Add AsyncWrite implementation for IntoAsyncRead

This implements AsyncWrite for IntoAsyncRead when the inner stream implements it,
forwarding all method calls.

This allows working on Types that keep both impls, and allows framing
them with codecs where those require both traits (like tokio codec).

Author: najamelan

futures-util/src/try_stream/into_async_read.rs

@@ -2,7 +2,7 @@ use crate::try_stream::TryStreamExt;
 use core::pin::Pin;
 use futures_core::stream::TryStream;
 use futures_core::task::{Context, Poll};
-use futures_io::{AsyncRead, AsyncBufRead};
+use futures_io::{AsyncRead, AsyncWrite, AsyncBufRead};
 use std::cmp;
 use std::io::{Error, Result};
 
@@ -100,6 +100,34 @@ where
     }
 }
 
+impl<St> AsyncWrite for IntoAsyncRead<St>
+where
+    St: TryStream<Error = Error> + AsyncWrite + Unpin,
+    St::Ok: AsRef<[u8]>,
+{
+    fn poll_write(
+        mut self: Pin<&mut Self>,
+        cx: &mut Context<'_>,
+        buf: &[u8]
+    ) -> Poll<Result<usize>> {
+        Pin::new( &mut self.stream ).poll_write( cx, buf )
+    }
+
+    fn poll_flush(
+        mut self: Pin<&mut Self>,
+        cx: &mut Context<'_>
+    ) -> Poll<Result<()>> {
+        Pin::new( &mut self.stream ).poll_flush( cx )
+    }
+
+    fn poll_close(
+        mut self: Pin<&mut Self>,
+        cx: &mut Context<'_>
+    ) -> Poll<Result<()>> {
+        Pin::new( &mut self.stream ).poll_close( cx )
+    }
+}
+
 impl<St> AsyncBufRead for IntoAsyncRead<St>
 where
     St: TryStream<Error = Error> + Unpin,