1 files changed, 115 insertions, 0 deletions
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> {}