a, T: ?Sized> Future for MutexLockFuture<'a, T> {
+    type Output = MutexGuard<'a, T>;
+
+    fn poll(mut self: Pin<&mut Self>, cx: &mut Context<'_>) -> Poll<Self::Output> {
+        let mutex = self.mutex.expect("polled MutexLockFuture after completion");
+
+        if let Some(lock) = mutex.try_lock() {
+            mutex.remove_waker(self.wait_key, false);
+            self.mutex = None;
+            return Poll::Ready(lock);
+        }
+
+        {
+            let mut waiters = mutex.waiters.lock().unwrap();
+            if self.wait_key == WAIT_KEY_NONE {
+                self.wait_key = waiters.insert(Waiter::Waiting(cx.waker().clone()));
+                if waiters.len() == 1 {
+                    mutex.state.fetch_or(HAS_WAITERS, Ordering::Relaxed); // released by mutex unlock
+                }
+            } else {
+                waiters[self.wait_key].register(cx.waker());
+            }
+        }
+
+        // Ensure that we haven't raced `MutexGuard::drop`'s unlock path by
+        // attempting to acquire the lock again.
+        if let Some(lock) = mutex.try_lock() {
+            mutex.remove_waker(self.wait_key, false);
+            self.mutex = None;
+            return Poll::Ready(lock);
+        }
+
+        Poll::Pending
+    }
+}
+
+impl<T: ?Sized> Drop for MutexLockFuture<'_, T> {
+    fn drop(&mut self) {
+        if let Some(mutex) = self.mutex {
+            // This future was dropped before it acquired the mutex.
+            //
+            // Remove ourselves from the map, waking up another waiter if we
+            // had been awoken to acquire the lock.
+            mutex.remove_waker(self.wait_key, true);
+        }
+    }
+}
+
+/// An RAII guard returned by the `lock` and `try_lock` methods.
+/// When this structure is dropped (falls out of scope), the lock will be
+/// unlocked.
+pub struct MutexGuard<'a, T: ?Sized> {
+    mutex: &'a Mutex<T>,
+}
+
+impl<'a, T: ?Sized> MutexGuard<'a, T> {
+    /// Returns a locked view over a portion of the locked data.
+    ///
+    /// # Example
+    ///
+    /// ```
+    /// # futures::executor::block_on(async {
+    /// use futures::lock::{Mutex, MutexGuard};
+    ///
+    /// let data = Mutex::new(Some("value".to_string()));
+    /// {
+    ///     let locked_str = MutexGuard::map(data.lock().await, |opt| opt.as_mut().unwrap());
+    ///     assert_eq!(&*locked_str, "value");
+    /// }
+    /// # });
+    /// ```
+    #[inline]
+    pub fn map<U: ?Sized, F>(this: Self, f: F) -> MappedMutexGuard<'a, T, U>
+    where
+        F: FnOnce(&mut T) -> &mut U,
+    {
+        let mutex = this.mutex;
+        let value = f(unsafe { &mut *this.mutex.value.get() });
+        // Don't run the `drop` method for MutexGuard. The ownership of the underlying
+        // locked state is being moved to the returned MappedMutexGuard.
+        mem::forget(this);
+        MappedMutexGuard { mutex, value, _marker: PhantomData }
+    }
+}
+
+impl<T: ?Sized + fmt::Debug> fmt::Debug for MutexGuard<'_, T> {
+    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
+        f.debug_struct("MutexGuard").field("value", &&**self).field("mutex", &self.mutex).finish()
+    }
+}
+
+impl<T: ?Sized> Drop for MutexGuard<'_, T> {
+    fn drop(&mut self) {
+        self.mutex.unlock()
+    }
+}
+
+impl<T: ?Sized> Deref for MutexGuard<'_, T> {
+    type Target = T;
+    fn deref(&self) -> &T {
+        unsafe { &*self.mutex.value.get() }
+    }
+}
+
+impl<T: ?Sized> DerefMut for MutexGuard<'_, T> {
+    fn deref_mut(&mut self) -> &mut T {
+        unsafe { &mut *self.mutex.value.get() }
+    }
+}
+
+/// An RAII guard returned by the `MutexGuard::map` and `MappedMutexGuard::map` methods.
+/// When this structure is dropped (falls out of scope), the lock will be unlocked.
+pub struct MappedMutexGuard<'a, T: ?Sized, U: ?Sized> {
+    mutex: &'a Mutex<T>,
+    value: *mut U,
+    _marker: PhantomData<&'a mut U>,
+}
+
+impl<'a, T: ?Sized, U: ?Sized> MappedMutexGuard<'a, T, U> {
+    /// Returns a locked view over a portion of the locked data.
+    ///
+    /// # Example
+    ///
+    /// ```
+    /// # futures::executor::block_on(async {
+    /// use futures::lock::{MappedMutexGuard, Mutex, MutexGuard};
+    ///
+    /// let data = Mutex::new(Some("value".to_string()));
+    /// {
+    ///     let locked_str = MutexGuard::map(data.lock().await, |opt| opt.as_mut().unwrap());
+    ///     let locked_char = MappedMutexGuard::map(locked_str, |s| s.get_mut(0..1).unwrap());
+    ///     assert_eq!(&*locked_char, "v");
+    /// }
+    /// # });
+    /// ```
+    #[inline]
+    pub fn map<V: ?Sized, F>(this: Self, f: F) -> MappedMutexGuard<'a, T, V>
+    where
+        F: FnOnce(&mut U) -> &mut V,
+    {
+        let mutex = this.mutex;
+        let value = f(unsafe { &mut *this.value });
+        // Don't run the `drop` method for MappedMutexGuard. The ownership of the underlying
+        // locked state is being moved to the returned MappedMutexGuard.
+        mem::forget(this);
+        MappedMutexGuard { mutex, value, _marker: PhantomData }
+    }
+}
+
+impl<T: ?Sized, U: ?Sized + fmt::Debug> fmt::Debug for MappedMutexGuard<'_, T, U> {
+    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
+        f.debug_struct("MappedMutexGuard")
+            .field("value", &&**self)
+            .field("mutex", &self.mutex)
+            .finish()
+    }
+}
+
+impl<T: ?Sized, U: ?Sized> Drop for MappedMutexGuard<'_, T, U> {
+    fn drop(&mut self) {
+        self.mutex.unlock()
+    }
+}
+
+impl<T: ?Sized, U: ?Sized> Deref for MappedMutexGuard<'_, T, U> {
+    type Target = U;
+    fn deref(&self) -> &U {
+        unsafe { &*self.value }
+    }
+}
+
+impl<T: ?Sized, U: ?Sized> DerefMut for MappedMutexGuard<'_, T, U> {
+    fn deref_mut(&mut self) -> &mut U {
+        unsafe { &mut *self.value }
+    }
+}
+
+// Mutexes can be moved freely between threads and acquired on any thread so long
+// as the inner value can be safely sent between threads.
+unsafe impl<T: ?Sized + Send> Send for Mutex<T> {}
+unsafe impl<T: ?Sized + Send> Sync for Mutex<T> {}
+
+// It's safe to switch which thread the acquire is being attempted on so long as
+// `T` can be accessed on that thread.
+unsafe impl<T: ?Sized + Send> Send for MutexLockFuture<'_, T> {}
+
+// doesn't have any interesting `&self` methods (only Debug)
+unsafe impl<T: ?Sized> Sync for MutexLockFuture<'_, T> {}
+
+// It's safe to switch which thread the acquire is being attempted on so long as
+// `T` can be accessed on that thread.
+unsafe impl<T: ?Sized + Send> Send for OwnedMutexLockFuture<T> {}
+
+// doesn't have any interesting `&self` methods (only Debug)
+unsafe impl<T: ?Sized> Sync for OwnedMutexLockFuture<T> {}
+
+// Safe to send since we don't track any thread-specific details-- the inner
+// lock is essentially spinlock-equivalent (attempt to flip an atomic bool)
+unsafe impl<T: ?Sized + Send> Send for MutexGuard<'_, T> {}
+unsafe impl<T: ?Sized + Sync> Sync for MutexGuard<'_, T> {}
+
+unsafe impl<T: ?Sized + Send> Send for OwnedMutexGuard<T> {}
+unsafe impl<T: ?Sized + Sync> Sync for OwnedMutexGuard<T> {}
+
+unsafe impl<T: ?Sized + Send, U: ?Sized + Send> Send for MappedMutexGuard<'_, T, U> {}
+unsafe impl<T: ?Sized + Sync, U: ?Sized + Sync> Sync for MappedMutexGuard<'_, T, U> {}
+
+#[test]
+fn test_mutex_guard_debug_not_recurse() {
+    let mutex = Mutex::new(42);
+    let guard = mutex.try_lock().unwrap();
+    let _ = format!("{:?}", guard);
+    let guard = MutexGuard::map(guard, |n| n);
+    let _ = format!("{:?}", guard);
+}
diff --git a/third_party/rust/futures-util/src/never.rs b/third_party/rust/futures-util/src/never.rs
new file mode 100644
index 0000000000..e811f97df7
--- /dev/null
+++ b/third_party/rust/futures-util/src/never.rs
@@ -0,0 +1,18 @@
+//! This module contains the `Never` type.
+//!
+//! Values of this type can never be created and will never exist.
+
+/// A type with no possible values.
+///
+/// This is used to indicate values which can never be created, such as the
+/// error type of infallible futures.
+///
+/// This type is a stable equivalent to the `!` type from `std`.
+///
+/// This is currently an alias for [`std::convert::Infallible`], but in
+/// the future it may be an alias for [`!`][never].
+/// See ["Future compatibility" section of `std::convert::Infallible`][infallible] for more.
+///
+/// [never]: https://doc.rust-lang.org/nightly/std/primitive.never.html
+/// [infallible]: https://doc.rust-lang.org/nightly/std/convert/enum.Infallible.html#future-compatibility
+pub type Never = core::convert::Infallible;
diff --git a/third_party/rust/futures-util/src/sink/buffer.rs b/third_party/rust/futures-util/src/sink/buffer.rs
new file mode 100644
index 0000000000..4aa6c36033
--- /dev/null
+++ b/third_party/rust/futures-util/src/sink/buffer.rs
@@ -0,0 +1,105 @@
+use alloc::collections::VecDeque;
+use core::pin::Pin;
+use futures_core::ready;
+use futures_core::stream::{FusedStream, Stream};
+use futures_core::task::{Context, Poll};
+use futures_sink::Sink;
+use pin_project_lite::pin_project;
+
+pin_project! {
+    /// Sink for the [`buffer`](super::SinkExt::buffer) method.
+    #[derive(Debug)]
+    #[must_use = "sinks do nothing unless polled"]
+    pub struct Buffer<Si, Item> {
+        #[pin]
+        sink: Si,
+        buf: VecDeque<Item>,
+
+        // Track capacity separately from the `VecDeque`, which may be rounded up
+        capacity: usize,
+    }
+}
+
+impl<Si: Sink<Item>, Item> Buffer<Si, Item> {
+    pub(super) fn new(sink: Si, capacity: usize) -> Self {
+        Self { sink, buf: VecDeque::with_capacity(capacity), capacity }
+    }
+
+    delegate_access_inner!(sink, Si, ());
+
+    fn try_empty_buffer(self: Pin<&mut Self>, cx: &mut Context<'_>) -> Poll<Result<(), Si::Error>> {
+        let mut this = self.project();
+        ready!(this.sink.as_mut().poll_ready(cx))?;
+        while let Some(item) = this.buf.pop_front() {
+            this.sink.as_mut().start_send(item)?;
+            if !this.buf.is_empty() {
+                ready!(this.sink.as_mut().poll_ready(cx))?;
+            }
+        }
+        Poll::Ready(Ok(()))
+    }
+}
+
+// Forwarding impl of Stream from the underlying sink
+impl<S, Item> Stream for Buffer<S, Item>
+where
+    S: Sink<Item> + Stream,
+{
+    type Item = S::Item;
+
+    fn poll_next(self: Pin<&mut Self>, cx: &mut Context<'_>) -> Poll<Option<S::Item>> {
+        self.project().sink.poll_next(cx)
+    }
+
+    fn size_hint(&self) -> (usize, Option<usize>) {
+        self.sink.size_hint()
+    }
+}
+
+impl<S, Item> FusedStream for Buffer<S, Item>
+where
+    S: Sink<Item> + FusedStream,
+{
+    fn is_terminated(&self) -> bool {
+        self.sink.is_terminated()
+    }
+}
+
+impl<Si: Sink<Item>, Item> Sink<Item> for Buffer<Si, Item> {
+    type Error = Si::Error;
+
+    fn poll_ready(mut self: Pin<&mut Self>, cx: &mut Context<'_>) -> Poll<Result<(), Self::Error>> {
+        if self.capacity == 0 {
+            return self.project().sink.poll_ready(cx);
+        }
+
+        let _ = self.as_mut().try_empty_buffer(cx)?;
+
+        if self.buf.len() >= self.capacity {
+            Poll::Pending
+        } else {
+            Poll::Ready(Ok(()))
+        }
+    }
+
+    fn start_send(self: Pin<&mut Self>, item: Item) -> Result<(), Self::Error> {
+        if self.capacity == 0 {
+            self.project().sink.start_send(item)
+        } else {
+            self.project().buf.push_back(item);
+            Ok(())
+        }
+    }
+
+    fn poll_flush(mut self: Pin<&mut Self>, cx: &mut Context<'_>) -> Poll<Result<(), Self::Error>> {
+        ready!(self.as_mut().try_empty_buffer(cx))?;
+        debug_assert!(self.buf.is_empty());
+        self.project().sink.poll_flush(cx)
+    }
+
+    fn poll_close(mut self: Pin<&mut Self>, cx: &mut Context<'_>) -> Poll<Result<(), Self::Error>> {
+        ready!(self.as_mut().try_empty_buffer(cx))?;
+        debug_assert!(self.buf.is_empty());
+        self.project().sink.poll_close(cx)
+    }
+}
diff --git a/third_party/rust/futures-util/src/sink/close.rs b/third_party/rust/futures-util/src/sink/close.rs
new file mode 100644
index 0000000000..43eea74b0f
--- /dev/null
+++ b/third_party/rust/futures-util/src/sink/close.rs
@@ -0,0 +1,32 @@
+use core::marker::PhantomData;
+use core::pin::Pin;
+use futures_core::future::Future;
+use futures_core::task::{Context, Poll};
+use futures_sink::Sink;
+
+/// Future for the [`close`](super::SinkExt::close) method.
+#[derive(Debug)]
+#[must_use = "futures do nothing unless you `.await` or poll them"]
+pub struct Close<'a, Si: ?Sized, Item> {
+    sink: &'a mut Si,
+    _phantom: PhantomData<fn(Item)>,
+}
+
+impl<Si: Unpin + ?Sized, Item> Unpin for Close<'_, Si, Item> {}
+
+/// A future that completes when the sink has finished closing.
+///
+/// The sink itself is returned after closing is complete.
+impl<'a, Si: Sink<Item> + Unpin + ?Sized, Item> Close<'a, Si, Item> {
+    pub(super) fn new(sink: &'a mut Si) -> Self {
+        Self { sink, _phantom: PhantomData }
+    }
+}
+
+impl<Si: Sink<Item> + Unpin + ?Sized, Item> Future for Close<'_, Si, Item> {
+    type Output = Result<(), Si::Error>;
+
+    fn poll(mut self: Pin<&mut Self>, cx: &mut Context<'_>) -> Poll<Self::Output> {
+        Pin::new(&mut self.sink).poll_close(cx)
+    }
+}
diff --git a/third_party/rust/futures-util/src/sink/drain.rs b/third_party/rust/futures-util/src/sink/drain.rs
new file mode 100644
index 0000000000..1a5480c0d6
--- /dev/null
+++ b/third_party/rust/futures-util/src/sink/drain.rs
@@ -0,0 +1,59 @@
+use super::assert_sink;
+use crate::never::Never;
+use core::marker::PhantomData;
+use core::pin::Pin;
+use futures_core::task::{Context, Poll};
+use futures_sink::Sink;
+
+/// Sink for the [`drain`] function.
+#[derive(Debug)]
+#[must_use = "sinks do nothing unless polled"]
+pub struct Drain<T> {
+    marker: PhantomData<T>,
+}
+
+/// Create a sink that will just discard all items given to it.
+///
+/// Similar to [`io::Sink`](::std::io::Sink).
+///
+/// # Examples
+///
+/// ```
+/// # futures::executor::block_on(async {
+/// use futures::sink::{self, SinkExt};
+///
+/// let mut drain = sink::drain();
+/// drain.send(5).await?;
+/// # Ok::<(), futures::never::Never>(()) }).unwrap();
+/// ```
+pub fn drain<T>() -> Drain<T> {
+    assert_sink::<T, Never, _>(Drain { marker: PhantomData })
+}
+
+impl<T> Unpin for Drain<T> {}
+
+impl<T> Clone for Drain<T> {
+    fn clone(&self) -> Self {
+        drain()
+    }
+}
+
+impl<T> Sink<T> for Drain<T> {
+    type Error = Never;
+
+    fn poll_ready(self: Pin<&mut Self>, _cx: &mut Context<'_>) -> Poll<Result<(), Self::Error>> {
+        Poll::Ready(Ok(()))
+    }
+
+    fn start_send(self: Pin<&mut Self>, _item: T) -> Result<(), Self::Error> {
+        Ok(())
+    }
+
+    fn poll_flush(self: Pin<&mut Self>, _cx: &mut Context<'_>) -> Poll<Result<(), Self::Error>> {
+        Poll::Ready(Ok(()))
+    }
+
+    fn poll_close(self: Pin<&mut Self>, _cx: &mut Context<'_>) -> Poll<Result<(), Self::Error>> {
+        Poll::Ready(Ok(()))
+    }
+}
diff --git a/third_party/rust/futures-util/src/sink/err_into.rs b/third_party/rust/futures-util/src/sink/err_into.rs
new file mode 100644
index 0000000000..a64d1337ba
--- /dev/null
+++ b/third_party/rust/futures-util/src/sink/err_into.rs
@@ -0,0 +1,57 @@
+use crate::sink::{SinkExt, SinkMapErr};
+use futures_core::stream::{FusedStream, Stream};
+use futures_sink::Sink;
+use pin_project_lite::pin_project;
+
+pin_project! {
+    /// Sink for the [`sink_err_into`](super::SinkExt::sink_err_into) method.
+    #[derive(Debug)]
+    #[must_use = "sinks do nothing unless polled"]
+    pub struct SinkErrInto<Si: Sink<Item>, Item, E> {
+        #[pin]
+        sink: SinkMapErr<Si, fn(Si::Error) -> E>,
+    }
+}
+
+impl<Si, E, Item> SinkErrInto<Si, Item, E>
+where
+    Si: Sink<Item>,
+    Si::Error: Into<E>,
+{
+    pub(super) fn new(sink: Si) -> Self {
+        Self { sink: SinkExt::sink_map_err(sink, Into::into) }
+    }
+
+    delegate_access_inner!(sink, Si, (.));
+}
+
+impl<Si, Item, E> Sink<Item> for SinkErrInto<Si, Item, E>
+where
+    Si: Sink<Item>,
+    Si::Error: Into<E>,
+{
+    type Error = E;
+
+    delegate_sink!(sink, Item);
+}
+
+// Forwarding impl of Stream from the underlying sink
+impl<S, Item, E> Stream for SinkErrInto<S, Item, E>
+where
+    S: Sink<Item> + Stream,
+    S::Error: Into<E>,
+{
+    type Item = S::Item;
+
+    delegate_stream!(sink);
+}
+
+impl<S, Item, E> FusedStream for SinkErrInto<S, Item, E>
+where
+    S: Sink<Item> + FusedStream,
+    S::Error: Into<E>,
+{
+    fn is_terminated(&self) -> bool {
+        self.sink.is_terminated()
+    }
+}
diff --git a/third_party/rust/futures-util/src/sink/fanout.rs b/third_party/rust/futures-util/src/sink/fanout.rs
new file mode 100644
index 0000000000..fe2038f27f
--- /dev/null
+++ b/third_party/rust/futures-util/src/sink/fanout.rs
@@ -0,0 +1,111 @@
+use core::fmt::{Debug, Formatter, Result as FmtResult};
+use core::pin::Pin;
+use futures_core::task::{Context, Poll};
+use futures_sink::Sink;
+use pin_project_lite::pin_project;
+
+pin_project! {
+    /// Sink that clones incoming items and forwards them to two sinks at the same time.
+    ///
+    /// Backpressure from any downstream sink propagates up, which means that this sink
+    /// can only process items as fast as its _slowest_ downstream sink.
+    #[must_use = "sinks do nothing unless polled"]
+    pub struct Fanout<Si1, Si2> {
+        #[pin]
+        sink1: Si1,
+        #[pin]
+        sink2: Si2
+    }
+}
+
+impl<Si1, Si2> Fanout<Si1, Si2> {
+    pub(super) fn new(sink1: Si1, sink2: Si2) -> Self {
+        Self { sink1, sink2 }
+    }
+
+    /// Get a shared reference to the inner sinks.
+    pub fn get_ref(&self) -> (&Si1, &Si2) {
+        (&self.sink1, &self.sink2)
+    }
+
+    /// Get a mutable reference to the inner sinks.
+    pub fn get_mut(&mut self) -> (&mut Si1, &mut Si2) {
+        (&mut self.sink1, &mut self.sink2)
+    }
+
+    /// Get a pinned mutable reference to the inner sinks.
+    pub fn get_pin_mut(self: Pin<&mut Self>) -> (Pin<&mut Si1>, Pin<&mut Si2>) {
+        let this = self.project();
+        (this.sink1, this.sink2)
+    }
+
+    /// Consumes this combinator, returning the underlying sinks.
+    ///
+    /// Note that this may discard intermediate state of this combinator,
+    /// so care should be taken to avoid losing resources when this is called.
+    pub fn into_inner(self) -> (Si1, Si2) {
+        (self.sink1, self.sink2)
+    }
+}
+
+impl<Si1: Debug, Si2: Debug> Debug for Fanout<Si1, Si2> {
+    fn fmt(&self, f: &mut Formatter<'_>) -> FmtResult {
+        f.debug_struct("Fanout").field("sink1", &self.sink1).field("sink2", &self.sink2).finish()
+    }
+}
+
+impl<Si1, Si2, Item> Sink<Item> for Fanout<Si1, Si2>
+where
+    Si1: Sink<Item>,
+    Item: Clone,
+    Si2: Sink<Item, Error = Si1::Error>,
+{
+    type Error = Si1::Error;
+
+    fn poll_ready(self: Pin<&mut Self>, cx: &mut Context<'_>) -> Poll<Result<(), Self::Error>> {
+        let this = self.project();
+
+        let sink1_ready = this.sink1.poll_ready(cx)?.is_ready();
+        let sink2_ready = this.sink2.poll_ready(cx)?.is_ready();
+        let ready = sink1_ready && sink2_ready;
+        if ready {
+            Poll::Ready(Ok(()))
+        } else {
+            Poll::Pending
+        }
+    }
+
+    fn start_send(self: Pin<&mut Self>, item: Item) -> Result<(), Self::Error> {
+        let this = self.project();
+
+        this.sink1.start_send(item.clone())?;
+        this.sink2.start_send(item)?;
+        Ok(())
+    }
+
+    fn poll_flush(self: Pin<&mut Self>, cx: &mut Context<'_>) -> Poll<Result<(), Self::Error>> {
+        let this = self.project();
+
+        let sink1_ready = this.sink1.poll_flush(cx)?.is_ready();
+        let sink2_ready = this.sink2.poll_flush(cx)?.is_ready();
+        let ready = sink1_ready && sink2_ready;
+        if ready {
+            Poll::Ready(Ok(()))
+        } else {
+            Poll::Pending
+        }
+    }
+
+    fn poll_close(self: Pin<&mut Self>, cx: &mut Context<'_>) -> Poll<Result<(), Self::Error>> {
+        let this = self.project();
+
+        let sink1_ready = this.sink1.poll_close(cx)?.is_ready();
+        let sink2_ready = this.sink2.poll_close(cx)?.is_ready();
+        let ready = sink1_ready && sink2_ready;
+        if ready {
+            Poll::Ready(Ok(()))
+        } else {
+            Poll::Pending
+        }
+    }
+}
diff --git a/third_party/rust/futures-util/src/sink/feed.rs b/third_party/rust/futures-util/src/sink/feed.rs
new file mode 100644
index 0000000000..6701f7a1b4
--- /dev/null
+++ b/third_party/rust/futures-util/src/sink/feed.rs
@@ -0,0 +1,43 @@
+use core::pin::Pin;
+use futures_core::future::Future;
+use futures_core::ready;
+use futures_core::task::{Context, Poll};
+use futures_sink::Sink;
+
+/// Future for the [`feed`](super::SinkExt::feed) method.
+#[derive(Debug)]
+#[must_use = "futures do nothing unless you `.await` or poll them"]
+pub struct Feed<'a, Si: ?Sized, Item> {
+    sink: &'a mut Si,
+    item: Option<Item>,
+}
+
+// Pinning is never projected to children
+impl<Si: Unpin + ?Sized, Item> Unpin for Feed<'_, Si, Item> {}
+
+impl<'a, Si: Sink<Item> + Unpin + ?Sized, Item> Feed<'a, Si, Item> {
+    pub(super) fn new(sink: &'a mut Si, item: Item) -> Self {
+        Feed { sink, item: Some(item) }
+    }
+
+    pub(super) fn sink_pin_mut(&mut self) -> Pin<&mut Si> {
+        Pin::new(self.sink)
+    }
+
+    pub(super) fn is_item_pending(&self) -> bool {
+        self.item.is_some()
+    }
+}
+
+impl<Si: Sink<Item> + Unpin + ?Sized, Item> Future for Feed<'_, Si, Item> {
+    type Output = Result<(), Si::Error>;
+
+    fn poll(self: Pin<&mut Self>, cx: &mut Context<'_>) -> Poll<Self::Output> {
+        let this = self.get_mut();
+        let mut sink = Pin::new(&mut this.sink);
+        ready!(sink.as_mut().poll_ready(cx))?;
+        let item = this.item.take().expect("polled Feed after completion");
+        sink.as_mut().start_send(item)?;
+        Poll::Ready(Ok(()))
+    }
+}
diff --git a/third_party/rust/futures-util/src/sink/flush.rs b/third_party/rust/futures-util/src/sink/flush.rs
new file mode 100644
index 0000000000..35a8372de7
--- /dev/null
+++ b/third_party/rust/futures-util/src/sink/flush.rs
@@ -0,0 +1,36 @@
+use core::marker::PhantomData;
+use core::pin::Pin;
+use futures_core::future::Future;
+use futures_core::task::{Context, Poll};
+use futures_sink::Sink;
+
+/// Future for the [`flush`](super::SinkExt::flush) method.
+#[derive(Debug)]
+#[must_use = "futures do nothing unless you `.await` or poll them"]
+pub struct Flush<'a, Si: ?Sized, Item> {
+    sink: &'a mut Si,
+    _phantom: PhantomData<fn(Item)>,
+}
+
+// Pin is never projected to a field.
+impl<Si: Unpin + ?Sized, Item> Unpin for Flush<'_, Si, Item> {}
+
+/// A future that completes when the sink has finished processing all
+/// pending requests.
+///
+/// The sink itself is returned after flushing is complete; this adapter is
+/// intended to be used when you want to stop sending to the sink until
+/// all current requests are processed.
+impl<'a, Si: Sink<Item> + Unpin + ?Sized, Item> Flush<'a, Si, Item> {
+    pub(super) fn new(sink: &'a mut Si) -> Self {
+        Self { sink, _phantom: PhantomData }
+    }
+}
+
+impl<Si: Sink<Item> + Unpin + ?Sized, Item> Future for Flush<'_, Si, Item> {
+    type Output = Result<(), Si::Error>;
+
+    fn poll(mut self: Pin<&mut Self>, cx: &mut Context<'_>) -> Poll<Self::Output> {
+        Pin::new(&mut self.sink).poll_flush(cx)
+    }
+}
diff --git a/third_party/rust/futures-util/src/sink/map_err.rs b/third_party/rust/futures-util/src/sink/map_err.rs
new file mode 100644
index 0000000000..9d2ab7b24b
--- /dev/null
+++ b/third_party/rust/futures-util/src/sink/map_err.rs
@@ -0,0 +1,65 @@
+use core::pin::Pin;
+use futures_core::stream::{FusedStream, Stream};
+use futures_core::task::{Context, Poll};
+use futures_sink::Sink;
+use pin_project_lite::pin_project;
+
+pin_project! {
+    /// Sink for the [`sink_map_err`](super::SinkExt::sink_map_err) method.
+    #[derive(Debug, Clone)]
+    #[must_use = "sinks do nothing unless polled"]
+    pub struct SinkMapErr<Si, F> {
+        #[pin]
+        sink: Si,
+        f: Option<F>,
+    }
+}
+
+impl<Si, F> SinkMapErr<Si, F> {
+    pub(super) fn new(sink: Si, f: F) -> Self {
+        Self { sink, f: Some(f) }
+    }
+
+    delegate_access_inner!(sink, Si, ());
+
+    fn take_f(self: Pin<&mut Self>) -> F {
+        self.project().f.take().expect("polled MapErr after completion")
+    }
+}
+
+impl<Si, F, E, Item> Sink<Item> for SinkMapErr<Si, F>
+where
+    Si: Sink<Item>,
+    F: FnOnce(Si::Error) -> E,
+{
+    type Error = E;
+
+    fn poll_ready(mut self: Pin<&mut Self>, cx: &mut Context<'_>) -> Poll<Result<(), Self::Error>> {
+        self.as_mut().project().sink.poll_ready(cx).map_err(|e| self.as_mut().take_f()(e))
+    }
+
+    fn start_send(mut self: Pin<&mut Self>, item: Item) -> Result<(), Self::Error> {
+        self.as_mut().project().sink.start_send(item).map_err(|e| self.as_mut().take_f()(e))
+    }
+
+    fn poll_flush(mut self: Pin<&mut Self>, cx: &mut Context<'_>) -> Poll<Result<(), Self::Error>> {
+        self.as_mut().project().sink.poll_flush(cx).map_err(|e| self.as_mut().take_f()(e))
+    }
+
+    fn poll_close(mut self: Pin<&mut Self>, cx: &mut Context<'_>) -> Poll<Result<(), Self::Error>> {
+        self.as_mut().project().sink.poll_close(cx).map_err(|e| self.as_mut().take_f()(e))
+    }
+}
+
+// Forwarding impl of Stream from the underlying sink
+impl<S: Stream, F> Stream for SinkMapErr<S, F> {
+    type Item = S::Item;
+
+    delegate_stream!(sink);
+}
+
+impl<S: FusedStream, F> FusedStream for SinkMapErr<S, F> {
+    fn is_terminated(&self) -> bool {
+        self.sink.is_terminated()
+    }
+}
diff --git a/third_party/rust/futures-util/src/sink/mod.rs b/third_party/rust/futures-util/src/sink/mod.rs
new file mode 100644
index 0000000000..147e9adc93
--- /dev/null
+++ b/third_party/rust/futures-util/src/sink/mod.rs
@@ -0,0 +1,344 @@
+//! Asynchronous sinks.
+//!
+//! This module contains:
+//!
+//! - The [`Sink`] trait, which allows you to asynchronously write data.
+//! - The [`SinkExt`] trait, which provides adapters for chaining and composing
+//!   sinks.
+
+use crate::future::{assert_future, Either};
+use core::pin::Pin;
+use futures_core::future::Future;
+use futures_core::stream::{Stream, TryStream};
+use futures_core::task::{Context, Poll};
+
+#[cfg(feature = "compat")]
+use crate::compat::CompatSink;
+
+pub use futures_sink::Sink;
+
+mod close;
+pub use self::close::Close;
+
+mod drain;
+pub use self::drain::{drain, Drain};
+
+mod fanout;
+pub use self::fanout::Fanout;
+
+mod feed;
+pub use self::feed::Feed;
+
+mod flush;
+pub use self::flush::Flush;
+
+mod err_into;
+pub use self::err_into::SinkErrInto;
+
+mod map_err;
+pub use self::map_err::SinkMapErr;
+
+mod send;
+pub use self::send::Send;
+
+mod send_all;
+pub use self::send_all::SendAll;
+
+mod unfold;
+pub use self::unfold::{unfold, Unfold};
+
+mod with;
+pub use self::with::With;
+
+mod with_flat_map;
+pub use self::with_flat_map::WithFlatMap;
+
+#[cfg(feature = "alloc")]
+mod buffer;
+#[cfg(feature = "alloc")]
+pub use self::buffer::Buffer;
+
+impl<T: ?Sized, Item> SinkExt<Item> for T where T: Sink<Item> {}
+
+/// An extension trait for `Sink`s that provides a variety of convenient
+/// combinator functions.
+pub trait SinkExt<Item>: Sink<Item> {
+    /// Composes a function *in front of* the sink.
+    ///
+    /// This adapter produces a new sink that passes each value through the
+    /// given function `f` before sending it to `self`.
+    ///
+    /// To process each value, `f` produces a *future*, which is then polled to
+    /// completion before passing its result down to the underlying sink. If the
+    /// future produces an error, that error is returned by the new sink.
+    ///
+    /// Note that this function consumes the given sink, returning a wrapped
+    /// version, much like `Iterator::map`.
+    fn with<U, Fut, F, E>(self, f: F) -> With<Self, Item, U, Fut, F>
+    where
+        F: FnMut(U) -> Fut,
+        Fut: Future<Output = Result<Item, E>>,
+        E: From<Self::Error>,
+        Self: Sized,
+    {
+        assert_sink::<U, E, _>(With::new(self, f))
+    }
+
+    /// Composes a function *in front of* the sink.
+    ///
+    /// This adapter produces a new sink that passes each value through the
+    /// given function `f` before sending it to `self`.
+    ///
+    /// To process each value, `f` produces a *stream*, of which each value
+    /// is passed to the underlying sink. A new value will not be accepted until
+    /// the stream has been drained
+    ///
+    /// Note that this function consumes the given sink, returning a wrapped
+    /// version, much like `Iterator::flat_map`.
+    ///
+    /// # Examples
+    ///
+    /// ```
+    /// # futures::executor::block_on(async {
+    /// use futures::channel::mpsc;
+    /// use futures::sink::SinkExt;
+    /// use futures::stream::{self, StreamExt};
+    ///
+    /// let (tx, rx) = mpsc::channel(5);
+    ///
+    /// let mut tx = tx.with_flat_map(|x| {
+    ///     stream::iter(vec![Ok(42); x])
+    /// });
+    ///
+    /// tx.send(5).await.unwrap();
+    /// drop(tx);
+    /// let received: Vec<i32> = rx.collect().await;
+    /// assert_eq!(received, vec![42, 42, 42, 42, 42]);
+    /// # });
+    /// ```
+    fn with_flat_map<U, St, F>(self, f: F) -> WithFlatMap<Self, Item, U, St, F>
+    where
+        F: FnMut(U) -> St,
+        St: Stream<Item = Result<Item, Self::Error>>,
+        Self: Sized,
+    {
+        assert_sink::<U, Self::Error, _>(WithFlatMap::new(self, f))
+    }
+
+    /*
+    fn with_map<U, F>(self, f: F) -> WithMap<Self, U, F>
+        where F: FnMut(U) -> Self::SinkItem,
+              Self: Sized;
+
+    fn with_filter<F>(self, f: F) -> WithFilter<Self, F>
+        where F: FnMut(Self::SinkItem) -> bool,
+              Self: Sized;
+
+    fn with_filter_map<U, F>(self, f: F) -> WithFilterMap<Self, U, F>
+        where F: FnMut(U) -> Option<Self::SinkItem>,
+              Self: Sized;
+     */
+
+    /// Transforms the error returned by the sink.
+    fn sink_map_err<E, F>(self, f: F) -> SinkMapErr<Self, F>
+    where
+        F: FnOnce(Self::Error) -> E,
+        Self: Sized,
+    {
+        assert_sink::<Item, E, _>(SinkMapErr::new(self, f))
+    }
+
+    /// Map this sink's error to a different error type using the `Into` trait.
+    ///
+    /// If wanting to map errors of a `Sink + Stream`, use `.sink_err_into().err_into()`.
+    fn sink_err_into<E>(self) -> err_into::SinkErrInto<Self, Item, E>
+    where
+        Self: Sized,
+        Self::Error: Into<E>,
+    {
+        assert_sink::<Item, E, _>(SinkErrInto::new(self))
+    }
+
+    /// Adds a fixed-size buffer to the current sink.
+    ///
+    /// The resulting sink will buffer up to `capacity` items when the
+    /// underlying sink is unwilling to accept additional items. Calling `flush`
+    /// on the buffered sink will attempt to both empty the buffer and complete
+    /// processing on the underlying sink.
+    ///
+    /// Note that this function consumes the given sink, returning a wrapped
+    /// version, much like `Iterator::map`.
+    ///
+    /// This method is only available when the `std` or `alloc` feature of this
+    /// library is activated, and it is activated by default.
+    #[cfg(feature = "alloc")]
+    fn buffer(self, capacity: usize) -> Buffer<Self, Item>
+    where
+        Self: Sized,
+    {
+        assert_sink::<Item, Self::Error, _>(Buffer::new(self, capacity))
+    }
+
+    /// Close the sink.
+    fn close(&mut self) -> Close<'_, Self, Item>
+    where
+        Self: Unpin,
+    {
+        assert_future::<Result<(), Self::Error>, _>(Close::new(self))
+    }
+
+    /// Fanout items to multiple sinks.
+    ///
+    /// This adapter clones each incoming item and forwards it to both this as well as
+    /// the other sink at the same time.
+    fn fanout<Si>(self, other: Si) -> Fanout<Self, Si>
+    where
+        Self: Sized,
+        Item: Clone,
+        Si: Sink<Item, Error = Self::Error>,
+    {
+        assert_sink::<Item, Self::Error, _>(Fanout::new(self, other))
+    }
+
+    /// Flush the sink, processing all pending items.
+    ///
+    /// This adapter is intended to be used when you want to stop sending to the sink
+    /// until all current requests are processed.
+    fn flush(&mut self) -> Flush<'_, Self, Item>
+    where
+        Self: Unpin,
+    {
+        assert_future::<Result<(), Self::Error>, _>(Flush::new(self))
+    }
+
+    /// A future that completes after the given item has been fully processed
+    /// into the sink, including flushing.
+    ///
+    /// Note that, **because of the flushing requirement, it is usually better
+    /// to batch together items to send via `feed` or `send_all`,
+    /// rather than flushing between each item.**
+    fn send(&mut self, item: Item) -> Send<'_, Self, Item>
+    where
+        Self: Unpin,
+    {
+        assert_future::<Result<(), Self::Error>, _>(Send::new(self, item))
+    }
+
+    /// A future that completes after the given item has been received
+    /// by the sink.
+    ///
+    /// Unlike `send`, the returned future does not flush the sink.
+    /// It is the caller's responsibility to ensure all pending items
+    /// are processed, which can be done via `flush` or `close`.
+    fn feed(&mut self, item: Item) -> Feed<'_, Self, Item>
+    where
+        Self: Unpin,
+    {
+        assert_future::<Result<(), Self::Error>, _>(Feed::new(self, item))
+    }
+
+    /// A future that completes after the given stream has been fully processed
+    /// into the sink, including flushing.
+    ///
+    /// This future will drive the stream to keep producing items until it is
+    /// exhausted, sending each item to the sink. It will complete once both the
+    /// stream is exhausted, the sink has received all items, and the sink has
+    /// been flushed. Note that the sink is **not** closed. If the stream produces
+    /// an error, that error will be returned by this future without flushing the sink.
+    ///
+    /// Doing `sink.send_all(stream)` is roughly equivalent to
+    /// `stream.forward(sink)`. The returned future will exhaust all items from
+    /// `stream` and send them to `self`.
+    fn send_all<'a, St>(&'a mut self, stream: &'a mut St) -> SendAll<'a, Self, St>
+    where
+        St: TryStream<Ok = Item, Error = Self::Error> + Stream + Unpin + ?Sized,
+        // St: Stream<Item = Result<Item, Self::Error>> + Unpin + ?Sized,
+        Self: Unpin,
+    {
+        // TODO: type mismatch resolving `<St as Stream>::Item == std::result::Result<Item, <Self as futures_sink::Sink<Item>>::Error>`
+        // assert_future::<Result<(), Self::Error>, _>(SendAll::new(self, stream))
+        SendAll::new(self, stream)
+    }
+
+    /// Wrap this sink in an `Either` sink, making it the left-hand variant
+    /// of that `Either`.
+    ///
+    /// This can be used in combination with the `right_sink` method to write `if`
+    /// statements that evaluate to different streams in different branches.
+    fn left_sink<Si2>(self) -> Either<Self, Si2>
+    where
+        Si2: Sink<Item, Error = Self::Error>,
+        Self: Sized,
+    {
+        assert_sink::<Item, Self::Error, _>(Either::Left(self))
+    }
+
+    /// Wrap this stream in an `Either` stream, making it the right-hand variant
+    /// of that `Either`.
+    ///
+    /// This can be used in combination with the `left_sink` method to write `if`
+    /// statements that evaluate to different streams in different branches.
+    fn right_sink<Si1>(self) -> Either<Si1, Self>
+    where
+        Si1: Sink<Item, Error = Self::Error>,
+        Self: Sized,
+    {
+        assert_sink::<Item, Self::Error, _>(Either::Right(self))
+    }
+
+    /// Wraps a [`Sink`] into a sink compatible with libraries using
+    /// futures 0.1 `Sink`. Requires the `compat` feature to be enabled.
+    #[cfg(feature = "compat")]
+    #[cfg_attr(docsrs, doc(cfg(feature = "compat")))]
+    fn compat(self) -> CompatSink<Self, Item>
+    where
+        Self: Sized + Unpin,
+    {
+        CompatSink::new(self)
+    }
+
+    /// A convenience method for calling [`Sink::poll_ready`] on [`Unpin`]
+    /// sink types.
+    fn poll_ready_unpin(&mut self, cx: &mut Context<'_>) -> Poll<Result<(), Self::Error>>
+    where
+        Self: Unpin,
+    {
+        Pin::new(self).poll_ready(cx)
+    }
+
+    /// A convenience method for calling [`Sink::start_send`] on [`Unpin`]
+    /// sink types.
+    fn start_send_unpin(&mut self, item: Item) -> Result<(), Self::Error>
+    where
+        Self: Unpin,
+    {
+        Pin::new(self).start_send(item)
+    }
+
+    /// A convenience method for calling [`Sink::poll_flush`] on [`Unpin`]
+    /// sink types.
+    fn poll_flush_unpin(&mut self, cx: &mut Context<'_>) -> Poll<Result<(), Self::Error>>
+    where
+        Self: Unpin,
+    {
+        Pin::new(self).poll_flush(cx)
+    }
+
+    /// A convenience method for calling [`Sink::poll_close`] on [`Unpin`]
+    /// sink types.
+    fn poll_close_unpin(&mut self, cx: &mut Context<'_>) -> Poll<Result<(), Self::Error>>
+    where
+        Self: Unpin,
+    {
+        Pin::new(self).poll_close(cx)
+    }
+}
+
+// Just a helper function to ensure the sinks we're returning all have the
+// right implementations.
+pub(crate) fn assert_sink<T, E, S>(sink: S) -> S
+where
+    S: Sink<T, Error = E>,
+{
+    sink
+}
diff --git a/third_party/rust/futures-util/src/sink/send.rs b/third_party/rust/futures-util/src/sink/send.rs
new file mode 100644
index 0000000000..6d21f33fe4
--- /dev/null
+++ b/third_party/rust/futures-util/src/sink/send.rs
@@ -0,0 +1,41 @@
+use super::Feed;
+use core::pin::Pin;
+use futures_core::future::Future;
+use futures_core::ready;
+use futures_core::task::{Context, Poll};
+use futures_sink::Sink;
+
+/// Future for the [`send`](super::SinkExt::send) method.
+#[derive(Debug)]
+#[must_use = "futures do nothing unless you `.await` or poll them"]
+pub struct Send<'a, Si: ?Sized, Item> {
+    feed: Feed<'a, Si, Item>,
+}
+
+// Pinning is never projected to children
+impl<Si: Unpin + ?Sized, Item> Unpin for Send<'_, Si, Item> {}
+
+impl<'a, Si: Sink<Item> + Unpin + ?Sized, Item> Send<'a, Si, Item> {
+    pub(super) fn new(sink: &'a mut Si, item: Item) -> Self {
+        Self { feed: Feed::new(sink, item) }
+    }
+}
+
+impl<Si: Sink<Item> + Unpin + ?Sized, Item> Future for Send<'_, Si, Item> {
+    type Output = Result<(), Si::Error>;
+
+    fn poll(mut self: Pin<&mut Self>, cx: &mut Context<'_>) -> Poll<Self::Output> {
+        let this = &mut *self;
+
+        if this.feed.is_item_pending() {
+            ready!(Pin::new(&mut this.feed).poll(cx))?;
+            debug_assert!(!this.feed.is_item_pending());
+        }
+
+        // we're done sending the item, but want to block on flushing the
+        // sink
+        ready!(this.feed.sink_pin_mut().poll_flush(cx))?;
+
+        Poll::Ready(Ok(()))
+    }
+}
diff --git a/third_party/rust/futures-util/src/sink/send_all.rs b/third_party/rust/futures-util/src/sink/send_all.rs
new file mode 100644
index 0000000000..1302dd2148
--- /dev/null
+++ b/third_party/rust/futures-util/src/sink/send_all.rs
@@ -0,0 +1,100 @@
+use crate::stream::{Fuse, StreamExt, TryStreamExt};
+use core::fmt;
+use core::pin::Pin;
+use futures_core::future::Future;
+use futures_core::ready;
+use futures_core::stream::{Stream, TryStream};
+use futures_core::task::{Context, Poll};
+use futures_sink::Sink;
+
+/// Future for the [`send_all`](super::SinkExt::send_all) method.
+#[allow(explicit_outlives_requirements)] // https://github.com/rust-lang/rust/issues/60993
+#[must_use = "futures do nothing unless you `.await` or poll them"]
+pub struct SendAll<'a, Si, St>
+where
+    Si: ?Sized,
+    St: ?Sized + TryStream,
+{
+    sink: &'a mut Si,
+    stream: Fuse<&'a mut St>,
+    buffered: Option<St::Ok>,
+}
+
+impl<Si, St> fmt::Debug for SendAll<'_, Si, St>
+where
+    Si: fmt::Debug + ?Sized,
+    St: fmt::Debug + ?Sized + TryStream,
+    St::Ok: fmt::Debug,
+{
+    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
+        f.debug_struct("SendAll")
+            .field("sink", &self.sink)
+            .field("stream", &self.stream)
+            .field("buffered", &self.buffered)
+            .finish()
+    }
+}
+
+// Pinning is never projected to any fields
+impl<Si, St> Unpin for SendAll<'_, Si, St>
+where
+    Si: Unpin + ?Sized,
+    St: TryStream + Unpin + ?Sized,
+{
+}
+
+impl<'a, Si, St, Ok, Error> SendAll<'a, Si, St>
+where
+    Si: Sink<Ok, Error = Error> + Unpin + ?Sized,
+    St: TryStream<Ok = Ok, Error = Error> + Stream + Unpin + ?Sized,
+{
+    pub(super) fn new(sink: &'a mut Si, stream: &'a mut St) -> Self {
+        Self { sink, stream: stream.fuse(), buffered: None }
+    }
+
+    fn try_start_send(
+        &mut self,
+        cx: &mut Context<'_>,
+        item: St::Ok,
+    ) -> Poll<Result<(), Si::Error>> {
+        debug_assert!(self.buffered.is_none());
+        match Pin::new(&mut self.sink).poll_ready(cx)? {
+            Poll::Ready(()) => Poll::Ready(Pin::new(&mut self.sink).start_send(item)),
+            Poll::Pending => {
+                self.buffered = Some(item);
+                Poll::Pending
+            }
+        }
+    }
+}
+
+impl<Si, St, Ok, Error> Future for SendAll<'_, Si, St>
+where
+    Si: Sink<Ok, Error = Error> + Unpin + ?Sized,
+    St: Stream<Item = Result<Ok, Error>> + Unpin + ?Sized,
+{
+    type Output = Result<(), Error>;
+
+    fn poll(mut self: Pin<&mut Self>, cx: &mut Context<'_>) -> Poll<Self::Output> {
+        let this = &mut *self;
+        // If we've got an item buffered already, we need to write it to the
+        // sink before we can do anything else
+        if let Some(item) = this.buffered.take() {
+            ready!(this.try_start_send(cx, item))?
+        }
+
+        loop {
+            match this.stream.try_poll_next_unpin(cx)? {
+                Poll::Ready(Some(item)) => ready!(this.try_start_send(cx, item))?,
+                Poll::Ready(None) => {
+                    ready!(Pin::new(&mut this.sink).poll_flush(cx))?;
+                    return Poll::Ready(Ok(()));
+                }
+                Poll::Pending => {
+                    ready!(Pin::new(&mut this.sink).poll_flush(cx))?;
+                    return Poll::Pending;
+                }
+            }
+        }
+    }
+}
diff --git a/third_party/rust/futures-util/src/sink/unfold.rs b/third_party/rust/futures-util/src/sink/unfold.rs
new file mode 100644
index 0000000000..330a068c31
--- /dev/null
+++ b/third_party/rust/futures-util/src/sink/unfold.rs
@@ -0,0 +1,86 @@
+use super::assert_sink;
+use crate::unfold_state::UnfoldState;
+use core::{future::Future, pin::Pin};
+use futures_core::ready;
+use futures_core::task::{Context, Poll};
+use futures_sink::Sink;
+use pin_project_lite::pin_project;
+
+pin_project! {
+    /// Sink for the [`unfold`] function.
+    #[derive(Debug)]
+    #[must_use = "sinks do nothing unless polled"]
+    pub struct Unfold<T, F, R> {
+        function: F,
+        #[pin]
+        state: UnfoldState<T, R>,
+    }
+}
+
+/// Create a sink from a function which processes one item at a time.
+///
+/// # Examples
+///
+/// ```
+/// # futures::executor::block_on(async {
+/// use futures::sink::{self, SinkExt};
+///
+/// let unfold = sink::unfold(0, |mut sum, i: i32| {
+///     async move {
+///         sum += i;
+///         eprintln!("{}", i);
+///         Ok::<_, futures::never::Never>(sum)
+///     }
+/// });
+/// futures::pin_mut!(unfold);
+/// unfold.send(5).await?;
+/// # Ok::<(), futures::never::Never>(()) }).unwrap();
+/// ```
+pub fn unfold<T, F, R, Item, E>(init: T, function: F) -> Unfold<T, F, R>
+where
+    F: FnMut(T, Item) -> R,
+    R: Future<Output = Result<T, E>>,
+{
+    assert_sink::<Item, E, _>(Unfold { function, state: UnfoldState::Value { value: init } })
+}
+
+impl<T, F, R, Item, E> Sink<Item> for Unfold<T, F, R>
+where
+    F: FnMut(T, Item) -> R,
+    R: Future<Output = Result<T, E>>,
+{
+    type Error = E;
+
+    fn poll_ready(self: Pin<&mut Self>, cx: &mut Context<'_>) -> Poll<Result<(), Self::Error>> {
+        self.poll_flush(cx)
+    }
+
+    fn start_send(self: Pin<&mut Self>, item: Item) -> Result<(), Self::Error> {
+        let mut this = self.project();
+        let future = match this.state.as_mut().take_value() {
+            Some(value) => (this.function)(value, item),
+            None => panic!("start_send called without poll_ready being called first"),
+        };
+        this.state.set(UnfoldState::Future { future });
+        Ok(())
+    }
+
+    fn poll_flush(self: Pin<&mut Self>, cx: &mut Context<'_>) -> Poll<Result<(), Self::Error>> {
+        let mut this = self.project();
+        Poll::Ready(if let Some(future) = this.state.as_mut().project_future() {
+            match ready!(future.poll(cx)) {
+                Ok(state) => {
+                    this.state.set(UnfoldState::Value { value: state });
+                    Ok(())
+                }
+                Err(err) => Err(err),
+            }
+        } else {
+            Ok(())
+        })
+    }
+
+    fn poll_close(self: Pin<&mut Self>, cx: &mut Context<'_>) -> Poll<Result<(), Self::Error>> {
+        self.poll_flush(cx)
+    }
+}
diff --git a/third_party/rust/futures-util/src/sink/with.rs b/third_party/rust/futures-util/src/sink/with.rs
new file mode 100644
index 0000000000..86d3dcc7b8
--- /dev/null
+++ b/third_party/rust/futures-util/src/sink/with.rs
@@ -0,0 +1,134 @@
+use core::fmt;
+use core::marker::PhantomData;
+use core::pin::Pin;
+use futures_core::future::Future;
+use futures_core::ready;
+use futures_core::stream::Stream;
+use futures_core::task::{Context, Poll};
+use futures_sink::Sink;
+use pin_project_lite::pin_project;
+
+pin_project! {
+    /// Sink for the [`with`](super::SinkExt::with) method.
+    #[must_use = "sinks do nothing unless polled"]
+    pub struct With<Si, Item, U, Fut, F> {
+        #[pin]
+        sink: Si,
+        f: F,
+        #[pin]
+        state: Option<Fut>,
+        _phantom: PhantomData<fn(U) -> Item>,
+    }
+}
+
+impl<Si, Item, U, Fut, F> fmt::Debug for With<Si, Item, U, Fut, F>
+where
+    Si: fmt::Debug,
+    Fut: fmt::Debug,
+{
+    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
+        f.debug_struct("With").field("sink", &self.sink).field("state", &self.state).finish()
+    }
+}
+
+impl<Si, Item, U, Fut, F> With<Si, Item, U, Fut, F>
+where
+    Si: Sink<Item>,
+    F: FnMut(U) -> Fut,
+    Fut: Future,
+{
+    pub(super) fn new<E>(sink: Si, f: F) -> Self
+    where
+        Fut: Future<Output = Result<Item, E>>,
+        E: From<Si::Error>,
+    {
+        Self { state: None, sink, f, _phantom: PhantomData }
+    }
+}
+
+impl<Si, Item, U, Fut, F> Clone for With<Si, Item, U, Fut, F>
+where
+    Si: Clone,
+    F: Clone,
+    Fut: Clone,
+{
+    fn clone(&self) -> Self {
+        Self {
+            state: self.state.clone(),
+            sink: self.sink.clone(),
+            f: self.f.clone(),
+            _phantom: PhantomData,
+        }
+    }
+}
+
+// Forwarding impl of Stream from the underlying sink
+impl<S, Item, U, Fut, F> Stream for With<S, Item, U, Fut, F>
+where
+    S: Stream + Sink<Item>,
+    F: FnMut(U) -> Fut,
+    Fut: Future,
+{
+    type Item = S::Item;
+
+    delegate_stream!(sink);
+}
+
+impl<Si, Item, U, Fut, F, E> With<Si, Item, U, Fut, F>
+where
+    Si: Sink<Item>,
+    F: FnMut(U) -> Fut,
+    Fut: Future<Output = Result<Item, E>>,
+    E: From<Si::Error>,
+{
+    delegate_access_inner!(sink, Si, ());
+
+    /// Completes the processing of previous item if any.
+    fn poll(self: Pin<&mut Self>, cx: &mut Context<'_>) -> Poll<Result<(), E>> {
+        let mut this = self.project();
+
+        let item = match this.state.as_mut().as_pin_mut() {
+            None => return Poll::Ready(Ok(())),
+            Some(fut) => ready!(fut.poll(cx))?,
+        };
+        this.state.set(None);
+        this.sink.start_send(item)?;
+        Poll::Ready(Ok(()))
+    }
+}
+
+impl<Si, Item, U, Fut, F, E> Sink<U> for With<Si, Item, U, Fut, F>
+where
+    Si: Sink<Item>,
+    F: FnMut(U) -> Fut,
+    Fut: Future<Output = Result<Item, E>>,
+    E: From<Si::Error>,
+{
+    type Error = E;
+
+    fn poll_ready(mut self: Pin<&mut Self>, cx: &mut Context<'_>) -> Poll<Result<(), Self::Error>> {
+        ready!(self.as_mut().poll(cx))?;
+        ready!(self.project().sink.poll_ready(cx)?);
+        Poll::Ready(Ok(()))
+    }
+
+    fn start_send(self: Pin<&mut Self>, item: U) -> Result<(), Self::Error> {
+        let mut this = self.project();
+
+        assert!(this.state.is_none());
+        this.state.set(Some((this.f)(item)));
+        Ok(())
+    }
+
+    fn poll_flush(mut self: Pin<&mut Self>, cx: &mut Context<'_>) -> Poll<Result<(), Self::Error>> {
+        ready!(self.as_mut().poll(cx))?;
+        ready!(self.project().sink.poll_flush(cx)?);
+        Poll::Ready(Ok(()))
+    }
+
+    fn poll_close(mut self: Pin<&mut Self>, cx: &mut Context<'_>) -> Poll<Result<(), Self::Error>> {
+        ready!(self.as_mut().poll(cx))?;
+        ready!(self.project().sink.poll_close(cx)?);
+        Poll::Ready(Ok(()))
+    }
+}
diff --git a/third_party/rust/futures-util/src/sink/with_flat_map.rs b/third_party/rust/futures-util/src/sink/with_flat_map.rs
new file mode 100644
index 0000000000..2ae877a24b
--- /dev/null
+++ b/third_party/rust/futures-util/src/sink/with_flat_map.rs
@@ -0,0 +1,127 @@
+use core::fmt;
+use core::marker::PhantomData;
+use core::pin::Pin;
+use futures_core::ready;
+use futures_core::stream::{FusedStream, Stream};
+use futures_core::task::{Context, Poll};
+use futures_sink::Sink;
+use pin_project_lite::pin_project;
+
+pin_project! {
+    /// Sink for the [`with_flat_map`](super::SinkExt::with_flat_map) method.
+    #[must_use = "sinks do nothing unless polled"]
+    pub struct WithFlatMap<Si, Item, U, St, F> {
+        #[pin]
+        sink: Si,
+        f: F,
+        #[pin]
+        stream: Option<St>,
+        buffer: Option<Item>,
+        _marker: PhantomData<fn(U)>,
+    }
+}
+
+impl<Si, Item, U, St, F> fmt::Debug for WithFlatMap<Si, Item, U, St, F>
+where
+    Si: fmt::Debug,
+    St: fmt::Debug,
+    Item: fmt::Debug,
+{
+    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
+        f.debug_struct("WithFlatMap")
+            .field("sink", &self.sink)
+            .field("stream", &self.stream)
+            .field("buffer", &self.buffer)
+            .finish()
+    }
+}
+
+impl<Si, Item, U, St, F> WithFlatMap<Si, Item, U, St, F>
+where
+    Si: Sink<Item>,
+    F: FnMut(U) -> St,
+    St: Stream<Item = Result<Item, Si::Error>>,
+{
+    pub(super) fn new(sink: Si, f: F) -> Self {
+        Self { sink, f, stream: None, buffer: None, _marker: PhantomData }
+    }
+
+    delegate_access_inner!(sink, Si, ());
+
+    fn try_empty_stream(self: Pin<&mut Self>, cx: &mut Context<'_>) -> Poll<Result<(), Si::Error>> {
+        let mut this = self.project();
+
+        if this.buffer.is_some() {
+            ready!(this.sink.as_mut().poll_ready(cx))?;
+            let item = this.buffer.take().unwrap();
+            this.sink.as_mut().start_send(item)?;
+        }
+        if let Some(mut some_stream) = this.stream.as_mut().as_pin_mut() {
+            while let Some(item) = ready!(some_stream.as_mut().poll_next(cx)?) {
+                match this.sink.as_mut().poll_ready(cx)? {
+                    Poll::Ready(()) => this.sink.as_mut().start_send(item)?,
+                    Poll::Pending => {
+                        *this.buffer = Some(item);
+                        return Poll::Pending;
+                    }
+                };
+            }
+        }
+        this.stream.set(None);
+        Poll::Ready(Ok(()))
+    }
+}
+
+// Forwarding impl of Stream from the underlying sink
+impl<S, Item, U, St, F> Stream for WithFlatMap<S, Item, U, St, F>
+where
+    S: Stream + Sink<Item>,
+    F: FnMut(U) -> St,
+    St: Stream<Item = Result<Item, S::Error>>,
+{
+    type Item = S::Item;
+
+    delegate_stream!(sink);
+}
+
+impl<S, Item, U, St, F> FusedStream for WithFlatMap<S, Item, U, St, F>
+where
+    S: FusedStream + Sink<Item>,
+    F: FnMut(U) -> St,
+    St: Stream<Item = Result<Item, S::Error>>,
+{
+    fn is_terminated(&self) -> bool {
+        self.sink.is_terminated()
+    }
+}
+
+impl<Si, Item, U, St, F> Sink<U> for WithFlatMap<Si, Item, U, St, F>
+where
+    Si: Sink<Item>,
+    F: FnMut(U) -> St,
+    St: Stream<Item = Result<Item, Si::Error>>,
+{
+    type Error = Si::Error;
+
+    fn poll_ready(self: Pin<&mut Self>, cx: &mut Context<'_>) -> Poll<Result<(), Self::Error>> {
+        self.try_empty_stream(cx)
+    }
+
+    fn start_send(self: Pin<&mut Self>, item: U) -> Result<(), Self::Error> {
+        let mut this = self.project();
+
+        assert!(this.stream.is_none());
+        this.stream.set(Some((this.f)(item)));
+        Ok(())
+    }
+
+    fn poll_flush(mut self: Pin<&mut Self>, cx: &mut Context<'_>) -> Poll<Result<(), Self::Error>> {
+        ready!(self.as_mut().try_empty_stream(cx)?);
+        self.project().sink.poll_flush(cx)
+    }
+
+    fn poll_close(mut self: Pin<&mut Self>, cx: &mut Context<'_>) -> Poll<Result<(), Self::Error>> {
+        ready!(self.as_mut().try_empty_stream(cx)?);
+        self.project().sink.poll_close(cx)
+    }
+}
diff --git a/third_party/rust/futures-util/src/stream/abortable.rs b/third_party/rust/futures-util/src/stream/abortable.rs
new file mode 100644
index 0000000000..1fea895822
--- /dev/null
+++ b/third_party/rust/futures-util/src/stream/abortable.rs
@@ -0,0 +1,19 @@
+use super::assert_stream;
+use crate::stream::{AbortHandle, Abortable};
+use crate::Stream;
+
+/// Creates a new `Abortable` stream and an `AbortHandle` which can be used to stop it.
