1 files changed, 166 insertions, 0 deletions
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..64bbdec87a
--- /dev/null
+++ b/third_party/rust/futures-util/src/io/chain.rs
@@ -0,0 +1,166 @@
+use futures_core::task::{Context, Poll};
+#[cfg(feature = "read-initializer")]
+use futures_io::Initializer;
+use futures_io::{AsyncBufRead, AsyncRead, IoSliceMut};
+use pin_utils::{unsafe_pinned, unsafe_unpinned};
+use std::fmt;
+use std::io;
+use std::pin::Pin;
+
+/// Reader for the [`chain`](super::AsyncReadExt::chain) method.
+#[must_use = "readers do nothing unless polled"]
+pub struct Chain<T, U> {
+    first: T,
+    second: U,
+    done_first: bool,
+}
+
+impl<T, U> Unpin for Chain<T, U>
+where
+    T: Unpin,
+    U: Unpin,
+{
+}
+
+impl<T, U> Chain<T, U>
+where
+    T: AsyncRead,
+    U: AsyncRead,
+{
+    unsafe_pinned!(first: T);
+    unsafe_pinned!(second: U);
+    unsafe_unpinned!(done_first: bool);
+
+    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>) {
+        unsafe {
+            let Self { first, second, .. } = self.get_unchecked_mut();
+            (Pin::new_unchecked(first), Pin::new_unchecked(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(
+        mut self: Pin<&mut Self>,
+        cx: &mut Context<'_>,
+        buf: &mut [u8],
+    ) -> Poll<io::Result<usize>> {
+        if !self.done_first {
+            match ready!(self.as_mut().first().poll_read(cx, buf)?) {
+                0 if !buf.is_empty() => *self.as_mut().done_first() = true,
+                n => return Poll::Ready(Ok(n)),
+            }
+        }
+        self.second().poll_read(cx, buf)
+    }
+
+    fn poll_read_vectored(
+        mut self: Pin<&mut Self>,
+        cx: &mut Context<'_>,
+        bufs: &mut [IoSliceMut<'_>],
+    ) -> Poll<io::Result<usize>> {
+        if !self.done_first {
+            let n = ready!(self.as_mut().first().poll_read_vectored(cx, bufs)?);
+            if n == 0 && bufs.iter().any(|b| !b.is_empty()) {
+                *self.as_mut().done_first() = true
+            } else {
+                return Poll::Ready(Ok(n));
+            }
+        }
+        self.second().poll_read_vectored(cx, bufs)
+    }
+
+    #[cfg(feature = "read-initializer")]
+    unsafe fn initializer(&self) -> Initializer {
+        let initializer = self.first.initializer();
+        if initializer.should_initialize() {
+            initializer
+        } else {
+            self.second.initializer()
+        }
+    }
+}
+
+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 Self {
+            first,
+            second,
+            done_first,
+        } = unsafe { self.get_unchecked_mut() };
+        let first = unsafe { Pin::new_unchecked(first) };
+        let second = unsafe { Pin::new_unchecked(second) };
+
+        if !*done_first {
+            match ready!(first.poll_fill_buf(cx)?) {
+                buf if buf.is_empty() => {
+                    *done_first = true;
+                }
+                buf => return Poll::Ready(Ok(buf)),
+            }
+        }
+        second.poll_fill_buf(cx)
+    }
+
+    fn consume(self: Pin<&mut Self>, amt: usize) {
+        if !self.done_first {
+            self.first().consume(amt)
+        } else {
+            self.second().consume(amt)
+        }
+    }
+}