io: implement AsyncWrite for Vec<u8> (#1409)

tokio-io/src/async_write.rs

@@ -190,3 +190,22 @@ where
         self.get_mut().as_mut().poll_shutdown(cx)
     }
 }
+
+impl AsyncWrite for Vec<u8> {
+    fn poll_write(
+        self: Pin<&mut Self>,
+        _cx: &mut Context<'_>,
+        buf: &[u8],
+    ) -> Poll<io::Result<usize>> {
+        self.get_mut().extend_from_slice(buf);
+        Poll::Ready(Ok(buf.len()))
+    }
+
+    fn poll_flush(self: Pin<&mut Self>, _cx: &mut Context<'_>) -> Poll<io::Result<()>> {
+        Poll::Ready(Ok(()))
+    }
+
+    fn poll_shutdown(self: Pin<&mut Self>, _cx: &mut Context<'_>) -> Poll<io::Result<()>> {
+        Poll::Ready(Ok(()))
+    }
+}

tokio-io/tests/copy.rs

@@ -1,10 +1,9 @@
 #![deny(warnings, rust_2018_idioms)]
 #![feature(async_await)]
 
-use tokio_io::{AsyncRead, AsyncReadExt, AsyncWrite};
+use tokio_io::{AsyncRead, AsyncReadExt};
 use tokio_test::assert_ok;
 
-use bytes::BytesMut;
 use std::io;
 use std::pin::Pin;
 use std::task::{Context, Poll};
@@ -29,33 +28,10 @@ async fn copy() {
         }
     }
 
-    struct Wr(BytesMut);
-
-    impl Unpin for Wr {}
-    impl AsyncWrite for Wr {
-        fn poll_write(
-            mut self: Pin<&mut Self>,
-            _cx: &mut Context<'_>,
-            buf: &[u8],
-        ) -> Poll<io::Result<usize>> {
-            self.0.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 buf = BytesMut::with_capacity(64);
     let mut rd = Rd(true);
-    let mut wr = Wr(buf);
+    let mut wr = Vec::new();
 
     let n = assert_ok!(rd.copy(&mut wr).await);
     assert_eq!(n, 11);
-    assert_eq!(wr.0[..], b"hello world"[..]);
+    assert_eq!(wr, b"hello world");
 }