+///
+/// This function is a convenient (but less flexible) alternative to calling
+/// `AbortHandle::new` and `Abortable::new` manually.
+///
+/// This function is only available when the `std` or `alloc` feature of this
+/// library is activated, and it is activated by default.
+pub fn abortable<St>(stream: St) -> (Abortable<St>, AbortHandle)
+where
+    St: Stream,
+{
+    let (handle, reg) = AbortHandle::new_pair();
+    let abortable = assert_stream::<St::Item, _>(Abortable::new(stream, reg));
+    (abortable, handle)
+}
diff --git a/third_party/rust/futures-util/src/stream/empty.rs b/third_party/rust/futures-util/src/stream/empty.rs
new file mode 100644
index 0000000000..e4fd87326b
--- /dev/null
+++ b/third_party/rust/futures-util/src/stream/empty.rs
@@ -0,0 +1,45 @@
+use super::assert_stream;
+use core::marker::PhantomData;
+use core::pin::Pin;
+use futures_core::stream::{FusedStream, Stream};
+use futures_core::task::{Context, Poll};
+
+/// Stream for the [`empty`] function.
+#[derive(Debug)]
+#[must_use = "streams do nothing unless polled"]
+pub struct Empty<T> {
+    _phantom: PhantomData<T>,
+}
+
+/// Creates a stream which contains no elements.
+///
+/// The returned stream will always return `Ready(None)` when polled.
+pub fn empty<T>() -> Empty<T> {
+    assert_stream::<T, _>(Empty { _phantom: PhantomData })
+}
+
+impl<T> Unpin for Empty<T> {}
+
+impl<T> FusedStream for Empty<T> {
+    fn is_terminated(&self) -> bool {
+        true
+    }
+}
+
+impl<T> Stream for Empty<T> {
+    type Item = T;
+
+    fn poll_next(self: Pin<&mut Self>, _: &mut Context<'_>) -> Poll<Option<Self::Item>> {
+        Poll::Ready(None)
+    }
+
+    fn size_hint(&self) -> (usize, Option<usize>) {
+        (0, Some(0))
+    }
+}
+
+impl<T> Clone for Empty<T> {
+    fn clone(&self) -> Self {
+        empty()
+    }
+}
diff --git a/third_party/rust/futures-util/src/stream/futures_ordered.rs b/third_party/rust/futures-util/src/stream/futures_ordered.rs
new file mode 100644
index 0000000000..f1c93fd683
--- /dev/null
+++ b/third_party/rust/futures-util/src/stream/futures_ordered.rs
@@ -0,0 +1,248 @@
+use crate::stream::{FuturesUnordered, StreamExt};
+use alloc::collections::binary_heap::{BinaryHeap, PeekMut};
+use core::cmp::Ordering;
+use core::fmt::{self, Debug};
+use core::iter::FromIterator;
+use core::pin::Pin;
+use futures_core::future::Future;
+use futures_core::ready;
+use futures_core::stream::Stream;
+use futures_core::{
+    task::{Context, Poll},
+    FusedStream,
+};
+use pin_project_lite::pin_project;
+
+pin_project! {
+    #[must_use = "futures do nothing unless you `.await` or poll them"]
+    #[derive(Debug)]
+    struct OrderWrapper<T> {
+        #[pin]
+        data: T, // A future or a future's output
+        index: usize,
+    }
+}
+
+impl<T> PartialEq for OrderWrapper<T> {
+    fn eq(&self, other: &Self) -> bool {
+        self.index == other.index
+    }
+}
+
+impl<T> Eq for OrderWrapper<T> {}
+
+impl<T> PartialOrd for OrderWrapper<T> {
+    fn partial_cmp(&self, other: &Self) -> Option<Ordering> {
+        Some(self.cmp(other))
+    }
+}
+
+impl<T> Ord for OrderWrapper<T> {
+    fn cmp(&self, other: &Self) -> Ordering {
+        // BinaryHeap is a max heap, so compare backwards here.
+        other.index.cmp(&self.index)
+    }
+}
+
+impl<T> Future for OrderWrapper<T>
+where
+    T: Future,
+{
+    type Output = OrderWrapper<T::Output>;
+
+    fn poll(self: Pin<&mut Self>, cx: &mut Context<'_>) -> Poll<Self::Output> {
+        let index = self.index;
+        self.project().data.poll(cx).map(|output| OrderWrapper { data: output, index })
+    }
+}
+
+/// An unbounded queue of futures.
+///
+/// This "combinator" is similar to `FuturesUnordered`, but it imposes an order
+/// on top of the set of futures. While futures in the set will race to
+/// completion in parallel, results will only be returned in the order their
+/// originating futures were added to the queue.
+///
+/// Futures are pushed into this queue and their realized values are yielded in
+/// order. This structure is optimized to manage a large number of futures.
+/// Futures managed by `FuturesOrdered` will only be polled when they generate
+/// notifications. This reduces the required amount of work needed to coordinate
+/// large numbers of futures.
+///
+/// When a `FuturesOrdered` is first created, it does not contain any futures.
+/// Calling `poll` in this state will result in `Poll::Ready(None))` to be
+/// returned. Futures are submitted to the queue using `push`; however, the
+/// future will **not** be polled at this point. `FuturesOrdered` will only
+/// poll managed futures when `FuturesOrdered::poll` is called. As such, it
+/// is important to call `poll` after pushing new futures.
+///
+/// If `FuturesOrdered::poll` returns `Poll::Ready(None)` this means that
+/// the queue is currently not managing any futures. A future may be submitted
+/// to the queue at a later time. At that point, a call to
+/// `FuturesOrdered::poll` will either return the future's resolved value
+/// **or** `Poll::Pending` if the future has not yet completed. When
+/// multiple futures are submitted to the queue, `FuturesOrdered::poll` will
+/// return `Poll::Pending` until the first future completes, even if
+/// some of the later futures have already completed.
+///
+/// Note that you can create a ready-made `FuturesOrdered` via the
+/// [`collect`](Iterator::collect) method, or you can start with an empty queue
+/// with the `FuturesOrdered::new` constructor.
+///
+/// This type is only available when the `std` or `alloc` feature of this
+/// library is activated, and it is activated by default.
+#[must_use = "streams do nothing unless polled"]
+pub struct FuturesOrdered<T: Future> {
+    in_progress_queue: FuturesUnordered<OrderWrapper<T>>,
+    queued_outputs: BinaryHeap<OrderWrapper<T::Output>>,
+    next_incoming_index: usize,
+    next_outgoing_index: usize,
+}
+
+impl<T: Future> Unpin for FuturesOrdered<T> {}
+
+impl<Fut: Future> FuturesOrdered<Fut> {
+    /// Constructs a new, empty `FuturesOrdered`
+    ///
+    /// The returned `FuturesOrdered` does not contain any futures and, in this
+    /// state, `FuturesOrdered::poll_next` will return `Poll::Ready(None)`.
+    pub fn new() -> Self {
+        Self {
+            in_progress_queue: FuturesUnordered::new(),
+            queued_outputs: BinaryHeap::new(),
+            next_incoming_index: 0,
+            next_outgoing_index: 0,
+        }
+    }
+
+    /// Returns the number of futures contained in the queue.
+    ///
+    /// This represents the total number of in-flight futures, both
+    /// those currently processing and those that have completed but
+    /// which are waiting for earlier futures to complete.
+    pub fn len(&self) -> usize {
+        self.in_progress_queue.len() + self.queued_outputs.len()
+    }
+
+    /// Returns `true` if the queue contains no futures
+    pub fn is_empty(&self) -> bool {
+        self.in_progress_queue.is_empty() && self.queued_outputs.is_empty()
+    }
+
+    /// Push a future into the queue.
+    ///
+    /// This function submits the given future to the internal set for managing.
+    /// This function will not call `poll` on the submitted future. The caller
+    /// must ensure that `FuturesOrdered::poll` is called in order to receive
+    /// task notifications.
+    #[deprecated(note = "use `push_back` instead")]
+    pub fn push(&mut self, future: Fut) {
+        self.push_back(future);
+    }
+
+    /// Pushes a future to the back of the queue.
+    ///
+    /// This function submits the given future to the internal set for managing.
+    /// This function will not call `poll` on the submitted future. The caller
+    /// must ensure that `FuturesOrdered::poll` is called in order to receive
+    /// task notifications.
+    pub fn push_back(&mut self, future: Fut) {
+        let wrapped = OrderWrapper { data: future, index: self.next_incoming_index };
+        self.next_incoming_index += 1;
+        self.in_progress_queue.push(wrapped);
+    }
+
+    /// Pushes a future to the front of the queue.
+    ///
+    /// This function submits the given future to the internal set for managing.
+    /// This function will not call `poll` on the submitted future. The caller
+    /// must ensure that `FuturesOrdered::poll` is called in order to receive
+    /// task notifications. This future will be the next future to be returned
+    /// complete.
+    pub fn push_front(&mut self, future: Fut) {
+        if self.next_outgoing_index == 0 {
+            self.push_back(future)
+        } else {
+            let wrapped = OrderWrapper { data: future, index: self.next_outgoing_index - 1 };
+            self.next_outgoing_index -= 1;
+            self.in_progress_queue.push(wrapped);
+        }
+    }
+}
+
+impl<Fut: Future> Default for FuturesOrdered<Fut> {
+    fn default() -> Self {
+        Self::new()
+    }
+}
+
+impl<Fut: Future> Stream for FuturesOrdered<Fut> {
+    type Item = Fut::Output;
+
+    fn poll_next(mut self: Pin<&mut Self>, cx: &mut Context<'_>) -> Poll<Option<Self::Item>> {
+        let this = &mut *self;
+
+        // Check to see if we've already received the next value
+        if let Some(next_output) = this.queued_outputs.peek_mut() {
+            if next_output.index == this.next_outgoing_index {
+                this.next_outgoing_index += 1;
+                return Poll::Ready(Some(PeekMut::pop(next_output).data));
+            }
+        }
+
+        loop {
+            match ready!(this.in_progress_queue.poll_next_unpin(cx)) {
+                Some(output) => {
+                    if output.index == this.next_outgoing_index {
+                        this.next_outgoing_index += 1;
+                        return Poll::Ready(Some(output.data));
+                    } else {
+                        this.queued_outputs.push(output)
+                    }
+                }
+                None => return Poll::Ready(None),
+            }
+        }
+    }
+
+    fn size_hint(&self) -> (usize, Option<usize>) {
+        let len = self.len();
+        (len, Some(len))
+    }
+}
+
+impl<Fut: Future> Debug for FuturesOrdered<Fut> {
+    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
+        write!(f, "FuturesOrdered {{ ... }}")
+    }
+}
+
+impl<Fut: Future> FromIterator<Fut> for FuturesOrdered<Fut> {
+    fn from_iter<T>(iter: T) -> Self
+    where
+        T: IntoIterator<Item = Fut>,
+    {
+        let acc = Self::new();
+        iter.into_iter().fold(acc, |mut acc, item| {
+            acc.push_back(item);
+            acc
+        })
+    }
+}
+
+impl<Fut: Future> FusedStream for FuturesOrdered<Fut> {
+    fn is_terminated(&self) -> bool {
+        self.in_progress_queue.is_terminated() && self.queued_outputs.is_empty()
+    }
+}
+
+impl<Fut: Future> Extend<Fut> for FuturesOrdered<Fut> {
+    fn extend<I>(&mut self, iter: I)
+    where
+        I: IntoIterator<Item = Fut>,
+    {
+        for item in iter {
+            self.push_back(item);
+        }
+    }
+}
diff --git a/third_party/rust/futures-util/src/stream/futures_unordered/abort.rs b/third_party/rust/futures-util/src/stream/futures_unordered/abort.rs
new file mode 100644
index 0000000000..1a42d24369
--- /dev/null
+++ b/third_party/rust/futures-util/src/stream/futures_unordered/abort.rs
@@ -0,0 +1,12 @@
+pub(super) fn abort(s: &str) -> ! {
+    struct DoublePanic;
+
+    impl Drop for DoublePanic {
+        fn drop(&mut self) {
+            panic!("panicking twice to abort the program");
+        }
+    }
+
+    let _bomb = DoublePanic;
+    panic!("{}", s);
+}
diff --git a/third_party/rust/futures-util/src/stream/futures_unordered/iter.rs b/third_party/rust/futures-util/src/stream/futures_unordered/iter.rs
new file mode 100644
index 0000000000..20248c70fe
--- /dev/null
+++ b/third_party/rust/futures-util/src/stream/futures_unordered/iter.rs
@@ -0,0 +1,172 @@
+use super::task::Task;
+use super::FuturesUnordered;
+use core::marker::PhantomData;
+use core::pin::Pin;
+use core::ptr;
+use core::sync::atomic::Ordering::Relaxed;
+
+/// Mutable iterator over all futures in the unordered set.
+#[derive(Debug)]
+pub struct IterPinMut<'a, Fut> {
+    pub(super) task: *const Task<Fut>,
+    pub(super) len: usize,
+    pub(super) _marker: PhantomData<&'a mut FuturesUnordered<Fut>>,
+}
+
+/// Mutable iterator over all futures in the unordered set.
+#[derive(Debug)]
+pub struct IterMut<'a, Fut: Unpin>(pub(super) IterPinMut<'a, Fut>);
+
+/// Immutable iterator over all futures in the unordered set.
+#[derive(Debug)]
+pub struct IterPinRef<'a, Fut> {
+    pub(super) task: *const Task<Fut>,
+    pub(super) len: usize,
+    pub(super) pending_next_all: *mut Task<Fut>,
+    pub(super) _marker: PhantomData<&'a FuturesUnordered<Fut>>,
+}
+
+/// Immutable iterator over all the futures in the unordered set.
+#[derive(Debug)]
+pub struct Iter<'a, Fut: Unpin>(pub(super) IterPinRef<'a, Fut>);
+
+/// Owned iterator over all futures in the unordered set.
+#[derive(Debug)]
+pub struct IntoIter<Fut: Unpin> {
+    pub(super) len: usize,
+    pub(super) inner: FuturesUnordered<Fut>,
+}
+
+impl<Fut: Unpin> Iterator for IntoIter<Fut> {
+    type Item = Fut;
+
+    fn next(&mut self) -> Option<Self::Item> {
+        // `head_all` can be accessed directly and we don't need to spin on
+        // `Task::next_all` since we have exclusive access to the set.
+        let task = self.inner.head_all.get_mut();
+
+        if (*task).is_null() {
+            return None;
+        }
+
+        unsafe {
+            // Moving out of the future is safe because it is `Unpin`
+            let future = (*(**task).future.get()).take().unwrap();
+
+            // Mutable access to a previously shared `FuturesUnordered` implies
+            // that the other threads already released the object before the
+            // current thread acquired it, so relaxed ordering can be used and
+            // valid `next_all` checks can be skipped.
+            let next = (**task).next_all.load(Relaxed);
+            *task = next;
+            if !task.is_null() {
+                *(**task).prev_all.get() = ptr::null_mut();
+            }
+            self.len -= 1;
+            Some(future)
+        }
+    }
+
+    fn size_hint(&self) -> (usize, Option<usize>) {
+        (self.len, Some(self.len))
+    }
+}
+
+impl<Fut: Unpin> ExactSizeIterator for IntoIter<Fut> {}
+
+impl<'a, Fut> Iterator for IterPinMut<'a, Fut> {
+    type Item = Pin<&'a mut Fut>;
+
+    fn next(&mut self) -> Option<Self::Item> {
+        if self.task.is_null() {
+            return None;
+        }
+
+        unsafe {
+            let future = (*(*self.task).future.get()).as_mut().unwrap();
+
+            // Mutable access to a previously shared `FuturesUnordered` implies
+            // that the other threads already released the object before the
+            // current thread acquired it, so relaxed ordering can be used and
+            // valid `next_all` checks can be skipped.
+            let next = (*self.task).next_all.load(Relaxed);
+            self.task = next;
+            self.len -= 1;
+            Some(Pin::new_unchecked(future))
+        }
+    }
+
+    fn size_hint(&self) -> (usize, Option<usize>) {
+        (self.len, Some(self.len))
+    }
+}
+
+impl<Fut> ExactSizeIterator for IterPinMut<'_, Fut> {}
+
+impl<'a, Fut: Unpin> Iterator for IterMut<'a, Fut> {
+    type Item = &'a mut Fut;
+
+    fn next(&mut self) -> Option<Self::Item> {
+        self.0.next().map(Pin::get_mut)
+    }
+
+    fn size_hint(&self) -> (usize, Option<usize>) {
+        self.0.size_hint()
+    }
+}
+
+impl<Fut: Unpin> ExactSizeIterator for IterMut<'_, Fut> {}
+
+impl<'a, Fut> Iterator for IterPinRef<'a, Fut> {
+    type Item = Pin<&'a Fut>;
+
+    fn next(&mut self) -> Option<Self::Item> {
+        if self.task.is_null() {
+            return None;
+        }
+
+        unsafe {
+            let future = (*(*self.task).future.get()).as_ref().unwrap();
+
+            // Relaxed ordering can be used since acquire ordering when
+            // `head_all` was initially read for this iterator implies acquire
+            // ordering for all previously inserted nodes (and we don't need to
+            // read `len_all` again for any other nodes).
+            let next = (*self.task).spin_next_all(self.pending_next_all, Relaxed);
+            self.task = next;
+            self.len -= 1;
+            Some(Pin::new_unchecked(future))
+        }
+    }
+
+    fn size_hint(&self) -> (usize, Option<usize>) {
+        (self.len, Some(self.len))
+    }
+}
+
+impl<Fut> ExactSizeIterator for IterPinRef<'_, Fut> {}
+
+impl<'a, Fut: Unpin> Iterator for Iter<'a, Fut> {
+    type Item = &'a Fut;
+
+    fn next(&mut self) -> Option<Self::Item> {
+        self.0.next().map(Pin::get_ref)
+    }
+
+    fn size_hint(&self) -> (usize, Option<usize>) {
+        self.0.size_hint()
+    }
+}
+
+impl<Fut: Unpin> ExactSizeIterator for Iter<'_, Fut> {}
+
+// SAFETY: we do nothing thread-local and there is no interior mutability,
+// so the usual structural `Send`/`Sync` apply.
+unsafe impl<Fut: Send> Send for IterPinRef<'_, Fut> {}
+unsafe impl<Fut: Sync> Sync for IterPinRef<'_, Fut> {}
+
+unsafe impl<Fut: Send> Send for IterPinMut<'_, Fut> {}
+unsafe impl<Fut: Sync> Sync for IterPinMut<'_, Fut> {}
+
+unsafe impl<Fut: Send + Unpin> Send for IntoIter<Fut> {}
+unsafe impl<Fut: Sync + Unpin> Sync for IntoIter<Fut> {}
diff --git a/third_party/rust/futures-util/src/stream/futures_unordered/mod.rs b/third_party/rust/futures-util/src/stream/futures_unordered/mod.rs
new file mode 100644
index 0000000000..5e995fdb81
--- /dev/null
+++ b/third_party/rust/futures-util/src/stream/futures_unordered/mod.rs
@@ -0,0 +1,658 @@
+//! An unbounded set of futures.
+//!
+//! This module is only available when the `std` or `alloc` feature of this
+//! library is activated, and it is activated by default.
+
+use crate::task::AtomicWaker;
+use alloc::sync::{Arc, Weak};
+use core::cell::UnsafeCell;
+use core::fmt::{self, Debug};
+use core::iter::FromIterator;
+use core::marker::PhantomData;
+use core::mem;
+use core::pin::Pin;
+use core::ptr;
+use core::sync::atomic::Ordering::{AcqRel, Acquire, Relaxed, Release, SeqCst};
+use core::sync::atomic::{AtomicBool, AtomicPtr};
+use futures_core::future::Future;
+use futures_core::stream::{FusedStream, Stream};
+use futures_core::task::{Context, Poll};
+use futures_task::{FutureObj, LocalFutureObj, LocalSpawn, Spawn, SpawnError};
+
+mod abort;
+
+mod iter;
+#[allow(unreachable_pub)] // https://github.com/rust-lang/rust/issues/102352
+pub use self::iter::{IntoIter, Iter, IterMut, IterPinMut, IterPinRef};
+
+mod task;
+use self::task::Task;
+
+mod ready_to_run_queue;
+use self::ready_to_run_queue::{Dequeue, ReadyToRunQueue};
+
+/// A set of futures which may complete in any order.
+///
+/// This structure is optimized to manage a large number of futures.
+/// Futures managed by [`FuturesUnordered`] will only be polled when they
+/// generate wake-up notifications. This reduces the required amount of work
+/// needed to poll large numbers of futures.
+///
+/// [`FuturesUnordered`] can be filled by [`collect`](Iterator::collect)ing an
+/// iterator of futures into a [`FuturesUnordered`], or by
+/// [`push`](FuturesUnordered::push)ing futures onto an existing
+/// [`FuturesUnordered`]. When new futures are added,
+/// [`poll_next`](Stream::poll_next) must be called in order to begin receiving
+/// wake-ups for new futures.
+///
+/// Note that you can create a ready-made [`FuturesUnordered`] via the
+/// [`collect`](Iterator::collect) method, or you can start with an empty set
+/// with the [`FuturesUnordered::new`] constructor.
+///
+/// This type is only available when the `std` or `alloc` feature of this
+/// library is activated, and it is activated by default.
+#[must_use = "streams do nothing unless polled"]
+pub struct FuturesUnordered<Fut> {
+    ready_to_run_queue: Arc<ReadyToRunQueue<Fut>>,
+    head_all: AtomicPtr<Task<Fut>>,
+    is_terminated: AtomicBool,
+}
+
+unsafe impl<Fut: Send> Send for FuturesUnordered<Fut> {}
+unsafe impl<Fut: Sync> Sync for FuturesUnordered<Fut> {}
+impl<Fut> Unpin for FuturesUnordered<Fut> {}
+
+impl Spawn for FuturesUnordered<FutureObj<'_, ()>> {
+    fn spawn_obj(&self, future_obj: FutureObj<'static, ()>) -> Result<(), SpawnError> {
+        self.push(future_obj);
+        Ok(())
+    }
+}
+
+impl LocalSpawn for FuturesUnordered<LocalFutureObj<'_, ()>> {
+    fn spawn_local_obj(&self, future_obj: LocalFutureObj<'static, ()>) -> Result<(), SpawnError> {
+        self.push(future_obj);
+        Ok(())
+    }
+}
+
+// FuturesUnordered is implemented using two linked lists. One which links all
+// futures managed by a `FuturesUnordered` and one that tracks futures that have
+// been scheduled for polling. The first linked list allows for thread safe
+// insertion of nodes at the head as well as forward iteration, but is otherwise
+// not thread safe and is only accessed by the thread that owns the
+// `FuturesUnordered` value for any other operations. The second linked list is
+// an implementation of the intrusive MPSC queue algorithm described by
+// 1024cores.net.
+//
+// When a future is submitted to the set, a task is allocated and inserted in
+// both linked lists. The next call to `poll_next` will (eventually) see this
+// task and call `poll` on the future.
+//
+// Before a managed future is polled, the current context's waker is replaced
+// with one that is aware of the specific future being run. This ensures that
+// wake-up notifications generated by that specific future are visible to
+// `FuturesUnordered`. When a wake-up notification is received, the task is
+// inserted into the ready to run queue, so that its future can be polled later.
+//
+// Each task is wrapped in an `Arc` and thereby atomically reference counted.
+// Also, each task contains an `AtomicBool` which acts as a flag that indicates
+// whether the task is currently inserted in the atomic queue. When a wake-up
+// notification is received, the task will only be inserted into the ready to
+// run queue if it isn't inserted already.
+
+impl<Fut> Default for FuturesUnordered<Fut> {
+    fn default() -> Self {
+        Self::new()
+    }
+}
+
+impl<Fut> FuturesUnordered<Fut> {
+    /// Constructs a new, empty [`FuturesUnordered`].
+    ///
+    /// The returned [`FuturesUnordered`] does not contain any futures.
+    /// In this state, [`FuturesUnordered::poll_next`](Stream::poll_next) will
+    /// return [`Poll::Ready(None)`](Poll::Ready).
+    pub fn new() -> Self {
+        let stub = Arc::new(Task {
+            future: UnsafeCell::new(None),
+            next_all: AtomicPtr::new(ptr::null_mut()),
+            prev_all: UnsafeCell::new(ptr::null()),
+            len_all: UnsafeCell::new(0),
+            next_ready_to_run: AtomicPtr::new(ptr::null_mut()),
+            queued: AtomicBool::new(true),
+            ready_to_run_queue: Weak::new(),
+            woken: AtomicBool::new(false),
+        });
+        let stub_ptr = Arc::as_ptr(&stub);
+        let ready_to_run_queue = Arc::new(ReadyToRunQueue {
+            waker: AtomicWaker::new(),
+            head: AtomicPtr::new(stub_ptr as *mut _),
+            tail: UnsafeCell::new(stub_ptr),
+            stub,
+        });
+
+        Self {
+            head_all: AtomicPtr::new(ptr::null_mut()),
+            ready_to_run_queue,
+            is_terminated: AtomicBool::new(false),
+        }
+    }
+
+    /// Returns the number of futures contained in the set.
+    ///
+    /// This represents the total number of in-flight futures.
+    pub fn len(&self) -> usize {
+        let (_, len) = self.atomic_load_head_and_len_all();
+        len
+    }
+
+    /// Returns `true` if the set contains no futures.
+    pub fn is_empty(&self) -> bool {
+        // Relaxed ordering can be used here since we don't need to read from
+        // the head pointer, only check whether it is null.
+        self.head_all.load(Relaxed).is_null()
+    }
+
+    /// Push a future into the set.
+    ///
+    /// This method adds the given future to the set. This method will not
+    /// call [`poll`](core::future::Future::poll) on the submitted future. The caller must
+    /// ensure that [`FuturesUnordered::poll_next`](Stream::poll_next) is called
+    /// in order to receive wake-up notifications for the given future.
+    pub fn push(&self, future: Fut) {
+        let task = Arc::new(Task {
+            future: UnsafeCell::new(Some(future)),
+            next_all: AtomicPtr::new(self.pending_next_all()),
+            prev_all: UnsafeCell::new(ptr::null_mut()),
+            len_all: UnsafeCell::new(0),
+            next_ready_to_run: AtomicPtr::new(ptr::null_mut()),
+            queued: AtomicBool::new(true),
+            ready_to_run_queue: Arc::downgrade(&self.ready_to_run_queue),
+            woken: AtomicBool::new(false),
+        });
+
+        // Reset the `is_terminated` flag if we've previously marked ourselves
+        // as terminated.
+        self.is_terminated.store(false, Relaxed);
+
+        // Right now our task has a strong reference count of 1. We transfer
+        // ownership of this reference count to our internal linked list
+        // and we'll reclaim ownership through the `unlink` method below.
+        let ptr = self.link(task);
+
+        // We'll need to get the future "into the system" to start tracking it,
+        // e.g. getting its wake-up notifications going to us tracking which
+        // futures are ready. To do that we unconditionally enqueue it for
+        // polling here.
+        self.ready_to_run_queue.enqueue(ptr);
+    }
+
+    /// Returns an iterator that allows inspecting each future in the set.
+    pub fn iter(&self) -> Iter<'_, Fut>
+    where
+        Fut: Unpin,
+    {
+        Iter(Pin::new(self).iter_pin_ref())
+    }
+
+    /// Returns an iterator that allows inspecting each future in the set.
+    pub fn iter_pin_ref(self: Pin<&Self>) -> IterPinRef<'_, Fut> {
+        let (task, len) = self.atomic_load_head_and_len_all();
+        let pending_next_all = self.pending_next_all();
+
+        IterPinRef { task, len, pending_next_all, _marker: PhantomData }
+    }
+
+    /// Returns an iterator that allows modifying each future in the set.
+    pub fn iter_mut(&mut self) -> IterMut<'_, Fut>
+    where
+        Fut: Unpin,
+    {
+        IterMut(Pin::new(self).iter_pin_mut())
+    }
+
+    /// Returns an iterator that allows modifying each future in the set.
+    pub fn iter_pin_mut(mut self: Pin<&mut Self>) -> IterPinMut<'_, Fut> {
+        // `head_all` can be accessed directly and we don't need to spin on
+        // `Task::next_all` since we have exclusive access to the set.
+        let task = *self.head_all.get_mut();
+        let len = if task.is_null() { 0 } else { unsafe { *(*task).len_all.get() } };
+
+        IterPinMut { task, len, _marker: PhantomData }
+    }
+
+    /// Returns the current head node and number of futures in the list of all
+    /// futures within a context where access is shared with other threads
+    /// (mostly for use with the `len` and `iter_pin_ref` methods).
+    fn atomic_load_head_and_len_all(&self) -> (*const Task<Fut>, usize) {
+        let task = self.head_all.load(Acquire);
+        let len = if task.is_null() {
+            0
+        } else {
+            unsafe {
+                (*task).spin_next_all(self.pending_next_all(), Acquire);
+                *(*task).len_all.get()
+            }
+        };
+
+        (task, len)
+    }
+
+    /// Releases the task. It destroys the future inside and either drops
+    /// the `Arc<Task>` or transfers ownership to the ready to run queue.
+    /// The task this method is called on must have been unlinked before.
+    fn release_task(&mut self, task: Arc<Task<Fut>>) {
+        // `release_task` must only be called on unlinked tasks
+        debug_assert_eq!(task.next_all.load(Relaxed), self.pending_next_all());
+        unsafe {
+            debug_assert!((*task.prev_all.get()).is_null());
+        }
+
+        // The future is done, try to reset the queued flag. This will prevent
+        // `wake` from doing any work in the future
+        let prev = task.queued.swap(true, SeqCst);
+
+        // Drop the future, even if it hasn't finished yet. This is safe
+        // because we're dropping the future on the thread that owns
+        // `FuturesUnordered`, which correctly tracks `Fut`'s lifetimes and
+        // such.
+        unsafe {
+            // Set to `None` rather than `take()`ing to prevent moving the
+            // future.
+            *task.future.get() = None;
+        }
+
+        // If the queued flag was previously set, then it means that this task
+        // is still in our internal ready to run queue. We then transfer
+        // ownership of our reference count to the ready to run queue, and it'll
+        // come along and free it later, noticing that the future is `None`.
+        //
+        // If, however, the queued flag was *not* set then we're safe to
+        // release our reference count on the task. The queued flag was set
+        // above so all future `enqueue` operations will not actually
+        // enqueue the task, so our task will never see the ready to run queue
+        // again. The task itself will be deallocated once all reference counts
+        // have been dropped elsewhere by the various wakers that contain it.
+        if prev {
+            mem::forget(task);
+        }
+    }
+
+    /// Insert a new task into the internal linked list.
+    fn link(&self, task: Arc<Task<Fut>>) -> *const Task<Fut> {
+        // `next_all` should already be reset to the pending state before this
+        // function is called.
+        debug_assert_eq!(task.next_all.load(Relaxed), self.pending_next_all());
+        let ptr = Arc::into_raw(task);
+
+        // Atomically swap out the old head node to get the node that should be
+        // assigned to `next_all`.
+        let next = self.head_all.swap(ptr as *mut _, AcqRel);
+
+        unsafe {
+            // Store the new list length in the new node.
+            let new_len = if next.is_null() {
+                1
+            } else {
+                // Make sure `next_all` has been written to signal that it is
+                // safe to read `len_all`.
+                (*next).spin_next_all(self.pending_next_all(), Acquire);
+                *(*next).len_all.get() + 1
+            };
+            *(*ptr).len_all.get() = new_len;
+
+            // Write the old head as the next node pointer, signaling to other
+            // threads that `len_all` and `next_all` are ready to read.
+            (*ptr).next_all.store(next, Release);
+
+            // `prev_all` updates don't need to be synchronized, as the field is
+            // only ever used after exclusive access has been acquired.
+            if !next.is_null() {
+                *(*next).prev_all.get() = ptr;
+            }
+        }
+
+        ptr
+    }
+
+    /// Remove the task from the linked list tracking all tasks currently
+    /// managed by `FuturesUnordered`.
+    /// This method is unsafe because it has be guaranteed that `task` is a
+    /// valid pointer.
+    unsafe fn unlink(&mut self, task: *const Task<Fut>) -> Arc<Task<Fut>> {
+        // Compute the new list length now in case we're removing the head node
+        // and won't be able to retrieve the correct length later.
+        let head = *self.head_all.get_mut();
+        debug_assert!(!head.is_null());
+        let new_len = *(*head).len_all.get() - 1;
+
+        let task = Arc::from_raw(task);
+        let next = task.next_all.load(Relaxed);
+        let prev = *task.prev_all.get();
+        task.next_all.store(self.pending_next_all(), Relaxed);
+        *task.prev_all.get() = ptr::null_mut();
+
+        if !next.is_null() {
+            *(*next).prev_all.get() = prev;
+        }
+
+        if !prev.is_null() {
+            (*prev).next_all.store(next, Relaxed);
+        } else {
+            *self.head_all.get_mut() = next;
+        }
+
+        // Store the new list length in the head node.
+        let head = *self.head_all.get_mut();
+        if !head.is_null() {
+            *(*head).len_all.get() = new_len;
+        }
+
+        task
+    }
+
+    /// Returns the reserved value for `Task::next_all` to indicate a pending
+    /// assignment from the thread that inserted the task.
+    ///
+    /// `FuturesUnordered::link` needs to update `Task` pointers in an order
+    /// that ensures any iterators created on other threads can correctly
+    /// traverse the entire `Task` list using the chain of `next_all` pointers.
+    /// This could be solved with a compare-exchange loop that stores the
+    /// current `head_all` in `next_all` and swaps out `head_all` with the new
+    /// `Task` pointer if the head hasn't already changed. Under heavy thread
+    /// contention, this compare-exchange loop could become costly.
+    ///
+    /// An alternative is to initialize `next_all` to a reserved pending state
+    /// first, perform an atomic swap on `head_all`, and finally update
+    /// `next_all` with the old head node. Iterators will then either see the
+    /// pending state value or the correct next node pointer, and can reload
+    /// `next_all` as needed until the correct value is loaded. The number of
+    /// retries needed (if any) would be small and will always be finite, so
+    /// this should generally perform better than the compare-exchange loop.
+    ///
+    /// A valid `Task` pointer in the `head_all` list is guaranteed to never be
+    /// this value, so it is safe to use as a reserved value until the correct
+    /// value can be written.
+    fn pending_next_all(&self) -> *mut Task<Fut> {
+        // The `ReadyToRunQueue` stub is never inserted into the `head_all`
+        // list, and its pointer value will remain valid for the lifetime of
+        // this `FuturesUnordered`, so we can make use of its value here.
+        Arc::as_ptr(&self.ready_to_run_queue.stub) as *mut _
+    }
+}
+
+impl<Fut: Future> Stream for FuturesUnordered<Fut> {
+    type Item = Fut::Output;
+
+    fn poll_next(mut self: Pin<&mut Self>, cx: &mut Context<'_>) -> Poll<Option<Self::Item>> {
+        let len = self.len();
+
+        // Keep track of how many child futures we have polled,
+        // in case we want to forcibly yield.
+        let mut polled = 0;
+        let mut yielded = 0;
+
+        // Ensure `parent` is correctly set.
+        self.ready_to_run_queue.waker.register(cx.waker());
+
+        loop {
+            // Safety: &mut self guarantees the mutual exclusion `dequeue`
+            // expects
+            let task = match unsafe { self.ready_to_run_queue.dequeue() } {
+                Dequeue::Empty => {
+                    if self.is_empty() {
+                        // We can only consider ourselves terminated once we
+                        // have yielded a `None`
+                        *self.is_terminated.get_mut() = true;
+                        return Poll::Ready(None);
+                    } else {
+                        return Poll::Pending;
+                    }
+                }
+                Dequeue::Inconsistent => {
+                    // At this point, it may be worth yielding the thread &
+                    // spinning a few times... but for now, just yield using the
+                    // task system.
+                    cx.waker().wake_by_ref();
+                    return Poll::Pending;
+                }
+                Dequeue::Data(task) => task,
+            };
+
+            debug_assert!(task != self.ready_to_run_queue.stub());
+
+            // Safety:
+            // - `task` is a valid pointer.
+            // - We are the only thread that accesses the `UnsafeCell` that
+            //   contains the future
+            let future = match unsafe { &mut *(*task).future.get() } {
+                Some(future) => future,
+
+                // If the future has already gone away then we're just
+                // cleaning out this task. See the comment in
+                // `release_task` for more information, but we're basically
+                // just taking ownership of our reference count here.
+                None => {
+                    // This case only happens when `release_task` was called
+                    // for this task before and couldn't drop the task
+                    // because it was already enqueued in the ready to run
+                    // queue.
+
+                    // Safety: `task` is a valid pointer
+                    let task = unsafe { Arc::from_raw(task) };
+
+                    // Double check that the call to `release_task` really
+                    // happened. Calling it required the task to be unlinked.
+                    debug_assert_eq!(task.next_all.load(Relaxed), self.pending_next_all());
+                    unsafe {
+                        debug_assert!((*task.prev_all.get()).is_null());
+                    }
+                    continue;
+                }
+            };
+
+            // Safety: `task` is a valid pointer
+            let task = unsafe { self.unlink(task) };
+
+            // Unset queued flag: This must be done before polling to ensure
+            // that the future's task gets rescheduled if it sends a wake-up
+            // notification **during** the call to `poll`.
+            let prev = task.queued.swap(false, SeqCst);
+            assert!(prev);
+
+            // We're going to need to be very careful if the `poll`
+            // method below panics. We need to (a) not leak memory and
+            // (b) ensure that we still don't have any use-after-frees. To
+            // manage this we do a few things:
+            //
+            // * A "bomb" is created which if dropped abnormally will call
+            //   `release_task`. That way we'll be sure the memory management
+            //   of the `task` is managed correctly. In particular
+            //   `release_task` will drop the future. This ensures that it is
+            //   dropped on this thread and not accidentally on a different
+            //   thread (bad).
+            // * We unlink the task from our internal queue to preemptively
+            //   assume it'll panic, in which case we'll want to discard it
+            //   regardless.
+            struct Bomb<'a, Fut> {
+                queue: &'a mut FuturesUnordered<Fut>,
+                task: Option<Arc<Task<Fut>>>,
+            }
+
+            impl<Fut> Drop for Bomb<'_, Fut> {
+                fn drop(&mut self) {
+                    if let Some(task) = self.task.take() {
+                        self.queue.release_task(task);
+                    }
+                }
+            }
+
+            let mut bomb = Bomb { task: Some(task), queue: &mut *self };
+
+            // Poll the underlying future with the appropriate waker
+            // implementation. This is where a large bit of the unsafety
+            // starts to stem from internally. The waker is basically just
+            // our `Arc<Task<Fut>>` and can schedule the future for polling by
+            // enqueuing itself in the ready to run queue.
+            //
+            // Critically though `Task<Fut>` won't actually access `Fut`, the
+            // future, while it's floating around inside of wakers.
+            // These structs will basically just use `Fut` to size
+            // the internal allocation, appropriately accessing fields and
+            // deallocating the task if need be.
+            let res = {
+                let task = bomb.task.as_ref().unwrap();
+                // We are only interested in whether the future is awoken before it
+                // finishes polling, so reset the flag here.
+                task.woken.store(false, Relaxed);
+                let waker = Task::waker_ref(task);
+                let mut cx = Context::from_waker(&waker);
+
+                // Safety: We won't move the future ever again
+                let future = unsafe { Pin::new_unchecked(future) };
+
+                future.poll(&mut cx)
+            };
+            polled += 1;
+
+            match res {
+                Poll::Pending => {
+                    let task = bomb.task.take().unwrap();
+                    // If the future was awoken during polling, we assume
+                    // the future wanted to explicitly yield.
+                    yielded += task.woken.load(Relaxed) as usize;
+                    bomb.queue.link(task);
+
+                    // If a future yields, we respect it and yield here.
+                    // If all futures have been polled, we also yield here to
+                    // avoid starving other tasks waiting on the executor.
+                    // (polling the same future twice per iteration may cause
+                    // the problem: https://github.com/rust-lang/futures-rs/pull/2333)
+                    if yielded >= 2 || polled == len {
+                        cx.waker().wake_by_ref();
+                        return Poll::Pending;
+                    }
+                    continue;
+                }
+                Poll::Ready(output) => return Poll::Ready(Some(output)),
+            }
+        }
+    }
+
+    fn size_hint(&self) -> (usize, Option<usize>) {
+        let len = self.len();
+        (len, Some(len))
+    }
+}
+
+impl<Fut> Debug for FuturesUnordered<Fut> {
+    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
+        write!(f, "FuturesUnordered {{ ... }}")
+    }
+}
+
+impl<Fut> FuturesUnordered<Fut> {
+    /// Clears the set, removing all futures.
+    pub fn clear(&mut self) {
+        self.clear_head_all();
+
+        // we just cleared all the tasks, and we have &mut self, so this is safe.
+        unsafe { self.ready_to_run_queue.clear() };
+
+        self.is_terminated.store(false, Relaxed);
+    }
+
+    fn clear_head_all(&mut self) {
+        while !self.head_all.get_mut().is_null() {
+            let head = *self.head_all.get_mut();
+            let task = unsafe { self.unlink(head) };
+            self.release_task(task);
+        }
+    }
+}
+
+impl<Fut> Drop for FuturesUnordered<Fut> {
+    fn drop(&mut self) {
+        // When a `FuturesUnordered` is dropped we want to drop all futures
+        // associated with it. At the same time though there may be tons of
+        // wakers flying around which contain `Task<Fut>` references
+        // inside them. We'll let those naturally get deallocated.
+        self.clear_head_all();
+
+        // Note that at this point we could still have a bunch of tasks in the
+        // ready to run queue. None of those tasks, however, have futures
+        // associated with them so they're safe to destroy on any thread. At
+        // this point the `FuturesUnordered` struct, the owner of the one strong
+        // reference to the ready to run queue will drop the strong reference.
+        // At that point whichever thread releases the strong refcount last (be
+        // it this thread or some other thread as part of an `upgrade`) will
+        // clear out the ready to run queue and free all remaining tasks.
+        //
+        // While that freeing operation isn't guaranteed to happen here, it's
+        // guaranteed to happen "promptly" as no more "blocking work" will
+        // happen while there's a strong refcount held.
+    }
+}
+
+impl<'a, Fut: Unpin> IntoIterator for &'a FuturesUnordered<Fut> {
+    type Item = &'a Fut;
+    type IntoIter = Iter<'a, Fut>;
+
+    fn into_iter(self) -> Self::IntoIter {
+        self.iter()
+    }
+}
+
+impl<'a, Fut: Unpin> IntoIterator for &'a mut FuturesUnordered<Fut> {
+    type Item = &'a mut Fut;
+    type IntoIter = IterMut<'a, Fut>;
+
+    fn into_iter(self) -> Self::IntoIter {
+        self.iter_mut()
+    }
+}
+
+impl<Fut: Unpin> IntoIterator for FuturesUnordered<Fut> {
+    type Item = Fut;
+    type IntoIter = IntoIter<Fut>;
+
+    fn into_iter(mut self) -> Self::IntoIter {
+        // `head_all` can be accessed directly and we don't need to spin on
+        // `Task::next_all` since we have exclusive access to the set.
+        let task = *self.head_all.get_mut();
+        let len = if task.is_null() { 0 } else { unsafe { *(*task).len_all.get() } };
+
+        IntoIter { len, inner: self }
+    }
+}
+
+impl<Fut> FromIterator<Fut> for FuturesUnordered<Fut> {
+    fn from_iter<I>(iter: I) -> Self
+    where
+        I: IntoIterator<Item = Fut>,
+    {
+        let acc = Self::new();
+        iter.into_iter().fold(acc, |acc, item| {
+            acc.push(item);
+            acc
+        })
+    }
+}
+
+impl<Fut: Future> FusedStream for FuturesUnordered<Fut> {
+    fn is_terminated(&self) -> bool {
+        self.is_terminated.load(Relaxed)
+    }
+}
+
+impl<Fut> Extend<Fut> for FuturesUnordered<Fut> {
+    fn extend<I>(&mut self, iter: I)
+    where
+        I: IntoIterator<Item = Fut>,
+    {
+        for item in iter {
+            self.push(item);
+        }
+    }
+}
diff --git a/third_party/rust/futures-util/src/stream/futures_unordered/ready_to_run_queue.rs b/third_party/rust/futures-util/src/stream/futures_unordered/ready_to_run_queue.rs
new file mode 100644
index 0000000000..4518705320
--- /dev/null
+++ b/third_party/rust/futures-util/src/stream/futures_unordered/ready_to_run_queue.rs
@@ -0,0 +1,122 @@
+use crate::task::AtomicWaker;
+use alloc::sync::Arc;
+use core::cell::UnsafeCell;
+use core::ptr;
+use core::sync::atomic::AtomicPtr;
+use core::sync::atomic::Ordering::{AcqRel, Acquire, Relaxed, Release};
+
+use super::abort::abort;
+use super::task::Task;
+
+pub(super) enum Dequeue<Fut> {
+    Data(*const Task<Fut>),
+    Empty,
+    Inconsistent,
+}
+
+pub(super) struct ReadyToRunQueue<Fut> {
+    // The waker of the task using `FuturesUnordered`.
+    pub(super) waker: AtomicWaker,
+
+    // Head/tail of the readiness queue
+    pub(super) head: AtomicPtr<Task<Fut>>,
+    pub(super) tail: UnsafeCell<*const Task<Fut>>,
+    pub(super) stub: Arc<Task<Fut>>,
+}
+
+/// An MPSC queue into which the tasks containing the futures are inserted
+/// whenever the future inside is scheduled for polling.
+impl<Fut> ReadyToRunQueue<Fut> {
+    /// The enqueue function from the 1024cores intrusive MPSC queue algorithm.
+    pub(super) fn enqueue(&self, task: *const Task<Fut>) {
+        unsafe {
+            debug_assert!((*task).queued.load(Relaxed));
+
+            // This action does not require any coordination
+            (*task).next_ready_to_run.store(ptr::null_mut(), Relaxed);
+
+            // Note that these atomic orderings come from 1024cores
+            let task = task as *mut _;
+            let prev = self.head.swap(task, AcqRel);
+            (*prev).next_ready_to_run.store(task, Release);
+        }
+    }
+
+    /// The dequeue function from the 1024cores intrusive MPSC queue algorithm
+    ///
+    /// Note that this is unsafe as it required mutual exclusion (only one
+    /// thread can call this) to be guaranteed elsewhere.
+    pub(super) unsafe fn dequeue(&self) -> Dequeue<Fut> {
+        let mut tail = *self.tail.get();
+        let mut next = (*tail).next_ready_to_run.load(Acquire);
+
+        if tail == self.stub() {
+            if next.is_null() {
+                return Dequeue::Empty;
+            }
+
+            *self.tail.get() = next;
+            tail = next;
+            next = (*next).next_ready_to_run.load(Acquire);
+        }
+
+        if !next.is_null() {
+            *self.tail.get() = next;
+            debug_assert!(tail != self.stub());
+            return Dequeue::Data(tail);
+        }
+
+        if self.head.load(Acquire) as *const _ != tail {
+            return Dequeue::Inconsistent;
+        }
+
+        self.enqueue(self.stub());
+
+        next = (*tail).next_ready_to_run.load(Acquire);
+
+        if !next.is_null() {
+            *self.tail.get() = next;
+            return Dequeue::Data(tail);
+        }
+
+        Dequeue::Inconsistent
+    }
+
+    pub(super) fn stub(&self) -> *const Task<Fut> {
+        Arc::as_ptr(&self.stub)
+    }
+
+    // Clear the queue of tasks.
+    //
+    // Note that each task has a strong reference count associated with it
+    // which is owned by the ready to run queue. This method just pulls out
+    // tasks and drops their refcounts.
+    //
+    // # Safety
+    //
+    // - All tasks **must** have had their futures dropped already (by FuturesUnordered::clear)
+    // - The caller **must** guarantee unique access to `self`
+    pub(crate) unsafe fn clear(&self) {
+        loop {
+            // SAFETY: We have the guarantee of mutual exclusion required by `dequeue`.
+            match self.dequeue() {
+                Dequeue::Empty => break,
+                Dequeue::Inconsistent => abort("inconsistent in drop"),
+                Dequeue::Data(ptr) => drop(Arc::from_raw(ptr)),
+            }
+        }
+    }
+}
+
+impl<Fut> Drop for ReadyToRunQueue<Fut> {
+    fn drop(&mut self) {
+        // Once we're in the destructor for `Inner<Fut>` we need to clear out
+        // the ready to run queue of tasks if there's anything left in there.
+
+        // All tasks have had their futures dropped already by the `FuturesUnordered`
+        // destructor above, and we have &mut self, so this is safe.
+        unsafe {
+            self.clear();
+        }
+    }
+}
diff --git a/third_party/rust/futures-util/src/stream/futures_unordered/task.rs b/third_party/rust/futures-util/src/stream/futures_unordered/task.rs
new file mode 100644
index 0000000000..ec2114effa
--- /dev/null
+++ b/third_party/rust/futures-util/src/stream/futures_unordered/task.rs
@@ -0,0 +1,125 @@
+use alloc::sync::{Arc, Weak};
+use core::cell::UnsafeCell;
+use core::sync::atomic::Ordering::{self, Relaxed, SeqCst};
+use core::sync::atomic::{AtomicBool, AtomicPtr};
+
+use super::abort::abort;
+use super::ReadyToRunQueue;
+use crate::task::{waker_ref, ArcWake, WakerRef};
+
+pub(super) struct Task<Fut> {
+    // The future
+    pub(super) future: UnsafeCell<Option<Fut>>,
+
+    // Next pointer for linked list tracking all active tasks (use
+    // `spin_next_all` to read when access is shared across threads)
+    pub(super) next_all: AtomicPtr<Task<Fut>>,
+
+    // Previous task in linked list tracking all active tasks
+    pub(super) prev_all: UnsafeCell<*const Task<Fut>>,
+
+    // Length of the linked list tracking all active tasks when this node was
+    // inserted (use `spin_next_all` to synchronize before reading when access
+    // is shared across threads)
+    pub(super) len_all: UnsafeCell<usize>,
+
+    // Next pointer in ready to run queue
+    pub(super) next_ready_to_run: AtomicPtr<Task<Fut>>,
+
+    // Queue that we'll be enqueued to when woken
+    pub(super) ready_to_run_queue: Weak<ReadyToRunQueue<Fut>>,
+
+    // Whether or not this task is currently in the ready to run queue
+    pub(super) queued: AtomicBool,
+
+    // Whether the future was awoken during polling
+    // It is possible for this flag to be set to true after the polling,
+    // but it will be ignored.
+    pub(super) woken: AtomicBool,
+}
+
+// `Task` can be sent across threads safely because it ensures that
+// the underlying `Fut` type isn't touched from any of its methods.
+//
+// The parent (`super`) module is trusted not to access `future`
+// across different threads.
+unsafe impl<Fut> Send for Task<Fut> {}
+unsafe impl<Fut> Sync for Task<Fut> {}
+
+impl<Fut> ArcWake for Task<Fut> {
+    fn wake_by_ref(arc_self: &Arc<Self>) {
+        let inner = match arc_self.ready_to_run_queue.upgrade() {
+            Some(inner) => inner,
+            None => return,
+        };
+
+        arc_self.woken.store(true, Relaxed);
+
+        // It's our job to enqueue this task it into the ready to run queue. To
+        // do this we set the `queued` flag, and if successful we then do the
+        // actual queueing operation, ensuring that we're only queued once.
+        //
+        // Once the task is inserted call `wake` to notify the parent task,
+        // as it'll want to come along and run our task later.
+        //
+        // Note that we don't change the reference count of the task here,
+        // we merely enqueue the raw pointer. The `FuturesUnordered`
+        // implementation guarantees that if we set the `queued` flag that
+        // there's a reference count held by the main `FuturesUnordered` queue
+        // still.
+        let prev = arc_self.queued.swap(true, SeqCst);
+        if !prev {
+            inner.enqueue(Arc::as_ptr(arc_self));
+            inner.waker.wake();
+        }
+    }
+}
+
+impl<Fut> Task<Fut> {
+    /// Returns a waker reference for this task without cloning the Arc.
+    pub(super) fn waker_ref(this: &Arc<Self>) -> WakerRef<'_> {
+        waker_ref(this)
+    }
+
+    /// Spins until `next_all` is no longer set to `pending_next_all`.
+    ///
+    /// The temporary `pending_next_all` value is typically overwritten fairly
+    /// quickly after a node is inserted into the list of all futures, so this
+    /// should rarely spin much.
+    ///
+    /// When it returns, the correct `next_all` value is returned.
+    ///
+    /// `Relaxed` or `Acquire` ordering can be used. `Acquire` ordering must be
+    /// used before `len_all` can be safely read.
+    #[inline]
+    pub(super) fn spin_next_all(
+        &self,
+        pending_next_all: *mut Self,
+        ordering: Ordering,
+    ) -> *const Self {
+        loop {
+            let next = self.next_all.load(ordering);
+            if next != pending_next_all {
+                return next;
+            }
+        }
+    }
+}
+
+impl<Fut> Drop for Task<Fut> {
+    fn drop(&mut self) {
+        // Since `Task<Fut>` is sent across all threads for any lifetime,
+        // regardless of `Fut`, we, to guarantee memory safety, can't actually
+        // touch `Fut` at any time except when we have a reference to the
+        // `FuturesUnordered` itself .
+        //
+        // Consequently it *should* be the case that we always drop futures from
+        // the `FuturesUnordered` instance. This is a bomb, just in case there's
+        // a bug in that logic.
+        unsafe {
+            if (*self.future.get()).is_some() {
+                abort("future still here when dropping");
+            }
+        }
+    }
+}
diff --git a/third_party/rust/futures-util/src/stream/iter.rs b/third_party/rust/futures-util/src/stream/iter.rs
new file mode 100644
index 0000000000..20471c2ed0
--- /dev/null
+++ b/third_party/rust/futures-util/src/stream/iter.rs
@@ -0,0 +1,49 @@
+use super::assert_stream;
+use core::pin::Pin;
+use futures_core::stream::Stream;
+use futures_core::task::{Context, Poll};
+
+/// Stream for the [`iter`] function.
+#[derive(Debug, Clone)]
+#[must_use = "streams do nothing unless polled"]
+pub struct Iter<I> {
+    iter: I,
+}
+
+impl<I> Unpin for Iter<I> {}
+
+/// Converts an `Iterator` into a `Stream` which is always ready
+/// to yield the next value.
+///
+/// Iterators in Rust don't express the ability to block, so this adapter
+/// simply always calls `iter.next()` and returns that.
+///
+/// ```
+/// # futures::executor::block_on(async {
+/// use futures::stream::{self, StreamExt};
+///
+/// let stream = stream::iter(vec![17, 19]);
+/// assert_eq!(vec![17, 19], stream.collect::<Vec<i32>>().await);
+/// # });
+/// ```
+pub fn iter<I>(i: I) -> Iter<I::IntoIter>
+where
+    I: IntoIterator,
+{
+    assert_stream::<I::Item, _>(Iter { iter: i.into_iter() })
+}
+
+impl<I> Stream for Iter<I>
+where
+    I: Iterator,
+{
+    type Item = I::Item;
+
+    fn poll_next(mut self: Pin<&mut Self>, _: &mut Context<'_>) -> Poll<Option<I::Item>> {
+        Poll::Ready(self.iter.next())
+    }
+
+    fn size_hint(&self) -> (usize, Option<usize>) {
+        self.iter.size_hint()
+    }
+}
diff --git a/third_party/rust/futures-util/src/stream/mod.rs b/third_party/rust/futures-util/src/stream/mod.rs
new file mode 100644
index 0000000000..ec685b9848
--- /dev/null
+++ b/third_party/rust/futures-util/src/stream/mod.rs
@@ -0,0 +1,143 @@
+//! Asynchronous streams.
+//!
+//! This module contains:
+//!
+//! - The [`Stream`] trait, for objects that can asynchronously produce a
+//!   sequence of values.
+//! - The [`StreamExt`] and [`TryStreamExt`] trait, which provides adapters for
+//!   chaining and composing streams.
+//! - Top-level stream constructors like [`iter`](iter()) which creates a
+//!   stream from an iterator.
+
+#[cfg(feature = "alloc")]
+pub use futures_core::stream::{BoxStream, LocalBoxStream};
+pub use futures_core::stream::{FusedStream, Stream, TryStream};
+
+// Extension traits and combinators
+
+#[allow(clippy::module_inception)]
+mod stream;
+pub use self::stream::{
+    Chain, Collect, Concat, Cycle, Enumerate, Filter, FilterMap, FlatMap, Flatten, Fold, ForEach,
+    Fuse, Inspect, Map, Next, NextIf, NextIfEq, Peek, PeekMut, Peekable, Scan, SelectNextSome,
+    Skip, SkipWhile, StreamExt, StreamFuture, Take, TakeUntil, TakeWhile, Then, Unzip, Zip,
+};
+
+#[cfg(feature = "std")]
+pub use self::stream::CatchUnwind;
+
+#[cfg(feature = "alloc")]
+pub use self::stream::Chunks;
+
+#[cfg(feature = "alloc")]
+pub use self::stream::ReadyChunks;
+
+#[cfg(feature = "sink")]
+#[cfg_attr(docsrs, doc(cfg(feature = "sink")))]
+pub use self::stream::Forward;
+
+#[cfg(not(futures_no_atomic_cas))]
+#[cfg(feature = "alloc")]
+pub use self::stream::{BufferUnordered, Buffered, ForEachConcurrent};
+
+#[cfg(not(futures_no_atomic_cas))]
+#[cfg(feature = "sink")]
+#[cfg_attr(docsrs, doc(cfg(feature = "sink")))]
+#[cfg(feature = "alloc")]
+pub use self::stream::{ReuniteError, SplitSink, SplitStream};
+
+mod try_stream;
+pub use self::try_stream::{
+    try_unfold, AndThen, ErrInto, InspectErr, InspectOk, IntoStream, MapErr, MapOk, OrElse,
+    TryCollect, TryConcat, TryFilter, TryFilterMap, TryFlatten, TryFold, TryForEach, TryNext,
+    TrySkipWhile, TryStreamExt, TryTakeWhile, TryUnfold,
+};
+
+#[cfg(feature = "io")]
+#[cfg_attr(docsrs, doc(cfg(feature = "io")))]
+#[cfg(feature = "std")]
+pub use self::try_stream::IntoAsyncRead;
+
+#[cfg(not(futures_no_atomic_cas))]
+#[cfg(feature = "alloc")]
+pub use self::try_stream::{TryBufferUnordered, TryBuffered, TryForEachConcurrent};
+
+#[cfg(feature = "alloc")]
+pub use self::try_stream::{TryChunks, TryChunksError};
+
+// Primitive streams
+
+mod iter;
+pub use self::iter::{iter, Iter};
+
+mod repeat;
+pub use self::repeat::{repeat, Repeat};
+
+mod repeat_with;
+pub use self::repeat_with::{repeat_with, RepeatWith};
+
+mod empty;
+pub use self::empty::{empty, Empty};
+
+mod once;
+pub use self::once::{once, Once};
+
+mod pending;
+pub use self::pending::{pending, Pending};
+
+mod poll_fn;
+pub use self::poll_fn::{poll_fn, PollFn};
+
+mod poll_immediate;
+pub use self::poll_immediate::{poll_immediate, PollImmediate};
+
+mod select;
+pub use self::select::{select, Select};
+
+mod select_with_strategy;
+pub use self::select_with_strategy::{select_with_strategy, PollNext, SelectWithStrategy};
+
+mod unfold;
+pub use self::unfold::{unfold, Unfold};
+
+#[cfg(not(futures_no_atomic_cas))]
+#[cfg(feature = "alloc")]
+mod futures_ordered;
+#[cfg(not(futures_no_atomic_cas))]
+#[cfg(feature = "alloc")]
+pub use self::futures_ordered::FuturesOrdered;
+
+#[cfg(not(futures_no_atomic_cas))]
+#[cfg(feature = "alloc")]
+pub mod futures_unordered;
+#[cfg(not(futures_no_atomic_cas))]
+#[cfg(feature = "alloc")]
+#[doc(inline)]
+pub use self::futures_unordered::FuturesUnordered;
+
+#[cfg(not(futures_no_atomic_cas))]
+#[cfg(feature = "alloc")]
+pub mod select_all;
+#[cfg(not(futures_no_atomic_cas))]
+#[cfg(feature = "alloc")]
+#[doc(inline)]
+pub use self::select_all::{select_all, SelectAll};
+
+#[cfg(not(futures_no_atomic_cas))]
+#[cfg(feature = "alloc")]
+mod abortable;
+#[cfg(not(futures_no_atomic_cas))]
+#[cfg(feature = "alloc")]
+pub use crate::abortable::{AbortHandle, AbortRegistration, Abortable, Aborted};
+#[cfg(not(futures_no_atomic_cas))]
+#[cfg(feature = "alloc")]
+pub use abortable::abortable;
+
+// Just a helper function to ensure the streams we're returning all have the
+// right implementations.
