io: add vectored writes to `AsyncWrite` (#3149)

This adds `AsyncWrite::poll_write_vectored`, and implements it for
`TcpStream` and `UnixStream`.

Refs: #3135.

6 files changed, 89 insertions, 1 deletions

diff --git a/tokio/src/net/tcp/split.rs b/tokio/src/net/tcp/split.rs
index 9a257f8b..28c94eb4 100644
--- a/tokio/src/net/tcp/split.rs
+++ b/tokio/src/net/tcp/split.rs
@@ -147,6 +147,18 @@ impl AsyncWrite for WriteHalf<'_> {
         self.0.poll_write_priv(cx, buf)
     }
 
+    fn poll_write_vectored(
+        self: Pin<&mut Self>,
+        cx: &mut Context<'_>,
+        bufs: &[io::IoSlice<'_>],
+    ) -> Poll<io::Result<usize>> {
+        self.0.poll_write_vectored_priv(cx, bufs)
+    }
+
+    fn is_write_vectored(&self) -> bool {
+        self.0.is_write_vectored()
+    }
+
     #[inline]
     fn poll_flush(self: Pin<&mut Self>, _: &mut Context<'_>) -> Poll<io::Result<()>> {
         // tcp flush is a no-op
diff --git a/tokio/src/net/tcp/split_owned.rs b/tokio/src/net/tcp/split_owned.rs
index 4b4e2636..8d77c8ca 100644
--- a/tokio/src/net/tcp/split_owned.rs
+++ b/tokio/src/net/tcp/split_owned.rs
@@ -229,6 +229,18 @@ impl AsyncWrite for OwnedWriteHalf {
         self.inner.poll_write_priv(cx, buf)
     }
 
+    fn poll_write_vectored(
+        self: Pin<&mut Self>,
+        cx: &mut Context<'_>,
+        bufs: &[io::IoSlice<'_>],
+    ) -> Poll<io::Result<usize>> {
+        self.inner.poll_write_vectored_priv(cx, bufs)
+    }
+
+    fn is_write_vectored(&self) -> bool {
+        self.inner.is_write_vectored()
+    }
+
     #[inline]
     fn poll_flush(self: Pin<&mut Self>, _: &mut Context<'_>) -> Poll<io::Result<()>> {
         // tcp flush is a no-op
diff --git a/tokio/src/net/tcp/stream.rs b/tokio/src/net/tcp/stream.rs
index de7b4213..28118f73 100644
--- a/tokio/src/net/tcp/stream.rs
+++ b/tokio/src/net/tcp/stream.rs
@@ -832,6 +832,14 @@ impl TcpStream {
     ) -> Poll<io::Result<usize>> {
         self.io.poll_write(cx, buf)
     }
+
+    pub(super) fn poll_write_vectored_priv(
+        &self,
+        cx: &mut Context<'_>,
+        bufs: &[io::IoSlice<'_>],
+    ) -> Poll<io::Result<usize>> {
+        self.io.poll_write_vectored(cx, bufs)
+    }
 }
 
 impl TryFrom<std::net::TcpStream> for TcpStream {
@@ -867,6 +875,18 @@ impl AsyncWrite for TcpStream {
         self.poll_write_priv(cx, buf)
     }
 
+    fn poll_write_vectored(
+        self: Pin<&mut Self>,
+        cx: &mut Context<'_>,
+        bufs: &[io::IoSlice<'_>],
+    ) -> Poll<io::Result<usize>> {
+        self.poll_write_vectored_priv(cx, bufs)
+    }
+
+    fn is_write_vectored(&self) -> bool {
+        true
+    }
+
     #[inline]
     fn poll_flush(self: Pin<&mut Self>, _: &mut Context<'_>) -> Poll<io::Result<()>> {
         // tcp flush is a no-op
diff --git a/tokio/src/net/unix/split.rs b/tokio/src/net/unix/split.rs
index 460bbc19..af9c7624 100644
--- a/tokio/src/net/unix/split.rs
+++ b/tokio/src/net/unix/split.rs
@@ -68,6 +68,18 @@ impl AsyncWrite for WriteHalf<'_> {
         self.0.poll_write_priv(cx, buf)
     }
 
+    fn poll_write_vectored(
+        self: Pin<&mut Self>,
+        cx: &mut Context<'_>,
+        bufs: &[io::IoSlice<'_>],
+    ) -> Poll<io::Result<usize>> {
+        self.0.poll_write_vectored_priv(cx, bufs)
+    }
+
+    fn is_write_vectored(&self) -> bool {
+        self.0.is_write_vectored()
+    }
+
     fn poll_flush(self: Pin<&mut Self>, _: &mut Context<'_>) -> Poll<io::Result<()>> {
         Poll::Ready(Ok(()))
     }
diff --git a/tokio/src/net/unix/split_owned.rs b/tokio/src/net/unix/split_owned.rs
index ab233072..5f0a2593 100644
--- a/tokio/src/net/unix/split_owned.rs
+++ b/tokio/src/net/unix/split_owned.rs
@@ -153,6 +153,18 @@ impl AsyncWrite for OwnedWriteHalf {
         self.inner.poll_write_priv(cx, buf)
     }
 
+    fn poll_write_vectored(
+        self: Pin<&mut Self>,
+        cx: &mut Context<'_>,
+        bufs: &[io::IoSlice<'_>],
+    ) -> Poll<io::Result<usize>> {
+        self.inner.poll_write_vectored_priv(cx, bufs)
+    }
+
+    fn is_write_vectored(&self) -> bool {
+        self.inner.is_write_vectored()
+    }
+
     #[inline]
     fn poll_flush(self: Pin<&mut Self>, _: &mut Context<'_>) -> Poll<io::Result<()>> {
         // flush is a no-op
diff --git a/tokio/src/net/unix/stream.rs b/tokio/src/net/unix/stream.rs
index 1d840926..f9619942 100644
--- a/tokio/src/net/unix/stream.rs
+++ b/tokio/src/net/unix/stream.rs
@@ -172,6 +172,18 @@ impl AsyncWrite for UnixStream {
         self.poll_write_priv(cx, buf)
     }
 
+    fn poll_write_vectored(
+        self: Pin<&mut Self>,
+        cx: &mut Context<'_>,
+        bufs: &[io::IoSlice<'_>],
+    ) -> Poll<io::Result<usize>> {
+        self.poll_write_vectored_priv(cx, bufs)
+    }
+
+    fn is_write_vectored(&self) -> bool {
+        true
+    }
+
     fn poll_flush(self: Pin<&mut Self>, _: &mut Context<'_>) -> Poll<io::Result<()>> {
         Poll::Ready(Ok(()))
     }
@@ -199,7 +211,7 @@ impl UnixStream {
         cx: &mut Context<'_>,
         buf: &mut ReadBuf<'_>,
     ) -> Poll<io::Result<()>> {
-        // Safety: `UdpStream::read` correctly handles reads into uninitialized memory
+        // Safety: `UnixStream::read` correctly handles reads into uninitialized memory
         unsafe { self.io.poll_read(cx, buf) }
     }
 
@@ -210,6 +222,14 @@ impl UnixStream {
     ) -> Poll<io::Result<usize>> {
         self.io.poll_write(cx, buf)
     }
+
+    pub(super) fn poll_write_vectored_priv(
+        &self,
+        cx: &mut Context<'_>,
+        bufs: &[io::IoSlice<'_>],
+    ) -> Poll<io::Result<usize>> {
+        self.io.poll_write_vectored(cx, bufs)
+    }
 }
 
 impl fmt::Debug for UnixStream {