Implement Clone for TcpStream (#689)

* Implement Clone for TcpStream

* Update examples

* Remove accidentally added examples

examples/tcp-echo.rs

@@ -14,8 +14,9 @@ use async_std::task;
 async fn process(stream: TcpStream) -> io::Result<()> {
     println!("Accepted from: {}", stream.peer_addr()?);
 
-    let (reader, writer) = &mut (&stream, &stream);
-    io::copy(reader, writer).await?;
+    let mut reader = stream.clone();
+    let mut writer = stream;
+    io::copy(&mut reader, &mut writer).await?;
 
     Ok(())
 }

examples/tcp-ipv4-and-6-echo.rs

@@ -15,8 +15,9 @@ use async_std::task;
 async fn process(stream: TcpStream) -> io::Result<()> {
     println!("Accepted from: {}", stream.peer_addr()?);
 
-    let (reader, writer) = &mut (&stream, &stream);
-    io::copy(reader, writer).await?;
+    let mut reader = stream.clone();
+    let mut writer = stream;
+    io::copy(&mut reader, &mut writer).await?;
 
     Ok(())
 }

src/net/tcp/listener.rs

@@ -1,6 +1,7 @@
 use std::future::Future;
 use std::net::SocketAddr;
 use std::pin::Pin;
+use std::sync::Arc;
 
 use crate::future;
 use crate::io;
@@ -75,9 +76,7 @@ impl TcpListener {
     /// [`local_addr`]: #method.local_addr
     pub async fn bind<A: ToSocketAddrs>(addrs: A) -> io::Result<TcpListener> {
         let mut last_err = None;
-        let addrs = addrs
-            .to_socket_addrs()
-            .await?;
+        let addrs = addrs.to_socket_addrs().await?;
 
         for addr in addrs {
             match mio::net::TcpListener::bind(&addr) {
@@ -121,7 +120,7 @@ impl TcpListener {
 
         let mio_stream = mio::net::TcpStream::from_stream(io)?;
         let stream = TcpStream {
-            watcher: Watcher::new(mio_stream),
+            watcher: Arc::new(Watcher::new(mio_stream)),
         };
         Ok((stream, addr))
     }

src/net/tcp/stream.rs

@@ -1,6 +1,7 @@
 use std::io::{IoSlice, IoSliceMut, Read as _, Write as _};
 use std::net::SocketAddr;
 use std::pin::Pin;
+use std::sync::Arc;
 
 use crate::future;
 use crate::io::{self, Read, Write};
@@ -44,9 +45,9 @@ use crate::task::{Context, Poll};
 /// #
 /// # Ok(()) }) }
 /// ```
-#[derive(Debug)]
+#[derive(Debug, Clone)]
 pub struct TcpStream {
-    pub(super) watcher: Watcher<mio::net::TcpStream>,
+    pub(super) watcher: Arc<Watcher<mio::net::TcpStream>>,
 }
 
 impl TcpStream {
@@ -71,9 +72,7 @@ impl TcpStream {
     /// ```
     pub async fn connect<A: ToSocketAddrs>(addrs: A) -> io::Result<TcpStream> {
         let mut last_err = None;
-        let addrs = addrs
-            .to_socket_addrs()
-            .await?;
+        let addrs = addrs.to_socket_addrs().await?;
 
         for addr in addrs {
             // mio's TcpStream::connect is non-blocking and may just be in progress
@@ -84,16 +83,20 @@ impl TcpStream {
                 Ok(s) => Watcher::new(s),
                 Err(e) => {
                     last_err = Some(e);
-                    continue
+                    continue;
                 }
             };
 
             future::poll_fn(|cx| watcher.poll_write_ready(cx)).await;
 
             match watcher.get_ref().take_error() {
-                Ok(None) => return Ok(TcpStream { watcher }),
+                Ok(None) => {
+                    return Ok(TcpStream {
+                        watcher: Arc::new(watcher),
+                    });
+                }
                 Ok(Some(e)) => last_err = Some(e),
-                Err(e) => last_err = Some(e)
+                Err(e) => last_err = Some(e),
             }
         }
 
@@ -369,7 +372,7 @@ impl From<std::net::TcpStream> for TcpStream {
     fn from(stream: std::net::TcpStream) -> TcpStream {
         let mio_stream = mio::net::TcpStream::from_stream(stream).unwrap();
         TcpStream {
-            watcher: Watcher::new(mio_stream),
+            watcher: Arc::new(Watcher::new(mio_stream)),
         }
     }
 }
@@ -391,7 +394,10 @@ cfg_unix! {
 
     impl IntoRawFd for TcpStream {
         fn into_raw_fd(self) -> RawFd {
-            self.watcher.into_inner().into_raw_fd()
+            // TODO(stjepang): This does not mean `RawFd` is now the sole owner of the file
+            // descriptor because it's possible that there are other clones of this `TcpStream`
+            // using it at the same time. We should probably document that behavior.
+            self.as_raw_fd()
         }
     }
 }

tests/tcp.rs

@@ -94,3 +94,25 @@ fn smoke_async_stream_to_std_listener() -> io::Result<()> {
 
     Ok(())
 }
+
+#[test]
+fn cloned_streams() -> io::Result<()> {
+    task::block_on(async {
+        let listener = TcpListener::bind("127.0.0.1:0").await?;
+        let addr = listener.local_addr()?;
+
+        let mut stream = TcpStream::connect(&addr).await?;
+        let mut cloned_stream = stream.clone();
+        let mut incoming = listener.incoming();
+        let mut write_stream = incoming.next().await.unwrap()?;
+        write_stream.write_all(b"Each your doing").await?;
+
+        let mut buf = [0; 15];
+        stream.read_exact(&mut buf[..8]).await?;
+        cloned_stream.read_exact(&mut buf[8..]).await?;
+
+        assert_eq!(&buf[..15], b"Each your doing");
+
+        Ok(())
+    })
+}