+pub(crate) fn assert_stream<T, S>(stream: S) -> S
+where
+    S: Stream<Item = T>,
+{
+    stream
+}
diff --git a/third_party/rust/futures-util/src/stream/once.rs b/third_party/rust/futures-util/src/stream/once.rs
new file mode 100644
index 0000000000..ee21c8b594
--- /dev/null
+++ b/third_party/rust/futures-util/src/stream/once.rs
@@ -0,0 +1,67 @@
+use super::assert_stream;
+use core::pin::Pin;
+use futures_core::future::Future;
+use futures_core::ready;
+use futures_core::stream::{FusedStream, Stream};
+use futures_core::task::{Context, Poll};
+use pin_project_lite::pin_project;
+
+/// Creates a stream of a single element.
+///
+/// ```
+/// # futures::executor::block_on(async {
+/// use futures::stream::{self, StreamExt};
+///
+/// let stream = stream::once(async { 17 });
+/// let collected = stream.collect::<Vec<i32>>().await;
+/// assert_eq!(collected, vec![17]);
+/// # });
+/// ```
+pub fn once<Fut: Future>(future: Fut) -> Once<Fut> {
+    assert_stream::<Fut::Output, _>(Once::new(future))
+}
+
+pin_project! {
+    /// A stream which emits single element and then EOF.
+    #[derive(Debug)]
+    #[must_use = "streams do nothing unless polled"]
+    pub struct Once<Fut> {
+        #[pin]
+        future: Option<Fut>
+    }
+}
+
+impl<Fut> Once<Fut> {
+    pub(crate) fn new(future: Fut) -> Self {
+        Self { future: Some(future) }
+    }
+}
+
+impl<Fut: Future> Stream for Once<Fut> {
+    type Item = Fut::Output;
+
+    fn poll_next(self: Pin<&mut Self>, cx: &mut Context<'_>) -> Poll<Option<Self::Item>> {
+        let mut this = self.project();
+        let v = match this.future.as_mut().as_pin_mut() {
+            Some(fut) => ready!(fut.poll(cx)),
+            None => return Poll::Ready(None),
+        };
+
+        this.future.set(None);
+        Poll::Ready(Some(v))
+    }
+
+    fn size_hint(&self) -> (usize, Option<usize>) {
+        if self.future.is_some() {
+            (1, Some(1))
+        } else {
+            (0, Some(0))
+        }
+    }
+}
+
+impl<Fut: Future> FusedStream for Once<Fut> {
+    fn is_terminated(&self) -> bool {
+        self.future.is_none()
+    }
+}
diff --git a/third_party/rust/futures-util/src/stream/pending.rs b/third_party/rust/futures-util/src/stream/pending.rs
new file mode 100644
index 0000000000..d7030ff3cc
--- /dev/null
+++ b/third_party/rust/futures-util/src/stream/pending.rs
@@ -0,0 +1,45 @@
+use super::assert_stream;
+use core::marker;
+use core::pin::Pin;
+use futures_core::stream::{FusedStream, Stream};
+use futures_core::task::{Context, Poll};
+
+/// Stream for the [`pending()`] function.
+#[derive(Debug)]
+#[must_use = "streams do nothing unless polled"]
+pub struct Pending<T> {
+    _data: marker::PhantomData<T>,
+}
+
+/// Creates a stream which never returns any elements.
+///
+/// The returned stream will always return `Pending` when polled.
+pub fn pending<T>() -> Pending<T> {
+    assert_stream::<T, _>(Pending { _data: marker::PhantomData })
+}
+
+impl<T> Unpin for Pending<T> {}
+
+impl<T> FusedStream for Pending<T> {
+    fn is_terminated(&self) -> bool {
+        true
+    }
+}
+
+impl<T> Stream for Pending<T> {
+    type Item = T;
+
+    fn poll_next(self: Pin<&mut Self>, _: &mut Context<'_>) -> Poll<Option<Self::Item>> {
+        Poll::Pending
+    }
+
+    fn size_hint(&self) -> (usize, Option<usize>) {
+        (0, Some(0))
+    }
+}
+
+impl<T> Clone for Pending<T> {
+    fn clone(&self) -> Self {
+        pending()
+    }
+}
diff --git a/third_party/rust/futures-util/src/stream/poll_fn.rs b/third_party/rust/futures-util/src/stream/poll_fn.rs
new file mode 100644
index 0000000000..b9bd7d1664
--- /dev/null
+++ b/third_party/rust/futures-util/src/stream/poll_fn.rs
@@ -0,0 +1,57 @@
+//! Definition of the `PollFn` combinator
+
+use super::assert_stream;
+use core::fmt;
+use core::pin::Pin;
+use futures_core::stream::Stream;
+use futures_core::task::{Context, Poll};
+
+/// Stream for the [`poll_fn`] function.
+#[must_use = "streams do nothing unless polled"]
+pub struct PollFn<F> {
+    f: F,
+}
+
+impl<F> Unpin for PollFn<F> {}
+
+impl<F> fmt::Debug for PollFn<F> {
+    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
+        f.debug_struct("PollFn").finish()
+    }
+}
+
+/// Creates a new stream wrapping a function returning `Poll<Option<T>>`.
+///
+/// Polling the returned stream calls the wrapped function.
+///
+/// # Examples
+///
+/// ```
+/// use futures::stream::poll_fn;
+/// use futures::task::Poll;
+///
+/// let mut counter = 1usize;
+///
+/// let read_stream = poll_fn(move |_| -> Poll<Option<String>> {
+///     if counter == 0 { return Poll::Ready(None); }
+///     counter -= 1;
+///     Poll::Ready(Some("Hello, World!".to_owned()))
+/// });
+/// ```
+pub fn poll_fn<T, F>(f: F) -> PollFn<F>
+where
+    F: FnMut(&mut Context<'_>) -> Poll<Option<T>>,
+{
+    assert_stream::<T, _>(PollFn { f })
+}
+
+impl<T, F> Stream for PollFn<F>
+where
+    F: FnMut(&mut Context<'_>) -> Poll<Option<T>>,
+{
+    type Item = T;
+
+    fn poll_next(mut self: Pin<&mut Self>, cx: &mut Context<'_>) -> Poll<Option<T>> {
+        (&mut self.f)(cx)
+    }
+}
diff --git a/third_party/rust/futures-util/src/stream/poll_immediate.rs b/third_party/rust/futures-util/src/stream/poll_immediate.rs
new file mode 100644
index 0000000000..c7e8a5b3c6
--- /dev/null
+++ b/third_party/rust/futures-util/src/stream/poll_immediate.rs
@@ -0,0 +1,80 @@
+use core::pin::Pin;
+use futures_core::task::{Context, Poll};
+use futures_core::Stream;
+use pin_project_lite::pin_project;
+
+pin_project! {
+    /// Stream for the [poll_immediate](poll_immediate()) function.
+    ///
+    /// It will never return [Poll::Pending](core::task::Poll::Pending)
+    #[derive(Debug, Clone)]
+    #[must_use = "futures do nothing unless you `.await` or poll them"]
+    pub struct PollImmediate<S> {
+        #[pin]
+        stream: Option<S>
+    }
+}
+
+impl<T, S> Stream for PollImmediate<S>
+where
+    S: Stream<Item = T>,
+{
+    type Item = Poll<T>;
+
+    fn poll_next(self: Pin<&mut Self>, cx: &mut Context<'_>) -> Poll<Option<Self::Item>> {
+        let mut this = self.project();
+        let stream = match this.stream.as_mut().as_pin_mut() {
+            // inner is gone, so we can continue to signal that the stream is closed.
+            None => return Poll::Ready(None),
+            Some(inner) => inner,
+        };
+
+        match stream.poll_next(cx) {
+            Poll::Ready(Some(t)) => Poll::Ready(Some(Poll::Ready(t))),
+            Poll::Ready(None) => {
+                this.stream.set(None);
+                Poll::Ready(None)
+            }
+            Poll::Pending => Poll::Ready(Some(Poll::Pending)),
+        }
+    }
+
+    fn size_hint(&self) -> (usize, Option<usize>) {
+        self.stream.as_ref().map_or((0, Some(0)), Stream::size_hint)
+    }
+}
+
+impl<S: Stream> super::FusedStream for PollImmediate<S> {
+    fn is_terminated(&self) -> bool {
+        self.stream.is_none()
+    }
+}
+
+/// Creates a new stream that always immediately returns [Poll::Ready](core::task::Poll::Ready) when awaiting it.
+///
+/// This is useful when immediacy is more important than waiting for the next item to be ready.
+///
+/// # Examples
+///
+/// ```
+/// # futures::executor::block_on(async {
+/// use futures::stream::{self, StreamExt};
+/// use futures::task::Poll;
+///
+/// let mut r = stream::poll_immediate(Box::pin(stream::iter(1_u32..3)));
+/// assert_eq!(r.next().await, Some(Poll::Ready(1)));
+/// assert_eq!(r.next().await, Some(Poll::Ready(2)));
+/// assert_eq!(r.next().await, None);
+///
+/// let mut p = stream::poll_immediate(Box::pin(stream::once(async {
+///     futures::pending!();
+///     42_u8
+/// })));
+/// assert_eq!(p.next().await, Some(Poll::Pending));
+/// assert_eq!(p.next().await, Some(Poll::Ready(42)));
+/// assert_eq!(p.next().await, None);
+/// # });
+/// ```
+pub fn poll_immediate<S: Stream>(s: S) -> PollImmediate<S> {
+    super::assert_stream::<Poll<S::Item>, PollImmediate<S>>(PollImmediate { stream: Some(s) })
+}
diff --git a/third_party/rust/futures-util/src/stream/repeat.rs b/third_party/rust/futures-util/src/stream/repeat.rs
new file mode 100644
index 0000000000..3f9aa87d5c
--- /dev/null
+++ b/third_party/rust/futures-util/src/stream/repeat.rs
@@ -0,0 +1,58 @@
+use super::assert_stream;
+use core::pin::Pin;
+use futures_core::stream::{FusedStream, Stream};
+use futures_core::task::{Context, Poll};
+
+/// Stream for the [`repeat`] function.
+#[derive(Debug, Clone)]
+#[must_use = "streams do nothing unless polled"]
+pub struct Repeat<T> {
+    item: T,
+}
+
+/// Create a stream which produces the same item repeatedly.
+///
+/// The stream never terminates. Note that you likely want to avoid
+/// usage of `collect` or such on the returned stream as it will exhaust
+/// available memory as it tries to just fill up all RAM.
+///
+/// ```
+/// # futures::executor::block_on(async {
+/// use futures::stream::{self, StreamExt};
+///
+/// let stream = stream::repeat(9);
+/// assert_eq!(vec![9, 9, 9], stream.take(3).collect::<Vec<i32>>().await);
+/// # });
+/// ```
+pub fn repeat<T>(item: T) -> Repeat<T>
+where
+    T: Clone,
+{
+    assert_stream::<T, _>(Repeat { item })
+}
+
+impl<T> Unpin for Repeat<T> {}
+
+impl<T> Stream for Repeat<T>
+where
+    T: Clone,
+{
+    type Item = T;
+
+    fn poll_next(self: Pin<&mut Self>, _: &mut Context<'_>) -> Poll<Option<Self::Item>> {
+        Poll::Ready(Some(self.item.clone()))
+    }
+
+    fn size_hint(&self) -> (usize, Option<usize>) {
+        (usize::max_value(), None)
+    }
+}
+
+impl<T> FusedStream for Repeat<T>
+where
+    T: Clone,
+{
+    fn is_terminated(&self) -> bool {
+        false
+    }
+}
diff --git a/third_party/rust/futures-util/src/stream/repeat_with.rs b/third_party/rust/futures-util/src/stream/repeat_with.rs
new file mode 100644
index 0000000000..f5a81b4ed4
--- /dev/null
+++ b/third_party/rust/futures-util/src/stream/repeat_with.rs
@@ -0,0 +1,93 @@
+use super::assert_stream;
+use core::pin::Pin;
+use futures_core::stream::{FusedStream, Stream};
+use futures_core::task::{Context, Poll};
+
+/// An stream that repeats elements of type `A` endlessly by
+/// applying the provided closure `F: FnMut() -> A`.
+///
+/// This `struct` is created by the [`repeat_with()`] function.
+/// See its documentation for more.
+#[derive(Debug, Clone)]
+#[must_use = "streams do nothing unless polled"]
+pub struct RepeatWith<F> {
+    repeater: F,
+}
+
+impl<A, F: FnMut() -> A> Unpin for RepeatWith<F> {}
+
+impl<A, F: FnMut() -> A> Stream for RepeatWith<F> {
+    type Item = A;
+
+    fn poll_next(mut self: Pin<&mut Self>, _: &mut Context<'_>) -> Poll<Option<Self::Item>> {
+        Poll::Ready(Some((&mut self.repeater)()))
+    }
+
+    fn size_hint(&self) -> (usize, Option<usize>) {
+        (usize::max_value(), None)
+    }
+}
+
+impl<A, F: FnMut() -> A> FusedStream for RepeatWith<F> {
+    fn is_terminated(&self) -> bool {
+        false
+    }
+}
+
+/// Creates a new stream that repeats elements of type `A` endlessly by
+/// applying the provided closure, the repeater, `F: FnMut() -> A`.
+///
+/// The `repeat_with()` function calls the repeater over and over again.
+///
+/// Infinite stream like `repeat_with()` are often used with adapters like
+/// [`stream.take()`], in order to make them finite.
+///
+/// If the element type of the stream you need implements [`Clone`], and
+/// it is OK to keep the source element in memory, you should instead use
+/// the [`stream.repeat()`] function.
+///
+/// # Examples
+///
+/// Basic usage:
+///
+/// ```
+/// # futures::executor::block_on(async {
+/// use futures::stream::{self, StreamExt};
+///
+/// // let's assume we have some value of a type that is not `Clone`
+/// // or which don't want to have in memory just yet because it is expensive:
+/// #[derive(PartialEq, Debug)]
+/// struct Expensive;
+///
+/// // a particular value forever:
+/// let mut things = stream::repeat_with(|| Expensive);
+///
+/// assert_eq!(Some(Expensive), things.next().await);
+/// assert_eq!(Some(Expensive), things.next().await);
+/// assert_eq!(Some(Expensive), things.next().await);
+/// # });
+/// ```
+///
+/// Using mutation and going finite:
+///
+/// ```rust
+/// # futures::executor::block_on(async {
+/// use futures::stream::{self, StreamExt};
+///
+/// // From the zeroth to the third power of two:
+/// let mut curr = 1;
+/// let mut pow2 = stream::repeat_with(|| { let tmp = curr; curr *= 2; tmp })
+///                     .take(4);
+///
+/// assert_eq!(Some(1), pow2.next().await);
+/// assert_eq!(Some(2), pow2.next().await);
+/// assert_eq!(Some(4), pow2.next().await);
+/// assert_eq!(Some(8), pow2.next().await);
+///
+/// // ... and now we're done
+/// assert_eq!(None, pow2.next().await);
+/// # });
+/// ```
+pub fn repeat_with<A, F: FnMut() -> A>(repeater: F) -> RepeatWith<F> {
+    assert_stream::<A, _>(RepeatWith { repeater })
+}
diff --git a/third_party/rust/futures-util/src/stream/select.rs b/third_party/rust/futures-util/src/stream/select.rs
new file mode 100644
index 0000000000..0c1e3af782
--- /dev/null
+++ b/third_party/rust/futures-util/src/stream/select.rs
@@ -0,0 +1,117 @@
+use super::assert_stream;
+use crate::stream::{select_with_strategy, PollNext, SelectWithStrategy};
+use core::pin::Pin;
+use futures_core::stream::{FusedStream, Stream};
+use futures_core::task::{Context, Poll};
+use pin_project_lite::pin_project;
+
+pin_project! {
+    /// Stream for the [`select()`] function.
+    #[derive(Debug)]
+    #[must_use = "streams do nothing unless polled"]
+    pub struct Select<St1, St2> {
+        #[pin]
+        inner: SelectWithStrategy<St1, St2, fn(&mut PollNext)-> PollNext, PollNext>,
+    }
+}
+
+/// This function will attempt to pull items from both streams. Each
+/// stream will be polled in a round-robin fashion, and whenever a stream is
+/// ready to yield an item that item is yielded.
+///
+/// After one of the two input streams completes, the remaining one will be
+/// polled exclusively. The returned stream completes when both input
+/// streams have completed.
+///
+/// Note that this function consumes both streams and returns a wrapped
+/// version of them.
+///
+/// ## Examples
+///
+/// ```rust
+/// # futures::executor::block_on(async {
+/// use futures::stream::{ repeat, select, StreamExt };
+///
+/// let left = repeat(1);
+/// let right = repeat(2);
+///
+/// let mut out = select(left, right);
+///
+/// for _ in 0..100 {
+///     // We should be alternating.
+///     assert_eq!(1, out.select_next_some().await);
+///     assert_eq!(2, out.select_next_some().await);
+/// }
+/// # });
+/// ```
+pub fn select<St1, St2>(stream1: St1, stream2: St2) -> Select<St1, St2>
+where
+    St1: Stream,
+    St2: Stream<Item = St1::Item>,
+{
+    fn round_robin(last: &mut PollNext) -> PollNext {
+        last.toggle()
+    }
+
+    assert_stream::<St1::Item, _>(Select {
+        inner: select_with_strategy(stream1, stream2, round_robin),
+    })
+}
+
+impl<St1, St2> Select<St1, St2> {
+    /// Acquires a reference to the underlying streams that this combinator is
+    /// pulling from.
+    pub fn get_ref(&self) -> (&St1, &St2) {
+        self.inner.get_ref()
+    }
+
+    /// Acquires a mutable reference to the underlying streams that this
+    /// combinator is pulling from.
+    ///
+    /// Note that care must be taken to avoid tampering with the state of the
+    /// stream which may otherwise confuse this combinator.
+    pub fn get_mut(&mut self) -> (&mut St1, &mut St2) {
+        self.inner.get_mut()
+    }
+
+    /// Acquires a pinned mutable reference to the underlying streams that this
+    /// combinator is pulling from.
+    ///
+    /// Note that care must be taken to avoid tampering with the state of the
+    /// stream which may otherwise confuse this combinator.
+    pub fn get_pin_mut(self: Pin<&mut Self>) -> (Pin<&mut St1>, Pin<&mut St2>) {
+        let this = self.project();
+        this.inner.get_pin_mut()
+    }
+
+    /// Consumes this combinator, returning the underlying streams.
+    ///
+    /// Note that this may discard intermediate state of this combinator, so
+    /// care should be taken to avoid losing resources when this is called.
+    pub fn into_inner(self) -> (St1, St2) {
+        self.inner.into_inner()
+    }
+}
+
+impl<St1, St2> FusedStream for Select<St1, St2>
+where
+    St1: Stream,
+    St2: Stream<Item = St1::Item>,
+{
+    fn is_terminated(&self) -> bool {
+        self.inner.is_terminated()
+    }
+}
+
+impl<St1, St2> Stream for Select<St1, St2>
+where
+    St1: Stream,
+    St2: Stream<Item = St1::Item>,
+{
+    type Item = St1::Item;
+
+    fn poll_next(self: Pin<&mut Self>, cx: &mut Context<'_>) -> Poll<Option<St1::Item>> {
+        let this = self.project();
+        this.inner.poll_next(cx)
+    }
+}
diff --git a/third_party/rust/futures-util/src/stream/select_all.rs b/third_party/rust/futures-util/src/stream/select_all.rs
new file mode 100644
index 0000000000..3474331adc
--- /dev/null
+++ b/third_party/rust/futures-util/src/stream/select_all.rs
@@ -0,0 +1,254 @@
+//! An unbounded set of streams
+
+use core::fmt::{self, Debug};
+use core::iter::FromIterator;
+use core::pin::Pin;
+
+use futures_core::ready;
+use futures_core::stream::{FusedStream, Stream};
+use futures_core::task::{Context, Poll};
+
+use pin_project_lite::pin_project;
+
+use super::assert_stream;
+use crate::stream::{futures_unordered, FuturesUnordered, StreamExt, StreamFuture};
+
+pin_project! {
+    /// An unbounded set of streams
+    ///
+    /// This "combinator" provides the ability to maintain a set of streams
+    /// and drive them all to completion.
+    ///
+    /// Streams are pushed into this set and their realized values are
+    /// yielded as they become ready. Streams will only be polled when they
+    /// generate notifications. This allows to coordinate a large number of streams.
+    ///
+    /// Note that you can create a ready-made `SelectAll` via the
+    /// `select_all` function in the `stream` module, or you can start with an
+    /// empty set with the `SelectAll::new` constructor.
+    #[must_use = "streams do nothing unless polled"]
+    pub struct SelectAll<St> {
+        #[pin]
+        inner: FuturesUnordered<StreamFuture<St>>,
+    }
+}
+
+impl<St: Debug> Debug for SelectAll<St> {
+    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
+        write!(f, "SelectAll {{ ... }}")
+    }
+}
+
+impl<St: Stream + Unpin> SelectAll<St> {
+    /// Constructs a new, empty `SelectAll`
+    ///
+    /// The returned `SelectAll` does not contain any streams and, in this
+    /// state, `SelectAll::poll` will return `Poll::Ready(None)`.
+    pub fn new() -> Self {
+        Self { inner: FuturesUnordered::new() }
+    }
+
+    /// Returns the number of streams contained in the set.
+    ///
+    /// This represents the total number of in-flight streams.
+    pub fn len(&self) -> usize {
+        self.inner.len()
+    }
+
+    /// Returns `true` if the set contains no streams
+    pub fn is_empty(&self) -> bool {
+        self.inner.is_empty()
+    }
+
+    /// Push a stream into the set.
+    ///
+    /// This function submits the given stream to the set for managing. This
+    /// function will not call `poll` on the submitted stream. The caller must
+    /// ensure that `SelectAll::poll` is called in order to receive task
+    /// notifications.
+    pub fn push(&mut self, stream: St) {
+        self.inner.push(stream.into_future());
+    }
+
+    /// Returns an iterator that allows inspecting each stream in the set.
+    pub fn iter(&self) -> Iter<'_, St> {
+        Iter(self.inner.iter())
+    }
+
+    /// Returns an iterator that allows modifying each stream in the set.
+    pub fn iter_mut(&mut self) -> IterMut<'_, St> {
+        IterMut(self.inner.iter_mut())
+    }
+
+    /// Clears the set, removing all streams.
+    pub fn clear(&mut self) {
+        self.inner.clear()
+    }
+}
+
+impl<St: Stream + Unpin> Default for SelectAll<St> {
+    fn default() -> Self {
+        Self::new()
+    }
+}
+
+impl<St: Stream + Unpin> Stream for SelectAll<St> {
+    type Item = St::Item;
+
+    fn poll_next(mut self: Pin<&mut Self>, cx: &mut Context<'_>) -> Poll<Option<Self::Item>> {
+        loop {
+            match ready!(self.inner.poll_next_unpin(cx)) {
+                Some((Some(item), remaining)) => {
+                    self.push(remaining);
+                    return Poll::Ready(Some(item));
+                }
+                Some((None, _)) => {
+                    // `FuturesUnordered` thinks it isn't terminated
+                    // because it yielded a Some.
+                    // We do not return, but poll `FuturesUnordered`
+                    // in the next loop iteration.
+                }
+                None => return Poll::Ready(None),
+            }
+        }
+    }
+}
+
+impl<St: Stream + Unpin> FusedStream for SelectAll<St> {
+    fn is_terminated(&self) -> bool {
+        self.inner.is_terminated()
+    }
+}
+
+/// Convert a list of streams into a `Stream` of results from the streams.
+///
+/// This essentially takes a list of streams (e.g. a vector, an iterator, etc.)
+/// and bundles them together into a single stream.
+/// The stream will yield items as they become available on the underlying
+/// streams internally, in the order they become available.
+///
+/// Note that the returned set can also be used to dynamically push more
+/// streams into the set as they become available.
+///
+/// This function is only available when the `std` or `alloc` feature of this
+/// library is activated, and it is activated by default.
+pub fn select_all<I>(streams: I) -> SelectAll<I::Item>
+where
+    I: IntoIterator,
+    I::Item: Stream + Unpin,
+{
+    let mut set = SelectAll::new();
+
+    for stream in streams {
+        set.push(stream);
+    }
+
+    assert_stream::<<I::Item as Stream>::Item, _>(set)
+}
+
+impl<St: Stream + Unpin> FromIterator<St> for SelectAll<St> {
+    fn from_iter<T: IntoIterator<Item = St>>(iter: T) -> Self {
+        select_all(iter)
+    }
+}
+
+impl<St: Stream + Unpin> Extend<St> for SelectAll<St> {
+    fn extend<T: IntoIterator<Item = St>>(&mut self, iter: T) {
+        for st in iter {
+            self.push(st)
+        }
+    }
+}
+
+impl<St: Stream + Unpin> IntoIterator for SelectAll<St> {
+    type Item = St;
+    type IntoIter = IntoIter<St>;
+
+    fn into_iter(self) -> Self::IntoIter {
+        IntoIter(self.inner.into_iter())
+    }
+}
+
+impl<'a, St: Stream + Unpin> IntoIterator for &'a SelectAll<St> {
+    type Item = &'a St;
+    type IntoIter = Iter<'a, St>;
+
+    fn into_iter(self) -> Self::IntoIter {
+        self.iter()
+    }
+}
+
+impl<'a, St: Stream + Unpin> IntoIterator for &'a mut SelectAll<St> {
+    type Item = &'a mut St;
+    type IntoIter = IterMut<'a, St>;
+
+    fn into_iter(self) -> Self::IntoIter {
+        self.iter_mut()
+    }
+}
+
+/// Immutable iterator over all streams in the unordered set.
+#[derive(Debug)]
+pub struct Iter<'a, St: Unpin>(futures_unordered::Iter<'a, StreamFuture<St>>);
+
+/// Mutable iterator over all streams in the unordered set.
+#[derive(Debug)]
+pub struct IterMut<'a, St: Unpin>(futures_unordered::IterMut<'a, StreamFuture<St>>);
+
+/// Owned iterator over all streams in the unordered set.
+#[derive(Debug)]
+pub struct IntoIter<St: Unpin>(futures_unordered::IntoIter<StreamFuture<St>>);
+
+impl<'a, St: Stream + Unpin> Iterator for Iter<'a, St> {
+    type Item = &'a St;
+
+    fn next(&mut self) -> Option<Self::Item> {
+        let st = self.0.next()?;
+        let next = st.get_ref();
+        // This should always be true because FuturesUnordered removes completed futures.
+        debug_assert!(next.is_some());
+        next
+    }
+
+    fn size_hint(&self) -> (usize, Option<usize>) {
+        self.0.size_hint()
+    }
+}
+
+impl<St: Stream + Unpin> ExactSizeIterator for Iter<'_, St> {}
+
+impl<'a, St: Stream + Unpin> Iterator for IterMut<'a, St> {
+    type Item = &'a mut St;
+
+    fn next(&mut self) -> Option<Self::Item> {
+        let st = self.0.next()?;
+        let next = st.get_mut();
+        // This should always be true because FuturesUnordered removes completed futures.
+        debug_assert!(next.is_some());
+        next
+    }
+
+    fn size_hint(&self) -> (usize, Option<usize>) {
+        self.0.size_hint()
+    }
+}
+
+impl<St: Stream + Unpin> ExactSizeIterator for IterMut<'_, St> {}
+
+impl<St: Stream + Unpin> Iterator for IntoIter<St> {
+    type Item = St;
+
+    fn next(&mut self) -> Option<Self::Item> {
+        let st = self.0.next()?;
+        let next = st.into_inner();
+        // This should always be true because FuturesUnordered removes completed futures.
+        debug_assert!(next.is_some());
+        next
+    }
+
+    fn size_hint(&self) -> (usize, Option<usize>) {
+        self.0.size_hint()
+    }
+}
+
+impl<St: Stream + Unpin> ExactSizeIterator for IntoIter<St> {}
diff --git a/third_party/rust/futures-util/src/stream/select_with_strategy.rs b/third_party/rust/futures-util/src/stream/select_with_strategy.rs
new file mode 100644
index 0000000000..224d5f821c
--- /dev/null
+++ b/third_party/rust/futures-util/src/stream/select_with_strategy.rs
@@ -0,0 +1,304 @@
+use super::assert_stream;
+use core::{fmt, pin::Pin};
+use futures_core::stream::{FusedStream, Stream};
+use futures_core::task::{Context, Poll};
+use pin_project_lite::pin_project;
+
+/// Type to tell [`SelectWithStrategy`] which stream to poll next.
+#[derive(Debug, PartialEq, Eq, Copy, Clone, Hash)]
+pub enum PollNext {
+    /// Poll the first stream.
+    Left,
+    /// Poll the second stream.
+    Right,
+}
+
+impl PollNext {
+    /// Toggle the value and return the old one.
+    pub fn toggle(&mut self) -> Self {
+        let old = *self;
+        *self = self.other();
+        old
+    }
+
+    fn other(&self) -> PollNext {
+        match self {
+            PollNext::Left => PollNext::Right,
+            PollNext::Right => PollNext::Left,
+        }
+    }
+}
+
+impl Default for PollNext {
+    fn default() -> Self {
+        PollNext::Left
+    }
+}
+
+enum InternalState {
+    Start,
+    LeftFinished,
+    RightFinished,
+    BothFinished,
+}
+
+impl InternalState {
+    fn finish(&mut self, ps: PollNext) {
+        match (&self, ps) {
+            (InternalState::Start, PollNext::Left) => {
+                *self = InternalState::LeftFinished;
+            }
+            (InternalState::Start, PollNext::Right) => {
+                *self = InternalState::RightFinished;
+            }
+            (InternalState::LeftFinished, PollNext::Right)
+            | (InternalState::RightFinished, PollNext::Left) => {
+                *self = InternalState::BothFinished;
+            }
+            _ => {}
+        }
+    }
+}
+
+pin_project! {
+    /// Stream for the [`select_with_strategy()`] function. See function docs for details.
+    #[must_use = "streams do nothing unless polled"]
+    #[project = SelectWithStrategyProj]
+    pub struct SelectWithStrategy<St1, St2, Clos, State> {
+        #[pin]
+        stream1: St1,
+        #[pin]
+        stream2: St2,
+        internal_state: InternalState,
+        state: State,
+        clos: Clos,
+    }
+}
+
+/// This function will attempt to pull items from both streams. You provide a
+/// closure to tell [`SelectWithStrategy`] which stream to poll. The closure can
+/// store state on `SelectWithStrategy` to which it will receive a `&mut` on every
+/// invocation. This allows basing the strategy on prior choices.
+///
+/// After one of the two input streams completes, the remaining one will be
+/// polled exclusively. The returned stream completes when both input
+/// streams have completed.
+///
+/// Note that this function consumes both streams and returns a wrapped
+/// version of them.
+///
+/// ## Examples
+///
+/// ### Priority
+/// This example shows how to always prioritize the left stream.
+///
+/// ```rust
+/// # futures::executor::block_on(async {
+/// use futures::stream::{ repeat, select_with_strategy, PollNext, StreamExt };
+///
+/// let left = repeat(1);
+/// let right = repeat(2);
+///
+/// // We don't need any state, so let's make it an empty tuple.
+/// // We must provide some type here, as there is no way for the compiler
+/// // to infer it. As we don't need to capture variables, we can just
+/// // use a function pointer instead of a closure.
+/// fn prio_left(_: &mut ()) -> PollNext { PollNext::Left }
+///
+/// let mut out = select_with_strategy(left, right, prio_left);
+///
+/// for _ in 0..100 {
+///     // Whenever we poll out, we will alwas get `1`.
+///     assert_eq!(1, out.select_next_some().await);
+/// }
+/// # });
+/// ```
+///
+/// ### Round Robin
+/// This example shows how to select from both streams round robin.
+/// Note: this special case is provided by [`futures-util::stream::select`].
+///
+/// ```rust
+/// # futures::executor::block_on(async {
+/// use futures::stream::{ repeat, select_with_strategy, PollNext, StreamExt };
+///
+/// let left = repeat(1);
+/// let right = repeat(2);
+///
+/// let rrobin = |last: &mut PollNext| last.toggle();
+///
+/// let mut out = select_with_strategy(left, right, rrobin);
+///
+/// for _ in 0..100 {
+///     // We should be alternating now.
+///     assert_eq!(1, out.select_next_some().await);
+///     assert_eq!(2, out.select_next_some().await);
+/// }
+/// # });
+/// ```
+pub fn select_with_strategy<St1, St2, Clos, State>(
+    stream1: St1,
+    stream2: St2,
+    which: Clos,
+) -> SelectWithStrategy<St1, St2, Clos, State>
+where
+    St1: Stream,
+    St2: Stream<Item = St1::Item>,
+    Clos: FnMut(&mut State) -> PollNext,
+    State: Default,
+{
+    assert_stream::<St1::Item, _>(SelectWithStrategy {
+        stream1,
+        stream2,
+        state: Default::default(),
+        internal_state: InternalState::Start,
+        clos: which,
+    })
+}
+
+impl<St1, St2, Clos, State> SelectWithStrategy<St1, St2, Clos, State> {
+    /// Acquires a reference to the underlying streams that this combinator is
+    /// pulling from.
+    pub fn get_ref(&self) -> (&St1, &St2) {
+        (&self.stream1, &self.stream2)
+    }
+
+    /// Acquires a mutable reference to the underlying streams that this
+    /// combinator is pulling from.
+    ///
+    /// Note that care must be taken to avoid tampering with the state of the
+    /// stream which may otherwise confuse this combinator.
+    pub fn get_mut(&mut self) -> (&mut St1, &mut St2) {
+        (&mut self.stream1, &mut self.stream2)
+    }
+
+    /// Acquires a pinned mutable reference to the underlying streams that this
+    /// combinator is pulling from.
+    ///
+    /// Note that care must be taken to avoid tampering with the state of the
+    /// stream which may otherwise confuse this combinator.
+    pub fn get_pin_mut(self: Pin<&mut Self>) -> (Pin<&mut St1>, Pin<&mut St2>) {
+        let this = self.project();
+        (this.stream1, this.stream2)
+    }
+
+    /// Consumes this combinator, returning the underlying streams.
+    ///
+    /// Note that this may discard intermediate state of this combinator, so
+    /// care should be taken to avoid losing resources when this is called.
+    pub fn into_inner(self) -> (St1, St2) {
+        (self.stream1, self.stream2)
+    }
+}
+
+impl<St1, St2, Clos, State> FusedStream for SelectWithStrategy<St1, St2, Clos, State>
+where
+    St1: Stream,
+    St2: Stream<Item = St1::Item>,
+    Clos: FnMut(&mut State) -> PollNext,
+{
+    fn is_terminated(&self) -> bool {
+        match self.internal_state {
+            InternalState::BothFinished => true,
+            _ => false,
+        }
+    }
+}
+
+#[inline]
+fn poll_side<St1, St2, Clos, State>(
+    select: &mut SelectWithStrategyProj<'_, St1, St2, Clos, State>,
+    side: PollNext,
+    cx: &mut Context<'_>,
+) -> Poll<Option<St1::Item>>
+where
+    St1: Stream,
+    St2: Stream<Item = St1::Item>,
+{
+    match side {
+        PollNext::Left => select.stream1.as_mut().poll_next(cx),
+        PollNext::Right => select.stream2.as_mut().poll_next(cx),
+    }
+}
+
+#[inline]
+fn poll_inner<St1, St2, Clos, State>(
+    select: &mut SelectWithStrategyProj<'_, St1, St2, Clos, State>,
+    side: PollNext,
+    cx: &mut Context<'_>,
+) -> Poll<Option<St1::Item>>
+where
+    St1: Stream,
+    St2: Stream<Item = St1::Item>,
+{
+    let first_done = match poll_side(select, side, cx) {
+        Poll::Ready(Some(item)) => return Poll::Ready(Some(item)),
+        Poll::Ready(None) => {
+            select.internal_state.finish(side);
+            true
+        }
+        Poll::Pending => false,
+    };
+    let other = side.other();
+    match poll_side(select, other, cx) {
+        Poll::Ready(None) => {
+            select.internal_state.finish(other);
+            if first_done {
+                Poll::Ready(None)
+            } else {
+                Poll::Pending
+            }
+        }
+        a => a,
+    }
+}
+
+impl<St1, St2, Clos, State> Stream for SelectWithStrategy<St1, St2, Clos, State>
+where
+    St1: Stream,
+    St2: Stream<Item = St1::Item>,
+    Clos: FnMut(&mut State) -> PollNext,
+{
+    type Item = St1::Item;
+
+    fn poll_next(self: Pin<&mut Self>, cx: &mut Context<'_>) -> Poll<Option<St1::Item>> {
+        let mut this = self.project();
+
+        match this.internal_state {
+            InternalState::Start => {
+                let next_side = (this.clos)(this.state);
+                poll_inner(&mut this, next_side, cx)
+            }
+            InternalState::LeftFinished => match this.stream2.poll_next(cx) {
+                Poll::Ready(None) => {
+                    *this.internal_state = InternalState::BothFinished;
+                    Poll::Ready(None)
+                }
+                a => a,
+            },
+            InternalState::RightFinished => match this.stream1.poll_next(cx) {
+                Poll::Ready(None) => {
+                    *this.internal_state = InternalState::BothFinished;
+                    Poll::Ready(None)
+                }
+                a => a,
+            },
+            InternalState::BothFinished => Poll::Ready(None),
+        }
+    }
+}
+
+impl<St1, St2, Clos, State> fmt::Debug for SelectWithStrategy<St1, St2, Clos, State>
+where
+    St1: fmt::Debug,
+    St2: fmt::Debug,
+    State: fmt::Debug,
+{
+    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
+        f.debug_struct("SelectWithStrategy")
+            .field("stream1", &self.stream1)
+            .field("stream2", &self.stream2)
+            .field("state", &self.state)
+            .finish()
+    }
+}
diff --git a/third_party/rust/futures-util/src/stream/stream/all.rs b/third_party/rust/futures-util/src/stream/stream/all.rs
new file mode 100644
index 0000000000..ba2baa5cf1
--- /dev/null
+++ b/third_party/rust/futures-util/src/stream/stream/all.rs
@@ -0,0 +1,92 @@
+use core::fmt;
+use core::pin::Pin;
+use futures_core::future::{FusedFuture, Future};
+use futures_core::ready;
+use futures_core::stream::Stream;
+use futures_core::task::{Context, Poll};
+use pin_project_lite::pin_project;
+
+pin_project! {
+    /// Future for the [`all`](super::StreamExt::all) method.
+    #[must_use = "futures do nothing unless you `.await` or poll them"]
+    pub struct All<St, Fut, F> {
+        #[pin]
+        stream: St,
+        f: F,
+        accum: Option<bool>,
+        #[pin]
+        future: Option<Fut>,
+    }
+}
+
+impl<St, Fut, F> fmt::Debug for All<St, Fut, F>
+where
+    St: fmt::Debug,
+    Fut: fmt::Debug,
+{
+    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
+        f.debug_struct("All")
+            .field("stream", &self.stream)
+            .field("accum", &self.accum)
+            .field("future", &self.future)
+            .finish()
+    }
+}
+
+impl<St, Fut, F> All<St, Fut, F>
+where
+    St: Stream,
+    F: FnMut(St::Item) -> Fut,
+    Fut: Future<Output = bool>,
+{
+    pub(super) fn new(stream: St, f: F) -> Self {
+        Self { stream, f, accum: Some(true), future: None }
+    }
+}
+
+impl<St, Fut, F> FusedFuture for All<St, Fut, F>
+where
+    St: Stream,
+    F: FnMut(St::Item) -> Fut,
+    Fut: Future<Output = bool>,
+{
+    fn is_terminated(&self) -> bool {
+        self.accum.is_none() && self.future.is_none()
+    }
+}
+
+impl<St, Fut, F> Future for All<St, Fut, F>
+where
+    St: Stream,
+    F: FnMut(St::Item) -> Fut,
+    Fut: Future<Output = bool>,
+{
+    type Output = bool;
+
+    fn poll(self: Pin<&mut Self>, cx: &mut Context<'_>) -> Poll<bool> {
+        let mut this = self.project();
+        Poll::Ready(loop {
+            if let Some(fut) = this.future.as_mut().as_pin_mut() {
+                // we're currently processing a future to produce a new accum value
+                let acc = this.accum.unwrap() && ready!(fut.poll(cx));
+                if !acc {
+                    break false;
+                } // early exit
+                *this.accum = Some(acc);
+                this.future.set(None);
+            } else if this.accum.is_some() {
+                // we're waiting on a new item from the stream
+                match ready!(this.stream.as_mut().poll_next(cx)) {
+                    Some(item) => {
+                        this.future.set(Some((this.f)(item)));
+                    }
+                    None => {
+                        break this.accum.take().unwrap();
+                    }
+                }
+            } else {
+                panic!("All polled after completion")
+            }
+        })
+    }
+}
diff --git a/third_party/rust/futures-util/src/stream/stream/any.rs b/third_party/rust/futures-util/src/stream/stream/any.rs
new file mode 100644
index 0000000000..f023125c70
--- /dev/null
+++ b/third_party/rust/futures-util/src/stream/stream/any.rs
@@ -0,0 +1,92 @@
+use core::fmt;
+use core::pin::Pin;
+use futures_core::future::{FusedFuture, Future};
+use futures_core::ready;
+use futures_core::stream::Stream;
+use futures_core::task::{Context, Poll};
+use pin_project_lite::pin_project;
+
+pin_project! {
+    /// Future for the [`any`](super::StreamExt::any) method.
+    #[must_use = "futures do nothing unless you `.await` or poll them"]
+    pub struct Any<St, Fut, F> {
+        #[pin]
+        stream: St,
+        f: F,
+        accum: Option<bool>,
+        #[pin]
+        future: Option<Fut>,
+    }
+}
+
+impl<St, Fut, F> fmt::Debug for Any<St, Fut, F>
+where
+    St: fmt::Debug,
+    Fut: fmt::Debug,
+{
+    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
+        f.debug_struct("Any")
+            .field("stream", &self.stream)
+            .field("accum", &self.accum)
+            .field("future", &self.future)
+            .finish()
+    }
+}
+
+impl<St, Fut, F> Any<St, Fut, F>
+where
+    St: Stream,
+    F: FnMut(St::Item) -> Fut,
+    Fut: Future<Output = bool>,
+{
+    pub(super) fn new(stream: St, f: F) -> Self {
+        Self { stream, f, accum: Some(false), future: None }
+    }
+}
+
+impl<St, Fut, F> FusedFuture for Any<St, Fut, F>
+where
+    St: Stream,
+    F: FnMut(St::Item) -> Fut,
+    Fut: Future<Output = bool>,
+{
+    fn is_terminated(&self) -> bool {
+        self.accum.is_none() && self.future.is_none()
+    }
+}
+
+impl<St, Fut, F> Future for Any<St, Fut, F>
+where
+    St: Stream,
+    F: FnMut(St::Item) -> Fut,
+    Fut: Future<Output = bool>,
+{
+    type Output = bool;
+
+    fn poll(self: Pin<&mut Self>, cx: &mut Context<'_>) -> Poll<bool> {
+        let mut this = self.project();
+        Poll::Ready(loop {
+            if let Some(fut) = this.future.as_mut().as_pin_mut() {
+                // we're currently processing a future to produce a new accum value
+                let acc = this.accum.unwrap() || ready!(fut.poll(cx));
+                if acc {
+                    break true;
+                } // early exit
+                *this.accum = Some(acc);
+                this.future.set(None);
+            } else if this.accum.is_some() {
+                // we're waiting on a new item from the stream
+                match ready!(this.stream.as_mut().poll_next(cx)) {
+                    Some(item) => {
+                        this.future.set(Some((this.f)(item)));
+                    }
+                    None => {
+                        break this.accum.take().unwrap();
+                    }
+                }
+            } else {
+                panic!("Any polled after completion")
+            }
+        })
+    }
+}
diff --git a/third_party/rust/futures-util/src/stream/stream/buffer_unordered.rs b/third_party/rust/futures-util/src/stream/stream/buffer_unordered.rs
new file mode 100644
index 0000000000..91b0f6bcce
--- /dev/null
+++ b/third_party/rust/futures-util/src/stream/stream/buffer_unordered.rs
@@ -0,0 +1,120 @@
+use crate::stream::{Fuse, FuturesUnordered, StreamExt};
+use core::fmt;
+use core::pin::Pin;
+use futures_core::future::Future;
+use futures_core::stream::{FusedStream, Stream};
+use futures_core::task::{Context, Poll};
+#[cfg(feature = "sink")]
+use futures_sink::Sink;
+use pin_project_lite::pin_project;
+
+pin_project! {
+    /// Stream for the [`buffer_unordered`](super::StreamExt::buffer_unordered)
+    /// method.
+    #[must_use = "streams do nothing unless polled"]
+    pub struct BufferUnordered<St>
+    where
+        St: Stream,
+    {
+        #[pin]
+        stream: Fuse<St>,
+        in_progress_queue: FuturesUnordered<St::Item>,
+        max: usize,
+    }
+}
+
+impl<St> fmt::Debug for BufferUnordered<St>
+where
+    St: Stream + fmt::Debug,
+{
+    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
+        f.debug_struct("BufferUnordered")
+            .field("stream", &self.stream)
+            .field("in_progress_queue", &self.in_progress_queue)
+            .field("max", &self.max)
+            .finish()
+    }
+}
+
+impl<St> BufferUnordered<St>
+where
+    St: Stream,
+    St::Item: Future,
+{
+    pub(super) fn new(stream: St, n: usize) -> Self {
+        Self {
+            stream: super::Fuse::new(stream),
+            in_progress_queue: FuturesUnordered::new(),
+            max: n,
+        }
+    }
+
+    delegate_access_inner!(stream, St, (.));
+}
+
+impl<St> Stream for BufferUnordered<St>
+where
+    St: Stream,
+    St::Item: Future,
+{
+    type Item = <St::Item as Future>::Output;
+
+    fn poll_next(self: Pin<&mut Self>, cx: &mut Context<'_>) -> Poll<Option<Self::Item>> {
+        let mut this = self.project();
+
+        // First up, try to spawn off as many futures as possible by filling up
+        // our queue of futures.
+        while this.in_progress_queue.len() < *this.max {
+            match this.stream.as_mut().poll_next(cx) {
+                Poll::Ready(Some(fut)) => this.in_progress_queue.push(fut),
+                Poll::Ready(None) | Poll::Pending => break,
+            }
+        }
+
+        // Attempt to pull the next value from the in_progress_queue
+        match this.in_progress_queue.poll_next_unpin(cx) {
+            x @ Poll::Pending | x @ Poll::Ready(Some(_)) => return x,
+            Poll::Ready(None) => {}
+        }
+
+        // If more values are still coming from the stream, we're not done yet
+        if this.stream.is_done() {
+            Poll::Ready(None)
+        } else {
+            Poll::Pending
+        }
+    }
+
+    fn size_hint(&self) -> (usize, Option<usize>) {
+        let queue_len = self.in_progress_queue.len();
+        let (lower, upper) = self.stream.size_hint();
+        let lower = lower.saturating_add(queue_len);
+        let upper = match upper {
+            Some(x) => x.checked_add(queue_len),
+            None => None,
+        };
+        (lower, upper)
+    }
+}
+
+impl<St> FusedStream for BufferUnordered<St>
+where
+    St: Stream,
+    St::Item: Future,
+{
+    fn is_terminated(&self) -> bool {
+        self.in_progress_queue.is_terminated() && self.stream.is_terminated()
+    }
+}
+
+// Forwarding impl of Sink from the underlying stream
+#[cfg(feature = "sink")]
+impl<S, Item> Sink<Item> for BufferUnordered<S>
+where
+    S: Stream + Sink<Item>,
+    S::Item: Future,
+{
+    type Error = S::Error;
+
+    delegate_sink!(stream, Item);
+}
diff --git a/third_party/rust/futures-util/src/stream/stream/buffered.rs b/third_party/rust/futures-util/src/stream/stream/buffered.rs
new file mode 100644
index 0000000000..8ca0391c55
--- /dev/null
+++ b/third_party/rust/futures-util/src/stream/stream/buffered.rs
@@ -0,0 +1,108 @@
+use crate::stream::{Fuse, FuturesOrdered, StreamExt};
+use core::fmt;
+use core::pin::Pin;
+use futures_core::future::Future;
+use futures_core::ready;
+use futures_core::stream::Stream;
+use futures_core::task::{Context, Poll};
+#[cfg(feature = "sink")]
+use futures_sink::Sink;
+use pin_project_lite::pin_project;
+
+pin_project! {
+    /// Stream for the [`buffered`](super::StreamExt::buffered) method.
+    #[must_use = "streams do nothing unless polled"]
+    pub struct Buffered<St>
+    where
+        St: Stream,
+        St::Item: Future,
+    {
+        #[pin]
+        stream: Fuse<St>,
+        in_progress_queue: FuturesOrdered<St::Item>,
+        max: usize,
+    }
+}
+
+impl<St> fmt::Debug for Buffered<St>
+where
+    St: Stream + fmt::Debug,
+    St::Item: Future,
+{
+    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
+        f.debug_struct("Buffered")
+            .field("stream", &self.stream)
+            .field("in_progress_queue", &self.in_progress_queue)
+            .field("max", &self.max)
+            .finish()
+    }
+}
+
+impl<St> Buffered<St>
+where
+    St: Stream,
+    St::Item: Future,
+{
+    pub(super) fn new(stream: St, n: usize) -> Self {
+        Self { stream: super::Fuse::new(stream), in_progress_queue: FuturesOrdered::new(), max: n }
+    }
+
+    delegate_access_inner!(stream, St, (.));
+}
+
+impl<St> Stream for Buffered<St>
+where
+    St: Stream,
+    St::Item: Future,
+{
+    type Item = <St::Item as Future>::Output;
+
+    fn poll_next(self: Pin<&mut Self>, cx: &mut Context<'_>) -> Poll<Option<Self::Item>> {
+        let mut this = self.project();
+
+        // First up, try to spawn off as many futures as possible by filling up
+        // our queue of futures.
+        while this.in_progress_queue.len() < *this.max {
+            match this.stream.as_mut().poll_next(cx) {
+                Poll::Ready(Some(fut)) => this.in_progress_queue.push_back(fut),
+                Poll::Ready(None) | Poll::Pending => break,
+            }
+        }
+
+        // Attempt to pull the next value from the in_progress_queue
+        let res = this.in_progress_queue.poll_next_unpin(cx);
+        if let Some(val) = ready!(res) {
+            return Poll::Ready(Some(val));
+        }
+
+        // If more values are still coming from the stream, we're not done yet
+        if this.stream.is_done() {
+            Poll::Ready(None)
+        } else {
+            Poll::Pending
+        }
+    }
+
+    fn size_hint(&self) -> (usize, Option<usize>) {
+        let queue_len = self.in_progress_queue.len();
+        let (lower, upper) = self.stream.size_hint();
+        let lower = lower.saturating_add(queue_len);
+        let upper = match upper {
+            Some(x) => x.checked_add(queue_len),
+            None => None,
+        };
+        (lower, upper)
+    }
+}
+
+// Forwarding impl of Sink from the underlying stream
+#[cfg(feature = "sink")]
+impl<S, Item> Sink<Item> for Buffered<S>
+where
+    S: Stream + Sink<Item>,
+    S::Item: Future,
+{
+    type Error = S::Error;
+
+    delegate_sink!(stream, Item);
+}
diff --git a/third_party/rust/futures-util/src/stream/stream/catch_unwind.rs b/third_party/rust/futures-util/src/stream/stream/catch_unwind.rs
new file mode 100644
index 0000000000..09a6dc1b76
--- /dev/null
+++ b/third_party/rust/futures-util/src/stream/stream/catch_unwind.rs
@@ -0,0 +1,61 @@
+use futures_core::stream::{FusedStream, Stream};
+use futures_core::task::{Context, Poll};
+use pin_project_lite::pin_project;
+use std::any::Any;
+use std::panic::{catch_unwind, AssertUnwindSafe, UnwindSafe};
+use std::pin::Pin;
+
+pin_project! {
+    /// Stream for the [`catch_unwind`](super::StreamExt::catch_unwind) method.
+    #[derive(Debug)]
+    #[must_use = "streams do nothing unless polled"]
+    pub struct CatchUnwind<St> {
+        #[pin]
+        stream: St,
+        caught_unwind: bool,
+    }
+}
+
+impl<St: Stream + UnwindSafe> CatchUnwind<St> {
+    pub(super) fn new(stream: St) -> Self {
+        Self { stream, caught_unwind: false }
+    }
+
+    delegate_access_inner!(stream, St, ());
+}
+
+impl<St: Stream + UnwindSafe> Stream for CatchUnwind<St> {
+    type Item = Result<St::Item, Box<dyn Any + Send>>;
+
+    fn poll_next(self: Pin<&mut Self>, cx: &mut Context<'_>) -> Poll<Option<Self::Item>> {
+        let mut this = self.project();
+
+        if *this.caught_unwind {
+            Poll::Ready(None)
+        } else {
+            let res = catch_unwind(AssertUnwindSafe(|| this.stream.as_mut().poll_next(cx)));
+
+            match res {
+                Ok(poll) => poll.map(|opt| opt.map(Ok)),
+                Err(e) => {
+                    *this.caught_unwind = true;
+                    Poll::Ready(Some(Err(e)))
+                }
+            }
+        }
+    }
+
+    fn size_hint(&self) -> (usize, Option<usize>) {
+        if self.caught_unwind {
+            (0, Some(0))
+        } else {
+            self.stream.size_hint()
+        }
+    }
+}
+
+impl<St: FusedStream + UnwindSafe> FusedStream for CatchUnwind<St> {
+    fn is_terminated(&self) -> bool {
+        self.caught_unwind || self.stream.is_terminated()
+    }
+}
diff --git a/third_party/rust/futures-util/src/stream/stream/chain.rs b/third_party/rust/futures-util/src/stream/stream/chain.rs
new file mode 100644
index 0000000000..c5da35e25e
--- /dev/null
+++ b/third_party/rust/futures-util/src/stream/stream/chain.rs
@@ -0,0 +1,75 @@
+use core::pin::Pin;
+use futures_core::ready;
+use futures_core::stream::{FusedStream, Stream};
+use futures_core::task::{Context, Poll};
+use pin_project_lite::pin_project;
+
+pin_project! {
+    /// Stream for the [`chain`](super::StreamExt::chain) method.
+    #[derive(Debug)]
+    #[must_use = "streams do nothing unless polled"]
+    pub struct Chain<St1, St2> {
+        #[pin]
+        first: Option<St1>,
+        #[pin]
+        second: St2,
+    }
+}
+
+// All interactions with `Pin<&mut Chain<..>>` happen through these methods
+impl<St1, St2> Chain<St1, St2>
+where
+    St1: Stream,
+    St2: Stream<Item = St1::Item>,
+{
+    pub(super) fn new(stream1: St1, stream2: St2) -> Self {
+        Self { first: Some(stream1), second: stream2 }
+    }
+}
+
+impl<St1, St2> FusedStream for Chain<St1, St2>
+where
+    St1: Stream,
+    St2: FusedStream<Item = St1::Item>,
+{
+    fn is_terminated(&self) -> bool {
+        self.first.is_none() && self.second.is_terminated()
+    }
+}
+
+impl<St1, St2> Stream for Chain<St1, St2>
+where
+    St1: Stream,
+    St2: Stream<Item = St1::Item>,
+{
+    type Item = St1::Item;
+
+    fn poll_next(self: Pin<&mut Self>, cx: &mut Context<'_>) -> Poll<Option<Self::Item>> {
+        let mut this = self.project();
+        if let Some(first) = this.first.as_mut().as_pin_mut() {
+            if let Some(item) = ready!(first.poll_next(cx)) {
+                return Poll::Ready(Some(item));
+            }
+        }
+        this.first.set(None);
+        this.second.poll_next(cx)
+    }
+
+    fn size_hint(&self) -> (usize, Option<usize>) {
+        if let Some(first) = &self.first {
+            let (first_lower, first_upper) = first.size_hint();
+            let (second_lower, second_upper) = self.second.size_hint();
+
+            let lower = first_lower.saturating_add(second_lower);
+
+            let upper = match (first_upper, second_upper) {
+                (Some(x), Some(y)) => x.checked_add(y),
+                _ => None,
+            };
+
+            (lower, upper)
+        } else {
+            self.second.size_hint()
+        }
+    }
+}
diff --git a/third_party/rust/futures-util/src/stream/stream/chunks.rs b/third_party/rust/futures-util/src/stream/stream/chunks.rs
new file mode 100644
index 0000000000..2a71ebc6cc
--- /dev/null
+++ b/third_party/rust/futures-util/src/stream/stream/chunks.rs
@@ -0,0 +1,103 @@
+use crate::stream::Fuse;
+use alloc::vec::Vec;
+use core::mem;
+use core::pin::Pin;
+use futures_core::ready;
+use futures_core::stream::{FusedStream, Stream};
+use futures_core::task::{Context, Poll};
+#[cfg(feature = "sink")]
+use futures_sink::Sink;
+use pin_project_lite::pin_project;
+
+pin_project! {
+    /// Stream for the [`chunks`](super::StreamExt::chunks) method.
+    #[derive(Debug)]
+    #[must_use = "streams do nothing unless polled"]
+    pub struct Chunks<St: Stream> {
+        #[pin]
+        stream: Fuse<St>,
+        items: Vec<St::Item>,
+        cap: usize, // https://github.com/rust-lang/futures-rs/issues/1475
+    }
+}
+
+impl<St: Stream> Chunks<St> {
+    pub(super) fn new(stream: St, capacity: usize) -> Self {
+        assert!(capacity > 0);
+
+        Self {
+            stream: super::Fuse::new(stream),
+            items: Vec::with_capacity(capacity),
+            cap: capacity,
+        }
+    }
+
+    fn take(self: Pin<&mut Self>) -> Vec<St::Item> {
+        let cap = self.cap;
+        mem::replace(self.project().items, Vec::with_capacity(cap))
+    }
+
+    delegate_access_inner!(stream, St, (.));
+}
+
+impl<St: Stream> Stream for Chunks<St> {
+    type Item = Vec<St::Item>;
+
+    fn poll_next(mut self: Pin<&mut Self>, cx: &mut Context<'_>) -> Poll<Option<Self::Item>> {
+        let mut this = self.as_mut().project();
+        loop {
+            match ready!(this.stream.as_mut().poll_next(cx)) {
+                // Push the item into the buffer and check whether it is full.
+                // If so, replace our buffer with a new and empty one and return
+                // the full one.
+                Some(item) => {
+                    this.items.push(item);
+                    if this.items.len() >= *this.cap {
+                        return Poll::Ready(Some(self.take()));
+                    }
+                }
+
+                // Since the underlying stream ran out of values, return what we
+                // have buffered, if we have anything.
+                None => {
+                    let last = if this.items.is_empty() {
+                        None
+                    } else {
+                        let full_buf = mem::take(this.items);
+                        Some(full_buf)
+                    };
+
+                    return Poll::Ready(last);
+                }
+            }
+        }
+    }
+
+    fn size_hint(&self) -> (usize, Option<usize>) {
+        let chunk_len = usize::from(!self.items.is_empty());
+        let (lower, upper) = self.stream.size_hint();
+        let lower = (lower / self.cap).saturating_add(chunk_len);
+        let upper = match upper {
+            Some(x) => x.checked_add(chunk_len),
+            None => None,
+        };
+        (lower, upper)
+    }
+}
+
+impl<St: FusedStream> FusedStream for Chunks<St> {
+    fn is_terminated(&self) -> bool {
+        self.stream.is_terminated() && self.items.is_empty()
+    }
+}
+
+// Forwarding impl of Sink from the underlying stream
+#[cfg(feature = "sink")]
+impl<S, Item> Sink<Item> for Chunks<S>
+where
+    S: Stream + Sink<Item>,
+{
+    type Error = S::Error;
+
+    delegate_sink!(stream, Item);
+}
diff --git a/third_party/rust/futures-util/src/stream/stream/collect.rs b/third_party/rust/futures-util/src/stream/stream/collect.rs
new file mode 100644
index 0000000000..970ac26dbf
--- /dev/null
+++ b/third_party/rust/futures-util/src/stream/stream/collect.rs
@@ -0,0 +1,56 @@
+use core::mem;
+use core::pin::Pin;
+use futures_core::future::{FusedFuture, Future};
+use futures_core::ready;
+use futures_core::stream::{FusedStream, Stream};
+use futures_core::task::{Context, Poll};
+use pin_project_lite::pin_project;
+
+pin_project! {
+    /// Future for the [`collect`](super::StreamExt::collect) method.
+    #[derive(Debug)]
+    #[must_use = "futures do nothing unless you `.await` or poll them"]
+    pub struct Collect<St, C> {
+        #[pin]
+        stream: St,
+        collection: C,
+    }
+}
+
+impl<St: Stream, C: Default> Collect<St, C> {
+    fn finish(self: Pin<&mut Self>) -> C {
+        mem::take(self.project().collection)
+    }
+
+    pub(super) fn new(stream: St) -> Self {
+        Self { stream, collection: Default::default() }
+    }
+}
+
+impl<St, C> FusedFuture for Collect<St, C>
+where
+    St: FusedStream,
+    C: Default + Extend<St::Item>,
+{
+    fn is_terminated(&self) -> bool {
+        self.stream.is_terminated()
+    }
+}
+
+impl<St, C> Future for Collect<St, C>
+where
+    St: Stream,
+    C: Default + Extend<St::Item>,
+{
+    type Output = C;
+
+    fn poll(mut self: Pin<&mut Self>, cx: &mut Context<'_>) -> Poll<C> {
+        let mut this = self.as_mut().project();
+        loop {
+            match ready!(this.stream.as_mut().poll_next(cx)) {
+                Some(e) => this.collection.extend(Some(e)),
+                None => return Poll::Ready(self.finish()),
+            }
+        }
+    }
+}
diff --git a/third_party/rust/futures-util/src/stream/stream/concat.rs b/third_party/rust/futures-util/src/stream/stream/concat.rs
new file mode 100644
index 0000000000..7e058b2315
--- /dev/null
+++ b/third_party/rust/futures-util/src/stream/stream/concat.rs
@@ -0,0 +1,62 @@
+use core::pin::Pin;
+use futures_core::future::{FusedFuture, Future};
+use futures_core::ready;
+use futures_core::stream::{FusedStream, Stream};
+use futures_core::task::{Context, Poll};
+use pin_project_lite::pin_project;
+
+pin_project! {
+    /// Future for the [`concat`](super::StreamExt::concat) method.
