1 files changed, 118 insertions, 0 deletions
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..5854eb7ea5
--- /dev/null
+++ b/third_party/rust/futures-util/src/stream/stream/buffered.rs
@@ -0,0 +1,118 @@
+use crate::stream::{Fuse, FusedStream, 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)
+    }
+}
+
+impl<St> FusedStream for Buffered<St>
+where
+    St: Stream,
+    St::Item: Future,
+{
+    fn is_terminated(&self) -> bool {
+        self.stream.is_done() && self.in_progress_queue.is_terminated()
+    }
+}
+
+// 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);
+}