2 files changed, 158 insertions, 0 deletions
diff --git a/third_party/rust/hyper/src/common/io/mod.rs b/third_party/rust/hyper/src/common/io/mod.rs
new file mode 100644
index 0000000000..2e6d506153
--- /dev/null
+++ b/third_party/rust/hyper/src/common/io/mod.rs
@@ -0,0 +1,3 @@
+mod rewind;
+
+pub(crate) use self::rewind::Rewind;
diff --git a/third_party/rust/hyper/src/common/io/rewind.rs b/third_party/rust/hyper/src/common/io/rewind.rs
new file mode 100644
index 0000000000..0afef5f7ea
--- /dev/null
+++ b/third_party/rust/hyper/src/common/io/rewind.rs
@@ -0,0 +1,155 @@
+use std::marker::Unpin;
+use std::{cmp, io};
+
+use bytes::{Buf, Bytes};
+use tokio::io::{AsyncRead, AsyncWrite, ReadBuf};
+
+use crate::common::{task, Pin, Poll};
+
+/// Combine a buffer with an IO, rewinding reads to use the buffer.
+#[derive(Debug)]
+pub(crate) struct Rewind<T> {
+    pre: Option<Bytes>,
+    inner: T,
+}
+
+impl<T> Rewind<T> {
+    #[cfg(any(all(feature = "http2", feature = "server"), test))]
+    pub(crate) fn new(io: T) -> Self {
+        Rewind {
+            pre: None,
+            inner: io,
+        }
+    }
+
+    pub(crate) fn new_buffered(io: T, buf: Bytes) -> Self {
+        Rewind {
+            pre: Some(buf),
+            inner: io,
+        }
+    }
+
+    #[cfg(any(all(feature = "http1", feature = "http2", feature = "server"), test))]
+    pub(crate) fn rewind(&mut self, bs: Bytes) {
+        debug_assert!(self.pre.is_none());
+        self.pre = Some(bs);
+    }
+
+    pub(crate) fn into_inner(self) -> (T, Bytes) {
+        (self.inner, self.pre.unwrap_or_else(Bytes::new))
+    }
+
+    // pub(crate) fn get_mut(&mut self) -> &mut T {
+    //     &mut self.inner
+    // }
+}
+
+impl<T> AsyncRead for Rewind<T>
+where
+    T: AsyncRead + Unpin,
+{
+    fn poll_read(
+        mut self: Pin<&mut Self>,
+        cx: &mut task::Context<'_>,
+        buf: &mut ReadBuf<'_>,
+    ) -> Poll<io::Result<()>> {
+        if let Some(mut prefix) = self.pre.take() {
+            // If there are no remaining bytes, let the bytes get dropped.
+            if !prefix.is_empty() {
+                let copy_len = cmp::min(prefix.len(), buf.remaining());
+                // TODO: There should be a way to do following two lines cleaner...
+                buf.put_slice(&prefix[..copy_len]);
+                prefix.advance(copy_len);
+                // Put back what's left
+                if !prefix.is_empty() {
+                    self.pre = Some(prefix);
+                }
+
+                return Poll::Ready(Ok(()));
+            }
+        }
+        Pin::new(&mut self.inner).poll_read(cx, buf)
+    }
+}
+
+impl<T> AsyncWrite for Rewind<T>
+where
+    T: AsyncWrite + Unpin,
+{
+    fn poll_write(
+        mut self: Pin<&mut Self>,
+        cx: &mut task::Context<'_>,
+        buf: &[u8],
+    ) -> Poll<io::Result<usize>> {
+        Pin::new(&mut self.inner).poll_write(cx, buf)
+    }
+
+    fn poll_write_vectored(
+        mut self: Pin<&mut Self>,
+        cx: &mut task::Context<'_>,
+        bufs: &[io::IoSlice<'_>],
+    ) -> Poll<io::Result<usize>> {
+        Pin::new(&mut self.inner).poll_write_vectored(cx, bufs)
+    }
+
+    fn poll_flush(mut self: Pin<&mut Self>, cx: &mut task::Context<'_>) -> Poll<io::Result<()>> {
+        Pin::new(&mut self.inner).poll_flush(cx)
+    }
+
+    fn poll_shutdown(mut self: Pin<&mut Self>, cx: &mut task::Context<'_>) -> Poll<io::Result<()>> {
+        Pin::new(&mut self.inner).poll_shutdown(cx)
+    }
+
+    fn is_write_vectored(&self) -> bool {
+        self.inner.is_write_vectored()
+    }
+}
+
+#[cfg(test)]
+mod tests {
+    // FIXME: re-implement tests with `async/await`, this import should
+    // trigger a warning to remind us
+    use super::Rewind;
+    use bytes::Bytes;
+    use tokio::io::AsyncReadExt;
+
+    #[tokio::test]
+    async fn partial_rewind() {
+        let underlying = [104, 101, 108, 108, 111];
+
+        let mock = tokio_test::io::Builder::new().read(&underlying).build();
+
+        let mut stream = Rewind::new(mock);
+
+        // Read off some bytes, ensure we filled o1
+        let mut buf = [0; 2];
+        stream.read_exact(&mut buf).await.expect("read1");
+
+        // Rewind the stream so that it is as if we never read in the first place.
+        stream.rewind(Bytes::copy_from_slice(&buf[..]));
+
+        let mut buf = [0; 5];
+        stream.read_exact(&mut buf).await.expect("read1");
+
+        // At this point we should have read everything that was in the MockStream
+        assert_eq!(&buf, &underlying);
+    }
+
+    #[tokio::test]
+    async fn full_rewind() {
+        let underlying = [104, 101, 108, 108, 111];
+
+        let mock = tokio_test::io::Builder::new().read(&underlying).build();
+
+        let mut stream = Rewind::new(mock);
+
+        let mut buf = [0; 5];
+        stream.read_exact(&mut buf).await.expect("read1");
+
+        // Rewind the stream so that it is as if we never read in the first place.
+        stream.rewind(Bytes::copy_from_slice(&buf[..]));
+
+        let mut buf = [0; 5];
+        stream.read_exact(&mut buf).await.expect("read1");
+    }
+}