+    #[derive(Debug)]
+    #[must_use = "futures do nothing unless you `.await` or poll them"]
+    pub struct Concat<St: Stream> {
+        #[pin]
+        stream: St,
+        accum: Option<St::Item>,
+    }
+}
+
+impl<St> Concat<St>
+where
+    St: Stream,
+    St::Item: Extend<<St::Item as IntoIterator>::Item> + IntoIterator + Default,
+{
+    pub(super) fn new(stream: St) -> Self {
+        Self { stream, accum: None }
+    }
+}
+
+impl<St> Future for Concat<St>
+where
+    St: Stream,
+    St::Item: Extend<<St::Item as IntoIterator>::Item> + IntoIterator + Default,
+{
+    type Output = St::Item;
+
+    fn poll(self: Pin<&mut Self>, cx: &mut Context<'_>) -> Poll<Self::Output> {
+        let mut this = self.project();
+
+        loop {
+            match ready!(this.stream.as_mut().poll_next(cx)) {
+                None => return Poll::Ready(this.accum.take().unwrap_or_default()),
+                Some(e) => {
+                    if let Some(a) = this.accum {
+                        a.extend(e)
+                    } else {
+                        *this.accum = Some(e)
+                    }
+                }
+            }
+        }
+    }
+}
+
+impl<St> FusedFuture for Concat<St>
+where
+    St: FusedStream,
+    St::Item: Extend<<St::Item as IntoIterator>::Item> + IntoIterator + Default,
+{
+    fn is_terminated(&self) -> bool {
+        self.accum.is_none() && self.stream.is_terminated()
+    }
+}
diff --git a/third_party/rust/futures-util/src/stream/stream/count.rs b/third_party/rust/futures-util/src/stream/stream/count.rs
new file mode 100644
index 0000000000..513cab7b6a
--- /dev/null
+++ b/third_party/rust/futures-util/src/stream/stream/count.rs
@@ -0,0 +1,53 @@
+use core::fmt;
+use core::pin::Pin;
+use futures_core::future::{FusedFuture, Future};
+use futures_core::ready;
+use futures_core::stream::{FusedStream, Stream};
+use futures_core::task::{Context, Poll};
+use pin_project_lite::pin_project;
+
+pin_project! {
+    /// Future for the [`count`](super::StreamExt::count) method.
+    #[must_use = "futures do nothing unless you `.await` or poll them"]
+    pub struct Count<St> {
+        #[pin]
+        stream: St,
+        count: usize
+    }
+}
+
+impl<St> fmt::Debug for Count<St>
+where
+    St: fmt::Debug,
+{
+    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
+        f.debug_struct("Count").field("stream", &self.stream).field("count", &self.count).finish()
+    }
+}
+
+impl<St: Stream> Count<St> {
+    pub(super) fn new(stream: St) -> Self {
+        Self { stream, count: 0 }
+    }
+}
+
+impl<St: FusedStream> FusedFuture for Count<St> {
+    fn is_terminated(&self) -> bool {
+        self.stream.is_terminated()
+    }
+}
+
+impl<St: Stream> Future for Count<St> {
+    type Output = usize;
+
+    fn poll(self: Pin<&mut Self>, cx: &mut Context<'_>) -> Poll<Self::Output> {
+        let mut this = self.project();
+
+        Poll::Ready(loop {
+            match ready!(this.stream.as_mut().poll_next(cx)) {
+                Some(_) => *this.count += 1,
+                None => break *this.count,
+            }
+        })
+    }
+}
diff --git a/third_party/rust/futures-util/src/stream/stream/cycle.rs b/third_party/rust/futures-util/src/stream/stream/cycle.rs
new file mode 100644
index 0000000000..507431d24f
--- /dev/null
+++ b/third_party/rust/futures-util/src/stream/stream/cycle.rs
@@ -0,0 +1,68 @@
+use core::pin::Pin;
+use core::usize;
+use futures_core::ready;
+use futures_core::stream::{FusedStream, Stream};
+use futures_core::task::{Context, Poll};
+use pin_project_lite::pin_project;
+
+pin_project! {
+    /// Stream for the [`cycle`](super::StreamExt::cycle) method.
+    #[derive(Debug)]
+    #[must_use = "streams do nothing unless polled"]
+    pub struct Cycle<St> {
+        orig: St,
+        #[pin]
+        stream: St,
+    }
+}
+
+impl<St> Cycle<St>
+where
+    St: Clone + Stream,
+{
+    pub(super) fn new(stream: St) -> Self {
+        Self { orig: stream.clone(), stream }
+    }
+}
+
+impl<St> Stream for Cycle<St>
+where
+    St: Clone + Stream,
+{
+    type Item = St::Item;
+
+    fn poll_next(self: Pin<&mut Self>, cx: &mut Context<'_>) -> Poll<Option<Self::Item>> {
+        let mut this = self.project();
+
+        match ready!(this.stream.as_mut().poll_next(cx)) {
+            None => {
+                this.stream.set(this.orig.clone());
+                this.stream.poll_next(cx)
+            }
+            item => Poll::Ready(item),
+        }
+    }
+
+    fn size_hint(&self) -> (usize, Option<usize>) {
+        // the cycle stream is either empty or infinite
+        match self.orig.size_hint() {
+            size @ (0, Some(0)) => size,
+            (0, _) => (0, None),
+            _ => (usize::max_value(), None),
+        }
+    }
+}
+
+impl<St> FusedStream for Cycle<St>
+where
+    St: Clone + Stream,
+{
+    fn is_terminated(&self) -> bool {
+        // the cycle stream is either empty or infinite
+        if let (0, Some(0)) = self.size_hint() {
+            true
+        } else {
+            false
+        }
+    }
+}
diff --git a/third_party/rust/futures-util/src/stream/stream/enumerate.rs b/third_party/rust/futures-util/src/stream/stream/enumerate.rs
new file mode 100644
index 0000000000..1cf9d49aaa
--- /dev/null
+++ b/third_party/rust/futures-util/src/stream/stream/enumerate.rs
@@ -0,0 +1,64 @@
+use core::pin::Pin;
+use futures_core::ready;
+use futures_core::stream::{FusedStream, Stream};
+use futures_core::task::{Context, Poll};
+#[cfg(feature = "sink")]
+use futures_sink::Sink;
+use pin_project_lite::pin_project;
+
+pin_project! {
+    /// Stream for the [`enumerate`](super::StreamExt::enumerate) method.
+    #[derive(Debug)]
+    #[must_use = "streams do nothing unless polled"]
+    pub struct Enumerate<St> {
+        #[pin]
+        stream: St,
+        count: usize,
+    }
+}
+
+impl<St: Stream> Enumerate<St> {
+    pub(super) fn new(stream: St) -> Self {
+        Self { stream, count: 0 }
+    }
+
+    delegate_access_inner!(stream, St, ());
+}
+
+impl<St: Stream + FusedStream> FusedStream for Enumerate<St> {
+    fn is_terminated(&self) -> bool {
+        self.stream.is_terminated()
+    }
+}
+
+impl<St: Stream> Stream for Enumerate<St> {
+    type Item = (usize, St::Item);
+
+    fn poll_next(self: Pin<&mut Self>, cx: &mut Context<'_>) -> Poll<Option<Self::Item>> {
+        let this = self.project();
+
+        match ready!(this.stream.poll_next(cx)) {
+            Some(item) => {
+                let prev_count = *this.count;
+                *this.count += 1;
+                Poll::Ready(Some((prev_count, item)))
+            }
+            None => Poll::Ready(None),
+        }
+    }
+
+    fn size_hint(&self) -> (usize, Option<usize>) {
+        self.stream.size_hint()
+    }
+}
+
+// Forwarding impl of Sink from the underlying stream
+#[cfg(feature = "sink")]
+impl<S, Item> Sink<Item> for Enumerate<S>
+where
+    S: Stream + Sink<Item>,
+{
+    type Error = S::Error;
+
+    delegate_sink!(stream, Item);
+}
diff --git a/third_party/rust/futures-util/src/stream/stream/filter.rs b/third_party/rust/futures-util/src/stream/stream/filter.rs
new file mode 100644
index 0000000000..997fe9977e
--- /dev/null
+++ b/third_party/rust/futures-util/src/stream/stream/filter.rs
@@ -0,0 +1,117 @@
+use crate::fns::FnMut1;
+use core::fmt;
+use core::pin::Pin;
+use futures_core::future::Future;
+use futures_core::ready;
+use futures_core::stream::{FusedStream, Stream};
+use futures_core::task::{Context, Poll};
+#[cfg(feature = "sink")]
+use futures_sink::Sink;
+use pin_project_lite::pin_project;
+
+pin_project! {
+    /// Stream for the [`filter`](super::StreamExt::filter) method.
+    #[must_use = "streams do nothing unless polled"]
+    pub struct Filter<St, Fut, F>
+        where St: Stream,
+    {
+        #[pin]
+        stream: St,
+        f: F,
+        #[pin]
+        pending_fut: Option<Fut>,
+        pending_item: Option<St::Item>,
+    }
+}
+
+impl<St, Fut, F> fmt::Debug for Filter<St, Fut, F>
+where
+    St: Stream + fmt::Debug,
+    St::Item: fmt::Debug,
+    Fut: fmt::Debug,
+{
+    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
+        f.debug_struct("Filter")
+            .field("stream", &self.stream)
+            .field("pending_fut", &self.pending_fut)
+            .field("pending_item", &self.pending_item)
+            .finish()
+    }
+}
+
+#[allow(single_use_lifetimes)] // https://github.com/rust-lang/rust/issues/55058
+impl<St, Fut, F> Filter<St, Fut, F>
+where
+    St: Stream,
+    F: for<'a> FnMut1<&'a St::Item, Output = Fut>,
+    Fut: Future<Output = bool>,
+{
+    pub(super) fn new(stream: St, f: F) -> Self {
+        Self { stream, f, pending_fut: None, pending_item: None }
+    }
+
+    delegate_access_inner!(stream, St, ());
+}
+
+impl<St, Fut, F> FusedStream for Filter<St, Fut, F>
+where
+    St: Stream + FusedStream,
+    F: FnMut(&St::Item) -> Fut,
+    Fut: Future<Output = bool>,
+{
+    fn is_terminated(&self) -> bool {
+        self.pending_fut.is_none() && self.stream.is_terminated()
+    }
+}
+
+#[allow(single_use_lifetimes)] // https://github.com/rust-lang/rust/issues/55058
+impl<St, Fut, F> Stream for Filter<St, Fut, F>
+where
+    St: Stream,
+    F: for<'a> FnMut1<&'a St::Item, Output = Fut>,
+    Fut: Future<Output = bool>,
+{
+    type Item = St::Item;
+
+    fn poll_next(self: Pin<&mut Self>, cx: &mut Context<'_>) -> Poll<Option<St::Item>> {
+        let mut this = self.project();
+        Poll::Ready(loop {
+            if let Some(fut) = this.pending_fut.as_mut().as_pin_mut() {
+                let res = ready!(fut.poll(cx));
+                this.pending_fut.set(None);
+                if res {
+                    break this.pending_item.take();
+                }
+                *this.pending_item = None;
+            } else if let Some(item) = ready!(this.stream.as_mut().poll_next(cx)) {
+                this.pending_fut.set(Some(this.f.call_mut(&item)));
+                *this.pending_item = Some(item);
+            } else {
+                break None;
+            }
+        })
+    }
+
+    fn size_hint(&self) -> (usize, Option<usize>) {
+        let pending_len = usize::from(self.pending_item.is_some());
+        let (_, upper) = self.stream.size_hint();
+        let upper = match upper {
+            Some(x) => x.checked_add(pending_len),
+            None => None,
+        };
+        (0, upper) // can't know a lower bound, due to the predicate
+    }
+}
+
+// Forwarding impl of Sink from the underlying stream
+#[cfg(feature = "sink")]
+impl<S, Fut, F, Item> Sink<Item> for Filter<S, Fut, F>
+where
+    S: Stream + Sink<Item>,
+    F: FnMut(&S::Item) -> Fut,
+    Fut: Future<Output = bool>,
+{
+    type Error = S::Error;
+
+    delegate_sink!(stream, Item);
+}
diff --git a/third_party/rust/futures-util/src/stream/stream/filter_map.rs b/third_party/rust/futures-util/src/stream/stream/filter_map.rs
new file mode 100644
index 0000000000..6b7d0070df
--- /dev/null
+++ b/third_party/rust/futures-util/src/stream/stream/filter_map.rs
@@ -0,0 +1,111 @@
+use crate::fns::FnMut1;
+use core::fmt;
+use core::pin::Pin;
+use futures_core::future::Future;
+use futures_core::ready;
+use futures_core::stream::{FusedStream, Stream};
+use futures_core::task::{Context, Poll};
+#[cfg(feature = "sink")]
+use futures_sink::Sink;
+use pin_project_lite::pin_project;
+
+pin_project! {
+    /// Stream for the [`filter_map`](super::StreamExt::filter_map) method.
+    #[must_use = "streams do nothing unless polled"]
+    pub struct FilterMap<St, Fut, F> {
+        #[pin]
+        stream: St,
+        f: F,
+        #[pin]
+        pending: Option<Fut>,
+    }
+}
+
+impl<St, Fut, F> fmt::Debug for FilterMap<St, Fut, F>
+where
+    St: fmt::Debug,
+    Fut: fmt::Debug,
+{
+    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
+        f.debug_struct("FilterMap")
+            .field("stream", &self.stream)
+            .field("pending", &self.pending)
+            .finish()
+    }
+}
+
+impl<St, Fut, F> FilterMap<St, Fut, F>
+where
+    St: Stream,
+    F: FnMut(St::Item) -> Fut,
+    Fut: Future,
+{
+    pub(super) fn new(stream: St, f: F) -> Self {
+        Self { stream, f, pending: None }
+    }
+
+    delegate_access_inner!(stream, St, ());
+}
+
+impl<St, Fut, F, T> FusedStream for FilterMap<St, Fut, F>
+where
+    St: Stream + FusedStream,
+    F: FnMut1<St::Item, Output = Fut>,
+    Fut: Future<Output = Option<T>>,
+{
+    fn is_terminated(&self) -> bool {
+        self.pending.is_none() && self.stream.is_terminated()
+    }
+}
+
+impl<St, Fut, F, T> Stream for FilterMap<St, Fut, F>
+where
+    St: Stream,
+    F: FnMut1<St::Item, Output = Fut>,
+    Fut: Future<Output = Option<T>>,
+{
+    type Item = T;
+
+    fn poll_next(self: Pin<&mut Self>, cx: &mut Context<'_>) -> Poll<Option<T>> {
+        let mut this = self.project();
+        Poll::Ready(loop {
+            if let Some(p) = this.pending.as_mut().as_pin_mut() {
+                // We have an item in progress, poll that until it's done
+                let item = ready!(p.poll(cx));
+                this.pending.set(None);
+                if item.is_some() {
+                    break item;
+                }
+            } else if let Some(item) = ready!(this.stream.as_mut().poll_next(cx)) {
+                // No item in progress, but the stream is still going
+                this.pending.set(Some(this.f.call_mut(item)));
+            } else {
+                // The stream is done
+                break None;
+            }
+        })
+    }
+
+    fn size_hint(&self) -> (usize, Option<usize>) {
+        let pending_len = usize::from(self.pending.is_some());
+        let (_, upper) = self.stream.size_hint();
+        let upper = match upper {
+            Some(x) => x.checked_add(pending_len),
+            None => None,
+        };
+        (0, upper) // can't know a lower bound, due to the predicate
+    }
+}
+
+// Forwarding impl of Sink from the underlying stream
+#[cfg(feature = "sink")]
+impl<S, Fut, F, Item> Sink<Item> for FilterMap<S, Fut, F>
+where
+    S: Stream + Sink<Item>,
+    F: FnMut1<S::Item, Output = Fut>,
+    Fut: Future,
+{
+    type Error = S::Error;
+
+    delegate_sink!(stream, Item);
+}
diff --git a/third_party/rust/futures-util/src/stream/stream/flatten.rs b/third_party/rust/futures-util/src/stream/stream/flatten.rs
new file mode 100644
index 0000000000..9f6b7a472d
--- /dev/null
+++ b/third_party/rust/futures-util/src/stream/stream/flatten.rs
@@ -0,0 +1,73 @@
+use core::pin::Pin;
+use futures_core::ready;
+use futures_core::stream::{FusedStream, Stream};
+use futures_core::task::{Context, Poll};
+#[cfg(feature = "sink")]
+use futures_sink::Sink;
+use pin_project_lite::pin_project;
+
+pin_project! {
+    /// Stream for the [`flatten`](super::StreamExt::flatten) method.
+    #[derive(Debug)]
+    #[must_use = "streams do nothing unless polled"]
+    pub struct Flatten<St, U> {
+        #[pin]
+        stream: St,
+        #[pin]
+        next: Option<U>,
+    }
+}
+
+impl<St, U> Flatten<St, U> {
+    pub(super) fn new(stream: St) -> Self {
+        Self { stream, next: None }
+    }
+
+    delegate_access_inner!(stream, St, ());
+}
+
+impl<St> FusedStream for Flatten<St, St::Item>
+where
+    St: FusedStream,
+    St::Item: Stream,
+{
+    fn is_terminated(&self) -> bool {
+        self.next.is_none() && self.stream.is_terminated()
+    }
+}
+
+impl<St> Stream for Flatten<St, St::Item>
+where
+    St: Stream,
+    St::Item: Stream,
+{
+    type Item = <St::Item as Stream>::Item;
+
+    fn poll_next(self: Pin<&mut Self>, cx: &mut Context<'_>) -> Poll<Option<Self::Item>> {
+        let mut this = self.project();
+        Poll::Ready(loop {
+            if let Some(s) = this.next.as_mut().as_pin_mut() {
+                if let Some(item) = ready!(s.poll_next(cx)) {
+                    break Some(item);
+                } else {
+                    this.next.set(None);
+                }
+            } else if let Some(s) = ready!(this.stream.as_mut().poll_next(cx)) {
+                this.next.set(Some(s));
+            } else {
+                break None;
+            }
+        })
+    }
+}
+
+// Forwarding impl of Sink from the underlying stream
+#[cfg(feature = "sink")]
+impl<S, Item> Sink<Item> for Flatten<S, S::Item>
+where
+    S: Stream + Sink<Item>,
+{
+    type Error = S::Error;
+
+    delegate_sink!(stream, Item);
+}
diff --git a/third_party/rust/futures-util/src/stream/stream/flatten_unordered.rs b/third_party/rust/futures-util/src/stream/stream/flatten_unordered.rs
new file mode 100644
index 0000000000..07f971c55a
--- /dev/null
+++ b/third_party/rust/futures-util/src/stream/stream/flatten_unordered.rs
@@ -0,0 +1,509 @@
+use alloc::sync::Arc;
+use core::{
+    cell::UnsafeCell,
+    convert::identity,
+    fmt,
+    num::NonZeroUsize,
+    pin::Pin,
+    sync::atomic::{AtomicU8, Ordering},
+};
+
+use pin_project_lite::pin_project;
+
+use futures_core::{
+    future::Future,
+    ready,
+    stream::{FusedStream, Stream},
+    task::{Context, Poll, Waker},
+};
+#[cfg(feature = "sink")]
+use futures_sink::Sink;
+use futures_task::{waker, ArcWake};
+
+use crate::stream::FuturesUnordered;
+
+/// There is nothing to poll and stream isn't being
+/// polled or waking at the moment.
+const NONE: u8 = 0;
+
+/// Inner streams need to be polled.
+const NEED_TO_POLL_INNER_STREAMS: u8 = 1;
+
+/// The base stream needs to be polled.
+const NEED_TO_POLL_STREAM: u8 = 0b10;
+
+/// It needs to poll base stream and inner streams.
+const NEED_TO_POLL_ALL: u8 = NEED_TO_POLL_INNER_STREAMS | NEED_TO_POLL_STREAM;
+
+/// The current stream is being polled at the moment.
+const POLLING: u8 = 0b100;
+
+/// Inner streams are being woken at the moment.
+const WAKING_INNER_STREAMS: u8 = 0b1000;
+
+/// The base stream is being woken at the moment.
+const WAKING_STREAM: u8 = 0b10000;
+
+/// The base stream and inner streams are being woken at the moment.
+const WAKING_ALL: u8 = WAKING_STREAM | WAKING_INNER_STREAMS;
+
+/// The stream was waked and will be polled.
+const WOKEN: u8 = 0b100000;
+
+/// Determines what needs to be polled, and is stream being polled at the
+/// moment or not.
+#[derive(Clone, Debug)]
+struct SharedPollState {
+    state: Arc<AtomicU8>,
+}
+
+impl SharedPollState {
+    /// Constructs new `SharedPollState` with the given state.
+    fn new(value: u8) -> SharedPollState {
+        SharedPollState { state: Arc::new(AtomicU8::new(value)) }
+    }
+
+    /// Attempts to start polling, returning stored state in case of success.
+    /// Returns `None` if some waker is waking at the moment.
+    fn start_polling(
+        &self,
+    ) -> Option<(u8, PollStateBomb<'_, impl FnOnce(&SharedPollState) -> u8>)> {
+        let value = self
+            .state
+            .fetch_update(Ordering::SeqCst, Ordering::SeqCst, |value| {
+                if value & WAKING_ALL == NONE {
+                    Some(POLLING)
+                } else {
+                    None
+                }
+            })
+            .ok()?;
+        let bomb = PollStateBomb::new(self, SharedPollState::reset);
+
+        Some((value, bomb))
+    }
+
+    /// Starts the waking process and performs bitwise or with the given value.
+    fn start_waking(
+        &self,
+        to_poll: u8,
+        waking: u8,
+    ) -> Option<(u8, PollStateBomb<'_, impl FnOnce(&SharedPollState) -> u8>)> {
+        let value = self
+            .state
+            .fetch_update(Ordering::SeqCst, Ordering::SeqCst, |value| {
+                // Waking process for this waker already started
+                if value & waking != NONE {
+                    return None;
+                }
+                let mut next_value = value | to_poll;
+                // Only start the waking process if we're not in the polling phase and the stream isn't woken already
+                if value & (WOKEN | POLLING) == NONE {
+                    next_value |= waking;
+                }
+
+                if next_value != value {
+                    Some(next_value)
+                } else {
+                    None
+                }
+            })
+            .ok()?;
+
+        if value & (WOKEN | POLLING) == NONE {
+            let bomb = PollStateBomb::new(self, move |state| state.stop_waking(waking));
+
+            Some((value, bomb))
+        } else {
+            None
+        }
+    }
+
+    /// Sets current state to
+    /// - `!POLLING` allowing to use wakers
+    /// - `WOKEN` if the state was changed during `POLLING` phase as waker will be called,
+    ///   or `will_be_woken` flag supplied
+    /// - `!WAKING_ALL` as
+    ///   * Wakers called during the `POLLING` phase won't propagate their calls
+    ///   * `POLLING` phase can't start if some of the wakers are active
+    ///   So no wrapped waker can touch the inner waker's cell, it's safe to poll again.
+    fn stop_polling(&self, to_poll: u8, will_be_woken: bool) -> u8 {
+        self.state
+            .fetch_update(Ordering::SeqCst, Ordering::SeqCst, |mut value| {
+                let mut next_value = to_poll;
+
+                value &= NEED_TO_POLL_ALL;
+                if value != NONE || will_be_woken {
+                    next_value |= WOKEN;
+                }
+                next_value |= value;
+
+                Some(next_value & !POLLING & !WAKING_ALL)
+            })
+            .unwrap()
+    }
+
+    /// Toggles state to non-waking, allowing to start polling.
+    fn stop_waking(&self, waking: u8) -> u8 {
+        self.state
+            .fetch_update(Ordering::SeqCst, Ordering::SeqCst, |value| {
+                let mut next_value = value & !waking;
+                // Waker will be called only if the current waking state is the same as the specified waker state
+                if value & WAKING_ALL == waking {
+                    next_value |= WOKEN;
+                }
+
+                if next_value != value {
+                    Some(next_value)
+                } else {
+                    None
+                }
+            })
+            .unwrap_or_else(identity)
+    }
+
+    /// Resets current state allowing to poll the stream and wake up wakers.
+    fn reset(&self) -> u8 {
+        self.state.swap(NEED_TO_POLL_ALL, Ordering::AcqRel)
+    }
+}
+
+/// Used to execute some function on the given state when dropped.
+struct PollStateBomb<'a, F: FnOnce(&SharedPollState) -> u8> {
+    state: &'a SharedPollState,
+    drop: Option<F>,
+}
+
+impl<'a, F: FnOnce(&SharedPollState) -> u8> PollStateBomb<'a, F> {
+    /// Constructs new bomb with the given state.
+    fn new(state: &'a SharedPollState, drop: F) -> Self {
+        Self { state, drop: Some(drop) }
+    }
+
+    /// Deactivates bomb, forces it to not call provided function when dropped.
+    fn deactivate(mut self) {
+        self.drop.take();
+    }
+
+    /// Manually fires the bomb, returning supplied state.
+    fn fire(mut self) -> Option<u8> {
+        self.drop.take().map(|drop| (drop)(self.state))
+    }
+}
+
+impl<F: FnOnce(&SharedPollState) -> u8> Drop for PollStateBomb<'_, F> {
+    fn drop(&mut self) {
+        if let Some(drop) = self.drop.take() {
+            (drop)(self.state);
+        }
+    }
+}
+
+/// Will update state with the provided value on `wake_by_ref` call
+/// and then, if there is a need, call `inner_waker`.
+struct InnerWaker {
+    inner_waker: UnsafeCell<Option<Waker>>,
+    poll_state: SharedPollState,
+    need_to_poll: u8,
+}
+
+unsafe impl Send for InnerWaker {}
+unsafe impl Sync for InnerWaker {}
+
+impl InnerWaker {
+    /// Replaces given waker's inner_waker for polling stream/futures which will
+    /// update poll state on `wake_by_ref` call. Use only if you need several
+    /// contexts.
+    ///
+    /// ## Safety
+    ///
+    /// This function will modify waker's `inner_waker` via `UnsafeCell`, so
+    /// it should be used only during `POLLING` phase.
+    unsafe fn replace_waker(self_arc: &mut Arc<Self>, cx: &Context<'_>) -> Waker {
+        *self_arc.inner_waker.get() = cx.waker().clone().into();
+        waker(self_arc.clone())
+    }
+
+    /// Attempts to start the waking process for the waker with the given value.
+    /// If succeeded, then the stream isn't yet woken and not being polled at the moment.
+    fn start_waking(&self) -> Option<(u8, PollStateBomb<'_, impl FnOnce(&SharedPollState) -> u8>)> {
+        self.poll_state.start_waking(self.need_to_poll, self.waking_state())
+    }
+
+    /// Returns the corresponding waking state toggled by this waker.
+    fn waking_state(&self) -> u8 {
+        self.need_to_poll << 3
+    }
+}
+
+impl ArcWake for InnerWaker {
+    fn wake_by_ref(self_arc: &Arc<Self>) {
+        if let Some((_, state_bomb)) = self_arc.start_waking() {
+            // Safety: now state is not `POLLING`
+            let waker_opt = unsafe { self_arc.inner_waker.get().as_ref().unwrap() };
+
+            if let Some(inner_waker) = waker_opt.clone() {
+                // Stop waking to allow polling stream
+                let poll_state_value = state_bomb.fire().unwrap();
+
+                // Here we want to call waker only if stream isn't woken yet and
+                // also to optimize the case when two wakers are called at the same time.
+                //
+                // In this case the best strategy will be to propagate only the latest waker's awake,
+                // and then poll both entities in a single `poll_next` call
+                if poll_state_value & (WOKEN | WAKING_ALL) == self_arc.waking_state() {
+                    // Wake up inner waker
+                    inner_waker.wake();
+                }
+            }
+        }
+    }
+}
+
+pin_project! {
+    /// Future which contains optional stream.
+    ///
+    /// If it's `Some`, it will attempt to call `poll_next` on it,
+    /// returning `Some((item, next_item_fut))` in case of `Poll::Ready(Some(...))`
+    /// or `None` in case of `Poll::Ready(None)`.
+    ///
+    /// If `poll_next` will return `Poll::Pending`, it will be forwarded to
+    /// the future and current task will be notified by waker.
+    #[must_use = "futures do nothing unless you `.await` or poll them"]
+    struct PollStreamFut<St> {
+        #[pin]
+        stream: Option<St>,
+    }
+}
+
+impl<St> PollStreamFut<St> {
+    /// Constructs new `PollStreamFut` using given `stream`.
+    fn new(stream: impl Into<Option<St>>) -> Self {
+        Self { stream: stream.into() }
+    }
+}
+
+impl<St: Stream + Unpin> Future for PollStreamFut<St> {
+    type Output = Option<(St::Item, PollStreamFut<St>)>;
+
+    fn poll(self: Pin<&mut Self>, cx: &mut Context<'_>) -> Poll<Self::Output> {
+        let mut stream = self.project().stream;
+
+        let item = if let Some(stream) = stream.as_mut().as_pin_mut() {
+            ready!(stream.poll_next(cx))
+        } else {
+            None
+        };
+        let next_item_fut = PollStreamFut::new(stream.get_mut().take());
+        let out = item.map(|item| (item, next_item_fut));
+
+        Poll::Ready(out)
+    }
+}
+
+pin_project! {
+    /// Stream for the [`flatten_unordered`](super::StreamExt::flatten_unordered)
+    /// method.
+    #[project = FlattenUnorderedProj]
+    #[must_use = "streams do nothing unless polled"]
+    pub struct FlattenUnordered<St> where St: Stream {
+        #[pin]
+        inner_streams: FuturesUnordered<PollStreamFut<St::Item>>,
+        #[pin]
+        stream: St,
+        poll_state: SharedPollState,
+        limit: Option<NonZeroUsize>,
+        is_stream_done: bool,
+        inner_streams_waker: Arc<InnerWaker>,
+        stream_waker: Arc<InnerWaker>,
+    }
+}
+
+impl<St> fmt::Debug for FlattenUnordered<St>
+where
+    St: Stream + fmt::Debug,
+    St::Item: Stream + fmt::Debug,
+{
+    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
+        f.debug_struct("FlattenUnordered")
+            .field("poll_state", &self.poll_state)
+            .field("inner_streams", &self.inner_streams)
+            .field("limit", &self.limit)
+            .field("stream", &self.stream)
+            .field("is_stream_done", &self.is_stream_done)
+            .finish()
+    }
+}
+
+impl<St> FlattenUnordered<St>
+where
+    St: Stream,
+    St::Item: Stream + Unpin,
+{
+    pub(super) fn new(stream: St, limit: Option<usize>) -> FlattenUnordered<St> {
+        let poll_state = SharedPollState::new(NEED_TO_POLL_STREAM);
+
+        FlattenUnordered {
+            inner_streams: FuturesUnordered::new(),
+            stream,
+            is_stream_done: false,
+            limit: limit.and_then(NonZeroUsize::new),
+            inner_streams_waker: Arc::new(InnerWaker {
+                inner_waker: UnsafeCell::new(None),
+                poll_state: poll_state.clone(),
+                need_to_poll: NEED_TO_POLL_INNER_STREAMS,
+            }),
+            stream_waker: Arc::new(InnerWaker {
+                inner_waker: UnsafeCell::new(None),
+                poll_state: poll_state.clone(),
+                need_to_poll: NEED_TO_POLL_STREAM,
+            }),
+            poll_state,
+        }
+    }
+
+    delegate_access_inner!(stream, St, ());
+}
+
+impl<St> FlattenUnorderedProj<'_, St>
+where
+    St: Stream,
+{
+    /// Checks if current `inner_streams` size is less than optional limit.
+    fn is_exceeded_limit(&self) -> bool {
+        self.limit.map_or(false, |limit| self.inner_streams.len() >= limit.get())
+    }
+}
+
+impl<St> FusedStream for FlattenUnordered<St>
+where
+    St: FusedStream,
+    St::Item: FusedStream + Unpin,
+{
+    fn is_terminated(&self) -> bool {
+        self.stream.is_terminated() && self.inner_streams.is_empty()
+    }
+}
+
+impl<St> Stream for FlattenUnordered<St>
+where
+    St: Stream,
+    St::Item: Stream + Unpin,
+{
+    type Item = <St::Item as Stream>::Item;
+
+    fn poll_next(mut self: Pin<&mut Self>, cx: &mut Context<'_>) -> Poll<Option<Self::Item>> {
+        let mut next_item = None;
+        let mut need_to_poll_next = NONE;
+
+        let mut this = self.as_mut().project();
+
+        let (mut poll_state_value, state_bomb) = match this.poll_state.start_polling() {
+            Some(value) => value,
+            _ => {
+                // Waker was called, just wait for the next poll
+                return Poll::Pending;
+            }
+        };
+
+        if poll_state_value & NEED_TO_POLL_STREAM != NONE {
+            // Safety: now state is `POLLING`.
+            let stream_waker = unsafe { InnerWaker::replace_waker(this.stream_waker, cx) };
+
+            // Here we need to poll the base stream.
+            //
+            // To improve performance, we will attempt to place as many items as we can
+            // to the `FuturesUnordered` bucket before polling inner streams
+            loop {
+                if this.is_exceeded_limit() || *this.is_stream_done {
+                    // We either exceeded the limit or the stream is exhausted
+                    if !*this.is_stream_done {
+                        // The stream needs to be polled in the next iteration
+                        need_to_poll_next |= NEED_TO_POLL_STREAM;
+                    }
+
+                    break;
+                } else {
+                    match this.stream.as_mut().poll_next(&mut Context::from_waker(&stream_waker)) {
+                        Poll::Ready(Some(inner_stream)) => {
+                            // Add new stream to the inner streams bucket
+                            this.inner_streams.as_mut().push(PollStreamFut::new(inner_stream));
+                            // Inner streams must be polled afterward
+                            poll_state_value |= NEED_TO_POLL_INNER_STREAMS;
+                        }
+                        Poll::Ready(None) => {
+                            // Mark the stream as done
+                            *this.is_stream_done = true;
+                        }
+                        Poll::Pending => {
+                            break;
+                        }
+                    }
+                }
+            }
+        }
+
+        if poll_state_value & NEED_TO_POLL_INNER_STREAMS != NONE {
+            // Safety: now state is `POLLING`.
+            let inner_streams_waker =
+                unsafe { InnerWaker::replace_waker(this.inner_streams_waker, cx) };
+
+            match this
+                .inner_streams
+                .as_mut()
+                .poll_next(&mut Context::from_waker(&inner_streams_waker))
+            {
+                Poll::Ready(Some(Some((item, next_item_fut)))) => {
+                    // Push next inner stream item future to the list of inner streams futures
+                    this.inner_streams.as_mut().push(next_item_fut);
+                    // Take the received item
+                    next_item = Some(item);
+                    // On the next iteration, inner streams must be polled again
+                    need_to_poll_next |= NEED_TO_POLL_INNER_STREAMS;
+                }
+                Poll::Ready(Some(None)) => {
+                    // On the next iteration, inner streams must be polled again
+                    need_to_poll_next |= NEED_TO_POLL_INNER_STREAMS;
+                }
+                _ => {}
+            }
+        }
+
+        // We didn't have any `poll_next` panic, so it's time to deactivate the bomb
+        state_bomb.deactivate();
+
+        let mut force_wake =
+            // we need to poll the stream and didn't reach the limit yet
+            need_to_poll_next & NEED_TO_POLL_STREAM != NONE && !this.is_exceeded_limit()
+            // or we need to poll inner streams again
+            || need_to_poll_next & NEED_TO_POLL_INNER_STREAMS != NONE;
+
+        // Stop polling and swap the latest state
+        poll_state_value = this.poll_state.stop_polling(need_to_poll_next, force_wake);
+        // If state was changed during `POLLING` phase, need to manually call a waker
+        force_wake |= poll_state_value & NEED_TO_POLL_ALL != NONE;
+
+        let is_done = *this.is_stream_done && this.inner_streams.is_empty();
+
+        if next_item.is_some() || is_done {
+            Poll::Ready(next_item)
+        } else {
+            if force_wake {
+                cx.waker().wake_by_ref();
+            }
+
+            Poll::Pending
+        }
+    }
+}
+
+// Forwarding impl of Sink from the underlying stream
+#[cfg(feature = "sink")]
+impl<St, Item> Sink<Item> for FlattenUnordered<St>
+where
+    St: Stream + Sink<Item>,
+{
+    type Error = St::Error;
+
+    delegate_sink!(stream, Item);
+}
diff --git a/third_party/rust/futures-util/src/stream/stream/fold.rs b/third_party/rust/futures-util/src/stream/stream/fold.rs
new file mode 100644
index 0000000000..b8b55ecb67
--- /dev/null
+++ b/third_party/rust/futures-util/src/stream/stream/fold.rs
@@ -0,0 +1,88 @@
+use core::fmt;
+use core::pin::Pin;
+use futures_core::future::{FusedFuture, Future};
+use futures_core::ready;
+use futures_core::stream::Stream;
+use futures_core::task::{Context, Poll};
+use pin_project_lite::pin_project;
+
+pin_project! {
+    /// Future for the [`fold`](super::StreamExt::fold) method.
+    #[must_use = "futures do nothing unless you `.await` or poll them"]
+    pub struct Fold<St, Fut, T, F> {
+        #[pin]
+        stream: St,
+        f: F,
+        accum: Option<T>,
+        #[pin]
+        future: Option<Fut>,
+    }
+}
+
+impl<St, Fut, T, F> fmt::Debug for Fold<St, Fut, T, F>
+where
+    St: fmt::Debug,
+    Fut: fmt::Debug,
+    T: fmt::Debug,
+{
+    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
+        f.debug_struct("Fold")
+            .field("stream", &self.stream)
+            .field("accum", &self.accum)
+            .field("future", &self.future)
+            .finish()
+    }
+}
+
+impl<St, Fut, T, F> Fold<St, Fut, T, F>
+where
+    St: Stream,
+    F: FnMut(T, St::Item) -> Fut,
+    Fut: Future<Output = T>,
+{
+    pub(super) fn new(stream: St, f: F, t: T) -> Self {
+        Self { stream, f, accum: Some(t), future: None }
+    }
+}
+
+impl<St, Fut, T, F> FusedFuture for Fold<St, Fut, T, F>
+where
+    St: Stream,
+    F: FnMut(T, St::Item) -> Fut,
+    Fut: Future<Output = T>,
+{
+    fn is_terminated(&self) -> bool {
+        self.accum.is_none() && self.future.is_none()
+    }
+}
+
+impl<St, Fut, T, F> Future for Fold<St, Fut, T, F>
+where
+    St: Stream,
+    F: FnMut(T, St::Item) -> Fut,
+    Fut: Future<Output = T>,
+{
+    type Output = T;
+
+    fn poll(self: Pin<&mut Self>, cx: &mut Context<'_>) -> Poll<T> {
+        let mut this = self.project();
+        Poll::Ready(loop {
+            if let Some(fut) = this.future.as_mut().as_pin_mut() {
+                // we're currently processing a future to produce a new accum value
+                *this.accum = Some(ready!(fut.poll(cx)));
+                this.future.set(None);
+            } else if this.accum.is_some() {
+                // we're waiting on a new item from the stream
+                let res = ready!(this.stream.as_mut().poll_next(cx));
+                let a = this.accum.take().unwrap();
+                if let Some(item) = res {
+                    this.future.set(Some((this.f)(a, item)));
+                } else {
+                    break a;
+                }
+            } else {
+                panic!("Fold polled after completion")
+            }
+        })
+    }
+}
diff --git a/third_party/rust/futures-util/src/stream/stream/for_each.rs b/third_party/rust/futures-util/src/stream/stream/for_each.rs
new file mode 100644
index 0000000000..5302b0e034
--- /dev/null
+++ b/third_party/rust/futures-util/src/stream/stream/for_each.rs
@@ -0,0 +1,78 @@
+use core::fmt;
+use core::pin::Pin;
+use futures_core::future::{FusedFuture, Future};
+use futures_core::ready;
+use futures_core::stream::{FusedStream, Stream};
+use futures_core::task::{Context, Poll};
+use pin_project_lite::pin_project;
+
+pin_project! {
+    /// Future for the [`for_each`](super::StreamExt::for_each) method.
+    #[must_use = "futures do nothing unless you `.await` or poll them"]
+    pub struct ForEach<St, Fut, F> {
+        #[pin]
+        stream: St,
+        f: F,
+        #[pin]
+        future: Option<Fut>,
+    }
+}
+
+impl<St, Fut, F> fmt::Debug for ForEach<St, Fut, F>
+where
+    St: fmt::Debug,
+    Fut: fmt::Debug,
+{
+    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
+        f.debug_struct("ForEach")
+            .field("stream", &self.stream)
+            .field("future", &self.future)
+            .finish()
+    }
+}
+
+impl<St, Fut, F> ForEach<St, Fut, F>
+where
+    St: Stream,
+    F: FnMut(St::Item) -> Fut,
+    Fut: Future<Output = ()>,
+{
+    pub(super) fn new(stream: St, f: F) -> Self {
+        Self { stream, f, future: None }
+    }
+}
+
+impl<St, Fut, F> FusedFuture for ForEach<St, Fut, F>
+where
+    St: FusedStream,
+    F: FnMut(St::Item) -> Fut,
+    Fut: Future<Output = ()>,
+{
+    fn is_terminated(&self) -> bool {
+        self.future.is_none() && self.stream.is_terminated()
+    }
+}
+
+impl<St, Fut, F> Future for ForEach<St, Fut, F>
+where
+    St: Stream,
+    F: FnMut(St::Item) -> Fut,
+    Fut: Future<Output = ()>,
+{
+    type Output = ();
+
+    fn poll(self: Pin<&mut Self>, cx: &mut Context<'_>) -> Poll<()> {
+        let mut this = self.project();
+        loop {
+            if let Some(fut) = this.future.as_mut().as_pin_mut() {
+                ready!(fut.poll(cx));
+                this.future.set(None);
+            } else if let Some(item) = ready!(this.stream.as_mut().poll_next(cx)) {
+                this.future.set(Some((this.f)(item)));
+            } else {
+                break;
+            }
+        }
+        Poll::Ready(())
+    }
+}
diff --git a/third_party/rust/futures-util/src/stream/stream/for_each_concurrent.rs b/third_party/rust/futures-util/src/stream/stream/for_each_concurrent.rs
new file mode 100644
index 0000000000..6c18753eb9
--- /dev/null
+++ b/third_party/rust/futures-util/src/stream/stream/for_each_concurrent.rs
@@ -0,0 +1,119 @@
+use crate::stream::{FuturesUnordered, StreamExt};
+use core::fmt;
+use core::num::NonZeroUsize;
+use core::pin::Pin;
+use futures_core::future::{FusedFuture, Future};
+use futures_core::stream::Stream;
+use futures_core::task::{Context, Poll};
+use pin_project_lite::pin_project;
+
+pin_project! {
+    /// Future for the [`for_each_concurrent`](super::StreamExt::for_each_concurrent)
+    /// method.
+    #[must_use = "futures do nothing unless you `.await` or poll them"]
+    pub struct ForEachConcurrent<St, Fut, F> {
+        #[pin]
+        stream: Option<St>,
+        f: F,
+        futures: FuturesUnordered<Fut>,
+        limit: Option<NonZeroUsize>,
+    }
+}
+
+impl<St, Fut, F> fmt::Debug for ForEachConcurrent<St, Fut, F>
+where
+    St: fmt::Debug,
+    Fut: fmt::Debug,
+{
+    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
+        f.debug_struct("ForEachConcurrent")
+            .field("stream", &self.stream)
+            .field("futures", &self.futures)
+            .field("limit", &self.limit)
+            .finish()
+    }
+}
+
+impl<St, Fut, F> ForEachConcurrent<St, Fut, F>
+where
+    St: Stream,
+    F: FnMut(St::Item) -> Fut,
+    Fut: Future<Output = ()>,
+{
+    pub(super) fn new(stream: St, limit: Option<usize>, f: F) -> Self {
+        Self {
+            stream: Some(stream),
+            // Note: `limit` = 0 gets ignored.
+            limit: limit.and_then(NonZeroUsize::new),
+            f,
+            futures: FuturesUnordered::new(),
+        }
+    }
+}
+
+impl<St, Fut, F> FusedFuture for ForEachConcurrent<St, Fut, F>
+where
+    St: Stream,
+    F: FnMut(St::Item) -> Fut,
+    Fut: Future<Output = ()>,
+{
+    fn is_terminated(&self) -> bool {
+        self.stream.is_none() && self.futures.is_empty()
+    }
+}
+
+impl<St, Fut, F> Future for ForEachConcurrent<St, Fut, F>
+where
+    St: Stream,
+    F: FnMut(St::Item) -> Fut,
+    Fut: Future<Output = ()>,
+{
+    type Output = ();
+
+    fn poll(self: Pin<&mut Self>, cx: &mut Context<'_>) -> Poll<()> {
+        let mut this = self.project();
+        loop {
+            let mut made_progress_this_iter = false;
+
+            // Check if we've already created a number of futures greater than `limit`
+            if this.limit.map(|limit| limit.get() > this.futures.len()).unwrap_or(true) {
+                let mut stream_completed = false;
+                let elem = if let Some(stream) = this.stream.as_mut().as_pin_mut() {
+                    match stream.poll_next(cx) {
+                        Poll::Ready(Some(elem)) => {
+                            made_progress_this_iter = true;
+                            Some(elem)
+                        }
+                        Poll::Ready(None) => {
+                            stream_completed = true;
+                            None
+                        }
+                        Poll::Pending => None,
+                    }
+                } else {
+                    None
+                };
+                if stream_completed {
+                    this.stream.set(None);
+                }
+                if let Some(elem) = elem {
+                    this.futures.push((this.f)(elem));
+                }
+            }
+
+            match this.futures.poll_next_unpin(cx) {
+                Poll::Ready(Some(())) => made_progress_this_iter = true,
+                Poll::Ready(None) => {
+                    if this.stream.is_none() {
+                        return Poll::Ready(());
+                    }
+                }
+                Poll::Pending => {}
+            }
+
+            if !made_progress_this_iter {
+                return Poll::Pending;
+            }
+        }
+    }
+}
diff --git a/third_party/rust/futures-util/src/stream/stream/forward.rs b/third_party/rust/futures-util/src/stream/stream/forward.rs
new file mode 100644
index 0000000000..1fe24273aa
--- /dev/null
+++ b/third_party/rust/futures-util/src/stream/stream/forward.rs
@@ -0,0 +1,75 @@
+use crate::stream::Fuse;
+use core::pin::Pin;
+use futures_core::future::{FusedFuture, Future};
+use futures_core::ready;
+use futures_core::stream::Stream;
+use futures_core::task::{Context, Poll};
+use futures_sink::Sink;
+use pin_project_lite::pin_project;
+
+pin_project! {
+    /// Future for the [`forward`](super::StreamExt::forward) method.
+    #[project = ForwardProj]
+    #[derive(Debug)]
+    #[must_use = "futures do nothing unless you `.await` or poll them"]
+    pub struct Forward<St, Si, Item> {
+        #[pin]
+        sink: Option<Si>,
+        #[pin]
+        stream: Fuse<St>,
+        buffered_item: Option<Item>,
+    }
+}
+
+impl<St, Si, Item> Forward<St, Si, Item> {
+    pub(crate) fn new(stream: St, sink: Si) -> Self {
+        Self { sink: Some(sink), stream: Fuse::new(stream), buffered_item: None }
+    }
+}
+
+impl<St, Si, Item, E> FusedFuture for Forward<St, Si, Item>
+where
+    Si: Sink<Item, Error = E>,
+    St: Stream<Item = Result<Item, E>>,
+{
+    fn is_terminated(&self) -> bool {
+        self.sink.is_none()
+    }
+}
+
+impl<St, Si, Item, E> Future for Forward<St, Si, Item>
+where
+    Si: Sink<Item, Error = E>,
+    St: Stream<Item = Result<Item, E>>,
+{
+    type Output = Result<(), E>;
+
+    fn poll(self: Pin<&mut Self>, cx: &mut Context<'_>) -> Poll<Self::Output> {
+        let ForwardProj { mut sink, mut stream, buffered_item } = self.project();
+        let mut si = sink.as_mut().as_pin_mut().expect("polled `Forward` after completion");
+
+        loop {
+            // If we've got an item buffered already, we need to write it to the
+            // sink before we can do anything else
+            if buffered_item.is_some() {
+                ready!(si.as_mut().poll_ready(cx))?;
+                si.as_mut().start_send(buffered_item.take().unwrap())?;
+            }
+
+            match stream.as_mut().poll_next(cx)? {
+                Poll::Ready(Some(item)) => {
+                    *buffered_item = Some(item);
+                }
+                Poll::Ready(None) => {
+                    ready!(si.poll_close(cx))?;
+                    sink.set(None);
+                    return Poll::Ready(Ok(()));
+                }
+                Poll::Pending => {
+                    ready!(si.poll_flush(cx))?;
+                    return Poll::Pending;
+                }
+            }
+        }
+    }
+}
diff --git a/third_party/rust/futures-util/src/stream/stream/fuse.rs b/third_party/rust/futures-util/src/stream/stream/fuse.rs
new file mode 100644
index 0000000000..fe67813e81
--- /dev/null
+++ b/third_party/rust/futures-util/src/stream/stream/fuse.rs
@@ -0,0 +1,75 @@
+use core::pin::Pin;
+use futures_core::ready;
+use futures_core::stream::{FusedStream, Stream};
+use futures_core::task::{Context, Poll};
+#[cfg(feature = "sink")]
+use futures_sink::Sink;
+use pin_project_lite::pin_project;
+
+pin_project! {
+    /// Stream for the [`fuse`](super::StreamExt::fuse) method.
+    #[derive(Debug)]
+    #[must_use = "streams do nothing unless polled"]
+    pub struct Fuse<St> {
+        #[pin]
+        stream: St,
+        done: bool,
+    }
+}
+
+impl<St> Fuse<St> {
+    pub(super) fn new(stream: St) -> Self {
+        Self { stream, done: false }
+    }
+
+    /// Returns whether the underlying stream has finished or not.
+    ///
+    /// If this method returns `true`, then all future calls to poll are
+    /// guaranteed to return `None`. If this returns `false`, then the
+    /// underlying stream is still in use.
+    pub fn is_done(&self) -> bool {
+        self.done
+    }
+
+    delegate_access_inner!(stream, St, ());
+}
+
+impl<S: Stream> FusedStream for Fuse<S> {
+    fn is_terminated(&self) -> bool {
+        self.done
+    }
+}
+
+impl<S: Stream> Stream for Fuse<S> {
+    type Item = S::Item;
+
+    fn poll_next(self: Pin<&mut Self>, cx: &mut Context<'_>) -> Poll<Option<S::Item>> {
+        let this = self.project();
+
+        if *this.done {
+            return Poll::Ready(None);
+        }
+
+        let item = ready!(this.stream.poll_next(cx));
+        if item.is_none() {
+            *this.done = true;
+        }
+        Poll::Ready(item)
+    }
+
+    fn size_hint(&self) -> (usize, Option<usize>) {
+        if self.done {
+            (0, Some(0))
+        } else {
+            self.stream.size_hint()
+        }
+    }
+}
+
+// Forwarding impl of Sink from the underlying stream
+#[cfg(feature = "sink")]
+impl<S: Stream + Sink<Item>, Item> Sink<Item> for Fuse<S> {
+    type Error = S::Error;
+
+    delegate_sink!(stream, Item);
+}
diff --git a/third_party/rust/futures-util/src/stream/stream/into_future.rs b/third_party/rust/futures-util/src/stream/stream/into_future.rs
new file mode 100644
index 0000000000..8abfddcccd
--- /dev/null
+++ b/third_party/rust/futures-util/src/stream/stream/into_future.rs
@@ -0,0 +1,90 @@
+use crate::stream::StreamExt;
+use core::pin::Pin;
+use futures_core::future::{FusedFuture, Future};
+use futures_core::ready;
+use futures_core::stream::Stream;
+use futures_core::task::{Context, Poll};
+
+/// Future for the [`into_future`](super::StreamExt::into_future) method.
+#[derive(Debug)]
+#[must_use = "futures do nothing unless you `.await` or poll them"]
+pub struct StreamFuture<St> {
+    stream: Option<St>,
+}
+
+impl<St: Stream + Unpin> StreamFuture<St> {
+    pub(super) fn new(stream: St) -> Self {
+        Self { stream: Some(stream) }
+    }
+
+    /// Acquires a reference to the underlying stream that this combinator is
+    /// pulling from.
+    ///
+    /// This method returns an `Option` to account for the fact that `StreamFuture`'s
+    /// implementation of `Future::poll` consumes the underlying stream during polling
+    /// in order to return it to the caller of `Future::poll` if the stream yielded
+    /// an element.
+    pub fn get_ref(&self) -> Option<&St> {
+        self.stream.as_ref()
+    }
+
+    /// Acquires a mutable reference to the underlying stream that this
+    /// combinator is pulling from.
+    ///
+    /// Note that care must be taken to avoid tampering with the state of the
+    /// stream which may otherwise confuse this combinator.
+    ///
+    /// This method returns an `Option` to account for the fact that `StreamFuture`'s
+    /// implementation of `Future::poll` consumes the underlying stream during polling
+    /// in order to return it to the caller of `Future::poll` if the stream yielded
+    /// an element.
+    pub fn get_mut(&mut self) -> Option<&mut St> {
+        self.stream.as_mut()
+    }
+
+    /// Acquires a pinned mutable reference to the underlying stream that this
+    /// combinator is pulling from.
+    ///
+    /// Note that care must be taken to avoid tampering with the state of the
+    /// stream which may otherwise confuse this combinator.
+    ///
+    /// This method returns an `Option` to account for the fact that `StreamFuture`'s
+    /// implementation of `Future::poll` consumes the underlying stream during polling
+    /// in order to return it to the caller of `Future::poll` if the stream yielded
+    /// an element.
+    pub fn get_pin_mut(self: Pin<&mut Self>) -> Option<Pin<&mut St>> {
+        self.get_mut().stream.as_mut().map(Pin::new)
+    }
+
+    /// Consumes this combinator, returning the underlying stream.
+    ///
+    /// Note that this may discard intermediate state of this combinator, so
+    /// care should be taken to avoid losing resources when this is called.
+    ///
+    /// This method returns an `Option` to account for the fact that `StreamFuture`'s
+    /// implementation of `Future::poll` consumes the underlying stream during polling
+    /// in order to return it to the caller of `Future::poll` if the stream yielded
+    /// an element.
+    pub fn into_inner(self) -> Option<St> {
+        self.stream
+    }
+}
+
+impl<St: Stream + Unpin> FusedFuture for StreamFuture<St> {
+    fn is_terminated(&self) -> bool {
+        self.stream.is_none()
+    }
+}
+
+impl<St: Stream + Unpin> Future for StreamFuture<St> {
+    type Output = (Option<St::Item>, St);
+
+    fn poll(mut self: Pin<&mut Self>, cx: &mut Context<'_>) -> Poll<Self::Output> {
+        let item = {
+            let s = self.stream.as_mut().expect("polling StreamFuture twice");
+            ready!(s.poll_next_unpin(cx))
+        };
+        let stream = self.stream.take().unwrap();
+        Poll::Ready((item, stream))
+    }
+}
diff --git a/third_party/rust/futures-util/src/stream/stream/map.rs b/third_party/rust/futures-util/src/stream/stream/map.rs
new file mode 100644
index 0000000000..88bb6129d4
--- /dev/null
+++ b/third_party/rust/futures-util/src/stream/stream/map.rs
@@ -0,0 +1,77 @@
+use core::fmt;
+use core::pin::Pin;
+use futures_core::ready;
+use futures_core::stream::{FusedStream, Stream};
+use futures_core::task::{Context, Poll};
+#[cfg(feature = "sink")]
+use futures_sink::Sink;
+use pin_project_lite::pin_project;
+
+use crate::fns::FnMut1;
+
+pin_project! {
+    /// Stream for the [`map`](super::StreamExt::map) method.
+    #[must_use = "streams do nothing unless polled"]
+    pub struct Map<St, F> {
+        #[pin]
+        stream: St,
+        f: F,
+    }
+}
+
+impl<St, F> fmt::Debug for Map<St, F>
+where
+    St: fmt::Debug,
+{
+    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
+        f.debug_struct("Map").field("stream", &self.stream).finish()
+    }
+}
+
+impl<St, F> Map<St, F> {
+    pub(crate) fn new(stream: St, f: F) -> Self {
+        Self { stream, f }
+    }
+
+    delegate_access_inner!(stream, St, ());
+}
+
+impl<St, F> FusedStream for Map<St, F>
+where
+    St: FusedStream,
+    F: FnMut1<St::Item>,
+{
+    fn is_terminated(&self) -> bool {
+        self.stream.is_terminated()
+    }
+}
+
+impl<St, F> Stream for Map<St, F>
+where
+    St: Stream,
+    F: FnMut1<St::Item>,
+{
+    type Item = F::Output;
+
+    fn poll_next(self: Pin<&mut Self>, cx: &mut Context<'_>) -> Poll<Option<Self::Item>> {
+        let mut this = self.project();
+        let res = ready!(this.stream.as_mut().poll_next(cx));
+        Poll::Ready(res.map(|x| this.f.call_mut(x)))
+    }
+
+    fn size_hint(&self) -> (usize, Option<usize>) {
+        self.stream.size_hint()
+    }
+}
+
+// Forwarding impl of Sink from the underlying stream
+#[cfg(feature = "sink")]
+impl<St, F, Item> Sink<Item> for Map<St, F>
+where
+    St: Stream + Sink<Item>,
+    F: FnMut1<St::Item>,
+{
+    type Error = St::Error;
+
+    delegate_sink!(stream, Item);
+}
diff --git a/third_party/rust/futures-util/src/stream/stream/mod.rs b/third_party/rust/futures-util/src/stream/stream/mod.rs
new file mode 100644
index 0000000000..a823fab123
--- /dev/null
+++ b/third_party/rust/futures-util/src/stream/stream/mod.rs
@@ -0,0 +1,1685 @@
+//! Streams
+//!
+//! This module contains a number of functions for working with `Stream`s,
+//! including the `StreamExt` trait which adds methods to `Stream` types.
+
+use crate::future::{assert_future, Either};
+use crate::stream::assert_stream;
+#[cfg(feature = "alloc")]
+use alloc::boxed::Box;
+#[cfg(feature = "alloc")]
+use alloc::vec::Vec;
+use core::pin::Pin;
+#[cfg(feature = "sink")]
+use futures_core::stream::TryStream;
+#[cfg(feature = "alloc")]
+use futures_core::stream::{BoxStream, LocalBoxStream};
+use futures_core::{
+    future::Future,
+    stream::{FusedStream, Stream},
+    task::{Context, Poll},
+};
+#[cfg(feature = "sink")]
+use futures_sink::Sink;
+
+use crate::fns::{inspect_fn, InspectFn};
+
+mod chain;
+#[allow(unreachable_pub)] // https://github.com/rust-lang/rust/issues/57411
+pub use self::chain::Chain;
+
+mod collect;
+#[allow(unreachable_pub)] // https://github.com/rust-lang/rust/issues/57411
+pub use self::collect::Collect;
+
+mod unzip;
+#[allow(unreachable_pub)] // https://github.com/rust-lang/rust/issues/57411
+pub use self::unzip::Unzip;
+
+mod concat;
+#[allow(unreachable_pub)] // https://github.com/rust-lang/rust/issues/57411
+pub use self::concat::Concat;
+
+mod count;
+#[allow(unreachable_pub)] // https://github.com/rust-lang/rust/issues/57411
+pub use self::count::Count;
+
+mod cycle;
+#[allow(unreachable_pub)] // https://github.com/rust-lang/rust/issues/57411
+pub use self::cycle::Cycle;
+
+mod enumerate;
+#[allow(unreachable_pub)] // https://github.com/rust-lang/rust/issues/57411
+pub use self::enumerate::Enumerate;
+
+mod filter;
+#[allow(unreachable_pub)] // https://github.com/rust-lang/rust/issues/57411
+pub use self::filter::Filter;
+
+mod filter_map;
+#[allow(unreachable_pub)] // https://github.com/rust-lang/rust/issues/57411
+pub use self::filter_map::FilterMap;
+
+mod flatten;
+
+delegate_all!(
+    /// Stream for the [`flatten`](StreamExt::flatten) method.
+    Flatten<St>(
+        flatten::Flatten<St, St::Item>
+    ): Debug + Sink + Stream + FusedStream + AccessInner[St, (.)] + New[|x: St| flatten::Flatten::new(x)]
+    where St: Stream
+);
+
+mod fold;
+#[allow(unreachable_pub)] // https://github.com/rust-lang/rust/issues/57411
+pub use self::fold::Fold;
+
+mod any;
+#[allow(unreachable_pub)] // https://github.com/rust-lang/rust/issues/57411
+pub use self::any::Any;
+
+mod all;
+#[allow(unreachable_pub)] // https://github.com/rust-lang/rust/issues/57411
+pub use self::all::All;
+
+#[cfg(feature = "sink")]
+mod forward;
+
+#[cfg(feature = "sink")]
+delegate_all!(
+    /// Future for the [`forward`](super::StreamExt::forward) method.
