1 files changed, 78 insertions, 0 deletions
diff --git a/third_party/rust/futures-util/src/io/copy_buf.rs b/third_party/rust/futures-util/src/io/copy_buf.rs
new file mode 100644
index 0000000000..50f7abdca9
--- /dev/null
+++ b/third_party/rust/futures-util/src/io/copy_buf.rs
@@ -0,0 +1,78 @@
+use futures_core::future::Future;
+use futures_core::ready;
+use futures_core::task::{Context, Poll};
+use futures_io::{AsyncBufRead, AsyncWrite};
+use pin_project_lite::pin_project;
+use std::io;
+use std::pin::Pin;
+
+/// Creates a future which copies all the bytes from one object to another.
+///
+/// The returned future will copy all the bytes read from this `AsyncBufRead` into the
+/// `writer` specified. This future will only complete once the `reader` has hit
+/// EOF and all bytes have been written to and flushed from the `writer`
+/// provided.
+///
+/// On success the number of bytes is returned.
+///
+/// # Examples
+///
+/// ```
+/// # futures::executor::block_on(async {
+/// use futures::io::{self, AsyncWriteExt, Cursor};
+///
+/// let reader = Cursor::new([1, 2, 3, 4]);
+/// let mut writer = Cursor::new(vec![0u8; 5]);
+///
+/// let bytes = io::copy_buf(reader, &mut writer).await?;
+/// writer.close().await?;
+///
+/// assert_eq!(bytes, 4);
+/// assert_eq!(writer.into_inner(), [1, 2, 3, 4, 0]);
+/// # Ok::<(), Box<dyn std::error::Error>>(()) }).unwrap();
+/// ```
+pub fn copy_buf<R, W>(reader: R, writer: &mut W) -> CopyBuf<'_, R, W>
+where
+    R: AsyncBufRead,
+    W: AsyncWrite + Unpin + ?Sized,
+{
+    CopyBuf { reader, writer, amt: 0 }
+}
+
+pin_project! {
+    /// Future for the [`copy_buf()`] function.
+    #[derive(Debug)]
+    #[must_use = "futures do nothing unless you `.await` or poll them"]
+    pub struct CopyBuf<'a, R, W: ?Sized> {
+        #[pin]
+        reader: R,
+        writer: &'a mut W,
+        amt: u64,
+    }
+}
+
+impl<R, W> Future for CopyBuf<'_, R, W>
+where
+    R: AsyncBufRead,
+    W: AsyncWrite + Unpin + ?Sized,
+{
+    type Output = io::Result<u64>;
+
+    fn poll(self: Pin<&mut Self>, cx: &mut Context<'_>) -> Poll<Self::Output> {
+        let mut this = self.project();
+        loop {
+            let buffer = ready!(this.reader.as_mut().poll_fill_buf(cx))?;
+            if buffer.is_empty() {
+                ready!(Pin::new(&mut this.writer).poll_flush(cx))?;
+                return Poll::Ready(Ok(*this.amt));
+            }
+
+            let i = ready!(Pin::new(&mut this.writer).poll_write(cx, buffer))?;
+            if i == 0 {
+                return Poll::Ready(Err(io::ErrorKind::WriteZero.into()));
+            }
+            *this.amt += i as u64;
+            this.reader.as_mut().consume(i);
+        }
+    }
+}