1 files changed, 82 insertions, 0 deletions
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(()))
+    }
+}