+    #[cfg_attr(docsrs, doc(cfg(feature = "sink")))]
+    Forward<St, Si>(
+        forward::Forward<St, Si, St::Ok>
+    ): Debug + Future + FusedFuture + New[|x: St, y: Si| forward::Forward::new(x, y)]
+    where St: TryStream
+);
+
+mod for_each;
+#[allow(unreachable_pub)] // https://github.com/rust-lang/rust/issues/57411
+pub use self::for_each::ForEach;
+
+mod fuse;
+#[allow(unreachable_pub)] // https://github.com/rust-lang/rust/issues/57411
+pub use self::fuse::Fuse;
+
+mod into_future;
+#[allow(unreachable_pub)] // https://github.com/rust-lang/rust/issues/57411
+pub use self::into_future::StreamFuture;
+
+delegate_all!(
+    /// Stream for the [`inspect`](StreamExt::inspect) method.
+    Inspect<St, F>(
+        map::Map<St, InspectFn<F>>
+    ): Debug + Sink + Stream + FusedStream + AccessInner[St, (.)] + New[|x: St, f: F| map::Map::new(x, inspect_fn(f))]
+);
+
+mod map;
+#[allow(unreachable_pub)] // https://github.com/rust-lang/rust/issues/57411
+pub use self::map::Map;
+
+delegate_all!(
+    /// Stream for the [`flat_map`](StreamExt::flat_map) method.
+    FlatMap<St, U, F>(
+        flatten::Flatten<Map<St, F>, U>
+    ): Debug + Sink + Stream + FusedStream + AccessInner[St, (. .)] + New[|x: St, f: F| flatten::Flatten::new(Map::new(x, f))]
+);
+
+mod next;
+#[allow(unreachable_pub)] // https://github.com/rust-lang/rust/issues/57411
+pub use self::next::Next;
+
+mod select_next_some;
+#[allow(unreachable_pub)] // https://github.com/rust-lang/rust/issues/57411
+pub use self::select_next_some::SelectNextSome;
+
+mod peek;
+#[allow(unreachable_pub)] // https://github.com/rust-lang/rust/issues/57411
+pub use self::peek::{NextIf, NextIfEq, Peek, PeekMut, Peekable};
+
+mod skip;
+#[allow(unreachable_pub)] // https://github.com/rust-lang/rust/issues/57411
+pub use self::skip::Skip;
+
+mod skip_while;
+#[allow(unreachable_pub)] // https://github.com/rust-lang/rust/issues/57411
+pub use self::skip_while::SkipWhile;
+
+mod take;
+#[allow(unreachable_pub)] // https://github.com/rust-lang/rust/issues/57411
+pub use self::take::Take;
+
+mod take_while;
+#[allow(unreachable_pub)] // https://github.com/rust-lang/rust/issues/57411
+pub use self::take_while::TakeWhile;
+
+mod take_until;
+#[allow(unreachable_pub)] // https://github.com/rust-lang/rust/issues/57411
+pub use self::take_until::TakeUntil;
+
+mod then;
+#[allow(unreachable_pub)] // https://github.com/rust-lang/rust/issues/57411
+pub use self::then::Then;
+
+mod zip;
+#[allow(unreachable_pub)] // https://github.com/rust-lang/rust/issues/57411
+pub use self::zip::Zip;
+
+#[cfg(feature = "alloc")]
+mod chunks;
+#[cfg(feature = "alloc")]
+#[allow(unreachable_pub)] // https://github.com/rust-lang/rust/issues/57411
+pub use self::chunks::Chunks;
+
+#[cfg(feature = "alloc")]
+mod ready_chunks;
+#[cfg(feature = "alloc")]
+#[allow(unreachable_pub)] // https://github.com/rust-lang/rust/issues/57411
+pub use self::ready_chunks::ReadyChunks;
+
+mod scan;
+#[allow(unreachable_pub)] // https://github.com/rust-lang/rust/issues/57411
+pub use self::scan::Scan;
+
+#[cfg(not(futures_no_atomic_cas))]
+#[cfg(feature = "alloc")]
+mod buffer_unordered;
+#[cfg(not(futures_no_atomic_cas))]
+#[cfg(feature = "alloc")]
+#[allow(unreachable_pub)] // https://github.com/rust-lang/rust/issues/57411
+pub use self::buffer_unordered::BufferUnordered;
+
+#[cfg(not(futures_no_atomic_cas))]
+#[cfg(feature = "alloc")]
+mod buffered;
+#[cfg(not(futures_no_atomic_cas))]
+#[cfg(feature = "alloc")]
+#[allow(unreachable_pub)] // https://github.com/rust-lang/rust/issues/57411
+pub use self::buffered::Buffered;
+
+#[cfg(not(futures_no_atomic_cas))]
+#[cfg(feature = "alloc")]
+mod flatten_unordered;
+
+#[cfg(not(futures_no_atomic_cas))]
+#[cfg(feature = "alloc")]
+#[allow(unreachable_pub)]
+pub use self::flatten_unordered::FlattenUnordered;
+
+#[cfg(not(futures_no_atomic_cas))]
+#[cfg(feature = "alloc")]
+delegate_all!(
+    /// Stream for the [`flat_map_unordered`](StreamExt::flat_map_unordered) method.
+    FlatMapUnordered<St, U, F>(
+        FlattenUnordered<Map<St, F>>
+    ): Debug + Sink + Stream + FusedStream + AccessInner[St, (. .)] + New[|x: St, limit: Option<usize>, f: F| FlattenUnordered::new(Map::new(x, f), limit)]
+    where St: Stream, U: Stream, U: Unpin, F: FnMut(St::Item) -> U
+);
+
+#[cfg(not(futures_no_atomic_cas))]
+#[cfg(feature = "alloc")]
+mod for_each_concurrent;
+#[cfg(not(futures_no_atomic_cas))]
+#[cfg(feature = "alloc")]
+#[allow(unreachable_pub)] // https://github.com/rust-lang/rust/issues/57411
+pub use self::for_each_concurrent::ForEachConcurrent;
+
+#[cfg(not(futures_no_atomic_cas))]
+#[cfg(feature = "sink")]
+#[cfg_attr(docsrs, doc(cfg(feature = "sink")))]
+#[cfg(feature = "alloc")]
+mod split;
+#[cfg(not(futures_no_atomic_cas))]
+#[cfg(feature = "sink")]
+#[cfg_attr(docsrs, doc(cfg(feature = "sink")))]
+#[cfg(feature = "alloc")]
+#[allow(unreachable_pub)] // https://github.com/rust-lang/rust/issues/57411
+pub use self::split::{ReuniteError, SplitSink, SplitStream};
+
+#[cfg(feature = "std")]
+mod catch_unwind;
+#[cfg(feature = "std")]
+#[allow(unreachable_pub)] // https://github.com/rust-lang/rust/issues/57411
+pub use self::catch_unwind::CatchUnwind;
+
+impl<T: ?Sized> StreamExt for T where T: Stream {}
+
+/// An extension trait for `Stream`s that provides a variety of convenient
+/// combinator functions.
+pub trait StreamExt: Stream {
+    /// Creates a future that resolves to the next item in the stream.
+    ///
+    /// Note that because `next` doesn't take ownership over the stream,
+    /// the [`Stream`] type must be [`Unpin`]. If you want to use `next` with a
+    /// [`!Unpin`](Unpin) stream, you'll first have to pin the stream. This can
+    /// be done by boxing the stream using [`Box::pin`] or
+    /// pinning it to the stack using the `pin_mut!` macro from the `pin_utils`
+    /// crate.
+    ///
+    /// # Examples
+    ///
+    /// ```
+    /// # futures::executor::block_on(async {
+    /// use futures::stream::{self, StreamExt};
+    ///
+    /// let mut stream = stream::iter(1..=3);
+    ///
+    /// assert_eq!(stream.next().await, Some(1));
+    /// assert_eq!(stream.next().await, Some(2));
+    /// assert_eq!(stream.next().await, Some(3));
+    /// assert_eq!(stream.next().await, None);
+    /// # });
+    /// ```
+    fn next(&mut self) -> Next<'_, Self>
+    where
+        Self: Unpin,
+    {
+        assert_future::<Option<Self::Item>, _>(Next::new(self))
+    }
+
+    /// Converts this stream into a future of `(next_item, tail_of_stream)`.
+    /// If the stream terminates, then the next item is [`None`].
+    ///
+    /// The returned future can be used to compose streams and futures together
+    /// by placing everything into the "world of futures".
+    ///
+    /// Note that because `into_future` moves the stream, the [`Stream`] type
+    /// must be [`Unpin`]. If you want to use `into_future` with a
+    /// [`!Unpin`](Unpin) stream, you'll first have to pin the stream. This can
+    /// be done by boxing the stream using [`Box::pin`] or
+    /// pinning it to the stack using the `pin_mut!` macro from the `pin_utils`
+    /// crate.
+    ///
+    /// # Examples
+    ///
+    /// ```
+    /// # futures::executor::block_on(async {
+    /// use futures::stream::{self, StreamExt};
+    ///
+    /// let stream = stream::iter(1..=3);
+    ///
+    /// let (item, stream) = stream.into_future().await;
+    /// assert_eq!(Some(1), item);
+    ///
+    /// let (item, stream) = stream.into_future().await;
+    /// assert_eq!(Some(2), item);
+    /// # });
+    /// ```
+    fn into_future(self) -> StreamFuture<Self>
+    where
+        Self: Sized + Unpin,
+    {
+        assert_future::<(Option<Self::Item>, Self), _>(StreamFuture::new(self))
+    }
+
+    /// Maps this stream's items to a different type, returning a new stream of
+    /// the resulting type.
+    ///
+    /// The provided closure is executed over all elements of this stream as
+    /// they are made available. It is executed inline with calls to
+    /// [`poll_next`](Stream::poll_next).
+    ///
+    /// Note that this function consumes the stream passed into it and returns a
+    /// wrapped version of it, similar to the existing `map` methods in the
+    /// standard library.
+    ///
+    /// # Examples
+    ///
+    /// ```
+    /// # futures::executor::block_on(async {
+    /// use futures::stream::{self, StreamExt};
+    ///
+    /// let stream = stream::iter(1..=3);
+    /// let stream = stream.map(|x| x + 3);
+    ///
+    /// assert_eq!(vec![4, 5, 6], stream.collect::<Vec<_>>().await);
+    /// # });
+    /// ```
+    fn map<T, F>(self, f: F) -> Map<Self, F>
+    where
+        F: FnMut(Self::Item) -> T,
+        Self: Sized,
+    {
+        assert_stream::<T, _>(Map::new(self, f))
+    }
+
+    /// Creates a stream which gives the current iteration count as well as
+    /// the next value.
+    ///
+    /// The stream returned yields pairs `(i, val)`, where `i` is the
+    /// current index of iteration and `val` is the value returned by the
+    /// stream.
+    ///
+    /// `enumerate()` keeps its count as a [`usize`]. If you want to count by a
+    /// different sized integer, the [`zip`](StreamExt::zip) function provides similar
+    /// functionality.
+    ///
+    /// # Overflow Behavior
+    ///
+    /// The method does no guarding against overflows, so enumerating more than
+    /// [`prim@usize::max_value()`] elements either produces the wrong result or panics. If
+    /// debug assertions are enabled, a panic is guaranteed.
+    ///
+    /// # Panics
+    ///
+    /// The returned stream might panic if the to-be-returned index would
+    /// overflow a [`usize`].
+    ///
+    /// # Examples
+    ///
+    /// ```
+    /// # futures::executor::block_on(async {
+    /// use futures::stream::{self, StreamExt};
+    ///
+    /// let stream = stream::iter(vec!['a', 'b', 'c']);
+    ///
+    /// let mut stream = stream.enumerate();
+    ///
+    /// assert_eq!(stream.next().await, Some((0, 'a')));
+    /// assert_eq!(stream.next().await, Some((1, 'b')));
+    /// assert_eq!(stream.next().await, Some((2, 'c')));
+    /// assert_eq!(stream.next().await, None);
+    /// # });
+    /// ```
+    fn enumerate(self) -> Enumerate<Self>
+    where
+        Self: Sized,
+    {
+        assert_stream::<(usize, Self::Item), _>(Enumerate::new(self))
+    }
+
+    /// Filters the values produced by this stream according to the provided
+    /// asynchronous predicate.
+    ///
+    /// As values of this stream are made available, the provided predicate `f`
+    /// will be run against them. If the predicate returns a `Future` which
+    /// resolves to `true`, then the stream will yield the value, but if the
+    /// predicate returns a `Future` which resolves to `false`, then the value
+    /// will be discarded and the next value will be produced.
+    ///
+    /// Note that this function consumes the stream passed into it and returns a
+    /// wrapped version of it, similar to the existing `filter` methods in the
+    /// standard library.
+    ///
+    /// # Examples
+    ///
+    /// ```
+    /// # futures::executor::block_on(async {
+    /// use futures::future;
+    /// use futures::stream::{self, StreamExt};
+    ///
+    /// let stream = stream::iter(1..=10);
+    /// let events = stream.filter(|x| future::ready(x % 2 == 0));
+    ///
+    /// assert_eq!(vec![2, 4, 6, 8, 10], events.collect::<Vec<_>>().await);
+    /// # });
+    /// ```
+    fn filter<Fut, F>(self, f: F) -> Filter<Self, Fut, F>
+    where
+        F: FnMut(&Self::Item) -> Fut,
+        Fut: Future<Output = bool>,
+        Self: Sized,
+    {
+        assert_stream::<Self::Item, _>(Filter::new(self, f))
+    }
+
+    /// Filters the values produced by this stream while simultaneously mapping
+    /// them to a different type according to the provided asynchronous closure.
+    ///
+    /// As values of this stream are made available, the provided function will
+    /// be run on them. If the future returned by the predicate `f` resolves to
+    /// [`Some(item)`](Some) then the stream will yield the value `item`, but if
+    /// it resolves to [`None`] then the next value will be produced.
+    ///
+    /// Note that this function consumes the stream passed into it and returns a
+    /// wrapped version of it, similar to the existing `filter_map` methods in
+    /// the standard library.
+    ///
+    /// # Examples
+    /// ```
+    /// # futures::executor::block_on(async {
+    /// use futures::stream::{self, StreamExt};
+    ///
+    /// let stream = stream::iter(1..=10);
+    /// let events = stream.filter_map(|x| async move {
+    ///     if x % 2 == 0 { Some(x + 1) } else { None }
+    /// });
+    ///
+    /// assert_eq!(vec![3, 5, 7, 9, 11], events.collect::<Vec<_>>().await);
+    /// # });
+    /// ```
+    fn filter_map<Fut, T, F>(self, f: F) -> FilterMap<Self, Fut, F>
+    where
+        F: FnMut(Self::Item) -> Fut,
+        Fut: Future<Output = Option<T>>,
+        Self: Sized,
+    {
+        assert_stream::<T, _>(FilterMap::new(self, f))
+    }
+
+    /// Computes from this stream's items new items of a different type using
+    /// an asynchronous closure.
+    ///
+    /// The provided closure `f` will be called with an `Item` once a value is
+    /// ready, it returns a future which will then be run to completion
+    /// to produce the next value on this stream.
+    ///
+    /// Note that this function consumes the stream passed into it and returns a
+    /// wrapped version of it.
+    ///
+    /// # Examples
+    ///
+    /// ```
+    /// # futures::executor::block_on(async {
+    /// use futures::stream::{self, StreamExt};
+    ///
+    /// let stream = stream::iter(1..=3);
+    /// let stream = stream.then(|x| async move { x + 3 });
+    ///
+    /// assert_eq!(vec![4, 5, 6], stream.collect::<Vec<_>>().await);
+    /// # });
+    /// ```
+    fn then<Fut, F>(self, f: F) -> Then<Self, Fut, F>
+    where
+        F: FnMut(Self::Item) -> Fut,
+        Fut: Future,
+        Self: Sized,
+    {
+        assert_stream::<Fut::Output, _>(Then::new(self, f))
+    }
+
+    /// Transforms a stream into a collection, returning a
+    /// future representing the result of that computation.
+    ///
+    /// The returned future will be resolved when the stream terminates.
+    ///
+    /// # Examples
+    ///
+    /// ```
+    /// # futures::executor::block_on(async {
+    /// use futures::channel::mpsc;
+    /// use futures::stream::StreamExt;
+    /// use std::thread;
+    ///
+    /// let (tx, rx) = mpsc::unbounded();
+    ///
+    /// thread::spawn(move || {
+    ///     for i in 1..=5 {
+    ///         tx.unbounded_send(i).unwrap();
+    ///     }
+    /// });
+    ///
+    /// let output = rx.collect::<Vec<i32>>().await;
+    /// assert_eq!(output, vec![1, 2, 3, 4, 5]);
+    /// # });
+    /// ```
+    fn collect<C: Default + Extend<Self::Item>>(self) -> Collect<Self, C>
+    where
+        Self: Sized,
+    {
+        assert_future::<C, _>(Collect::new(self))
+    }
+
+    /// Converts a stream of pairs into a future, which
+    /// resolves to pair of containers.
+    ///
+    /// `unzip()` produces a future, which resolves to two
+    /// collections: one from the left elements of the pairs,
+    /// and one from the right elements.
+    ///
+    /// The returned future will be resolved when the stream terminates.
+    ///
+    /// # Examples
+    ///
+    /// ```
+    /// # futures::executor::block_on(async {
+    /// use futures::channel::mpsc;
+    /// use futures::stream::StreamExt;
+    /// use std::thread;
+    ///
+    /// let (tx, rx) = mpsc::unbounded();
+    ///
+    /// thread::spawn(move || {
+    ///     tx.unbounded_send((1, 2)).unwrap();
+    ///     tx.unbounded_send((3, 4)).unwrap();
+    ///     tx.unbounded_send((5, 6)).unwrap();
+    /// });
+    ///
+    /// let (o1, o2): (Vec<_>, Vec<_>) = rx.unzip().await;
+    /// assert_eq!(o1, vec![1, 3, 5]);
+    /// assert_eq!(o2, vec![2, 4, 6]);
+    /// # });
+    /// ```
+    fn unzip<A, B, FromA, FromB>(self) -> Unzip<Self, FromA, FromB>
+    where
+        FromA: Default + Extend<A>,
+        FromB: Default + Extend<B>,
+        Self: Sized + Stream<Item = (A, B)>,
+    {
+        assert_future::<(FromA, FromB), _>(Unzip::new(self))
+    }
+
+    /// Concatenate all items of a stream into a single extendable
+    /// destination, returning a future representing the end result.
+    ///
+    /// This combinator will extend the first item with the contents
+    /// of all the subsequent results of the stream. If the stream is
+    /// empty, the default value will be returned.
+    ///
+    /// Works with all collections that implement the
+    /// [`Extend`](std::iter::Extend) trait.
+    ///
+    /// # Examples
+    ///
+    /// ```
+    /// # futures::executor::block_on(async {
+    /// use futures::channel::mpsc;
+    /// use futures::stream::StreamExt;
+    /// use std::thread;
+    ///
+    /// let (tx, rx) = mpsc::unbounded();
+    ///
+    /// thread::spawn(move || {
+    ///     for i in (0..3).rev() {
+    ///         let n = i * 3;
+    ///         tx.unbounded_send(vec![n + 1, n + 2, n + 3]).unwrap();
+    ///     }
+    /// });
+    ///
+    /// let result = rx.concat().await;
+    ///
+    /// assert_eq!(result, vec![7, 8, 9, 4, 5, 6, 1, 2, 3]);
+    /// # });
+    /// ```
+    fn concat(self) -> Concat<Self>
+    where
+        Self: Sized,
+        Self::Item: Extend<<<Self as Stream>::Item as IntoIterator>::Item> + IntoIterator + Default,
+    {
+        assert_future::<Self::Item, _>(Concat::new(self))
+    }
+
+    /// Drives the stream to completion, counting the number of items.
+    ///
+    /// # Overflow Behavior
+    ///
+    /// The method does no guarding against overflows, so counting elements of a
+    /// stream with more than [`usize::MAX`] elements either produces the wrong
+    /// result or panics. If debug assertions are enabled, a panic is guaranteed.
+    ///
+    /// # Panics
+    ///
+    /// This function might panic if the iterator has more than [`usize::MAX`]
+    /// elements.
+    ///
+    /// # Examples
+    ///
+    /// ```
+    /// # futures::executor::block_on(async {
+    /// use futures::stream::{self, StreamExt};
+    ///
+    /// let stream = stream::iter(1..=10);
+    /// let count = stream.count().await;
+    ///
+    /// assert_eq!(count, 10);
+    /// # });
+    /// ```
+    fn count(self) -> Count<Self>
+    where
+        Self: Sized,
+    {
+        assert_future::<usize, _>(Count::new(self))
+    }
+
+    /// Repeats a stream endlessly.
+    ///
+    /// The stream never terminates. Note that you likely want to avoid
+    /// usage of `collect` or such on the returned stream as it will exhaust
+    /// available memory as it tries to just fill up all RAM.
+    ///
+    /// # Examples
+    ///
+    /// ```
+    /// # futures::executor::block_on(async {
+    /// use futures::stream::{self, StreamExt};
+    /// let a = [1, 2, 3];
+    /// let mut s = stream::iter(a.iter()).cycle();
+    ///
+    /// assert_eq!(s.next().await, Some(&1));
+    /// assert_eq!(s.next().await, Some(&2));
+    /// assert_eq!(s.next().await, Some(&3));
+    /// assert_eq!(s.next().await, Some(&1));
+    /// assert_eq!(s.next().await, Some(&2));
+    /// assert_eq!(s.next().await, Some(&3));
+    /// assert_eq!(s.next().await, Some(&1));
+    /// # });
+    /// ```
+    fn cycle(self) -> Cycle<Self>
+    where
+        Self: Sized + Clone,
+    {
+        assert_stream::<Self::Item, _>(Cycle::new(self))
+    }
+
+    /// Execute an accumulating asynchronous computation over a stream,
+    /// collecting all the values into one final result.
+    ///
+    /// This combinator will accumulate all values returned by this stream
+    /// according to the closure provided. The initial state is also provided to
+    /// this method and then is returned again by each execution of the closure.
+    /// Once the entire stream has been exhausted the returned future will
+    /// resolve to this value.
+    ///
+    /// # Examples
+    ///
+    /// ```
+    /// # futures::executor::block_on(async {
+    /// use futures::stream::{self, StreamExt};
+    ///
+    /// let number_stream = stream::iter(0..6);
+    /// let sum = number_stream.fold(0, |acc, x| async move { acc + x });
+    /// assert_eq!(sum.await, 15);
+    /// # });
+    /// ```
+    fn fold<T, Fut, F>(self, init: T, f: F) -> Fold<Self, Fut, T, F>
+    where
+        F: FnMut(T, Self::Item) -> Fut,
+        Fut: Future<Output = T>,
+        Self: Sized,
+    {
+        assert_future::<T, _>(Fold::new(self, f, init))
+    }
+
+    /// Execute predicate over asynchronous stream, and return `true` if any element in stream satisfied a predicate.
+    ///
+    /// # Examples
+    ///
+    /// ```
+    /// # futures::executor::block_on(async {
+    /// use futures::stream::{self, StreamExt};
+    ///
+    /// let number_stream = stream::iter(0..10);
+    /// let contain_three = number_stream.any(|i| async move { i == 3 });
+    /// assert_eq!(contain_three.await, true);
+    /// # });
+    /// ```
+    fn any<Fut, F>(self, f: F) -> Any<Self, Fut, F>
+    where
+        F: FnMut(Self::Item) -> Fut,
+        Fut: Future<Output = bool>,
+        Self: Sized,
+    {
+        assert_future::<bool, _>(Any::new(self, f))
+    }
+
+    /// Execute predicate over asynchronous stream, and return `true` if all element in stream satisfied a predicate.
+    ///
+    /// # Examples
+    ///
+    /// ```
+    /// # futures::executor::block_on(async {
+    /// use futures::stream::{self, StreamExt};
+    ///
+    /// let number_stream = stream::iter(0..10);
+    /// let less_then_twenty = number_stream.all(|i| async move { i < 20 });
+    /// assert_eq!(less_then_twenty.await, true);
+    /// # });
+    /// ```
+    fn all<Fut, F>(self, f: F) -> All<Self, Fut, F>
+    where
+        F: FnMut(Self::Item) -> Fut,
+        Fut: Future<Output = bool>,
+        Self: Sized,
+    {
+        assert_future::<bool, _>(All::new(self, f))
+    }
+
+    /// Flattens a stream of streams into just one continuous stream.
+    ///
+    /// # Examples
+    ///
+    /// ```
+    /// # futures::executor::block_on(async {
+    /// use futures::channel::mpsc;
+    /// use futures::stream::StreamExt;
+    /// use std::thread;
+    ///
+    /// let (tx1, rx1) = mpsc::unbounded();
+    /// let (tx2, rx2) = mpsc::unbounded();
+    /// let (tx3, rx3) = mpsc::unbounded();
+    ///
+    /// thread::spawn(move || {
+    ///     tx1.unbounded_send(1).unwrap();
+    ///     tx1.unbounded_send(2).unwrap();
+    /// });
+    /// thread::spawn(move || {
+    ///     tx2.unbounded_send(3).unwrap();
+    ///     tx2.unbounded_send(4).unwrap();
+    /// });
+    /// thread::spawn(move || {
+    ///     tx3.unbounded_send(rx1).unwrap();
+    ///     tx3.unbounded_send(rx2).unwrap();
+    /// });
+    ///
+    /// let output = rx3.flatten().collect::<Vec<i32>>().await;
+    /// assert_eq!(output, vec![1, 2, 3, 4]);
+    /// # });
+    /// ```
+    fn flatten(self) -> Flatten<Self>
+    where
+        Self::Item: Stream,
+        Self: Sized,
+    {
+        assert_stream::<<Self::Item as Stream>::Item, _>(Flatten::new(self))
+    }
+
+    /// Flattens a stream of streams into just one continuous stream. Polls
+    /// inner streams concurrently.
+    ///
+    /// # Examples
+    ///
+    /// ```
+    /// # futures::executor::block_on(async {
+    /// use futures::channel::mpsc;
+    /// use futures::stream::StreamExt;
+    /// use std::thread;
+    ///
+    /// let (tx1, rx1) = mpsc::unbounded();
+    /// let (tx2, rx2) = mpsc::unbounded();
+    /// let (tx3, rx3) = mpsc::unbounded();
+    ///
+    /// thread::spawn(move || {
+    ///     tx1.unbounded_send(1).unwrap();
+    ///     tx1.unbounded_send(2).unwrap();
+    /// });
+    /// thread::spawn(move || {
+    ///     tx2.unbounded_send(3).unwrap();
+    ///     tx2.unbounded_send(4).unwrap();
+    /// });
+    /// thread::spawn(move || {
+    ///     tx3.unbounded_send(rx1).unwrap();
+    ///     tx3.unbounded_send(rx2).unwrap();
+    /// });
+    ///
+    /// let mut output = rx3.flatten_unordered(None).collect::<Vec<i32>>().await;
+    /// output.sort();
+    ///
+    /// assert_eq!(output, vec![1, 2, 3, 4]);
+    /// # });
+    /// ```
+    #[cfg(not(futures_no_atomic_cas))]
+    #[cfg(feature = "alloc")]
+    fn flatten_unordered(self, limit: impl Into<Option<usize>>) -> FlattenUnordered<Self>
+    where
+        Self::Item: Stream + Unpin,
+        Self: Sized,
+    {
+        FlattenUnordered::new(self, limit.into())
+    }
+
+    /// Maps a stream like [`StreamExt::map`] but flattens nested `Stream`s.
+    ///
+    /// [`StreamExt::map`] is very useful, but if it produces a `Stream` instead,
+    /// you would have to chain combinators like `.map(f).flatten()` while this
+    /// combinator provides ability to write `.flat_map(f)` instead of chaining.
+    ///
+    /// The provided closure which produces inner streams is executed over all elements
+    /// of stream as last inner stream is terminated and next stream item is available.
+    ///
+    /// Note that this function consumes the stream passed into it and returns a
+    /// wrapped version of it, similar to the existing `flat_map` methods in the
+    /// standard library.
+    ///
+    /// # Examples
+    ///
+    /// ```
+    /// # futures::executor::block_on(async {
+    /// use futures::stream::{self, StreamExt};
+    ///
+    /// let stream = stream::iter(1..=3);
+    /// let stream = stream.flat_map(|x| stream::iter(vec![x + 3; x]));
+    ///
+    /// assert_eq!(vec![4, 5, 5, 6, 6, 6], stream.collect::<Vec<_>>().await);
+    /// # });
+    /// ```
+    fn flat_map<U, F>(self, f: F) -> FlatMap<Self, U, F>
+    where
+        F: FnMut(Self::Item) -> U,
+        U: Stream,
+        Self: Sized,
+    {
+        assert_stream::<U::Item, _>(FlatMap::new(self, f))
+    }
+
+    /// Maps a stream like [`StreamExt::map`] but flattens nested `Stream`s
+    /// and polls them concurrently, yielding items in any order, as they made
+    /// available.
+    ///
+    /// [`StreamExt::map`] is very useful, but if it produces `Stream`s
+    /// instead, and you need to poll all of them concurrently, you would
+    /// have to use something like `for_each_concurrent` and merge values
+    /// by hand. This combinator provides ability to collect all values
+    /// from concurrently polled streams into one stream.
+    ///
+    /// The first argument is an optional limit on the number of concurrently
+    /// polled streams. If this limit is not `None`, no more than `limit` streams
+    /// will be polled concurrently. The `limit` argument is of type
+    /// `Into<Option<usize>>`, and so can be provided as either `None`,
+    /// `Some(10)`, or just `10`. Note: a limit of zero is interpreted as
+    /// no limit at all, and will have the same result as passing in `None`.
+    ///
+    /// The provided closure which produces inner streams is executed over
+    /// all elements of stream as next stream item is available and limit
+    /// of concurrently processed streams isn't exceeded.
+    ///
+    /// Note that this function consumes the stream passed into it and
+    /// returns a wrapped version of it.
+    ///
+    /// # Examples
+    ///
+    /// ```
+    /// # futures::executor::block_on(async {
+    /// use futures::stream::{self, StreamExt};
+    ///
+    /// let stream = stream::iter(1..5);
+    /// let stream = stream.flat_map_unordered(1, |x| stream::iter(vec![x; x]));
+    /// let mut values = stream.collect::<Vec<_>>().await;
+    /// values.sort();
+    ///
+    /// assert_eq!(vec![1usize, 2, 2, 3, 3, 3, 4, 4, 4, 4], values);
+    /// # });
+    /// ```
+    #[cfg(not(futures_no_atomic_cas))]
+    #[cfg(feature = "alloc")]
+    fn flat_map_unordered<U, F>(
+        self,
+        limit: impl Into<Option<usize>>,
+        f: F,
+    ) -> FlatMapUnordered<Self, U, F>
+    where
+        U: Stream + Unpin,
+        F: FnMut(Self::Item) -> U,
+        Self: Sized,
+    {
+        FlatMapUnordered::new(self, limit.into(), f)
+    }
+
+    /// Combinator similar to [`StreamExt::fold`] that holds internal state
+    /// and produces a new stream.
+    ///
+    /// Accepts initial state and closure which will be applied to each element
+    /// of the stream until provided closure returns `None`. Once `None` is
+    /// returned, stream will be terminated.
+    ///
+    /// # Examples
+    ///
+    /// ```
+    /// # futures::executor::block_on(async {
+    /// use futures::future;
+    /// use futures::stream::{self, StreamExt};
+    ///
+    /// let stream = stream::iter(1..=10);
+    ///
+    /// let stream = stream.scan(0, |state, x| {
+    ///     *state += x;
+    ///     future::ready(if *state < 10 { Some(x) } else { None })
+    /// });
+    ///
+    /// assert_eq!(vec![1, 2, 3], stream.collect::<Vec<_>>().await);
+    /// # });
+    /// ```
+    fn scan<S, B, Fut, F>(self, initial_state: S, f: F) -> Scan<Self, S, Fut, F>
+    where
+        F: FnMut(&mut S, Self::Item) -> Fut,
+        Fut: Future<Output = Option<B>>,
+        Self: Sized,
+    {
+        assert_stream::<B, _>(Scan::new(self, initial_state, f))
+    }
+
+    /// Skip elements on this stream while the provided asynchronous predicate
+    /// resolves to `true`.
+    ///
+    /// This function, like `Iterator::skip_while`, will skip elements on the
+    /// stream until the predicate `f` resolves to `false`. Once one element
+    /// returns `false`, all future elements will be returned from the underlying
+    /// stream.
+    ///
+    /// # Examples
+    ///
+    /// ```
+    /// # futures::executor::block_on(async {
+    /// use futures::future;
+    /// use futures::stream::{self, StreamExt};
+    ///
+    /// let stream = stream::iter(1..=10);
+    ///
+    /// let stream = stream.skip_while(|x| future::ready(*x <= 5));
+    ///
+    /// assert_eq!(vec![6, 7, 8, 9, 10], stream.collect::<Vec<_>>().await);
+    /// # });
+    /// ```
+    fn skip_while<Fut, F>(self, f: F) -> SkipWhile<Self, Fut, F>
+    where
+        F: FnMut(&Self::Item) -> Fut,
+        Fut: Future<Output = bool>,
+        Self: Sized,
+    {
+        assert_stream::<Self::Item, _>(SkipWhile::new(self, f))
+    }
+
+    /// Take elements from this stream while the provided asynchronous predicate
+    /// resolves to `true`.
+    ///
+    /// This function, like `Iterator::take_while`, will take elements from the
+    /// stream until the predicate `f` resolves to `false`. Once one element
+    /// returns `false`, it will always return that the stream is done.
+    ///
+    /// # Examples
+    ///
+    /// ```
+    /// # futures::executor::block_on(async {
+    /// use futures::future;
+    /// use futures::stream::{self, StreamExt};
+    ///
+    /// let stream = stream::iter(1..=10);
+    ///
+    /// let stream = stream.take_while(|x| future::ready(*x <= 5));
+    ///
+    /// assert_eq!(vec![1, 2, 3, 4, 5], stream.collect::<Vec<_>>().await);
+    /// # });
+    /// ```
+    fn take_while<Fut, F>(self, f: F) -> TakeWhile<Self, Fut, F>
+    where
+        F: FnMut(&Self::Item) -> Fut,
+        Fut: Future<Output = bool>,
+        Self: Sized,
+    {
+        assert_stream::<Self::Item, _>(TakeWhile::new(self, f))
+    }
+
+    /// Take elements from this stream until the provided future resolves.
+    ///
+    /// This function will take elements from the stream until the provided
+    /// stopping future `fut` resolves. Once the `fut` future becomes ready,
+    /// this stream combinator will always return that the stream is done.
+    ///
+    /// The stopping future may return any type. Once the stream is stopped
+    /// the result of the stopping future may be accessed with `TakeUntil::take_result()`.
+    /// The stream may also be resumed with `TakeUntil::take_future()`.
+    /// See the documentation of [`TakeUntil`] for more information.
+    ///
+    /// # Examples
+    ///
+    /// ```
+    /// # futures::executor::block_on(async {
+    /// use futures::future;
+    /// use futures::stream::{self, StreamExt};
+    /// use futures::task::Poll;
+    ///
+    /// let stream = stream::iter(1..=10);
+    ///
+    /// let mut i = 0;
+    /// let stop_fut = future::poll_fn(|_cx| {
+    ///     i += 1;
+    ///     if i <= 5 {
+    ///         Poll::Pending
+    ///     } else {
+    ///         Poll::Ready(())
+    ///     }
+    /// });
+    ///
+    /// let stream = stream.take_until(stop_fut);
+    ///
+    /// assert_eq!(vec![1, 2, 3, 4, 5], stream.collect::<Vec<_>>().await);
+    /// # });
+    /// ```
+    fn take_until<Fut>(self, fut: Fut) -> TakeUntil<Self, Fut>
+    where
+        Fut: Future,
+        Self: Sized,
+    {
+        assert_stream::<Self::Item, _>(TakeUntil::new(self, fut))
+    }
+
+    /// Runs this stream to completion, executing the provided asynchronous
+    /// closure for each element on the stream.
+    ///
+    /// The closure provided will be called for each item this stream produces,
+    /// yielding a future. That future will then be executed to completion
+    /// before moving on to the next item.
+    ///
+    /// The returned value is a `Future` where the `Output` type is `()`; it is
+    /// executed entirely for its side effects.
+    ///
+    /// To process each item in the stream and produce another stream instead
+    /// of a single future, use `then` instead.
+    ///
+    /// # Examples
+    ///
+    /// ```
+    /// # futures::executor::block_on(async {
+    /// use futures::future;
+    /// use futures::stream::{self, StreamExt};
+    ///
+    /// let mut x = 0;
+    ///
+    /// {
+    ///     let fut = stream::repeat(1).take(3).for_each(|item| {
+    ///         x += item;
+    ///         future::ready(())
+    ///     });
+    ///     fut.await;
+    /// }
+    ///
+    /// assert_eq!(x, 3);
+    /// # });
+    /// ```
+    fn for_each<Fut, F>(self, f: F) -> ForEach<Self, Fut, F>
+    where
+        F: FnMut(Self::Item) -> Fut,
+        Fut: Future<Output = ()>,
+        Self: Sized,
+    {
+        assert_future::<(), _>(ForEach::new(self, f))
+    }
+
+    /// Runs this stream to completion, executing the provided asynchronous
+    /// closure for each element on the stream concurrently as elements become
+    /// available.
+    ///
+    /// This is similar to [`StreamExt::for_each`], but the futures
+    /// produced by the closure are run concurrently (but not in parallel--
+    /// this combinator does not introduce any threads).
+    ///
+    /// The closure provided will be called for each item this stream produces,
+    /// yielding a future. That future will then be executed to completion
+    /// concurrently with the other futures produced by the closure.
+    ///
+    /// The first argument is an optional limit on the number of concurrent
+    /// futures. If this limit is not `None`, no more than `limit` futures
+    /// will be run concurrently. The `limit` argument is of type
+    /// `Into<Option<usize>>`, and so can be provided as either `None`,
+    /// `Some(10)`, or just `10`. Note: a limit of zero is interpreted as
+    /// no limit at all, and will have the same result as passing in `None`.
+    ///
+    /// This method is only available when the `std` or `alloc` feature of this
+    /// library is activated, and it is activated by default.
+    ///
+    /// # Examples
+    ///
+    /// ```
+    /// # futures::executor::block_on(async {
+    /// use futures::channel::oneshot;
+    /// use futures::stream::{self, StreamExt};
+    ///
+    /// let (tx1, rx1) = oneshot::channel();
+    /// let (tx2, rx2) = oneshot::channel();
+    /// let (tx3, rx3) = oneshot::channel();
+    ///
+    /// let fut = stream::iter(vec![rx1, rx2, rx3]).for_each_concurrent(
+    ///     /* limit */ 2,
+    ///     |rx| async move {
+    ///         rx.await.unwrap();
+    ///     }
+    /// );
+    /// tx1.send(()).unwrap();
+    /// tx2.send(()).unwrap();
+    /// tx3.send(()).unwrap();
+    /// fut.await;
+    /// # })
+    /// ```
+    #[cfg(not(futures_no_atomic_cas))]
+    #[cfg(feature = "alloc")]
+    fn for_each_concurrent<Fut, F>(
+        self,
+        limit: impl Into<Option<usize>>,
+        f: F,
+    ) -> ForEachConcurrent<Self, Fut, F>
+    where
+        F: FnMut(Self::Item) -> Fut,
+        Fut: Future<Output = ()>,
+        Self: Sized,
+    {
+        assert_future::<(), _>(ForEachConcurrent::new(self, limit.into(), f))
+    }
+
+    /// Creates a new stream of at most `n` items of the underlying stream.
+    ///
+    /// Once `n` items have been yielded from this stream then it will always
+    /// return that the stream is done.
+    ///
+    /// # Examples
+    ///
+    /// ```
+    /// # futures::executor::block_on(async {
+    /// use futures::stream::{self, StreamExt};
+    ///
+    /// let stream = stream::iter(1..=10).take(3);
+    ///
+    /// assert_eq!(vec![1, 2, 3], stream.collect::<Vec<_>>().await);
+    /// # });
+    /// ```
+    fn take(self, n: usize) -> Take<Self>
+    where
+        Self: Sized,
+    {
+        assert_stream::<Self::Item, _>(Take::new(self, n))
+    }
+
+    /// Creates a new stream which skips `n` items of the underlying stream.
+    ///
+    /// Once `n` items have been skipped from this stream then it will always
+    /// return the remaining items on this stream.
+    ///
+    /// # Examples
+    ///
+    /// ```
+    /// # futures::executor::block_on(async {
+    /// use futures::stream::{self, StreamExt};
+    ///
+    /// let stream = stream::iter(1..=10).skip(5);
+    ///
+    /// assert_eq!(vec![6, 7, 8, 9, 10], stream.collect::<Vec<_>>().await);
+    /// # });
+    /// ```
+    fn skip(self, n: usize) -> Skip<Self>
+    where
+        Self: Sized,
+    {
+        assert_stream::<Self::Item, _>(Skip::new(self, n))
+    }
+
+    /// Fuse a stream such that [`poll_next`](Stream::poll_next) will never
+    /// again be called once it has finished. This method can be used to turn
+    /// any `Stream` into a `FusedStream`.
+    ///
+    /// Normally, once a stream has returned [`None`] from
+    /// [`poll_next`](Stream::poll_next) any further calls could exhibit bad
+    /// behavior such as block forever, panic, never return, etc. If it is known
+    /// that [`poll_next`](Stream::poll_next) may be called after stream
+    /// has already finished, then this method can be used to ensure that it has
+    /// defined semantics.
+    ///
+    /// The [`poll_next`](Stream::poll_next) method of a `fuse`d stream
+    /// is guaranteed to return [`None`] after the underlying stream has
+    /// finished.
+    ///
+    /// # Examples
+    ///
+    /// ```
+    /// use futures::executor::block_on_stream;
+    /// use futures::stream::{self, StreamExt};
+    /// use futures::task::Poll;
+    ///
+    /// let mut x = 0;
+    /// let stream = stream::poll_fn(|_| {
+    ///     x += 1;
+    ///     match x {
+    ///         0..=2 => Poll::Ready(Some(x)),
+    ///         3 => Poll::Ready(None),
+    ///         _ => panic!("should not happen")
+    ///     }
+    /// }).fuse();
+    ///
+    /// let mut iter = block_on_stream(stream);
+    /// assert_eq!(Some(1), iter.next());
+    /// assert_eq!(Some(2), iter.next());
+    /// assert_eq!(None, iter.next());
+    /// assert_eq!(None, iter.next());
+    /// // ...
+    /// ```
+    fn fuse(self) -> Fuse<Self>
+    where
+        Self: Sized,
+    {
+        assert_stream::<Self::Item, _>(Fuse::new(self))
+    }
+
+    /// Borrows a stream, rather than consuming it.
+    ///
+    /// This is useful to allow applying stream adaptors while still retaining
+    /// ownership of the original stream.
+    ///
+    /// # Examples
+    ///
+    /// ```
+    /// # futures::executor::block_on(async {
+    /// use futures::stream::{self, StreamExt};
+    ///
+    /// let mut stream = stream::iter(1..5);
+    ///
+    /// let sum = stream.by_ref()
+    ///                 .take(2)
+    ///                 .fold(0, |a, b| async move { a + b })
+    ///                 .await;
+    /// assert_eq!(sum, 3);
+    ///
+    /// // You can use the stream again
+    /// let sum = stream.take(2)
+    ///                 .fold(0, |a, b| async move { a + b })
+    ///                 .await;
+    /// assert_eq!(sum, 7);
+    /// # });
+    /// ```
+    fn by_ref(&mut self) -> &mut Self {
+        self
+    }
+
+    /// Catches unwinding panics while polling the stream.
+    ///
+    /// Caught panic (if any) will be the last element of the resulting stream.
+    ///
+    /// In general, panics within a stream can propagate all the way out to the
+    /// task level. This combinator makes it possible to halt unwinding within
+    /// the stream itself. It's most commonly used within task executors. This
+    /// method should not be used for error handling.
+    ///
+    /// Note that this method requires the `UnwindSafe` bound from the standard
+    /// library. This isn't always applied automatically, and the standard
+    /// library provides an `AssertUnwindSafe` wrapper type to apply it
+    /// after-the fact. To assist using this method, the [`Stream`] trait is
+    /// also implemented for `AssertUnwindSafe<St>` where `St` implements
+    /// [`Stream`].
+    ///
+    /// This method is only available when the `std` feature of this
+    /// library is activated, and it is activated by default.
+    ///
+    /// # Examples
+    ///
+    /// ```
+    /// # futures::executor::block_on(async {
+    /// use futures::stream::{self, StreamExt};
+    ///
+    /// let stream = stream::iter(vec![Some(10), None, Some(11)]);
+    /// // Panic on second element
+    /// let stream_panicking = stream.map(|o| o.unwrap());
+    /// // Collect all the results
+    /// let stream = stream_panicking.catch_unwind();
+    ///
+    /// let results: Vec<Result<i32, _>> = stream.collect().await;
+    /// match results[0] {
+    ///     Ok(10) => {}
+    ///     _ => panic!("unexpected result!"),
+    /// }
+    /// assert!(results[1].is_err());
+    /// assert_eq!(results.len(), 2);
+    /// # });
+    /// ```
+    #[cfg(feature = "std")]
+    fn catch_unwind(self) -> CatchUnwind<Self>
+    where
+        Self: Sized + std::panic::UnwindSafe,
+    {
+        assert_stream(CatchUnwind::new(self))
+    }
+
+    /// Wrap the stream in a Box, pinning it.
+    ///
+    /// This method is only available when the `std` or `alloc` feature of this
+    /// library is activated, and it is activated by default.
+    #[cfg(feature = "alloc")]
+    fn boxed<'a>(self) -> BoxStream<'a, Self::Item>
+    where
+        Self: Sized + Send + 'a,
+    {
+        assert_stream::<Self::Item, _>(Box::pin(self))
+    }
+
+    /// Wrap the stream in a Box, pinning it.
+    ///
+    /// Similar to `boxed`, but without the `Send` requirement.
+    ///
+    /// This method is only available when the `std` or `alloc` feature of this
+    /// library is activated, and it is activated by default.
+    #[cfg(feature = "alloc")]
+    fn boxed_local<'a>(self) -> LocalBoxStream<'a, Self::Item>
+    where
+        Self: Sized + 'a,
+    {
+        assert_stream::<Self::Item, _>(Box::pin(self))
+    }
+
+    /// An adaptor for creating a buffered list of pending futures.
+    ///
+    /// If this stream's item can be converted into a future, then this adaptor
+    /// will buffer up to at most `n` futures and then return the outputs in the
+    /// same order as the underlying stream. No more than `n` futures will be
+    /// buffered at any point in time, and less than `n` may also be buffered
+    /// depending on the state of each future.
+    ///
+    /// The returned stream will be a stream of each future's output.
+    ///
+    /// This method is only available when the `std` or `alloc` feature of this
+    /// library is activated, and it is activated by default.
+    #[cfg(not(futures_no_atomic_cas))]
+    #[cfg(feature = "alloc")]
+    fn buffered(self, n: usize) -> Buffered<Self>
+    where
+        Self::Item: Future,
+        Self: Sized,
+    {
+        assert_stream::<<Self::Item as Future>::Output, _>(Buffered::new(self, n))
+    }
+
+    /// An adaptor for creating a buffered list of pending futures (unordered).
+    ///
+    /// If this stream's item can be converted into a future, then this adaptor
+    /// will buffer up to `n` futures and then return the outputs in the order
+    /// in which they complete. No more than `n` futures will be buffered at
+    /// any point in time, and less than `n` may also be buffered depending on
+    /// the state of each future.
+    ///
+    /// The returned stream will be a stream of each future's output.
+    ///
+    /// This method is only available when the `std` or `alloc` feature of this
+    /// library is activated, and it is activated by default.
+    ///
+    /// # Examples
+    ///
+    /// ```
+    /// # futures::executor::block_on(async {
+    /// use futures::channel::oneshot;
+    /// use futures::stream::{self, StreamExt};
+    ///
+    /// let (send_one, recv_one) = oneshot::channel();
+    /// let (send_two, recv_two) = oneshot::channel();
+    ///
+    /// let stream_of_futures = stream::iter(vec![recv_one, recv_two]);
+    /// let mut buffered = stream_of_futures.buffer_unordered(10);
+    ///
+    /// send_two.send(2i32)?;
+    /// assert_eq!(buffered.next().await, Some(Ok(2i32)));
+    ///
+    /// send_one.send(1i32)?;
+    /// assert_eq!(buffered.next().await, Some(Ok(1i32)));
+    ///
+    /// assert_eq!(buffered.next().await, None);
+    /// # Ok::<(), i32>(()) }).unwrap();
+    /// ```
+    #[cfg(not(futures_no_atomic_cas))]
+    #[cfg(feature = "alloc")]
+    fn buffer_unordered(self, n: usize) -> BufferUnordered<Self>
+    where
+        Self::Item: Future,
+        Self: Sized,
+    {
+        assert_stream::<<Self::Item as Future>::Output, _>(BufferUnordered::new(self, n))
+    }
+
+    /// An adapter for zipping two streams together.
+    ///
+    /// The zipped stream waits for both streams to produce an item, and then
+    /// returns that pair. If either stream ends then the zipped stream will
+    /// also end.
+    ///
+    /// # Examples
+    ///
+    /// ```
+    /// # futures::executor::block_on(async {
+    /// use futures::stream::{self, StreamExt};
+    ///
+    /// let stream1 = stream::iter(1..=3);
+    /// let stream2 = stream::iter(5..=10);
+    ///
+    /// let vec = stream1.zip(stream2)
+    ///                  .collect::<Vec<_>>()
+    ///                  .await;
+    /// assert_eq!(vec![(1, 5), (2, 6), (3, 7)], vec);
+    /// # });
+    /// ```
+    ///
+    fn zip<St>(self, other: St) -> Zip<Self, St>
+    where
+        St: Stream,
+        Self: Sized,
+    {
+        assert_stream::<(Self::Item, St::Item), _>(Zip::new(self, other))
+    }
+
+    /// Adapter for chaining two streams.
+    ///
+    /// The resulting stream emits elements from the first stream, and when
+    /// first stream reaches the end, emits the elements from the second stream.
+    ///
+    /// ```
+    /// # futures::executor::block_on(async {
+    /// use futures::stream::{self, StreamExt};
+    ///
+    /// let stream1 = stream::iter(vec![Ok(10), Err(false)]);
+    /// let stream2 = stream::iter(vec![Err(true), Ok(20)]);
+    ///
+    /// let stream = stream1.chain(stream2);
+    ///
+    /// let result: Vec<_> = stream.collect().await;
+    /// assert_eq!(result, vec![
+    ///     Ok(10),
+    ///     Err(false),
+    ///     Err(true),
+    ///     Ok(20),
+    /// ]);
+    /// # });
+    /// ```
+    fn chain<St>(self, other: St) -> Chain<Self, St>
+    where
+        St: Stream<Item = Self::Item>,
+        Self: Sized,
+    {
+        assert_stream::<Self::Item, _>(Chain::new(self, other))
+    }
+
+    /// Creates a new stream which exposes a `peek` method.
+    ///
+    /// Calling `peek` returns a reference to the next item in the stream.
+    fn peekable(self) -> Peekable<Self>
+    where
+        Self: Sized,
+    {
+        assert_stream::<Self::Item, _>(Peekable::new(self))
+    }
+
+    /// An adaptor for chunking up items of the stream inside a vector.
+    ///
+    /// This combinator will attempt to pull items from this stream and buffer
+    /// them into a local vector. At most `capacity` items will get buffered
+    /// before they're yielded from the returned stream.
+    ///
+    /// Note that the vectors returned from this iterator may not always have
+    /// `capacity` elements. If the underlying stream ended and only a partial
+    /// vector was created, it'll be returned. Additionally if an error happens
+    /// from the underlying stream then the currently buffered items will be
+    /// yielded.
+    ///
+    /// This method is only available when the `std` or `alloc` feature of this
+    /// library is activated, and it is activated by default.
+    ///
+    /// # Panics
+    ///
+    /// This method will panic if `capacity` is zero.
+    #[cfg(feature = "alloc")]
+    fn chunks(self, capacity: usize) -> Chunks<Self>
+    where
+        Self: Sized,
+    {
+        assert_stream::<Vec<Self::Item>, _>(Chunks::new(self, capacity))
+    }
+
+    /// An adaptor for chunking up ready items of the stream inside a vector.
+    ///
+    /// This combinator will attempt to pull ready items from this stream and
+    /// buffer them into a local vector. At most `capacity` items will get
+    /// buffered before they're yielded from the returned stream. If underlying
+    /// stream returns `Poll::Pending`, and collected chunk is not empty, it will
+    /// be immediately returned.
+    ///
+    /// If the underlying stream ended and only a partial vector was created,
+    /// it'll be returned. Additionally if an error happens from the underlying
+    /// stream then the currently buffered items will be yielded.
+    ///
+    /// This method is only available when the `std` or `alloc` feature of this
+    /// library is activated, and it is activated by default.
+    ///
+    /// # Panics
+    ///
+    /// This method will panic if `capacity` is zero.
+    #[cfg(feature = "alloc")]
+    fn ready_chunks(self, capacity: usize) -> ReadyChunks<Self>
+    where
+        Self: Sized,
+    {
+        assert_stream::<Vec<Self::Item>, _>(ReadyChunks::new(self, capacity))
+    }
+
+    /// A future that completes after the given stream has been fully processed
+    /// into the sink and the sink has been flushed and closed.
+    ///
+    /// This future will drive the stream to keep producing items until it is
+    /// exhausted, sending each item to the sink. It will complete once the
+    /// stream is exhausted, the sink has received and flushed all items, and
+    /// the sink is closed. Note that neither the original stream nor provided
+    /// sink will be output by this future. Pass the sink by `Pin<&mut S>`
+    /// (for example, via `forward(&mut sink)` inside an `async` fn/block) in
+    /// order to preserve access to the `Sink`. If the stream produces an error,
+    /// that error will be returned by this future without flushing/closing the sink.
+    #[cfg(feature = "sink")]
+    #[cfg_attr(docsrs, doc(cfg(feature = "sink")))]
+    fn forward<S>(self, sink: S) -> Forward<Self, S>
+    where
+        S: Sink<Self::Ok, Error = Self::Error>,
+        Self: TryStream + Sized,
+        // Self: TryStream + Sized + Stream<Item = Result<<Self as TryStream>::Ok, <Self as TryStream>::Error>>,
+    {
+        // TODO: type mismatch resolving `<Self as futures_core::Stream>::Item == std::result::Result<<Self as futures_core::TryStream>::Ok, <Self as futures_core::TryStream>::Error>`
+        // assert_future::<Result<(), Self::Error>, _>(Forward::new(self, sink))
+        Forward::new(self, sink)
+    }
+
+    /// Splits this `Stream + Sink` object into separate `Sink` and `Stream`
+    /// objects.
+    ///
+    /// This can be useful when you want to split ownership between tasks, or
+    /// allow direct interaction between the two objects (e.g. via
+    /// `Sink::send_all`).
+    ///
+    /// This method is only available when the `std` or `alloc` feature of this
+    /// library is activated, and it is activated by default.
+    #[cfg(feature = "sink")]
+    #[cfg_attr(docsrs, doc(cfg(feature = "sink")))]
+    #[cfg(not(futures_no_atomic_cas))]
+    #[cfg(feature = "alloc")]
+    fn split<Item>(self) -> (SplitSink<Self, Item>, SplitStream<Self>)
+    where
+        Self: Sink<Item> + Sized,
+    {
+        let (sink, stream) = split::split(self);
+        (
+            crate::sink::assert_sink::<Item, Self::Error, _>(sink),
+            assert_stream::<Self::Item, _>(stream),
+        )
+    }
+
+    /// Do something with each item of this stream, afterwards passing it on.
+    ///
+    /// This is similar to the `Iterator::inspect` method in the standard
+    /// library where it allows easily inspecting each value as it passes
+    /// through the stream, for example to debug what's going on.
+    fn inspect<F>(self, f: F) -> Inspect<Self, F>
+    where
+        F: FnMut(&Self::Item),
+        Self: Sized,
+    {
+        assert_stream::<Self::Item, _>(Inspect::new(self, f))
+    }
+
+    /// Wrap this stream in an `Either` stream, making it the left-hand variant
+    /// of that `Either`.
+    ///
+    /// This can be used in combination with the `right_stream` method to write `if`
+    /// statements that evaluate to different streams in different branches.
+    fn left_stream<B>(self) -> Either<Self, B>
+    where
+        B: Stream<Item = Self::Item>,
+        Self: Sized,
+    {
+        assert_stream::<Self::Item, _>(Either::Left(self))
+    }
+
+    /// Wrap this stream in an `Either` stream, making it the right-hand variant
+    /// of that `Either`.
+    ///
+    /// This can be used in combination with the `left_stream` method to write `if`
+    /// statements that evaluate to different streams in different branches.
+    fn right_stream<B>(self) -> Either<B, Self>
+    where
+        B: Stream<Item = Self::Item>,
+        Self: Sized,
+    {
+        assert_stream::<Self::Item, _>(Either::Right(self))
+    }
+
+    /// A convenience method for calling [`Stream::poll_next`] on [`Unpin`]
+    /// stream types.
+    fn poll_next_unpin(&mut self, cx: &mut Context<'_>) -> Poll<Option<Self::Item>>
+    where
+        Self: Unpin,
+    {
+        Pin::new(self).poll_next(cx)
+    }
+
+    /// Returns a [`Future`] that resolves when the next item in this stream is
+    /// ready.
+    ///
+    /// This is similar to the [`next`][StreamExt::next] method, but it won't
+    /// resolve to [`None`] if used on an empty [`Stream`]. Instead, the
+    /// returned future type will return `true` from
+    /// [`FusedFuture::is_terminated`][] when the [`Stream`] is empty, allowing
+    /// [`select_next_some`][StreamExt::select_next_some] to be easily used with
+    /// the [`select!`] macro.
+    ///
+    /// If the future is polled after this [`Stream`] is empty it will panic.
+    /// Using the future with a [`FusedFuture`][]-aware primitive like the
+    /// [`select!`] macro will prevent this.
+    ///
+    /// [`FusedFuture`]: futures_core::future::FusedFuture
+    /// [`FusedFuture::is_terminated`]: futures_core::future::FusedFuture::is_terminated
+    ///
+    /// # Examples
+    ///
+    /// ```
+    /// # futures::executor::block_on(async {
+    /// use futures::{future, select};
+    /// use futures::stream::{StreamExt, FuturesUnordered};
+    ///
+    /// let mut fut = future::ready(1);
+    /// let mut async_tasks = FuturesUnordered::new();
+    /// let mut total = 0;
+    /// loop {
+    ///     select! {
+    ///         num = fut => {
+    ///             // First, the `ready` future completes.
+    ///             total += num;
+    ///             // Then we spawn a new task onto `async_tasks`,
+    ///             async_tasks.push(async { 5 });
+    ///         },
+    ///         // On the next iteration of the loop, the task we spawned
+    ///         // completes.
+    ///         num = async_tasks.select_next_some() => {
+    ///             total += num;
+    ///         }
+    ///         // Finally, both the `ready` future and `async_tasks` have
+    ///         // finished, so we enter the `complete` branch.
+    ///         complete => break,
+    ///     }
+    /// }
+    /// assert_eq!(total, 6);
+    /// # });
+    /// ```
+    ///
+    /// [`select!`]: crate::select
+    fn select_next_some(&mut self) -> SelectNextSome<'_, Self>
+    where
+        Self: Unpin + FusedStream,
+    {
+        assert_future::<Self::Item, _>(SelectNextSome::new(self))
+    }
+}
diff --git a/third_party/rust/futures-util/src/stream/stream/next.rs b/third_party/rust/futures-util/src/stream/stream/next.rs
new file mode 100644
index 0000000000..8d8347aa03
--- /dev/null
+++ b/third_party/rust/futures-util/src/stream/stream/next.rs
@@ -0,0 +1,34 @@
+use crate::stream::StreamExt;
+use core::pin::Pin;
+use futures_core::future::{FusedFuture, Future};
+use futures_core::stream::{FusedStream, Stream};
+use futures_core::task::{Context, Poll};
+
+/// Future for the [`next`](super::StreamExt::next) method.
+#[derive(Debug)]
+#[must_use = "futures do nothing unless you `.await` or poll them"]
+pub struct Next<'a, St: ?Sized> {
+    stream: &'a mut St,
+}
+
+impl<St: ?Sized + Unpin> Unpin for Next<'_, St> {}
+
+impl<'a, St: ?Sized + Stream + Unpin> Next<'a, St> {
+    pub(super) fn new(stream: &'a mut St) -> Self {
+        Self { stream }
+    }
+}
+
+impl<St: ?Sized + FusedStream + Unpin> FusedFuture for Next<'_, St> {
+    fn is_terminated(&self) -> bool {
+        self.stream.is_terminated()
+    }
+}
+
+impl<St: ?Sized + Stream + Unpin> Future for Next<'_, St> {
+    type Output = Option<St::Item>;
+
+    fn poll(mut self: Pin<&mut Self>, cx: &mut Context<'_>) -> Poll<Self::Output> {
+        self.stream.poll_next_unpin(cx)
+    }
+}
diff --git a/third_party/rust/futures-util/src/stream/stream/peek.rs b/third_party/rust/futures-util/src/stream/stream/peek.rs
new file mode 100644
index 0000000000..ea3d6243f3
--- /dev/null
+++ b/third_party/rust/futures-util/src/stream/stream/peek.rs
@@ -0,0 +1,433 @@
+use crate::fns::FnOnce1;
+use crate::stream::{Fuse, StreamExt};
+use core::fmt;
+use core::marker::PhantomData;
+use core::pin::Pin;
+use futures_core::future::{FusedFuture, Future};
+use futures_core::ready;
+use futures_core::stream::{FusedStream, Stream};
+use futures_core::task::{Context, Poll};
+#[cfg(feature = "sink")]
+use futures_sink::Sink;
+use pin_project_lite::pin_project;
+
+pin_project! {
+    /// A `Stream` that implements a `peek` method.
