tokio: add AsyncWriteExt::write_all (#1277)

tokio/src/io/async_write_ext.rs

@@ -1,13 +1,11 @@
 use crate::io::write::{write, Write};
+use crate::io::write_all::{write_all, WriteAll};
 
 use tokio_io::AsyncWrite;
 
 /// An extension trait which adds utility methods to `AsyncWrite` types.
 pub trait AsyncWriteExt: AsyncWrite {
-    /// Write the provided data into `self`.
+    /// Write a buffer into this writter, returning how many bytes were written.
-    ///
-    /// The returned future will resolve to the number of bytes written once the
-    /// write operation is completed.
     ///
     /// # Examples
     ///
@@ -20,6 +18,20 @@ pub trait AsyncWriteExt: AsyncWrite {
     {
         write(self, src)
     }
+
+    /// Attempt to write an entire buffer into this writter.
+    ///
+    /// # Examples
+    ///
+    /// ```
+    /// unimplemented!();
+    /// ```
+    fn write_all<'a>(&'a mut self, src: &'a [u8]) -> WriteAll<'a, Self>
+    where
+        Self: Unpin,
+    {
+        write_all(self, src)
+    }
 }
 
 impl<W: AsyncWrite + ?Sized> AsyncWriteExt for W {}

tokio/src/io/mod.rs

@@ -42,6 +42,7 @@ mod copy;
 mod read;
 mod read_exact;
 mod write;
+mod write_all;
 
 pub use self::async_read_ext::AsyncReadExt;
 pub use self::async_write_ext::AsyncWriteExt;

tokio/src/io/write_all.rs

@@ -0,0 +1,46 @@
+use tokio_io::AsyncWrite;
+
+use std::future::Future;
+use std::io;
+use std::mem;
+use std::pin::Pin;
+use std::task::{Context, Poll};
+
+#[derive(Debug)]
+#[must_use = "futures do nothing unless you `.await` or poll them"]
+pub struct WriteAll<'a, W: ?Sized> {
+    writer: &'a mut W,
+    buf: &'a [u8],
+}
+
+pub(crate) fn write_all<'a, W>(writer: &'a mut W, buf: &'a [u8]) -> WriteAll<'a, W>
+where
+    W: AsyncWrite + Unpin + ?Sized,
+{
+    WriteAll { writer, buf }
+}
+
+impl<W: ?Sized + Unpin> Unpin for WriteAll<'_, W> {}
+
+impl<W> Future for WriteAll<'_, W>
+where
+    W: AsyncWrite + Unpin + ?Sized,
+{
+    type Output = io::Result<()>;
+
+    fn poll(mut self: Pin<&mut Self>, cx: &mut Context<'_>) -> Poll<io::Result<()>> {
+        let me = &mut *self;
+        while !me.buf.is_empty() {
+            let n = ready!(Pin::new(&mut me.writer).poll_write(cx, me.buf))?;
+            {
+                let (_, rest) = mem::replace(&mut me.buf, &[]).split_at(n);
+                me.buf = rest;
+            }
+            if n == 0 {
+                return Poll::Ready(Err(io::ErrorKind::WriteZero.into()));
+            }
+        }
+
+        Poll::Ready(Ok(()))
+    }
+}

tokio/tests/io_write.rs

@@ -11,7 +11,10 @@ use std::task::{Context, Poll};
 
 #[tokio::test]
 async fn write() {
-    struct Wr(BytesMut);
+    struct Wr {
+        buf: BytesMut,
+        cnt: usize,
+    }
 
     impl AsyncWrite for Wr {
         fn poll_write(
@@ -19,8 +22,9 @@ async fn write() {
             _cx: &mut Context<'_>,
             buf: &[u8],
         ) -> Poll<io::Result<usize>> {
-            self.0.extend(buf);
+            assert_eq!(self.cnt, 0);
-            Ok(buf.len()).into()
+            self.buf.extend(&buf[0..4]);
+            Ok(4).into()
         }
 
         fn poll_flush(self: Pin<&mut Self>, _cx: &mut Context<'_>) -> Poll<io::Result<()>> {
@@ -32,8 +36,12 @@ async fn write() {
         }
     }
 
-    let mut wr = Wr(BytesMut::with_capacity(64));
+    let mut wr = Wr {
+        buf: BytesMut::with_capacity(64),
+        cnt: 0,
+    };
 
     let n = assert_ok!(wr.write(b"hello world").await);
-    assert_eq!(n, 11);
+    assert_eq!(n, 4);
+    assert_eq!(wr.buf, b"hell"[..]);
 }

tokio/tests/io_write_all.rs

@@ -0,0 +1,51 @@
+#![deny(warnings, rust_2018_idioms)]
+#![feature(async_await)]
+
+use tokio::io::{AsyncWrite, AsyncWriteExt};
+use tokio_test::assert_ok;
+
+use bytes::BytesMut;
+use std::cmp;
+use std::io;
+use std::pin::Pin;
+use std::task::{Context, Poll};
+
+#[tokio::test]
+async fn write_all() {
+    struct Wr {
+        buf: BytesMut,
+        cnt: usize,
+    }
+
+    impl AsyncWrite for Wr {
+        fn poll_write(
+            mut self: Pin<&mut Self>,
+            _cx: &mut Context<'_>,
+            buf: &[u8],
+        ) -> Poll<io::Result<usize>> {
+            let n = cmp::min(4, buf.len());
+            let buf = &buf[0..n];
+
+            self.cnt += 1;
+            self.buf.extend(buf);
+            Ok(buf.len()).into()
+        }
+
+        fn poll_flush(self: Pin<&mut Self>, _cx: &mut Context<'_>) -> Poll<io::Result<()>> {
+            Ok(()).into()
+        }
+
+        fn poll_shutdown(self: Pin<&mut Self>, _cx: &mut Context<'_>) -> Poll<io::Result<()>> {
+            Ok(()).into()
+        }
+    }
+
+    let mut wr = Wr {
+        buf: BytesMut::with_capacity(64),
+        cnt: 0,
+    };
+
+    assert_ok!(wr.write_all(b"hello world").await);
+    assert_eq!(wr.buf, b"hello world"[..]);
+    assert_eq!(wr.cnt, 3);
+}