1 files changed, 55 insertions, 0 deletions
diff --git a/tokio/src/io/util/write_buf.rs b/tokio/src/io/util/write_buf.rs
new file mode 100644
index 00000000..1310e5c1
--- /dev/null
+++ b/tokio/src/io/util/write_buf.rs
@@ -0,0 +1,55 @@
+use crate::io::AsyncWrite;
+
+use bytes::Buf;
+use pin_project_lite::pin_project;
+use std::future::Future;
+use std::io;
+use std::marker::PhantomPinned;
+use std::pin::Pin;
+use std::task::{Context, Poll};
+
+pin_project! {
+    /// A future to write some of the buffer to an `AsyncWrite`.
+    #[derive(Debug)]
+    #[must_use = "futures do nothing unless you `.await` or poll them"]
+    pub struct WriteBuf<'a, W, B> {
+        writer: &'a mut W,
+        buf: &'a mut B,
+        #[pin]
+        _pin: PhantomPinned,
+    }
+}
+
+/// Tries to write some bytes from the given `buf` to the writer in an
+/// asynchronous manner, returning a future.
+pub(crate) fn write_buf<'a, W, B>(writer: &'a mut W, buf: &'a mut B) -> WriteBuf<'a, W, B>
+where
+    W: AsyncWrite + Unpin,
+    B: Buf,
+{
+    WriteBuf {
+        writer,
+        buf,
+        _pin: PhantomPinned,
+    }
+}
+
+impl<W, B> Future for WriteBuf<'_, W, B>
+where
+    W: AsyncWrite + Unpin,
+    B: Buf,
+{
+    type Output = io::Result<usize>;
+
+    fn poll(self: Pin<&mut Self>, cx: &mut Context<'_>) -> Poll<io::Result<usize>> {
+        let me = self.project();
+
+        if !me.buf.has_remaining() {
+            return Poll::Ready(Ok(0));
+        }
+
+        let n = ready!(Pin::new(me.writer).poll_write(cx, me.buf.bytes()))?;
+        me.buf.advance(n);
+        Poll::Ready(Ok(n))
+    }
+}