+    ///
+    /// The `peek` method can be used to retrieve a reference
+    /// to the next `Stream::Item` if available. A subsequent
+    /// call to `poll` will return the owned item.
+    #[derive(Debug)]
+    #[must_use = "streams do nothing unless polled"]
+    pub struct Peekable<St: Stream> {
+        #[pin]
+        stream: Fuse<St>,
+        peeked: Option<St::Item>,
+    }
+}
+
+impl<St: Stream> Peekable<St> {
+    pub(super) fn new(stream: St) -> Self {
+        Self { stream: stream.fuse(), peeked: None }
+    }
+
+    delegate_access_inner!(stream, St, (.));
+
+    /// Produces a future which retrieves a reference to the next item
+    /// in the stream, or `None` if the underlying stream terminates.
+    pub fn peek(self: Pin<&mut Self>) -> Peek<'_, St> {
+        Peek { inner: Some(self) }
+    }
+
+    /// Peek retrieves a reference to the next item in the stream.
+    ///
+    /// This method polls the underlying stream and return either a reference
+    /// to the next item if the stream is ready or passes through any errors.
+    pub fn poll_peek(self: Pin<&mut Self>, cx: &mut Context<'_>) -> Poll<Option<&St::Item>> {
+        let mut this = self.project();
+
+        Poll::Ready(loop {
+            if this.peeked.is_some() {
+                break this.peeked.as_ref();
+            } else if let Some(item) = ready!(this.stream.as_mut().poll_next(cx)) {
+                *this.peeked = Some(item);
+            } else {
+                break None;
+            }
+        })
+    }
+
+    /// Produces a future which retrieves a mutable reference to the next item
+    /// in the stream, or `None` if the underlying stream terminates.
+    ///
+    /// # Examples
+    ///
+    /// ```
+    /// # futures::executor::block_on(async {
+    /// use futures::stream::{self, StreamExt};
+    /// use futures::pin_mut;
+    ///
+    /// let stream = stream::iter(vec![1, 2, 3]).peekable();
+    /// pin_mut!(stream);
+    ///
+    /// assert_eq!(stream.as_mut().peek_mut().await, Some(&mut 1));
+    /// assert_eq!(stream.as_mut().next().await, Some(1));
+    ///
+    /// // Peek into the stream and modify the value which will be returned next
+    /// if let Some(p) = stream.as_mut().peek_mut().await {
+    ///     if *p == 2 {
+    ///         *p = 5;
+    ///     }
+    /// }
+    ///
+    /// assert_eq!(stream.collect::<Vec<_>>().await, vec![5, 3]);
+    /// # });
+    /// ```
+    pub fn peek_mut(self: Pin<&mut Self>) -> PeekMut<'_, St> {
+        PeekMut { inner: Some(self) }
+    }
+
+    /// Peek retrieves a mutable reference to the next item in the stream.
+    pub fn poll_peek_mut(
+        self: Pin<&mut Self>,
+        cx: &mut Context<'_>,
+    ) -> Poll<Option<&mut St::Item>> {
+        let mut this = self.project();
+
+        Poll::Ready(loop {
+            if this.peeked.is_some() {
+                break this.peeked.as_mut();
+            } else if let Some(item) = ready!(this.stream.as_mut().poll_next(cx)) {
+                *this.peeked = Some(item);
+            } else {
+                break None;
+            }
+        })
+    }
+
+    /// Creates a future which will consume and return the next value of this
+    /// stream if a condition is true.
+    ///
+    /// If `func` returns `true` for the next value of this stream, consume and
+    /// return it. Otherwise, return `None`.
+    ///
+    /// # Examples
+    ///
+    /// Consume a number if it's equal to 0.
+    ///
+    /// ```
+    /// # futures::executor::block_on(async {
+    /// use futures::stream::{self, StreamExt};
+    /// use futures::pin_mut;
+    ///
+    /// let stream = stream::iter(0..5).peekable();
+    /// pin_mut!(stream);
+    /// // The first item of the stream is 0; consume it.
+    /// assert_eq!(stream.as_mut().next_if(|&x| x == 0).await, Some(0));
+    /// // The next item returned is now 1, so `consume` will return `false`.
+    /// assert_eq!(stream.as_mut().next_if(|&x| x == 0).await, None);
+    /// // `next_if` saves the value of the next item if it was not equal to `expected`.
+    /// assert_eq!(stream.next().await, Some(1));
+    /// # });
+    /// ```
+    ///
+    /// Consume any number less than 10.
+    ///
+    /// ```
+    /// # futures::executor::block_on(async {
+    /// use futures::stream::{self, StreamExt};
+    /// use futures::pin_mut;
+    ///
+    /// let stream = stream::iter(1..20).peekable();
+    /// pin_mut!(stream);
+    /// // Consume all numbers less than 10
+    /// while stream.as_mut().next_if(|&x| x < 10).await.is_some() {}
+    /// // The next value returned will be 10
+    /// assert_eq!(stream.next().await, Some(10));
+    /// # });
+    /// ```
+    pub fn next_if<F>(self: Pin<&mut Self>, func: F) -> NextIf<'_, St, F>
+    where
+        F: FnOnce(&St::Item) -> bool,
+    {
+        NextIf { inner: Some((self, func)) }
+    }
+
+    /// Creates a future which will consume and return the next item if it is
+    /// equal to `expected`.
+    ///
+    /// # Example
+    ///
+    /// Consume a number if it's equal to 0.
+    ///
+    /// ```
+    /// # futures::executor::block_on(async {
+    /// use futures::stream::{self, StreamExt};
+    /// use futures::pin_mut;
+    ///
+    /// let stream = stream::iter(0..5).peekable();
+    /// pin_mut!(stream);
+    /// // The first item of the stream is 0; consume it.
+    /// assert_eq!(stream.as_mut().next_if_eq(&0).await, Some(0));
+    /// // The next item returned is now 1, so `consume` will return `false`.
+    /// assert_eq!(stream.as_mut().next_if_eq(&0).await, None);
+    /// // `next_if_eq` saves the value of the next item if it was not equal to `expected`.
+    /// assert_eq!(stream.next().await, Some(1));
+    /// # });
+    /// ```
+    pub fn next_if_eq<'a, T>(self: Pin<&'a mut Self>, expected: &'a T) -> NextIfEq<'a, St, T>
+    where
+        T: ?Sized,
+        St::Item: PartialEq<T>,
+    {
+        NextIfEq {
+            inner: NextIf { inner: Some((self, NextIfEqFn { expected, _next: PhantomData })) },
+        }
+    }
+}
+
+impl<St: Stream> FusedStream for Peekable<St> {
+    fn is_terminated(&self) -> bool {
+        self.peeked.is_none() && self.stream.is_terminated()
+    }
+}
+
+impl<S: Stream> Stream for Peekable<S> {
+    type Item = S::Item;
+
+    fn poll_next(self: Pin<&mut Self>, cx: &mut Context<'_>) -> Poll<Option<Self::Item>> {
+        let this = self.project();
+        if let Some(item) = this.peeked.take() {
+            return Poll::Ready(Some(item));
+        }
+        this.stream.poll_next(cx)
+    }
+
+    fn size_hint(&self) -> (usize, Option<usize>) {
+        let peek_len = usize::from(self.peeked.is_some());
+        let (lower, upper) = self.stream.size_hint();
+        let lower = lower.saturating_add(peek_len);
+        let upper = match upper {
+            Some(x) => x.checked_add(peek_len),
+            None => None,
+        };
+        (lower, upper)
+    }
+}
+
+// Forwarding impl of Sink from the underlying stream
+#[cfg(feature = "sink")]
+impl<S, Item> Sink<Item> for Peekable<S>
+where
+    S: Sink<Item> + Stream,
+{
+    type Error = S::Error;
+
+    delegate_sink!(stream, Item);
+}
+
+pin_project! {
+    /// Future for the [`Peekable::peek`](self::Peekable::peek) method.
+    #[must_use = "futures do nothing unless polled"]
+    pub struct Peek<'a, St: Stream> {
+        inner: Option<Pin<&'a mut Peekable<St>>>,
+    }
+}
+
+impl<St> fmt::Debug for Peek<'_, St>
+where
+    St: Stream + fmt::Debug,
+    St::Item: fmt::Debug,
+{
+    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
+        f.debug_struct("Peek").field("inner", &self.inner).finish()
+    }
+}
+
+impl<St: Stream> FusedFuture for Peek<'_, St> {
+    fn is_terminated(&self) -> bool {
+        self.inner.is_none()
+    }
+}
+
+impl<'a, St> Future for Peek<'a, St>
+where
+    St: Stream,
+{
+    type Output = Option<&'a St::Item>;
+
+    fn poll(self: Pin<&mut Self>, cx: &mut Context<'_>) -> Poll<Self::Output> {
+        let inner = self.project().inner;
+        if let Some(peekable) = inner {
+            ready!(peekable.as_mut().poll_peek(cx));
+
+            inner.take().unwrap().poll_peek(cx)
+        } else {
+            panic!("Peek polled after completion")
+        }
+    }
+}
+
+pin_project! {
+    /// Future for the [`Peekable::peek_mut`](self::Peekable::peek_mut) method.
+    #[must_use = "futures do nothing unless polled"]
+    pub struct PeekMut<'a, St: Stream> {
+        inner: Option<Pin<&'a mut Peekable<St>>>,
+    }
+}
+
+impl<St> fmt::Debug for PeekMut<'_, St>
+where
+    St: Stream + fmt::Debug,
+    St::Item: fmt::Debug,
+{
+    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
+        f.debug_struct("PeekMut").field("inner", &self.inner).finish()
+    }
+}
+
+impl<St: Stream> FusedFuture for PeekMut<'_, St> {
+    fn is_terminated(&self) -> bool {
+        self.inner.is_none()
+    }
+}
+
+impl<'a, St> Future for PeekMut<'a, St>
+where
+    St: Stream,
+{
+    type Output = Option<&'a mut St::Item>;
+
+    fn poll(self: Pin<&mut Self>, cx: &mut Context<'_>) -> Poll<Self::Output> {
+        let inner = self.project().inner;
+        if let Some(peekable) = inner {
+            ready!(peekable.as_mut().poll_peek_mut(cx));
+
+            inner.take().unwrap().poll_peek_mut(cx)
+        } else {
+            panic!("PeekMut polled after completion")
+        }
+    }
+}
+
+pin_project! {
+    /// Future for the [`Peekable::next_if`](self::Peekable::next_if) method.
+    #[must_use = "futures do nothing unless polled"]
+    pub struct NextIf<'a, St: Stream, F> {
+        inner: Option<(Pin<&'a mut Peekable<St>>, F)>,
+    }
+}
+
+impl<St, F> fmt::Debug for NextIf<'_, St, F>
+where
+    St: Stream + fmt::Debug,
+    St::Item: fmt::Debug,
+{
+    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
+        f.debug_struct("NextIf").field("inner", &self.inner.as_ref().map(|(s, _f)| s)).finish()
+    }
+}
+
+#[allow(single_use_lifetimes)] // https://github.com/rust-lang/rust/issues/55058
+impl<St, F> FusedFuture for NextIf<'_, St, F>
+where
+    St: Stream,
+    F: for<'a> FnOnce1<&'a St::Item, Output = bool>,
+{
+    fn is_terminated(&self) -> bool {
+        self.inner.is_none()
+    }
+}
+
+#[allow(single_use_lifetimes)] // https://github.com/rust-lang/rust/issues/55058
+impl<St, F> Future for NextIf<'_, St, F>
+where
+    St: Stream,
+    F: for<'a> FnOnce1<&'a St::Item, Output = bool>,
+{
+    type Output = Option<St::Item>;
+
+    fn poll(self: Pin<&mut Self>, cx: &mut Context<'_>) -> Poll<Self::Output> {
+        let inner = self.project().inner;
+        if let Some((peekable, _)) = inner {
+            let res = ready!(peekable.as_mut().poll_next(cx));
+
+            let (peekable, func) = inner.take().unwrap();
+            match res {
+                Some(ref matched) if func.call_once(matched) => Poll::Ready(res),
+                other => {
+                    let peekable = peekable.project();
+                    // Since we called `self.next()`, we consumed `self.peeked`.
+                    assert!(peekable.peeked.is_none());
+                    *peekable.peeked = other;
+                    Poll::Ready(None)
+                }
+            }
+        } else {
+            panic!("NextIf polled after completion")
+        }
+    }
+}
+
+pin_project! {
+    /// Future for the [`Peekable::next_if_eq`](self::Peekable::next_if_eq) method.
+    #[must_use = "futures do nothing unless polled"]
+    pub struct NextIfEq<'a, St: Stream, T: ?Sized> {
+        #[pin]
+        inner: NextIf<'a, St, NextIfEqFn<'a, T, St::Item>>,
+    }
+}
+
+impl<St, T> fmt::Debug for NextIfEq<'_, St, T>
+where
+    St: Stream + fmt::Debug,
+    St::Item: fmt::Debug,
+    T: ?Sized,
+{
+    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
+        f.debug_struct("NextIfEq")
+            .field("inner", &self.inner.inner.as_ref().map(|(s, _f)| s))
+            .finish()
+    }
+}
+
+impl<St, T> FusedFuture for NextIfEq<'_, St, T>
+where
+    St: Stream,
+    T: ?Sized,
+    St::Item: PartialEq<T>,
+{
+    fn is_terminated(&self) -> bool {
+        self.inner.is_terminated()
+    }
+}
+
+impl<St, T> Future for NextIfEq<'_, St, T>
+where
+    St: Stream,
+    T: ?Sized,
+    St::Item: PartialEq<T>,
+{
+    type Output = Option<St::Item>;
+
+    fn poll(self: Pin<&mut Self>, cx: &mut Context<'_>) -> Poll<Self::Output> {
+        self.project().inner.poll(cx)
+    }
+}
+
+struct NextIfEqFn<'a, T: ?Sized, Item> {
+    expected: &'a T,
+    _next: PhantomData<Item>,
+}
+
+impl<T, Item> FnOnce1<&Item> for NextIfEqFn<'_, T, Item>
+where
+    T: ?Sized,
+    Item: PartialEq<T>,
+{
+    type Output = bool;
+
+    fn call_once(self, next: &Item) -> Self::Output {
+        next == self.expected
+    }
+}
diff --git a/third_party/rust/futures-util/src/stream/stream/ready_chunks.rs b/third_party/rust/futures-util/src/stream/stream/ready_chunks.rs
new file mode 100644
index 0000000000..49116d49e7
--- /dev/null
+++ b/third_party/rust/futures-util/src/stream/stream/ready_chunks.rs
@@ -0,0 +1,111 @@
+use crate::stream::Fuse;
+use alloc::vec::Vec;
+use core::mem;
+use core::pin::Pin;
+use futures_core::stream::{FusedStream, Stream};
+use futures_core::task::{Context, Poll};
+#[cfg(feature = "sink")]
+use futures_sink::Sink;
+use pin_project_lite::pin_project;
+
+pin_project! {
+    /// Stream for the [`ready_chunks`](super::StreamExt::ready_chunks) method.
+    #[derive(Debug)]
+    #[must_use = "streams do nothing unless polled"]
+    pub struct ReadyChunks<St: Stream> {
+        #[pin]
+        stream: Fuse<St>,
+        items: Vec<St::Item>,
+        cap: usize, // https://github.com/rust-lang/futures-rs/issues/1475
+    }
+}
+
+impl<St: Stream> ReadyChunks<St> {
+    pub(super) fn new(stream: St, capacity: usize) -> Self {
+        assert!(capacity > 0);
+
+        Self {
+            stream: super::Fuse::new(stream),
+            items: Vec::with_capacity(capacity),
+            cap: capacity,
+        }
+    }
+
+    delegate_access_inner!(stream, St, (.));
+}
+
+impl<St: Stream> Stream for ReadyChunks<St> {
+    type Item = Vec<St::Item>;
+
+    fn poll_next(self: Pin<&mut Self>, cx: &mut Context<'_>) -> Poll<Option<Self::Item>> {
+        let mut this = self.project();
+
+        loop {
+            match this.stream.as_mut().poll_next(cx) {
+                // Flush all collected data if underlying stream doesn't contain
+                // more ready values
+                Poll::Pending => {
+                    return if this.items.is_empty() {
+                        Poll::Pending
+                    } else {
+                        Poll::Ready(Some(mem::replace(this.items, Vec::with_capacity(*this.cap))))
+                    }
+                }
+
+                // Push the ready item into the buffer and check whether it is full.
+                // If so, replace our buffer with a new and empty one and return
+                // the full one.
+                Poll::Ready(Some(item)) => {
+                    this.items.push(item);
+                    if this.items.len() >= *this.cap {
+                        return Poll::Ready(Some(mem::replace(
+                            this.items,
+                            Vec::with_capacity(*this.cap),
+                        )));
+                    }
+                }
+
+                // Since the underlying stream ran out of values, return what we
+                // have buffered, if we have anything.
+                Poll::Ready(None) => {
+                    let last = if this.items.is_empty() {
+                        None
+                    } else {
+                        let full_buf = mem::take(this.items);
+                        Some(full_buf)
+                    };
+
+                    return Poll::Ready(last);
+                }
+            }
+        }
+    }
+
+    fn size_hint(&self) -> (usize, Option<usize>) {
+        let chunk_len = usize::from(!self.items.is_empty());
+        let (lower, upper) = self.stream.size_hint();
+        let lower = (lower / self.cap).saturating_add(chunk_len);
+        let upper = match upper {
+            Some(x) => x.checked_add(chunk_len),
+            None => None,
+        };
+        (lower, upper)
+    }
+}
+
+impl<St: FusedStream> FusedStream for ReadyChunks<St> {
+    fn is_terminated(&self) -> bool {
+        self.stream.is_terminated() && self.items.is_empty()
+    }
+}
+
+// Forwarding impl of Sink from the underlying stream
+#[cfg(feature = "sink")]
+impl<S, Item> Sink<Item> for ReadyChunks<S>
+where
+    S: Stream + Sink<Item>,
+{
+    type Error = S::Error;
+
+    delegate_sink!(stream, Item);
+}
diff --git a/third_party/rust/futures-util/src/stream/stream/scan.rs b/third_party/rust/futures-util/src/stream/stream/scan.rs
new file mode 100644
index 0000000000..f5cfde9c36
--- /dev/null
+++ b/third_party/rust/futures-util/src/stream/stream/scan.rs
@@ -0,0 +1,128 @@
+use core::fmt;
+use core::pin::Pin;
+use futures_core::future::Future;
+use futures_core::ready;
+use futures_core::stream::{FusedStream, Stream};
+use futures_core::task::{Context, Poll};
+#[cfg(feature = "sink")]
+use futures_sink::Sink;
+use pin_project_lite::pin_project;
+
+struct StateFn<S, F> {
+    state: S,
+    f: F,
+}
+
+pin_project! {
+    /// Stream for the [`scan`](super::StreamExt::scan) method.
+    #[must_use = "streams do nothing unless polled"]
+    pub struct Scan<St: Stream, S, Fut, F> {
+        #[pin]
+        stream: St,
+        state_f: Option<StateFn<S, F>>,
+        #[pin]
+        future: Option<Fut>,
+    }
+}
+
+impl<St, S, Fut, F> fmt::Debug for Scan<St, S, Fut, F>
+where
+    St: Stream + fmt::Debug,
+    St::Item: fmt::Debug,
+    S: fmt::Debug,
+    Fut: fmt::Debug,
+{
+    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
+        f.debug_struct("Scan")
+            .field("stream", &self.stream)
+            .field("state", &self.state_f.as_ref().map(|s| &s.state))
+            .field("future", &self.future)
+            .field("done_taking", &self.is_done_taking())
+            .finish()
+    }
+}
+
+impl<St: Stream, S, Fut, F> Scan<St, S, Fut, F> {
+    /// Checks if internal state is `None`.
+    fn is_done_taking(&self) -> bool {
+        self.state_f.is_none()
+    }
+}
+
+impl<B, St, S, Fut, F> Scan<St, S, Fut, F>
+where
+    St: Stream,
+    F: FnMut(&mut S, St::Item) -> Fut,
+    Fut: Future<Output = Option<B>>,
+{
+    pub(super) fn new(stream: St, initial_state: S, f: F) -> Self {
+        Self { stream, state_f: Some(StateFn { state: initial_state, f }), future: None }
+    }
+
+    delegate_access_inner!(stream, St, ());
+}
+
+impl<B, St, S, Fut, F> Stream for Scan<St, S, Fut, F>
+where
+    St: Stream,
+    F: FnMut(&mut S, St::Item) -> Fut,
+    Fut: Future<Output = Option<B>>,
+{
+    type Item = B;
+
+    fn poll_next(self: Pin<&mut Self>, cx: &mut Context<'_>) -> Poll<Option<B>> {
+        if self.is_done_taking() {
+            return Poll::Ready(None);
+        }
+
+        let mut this = self.project();
+
+        Poll::Ready(loop {
+            if let Some(fut) = this.future.as_mut().as_pin_mut() {
+                let item = ready!(fut.poll(cx));
+                this.future.set(None);
+
+                if item.is_none() {
+                    *this.state_f = None;
+                }
+
+                break item;
+            } else if let Some(item) = ready!(this.stream.as_mut().poll_next(cx)) {
+                let state_f = this.state_f.as_mut().unwrap();
+                this.future.set(Some((state_f.f)(&mut state_f.state, item)))
+            } else {
+                break None;
+            }
+        })
+    }
+
+    fn size_hint(&self) -> (usize, Option<usize>) {
+        if self.is_done_taking() {
+            (0, Some(0))
+        } else {
+            self.stream.size_hint() // can't know a lower bound, due to the predicate
+        }
+    }
+}
+
+impl<B, St, S, Fut, F> FusedStream for Scan<St, S, Fut, F>
+where
+    St: FusedStream,
+    F: FnMut(&mut S, St::Item) -> Fut,
+    Fut: Future<Output = Option<B>>,
+{
+    fn is_terminated(&self) -> bool {
+        self.is_done_taking() || self.future.is_none() && self.stream.is_terminated()
+    }
+}
+
+// Forwarding impl of Sink from the underlying stream
+#[cfg(feature = "sink")]
+impl<St, S, Fut, F, Item> Sink<Item> for Scan<St, S, Fut, F>
+where
+    St: Stream + Sink<Item>,
+{
+    type Error = St::Error;
+
+    delegate_sink!(stream, Item);
+}
diff --git a/third_party/rust/futures-util/src/stream/stream/select_next_some.rs b/third_party/rust/futures-util/src/stream/stream/select_next_some.rs
new file mode 100644
index 0000000000..3115e14d9a
--- /dev/null
+++ b/third_party/rust/futures-util/src/stream/stream/select_next_some.rs
@@ -0,0 +1,42 @@
+use crate::stream::StreamExt;
+use core::pin::Pin;
+use futures_core::future::{FusedFuture, Future};
+use futures_core::ready;
+use futures_core::stream::FusedStream;
+use futures_core::task::{Context, Poll};
+
+/// Future for the [`select_next_some`](super::StreamExt::select_next_some)
+/// method.
+#[derive(Debug)]
+#[must_use = "futures do nothing unless you `.await` or poll them"]
+pub struct SelectNextSome<'a, St: ?Sized> {
+    stream: &'a mut St,
+}
+
+impl<'a, St: ?Sized> SelectNextSome<'a, St> {
+    pub(super) fn new(stream: &'a mut St) -> Self {
+        Self { stream }
+    }
+}
+
+impl<St: ?Sized + FusedStream + Unpin> FusedFuture for SelectNextSome<'_, St> {
+    fn is_terminated(&self) -> bool {
+        self.stream.is_terminated()
+    }
+}
+
+impl<St: ?Sized + FusedStream + Unpin> Future for SelectNextSome<'_, St> {
+    type Output = St::Item;
+
+    fn poll(mut self: Pin<&mut Self>, cx: &mut Context<'_>) -> Poll<Self::Output> {
+        assert!(!self.stream.is_terminated(), "SelectNextSome polled after terminated");
+
+        if let Some(item) = ready!(self.stream.poll_next_unpin(cx)) {
+            Poll::Ready(item)
+        } else {
+            debug_assert!(self.stream.is_terminated());
+            cx.waker().wake_by_ref();
+            Poll::Pending
+        }
+    }
+}
diff --git a/third_party/rust/futures-util/src/stream/stream/skip.rs b/third_party/rust/futures-util/src/stream/stream/skip.rs
new file mode 100644
index 0000000000..f495779521
--- /dev/null
+++ b/third_party/rust/futures-util/src/stream/stream/skip.rs
@@ -0,0 +1,70 @@
+use core::pin::Pin;
+use futures_core::ready;
+use futures_core::stream::{FusedStream, Stream};
+use futures_core::task::{Context, Poll};
+#[cfg(feature = "sink")]
+use futures_sink::Sink;
+use pin_project_lite::pin_project;
+
+pin_project! {
+    /// Stream for the [`skip`](super::StreamExt::skip) method.
+    #[derive(Debug)]
+    #[must_use = "streams do nothing unless polled"]
+    pub struct Skip<St> {
+        #[pin]
+        stream: St,
+        remaining: usize,
+    }
+}
+
+impl<St: Stream> Skip<St> {
+    pub(super) fn new(stream: St, n: usize) -> Self {
+        Self { stream, remaining: n }
+    }
+
+    delegate_access_inner!(stream, St, ());
+}
+
+impl<St: FusedStream> FusedStream for Skip<St> {
+    fn is_terminated(&self) -> bool {
+        self.stream.is_terminated()
+    }
+}
+
+impl<St: Stream> Stream for Skip<St> {
+    type Item = St::Item;
+
+    fn poll_next(self: Pin<&mut Self>, cx: &mut Context<'_>) -> Poll<Option<St::Item>> {
+        let mut this = self.project();
+
+        while *this.remaining > 0 {
+            if ready!(this.stream.as_mut().poll_next(cx)).is_some() {
+                *this.remaining -= 1;
+            } else {
+                return Poll::Ready(None);
+            }
+        }
+
+        this.stream.poll_next(cx)
+    }
+
+    fn size_hint(&self) -> (usize, Option<usize>) {
+        let (lower, upper) = self.stream.size_hint();
+
+        let lower = lower.saturating_sub(self.remaining);
+        let upper = upper.map(|x| x.saturating_sub(self.remaining));
+
+        (lower, upper)
+    }
+}
+
+// Forwarding impl of Sink from the underlying stream
+#[cfg(feature = "sink")]
+impl<S, Item> Sink<Item> for Skip<S>
+where
+    S: Stream + Sink<Item>,
+{
+    type Error = S::Error;
+
+    delegate_sink!(stream, Item);
+}
diff --git a/third_party/rust/futures-util/src/stream/stream/skip_while.rs b/third_party/rust/futures-util/src/stream/stream/skip_while.rs
new file mode 100644
index 0000000000..dabd5eefae
--- /dev/null
+++ b/third_party/rust/futures-util/src/stream/stream/skip_while.rs
@@ -0,0 +1,124 @@
+use core::fmt;
+use core::pin::Pin;
+use futures_core::future::Future;
+use futures_core::ready;
+use futures_core::stream::{FusedStream, Stream};
+use futures_core::task::{Context, Poll};
+#[cfg(feature = "sink")]
+use futures_sink::Sink;
+use pin_project_lite::pin_project;
+
+pin_project! {
+    /// Stream for the [`skip_while`](super::StreamExt::skip_while) method.
+    #[must_use = "streams do nothing unless polled"]
+    pub struct SkipWhile<St, Fut, F> where St: Stream {
+        #[pin]
+        stream: St,
+        f: F,
+        #[pin]
+        pending_fut: Option<Fut>,
+        pending_item: Option<St::Item>,
+        done_skipping: bool,
+    }
+}
+
+impl<St, Fut, F> fmt::Debug for SkipWhile<St, Fut, F>
+where
+    St: Stream + fmt::Debug,
+    St::Item: fmt::Debug,
+    Fut: fmt::Debug,
+{
+    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
+        f.debug_struct("SkipWhile")
+            .field("stream", &self.stream)
+            .field("pending_fut", &self.pending_fut)
+            .field("pending_item", &self.pending_item)
+            .field("done_skipping", &self.done_skipping)
+            .finish()
+    }
+}
+
+impl<St, Fut, F> SkipWhile<St, Fut, F>
+where
+    St: Stream,
+    F: FnMut(&St::Item) -> Fut,
+    Fut: Future<Output = bool>,
+{
+    pub(super) fn new(stream: St, f: F) -> Self {
+        Self { stream, f, pending_fut: None, pending_item: None, done_skipping: false }
+    }
+
+    delegate_access_inner!(stream, St, ());
+}
+
+impl<St, Fut, F> FusedStream for SkipWhile<St, Fut, F>
+where
+    St: FusedStream,
+    F: FnMut(&St::Item) -> Fut,
+    Fut: Future<Output = bool>,
+{
+    fn is_terminated(&self) -> bool {
+        self.pending_item.is_none() && self.stream.is_terminated()
+    }
+}
+
+impl<St, Fut, F> Stream for SkipWhile<St, Fut, F>
+where
+    St: Stream,
+    F: FnMut(&St::Item) -> Fut,
+    Fut: Future<Output = bool>,
+{
+    type Item = St::Item;
+
+    fn poll_next(self: Pin<&mut Self>, cx: &mut Context<'_>) -> Poll<Option<St::Item>> {
+        let mut this = self.project();
+
+        if *this.done_skipping {
+            return this.stream.poll_next(cx);
+        }
+
+        Poll::Ready(loop {
+            if let Some(fut) = this.pending_fut.as_mut().as_pin_mut() {
+                let skipped = ready!(fut.poll(cx));
+                let item = this.pending_item.take();
+                this.pending_fut.set(None);
+                if !skipped {
+                    *this.done_skipping = true;
+                    break item;
+                }
+            } else if let Some(item) = ready!(this.stream.as_mut().poll_next(cx)) {
+                this.pending_fut.set(Some((this.f)(&item)));
+                *this.pending_item = Some(item);
+            } else {
+                break None;
+            }
+        })
+    }
+
+    fn size_hint(&self) -> (usize, Option<usize>) {
+        if self.done_skipping {
+            self.stream.size_hint()
+        } else {
+            let pending_len = usize::from(self.pending_item.is_some());
+            let (_, upper) = self.stream.size_hint();
+            let upper = match upper {
+                Some(x) => x.checked_add(pending_len),
+                None => None,
+            };
+            (0, upper) // can't know a lower bound, due to the predicate
+        }
+    }
+}
+
+// Forwarding impl of Sink from the underlying stream
+#[cfg(feature = "sink")]
+impl<S, Fut, F, Item> Sink<Item> for SkipWhile<S, Fut, F>
+where
+    S: Stream + Sink<Item>,
+    F: FnMut(&S::Item) -> Fut,
+    Fut: Future<Output = bool>,
+{
+    type Error = S::Error;
+
+    delegate_sink!(stream, Item);
+}
diff --git a/third_party/rust/futures-util/src/stream/stream/split.rs b/third_party/rust/futures-util/src/stream/stream/split.rs
new file mode 100644
index 0000000000..e2034e0c27
--- /dev/null
+++ b/third_party/rust/futures-util/src/stream/stream/split.rs
@@ -0,0 +1,144 @@
+use core::fmt;
+use core::pin::Pin;
+use futures_core::ready;
+use futures_core::stream::Stream;
+use futures_core::task::{Context, Poll};
+use futures_sink::Sink;
+
+use crate::lock::BiLock;
+
+/// A `Stream` part of the split pair
+#[derive(Debug)]
+#[must_use = "streams do nothing unless polled"]
+#[cfg_attr(docsrs, doc(cfg(feature = "sink")))]
+pub struct SplitStream<S>(BiLock<S>);
+
+impl<S> Unpin for SplitStream<S> {}
+
+impl<S: Unpin> SplitStream<S> {
+    /// Attempts to put the two "halves" of a split `Stream + Sink` back
+    /// together. Succeeds only if the `SplitStream<S>` and `SplitSink<S>` are
+    /// a matching pair originating from the same call to `StreamExt::split`.
+    pub fn reunite<Item>(self, other: SplitSink<S, Item>) -> Result<S, ReuniteError<S, Item>>
+    where
+        S: Sink<Item>,
+    {
+        other.reunite(self)
+    }
+}
+
+impl<S: Stream> Stream for SplitStream<S> {
+    type Item = S::Item;
+
+    fn poll_next(self: Pin<&mut Self>, cx: &mut Context<'_>) -> Poll<Option<S::Item>> {
+        ready!(self.0.poll_lock(cx)).as_pin_mut().poll_next(cx)
+    }
+}
+
+#[allow(non_snake_case)]
+fn SplitSink<S: Sink<Item>, Item>(lock: BiLock<S>) -> SplitSink<S, Item> {
+    SplitSink { lock, slot: None }
+}
+
+/// A `Sink` part of the split pair
+#[derive(Debug)]
+#[must_use = "sinks do nothing unless polled"]
+#[cfg_attr(docsrs, doc(cfg(feature = "sink")))]
+pub struct SplitSink<S, Item> {
+    lock: BiLock<S>,
+    slot: Option<Item>,
+}
+
+impl<S, Item> Unpin for SplitSink<S, Item> {}
+
+impl<S: Sink<Item> + Unpin, Item> SplitSink<S, Item> {
+    /// Attempts to put the two "halves" of a split `Stream + Sink` back
+    /// together. Succeeds only if the `SplitStream<S>` and `SplitSink<S>` are
+    /// a matching pair originating from the same call to `StreamExt::split`.
+    pub fn reunite(self, other: SplitStream<S>) -> Result<S, ReuniteError<S, Item>> {
+        self.lock.reunite(other.0).map_err(|err| ReuniteError(SplitSink(err.0), SplitStream(err.1)))
+    }
+}
+
+impl<S: Sink<Item>, Item> SplitSink<S, Item> {
+    fn poll_flush_slot(
+        mut inner: Pin<&mut S>,
+        slot: &mut Option<Item>,
+        cx: &mut Context<'_>,
+    ) -> Poll<Result<(), S::Error>> {
+        if slot.is_some() {
+            ready!(inner.as_mut().poll_ready(cx))?;
+            Poll::Ready(inner.start_send(slot.take().unwrap()))
+        } else {
+            Poll::Ready(Ok(()))
+        }
+    }
+
+    fn poll_lock_and_flush_slot(
+        mut self: Pin<&mut Self>,
+        cx: &mut Context<'_>,
+    ) -> Poll<Result<(), S::Error>> {
+        let this = &mut *self;
+        let mut inner = ready!(this.lock.poll_lock(cx));
+        Self::poll_flush_slot(inner.as_pin_mut(), &mut this.slot, cx)
+    }
+}
+
+impl<S: Sink<Item>, Item> Sink<Item> for SplitSink<S, Item> {
+    type Error = S::Error;
+
+    fn poll_ready(mut self: Pin<&mut Self>, cx: &mut Context<'_>) -> Poll<Result<(), S::Error>> {
+        loop {
+            if self.slot.is_none() {
+                return Poll::Ready(Ok(()));
+            }
+            ready!(self.as_mut().poll_lock_and_flush_slot(cx))?;
+        }
+    }
+
+    fn start_send(mut self: Pin<&mut Self>, item: Item) -> Result<(), S::Error> {
+        self.slot = Some(item);
+        Ok(())
+    }
+
+    fn poll_flush(mut self: Pin<&mut Self>, cx: &mut Context<'_>) -> Poll<Result<(), S::Error>> {
+        let this = &mut *self;
+        let mut inner = ready!(this.lock.poll_lock(cx));
+        ready!(Self::poll_flush_slot(inner.as_pin_mut(), &mut this.slot, cx))?;
+        inner.as_pin_mut().poll_flush(cx)
+    }
+
+    fn poll_close(mut self: Pin<&mut Self>, cx: &mut Context<'_>) -> Poll<Result<(), S::Error>> {
+        let this = &mut *self;
+        let mut inner = ready!(this.lock.poll_lock(cx));
+        ready!(Self::poll_flush_slot(inner.as_pin_mut(), &mut this.slot, cx))?;
+        inner.as_pin_mut().poll_close(cx)
+    }
+}
+
+pub(super) fn split<S: Stream + Sink<Item>, Item>(s: S) -> (SplitSink<S, Item>, SplitStream<S>) {
+    let (a, b) = BiLock::new(s);
+    let read = SplitStream(a);
+    let write = SplitSink(b);
+    (write, read)
+}
+
+/// Error indicating a `SplitSink<S>` and `SplitStream<S>` were not two halves
+/// of a `Stream + Split`, and thus could not be `reunite`d.
+#[cfg_attr(docsrs, doc(cfg(feature = "sink")))]
+pub struct ReuniteError<T, Item>(pub SplitSink<T, Item>, pub SplitStream<T>);
+
+impl<T, Item> fmt::Debug for ReuniteError<T, Item> {
+    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
+        f.debug_tuple("ReuniteError").field(&"...").finish()
+    }
+}
+
+impl<T, Item> fmt::Display for ReuniteError<T, Item> {
+    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
+        write!(f, "tried to reunite a SplitStream and SplitSink that don't form a pair")
+    }
+}
+
+#[cfg(feature = "std")]
+impl<T: core::any::Any, Item> std::error::Error for ReuniteError<T, Item> {}
diff --git a/third_party/rust/futures-util/src/stream/stream/take.rs b/third_party/rust/futures-util/src/stream/stream/take.rs
new file mode 100644
index 0000000000..29d6c39ee3
--- /dev/null
+++ b/third_party/rust/futures-util/src/stream/stream/take.rs
@@ -0,0 +1,86 @@
+use core::cmp;
+use core::pin::Pin;
+use futures_core::ready;
+use futures_core::stream::{FusedStream, Stream};
+use futures_core::task::{Context, Poll};
+#[cfg(feature = "sink")]
+use futures_sink::Sink;
+use pin_project_lite::pin_project;
+
+pin_project! {
+    /// Stream for the [`take`](super::StreamExt::take) method.
+    #[derive(Debug)]
+    #[must_use = "streams do nothing unless polled"]
+    pub struct Take<St> {
+        #[pin]
+        stream: St,
+        remaining: usize,
+    }
+}
+
+impl<St: Stream> Take<St> {
+    pub(super) fn new(stream: St, n: usize) -> Self {
+        Self { stream, remaining: n }
+    }
+
+    delegate_access_inner!(stream, St, ());
+}
+
+impl<St> Stream for Take<St>
+where
+    St: Stream,
+{
+    type Item = St::Item;
+
+    fn poll_next(self: Pin<&mut Self>, cx: &mut Context<'_>) -> Poll<Option<St::Item>> {
+        if self.remaining == 0 {
+            Poll::Ready(None)
+        } else {
+            let this = self.project();
+            let next = ready!(this.stream.poll_next(cx));
+            if next.is_some() {
+                *this.remaining -= 1;
+            } else {
+                *this.remaining = 0;
+            }
+            Poll::Ready(next)
+        }
+    }
+
+    fn size_hint(&self) -> (usize, Option<usize>) {
+        if self.remaining == 0 {
+            return (0, Some(0));
+        }
+
+        let (lower, upper) = self.stream.size_hint();
+
+        let lower = cmp::min(lower, self.remaining);
+
+        let upper = match upper {
+            Some(x) if x < self.remaining => Some(x),
+            _ => Some(self.remaining),
+        };
+
+        (lower, upper)
+    }
+}
+
+impl<St> FusedStream for Take<St>
+where
+    St: FusedStream,
+{
+    fn is_terminated(&self) -> bool {
+        self.remaining == 0 || self.stream.is_terminated()
+    }
+}
+
+// Forwarding impl of Sink from the underlying stream
+#[cfg(feature = "sink")]
+impl<S, Item> Sink<Item> for Take<S>
+where
+    S: Stream + Sink<Item>,
+{
+    type Error = S::Error;
+
+    delegate_sink!(stream, Item);
+}
diff --git a/third_party/rust/futures-util/src/stream/stream/take_until.rs b/third_party/rust/futures-util/src/stream/stream/take_until.rs
new file mode 100644
index 0000000000..d14f9ce100
--- /dev/null
+++ b/third_party/rust/futures-util/src/stream/stream/take_until.rs
@@ -0,0 +1,170 @@
+use core::fmt;
+use core::pin::Pin;
+use futures_core::future::Future;
+use futures_core::ready;
+use futures_core::stream::{FusedStream, Stream};
+use futures_core::task::{Context, Poll};
+#[cfg(feature = "sink")]
+use futures_sink::Sink;
+use pin_project_lite::pin_project;
+
+// FIXME: docs, tests
+
+pin_project! {
+    /// Stream for the [`take_until`](super::StreamExt::take_until) method.
+    #[must_use = "streams do nothing unless polled"]
+    pub struct TakeUntil<St: Stream, Fut: Future> {
+        #[pin]
+        stream: St,
+        // Contains the inner Future on start and None once the inner Future is resolved
+        // or taken out by the user.
+        #[pin]
+        fut: Option<Fut>,
+        // Contains fut's return value once fut is resolved
+        fut_result: Option<Fut::Output>,
+        // Whether the future was taken out by the user.
+        free: bool,
+    }
+}
+
+impl<St, Fut> fmt::Debug for TakeUntil<St, Fut>
+where
+    St: Stream + fmt::Debug,
+    St::Item: fmt::Debug,
+    Fut: Future + fmt::Debug,
+{
+    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
+        f.debug_struct("TakeUntil").field("stream", &self.stream).field("fut", &self.fut).finish()
+    }
+}
+
+impl<St, Fut> TakeUntil<St, Fut>
+where
+    St: Stream,
+    Fut: Future,
+{
+    pub(super) fn new(stream: St, fut: Fut) -> Self {
+        Self { stream, fut: Some(fut), fut_result: None, free: false }
+    }
+
+    delegate_access_inner!(stream, St, ());
+
+    /// Extract the stopping future out of the combinator.
+    /// The future is returned only if it isn't resolved yet, ie. if the stream isn't stopped yet.
+    /// Taking out the future means the combinator will be yielding
+    /// elements from the wrapped stream without ever stopping it.
+    pub fn take_future(&mut self) -> Option<Fut> {
+        if self.fut.is_some() {
+            self.free = true;
+        }
+
+        self.fut.take()
+    }
+
+    /// Once the stopping future is resolved, this method can be used
+    /// to extract the value returned by the stopping future.
+    ///
+    /// This may be used to retrieve arbitrary data from the stopping
+    /// future, for example a reason why the stream was stopped.
+    ///
+    /// This method will return `None` if the future isn't resolved yet,
+    /// or if the result was already taken out.
+    ///
+    /// # Examples
+    ///
+    /// ```
+    /// # futures::executor::block_on(async {
+    /// use futures::future;
+    /// use futures::stream::{self, StreamExt};
+    /// use futures::task::Poll;
+    ///
+    /// let stream = stream::iter(1..=10);
+    ///
+    /// let mut i = 0;
+    /// let stop_fut = future::poll_fn(|_cx| {
+    ///     i += 1;
+    ///     if i <= 5 {
+    ///         Poll::Pending
+    ///     } else {
+    ///         Poll::Ready("reason")
+    ///     }
+    /// });
+    ///
+    /// let mut stream = stream.take_until(stop_fut);
+    /// let _ = stream.by_ref().collect::<Vec<_>>().await;
+    ///
+    /// let result = stream.take_result().unwrap();
+    /// assert_eq!(result, "reason");
+    /// # });
+    /// ```
+    pub fn take_result(&mut self) -> Option<Fut::Output> {
+        self.fut_result.take()
+    }
+
+    /// Whether the stream was stopped yet by the stopping future
+    /// being resolved.
+    pub fn is_stopped(&self) -> bool {
+        !self.free && self.fut.is_none()
+    }
+}
+
+impl<St, Fut> Stream for TakeUntil<St, Fut>
+where
+    St: Stream,
+    Fut: Future,
+{
+    type Item = St::Item;
+
+    fn poll_next(self: Pin<&mut Self>, cx: &mut Context<'_>) -> Poll<Option<St::Item>> {
+        let mut this = self.project();
+
+        if let Some(f) = this.fut.as_mut().as_pin_mut() {
+            if let Poll::Ready(result) = f.poll(cx) {
+                this.fut.set(None);
+                *this.fut_result = Some(result);
+            }
+        }
+
+        if !*this.free && this.fut.is_none() {
+            // Future resolved, inner stream stopped
+            Poll::Ready(None)
+        } else {
+            // Future either not resolved yet or taken out by the user
+            let item = ready!(this.stream.poll_next(cx));
+            if item.is_none() {
+                this.fut.set(None);
+            }
+            Poll::Ready(item)
+        }
+    }
+
+    fn size_hint(&self) -> (usize, Option<usize>) {
+        if self.is_stopped() {
+            return (0, Some(0));
+        }
+
+        self.stream.size_hint()
+    }
+}
+
+impl<St, Fut> FusedStream for TakeUntil<St, Fut>
+where
+    St: Stream,
+    Fut: Future,
+{
+    fn is_terminated(&self) -> bool {
+        self.is_stopped()
+    }
+}
+
+// Forwarding impl of Sink from the underlying stream
+#[cfg(feature = "sink")]
+impl<S, Fut, Item> Sink<Item> for TakeUntil<S, Fut>
+where
+    S: Stream + Sink<Item>,
+    Fut: Future,
+{
+    type Error = S::Error;
+
+    delegate_sink!(stream, Item);
+}
diff --git a/third_party/rust/futures-util/src/stream/stream/take_while.rs b/third_party/rust/futures-util/src/stream/stream/take_while.rs
new file mode 100644
index 0000000000..9256943010
--- /dev/null
+++ b/third_party/rust/futures-util/src/stream/stream/take_while.rs
@@ -0,0 +1,124 @@
+use core::fmt;
+use core::pin::Pin;
+use futures_core::future::Future;
+use futures_core::ready;
+use futures_core::stream::{FusedStream, Stream};
+use futures_core::task::{Context, Poll};
+#[cfg(feature = "sink")]
+use futures_sink::Sink;
+use pin_project_lite::pin_project;
+
+pin_project! {
+    /// Stream for the [`take_while`](super::StreamExt::take_while) method.
+    #[must_use = "streams do nothing unless polled"]
+    pub struct TakeWhile<St: Stream, Fut, F> {
+        #[pin]
+        stream: St,
+        f: F,
+        #[pin]
+        pending_fut: Option<Fut>,
+        pending_item: Option<St::Item>,
+        done_taking: bool,
+    }
+}
+
+impl<St, Fut, F> fmt::Debug for TakeWhile<St, Fut, F>
+where
+    St: Stream + fmt::Debug,
+    St::Item: fmt::Debug,
+    Fut: fmt::Debug,
+{
+    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
+        f.debug_struct("TakeWhile")
+            .field("stream", &self.stream)
+            .field("pending_fut", &self.pending_fut)
+            .field("pending_item", &self.pending_item)
+            .field("done_taking", &self.done_taking)
+            .finish()
+    }
+}
+
+impl<St, Fut, F> TakeWhile<St, Fut, F>
+where
+    St: Stream,
+    F: FnMut(&St::Item) -> Fut,
+    Fut: Future<Output = bool>,
+{
+    pub(super) fn new(stream: St, f: F) -> Self {
+        Self { stream, f, pending_fut: None, pending_item: None, done_taking: false }
+    }
+
+    delegate_access_inner!(stream, St, ());
+}
+
+impl<St, Fut, F> Stream for TakeWhile<St, Fut, F>
+where
+    St: Stream,
+    F: FnMut(&St::Item) -> Fut,
+    Fut: Future<Output = bool>,
+{
+    type Item = St::Item;
+
+    fn poll_next(self: Pin<&mut Self>, cx: &mut Context<'_>) -> Poll<Option<St::Item>> {
+        if self.done_taking {
+            return Poll::Ready(None);
+        }
+
+        let mut this = self.project();
+
+        Poll::Ready(loop {
+            if let Some(fut) = this.pending_fut.as_mut().as_pin_mut() {
+                let take = ready!(fut.poll(cx));
+                let item = this.pending_item.take();
+                this.pending_fut.set(None);
+                if take {
+                    break item;
+                } else {
+                    *this.done_taking = true;
+                    break None;
+                }
+            } else if let Some(item) = ready!(this.stream.as_mut().poll_next(cx)) {
+                this.pending_fut.set(Some((this.f)(&item)));
+                *this.pending_item = Some(item);
+            } else {
+                break None;
+            }
+        })
+    }
+
+    fn size_hint(&self) -> (usize, Option<usize>) {
+        if self.done_taking {
+            return (0, Some(0));
+        }
+
+        let pending_len = usize::from(self.pending_item.is_some());
+        let (_, upper) = self.stream.size_hint();
+        let upper = match upper {
+            Some(x) => x.checked_add(pending_len),
+            None => None,
+        };
+        (0, upper) // can't know a lower bound, due to the predicate
+    }
+}
+
+impl<St, Fut, F> FusedStream for TakeWhile<St, Fut, F>
+where
+    St: FusedStream,
+    F: FnMut(&St::Item) -> Fut,
+    Fut: Future<Output = bool>,
+{
+    fn is_terminated(&self) -> bool {
+        self.done_taking || self.pending_item.is_none() && self.stream.is_terminated()
+    }
+}
+
+// Forwarding impl of Sink from the underlying stream
+#[cfg(feature = "sink")]
+impl<S, Fut, F, Item> Sink<Item> for TakeWhile<S, Fut, F>
+where
+    S: Stream + Sink<Item>,
+{
+    type Error = S::Error;
+
+    delegate_sink!(stream, Item);
+}
diff --git a/third_party/rust/futures-util/src/stream/stream/then.rs b/third_party/rust/futures-util/src/stream/stream/then.rs
new file mode 100644
index 0000000000..9192c0b0cf
--- /dev/null
+++ b/third_party/rust/futures-util/src/stream/stream/then.rs
@@ -0,0 +1,101 @@
+use core::fmt;
+use core::pin::Pin;
+use futures_core::future::Future;
+use futures_core::ready;
+use futures_core::stream::{FusedStream, Stream};
+use futures_core::task::{Context, Poll};
+#[cfg(feature = "sink")]
+use futures_sink::Sink;
+use pin_project_lite::pin_project;
+
+pin_project! {
+    /// Stream for the [`then`](super::StreamExt::then) method.
+    #[must_use = "streams do nothing unless polled"]
+    pub struct Then<St, Fut, F> {
+        #[pin]
+        stream: St,
+        #[pin]
+        future: Option<Fut>,
+        f: F,
+    }
+}
+
+impl<St, Fut, F> fmt::Debug for Then<St, Fut, F>
+where
+    St: fmt::Debug,
+    Fut: fmt::Debug,
+{
+    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
+        f.debug_struct("Then").field("stream", &self.stream).field("future", &self.future).finish()
+    }
+}
+
+impl<St, Fut, F> Then<St, Fut, F>
+where
+    St: Stream,
+    F: FnMut(St::Item) -> Fut,
+{
+    pub(super) fn new(stream: St, f: F) -> Self {
+        Self { stream, future: None, f }
+    }
+
+    delegate_access_inner!(stream, St, ());
+}
+
+impl<St, Fut, F> FusedStream for Then<St, Fut, F>
+where
+    St: FusedStream,
+    F: FnMut(St::Item) -> Fut,
+    Fut: Future,
+{
+    fn is_terminated(&self) -> bool {
+        self.future.is_none() && self.stream.is_terminated()
+    }
+}
+
+impl<St, Fut, F> Stream for Then<St, Fut, F>
+where
+    St: Stream,
+    F: FnMut(St::Item) -> Fut,
+    Fut: Future,
+{
+    type Item = Fut::Output;
+
+    fn poll_next(self: Pin<&mut Self>, cx: &mut Context<'_>) -> Poll<Option<Self::Item>> {
+        let mut this = self.project();
+
+        Poll::Ready(loop {
+            if let Some(fut) = this.future.as_mut().as_pin_mut() {
+                let item = ready!(fut.poll(cx));
+                this.future.set(None);
+                break Some(item);
+            } else if let Some(item) = ready!(this.stream.as_mut().poll_next(cx)) {
+                this.future.set(Some((this.f)(item)));
+            } else {
+                break None;
+            }
+        })
+    }
+
+    fn size_hint(&self) -> (usize, Option<usize>) {
+        let future_len = usize::from(self.future.is_some());
+        let (lower, upper) = self.stream.size_hint();
+        let lower = lower.saturating_add(future_len);
+        let upper = match upper {
+            Some(x) => x.checked_add(future_len),
+            None => None,
+        };
+        (lower, upper)
+    }
+}
+
+// Forwarding impl of Sink from the underlying stream
+#[cfg(feature = "sink")]
+impl<S, Fut, F, Item> Sink<Item> for Then<S, Fut, F>
+where
+    S: Sink<Item>,
+{
+    type Error = S::Error;
+
+    delegate_sink!(stream, Item);
+}
diff --git a/third_party/rust/futures-util/src/stream/stream/unzip.rs b/third_party/rust/futures-util/src/stream/stream/unzip.rs
new file mode 100644
index 0000000000..a88cf03266
--- /dev/null
+++ b/third_party/rust/futures-util/src/stream/stream/unzip.rs
@@ -0,0 +1,63 @@
+use core::mem;
+use core::pin::Pin;
+use futures_core::future::{FusedFuture, Future};
+use futures_core::ready;
+use futures_core::stream::{FusedStream, Stream};
+use futures_core::task::{Context, Poll};
+use pin_project_lite::pin_project;
+
+pin_project! {
+    /// Future for the [`unzip`](super::StreamExt::unzip) method.
+    #[derive(Debug)]
+    #[must_use = "futures do nothing unless you `.await` or poll them"]
+    pub struct Unzip<St, FromA, FromB> {
+        #[pin]
+        stream: St,
+        left: FromA,
+        right: FromB,
+    }
+}
+
+impl<St: Stream, FromA: Default, FromB: Default> Unzip<St, FromA, FromB> {
+    fn finish(self: Pin<&mut Self>) -> (FromA, FromB) {
+        let this = self.project();
+        (mem::take(this.left), mem::take(this.right))
+    }
+
+    pub(super) fn new(stream: St) -> Self {
+        Self { stream, left: Default::default(), right: Default::default() }
+    }
+}
+
+impl<St, A, B, FromA, FromB> FusedFuture for Unzip<St, FromA, FromB>
+where
+    St: FusedStream<Item = (A, B)>,
+    FromA: Default + Extend<A>,
+    FromB: Default + Extend<B>,
+{
+    fn is_terminated(&self) -> bool {
+        self.stream.is_terminated()
+    }
+}
+
+impl<St, A, B, FromA, FromB> Future for Unzip<St, FromA, FromB>
+where
+    St: Stream<Item = (A, B)>,
+    FromA: Default + Extend<A>,
+    FromB: Default + Extend<B>,
+{
+    type Output = (FromA, FromB);
+
+    fn poll(mut self: Pin<&mut Self>, cx: &mut Context<'_>) -> Poll<(FromA, FromB)> {
+        let mut this = self.as_mut().project();
+        loop {
+            match ready!(this.stream.as_mut().poll_next(cx)) {
+                Some(e) => {
+                    this.left.extend(Some(e.0));
+                    this.right.extend(Some(e.1));
+                }
+                None => return Poll::Ready(self.finish()),
+            }
+        }
+    }
+}
diff --git a/third_party/rust/futures-util/src/stream/stream/zip.rs b/third_party/rust/futures-util/src/stream/stream/zip.rs
new file mode 100644
index 0000000000..25a47e96be
--- /dev/null
+++ b/third_party/rust/futures-util/src/stream/stream/zip.rs
@@ -0,0 +1,128 @@
+use crate::stream::{Fuse, StreamExt};
+use core::cmp;
+use core::pin::Pin;
+use futures_core::stream::{FusedStream, Stream};
+use futures_core::task::{Context, Poll};
+use pin_project_lite::pin_project;
+
+pin_project! {
+    /// Stream for the [`zip`](super::StreamExt::zip) method.
+    #[derive(Debug)]
+    #[must_use = "streams do nothing unless polled"]
+    pub struct Zip<St1: Stream, St2: Stream> {
+        #[pin]
+        stream1: Fuse<St1>,
+        #[pin]
+        stream2: Fuse<St2>,
+        queued1: Option<St1::Item>,
+        queued2: Option<St2::Item>,
+    }
+}
+
+impl<St1: Stream, St2: Stream> Zip<St1, St2> {
+    pub(super) fn new(stream1: St1, stream2: St2) -> Self {
+        Self { stream1: stream1.fuse(), stream2: stream2.fuse(), queued1: None, queued2: None }
+    }
+
+    /// Acquires a reference to the underlying streams that this combinator is
+    /// pulling from.
+    pub fn get_ref(&self) -> (&St1, &St2) {
+        (self.stream1.get_ref(), self.stream2.get_ref())
+    }
+
+    /// Acquires a mutable reference to the underlying streams that this
+    /// combinator is pulling from.
+    ///
+    /// Note that care must be taken to avoid tampering with the state of the
+    /// stream which may otherwise confuse this combinator.
+    pub fn get_mut(&mut self) -> (&mut St1, &mut St2) {
+        (self.stream1.get_mut(), self.stream2.get_mut())
+    }
+
+    /// Acquires a pinned mutable reference to the underlying streams that this
+    /// combinator is pulling from.
+    ///
+    /// Note that care must be taken to avoid tampering with the state of the
+    /// stream which may otherwise confuse this combinator.
+    pub fn get_pin_mut(self: Pin<&mut Self>) -> (Pin<&mut St1>, Pin<&mut St2>) {
+        let this = self.project();
+        (this.stream1.get_pin_mut(), this.stream2.get_pin_mut())
+    }
+
+    /// Consumes this combinator, returning the underlying streams.
+    ///
+    /// Note that this may discard intermediate state of this combinator, so
+    /// care should be taken to avoid losing resources when this is called.
+    pub fn into_inner(self) -> (St1, St2) {
+        (self.stream1.into_inner(), self.stream2.into_inner())
+    }
+}
+
+impl<St1, St2> FusedStream for Zip<St1, St2>
+where
+    St1: Stream,
+    St2: Stream,
+{
+    fn is_terminated(&self) -> bool {
+        self.stream1.is_terminated() && self.stream2.is_terminated()
+    }
+}
+
+impl<St1, St2> Stream for Zip<St1, St2>
+where
+    St1: Stream,
+    St2: Stream,
+{
+    type Item = (St1::Item, St2::Item);
+
+    fn poll_next(self: Pin<&mut Self>, cx: &mut Context<'_>) -> Poll<Option<Self::Item>> {
+        let mut this = self.project();
+
+        if this.queued1.is_none() {
+            match this.stream1.as_mut().poll_next(cx) {
+                Poll::Ready(Some(item1)) => *this.queued1 = Some(item1),
+                Poll::Ready(None) | Poll::Pending => {}
+            }
+        }
+        if this.queued2.is_none() {
+            match this.stream2.as_mut().poll_next(cx) {
+                Poll::Ready(Some(item2)) => *this.queued2 = Some(item2),
+                Poll::Ready(None) | Poll::Pending => {}
+            }
+        }
+
+        if this.queued1.is_some() && this.queued2.is_some() {
+            let pair = (this.queued1.take().unwrap(), this.queued2.take().unwrap());
+            Poll::Ready(Some(pair))
+        } else if this.stream1.is_done() || this.stream2.is_done() {
+            Poll::Ready(None)
+        } else {
+            Poll::Pending
+        }
+    }
+
+    fn size_hint(&self) -> (usize, Option<usize>) {
+        let queued1_len = usize::from(self.queued1.is_some());
+        let queued2_len = usize::from(self.queued2.is_some());
+        let (stream1_lower, stream1_upper) = self.stream1.size_hint();
+        let (stream2_lower, stream2_upper) = self.stream2.size_hint();
+
+        let stream1_lower = stream1_lower.saturating_add(queued1_len);
+        let stream2_lower = stream2_lower.saturating_add(queued2_len);
+
+        let lower = cmp::min(stream1_lower, stream2_lower);
+
+        let upper = match (stream1_upper, stream2_upper) {
+            (Some(x), Some(y)) => {
+                let x = x.saturating_add(queued1_len);
+                let y = y.saturating_add(queued2_len);
+                Some(cmp::min(x, y))
+            }
+            (Some(x), None) => x.checked_add(queued1_len),
+            (None, Some(y)) => y.checked_add(queued2_len),
+            (None, None) => None,
+        };
+
+        (lower, upper)
+    }
+}
diff --git a/third_party/rust/futures-util/src/stream/try_stream/and_then.rs b/third_party/rust/futures-util/src/stream/try_stream/and_then.rs
new file mode 100644
index 0000000000..2f8b6f2589
--- /dev/null
+++ b/third_party/rust/futures-util/src/stream/try_stream/and_then.rs
@@ -0,0 +1,105 @@
+use core::fmt;
+use core::pin::Pin;
+use futures_core::future::TryFuture;
+use futures_core::ready;
+use futures_core::stream::{FusedStream, Stream, TryStream};
+use futures_core::task::{Context, Poll};
+#[cfg(feature = "sink")]
+use futures_sink::Sink;
+use pin_project_lite::pin_project;
+
+pin_project! {
+    /// Stream for the [`and_then`](super::TryStreamExt::and_then) method.
