1 files changed, 105 insertions, 0 deletions
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)
+    }
+}