+    #[must_use = "streams do nothing unless polled"]
+    pub struct AndThen<St, Fut, F> {
+        #[pin]
+        stream: St,
+        #[pin]
+        future: Option<Fut>,
+        f: F,
+    }
+}
+
+impl<St, Fut, F> fmt::Debug for AndThen<St, Fut, F>
+where
+    St: fmt::Debug,
+    Fut: fmt::Debug,
+{
+    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
+        f.debug_struct("AndThen")
+            .field("stream", &self.stream)
+            .field("future", &self.future)
+            .finish()
+    }
+}
+
+impl<St, Fut, F> AndThen<St, Fut, F>
+where
+    St: TryStream,
+    F: FnMut(St::Ok) -> Fut,
+    Fut: TryFuture<Error = St::Error>,
+{
+    pub(super) fn new(stream: St, f: F) -> Self {
+        Self { stream, future: None, f }
+    }
+
+    delegate_access_inner!(stream, St, ());
+}
+
+impl<St, Fut, F> Stream for AndThen<St, Fut, F>
+where
+    St: TryStream,
+    F: FnMut(St::Ok) -> Fut,
+    Fut: TryFuture<Error = St::Error>,
+{
+    type Item = Result<Fut::Ok, St::Error>;
+
+    fn poll_next(self: Pin<&mut Self>, cx: &mut Context<'_>) -> Poll<Option<Self::Item>> {
+        let mut this = self.project();
+
+        Poll::Ready(loop {
+            if let Some(fut) = this.future.as_mut().as_pin_mut() {
+                let item = ready!(fut.try_poll(cx));
+                this.future.set(None);
+                break Some(item);
+            } else if let Some(item) = ready!(this.stream.as_mut().try_poll_next(cx)?) {
+                this.future.set(Some((this.f)(item)));
+            } else {
+                break None;
+            }
+        })
+    }
+
+    fn size_hint(&self) -> (usize, Option<usize>) {
+        let future_len = usize::from(self.future.is_some());
+        let (lower, upper) = self.stream.size_hint();
+        let lower = lower.saturating_add(future_len);
+        let upper = match upper {
+            Some(x) => x.checked_add(future_len),
+            None => None,
+        };
+        (lower, upper)
+    }
+}
+
+impl<St, Fut, F> FusedStream for AndThen<St, Fut, F>
+where
+    St: TryStream + FusedStream,
+    F: FnMut(St::Ok) -> Fut,
+    Fut: TryFuture<Error = St::Error>,
+{
+    fn is_terminated(&self) -> bool {
+        self.future.is_none() && self.stream.is_terminated()
+    }
+}
+
+// Forwarding impl of Sink from the underlying stream
+#[cfg(feature = "sink")]
+impl<S, Fut, F, Item> Sink<Item> for AndThen<S, Fut, F>
+where
+    S: Sink<Item>,
+{
+    type Error = S::Error;
+
+    delegate_sink!(stream, Item);
+}
diff --git a/third_party/rust/futures-util/src/stream/try_stream/into_async_read.rs b/third_party/rust/futures-util/src/stream/try_stream/into_async_read.rs
new file mode 100644
index 0000000000..ffbfc7eae9
--- /dev/null
+++ b/third_party/rust/futures-util/src/stream/try_stream/into_async_read.rs
@@ -0,0 +1,166 @@
+use core::pin::Pin;
+use futures_core::ready;
+use futures_core::stream::TryStream;
+use futures_core::task::{Context, Poll};
+use futures_io::{AsyncBufRead, AsyncRead, AsyncWrite};
+use pin_project_lite::pin_project;
+use std::cmp;
+use std::io::{Error, Result};
+
+pin_project! {
+    /// Reader for the [`into_async_read`](super::TryStreamExt::into_async_read) method.
+    #[derive(Debug)]
+    #[must_use = "readers do nothing unless polled"]
+    #[cfg_attr(docsrs, doc(cfg(feature = "io")))]
+    pub struct IntoAsyncRead<St>
+    where
+        St: TryStream<Error = Error>,
+        St::Ok: AsRef<[u8]>,
+    {
+        #[pin]
+        stream: St,
+        state: ReadState<St::Ok>,
+    }
+}
+
+#[derive(Debug)]
+enum ReadState<T: AsRef<[u8]>> {
+    Ready { chunk: T, chunk_start: usize },
+    PendingChunk,
+    Eof,
+}
+
+impl<St> IntoAsyncRead<St>
+where
+    St: TryStream<Error = Error>,
+    St::Ok: AsRef<[u8]>,
+{
+    pub(super) fn new(stream: St) -> Self {
+        Self { stream, state: ReadState::PendingChunk }
+    }
+}
+
+impl<St> AsyncRead for IntoAsyncRead<St>
+where
+    St: TryStream<Error = Error>,
+    St::Ok: AsRef<[u8]>,
+{
+    fn poll_read(
+        self: Pin<&mut Self>,
+        cx: &mut Context<'_>,
+        buf: &mut [u8],
+    ) -> Poll<Result<usize>> {
+        let mut this = self.project();
+
+        loop {
+            match this.state {
+                ReadState::Ready { chunk, chunk_start } => {
+                    let chunk = chunk.as_ref();
+                    let len = cmp::min(buf.len(), chunk.len() - *chunk_start);
+
+                    buf[..len].copy_from_slice(&chunk[*chunk_start..*chunk_start + len]);
+                    *chunk_start += len;
+
+                    if chunk.len() == *chunk_start {
+                        *this.state = ReadState::PendingChunk;
+                    }
+
+                    return Poll::Ready(Ok(len));
+                }
+                ReadState::PendingChunk => match ready!(this.stream.as_mut().try_poll_next(cx)) {
+                    Some(Ok(chunk)) => {
+                        if !chunk.as_ref().is_empty() {
+                            *this.state = ReadState::Ready { chunk, chunk_start: 0 };
+                        }
+                    }
+                    Some(Err(err)) => {
+                        *this.state = ReadState::Eof;
+                        return Poll::Ready(Err(err));
+                    }
+                    None => {
+                        *this.state = ReadState::Eof;
+                        return Poll::Ready(Ok(0));
+                    }
+                },
+                ReadState::Eof => {
+                    return Poll::Ready(Ok(0));
+                }
+            }
+        }
+    }
+}
+
+impl<St> AsyncWrite for IntoAsyncRead<St>
+where
+    St: TryStream<Error = Error> + AsyncWrite,
+    St::Ok: AsRef<[u8]>,
+{
+    fn poll_write(self: Pin<&mut Self>, cx: &mut Context<'_>, buf: &[u8]) -> Poll<Result<usize>> {
+        let this = self.project();
+        this.stream.poll_write(cx, buf)
+    }
+
+    fn poll_flush(self: Pin<&mut Self>, cx: &mut Context<'_>) -> Poll<Result<()>> {
+        let this = self.project();
+        this.stream.poll_flush(cx)
+    }
+
+    fn poll_close(self: Pin<&mut Self>, cx: &mut Context<'_>) -> Poll<Result<()>> {
+        let this = self.project();
+        this.stream.poll_close(cx)
+    }
+}
+
+impl<St> AsyncBufRead for IntoAsyncRead<St>
+where
+    St: TryStream<Error = Error>,
+    St::Ok: AsRef<[u8]>,
+{
+    fn poll_fill_buf(self: Pin<&mut Self>, cx: &mut Context<'_>) -> Poll<Result<&[u8]>> {
+        let mut this = self.project();
+
+        while let ReadState::PendingChunk = this.state {
+            match ready!(this.stream.as_mut().try_poll_next(cx)) {
+                Some(Ok(chunk)) => {
+                    if !chunk.as_ref().is_empty() {
+                        *this.state = ReadState::Ready { chunk, chunk_start: 0 };
+                    }
+                }
+                Some(Err(err)) => {
+                    *this.state = ReadState::Eof;
+                    return Poll::Ready(Err(err));
+                }
+                None => {
+                    *this.state = ReadState::Eof;
+                    return Poll::Ready(Ok(&[]));
+                }
+            }
+        }
+
+        if let &mut ReadState::Ready { ref chunk, chunk_start } = this.state {
+            let chunk = chunk.as_ref();
+            return Poll::Ready(Ok(&chunk[chunk_start..]));
+        }
+
+        // To get to this point we must be in ReadState::Eof
+        Poll::Ready(Ok(&[]))
+    }
+
+    fn consume(self: Pin<&mut Self>, amount: usize) {
+        let this = self.project();
+
+        // https://github.com/rust-lang/futures-rs/pull/1556#discussion_r281644295
+        if amount == 0 {
+            return;
+        }
+        if let ReadState::Ready { chunk, chunk_start } = this.state {
+            *chunk_start += amount;
+            debug_assert!(*chunk_start <= chunk.as_ref().len());
+            if *chunk_start >= chunk.as_ref().len() {
+                *this.state = ReadState::PendingChunk;
+            }
+        } else {
+            debug_assert!(false, "Attempted to consume from IntoAsyncRead without chunk");
+        }
+    }
+}
diff --git a/third_party/rust/futures-util/src/stream/try_stream/into_stream.rs b/third_party/rust/futures-util/src/stream/try_stream/into_stream.rs
new file mode 100644
index 0000000000..2126258af7
--- /dev/null
+++ b/third_party/rust/futures-util/src/stream/try_stream/into_stream.rs
@@ -0,0 +1,52 @@
+use core::pin::Pin;
+use futures_core::stream::{FusedStream, Stream, TryStream};
+use futures_core::task::{Context, Poll};
+#[cfg(feature = "sink")]
+use futures_sink::Sink;
+use pin_project_lite::pin_project;
+
+pin_project! {
+    /// Stream for the [`into_stream`](super::TryStreamExt::into_stream) method.
+    #[derive(Debug)]
+    #[must_use = "streams do nothing unless polled"]
+    pub struct IntoStream<St> {
+        #[pin]
+        stream: St,
+    }
+}
+
+impl<St> IntoStream<St> {
+    #[inline]
+    pub(super) fn new(stream: St) -> Self {
+        Self { stream }
+    }
+
+    delegate_access_inner!(stream, St, ());
+}
+
+impl<St: TryStream + FusedStream> FusedStream for IntoStream<St> {
+    fn is_terminated(&self) -> bool {
+        self.stream.is_terminated()
+    }
+}
+
+impl<St: TryStream> Stream for IntoStream<St> {
+    type Item = Result<St::Ok, St::Error>;
+
+    #[inline]
+    fn poll_next(self: Pin<&mut Self>, cx: &mut Context<'_>) -> Poll<Option<Self::Item>> {
+        self.project().stream.try_poll_next(cx)
+    }
+
+    fn size_hint(&self) -> (usize, Option<usize>) {
+        self.stream.size_hint()
+    }
+}
+
+// Forwarding impl of Sink from the underlying stream
+#[cfg(feature = "sink")]
+impl<S: Sink<Item>, Item> Sink<Item> for IntoStream<S> {
+    type Error = S::Error;
+
+    delegate_sink!(stream, Item);
+}
diff --git a/third_party/rust/futures-util/src/stream/try_stream/mod.rs b/third_party/rust/futures-util/src/stream/try_stream/mod.rs
new file mode 100644
index 0000000000..bc4c6e4f6a
--- /dev/null
+++ b/third_party/rust/futures-util/src/stream/try_stream/mod.rs
@@ -0,0 +1,1064 @@
+//! Streams
+//!
+//! This module contains a number of functions for working with `Streams`s
+//! that return `Result`s, allowing for short-circuiting computations.
+
+#[cfg(feature = "compat")]
+use crate::compat::Compat;
+use crate::fns::{
+    inspect_err_fn, inspect_ok_fn, into_fn, map_err_fn, map_ok_fn, InspectErrFn, InspectOkFn,
+    IntoFn, MapErrFn, MapOkFn,
+};
+use crate::future::assert_future;
+use crate::stream::assert_stream;
+use crate::stream::{Inspect, Map};
+#[cfg(feature = "alloc")]
+use alloc::vec::Vec;
+use core::pin::Pin;
+use futures_core::{
+    future::{Future, TryFuture},
+    stream::TryStream,
+    task::{Context, Poll},
+};
+
+mod and_then;
+#[allow(unreachable_pub)] // https://github.com/rust-lang/rust/issues/57411
+pub use self::and_then::AndThen;
+
+delegate_all!(
+    /// Stream for the [`err_into`](super::TryStreamExt::err_into) method.
+    ErrInto<St, E>(
+        MapErr<St, IntoFn<E>>
+    ): Debug + Sink + Stream + FusedStream + AccessInner[St, (.)] + New[|x: St| MapErr::new(x, into_fn())]
+);
+
+delegate_all!(
+    /// Stream for the [`inspect_ok`](super::TryStreamExt::inspect_ok) method.
+    InspectOk<St, F>(
+        Inspect<IntoStream<St>, InspectOkFn<F>>
+    ): Debug + Sink + Stream + FusedStream + AccessInner[St, (. .)] + New[|x: St, f: F| Inspect::new(IntoStream::new(x), inspect_ok_fn(f))]
+);
+
+delegate_all!(
+    /// Stream for the [`inspect_err`](super::TryStreamExt::inspect_err) method.
+    InspectErr<St, F>(
+        Inspect<IntoStream<St>, InspectErrFn<F>>
+    ): Debug + Sink + Stream + FusedStream + AccessInner[St, (. .)] + New[|x: St, f: F| Inspect::new(IntoStream::new(x), inspect_err_fn(f))]
+);
+
+mod into_stream;
+#[allow(unreachable_pub)] // https://github.com/rust-lang/rust/issues/57411
+pub use self::into_stream::IntoStream;
+
+delegate_all!(
+    /// Stream for the [`map_ok`](super::TryStreamExt::map_ok) method.
+    MapOk<St, F>(
+        Map<IntoStream<St>, MapOkFn<F>>
+    ): Debug + Sink + Stream + FusedStream + AccessInner[St, (. .)] + New[|x: St, f: F| Map::new(IntoStream::new(x), map_ok_fn(f))]
+);
+
+delegate_all!(
+    /// Stream for the [`map_err`](super::TryStreamExt::map_err) method.
+    MapErr<St, F>(
+        Map<IntoStream<St>, MapErrFn<F>>
+    ): Debug + Sink + Stream + FusedStream + AccessInner[St, (. .)] + New[|x: St, f: F| Map::new(IntoStream::new(x), map_err_fn(f))]
+);
+
+mod or_else;
+#[allow(unreachable_pub)] // https://github.com/rust-lang/rust/issues/57411
+pub use self::or_else::OrElse;
+
+mod try_next;
+#[allow(unreachable_pub)] // https://github.com/rust-lang/rust/issues/57411
+pub use self::try_next::TryNext;
+
+mod try_for_each;
+#[allow(unreachable_pub)] // https://github.com/rust-lang/rust/issues/57411
+pub use self::try_for_each::TryForEach;
+
+mod try_filter;
+#[allow(unreachable_pub)] // https://github.com/rust-lang/rust/issues/57411
+pub use self::try_filter::TryFilter;
+
+mod try_filter_map;
+#[allow(unreachable_pub)] // https://github.com/rust-lang/rust/issues/57411
+pub use self::try_filter_map::TryFilterMap;
+
+mod try_flatten;
+#[allow(unreachable_pub)] // https://github.com/rust-lang/rust/issues/57411
+pub use self::try_flatten::TryFlatten;
+
+mod try_collect;
+#[allow(unreachable_pub)] // https://github.com/rust-lang/rust/issues/57411
+pub use self::try_collect::TryCollect;
+
+mod try_concat;
+#[allow(unreachable_pub)] // https://github.com/rust-lang/rust/issues/57411
+pub use self::try_concat::TryConcat;
+
+#[cfg(feature = "alloc")]
+mod try_chunks;
+#[cfg(feature = "alloc")]
+#[allow(unreachable_pub)] // https://github.com/rust-lang/rust/issues/57411
+pub use self::try_chunks::{TryChunks, TryChunksError};
+
+mod try_fold;
+#[allow(unreachable_pub)] // https://github.com/rust-lang/rust/issues/57411
+pub use self::try_fold::TryFold;
+
+mod try_unfold;
+#[allow(unreachable_pub)] // https://github.com/rust-lang/rust/issues/57411
+pub use self::try_unfold::{try_unfold, TryUnfold};
+
+mod try_skip_while;
+#[allow(unreachable_pub)] // https://github.com/rust-lang/rust/issues/57411
+pub use self::try_skip_while::TrySkipWhile;
+
+mod try_take_while;
+#[allow(unreachable_pub)] // https://github.com/rust-lang/rust/issues/57411
+pub use self::try_take_while::TryTakeWhile;
+
+#[cfg(not(futures_no_atomic_cas))]
+#[cfg(feature = "alloc")]
+mod try_buffer_unordered;
+#[cfg(not(futures_no_atomic_cas))]
+#[cfg(feature = "alloc")]
+#[allow(unreachable_pub)] // https://github.com/rust-lang/rust/issues/57411
+pub use self::try_buffer_unordered::TryBufferUnordered;
+
+#[cfg(not(futures_no_atomic_cas))]
+#[cfg(feature = "alloc")]
+mod try_buffered;
+#[cfg(not(futures_no_atomic_cas))]
+#[cfg(feature = "alloc")]
+#[allow(unreachable_pub)] // https://github.com/rust-lang/rust/issues/57411
+pub use self::try_buffered::TryBuffered;
+
+#[cfg(not(futures_no_atomic_cas))]
+#[cfg(feature = "alloc")]
+mod try_for_each_concurrent;
+#[cfg(not(futures_no_atomic_cas))]
+#[cfg(feature = "alloc")]
+#[allow(unreachable_pub)] // https://github.com/rust-lang/rust/issues/57411
+pub use self::try_for_each_concurrent::TryForEachConcurrent;
+
+#[cfg(feature = "io")]
+#[cfg(feature = "std")]
+mod into_async_read;
+#[cfg(feature = "io")]
+#[cfg_attr(docsrs, doc(cfg(feature = "io")))]
+#[cfg(feature = "std")]
+#[allow(unreachable_pub)] // https://github.com/rust-lang/rust/issues/57411
+pub use self::into_async_read::IntoAsyncRead;
+
+impl<S: ?Sized + TryStream> TryStreamExt for S {}
+
+/// Adapters specific to `Result`-returning streams
+pub trait TryStreamExt: TryStream {
+    /// Wraps the current stream in a new stream which converts the error type
+    /// into the one provided.
+    ///
+    /// # Examples
+    ///
+    /// ```
+    /// # futures::executor::block_on(async {
+    /// use futures::stream::{self, TryStreamExt};
+    ///
+    /// let mut stream =
+    ///     stream::iter(vec![Ok(()), Err(5i32)])
+    ///         .err_into::<i64>();
+    ///
+    /// assert_eq!(stream.try_next().await, Ok(Some(())));
+    /// assert_eq!(stream.try_next().await, Err(5i64));
+    /// # })
+    /// ```
+    fn err_into<E>(self) -> ErrInto<Self, E>
+    where
+        Self: Sized,
+        Self::Error: Into<E>,
+    {
+        assert_stream::<Result<Self::Ok, E>, _>(ErrInto::new(self))
+    }
+
+    /// Wraps the current stream in a new stream which maps the success value
+    /// using the provided closure.
+    ///
+    /// # Examples
+    ///
+    /// ```
+    /// # futures::executor::block_on(async {
+    /// use futures::stream::{self, TryStreamExt};
+    ///
+    /// let mut stream =
+    ///     stream::iter(vec![Ok(5), Err(0)])
+    ///         .map_ok(|x| x + 2);
+    ///
+    /// assert_eq!(stream.try_next().await, Ok(Some(7)));
+    /// assert_eq!(stream.try_next().await, Err(0));
+    /// # })
+    /// ```
+    fn map_ok<T, F>(self, f: F) -> MapOk<Self, F>
+    where
+        Self: Sized,
+        F: FnMut(Self::Ok) -> T,
+    {
+        assert_stream::<Result<T, Self::Error>, _>(MapOk::new(self, f))
+    }
+
+    /// Wraps the current stream in a new stream which maps the error value
+    /// using the provided closure.
+    ///
+    /// # Examples
+    ///
+    /// ```
+    /// # futures::executor::block_on(async {
+    /// use futures::stream::{self, TryStreamExt};
+    ///
+    /// let mut stream =
+    ///     stream::iter(vec![Ok(5), Err(0)])
+    ///         .map_err(|x| x + 2);
+    ///
+    /// assert_eq!(stream.try_next().await, Ok(Some(5)));
+    /// assert_eq!(stream.try_next().await, Err(2));
+    /// # })
+    /// ```
+    fn map_err<E, F>(self, f: F) -> MapErr<Self, F>
+    where
+        Self: Sized,
+        F: FnMut(Self::Error) -> E,
+    {
+        assert_stream::<Result<Self::Ok, E>, _>(MapErr::new(self, f))
+    }
+
+    /// Chain on a computation for when a value is ready, passing the successful
+    /// results to the provided closure `f`.
+    ///
+    /// This function can be used to run a unit of work when the next successful
+    /// value on a stream is ready. The closure provided will be yielded a value
+    /// when ready, and the returned future will then be run to completion to
+    /// produce the next value on this stream.
+    ///
+    /// Any errors produced by this stream will not be passed to the closure,
+    /// and will be passed through.
+    ///
+    /// The returned value of the closure must implement the `TryFuture` trait
+    /// and can represent some more work to be done before the composed stream
+    /// is finished.
+    ///
+    /// Note that this function consumes the receiving stream and returns a
+    /// wrapped version of it.
+    ///
+    /// To process the entire stream and return a single future representing
+    /// success or error, use `try_for_each` instead.
+    ///
+    /// # Examples
+    ///
+    /// ```
+    /// use futures::channel::mpsc;
+    /// use futures::future;
+    /// use futures::stream::TryStreamExt;
+    ///
+    /// let (_tx, rx) = mpsc::channel::<Result<i32, ()>>(1);
+    ///
+    /// let rx = rx.and_then(|result| {
+    ///     future::ok(if result % 2 == 0 {
+    ///         Some(result)
+    ///     } else {
+    ///         None
+    ///     })
+    /// });
+    /// ```
+    fn and_then<Fut, F>(self, f: F) -> AndThen<Self, Fut, F>
+    where
+        F: FnMut(Self::Ok) -> Fut,
+        Fut: TryFuture<Error = Self::Error>,
+        Self: Sized,
+    {
+        assert_stream::<Result<Fut::Ok, Fut::Error>, _>(AndThen::new(self, f))
+    }
+
+    /// Chain on a computation for when an error happens, passing the
+    /// erroneous result to the provided closure `f`.
+    ///
+    /// This function can be used to run a unit of work and attempt to recover from
+    /// an error if one happens. The closure provided will be yielded an error
+    /// when one appears, and the returned future will then be run to completion
+    /// to produce the next value on this stream.
+    ///
+    /// Any successful values produced by this stream will not be passed to the
+    /// closure, and will be passed through.
+    ///
+    /// The returned value of the closure must implement the [`TryFuture`](futures_core::future::TryFuture) trait
+    /// and can represent some more work to be done before the composed stream
+    /// is finished.
+    ///
+    /// Note that this function consumes the receiving stream and returns a
+    /// wrapped version of it.
+    fn or_else<Fut, F>(self, f: F) -> OrElse<Self, Fut, F>
+    where
+        F: FnMut(Self::Error) -> Fut,
+        Fut: TryFuture<Ok = Self::Ok>,
+        Self: Sized,
+    {
+        assert_stream::<Result<Self::Ok, Fut::Error>, _>(OrElse::new(self, f))
+    }
+
+    /// Do something with the success value of this stream, afterwards passing
+    /// it on.
+    ///
+    /// This is similar to the `StreamExt::inspect` method where it allows
+    /// easily inspecting the success value as it passes through the stream, for
+    /// example to debug what's going on.
+    fn inspect_ok<F>(self, f: F) -> InspectOk<Self, F>
+    where
+        F: FnMut(&Self::Ok),
+        Self: Sized,
+    {
+        assert_stream::<Result<Self::Ok, Self::Error>, _>(InspectOk::new(self, f))
+    }
+
+    /// Do something with the error value of this stream, afterwards passing it on.
+    ///
+    /// This is similar to the `StreamExt::inspect` method where it allows
+    /// easily inspecting the error value as it passes through the stream, for
+    /// example to debug what's going on.
+    fn inspect_err<F>(self, f: F) -> InspectErr<Self, F>
+    where
+        F: FnMut(&Self::Error),
+        Self: Sized,
+    {
+        assert_stream::<Result<Self::Ok, Self::Error>, _>(InspectErr::new(self, f))
+    }
+
+    /// Wraps a [`TryStream`] into a type that implements
+    /// [`Stream`](futures_core::stream::Stream)
+    ///
+    /// [`TryStream`]s currently do not implement the
+    /// [`Stream`](futures_core::stream::Stream) trait because of limitations
+    /// of the compiler.
+    ///
+    /// # Examples
+    ///
+    /// ```
+    /// use futures::stream::{Stream, TryStream, TryStreamExt};
+    ///
+    /// # type T = i32;
+    /// # type E = ();
+    /// fn make_try_stream() -> impl TryStream<Ok = T, Error = E> { // ... }
+    /// # futures::stream::empty()
+    /// # }
+    /// fn take_stream(stream: impl Stream<Item = Result<T, E>>) { /* ... */ }
+    ///
+    /// take_stream(make_try_stream().into_stream());
+    /// ```
+    fn into_stream(self) -> IntoStream<Self>
+    where
+        Self: Sized,
+    {
+        assert_stream::<Result<Self::Ok, Self::Error>, _>(IntoStream::new(self))
+    }
+
+    /// Creates a future that attempts to resolve the next item in the stream.
+    /// If an error is encountered before the next item, the error is returned
+    /// instead.
+    ///
+    /// This is similar to the `Stream::next` combinator, but returns a
+    /// `Result<Option<T>, E>` rather than an `Option<Result<T, E>>`, making
+    /// for easy use with the `?` operator.
+    ///
+    /// # Examples
+    ///
+    /// ```
+    /// # futures::executor::block_on(async {
+    /// use futures::stream::{self, TryStreamExt};
+    ///
+    /// let mut stream = stream::iter(vec![Ok(()), Err(())]);
+    ///
+    /// assert_eq!(stream.try_next().await, Ok(Some(())));
+    /// assert_eq!(stream.try_next().await, Err(()));
+    /// # })
+    /// ```
+    fn try_next(&mut self) -> TryNext<'_, Self>
+    where
+        Self: Unpin,
+    {
+        assert_future::<Result<Option<Self::Ok>, Self::Error>, _>(TryNext::new(self))
+    }
+
+    /// Attempts to run this stream to completion, executing the provided
+    /// asynchronous closure for each element on the stream.
+    ///
+    /// The provided closure will be called for each item this stream produces,
+    /// yielding a future. That future will then be executed to completion
+    /// before moving on to the next item.
+    ///
+    /// The returned value is a [`Future`](futures_core::future::Future) where the
+    /// [`Output`](futures_core::future::Future::Output) type is
+    /// `Result<(), Self::Error>`. If any of the intermediate
+    /// futures or the stream returns an error, this future will return
+    /// immediately with an error.
+    ///
+    /// # Examples
+    ///
+    /// ```
+    /// # futures::executor::block_on(async {
+    /// use futures::future;
+    /// use futures::stream::{self, TryStreamExt};
+    ///
+    /// let mut x = 0i32;
+    ///
+    /// {
+    ///     let fut = stream::repeat(Ok(1)).try_for_each(|item| {
+    ///         x += item;
+    ///         future::ready(if x == 3 { Err(()) } else { Ok(()) })
+    ///     });
+    ///     assert_eq!(fut.await, Err(()));
+    /// }
+    ///
+    /// assert_eq!(x, 3);
+    /// # })
+    /// ```
+    fn try_for_each<Fut, F>(self, f: F) -> TryForEach<Self, Fut, F>
+    where
+        F: FnMut(Self::Ok) -> Fut,
+        Fut: TryFuture<Ok = (), Error = Self::Error>,
+        Self: Sized,
+    {
+        assert_future::<Result<(), Self::Error>, _>(TryForEach::new(self, f))
+    }
+
+    /// Skip elements on this stream while the provided asynchronous predicate
+    /// resolves to `true`.
+    ///
+    /// This function is similar to
+    /// [`StreamExt::skip_while`](crate::stream::StreamExt::skip_while) but exits
+    /// early if an error occurs.
+    ///
+    /// # Examples
+    ///
+    /// ```
+    /// # futures::executor::block_on(async {
+    /// use futures::future;
+    /// use futures::stream::{self, TryStreamExt};
+    ///
+    /// let stream = stream::iter(vec![Ok::<i32, i32>(1), Ok(3), Ok(2)]);
+    /// let stream = stream.try_skip_while(|x| future::ready(Ok(*x < 3)));
+    ///
+    /// let output: Result<Vec<i32>, i32> = stream.try_collect().await;
+    /// assert_eq!(output, Ok(vec![3, 2]));
+    /// # })
+    /// ```
+    fn try_skip_while<Fut, F>(self, f: F) -> TrySkipWhile<Self, Fut, F>
+    where
+        F: FnMut(&Self::Ok) -> Fut,
+        Fut: TryFuture<Ok = bool, Error = Self::Error>,
+        Self: Sized,
+    {
+        assert_stream::<Result<Self::Ok, Self::Error>, _>(TrySkipWhile::new(self, f))
+    }
+
+    /// Take elements on this stream while the provided asynchronous predicate
+    /// resolves to `true`.
+    ///
+    /// This function is similar to
+    /// [`StreamExt::take_while`](crate::stream::StreamExt::take_while) but exits
+    /// early if an error occurs.
+    ///
+    /// # Examples
+    ///
+    /// ```
+    /// # futures::executor::block_on(async {
+    /// use futures::future;
+    /// use futures::stream::{self, TryStreamExt};
+    ///
+    /// let stream = stream::iter(vec![Ok::<i32, i32>(1), Ok(2), Ok(3), Ok(2)]);
+    /// let stream = stream.try_take_while(|x| future::ready(Ok(*x < 3)));
+    ///
+    /// let output: Result<Vec<i32>, i32> = stream.try_collect().await;
+    /// assert_eq!(output, Ok(vec![1, 2]));
+    /// # })
+    /// ```
+    fn try_take_while<Fut, F>(self, f: F) -> TryTakeWhile<Self, Fut, F>
+    where
+        F: FnMut(&Self::Ok) -> Fut,
+        Fut: TryFuture<Ok = bool, Error = Self::Error>,
+        Self: Sized,
+    {
+        assert_stream::<Result<Self::Ok, Self::Error>, _>(TryTakeWhile::new(self, f))
+    }
+
+    /// Attempts to run this stream to completion, executing the provided asynchronous
+    /// closure for each element on the stream concurrently as elements become
+    /// available, exiting as soon as an error occurs.
+    ///
+    /// This is similar to
+    /// [`StreamExt::for_each_concurrent`](crate::stream::StreamExt::for_each_concurrent),
+    /// but will resolve to an error immediately if the underlying stream or the provided
+    /// closure return an error.
+    ///
+    /// This method is only available when the `std` or `alloc` feature of this
+    /// library is activated, and it is activated by default.
+    ///
+    /// # Examples
+    ///
+    /// ```
+    /// # futures::executor::block_on(async {
+    /// use futures::channel::oneshot;
+    /// use futures::stream::{self, StreamExt, TryStreamExt};
+    ///
+    /// let (tx1, rx1) = oneshot::channel();
+    /// let (tx2, rx2) = oneshot::channel();
+    /// let (_tx3, rx3) = oneshot::channel();
+    ///
+    /// let stream = stream::iter(vec![rx1, rx2, rx3]);
+    /// let fut = stream.map(Ok).try_for_each_concurrent(
+    ///     /* limit */ 2,
+    ///     |rx| async move {
+    ///         let res: Result<(), oneshot::Canceled> = rx.await;
+    ///         res
+    ///     }
+    /// );
+    ///
+    /// tx1.send(()).unwrap();
+    /// // Drop the second sender so that `rx2` resolves to `Canceled`.
+    /// drop(tx2);
+    ///
+    /// // The final result is an error because the second future
+    /// // resulted in an error.
+    /// assert_eq!(Err(oneshot::Canceled), fut.await);
+    /// # })
+    /// ```
+    #[cfg(not(futures_no_atomic_cas))]
+    #[cfg(feature = "alloc")]
+    fn try_for_each_concurrent<Fut, F>(
+        self,
+        limit: impl Into<Option<usize>>,
+        f: F,
+    ) -> TryForEachConcurrent<Self, Fut, F>
+    where
+        F: FnMut(Self::Ok) -> Fut,
+        Fut: Future<Output = Result<(), Self::Error>>,
+        Self: Sized,
+    {
+        assert_future::<Result<(), Self::Error>, _>(TryForEachConcurrent::new(
+            self,
+            limit.into(),
+            f,
+        ))
+    }
+
+    /// Attempt to transform a stream into a collection,
+    /// returning a future representing the result of that computation.
+    ///
+    /// This combinator will collect all successful results of this stream and
+    /// collect them into the specified collection type. If an error happens then all
+    /// collected elements will be dropped and the error will be returned.
+    ///
+    /// The returned future will be resolved when the stream terminates.
+    ///
+    /// # Examples
+    ///
+    /// ```
+    /// # futures::executor::block_on(async {
+    /// use futures::channel::mpsc;
+    /// use futures::stream::TryStreamExt;
+    /// use std::thread;
+    ///
+    /// let (tx, rx) = mpsc::unbounded();
+    ///
+    /// thread::spawn(move || {
+    ///     for i in 1..=5 {
+    ///         tx.unbounded_send(Ok(i)).unwrap();
+    ///     }
+    ///     tx.unbounded_send(Err(6)).unwrap();
+    /// });
+    ///
+    /// let output: Result<Vec<i32>, i32> = rx.try_collect().await;
+    /// assert_eq!(output, Err(6));
+    /// # })
+    /// ```
+    fn try_collect<C: Default + Extend<Self::Ok>>(self) -> TryCollect<Self, C>
+    where
+        Self: Sized,
+    {
+        assert_future::<Result<C, Self::Error>, _>(TryCollect::new(self))
+    }
+
+    /// An adaptor for chunking up successful items of the stream inside a vector.
+    ///
+    /// This combinator will attempt to pull successful items from this stream and buffer
+    /// them into a local vector. At most `capacity` items will get buffered
+    /// before they're yielded from the returned stream.
+    ///
+    /// Note that the vectors returned from this iterator may not always have
+    /// `capacity` elements. If the underlying stream ended and only a partial
+    /// vector was created, it'll be returned. Additionally if an error happens
+    /// from the underlying stream then the currently buffered items will be
+    /// yielded.
+    ///
+    /// This method is only available when the `std` or `alloc` feature of this
+    /// library is activated, and it is activated by default.
+    ///
+    /// This function is similar to
+    /// [`StreamExt::chunks`](crate::stream::StreamExt::chunks) but exits
+    /// early if an error occurs.
+    ///
+    /// # Examples
+    ///
+    /// ```
+    /// # futures::executor::block_on(async {
+    /// use futures::stream::{self, TryChunksError, TryStreamExt};
+    ///
+    /// let stream = stream::iter(vec![Ok::<i32, i32>(1), Ok(2), Ok(3), Err(4), Ok(5), Ok(6)]);
+    /// let mut stream = stream.try_chunks(2);
+    ///
+    /// assert_eq!(stream.try_next().await, Ok(Some(vec![1, 2])));
+    /// assert_eq!(stream.try_next().await, Err(TryChunksError(vec![3], 4)));
+    /// assert_eq!(stream.try_next().await, Ok(Some(vec![5, 6])));
+    /// # })
+    /// ```
+    ///
+    /// # Panics
+    ///
+    /// This method will panic if `capacity` is zero.
+    #[cfg(feature = "alloc")]
+    fn try_chunks(self, capacity: usize) -> TryChunks<Self>
+    where
+        Self: Sized,
+    {
+        assert_stream::<Result<Vec<Self::Ok>, TryChunksError<Self::Ok, Self::Error>>, _>(
+            TryChunks::new(self, capacity),
+        )
+    }
+
+    /// Attempt to filter the values produced by this stream according to the
+    /// provided asynchronous closure.
+    ///
+    /// As values of this stream are made available, the provided predicate `f`
+    /// will be run on them. If the predicate returns a `Future` which resolves
+    /// to `true`, then the stream will yield the value, but if the predicate
+    /// return a `Future` which resolves to `false`, then the value will be
+    /// discarded and the next value will be produced.
+    ///
+    /// All errors are passed through without filtering in this combinator.
+    ///
+    /// Note that this function consumes the stream passed into it and returns a
+    /// wrapped version of it, similar to the existing `filter` methods in
+    /// the standard library.
+    ///
+    /// # Examples
+    /// ```
+    /// # futures::executor::block_on(async {
+    /// use futures::future;
+    /// use futures::stream::{self, StreamExt, TryStreamExt};
+    ///
+    /// let stream = stream::iter(vec![Ok(1i32), Ok(2i32), Ok(3i32), Err("error")]);
+    /// let mut evens = stream.try_filter(|x| {
+    ///     future::ready(x % 2 == 0)
+    /// });
+    ///
+    /// assert_eq!(evens.next().await, Some(Ok(2)));
+    /// assert_eq!(evens.next().await, Some(Err("error")));
+    /// # })
+    /// ```
+    fn try_filter<Fut, F>(self, f: F) -> TryFilter<Self, Fut, F>
+    where
+        Fut: Future<Output = bool>,
+        F: FnMut(&Self::Ok) -> Fut,
+        Self: Sized,
+    {
+        assert_stream::<Result<Self::Ok, Self::Error>, _>(TryFilter::new(self, f))
+    }
+
+    /// Attempt to filter the values produced by this stream while
+    /// simultaneously mapping them to a different type according to the
+    /// provided asynchronous closure.
+    ///
+    /// As values of this stream are made available, the provided function will
+    /// be run on them. If the future returned by the predicate `f` resolves to
+    /// [`Some(item)`](Some) then the stream will yield the value `item`, but if
+    /// it resolves to [`None`] then the next value will be produced.
+    ///
+    /// All errors are passed through without filtering in this combinator.
+    ///
+    /// Note that this function consumes the stream passed into it and returns a
+    /// wrapped version of it, similar to the existing `filter_map` methods in
+    /// the standard library.
+    ///
+    /// # Examples
+    /// ```
+    /// # futures::executor::block_on(async {
+    /// use futures::stream::{self, StreamExt, TryStreamExt};
+    /// use futures::pin_mut;
+    ///
+    /// let stream = stream::iter(vec![Ok(1i32), Ok(6i32), Err("error")]);
+    /// let halves = stream.try_filter_map(|x| async move {
+    ///     let ret = if x % 2 == 0 { Some(x / 2) } else { None };
+    ///     Ok(ret)
+    /// });
+    ///
+    /// pin_mut!(halves);
+    /// assert_eq!(halves.next().await, Some(Ok(3)));
+    /// assert_eq!(halves.next().await, Some(Err("error")));
+    /// # })
+    /// ```
+    fn try_filter_map<Fut, F, T>(self, f: F) -> TryFilterMap<Self, Fut, F>
+    where
+        Fut: TryFuture<Ok = Option<T>, Error = Self::Error>,
+        F: FnMut(Self::Ok) -> Fut,
+        Self: Sized,
+    {
+        assert_stream::<Result<T, Self::Error>, _>(TryFilterMap::new(self, f))
+    }
+
+    /// Flattens a stream of streams into just one continuous stream.
+    ///
+    /// If this stream's elements are themselves streams then this combinator
+    /// will flatten out the entire stream to one long chain of elements. Any
+    /// errors are passed through without looking at them, but otherwise each
+    /// individual stream will get exhausted before moving on to the next.
+    ///
+    /// # Examples
+    ///
+    /// ```
+    /// # futures::executor::block_on(async {
+    /// use futures::channel::mpsc;
+    /// use futures::stream::{StreamExt, TryStreamExt};
+    /// use std::thread;
+    ///
+    /// let (tx1, rx1) = mpsc::unbounded();
+    /// let (tx2, rx2) = mpsc::unbounded();
+    /// let (tx3, rx3) = mpsc::unbounded();
+    ///
+    /// thread::spawn(move || {
+    ///     tx1.unbounded_send(Ok(1)).unwrap();
+    /// });
+    /// thread::spawn(move || {
+    ///     tx2.unbounded_send(Ok(2)).unwrap();
+    ///     tx2.unbounded_send(Err(3)).unwrap();
+    ///     tx2.unbounded_send(Ok(4)).unwrap();
+    /// });
+    /// thread::spawn(move || {
+    ///     tx3.unbounded_send(Ok(rx1)).unwrap();
+    ///     tx3.unbounded_send(Ok(rx2)).unwrap();
+    ///     tx3.unbounded_send(Err(5)).unwrap();
+    /// });
+    ///
+    /// let mut stream = rx3.try_flatten();
+    /// assert_eq!(stream.next().await, Some(Ok(1)));
+    /// assert_eq!(stream.next().await, Some(Ok(2)));
+    /// assert_eq!(stream.next().await, Some(Err(3)));
+    /// assert_eq!(stream.next().await, Some(Ok(4)));
+    /// assert_eq!(stream.next().await, Some(Err(5)));
+    /// assert_eq!(stream.next().await, None);
+    /// # });
+    /// ```
+    fn try_flatten(self) -> TryFlatten<Self>
+    where
+        Self::Ok: TryStream,
+        <Self::Ok as TryStream>::Error: From<Self::Error>,
+        Self: Sized,
+    {
+        assert_stream::<Result<<Self::Ok as TryStream>::Ok, <Self::Ok as TryStream>::Error>, _>(
+            TryFlatten::new(self),
+        )
+    }
+
+    /// Attempt to execute an accumulating asynchronous computation over a
+    /// stream, collecting all the values into one final result.
+    ///
+    /// This combinator will accumulate all values returned by this stream
+    /// according to the closure provided. The initial state is also provided to
+    /// this method and then is returned again by each execution of the closure.
+    /// Once the entire stream has been exhausted the returned future will
+    /// resolve to this value.
+    ///
+    /// This method is similar to [`fold`](crate::stream::StreamExt::fold), but will
+    /// exit early if an error is encountered in either the stream or the
+    /// provided closure.
+    ///
+    /// # Examples
+    ///
+    /// ```
+    /// # futures::executor::block_on(async {
+    /// use futures::stream::{self, TryStreamExt};
+    ///
+    /// let number_stream = stream::iter(vec![Ok::<i32, i32>(1), Ok(2)]);
+    /// let sum = number_stream.try_fold(0, |acc, x| async move { Ok(acc + x) });
+    /// assert_eq!(sum.await, Ok(3));
+    ///
+    /// let number_stream_with_err = stream::iter(vec![Ok::<i32, i32>(1), Err(2), Ok(1)]);
+    /// let sum = number_stream_with_err.try_fold(0, |acc, x| async move { Ok(acc + x) });
+    /// assert_eq!(sum.await, Err(2));
+    /// # })
+    /// ```
+    fn try_fold<T, Fut, F>(self, init: T, f: F) -> TryFold<Self, Fut, T, F>
+    where
+        F: FnMut(T, Self::Ok) -> Fut,
+        Fut: TryFuture<Ok = T, Error = Self::Error>,
+        Self: Sized,
+    {
+        assert_future::<Result<T, Self::Error>, _>(TryFold::new(self, f, init))
+    }
+
+    /// Attempt to concatenate all items of a stream into a single
+    /// extendable destination, returning a future representing the end result.
+    ///
+    /// This combinator will extend the first item with the contents of all
+    /// the subsequent successful results of the stream. If the stream is empty,
+    /// the default value will be returned.
+    ///
+    /// Works with all collections that implement the [`Extend`](std::iter::Extend) trait.
+    ///
+    /// This method is similar to [`concat`](crate::stream::StreamExt::concat), but will
+    /// exit early if an error is encountered in the stream.
+    ///
+    /// # Examples
+    ///
+    /// ```
+    /// # futures::executor::block_on(async {
+    /// use futures::channel::mpsc;
+    /// use futures::stream::TryStreamExt;
+    /// use std::thread;
+    ///
+    /// let (tx, rx) = mpsc::unbounded::<Result<Vec<i32>, ()>>();
+    ///
+    /// thread::spawn(move || {
+    ///     for i in (0..3).rev() {
+    ///         let n = i * 3;
+    ///         tx.unbounded_send(Ok(vec![n + 1, n + 2, n + 3])).unwrap();
+    ///     }
+    /// });
+    ///
+    /// let result = rx.try_concat().await;
+    ///
+    /// assert_eq!(result, Ok(vec![7, 8, 9, 4, 5, 6, 1, 2, 3]));
+    /// # });
+    /// ```
+    fn try_concat(self) -> TryConcat<Self>
+    where
+        Self: Sized,
+        Self::Ok: Extend<<<Self as TryStream>::Ok as IntoIterator>::Item> + IntoIterator + Default,
+    {
+        assert_future::<Result<Self::Ok, Self::Error>, _>(TryConcat::new(self))
+    }
+
+    /// Attempt to execute several futures from a stream concurrently (unordered).
+    ///
+    /// This stream's `Ok` type must be a [`TryFuture`](futures_core::future::TryFuture) with an `Error` type
+    /// that matches the stream's `Error` type.
+    ///
+    /// This adaptor will buffer up to `n` futures and then return their
+    /// outputs in the order in which they complete. If the underlying stream
+    /// returns an error, it will be immediately propagated.
+    ///
+    /// The returned stream will be a stream of results, each containing either
+    /// an error or a future's output. An error can be produced either by the
+    /// underlying stream itself or by one of the futures it yielded.
+    ///
+    /// This method is only available when the `std` or `alloc` feature of this
+    /// library is activated, and it is activated by default.
+    ///
+    /// # Examples
+    ///
+    /// Results are returned in the order of completion:
+    /// ```
+    /// # futures::executor::block_on(async {
+    /// use futures::channel::oneshot;
+    /// use futures::stream::{self, StreamExt, TryStreamExt};
+    ///
+    /// let (send_one, recv_one) = oneshot::channel();
+    /// let (send_two, recv_two) = oneshot::channel();
+    ///
+    /// let stream_of_futures = stream::iter(vec![Ok(recv_one), Ok(recv_two)]);
+    ///
+    /// let mut buffered = stream_of_futures.try_buffer_unordered(10);
+    ///
+    /// send_two.send(2i32)?;
+    /// assert_eq!(buffered.next().await, Some(Ok(2i32)));
+    ///
+    /// send_one.send(1i32)?;
+    /// assert_eq!(buffered.next().await, Some(Ok(1i32)));
+    ///
+    /// assert_eq!(buffered.next().await, None);
+    /// # Ok::<(), i32>(()) }).unwrap();
+    /// ```
+    ///
+    /// Errors from the underlying stream itself are propagated:
+    /// ```
+    /// # futures::executor::block_on(async {
+    /// use futures::channel::mpsc;
+    /// use futures::stream::{StreamExt, TryStreamExt};
+    ///
+    /// let (sink, stream_of_futures) = mpsc::unbounded();
+    /// let mut buffered = stream_of_futures.try_buffer_unordered(10);
+    ///
+    /// sink.unbounded_send(Ok(async { Ok(7i32) }))?;
+    /// assert_eq!(buffered.next().await, Some(Ok(7i32)));
+    ///
+    /// sink.unbounded_send(Err("error in the stream"))?;
+    /// assert_eq!(buffered.next().await, Some(Err("error in the stream")));
+    /// # Ok::<(), Box<dyn std::error::Error>>(()) }).unwrap();
+    /// ```
+    #[cfg(not(futures_no_atomic_cas))]
+    #[cfg(feature = "alloc")]
+    fn try_buffer_unordered(self, n: usize) -> TryBufferUnordered<Self>
+    where
+        Self::Ok: TryFuture<Error = Self::Error>,
+        Self: Sized,
+    {
+        assert_stream::<Result<<Self::Ok as TryFuture>::Ok, Self::Error>, _>(
+            TryBufferUnordered::new(self, n),
+        )
+    }
+
+    /// Attempt to execute several futures from a stream concurrently.
+    ///
+    /// This stream's `Ok` type must be a [`TryFuture`](futures_core::future::TryFuture) with an `Error` type
+    /// that matches the stream's `Error` type.
+    ///
+    /// This adaptor will buffer up to `n` futures and then return their
+    /// outputs in the same order as the underlying stream. If the underlying stream returns an error, it will
+    /// be immediately propagated.
+    ///
+    /// The returned stream will be a stream of results, each containing either
+    /// an error or a future's output. An error can be produced either by the
+    /// underlying stream itself or by one of the futures it yielded.
+    ///
+    /// This method is only available when the `std` or `alloc` feature of this
+    /// library is activated, and it is activated by default.
+    ///
+    /// # Examples
+    ///
+    /// Results are returned in the order of addition:
+    /// ```
+    /// # futures::executor::block_on(async {
+    /// use futures::channel::oneshot;
+    /// use futures::future::lazy;
+    /// use futures::stream::{self, StreamExt, TryStreamExt};
+    ///
+    /// let (send_one, recv_one) = oneshot::channel();
+    /// let (send_two, recv_two) = oneshot::channel();
+    ///
+    /// let mut buffered = lazy(move |cx| {
+    ///     let stream_of_futures = stream::iter(vec![Ok(recv_one), Ok(recv_two)]);
+    ///
+    ///     let mut buffered = stream_of_futures.try_buffered(10);
+    ///
+    ///     assert!(buffered.try_poll_next_unpin(cx).is_pending());
+    ///
+    ///     send_two.send(2i32)?;
+    ///     assert!(buffered.try_poll_next_unpin(cx).is_pending());
+    ///     Ok::<_, i32>(buffered)
+    /// }).await?;
+    ///
+    /// send_one.send(1i32)?;
+    /// assert_eq!(buffered.next().await, Some(Ok(1i32)));
+    /// assert_eq!(buffered.next().await, Some(Ok(2i32)));
+    ///
+    /// assert_eq!(buffered.next().await, None);
+    /// # Ok::<(), i32>(()) }).unwrap();
+    /// ```
+    ///
+    /// Errors from the underlying stream itself are propagated:
+    /// ```
+    /// # futures::executor::block_on(async {
+    /// use futures::channel::mpsc;
+    /// use futures::stream::{StreamExt, TryStreamExt};
+    ///
+    /// let (sink, stream_of_futures) = mpsc::unbounded();
+    /// let mut buffered = stream_of_futures.try_buffered(10);
+    ///
+    /// sink.unbounded_send(Ok(async { Ok(7i32) }))?;
+    /// assert_eq!(buffered.next().await, Some(Ok(7i32)));
+    ///
+    /// sink.unbounded_send(Err("error in the stream"))?;
+    /// assert_eq!(buffered.next().await, Some(Err("error in the stream")));
+    /// # Ok::<(), Box<dyn std::error::Error>>(()) }).unwrap();
+    /// ```
+    #[cfg(not(futures_no_atomic_cas))]
+    #[cfg(feature = "alloc")]
+    fn try_buffered(self, n: usize) -> TryBuffered<Self>
+    where
+        Self::Ok: TryFuture<Error = Self::Error>,
+        Self: Sized,
+    {
+        assert_stream::<Result<<Self::Ok as TryFuture>::Ok, Self::Error>, _>(TryBuffered::new(
+            self, n,
+        ))
+    }
+
+    // TODO: false positive warning from rustdoc. Verify once #43466 settles
+    //
+    /// A convenience method for calling [`TryStream::try_poll_next`] on [`Unpin`]
+    /// stream types.
+    fn try_poll_next_unpin(
+        &mut self,
+        cx: &mut Context<'_>,
+    ) -> Poll<Option<Result<Self::Ok, Self::Error>>>
+    where
+        Self: Unpin,
+    {
+        Pin::new(self).try_poll_next(cx)
+    }
+
+    /// Wraps a [`TryStream`] into a stream compatible with libraries using
+    /// futures 0.1 `Stream`. Requires the `compat` feature to be enabled.
+    /// ```
+    /// # if cfg!(miri) { return; } // Miri does not support epoll
+    /// use futures::future::{FutureExt, TryFutureExt};
+    /// # let (tx, rx) = futures::channel::oneshot::channel();
+    ///
+    /// let future03 = async {
+    ///     println!("Running on the pool");
+    ///     tx.send(42).unwrap();
+    /// };
+    ///
+    /// let future01 = future03
+    ///     .unit_error() // Make it a TryFuture
+    ///     .boxed()  // Make it Unpin
+    ///     .compat();
+    ///
+    /// tokio::run(future01);
+    /// # assert_eq!(42, futures::executor::block_on(rx).unwrap());
+    /// ```
+    #[cfg(feature = "compat")]
+    #[cfg_attr(docsrs, doc(cfg(feature = "compat")))]
+    fn compat(self) -> Compat<Self>
+    where
+        Self: Sized + Unpin,
+    {
+        Compat::new(self)
+    }
+
+    /// Adapter that converts this stream into an [`AsyncBufRead`](crate::io::AsyncBufRead).
+    ///
+    /// This method is only available when the `std` feature of this
+    /// library is activated, and it is activated by default.
+    ///
+    /// # Examples
+    ///
+    /// ```
+    /// # futures::executor::block_on(async {
+    /// use futures::stream::{self, TryStreamExt};
+    /// use futures::io::AsyncReadExt;
+    ///
+    /// let stream = stream::iter([Ok(vec![1, 2, 3]), Ok(vec![4, 5])]);
+    /// let mut reader = stream.into_async_read();
+    ///
+    /// let mut buf = Vec::new();
+    /// reader.read_to_end(&mut buf).await.unwrap();
+    /// assert_eq!(buf, [1, 2, 3, 4, 5]);
+    /// # })
+    /// ```
+    #[cfg(feature = "io")]
+    #[cfg_attr(docsrs, doc(cfg(feature = "io")))]
+    #[cfg(feature = "std")]
+    fn into_async_read(self) -> IntoAsyncRead<Self>
+    where
+        Self: Sized + TryStreamExt<Error = std::io::Error>,
+        Self::Ok: AsRef<[u8]>,
+    {
+        crate::io::assert_read(IntoAsyncRead::new(self))
+    }
+}
diff --git a/third_party/rust/futures-util/src/stream/try_stream/or_else.rs b/third_party/rust/futures-util/src/stream/try_stream/or_else.rs
new file mode 100644
index 0000000000..53aceb8e64
--- /dev/null
+++ b/third_party/rust/futures-util/src/stream/try_stream/or_else.rs
@@ -0,0 +1,109 @@
+use core::fmt;
+use core::pin::Pin;
+use futures_core::future::TryFuture;
+use futures_core::ready;
+use futures_core::stream::{FusedStream, Stream, TryStream};
+use futures_core::task::{Context, Poll};
+#[cfg(feature = "sink")]
+use futures_sink::Sink;
+use pin_project_lite::pin_project;
+
+pin_project! {
+    /// Stream for the [`or_else`](super::TryStreamExt::or_else) method.
+    #[must_use = "streams do nothing unless polled"]
+    pub struct OrElse<St, Fut, F> {
+        #[pin]
+        stream: St,
+        #[pin]
+        future: Option<Fut>,
+        f: F,
+    }
+}
+
+impl<St, Fut, F> fmt::Debug for OrElse<St, Fut, F>
+where
+    St: fmt::Debug,
+    Fut: fmt::Debug,
+{
+    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
+        f.debug_struct("OrElse")
+            .field("stream", &self.stream)
+            .field("future", &self.future)
+            .finish()
+    }
+}
+
+impl<St, Fut, F> OrElse<St, Fut, F>
+where
+    St: TryStream,
+    F: FnMut(St::Error) -> Fut,
+    Fut: TryFuture<Ok = St::Ok>,
+{
+    pub(super) fn new(stream: St, f: F) -> Self {
+        Self { stream, future: None, f }
+    }
+
+    delegate_access_inner!(stream, St, ());
+}
+
+impl<St, Fut, F> Stream for OrElse<St, Fut, F>
+where
+    St: TryStream,
+    F: FnMut(St::Error) -> Fut,
+    Fut: TryFuture<Ok = St::Ok>,
+{
+    type Item = Result<St::Ok, Fut::Error>;
+
+    fn poll_next(self: Pin<&mut Self>, cx: &mut Context<'_>) -> Poll<Option<Self::Item>> {
+        let mut this = self.project();
+
+        Poll::Ready(loop {
+            if let Some(fut) = this.future.as_mut().as_pin_mut() {
+                let item = ready!(fut.try_poll(cx));
+                this.future.set(None);
+                break Some(item);
+            } else {
+                match ready!(this.stream.as_mut().try_poll_next(cx)) {
+                    Some(Ok(item)) => break Some(Ok(item)),
+                    Some(Err(e)) => {
+                        this.future.set(Some((this.f)(e)));
+                    }
+                    None => break None,
+                }
+            }
+        })
+    }
+
+    fn size_hint(&self) -> (usize, Option<usize>) {
+        let future_len = usize::from(self.future.is_some());
+        let (lower, upper) = self.stream.size_hint();
+        let lower = lower.saturating_add(future_len);
+        let upper = match upper {
+            Some(x) => x.checked_add(future_len),
+            None => None,
+        };
+        (lower, upper)
+    }
+}
+
+impl<St, Fut, F> FusedStream for OrElse<St, Fut, F>
+where
+    St: TryStream + FusedStream,
+    F: FnMut(St::Error) -> Fut,
+    Fut: TryFuture<Ok = St::Ok>,
+{
+    fn is_terminated(&self) -> bool {
+        self.future.is_none() && self.stream.is_terminated()
+    }
+}
+
+// Forwarding impl of Sink from the underlying stream
+#[cfg(feature = "sink")]
+impl<S, Fut, F, Item> Sink<Item> for OrElse<S, Fut, F>
+where
+    S: Sink<Item>,
+{
+    type Error = S::Error;
+
+    delegate_sink!(stream, Item);
+}
diff --git a/third_party/rust/futures-util/src/stream/try_stream/try_buffer_unordered.rs b/third_party/rust/futures-util/src/stream/try_stream/try_buffer_unordered.rs
new file mode 100644
index 0000000000..9a899d4ea6
--- /dev/null
+++ b/third_party/rust/futures-util/src/stream/try_stream/try_buffer_unordered.rs
@@ -0,0 +1,86 @@
+use crate::future::{IntoFuture, TryFutureExt};
+use crate::stream::{Fuse, FuturesUnordered, IntoStream, StreamExt};
+use core::pin::Pin;
+use futures_core::future::TryFuture;
+use futures_core::stream::{Stream, TryStream};
+use futures_core::task::{Context, Poll};
+#[cfg(feature = "sink")]
+use futures_sink::Sink;
+use pin_project_lite::pin_project;
+
+pin_project! {
+    /// Stream for the
+    /// [`try_buffer_unordered`](super::TryStreamExt::try_buffer_unordered) method.
+    #[derive(Debug)]
+    #[must_use = "streams do nothing unless polled"]
+    pub struct TryBufferUnordered<St>
+        where St: TryStream
+    {
+        #[pin]
+        stream: Fuse<IntoStream<St>>,
+        in_progress_queue: FuturesUnordered<IntoFuture<St::Ok>>,
+        max: usize,
+    }
+}
+
+impl<St> TryBufferUnordered<St>
+where
+    St: TryStream,
+    St::Ok: TryFuture,
+{
+    pub(super) fn new(stream: St, n: usize) -> Self {
+        Self {
+            stream: IntoStream::new(stream).fuse(),
+            in_progress_queue: FuturesUnordered::new(),
+            max: n,
+        }
+    }
+
+    delegate_access_inner!(stream, St, (. .));
+}
+
+impl<St> Stream for TryBufferUnordered<St>
+where
+    St: TryStream,
+    St::Ok: TryFuture<Error = St::Error>,
+{
+    type Item = Result<<St::Ok as TryFuture>::Ok, St::Error>;
+
+    fn poll_next(self: Pin<&mut Self>, cx: &mut Context<'_>) -> Poll<Option<Self::Item>> {
+        let mut this = self.project();
+
+        // First up, try to spawn off as many futures as possible by filling up
+        // our queue of futures. Propagate errors from the stream immediately.
+        while this.in_progress_queue.len() < *this.max {
+            match this.stream.as_mut().poll_next(cx)? {
+                Poll::Ready(Some(fut)) => this.in_progress_queue.push(fut.into_future()),
+                Poll::Ready(None) | Poll::Pending => break,
+            }
+        }
+
+        // Attempt to pull the next value from the in_progress_queue
+        match this.in_progress_queue.poll_next_unpin(cx) {
+            x @ Poll::Pending | x @ Poll::Ready(Some(_)) => return x,
+            Poll::Ready(None) => {}
+        }
+
+        // If more values are still coming from the stream, we're not done yet
+        if this.stream.is_done() {
+            Poll::Ready(None)
+        } else {
+            Poll::Pending
+        }
+    }
+}
+
+// Forwarding impl of Sink from the underlying stream
+#[cfg(feature = "sink")]
+impl<S, Item, E> Sink<Item> for TryBufferUnordered<S>
+where
+    S: TryStream + Sink<Item, Error = E>,
+    S::Ok: TryFuture<Error = E>,
+{
+    type Error = E;
+
+    delegate_sink!(stream, Item);
+}
diff --git a/third_party/rust/futures-util/src/stream/try_stream/try_buffered.rs b/third_party/rust/futures-util/src/stream/try_stream/try_buffered.rs
new file mode 100644
index 0000000000..9f48e5c0a7
--- /dev/null
+++ b/third_party/rust/futures-util/src/stream/try_stream/try_buffered.rs
@@ -0,0 +1,87 @@
+use crate::future::{IntoFuture, TryFutureExt};
+use crate::stream::{Fuse, FuturesOrdered, IntoStream, StreamExt};
+use core::pin::Pin;
+use futures_core::future::TryFuture;
+use futures_core::stream::{Stream, TryStream};
+use futures_core::task::{Context, Poll};
+#[cfg(feature = "sink")]
+use futures_sink::Sink;
+use pin_project_lite::pin_project;
+
+pin_project! {
+    /// Stream for the [`try_buffered`](super::TryStreamExt::try_buffered) method.
+    #[derive(Debug)]
+    #[must_use = "streams do nothing unless polled"]
+    pub struct TryBuffered<St>
+    where
+        St: TryStream,
+        St::Ok: TryFuture,
+    {
+        #[pin]
+        stream: Fuse<IntoStream<St>>,
+        in_progress_queue: FuturesOrdered<IntoFuture<St::Ok>>,
+        max: usize,
+    }
+}
+
+impl<St> TryBuffered<St>
+where
+    St: TryStream,
+    St::Ok: TryFuture,
+{
+    pub(super) fn new(stream: St, n: usize) -> Self {
+        Self {
+            stream: IntoStream::new(stream).fuse(),
+            in_progress_queue: FuturesOrdered::new(),
+            max: n,
+        }
+    }
+
+    delegate_access_inner!(stream, St, (. .));
+}
+
+impl<St> Stream for TryBuffered<St>
+where
+    St: TryStream,
+    St::Ok: TryFuture<Error = St::Error>,
+{
+    type Item = Result<<St::Ok as TryFuture>::Ok, St::Error>;
+
+    fn poll_next(self: Pin<&mut Self>, cx: &mut Context<'_>) -> Poll<Option<Self::Item>> {
+        let mut this = self.project();
+
+        // First up, try to spawn off as many futures as possible by filling up
+        // our queue of futures. Propagate errors from the stream immediately.
+        while this.in_progress_queue.len() < *this.max {
+            match this.stream.as_mut().poll_next(cx)? {
+                Poll::Ready(Some(fut)) => this.in_progress_queue.push_back(fut.into_future()),
+                Poll::Ready(None) | Poll::Pending => break,
+            }
+        }
+
+        // Attempt to pull the next value from the in_progress_queue
+        match this.in_progress_queue.poll_next_unpin(cx) {
+            x @ Poll::Pending | x @ Poll::Ready(Some(_)) => return x,
+            Poll::Ready(None) => {}
+        }
+
+        // If more values are still coming from the stream, we're not done yet
+        if this.stream.is_done() {
+            Poll::Ready(None)
+        } else {
+            Poll::Pending
+        }
+    }
+}
+
+// Forwarding impl of Sink from the underlying stream
+#[cfg(feature = "sink")]
+impl<S, Item, E> Sink<Item> for TryBuffered<S>
+where
+    S: TryStream + Sink<Item, Error = E>,
+    S::Ok: TryFuture<Error = E>,
+{
+    type Error = E;
+
+    delegate_sink!(stream, Item);
+}
diff --git a/third_party/rust/futures-util/src/stream/try_stream/try_chunks.rs b/third_party/rust/futures-util/src/stream/try_stream/try_chunks.rs
new file mode 100644
index 0000000000..3bb253a714
--- /dev/null
+++ b/third_party/rust/futures-util/src/stream/try_stream/try_chunks.rs
@@ -0,0 +1,131 @@
+use crate::stream::{Fuse, IntoStream, StreamExt};
+
+use alloc::vec::Vec;
+use core::pin::Pin;
+use core::{fmt, mem};
+use futures_core::ready;
+use futures_core::stream::{FusedStream, Stream, TryStream};
+use futures_core::task::{Context, Poll};
+#[cfg(feature = "sink")]
+use futures_sink::Sink;
+use pin_project_lite::pin_project;
+
+pin_project! {
+    /// Stream for the [`try_chunks`](super::TryStreamExt::try_chunks) method.
+    #[derive(Debug)]
+    #[must_use = "streams do nothing unless polled"]
+    pub struct TryChunks<St: TryStream> {
+        #[pin]
+        stream: Fuse<IntoStream<St>>,
+        items: Vec<St::Ok>,
+        cap: usize, // https://github.com/rust-lang/futures-rs/issues/1475
+    }
+}
+
+impl<St: TryStream> TryChunks<St> {
+    pub(super) fn new(stream: St, capacity: usize) -> Self {
+        assert!(capacity > 0);
+
+        Self {
+            stream: IntoStream::new(stream).fuse(),
+            items: Vec::with_capacity(capacity),
+            cap: capacity,
+        }
+    }
+
+    fn take(self: Pin<&mut Self>) -> Vec<St::Ok> {
+        let cap = self.cap;
+        mem::replace(self.project().items, Vec::with_capacity(cap))
+    }
+
+    delegate_access_inner!(stream, St, (. .));
+}
+
+impl<St: TryStream> Stream for TryChunks<St> {
+    #[allow(clippy::type_complexity)]
+    type Item = Result<Vec<St::Ok>, TryChunksError<St::Ok, St::Error>>;
+
+    fn poll_next(mut self: Pin<&mut Self>, cx: &mut Context<'_>) -> Poll<Option<Self::Item>> {
+        let mut this = self.as_mut().project();
+        loop {
+            match ready!(this.stream.as_mut().try_poll_next(cx)) {
+                // Push the item into the buffer and check whether it is full.
+                // If so, replace our buffer with a new and empty one and return
+                // the full one.
+                Some(item) => match item {
+                    Ok(item) => {
+                        this.items.push(item);
+                        if this.items.len() >= *this.cap {
+                            return Poll::Ready(Some(Ok(self.take())));
+                        }
+                    }
+                    Err(e) => {
+                        return Poll::Ready(Some(Err(TryChunksError(self.take(), e))));
+                    }
+                },
+
+                // Since the underlying stream ran out of values, return what we
+                // have buffered, if we have anything.
+                None => {
+                    let last = if this.items.is_empty() {
+                        None
+                    } else {
+                        let full_buf = mem::take(this.items);
+                        Some(full_buf)
+                    };
+
+                    return Poll::Ready(last.map(Ok));
+                }
+            }
+        }
+    }
+
+    fn size_hint(&self) -> (usize, Option<usize>) {
+        let chunk_len = usize::from(!self.items.is_empty());
+        let (lower, upper) = self.stream.size_hint();
+        let lower = (lower / self.cap).saturating_add(chunk_len);
+        let upper = match upper {
+            Some(x) => x.checked_add(chunk_len),
+            None => None,
+        };
+        (lower, upper)
+    }
+}
+
+impl<St: TryStream + FusedStream> FusedStream for TryChunks<St> {
+    fn is_terminated(&self) -> bool {
+        self.stream.is_terminated() && self.items.is_empty()
+    }
+}
+
+// Forwarding impl of Sink from the underlying stream
+#[cfg(feature = "sink")]
+impl<S, Item> Sink<Item> for TryChunks<S>
+where
+    S: TryStream + Sink<Item>,
+{
+    type Error = <S as Sink<Item>>::Error;
+
+    delegate_sink!(stream, Item);
+}
+
+/// Error indicating, that while chunk was collected inner stream produced an error.
+///
+/// Contains all items that were collected before an error occurred, and the stream error itself.
+#[derive(PartialEq, Eq)]
+pub struct TryChunksError<T, E>(pub Vec<T>, pub E);
+
+impl<T, E: fmt::Debug> fmt::Debug for TryChunksError<T, E> {
+    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
+        self.1.fmt(f)
+    }
+}
+
+impl<T, E: fmt::Display> fmt::Display for TryChunksError<T, E> {
+    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
+        self.1.fmt(f)
+    }
+}
+
+#[cfg(feature = "std")]
+impl<T, E: fmt::Debug + fmt::Display> std::error::Error for TryChunksError<T, E> {}
diff --git a/third_party/rust/futures-util/src/stream/try_stream/try_collect.rs b/third_party/rust/futures-util/src/stream/try_stream/try_collect.rs
new file mode 100644
index 0000000000..3e5963f033
--- /dev/null
+++ b/third_party/rust/futures-util/src/stream/try_stream/try_collect.rs
@@ -0,0 +1,52 @@
+use core::mem;
+use core::pin::Pin;
+use futures_core::future::{FusedFuture, Future};
+use futures_core::ready;
+use futures_core::stream::{FusedStream, TryStream};
+use futures_core::task::{Context, Poll};
+use pin_project_lite::pin_project;
+
+pin_project! {
+    /// Future for the [`try_collect`](super::TryStreamExt::try_collect) method.
+    #[derive(Debug)]
+    #[must_use = "futures do nothing unless you `.await` or poll them"]
+    pub struct TryCollect<St, C> {
+        #[pin]
+        stream: St,
+        items: C,
+    }
+}
+
+impl<St: TryStream, C: Default> TryCollect<St, C> {
+    pub(super) fn new(s: St) -> Self {
+        Self { stream: s, items: Default::default() }
+    }
+}
+
+impl<St, C> FusedFuture for TryCollect<St, C>
+where
+    St: TryStream + FusedStream,
+    C: Default + Extend<St::Ok>,
+{
+    fn is_terminated(&self) -> bool {
+        self.stream.is_terminated()
+    }
+}
+
+impl<St, C> Future for TryCollect<St, C>
+where
+    St: TryStream,
+    C: Default + Extend<St::Ok>,
+{
+    type Output = Result<C, St::Error>;
+
+    fn poll(self: Pin<&mut Self>, cx: &mut Context<'_>) -> Poll<Self::Output> {
+        let mut this = self.project();
+        Poll::Ready(Ok(loop {
+            match ready!(this.stream.as_mut().try_poll_next(cx)?) {
+                Some(x) => this.items.extend(Some(x)),
+                None => break mem::take(this.items),
+            }
+        }))
+    }
+}
diff --git a/third_party/rust/futures-util/src/stream/try_stream/try_concat.rs b/third_party/rust/futures-util/src/stream/try_stream/try_concat.rs
new file mode 100644
index 0000000000..58fb6a5413
--- /dev/null
+++ b/third_party/rust/futures-util/src/stream/try_stream/try_concat.rs
@@ -0,0 +1,51 @@
+use core::pin::Pin;
+use futures_core::future::Future;
+use futures_core::ready;
+use futures_core::stream::TryStream;
+use futures_core::task::{Context, Poll};
+use pin_project_lite::pin_project;
+
+pin_project! {
+    /// Future for the [`try_concat`](super::TryStreamExt::try_concat) method.
+    #[derive(Debug)]
+    #[must_use = "futures do nothing unless you `.await` or poll them"]
+    pub struct TryConcat<St: TryStream> {
+        #[pin]
+        stream: St,
+        accum: Option<St::Ok>,
+    }
+}
+
+impl<St> TryConcat<St>
+where
+    St: TryStream,
+    St::Ok: Extend<<St::Ok as IntoIterator>::Item> + IntoIterator + Default,
+{
+    pub(super) fn new(stream: St) -> Self {
+        Self { stream, accum: None }
+    }
+}
+
+impl<St> Future for TryConcat<St>
+where
+    St: TryStream,
+    St::Ok: Extend<<St::Ok as IntoIterator>::Item> + IntoIterator + Default,
+{
+    type Output = Result<St::Ok, St::Error>;
+
+    fn poll(self: Pin<&mut Self>, cx: &mut Context<'_>) -> Poll<Self::Output> {
+        let mut this = self.project();
+
+        Poll::Ready(Ok(loop {
+            if let Some(x) = ready!(this.stream.as_mut().try_poll_next(cx)?) {
+                if let Some(a) = this.accum {
+                    a.extend(x)
+                } else {
+                    *this.accum = Some(x)
+                }
+            } else {
+                break this.accum.take().unwrap_or_default();
+            }
+        }))
+    }
+}
diff --git a/third_party/rust/futures-util/src/stream/try_stream/try_filter.rs b/third_party/rust/futures-util/src/stream/try_stream/try_filter.rs
new file mode 100644
index 0000000000..11d58243fd
--- /dev/null
+++ b/third_party/rust/futures-util/src/stream/try_stream/try_filter.rs
@@ -0,0 +1,112 @@
+use core::fmt;
+use core::pin::Pin;
+use futures_core::future::Future;
+use futures_core::ready;
+use futures_core::stream::{FusedStream, Stream, TryStream};
+use futures_core::task::{Context, Poll};
+#[cfg(feature = "sink")]
+use futures_sink::Sink;
+use pin_project_lite::pin_project;
+
+pin_project! {
+    /// Stream for the [`try_filter`](super::TryStreamExt::try_filter)
+    /// method.
+    #[must_use = "streams do nothing unless polled"]
+    pub struct TryFilter<St, Fut, F>
+        where St: TryStream
+    {
+        #[pin]
+        stream: St,
+        f: F,
+        #[pin]
+        pending_fut: Option<Fut>,
+        pending_item: Option<St::Ok>,
+    }
+}
+
+impl<St, Fut, F> fmt::Debug for TryFilter<St, Fut, F>
+where
+    St: TryStream + fmt::Debug,
+    St::Ok: fmt::Debug,
+    Fut: fmt::Debug,
+{
+    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
+        f.debug_struct("TryFilter")
+            .field("stream", &self.stream)
+            .field("pending_fut", &self.pending_fut)
+            .field("pending_item", &self.pending_item)
+            .finish()
+    }
+}
+
+impl<St, Fut, F> TryFilter<St, Fut, F>
+where
+    St: TryStream,
+{
+    pub(super) fn new(stream: St, f: F) -> Self {
+        Self { stream, f, pending_fut: None, pending_item: None }
+    }
+
+    delegate_access_inner!(stream, St, ());
+}
+
+impl<St, Fut, F> FusedStream for TryFilter<St, Fut, F>
+where
+    St: TryStream + FusedStream,
+    F: FnMut(&St::Ok) -> Fut,
+    Fut: Future<Output = bool>,
+{
+    fn is_terminated(&self) -> bool {
+        self.pending_fut.is_none() && self.stream.is_terminated()
+    }
+}
+
+impl<St, Fut, F> Stream for TryFilter<St, Fut, F>
+where
+    St: TryStream,
+    Fut: Future<Output = bool>,
+    F: FnMut(&St::Ok) -> Fut,
+{
+    type Item = Result<St::Ok, St::Error>;
+
+    fn poll_next(self: Pin<&mut Self>, cx: &mut Context<'_>) -> Poll<Option<Self::Item>> {
+        let mut this = self.project();
+
+        Poll::Ready(loop {
+            if let Some(fut) = this.pending_fut.as_mut().as_pin_mut() {
+                let res = ready!(fut.poll(cx));
+                this.pending_fut.set(None);
+                if res {
+                    break this.pending_item.take().map(Ok);
+                }
+                *this.pending_item = None;
+            } else if let Some(item) = ready!(this.stream.as_mut().try_poll_next(cx)?) {
+                this.pending_fut.set(Some((this.f)(&item)));
+                *this.pending_item = Some(item);
+            } else {
+                break None;
+            }
+        })
+    }
+
+    fn size_hint(&self) -> (usize, Option<usize>) {
+        let pending_len = usize::from(self.pending_fut.is_some());
+        let (_, upper) = self.stream.size_hint();
+        let upper = match upper {
+            Some(x) => x.checked_add(pending_len),
+            None => None,
+        };
+        (0, upper) // can't know a lower bound, due to the predicate
+    }
+}
+
+// Forwarding impl of Sink from the underlying stream
+#[cfg(feature = "sink")]
+impl<S, Fut, F, Item, E> Sink<Item> for TryFilter<S, Fut, F>
+where
+    S: TryStream + Sink<Item, Error = E>,
+{
+    type Error = E;
+
+    delegate_sink!(stream, Item);
+}
diff --git a/third_party/rust/futures-util/src/stream/try_stream/try_filter_map.rs b/third_party/rust/futures-util/src/stream/try_stream/try_filter_map.rs
new file mode 100644
index 0000000000..ed1201732b
--- /dev/null
+++ b/third_party/rust/futures-util/src/stream/try_stream/try_filter_map.rs
@@ -0,0 +1,106 @@
+use core::fmt;
+use core::pin::Pin;
+use futures_core::future::TryFuture;
+use futures_core::ready;
+use futures_core::stream::{FusedStream, Stream, TryStream};
+use futures_core::task::{Context, Poll};
+#[cfg(feature = "sink")]
+use futures_sink::Sink;
+use pin_project_lite::pin_project;
+
+pin_project! {
+    /// Stream for the [`try_filter_map`](super::TryStreamExt::try_filter_map)
+    /// method.
+    #[must_use = "streams do nothing unless polled"]
+    pub struct TryFilterMap<St, Fut, F> {
+        #[pin]
+        stream: St,
+        f: F,
+        #[pin]
+        pending: Option<Fut>,
+    }
+}
+
+impl<St, Fut, F> fmt::Debug for TryFilterMap<St, Fut, F>
+where
+    St: fmt::Debug,
+    Fut: fmt::Debug,
+{
+    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
+        f.debug_struct("TryFilterMap")
+            .field("stream", &self.stream)
+            .field("pending", &self.pending)
+            .finish()
+    }
+}
+
+impl<St, Fut, F> TryFilterMap<St, Fut, F> {
+    pub(super) fn new(stream: St, f: F) -> Self {
+        Self { stream, f, pending: None }
+    }
+
+    delegate_access_inner!(stream, St, ());
+}
+
+impl<St, Fut, F, T> FusedStream for TryFilterMap<St, Fut, F>
+where
+    St: TryStream + FusedStream,
+    Fut: TryFuture<Ok = Option<T>, Error = St::Error>,
+    F: FnMut(St::Ok) -> Fut,
+{
+    fn is_terminated(&self) -> bool {
+        self.pending.is_none() && self.stream.is_terminated()
+    }
+}
+
+impl<St, Fut, F, T> Stream for TryFilterMap<St, Fut, F>
+where
+    St: TryStream,
+    Fut: TryFuture<Ok = Option<T>, Error = St::Error>,
+    F: FnMut(St::Ok) -> Fut,
+{
+    type Item = Result<T, St::Error>;
+
+    fn poll_next(self: Pin<&mut Self>, cx: &mut Context<'_>) -> Poll<Option<Self::Item>> {
+        let mut this = self.project();
+
+        Poll::Ready(loop {
+            if let Some(p) = this.pending.as_mut().as_pin_mut() {
+                // We have an item in progress, poll that until it's done
+                let res = ready!(p.try_poll(cx));
+                this.pending.set(None);
+                let item = res?;
+                if item.is_some() {
+                    break item.map(Ok);
+                }
+            } else if let Some(item) = ready!(this.stream.as_mut().try_poll_next(cx)?) {
+                // No item in progress, but the stream is still going
+                this.pending.set(Some((this.f)(item)));
+            } else {
+                // The stream is done
+                break None;
+            }
+        })
+    }
+
+    fn size_hint(&self) -> (usize, Option<usize>) {
+        let pending_len = usize::from(self.pending.is_some());
+        let (_, upper) = self.stream.size_hint();
+        let upper = match upper {
+            Some(x) => x.checked_add(pending_len),
+            None => None,
+        };
+        (0, upper) // can't know a lower bound, due to the predicate
+    }
+}
+
+// Forwarding impl of Sink from the underlying stream
+#[cfg(feature = "sink")]
+impl<S, Fut, F, Item> Sink<Item> for TryFilterMap<S, Fut, F>
+where
+    S: Sink<Item>,
+{
+    type Error = S::Error;
+
+    delegate_sink!(stream, Item);
+}
diff --git a/third_party/rust/futures-util/src/stream/try_stream/try_flatten.rs b/third_party/rust/futures-util/src/stream/try_stream/try_flatten.rs
new file mode 100644
index 0000000000..4fc04a07bb
--- /dev/null
+++ b/third_party/rust/futures-util/src/stream/try_stream/try_flatten.rs
@@ -0,0 +1,84 @@
+use core::pin::Pin;
+use futures_core::ready;
+use futures_core::stream::{FusedStream, Stream, TryStream};
+use futures_core::task::{Context, Poll};
+#[cfg(feature = "sink")]
+use futures_sink::Sink;
+use pin_project_lite::pin_project;
+
+pin_project! {
+    /// Stream for the [`try_flatten`](super::TryStreamExt::try_flatten) method.
+    #[derive(Debug)]
+    #[must_use = "streams do nothing unless polled"]
+    pub struct TryFlatten<St>
+    where
+        St: TryStream,
+    {
+        #[pin]
+        stream: St,
+        #[pin]
+        next: Option<St::Ok>,
+    }
+}
+
+impl<St> TryFlatten<St>
+where
+    St: TryStream,
+    St::Ok: TryStream,
+    <St::Ok as TryStream>::Error: From<St::Error>,
+{
+    pub(super) fn new(stream: St) -> Self {
+        Self { stream, next: None }
+    }
+
+    delegate_access_inner!(stream, St, ());
+}
+
+impl<St> FusedStream for TryFlatten<St>
+where
+    St: TryStream + FusedStream,
+    St::Ok: TryStream,
+    <St::Ok as TryStream>::Error: From<St::Error>,
+{
+    fn is_terminated(&self) -> bool {
+        self.next.is_none() && self.stream.is_terminated()
+    }
+}
+
+impl<St> Stream for TryFlatten<St>
+where
+    St: TryStream,
+    St::Ok: TryStream,
+    <St::Ok as TryStream>::Error: From<St::Error>,
+{
+    type Item = Result<<St::Ok as TryStream>::Ok, <St::Ok as TryStream>::Error>;
+
+    fn poll_next(self: Pin<&mut Self>, cx: &mut Context<'_>) -> Poll<Option<Self::Item>> {
+        let mut this = self.project();
+
+        Poll::Ready(loop {
+            if let Some(s) = this.next.as_mut().as_pin_mut() {
+                if let Some(item) = ready!(s.try_poll_next(cx)?) {
+                    break Some(Ok(item));
+                } else {
+                    this.next.set(None);
+                }
+            } else if let Some(s) = ready!(this.stream.as_mut().try_poll_next(cx)?) {
+                this.next.set(Some(s));
+            } else {
+                break None;
+            }
+        })
+    }
+}
+
+// Forwarding impl of Sink from the underlying stream
+#[cfg(feature = "sink")]
+impl<S, Item> Sink<Item> for TryFlatten<S>
+where
+    S: TryStream + Sink<Item>,
+{
+    type Error = <S as Sink<Item>>::Error;
+
+    delegate_sink!(stream, Item);
+}
diff --git a/third_party/rust/futures-util/src/stream/try_stream/try_fold.rs b/third_party/rust/futures-util/src/stream/try_stream/try_fold.rs
new file mode 100644
index 0000000000..d344d96e7d
--- /dev/null
+++ b/third_party/rust/futures-util/src/stream/try_stream/try_fold.rs
@@ -0,0 +1,93 @@
+use core::fmt;
+use core::pin::Pin;
+use futures_core::future::{FusedFuture, Future, TryFuture};
+use futures_core::ready;
+use futures_core::stream::TryStream;
+use futures_core::task::{Context, Poll};
+use pin_project_lite::pin_project;
+
+pin_project! {
+    /// Future for the [`try_fold`](super::TryStreamExt::try_fold) method.
+    #[must_use = "futures do nothing unless you `.await` or poll them"]
+    pub struct TryFold<St, Fut, T, F> {
+        #[pin]
+        stream: St,
+        f: F,
+        accum: Option<T>,
+        #[pin]
+        future: Option<Fut>,
+    }
+}
+
+impl<St, Fut, T, F> fmt::Debug for TryFold<St, Fut, T, F>
+where
+    St: fmt::Debug,
+    Fut: fmt::Debug,
+    T: fmt::Debug,
+{
+    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
+        f.debug_struct("TryFold")
+            .field("stream", &self.stream)
+            .field("accum", &self.accum)
+            .field("future", &self.future)
+            .finish()
+    }
+}
+
+impl<St, Fut, T, F> TryFold<St, Fut, T, F>
+where
+    St: TryStream,
+    F: FnMut(T, St::Ok) -> Fut,
+    Fut: TryFuture<Ok = T, Error = St::Error>,
+{
+    pub(super) fn new(stream: St, f: F, t: T) -> Self {
+        Self { stream, f, accum: Some(t), future: None }
+    }
+}
+
+impl<St, Fut, T, F> FusedFuture for TryFold<St, Fut, T, F>
+where
+    St: TryStream,
+    F: FnMut(T, St::Ok) -> Fut,
+    Fut: TryFuture<Ok = T, Error = St::Error>,
+{
+    fn is_terminated(&self) -> bool {
+        self.accum.is_none() && self.future.is_none()
+    }
+}
+
+impl<St, Fut, T, F> Future for TryFold<St, Fut, T, F>
+where
+    St: TryStream,
+    F: FnMut(T, St::Ok) -> Fut,
+    Fut: TryFuture<Ok = T, Error = St::Error>,
+{
+    type Output = Result<T, St::Error>;
+
+    fn poll(self: Pin<&mut Self>, cx: &mut Context<'_>) -> Poll<Self::Output> {
+        let mut this = self.project();
+
+        Poll::Ready(loop {
+            if let Some(fut) = this.future.as_mut().as_pin_mut() {
+                // we're currently processing a future to produce a new accum value
+                let res = ready!(fut.try_poll(cx));
+                this.future.set(None);
+                match res {
+                    Ok(a) => *this.accum = Some(a),
+                    Err(e) => break Err(e),
+                }
+            } else if this.accum.is_some() {
+                // we're waiting on a new item from the stream
+                let res = ready!(this.stream.as_mut().try_poll_next(cx));
+                let a = this.accum.take().unwrap();
+                match res {
+                    Some(Ok(item)) => this.future.set(Some((this.f)(a, item))),
+                    Some(Err(e)) => break Err(e),
+                    None => break Ok(a),
+                }
+            } else {
+                panic!("Fold polled after completion")
+            }
+        })
+    }
+}
diff --git a/third_party/rust/futures-util/src/stream/try_stream/try_for_each.rs b/third_party/rust/futures-util/src/stream/try_stream/try_for_each.rs
new file mode 100644
index 0000000000..6a081d84e7
--- /dev/null
+++ b/third_party/rust/futures-util/src/stream/try_stream/try_for_each.rs
@@ -0,0 +1,68 @@
+use core::fmt;
+use core::pin::Pin;
+use futures_core::future::{Future, TryFuture};
+use futures_core::ready;
+use futures_core::stream::TryStream;
+use futures_core::task::{Context, Poll};
+use pin_project_lite::pin_project;
+
+pin_project! {
+    /// Future for the [`try_for_each`](super::TryStreamExt::try_for_each) method.
+    #[must_use = "futures do nothing unless you `.await` or poll them"]
+    pub struct TryForEach<St, Fut, F> {
+        #[pin]
+        stream: St,
+        f: F,
+        #[pin]
+        future: Option<Fut>,
+    }
+}
+
+impl<St, Fut, F> fmt::Debug for TryForEach<St, Fut, F>
+where
+    St: fmt::Debug,
+    Fut: fmt::Debug,
+{
+    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
+        f.debug_struct("TryForEach")
+            .field("stream", &self.stream)
+            .field("future", &self.future)
+            .finish()
+    }
+}
+
+impl<St, Fut, F> TryForEach<St, Fut, F>
+where
+    St: TryStream,
+    F: FnMut(St::Ok) -> Fut,
+    Fut: TryFuture<Ok = (), Error = St::Error>,
+{
+    pub(super) fn new(stream: St, f: F) -> Self {
+        Self { stream, f, future: None }
+    }
+}
+
+impl<St, Fut, F> Future for TryForEach<St, Fut, F>
+where
+    St: TryStream,
+    F: FnMut(St::Ok) -> Fut,
+    Fut: TryFuture<Ok = (), Error = St::Error>,
+{
+    type Output = Result<(), St::Error>;
+
+    fn poll(self: Pin<&mut Self>, cx: &mut Context<'_>) -> Poll<Self::Output> {
+        let mut this = self.project();
+        loop {
+            if let Some(fut) = this.future.as_mut().as_pin_mut() {
+                ready!(fut.try_poll(cx))?;
+                this.future.set(None);
+            } else {
+                match ready!(this.stream.as_mut().try_poll_next(cx)?) {
+                    Some(e) => this.future.set(Some((this.f)(e))),
+                    None => break,
+                }
+            }
+        }
+        Poll::Ready(Ok(()))
+    }
+}
diff --git a/third_party/rust/futures-util/src/stream/try_stream/try_for_each_concurrent.rs b/third_party/rust/futures-util/src/stream/try_stream/try_for_each_concurrent.rs
new file mode 100644
index 0000000000..62734c746b
--- /dev/null
+++ b/third_party/rust/futures-util/src/stream/try_stream/try_for_each_concurrent.rs
@@ -0,0 +1,133 @@
+use crate::stream::{FuturesUnordered, StreamExt};
+use core::fmt;
+use core::mem;
+use core::num::NonZeroUsize;
+use core::pin::Pin;
+use futures_core::future::{FusedFuture, Future};
+use futures_core::stream::TryStream;
+use futures_core::task::{Context, Poll};
+use pin_project_lite::pin_project;
+
+pin_project! {
+    /// Future for the
+    /// [`try_for_each_concurrent`](super::TryStreamExt::try_for_each_concurrent)
+    /// method.
+    #[must_use = "futures do nothing unless you `.await` or poll them"]
+    pub struct TryForEachConcurrent<St, Fut, F> {
+        #[pin]
+        stream: Option<St>,
+        f: F,
+        futures: FuturesUnordered<Fut>,
+        limit: Option<NonZeroUsize>,
+    }
+}
+
+impl<St, Fut, F> fmt::Debug for TryForEachConcurrent<St, Fut, F>
+where
+    St: fmt::Debug,
+    Fut: fmt::Debug,
+{
+    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
+        f.debug_struct("TryForEachConcurrent")
+            .field("stream", &self.stream)
+            .field("futures", &self.futures)
+            .field("limit", &self.limit)
+            .finish()
+    }
+}
+
+impl<St, Fut, F> FusedFuture for TryForEachConcurrent<St, Fut, F>
+where
+    St: TryStream,
+    F: FnMut(St::Ok) -> Fut,
+    Fut: Future<Output = Result<(), St::Error>>,
+{
+    fn is_terminated(&self) -> bool {
+        self.stream.is_none() && self.futures.is_empty()
+    }
+}
+
+impl<St, Fut, F> TryForEachConcurrent<St, Fut, F>
+where
+    St: TryStream,
+    F: FnMut(St::Ok) -> Fut,
+    Fut: Future<Output = Result<(), St::Error>>,
+{
+    pub(super) fn new(stream: St, limit: Option<usize>, f: F) -> Self {
+        Self {
+            stream: Some(stream),
+            // Note: `limit` = 0 gets ignored.
+            limit: limit.and_then(NonZeroUsize::new),
+            f,
+            futures: FuturesUnordered::new(),
+        }
+    }
+}
+
+impl<St, Fut, F> Future for TryForEachConcurrent<St, Fut, F>
+where
+    St: TryStream,
+    F: FnMut(St::Ok) -> Fut,
+    Fut: Future<Output = Result<(), St::Error>>,
+{
+    type Output = Result<(), St::Error>;
+
+    fn poll(self: Pin<&mut Self>, cx: &mut Context<'_>) -> Poll<Self::Output> {
+        let mut this = self.project();
+        loop {
+            let mut made_progress_this_iter = false;
+
+            // Check if we've already created a number of futures greater than `limit`
+            if this.limit.map(|limit| limit.get() > this.futures.len()).unwrap_or(true) {
+                let poll_res = match this.stream.as_mut().as_pin_mut() {
+                    Some(stream) => stream.try_poll_next(cx),
+                    None => Poll::Ready(None),
+                };
+
+                let elem = match poll_res {
+                    Poll::Ready(Some(Ok(elem))) => {
+                        made_progress_this_iter = true;
+                        Some(elem)
+                    }
+                    Poll::Ready(None) => {
+                        this.stream.set(None);
+                        None
+                    }
+                    Poll::Pending => None,
+                    Poll::Ready(Some(Err(e))) => {
+                        // Empty the stream and futures so that we know
+                        // the future has completed.
+                        this.stream.set(None);
+                        drop(mem::replace(this.futures, FuturesUnordered::new()));
+                        return Poll::Ready(Err(e));
+                    }
+                };
+
+                if let Some(elem) = elem {
+                    this.futures.push((this.f)(elem));
+                }
+            }
+
+            match this.futures.poll_next_unpin(cx) {
+                Poll::Ready(Some(Ok(()))) => made_progress_this_iter = true,
+                Poll::Ready(None) => {
+                    if this.stream.is_none() {
+                        return Poll::Ready(Ok(()));
+                    }
+                }
+                Poll::Pending => {}
+                Poll::Ready(Some(Err(e))) => {
+                    // Empty the stream and futures so that we know
+                    // the future has completed.
+                    this.stream.set(None);
+                    drop(mem::replace(this.futures, FuturesUnordered::new()));
+                    return Poll::Ready(Err(e));
+                }
+            }
+
+            if !made_progress_this_iter {
+                return Poll::Pending;
+            }
+        }
+    }
+}
diff --git a/third_party/rust/futures-util/src/stream/try_stream/try_next.rs b/third_party/rust/futures-util/src/stream/try_stream/try_next.rs
new file mode 100644
index 0000000000..13fcf80cae
--- /dev/null
+++ b/third_party/rust/futures-util/src/stream/try_stream/try_next.rs
@@ -0,0 +1,34 @@
+use crate::stream::TryStreamExt;
+use core::pin::Pin;
+use futures_core::future::{FusedFuture, Future};
+use futures_core::stream::{FusedStream, TryStream};
+use futures_core::task::{Context, Poll};
+
+/// Future for the [`try_next`](super::TryStreamExt::try_next) method.
+#[derive(Debug)]
+#[must_use = "futures do nothing unless you `.await` or poll them"]
+pub struct TryNext<'a, St: ?Sized> {
+    stream: &'a mut St,
+}
+
+impl<St: ?Sized + Unpin> Unpin for TryNext<'_, St> {}
+
+impl<'a, St: ?Sized + TryStream + Unpin> TryNext<'a, St> {
+    pub(super) fn new(stream: &'a mut St) -> Self {
+        Self { stream }
+    }
+}
+
+impl<St: ?Sized + TryStream + Unpin + FusedStream> FusedFuture for TryNext<'_, St> {
+    fn is_terminated(&self) -> bool {
+        self.stream.is_terminated()
+    }
+}
+
+impl<St: ?Sized + TryStream + Unpin> Future for TryNext<'_, St> {
+    type Output = Result<Option<St::Ok>, St::Error>;
+
+    fn poll(mut self: Pin<&mut Self>, cx: &mut Context<'_>) -> Poll<Self::Output> {
+        self.stream.try_poll_next_unpin(cx)?.map(Ok)
+    }
+}
diff --git a/third_party/rust/futures-util/src/stream/try_stream/try_skip_while.rs b/third_party/rust/futures-util/src/stream/try_stream/try_skip_while.rs
new file mode 100644
index 0000000000..52aa2d478b
--- /dev/null
+++ b/third_party/rust/futures-util/src/stream/try_stream/try_skip_while.rs
@@ -0,0 +1,120 @@
+use core::fmt;
+use core::pin::Pin;
+use futures_core::future::TryFuture;
+use futures_core::ready;
+use futures_core::stream::{FusedStream, Stream, TryStream};
+use futures_core::task::{Context, Poll};
+#[cfg(feature = "sink")]
+use futures_sink::Sink;
+use pin_project_lite::pin_project;
+
+pin_project! {
+    /// Stream for the [`try_skip_while`](super::TryStreamExt::try_skip_while)
+    /// method.
+    #[must_use = "streams do nothing unless polled"]
+    pub struct TrySkipWhile<St, Fut, F> where St: TryStream {
+        #[pin]
+        stream: St,
+        f: F,
+        #[pin]
+        pending_fut: Option<Fut>,
+        pending_item: Option<St::Ok>,
+        done_skipping: bool,
+    }
+}
+
+impl<St, Fut, F> fmt::Debug for TrySkipWhile<St, Fut, F>
+where
+    St: TryStream + fmt::Debug,
+    St::Ok: fmt::Debug,
+    Fut: fmt::Debug,
+{
+    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
+        f.debug_struct("TrySkipWhile")
+            .field("stream", &self.stream)
+            .field("pending_fut", &self.pending_fut)
+            .field("pending_item", &self.pending_item)
+            .field("done_skipping", &self.done_skipping)
+            .finish()
+    }
+}
+
+impl<St, Fut, F> TrySkipWhile<St, Fut, F>
+where
+    St: TryStream,
+    F: FnMut(&St::Ok) -> Fut,
+    Fut: TryFuture<Ok = bool, Error = St::Error>,
+{
+    pub(super) fn new(stream: St, f: F) -> Self {
+        Self { stream, f, pending_fut: None, pending_item: None, done_skipping: false }
+    }
+
+    delegate_access_inner!(stream, St, ());
+}
+
+impl<St, Fut, F> Stream for TrySkipWhile<St, Fut, F>
+where
+    St: TryStream,
+    F: FnMut(&St::Ok) -> Fut,
+    Fut: TryFuture<Ok = bool, Error = St::Error>,
+{
+    type Item = Result<St::Ok, St::Error>;
+
+    fn poll_next(self: Pin<&mut Self>, cx: &mut Context<'_>) -> Poll<Option<Self::Item>> {
+        let mut this = self.project();
+
+        if *this.done_skipping {
+            return this.stream.try_poll_next(cx);
+        }
+
+        Poll::Ready(loop {
+            if let Some(fut) = this.pending_fut.as_mut().as_pin_mut() {
+                let res = ready!(fut.try_poll(cx));
+                this.pending_fut.set(None);
+                let skipped = res?;
+                let item = this.pending_item.take();
+                if !skipped {
+                    *this.done_skipping = true;
+                    break item.map(Ok);
+                }
+            } else if let Some(item) = ready!(this.stream.as_mut().try_poll_next(cx)?) {
+                this.pending_fut.set(Some((this.f)(&item)));
+                *this.pending_item = Some(item);
+            } else {
+                break None;
+            }
+        })
+    }
+
+    fn size_hint(&self) -> (usize, Option<usize>) {
+        let pending_len = usize::from(self.pending_item.is_some());
+        let (_, upper) = self.stream.size_hint();
+        let upper = match upper {
+            Some(x) => x.checked_add(pending_len),
+            None => None,
+        };
+        (0, upper) // can't know a lower bound, due to the predicate
+    }
+}
+
+impl<St, Fut, F> FusedStream for TrySkipWhile<St, Fut, F>
+where
+    St: TryStream + FusedStream,
+    F: FnMut(&St::Ok) -> Fut,
+    Fut: TryFuture<Ok = bool, Error = St::Error>,
+{
+    fn is_terminated(&self) -> bool {
+        self.pending_item.is_none() && self.stream.is_terminated()
+    }
+}
+
+// Forwarding impl of Sink from the underlying stream
+#[cfg(feature = "sink")]
+impl<S, Fut, F, Item, E> Sink<Item> for TrySkipWhile<S, Fut, F>
+where
+    S: TryStream + Sink<Item, Error = E>,
+{
+    type Error = E;
+
+    delegate_sink!(stream, Item);
+}
diff --git a/third_party/rust/futures-util/src/stream/try_stream/try_take_while.rs b/third_party/rust/futures-util/src/stream/try_stream/try_take_while.rs
new file mode 100644
index 0000000000..4b5ff1ad38
--- /dev/null
+++ b/third_party/rust/futures-util/src/stream/try_stream/try_take_while.rs
@@ -0,0 +1,129 @@
+use core::fmt;
+use core::pin::Pin;
+use futures_core::future::TryFuture;
+use futures_core::ready;
+use futures_core::stream::{FusedStream, Stream, TryStream};
+use futures_core::task::{Context, Poll};
+#[cfg(feature = "sink")]
+use futures_sink::Sink;
+use pin_project_lite::pin_project;
+
+pin_project! {
+    /// Stream for the [`try_take_while`](super::TryStreamExt::try_take_while)
+    /// method.
+    #[must_use = "streams do nothing unless polled"]
+    pub struct TryTakeWhile<St, Fut, F>
+    where
+        St: TryStream,
+    {
+        #[pin]
+        stream: St,
+        f: F,
+        #[pin]
+        pending_fut: Option<Fut>,
+        pending_item: Option<St::Ok>,
+        done_taking: bool,
+    }
+}
+
+impl<St, Fut, F> fmt::Debug for TryTakeWhile<St, Fut, F>
+where
+    St: TryStream + fmt::Debug,
+    St::Ok: fmt::Debug,
+    Fut: fmt::Debug,
+{
+    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
+        f.debug_struct("TryTakeWhile")
+            .field("stream", &self.stream)
+            .field("pending_fut", &self.pending_fut)
+            .field("pending_item", &self.pending_item)
+            .field("done_taking", &self.done_taking)
+            .finish()
+    }
+}
+
+impl<St, Fut, F> TryTakeWhile<St, Fut, F>
+where
+    St: TryStream,
+    F: FnMut(&St::Ok) -> Fut,
+    Fut: TryFuture<Ok = bool, Error = St::Error>,
+{
+    pub(super) fn new(stream: St, f: F) -> Self {
+        Self { stream, f, pending_fut: None, pending_item: None, done_taking: false }
+    }
+
+    delegate_access_inner!(stream, St, ());
+}
+
+impl<St, Fut, F> Stream for TryTakeWhile<St, Fut, F>
+where
+    St: TryStream,
+    F: FnMut(&St::Ok) -> Fut,
+    Fut: TryFuture<Ok = bool, Error = St::Error>,
+{
+    type Item = Result<St::Ok, St::Error>;
+
+    fn poll_next(self: Pin<&mut Self>, cx: &mut Context<'_>) -> Poll<Option<Self::Item>> {
+        let mut this = self.project();
+
+        if *this.done_taking {
+            return Poll::Ready(None);
+        }
+
+        Poll::Ready(loop {
+            if let Some(fut) = this.pending_fut.as_mut().as_pin_mut() {
+                let res = ready!(fut.try_poll(cx));
+                this.pending_fut.set(None);
+                let take = res?;
+                let item = this.pending_item.take();
+                if take {
+                    break item.map(Ok);
+                } else {
+                    *this.done_taking = true;
+                    break None;
+                }
+            } else if let Some(item) = ready!(this.stream.as_mut().try_poll_next(cx)?) {
+                this.pending_fut.set(Some((this.f)(&item)));
+                *this.pending_item = Some(item);
+            } else {
+                break None;
+            }
+        })
+    }
+
+    fn size_hint(&self) -> (usize, Option<usize>) {
+        if self.done_taking {
+            return (0, Some(0));
+        }
+
+        let pending_len = usize::from(self.pending_item.is_some());
+        let (_, upper) = self.stream.size_hint();
+        let upper = match upper {
+            Some(x) => x.checked_add(pending_len),
+            None => None,
+        };
+        (0, upper) // can't know a lower bound, due to the predicate
+    }
+}
+
+impl<St, Fut, F> FusedStream for TryTakeWhile<St, Fut, F>
+where
+    St: TryStream + FusedStream,
+    F: FnMut(&St::Ok) -> Fut,
+    Fut: TryFuture<Ok = bool, Error = St::Error>,
+{
+    fn is_terminated(&self) -> bool {
+        self.done_taking || self.pending_item.is_none() && self.stream.is_terminated()
+    }
+}
+
+// Forwarding impl of Sink from the underlying stream
+#[cfg(feature = "sink")]
+impl<S, Fut, F, Item, E> Sink<Item> for TryTakeWhile<S, Fut, F>
+where
+    S: TryStream + Sink<Item, Error = E>,
+{
+    type Error = E;
+
+    delegate_sink!(stream, Item);
+}
diff --git a/third_party/rust/futures-util/src/stream/try_stream/try_unfold.rs b/third_party/rust/futures-util/src/stream/try_stream/try_unfold.rs
new file mode 100644
index 0000000000..fd9cdf1d8c
--- /dev/null
+++ b/third_party/rust/futures-util/src/stream/try_stream/try_unfold.rs
@@ -0,0 +1,122 @@
+use super::assert_stream;
+use core::fmt;
+use core::pin::Pin;
+use futures_core::future::TryFuture;
+use futures_core::ready;
+use futures_core::stream::Stream;
+use futures_core::task::{Context, Poll};
+use pin_project_lite::pin_project;
+
+/// Creates a `TryStream` from a seed and a closure returning a `TryFuture`.
+///
+/// This function is the dual for the `TryStream::try_fold()` adapter: while
+/// `TryStream::try_fold()` reduces a `TryStream` to one single value,
+/// `try_unfold()` creates a `TryStream` from a seed value.
+///
+/// `try_unfold()` will call the provided closure with the provided seed, then
+/// wait for the returned `TryFuture` to complete with `(a, b)`. It will then
+/// yield the value `a`, and use `b` as the next internal state.
+///
+/// If the closure returns `None` instead of `Some(TryFuture)`, then the
+/// `try_unfold()` will stop producing items and return `Poll::Ready(None)` in
+/// future calls to `poll()`.
+///
+/// In case of error generated by the returned `TryFuture`, the error will be
+/// returned by the `TryStream`. The `TryStream` will then yield
+/// `Poll::Ready(None)` in future calls to `poll()`.
+///
+/// This function can typically be used when wanting to go from the "world of
+/// futures" to the "world of streams": the provided closure can build a
+/// `TryFuture` using other library functions working on futures, and
+/// `try_unfold()` will turn it into a `TryStream` by repeating the operation.
+///
+/// # Example
+///
+/// ```
+/// # #[derive(Debug, PartialEq)]
+/// # struct SomeError;
+/// # futures::executor::block_on(async {
+/// use futures::stream::{self, TryStreamExt};
+///
+/// let stream = stream::try_unfold(0, |state| async move {
+///     if state < 0 {
+///         return Err(SomeError);
+///     }
+///
+///     if state <= 2 {
+///         let next_state = state + 1;
+///         let yielded = state * 2;
+///         Ok(Some((yielded, next_state)))
+///     } else {
+///         Ok(None)
+///     }
+/// });
+///
+/// let result: Result<Vec<i32>, _> = stream.try_collect().await;
+/// assert_eq!(result, Ok(vec![0, 2, 4]));
+/// # });
+/// ```
+pub fn try_unfold<T, F, Fut, Item>(init: T, f: F) -> TryUnfold<T, F, Fut>
+where
+    F: FnMut(T) -> Fut,
+    Fut: TryFuture<Ok = Option<(Item, T)>>,
+{
+    assert_stream::<Result<Item, Fut::Error>, _>(TryUnfold { f, state: Some(init), fut: None })
+}
+
+pin_project! {
+    /// Stream for the [`try_unfold`] function.
+    #[must_use = "streams do nothing unless polled"]
+    pub struct TryUnfold<T, F, Fut> {
+        f: F,
+        state: Option<T>,
+        #[pin]
+        fut: Option<Fut>,
+    }
+}
+
+impl<T, F, Fut> fmt::Debug for TryUnfold<T, F, Fut>
+where
+    T: fmt::Debug,
+    Fut: fmt::Debug,
+{
+    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
+        f.debug_struct("TryUnfold").field("state", &self.state).field("fut", &self.fut).finish()
+    }
+}
+
+impl<T, F, Fut, Item> Stream for TryUnfold<T, F, Fut>
+where
+    F: FnMut(T) -> Fut,
+    Fut: TryFuture<Ok = Option<(Item, T)>>,
+{
+    type Item = Result<Item, Fut::Error>;
+
+    fn poll_next(self: Pin<&mut Self>, cx: &mut Context<'_>) -> Poll<Option<Self::Item>> {
+        let mut this = self.project();
+
+        if let Some(state) = this.state.take() {
+            this.fut.set(Some((this.f)(state)));
+        }
+
+        match this.fut.as_mut().as_pin_mut() {
+            None => {
+                // The future previously errored
+                Poll::Ready(None)
+            }
+            Some(future) => {
+                let step = ready!(future.try_poll(cx));
+                this.fut.set(None);
+
+                match step {
+                    Ok(Some((item, next_state))) => {
+                        *this.state = Some(next_state);
+                        Poll::Ready(Some(Ok(item)))
+                    }
+                    Ok(None) => Poll::Ready(None),
+                    Err(e) => Poll::Ready(Some(Err(e))),
+                }
+            }
+        }
+    }
+}
diff --git a/third_party/rust/futures-util/src/stream/unfold.rs b/third_party/rust/futures-util/src/stream/unfold.rs
new file mode 100644
index 0000000000..7d8ef6babc
--- /dev/null
+++ b/third_party/rust/futures-util/src/stream/unfold.rs
@@ -0,0 +1,119 @@
+use super::assert_stream;
+use crate::unfold_state::UnfoldState;
+use core::fmt;
+use core::pin::Pin;
+use futures_core::future::Future;
+use futures_core::ready;
+use futures_core::stream::{FusedStream, Stream};
+use futures_core::task::{Context, Poll};
+use pin_project_lite::pin_project;
+
+/// Creates a `Stream` from a seed and a closure returning a `Future`.
+///
+/// This function is the dual for the `Stream::fold()` adapter: while
+/// `Stream::fold()` reduces a `Stream` to one single value, `unfold()` creates a
+/// `Stream` from a seed value.
+///
+/// `unfold()` will call the provided closure with the provided seed, then wait
+/// for the returned `Future` to complete with `(a, b)`. It will then yield the
+/// value `a`, and use `b` as the next internal state.
+///
+/// If the closure returns `None` instead of `Some(Future)`, then the `unfold()`
+/// will stop producing items and return `Poll::Ready(None)` in future
+/// calls to `poll()`.
+///
+/// This function can typically be used when wanting to go from the "world of
+/// futures" to the "world of streams": the provided closure can build a
+/// `Future` using other library functions working on futures, and `unfold()`
+/// will turn it into a `Stream` by repeating the operation.
+///
+/// # Example
+///
+/// ```
+/// # futures::executor::block_on(async {
+/// use futures::stream::{self, StreamExt};
+///
+/// let stream = stream::unfold(0, |state| async move {
+///     if state <= 2 {
+///         let next_state = state + 1;
+///         let yielded = state  * 2;
+///         Some((yielded, next_state))
+///     } else {
+///         None
+///     }
+/// });
+///
+/// let result = stream.collect::<Vec<i32>>().await;
+/// assert_eq!(result, vec![0, 2, 4]);
+/// # });
+/// ```
+pub fn unfold<T, F, Fut, Item>(init: T, f: F) -> Unfold<T, F, Fut>
+where
+    F: FnMut(T) -> Fut,
+    Fut: Future<Output = Option<(Item, T)>>,
+{
+    assert_stream::<Item, _>(Unfold { f, state: UnfoldState::Value { value: init } })
+}
+
+pin_project! {
+    /// Stream for the [`unfold`] function.
+    #[must_use = "streams do nothing unless polled"]
+    pub struct Unfold<T, F, Fut> {
+        f: F,
+        #[pin]
+        state: UnfoldState<T, Fut>,
+    }
+}
+
+impl<T, F, Fut> fmt::Debug for Unfold<T, F, Fut>
+where
+    T: fmt::Debug,
+    Fut: fmt::Debug,
+{
+    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
+        f.debug_struct("Unfold").field("state", &self.state).finish()
+    }
+}
+
+impl<T, F, Fut, Item> FusedStream for Unfold<T, F, Fut>
+where
+    F: FnMut(T) -> Fut,
+    Fut: Future<Output = Option<(Item, T)>>,
+{
+    fn is_terminated(&self) -> bool {
+        if let UnfoldState::Empty = self.state {
+            true
+        } else {
+            false
+        }
+    }
+}
+
+impl<T, F, Fut, Item> Stream for Unfold<T, F, Fut>
+where
+    F: FnMut(T) -> Fut,
+    Fut: Future<Output = Option<(Item, T)>>,
+{
+    type Item = Item;
+
+    fn poll_next(self: Pin<&mut Self>, cx: &mut Context<'_>) -> Poll<Option<Self::Item>> {
+        let mut this = self.project();
+
+        if let Some(state) = this.state.as_mut().take_value() {
+            this.state.set(UnfoldState::Future { future: (this.f)(state) });
+        }
+
+        let step = match this.state.as_mut().project_future() {
+            Some(fut) => ready!(fut.poll(cx)),
+            None => panic!("Unfold must not be polled after it returned `Poll::Ready(None)`"),
+        };
+
+        if let Some((item, next_state)) = step {
+            this.state.set(UnfoldState::Value { value: next_state });
+            Poll::Ready(Some(item))
+        } else {
+            this.state.set(UnfoldState::Empty);
+            Poll::Ready(None)
+        }
+    }
+}
diff --git a/third_party/rust/futures-util/src/task/mod.rs b/third_party/rust/futures-util/src/task/mod.rs
new file mode 100644
index 0000000000..0a31eeac14
--- /dev/null
+++ b/third_party/rust/futures-util/src/task/mod.rs
@@ -0,0 +1,37 @@
+//! Tools for working with tasks.
+//!
+//! This module contains:
+//!
+//! - [`Spawn`], a trait for spawning new tasks.
+//! - [`Context`], a context of an asynchronous task,
+//!   including a handle for waking up the task.
+//! - [`Waker`], a handle for waking up a task.
+//!
+//! The remaining types and traits in the module are used for implementing
+//! executors or dealing with synchronization issues around task wakeup.
+
+#[doc(no_inline)]
+pub use core::task::{Context, Poll, RawWaker, RawWakerVTable, Waker};
+
+pub use futures_task::{FutureObj, LocalFutureObj, LocalSpawn, Spawn, SpawnError, UnsafeFutureObj};
+
+pub use futures_task::noop_waker;
+pub use futures_task::noop_waker_ref;
+
+#[cfg(not(futures_no_atomic_cas))]
+#[cfg(feature = "alloc")]
+pub use futures_task::ArcWake;
+
+#[cfg(not(futures_no_atomic_cas))]
+#[cfg(feature = "alloc")]
+pub use futures_task::waker;
+
+#[cfg(not(futures_no_atomic_cas))]
+#[cfg(feature = "alloc")]
+pub use futures_task::{waker_ref, WakerRef};
+
+#[cfg(not(futures_no_atomic_cas))]
+pub use futures_core::task::__internal::AtomicWaker;
+
+mod spawn;
+pub use self::spawn::{LocalSpawnExt, SpawnExt};
diff --git a/third_party/rust/futures-util/src/task/spawn.rs b/third_party/rust/futures-util/src/task/spawn.rs
new file mode 100644
index 0000000000..d9e9985309
--- /dev/null
+++ b/third_party/rust/futures-util/src/task/spawn.rs
@@ -0,0 +1,169 @@
+use futures_task::{LocalSpawn, Spawn};
+
+#[cfg(feature = "compat")]
+use crate::compat::Compat;
+
+#[cfg(feature = "channel")]
+#[cfg(feature = "std")]
+use crate::future::{FutureExt, RemoteHandle};
+#[cfg(feature = "alloc")]
+use alloc::boxed::Box;
+#[cfg(feature = "alloc")]
+use futures_core::future::Future;
+#[cfg(feature = "alloc")]
+use futures_task::{FutureObj, LocalFutureObj, SpawnError};
+
+impl<Sp: ?Sized> SpawnExt for Sp where Sp: Spawn {}
+impl<Sp: ?Sized> LocalSpawnExt for Sp where Sp: LocalSpawn {}
+
+/// Extension trait for `Spawn`.
+pub trait SpawnExt: Spawn {
+    /// Spawns a task that polls the given future with output `()` to
+    /// completion.
+    ///
+    /// This method returns a [`Result`] that contains a [`SpawnError`] if
+    /// spawning fails.
+    ///
+    /// You can use [`spawn_with_handle`](SpawnExt::spawn_with_handle) if
+    /// you want to spawn a future with output other than `()` or if you want
+    /// to be able to await its completion.
+    ///
+    /// Note this method will eventually be replaced with the upcoming
+    /// `Spawn::spawn` method which will take a `dyn Future` as input.
+    /// Technical limitations prevent `Spawn::spawn` from being implemented
+    /// today. Feel free to use this method in the meantime.
+    ///
+    /// ```
+    /// # {
+    /// use futures::executor::ThreadPool;
+    /// use futures::task::SpawnExt;
+    ///
+    /// let executor = ThreadPool::new().unwrap();
+    ///
+    /// let future = async { /* ... */ };
+    /// executor.spawn(future).unwrap();
+    /// # }
+    /// # std::thread::sleep(std::time::Duration::from_millis(500)); // wait for background threads closed: https://github.com/rust-lang/miri/issues/1371
+    /// ```
+    #[cfg(feature = "alloc")]
+    fn spawn<Fut>(&self, future: Fut) -> Result<(), SpawnError>
+    where
+        Fut: Future<Output = ()> + Send + 'static,
+    {
+        self.spawn_obj(FutureObj::new(Box::new(future)))
+    }
+
+    /// Spawns a task that polls the given future to completion and returns a
+    /// future that resolves to the spawned future's output.
+    ///
+    /// This method returns a [`Result`] that contains a [`RemoteHandle`](crate::future::RemoteHandle), or, if
+    /// spawning fails, a [`SpawnError`]. [`RemoteHandle`](crate::future::RemoteHandle) is a future that
+    /// resolves to the output of the spawned future.
+    ///
+    /// ```
+    /// # {
+    /// use futures::executor::{block_on, ThreadPool};
+    /// use futures::future;
+    /// use futures::task::SpawnExt;
+    ///
+    /// let executor = ThreadPool::new().unwrap();
+    ///
+    /// let future = future::ready(1);
+    /// let join_handle_fut = executor.spawn_with_handle(future).unwrap();
+    /// assert_eq!(block_on(join_handle_fut), 1);
+    /// # }
+    /// # std::thread::sleep(std::time::Duration::from_millis(500)); // wait for background threads closed: https://github.com/rust-lang/miri/issues/1371
+    /// ```
+    #[cfg(feature = "channel")]
+    #[cfg_attr(docsrs, doc(cfg(feature = "channel")))]
+    #[cfg(feature = "std")]
+    fn spawn_with_handle<Fut>(&self, future: Fut) -> Result<RemoteHandle<Fut::Output>, SpawnError>
+    where
+        Fut: Future + Send + 'static,
+        Fut::Output: Send,
+    {
+        let (future, handle) = future.remote_handle();
+        self.spawn(future)?;
+        Ok(handle)
+    }
+
+    /// Wraps a [`Spawn`] and makes it usable as a futures 0.1 `Executor`.
+    /// Requires the `compat` feature to enable.
+    #[cfg(feature = "compat")]
+    #[cfg_attr(docsrs, doc(cfg(feature = "compat")))]
+    fn compat(self) -> Compat<Self>
+    where
+        Self: Sized,
+    {
+        Compat::new(self)
+    }
+}
+
+/// Extension trait for `LocalSpawn`.
+pub trait LocalSpawnExt: LocalSpawn {
+    /// Spawns a task that polls the given future with output `()` to
+    /// completion.
+    ///
+    /// This method returns a [`Result`] that contains a [`SpawnError`] if
+    /// spawning fails.
+    ///
+    /// You can use [`spawn_with_handle`](SpawnExt::spawn_with_handle) if
+    /// you want to spawn a future with output other than `()` or if you want
+    /// to be able to await its completion.
+    ///
+    /// Note this method will eventually be replaced with the upcoming
+    /// `Spawn::spawn` method which will take a `dyn Future` as input.
+    /// Technical limitations prevent `Spawn::spawn` from being implemented
+    /// today. Feel free to use this method in the meantime.
+    ///
+    /// ```
+    /// use futures::executor::LocalPool;
+    /// use futures::task::LocalSpawnExt;
+    ///
+    /// let executor = LocalPool::new();
+    /// let spawner = executor.spawner();
+    ///
+    /// let future = async { /* ... */ };
+    /// spawner.spawn_local(future).unwrap();
+    /// ```
+    #[cfg(feature = "alloc")]
+    fn spawn_local<Fut>(&self, future: Fut) -> Result<(), SpawnError>
+    where
+        Fut: Future<Output = ()> + 'static,
+    {
+        self.spawn_local_obj(LocalFutureObj::new(Box::new(future)))
+    }
+
+    /// Spawns a task that polls the given future to completion and returns a
+    /// future that resolves to the spawned future's output.
+    ///
+    /// This method returns a [`Result`] that contains a [`RemoteHandle`](crate::future::RemoteHandle), or, if
+    /// spawning fails, a [`SpawnError`]. [`RemoteHandle`](crate::future::RemoteHandle) is a future that
+    /// resolves to the output of the spawned future.
+    ///
+    /// ```
+    /// use futures::executor::LocalPool;
+    /// use futures::task::LocalSpawnExt;
+    ///
+    /// let mut executor = LocalPool::new();
+    /// let spawner = executor.spawner();
+    ///
+    /// let future = async { 1 };
+    /// let join_handle_fut = spawner.spawn_local_with_handle(future).unwrap();
+    /// assert_eq!(executor.run_until(join_handle_fut), 1);
+    /// ```
+    #[cfg(feature = "channel")]
+    #[cfg_attr(docsrs, doc(cfg(feature = "channel")))]
+    #[cfg(feature = "std")]
+    fn spawn_local_with_handle<Fut>(
+        &self,
+        future: Fut,
+    ) -> Result<RemoteHandle<Fut::Output>, SpawnError>
+    where
+        Fut: Future + 'static,
+    {
+        let (future, handle) = future.remote_handle();
+        self.spawn_local(future)?;
+        Ok(handle)
+    }
+}
diff --git a/third_party/rust/futures-util/src/unfold_state.rs b/third_party/rust/futures-util/src/unfold_state.rs
new file mode 100644
index 0000000000..0edc15e437
--- /dev/null
+++ b/third_party/rust/futures-util/src/unfold_state.rs
@@ -0,0 +1,39 @@
+use core::pin::Pin;
+
+use pin_project_lite::pin_project;
+
+pin_project! {
+    /// UnfoldState used for stream and sink unfolds
+    #[project = UnfoldStateProj]
+    #[project_replace = UnfoldStateProjReplace]
+    #[derive(Debug)]
+    pub(crate) enum UnfoldState<T, R> {
+        Value {
+            value: T,
+        },
+        Future {
+            #[pin]
+            future: R,
+        },
+        Empty,
+    }
+}
+
+impl<T, R> UnfoldState<T, R> {
+    pub(crate) fn project_future(self: Pin<&mut Self>) -> Option<Pin<&mut R>> {
+        match self.project() {
+            UnfoldStateProj::Future { future } => Some(future),
+            _ => None,
+        }
+    }
+
+    pub(crate) fn take_value(self: Pin<&mut Self>) -> Option<T> {
+        match &*self {
+            UnfoldState::Value { .. } => match self.project_replace(UnfoldState::Empty) {
+                UnfoldStateProjReplace::Value { value } => Some(value),
+                _ => unreachable!(),
+            },
+            _ => None,
+        }
+    }
+}