stream: add next and map utility fn (#1962)

Introduces `StreamExt` trait. This trait will be used to add utility functions
to make working with streams easier. This patch includes two functions:

* `next`: a future returning the item in the stream.
* `map`: transform each item in the stream.

examples/chat.rs

@@ -27,10 +27,11 @@
 #![warn(rust_2018_idioms)]
 
 use tokio::net::{TcpListener, TcpStream};
+use tokio::stream::{Stream, StreamExt};
 use tokio::sync::{mpsc, Mutex};
 use tokio_util::codec::{Framed, LinesCodec, LinesCodecError};
 
-use futures::{SinkExt, Stream, StreamExt};
+use futures::SinkExt;
 use std::collections::HashMap;
 use std::env;
 use std::error::Error;
@@ -163,12 +164,12 @@ impl Stream for Peer {
     fn poll_next(mut self: Pin<&mut Self>, cx: &mut Context<'_>) -> Poll<Option<Self::Item>> {
         // First poll the `UnboundedReceiver`.
 
-        if let Poll::Ready(Some(v)) = self.rx.poll_next_unpin(cx) {
+        if let Poll::Ready(Some(v)) = Pin::new(&mut self.rx).poll_next(cx) {
             return Poll::Ready(Some(Ok(Message::Received(v))));
         }
 
         // Secondly poll the `Framed` stream.
-        let result: Option<_> = futures::ready!(self.lines.poll_next_unpin(cx));
+        let result: Option<_> = futures::ready!(Pin::new(&mut self.lines).poll_next(cx));
 
         Poll::Ready(match result {
             // We've received a message we should broadcast to others.

examples/connect.rs

@@ -55,19 +55,21 @@ async fn main() -> Result<(), Box<dyn Error>> {
 
 mod tcp {
     use super::codec;
-    use futures::{future, Sink, SinkExt, Stream, StreamExt};
+    use futures::StreamExt;
+    use futures::{future, Sink, SinkExt};
     use std::{error::Error, io, net::SocketAddr};
     use tokio::net::TcpStream;
+    use tokio::stream::Stream;
     use tokio_util::codec::{FramedRead, FramedWrite};
 
     pub async fn connect(
         addr: &SocketAddr,
-        stdin: impl Stream<Item = Result<Vec<u8>, io::Error>> + Unpin,
+        mut stdin: impl Stream<Item = Result<Vec<u8>, io::Error>> + Unpin,
         mut stdout: impl Sink<Vec<u8>, Error = io::Error> + Unpin,
     ) -> Result<(), Box<dyn Error>> {
         let mut stream = TcpStream::connect(addr).await?;
         let (r, w) = stream.split();
-        let sink = FramedWrite::new(w, codec::Bytes);
+        let mut sink = FramedWrite::new(w, codec::Bytes);
         let mut stream = FramedRead::new(r, codec::Bytes)
             .filter_map(|i| match i {
                 Ok(i) => future::ready(Some(i)),
@@ -78,7 +80,7 @@ mod tcp {
             })
             .map(Ok);
 
-        match future::join(stdin.forward(sink), stdout.send_all(&mut stream)).await {
+        match future::join(sink.send_all(&mut stdin), stdout.send_all(&mut stream)).await {
             (Err(e), _) | (_, Err(e)) => Err(e.into()),
             _ => Ok(()),
         }
@@ -88,8 +90,9 @@ mod tcp {
 mod udp {
     use tokio::net::udp::{RecvHalf, SendHalf};
     use tokio::net::UdpSocket;
+    use tokio::stream::{Stream, StreamExt};
 
-    use futures::{future, Sink, SinkExt, Stream, StreamExt};
+    use futures::{future, Sink, SinkExt};
     use std::error::Error;
     use std::io;
     use std::net::SocketAddr;

examples/print_each_packet.rs

@@ -55,9 +55,9 @@
 #![warn(rust_2018_idioms)]
 
 use tokio::net::TcpListener;
+use tokio::stream::StreamExt;
 use tokio_util::codec::{BytesCodec, Decoder};
 
-use futures::StreamExt;
 use std::env;
 
 #[tokio::main]

examples/tinydb.rs

@@ -42,9 +42,10 @@
 #![warn(rust_2018_idioms)]
 
 use tokio::net::TcpListener;
+use tokio::stream::StreamExt;
 use tokio_util::codec::{Framed, LinesCodec};
 
-use futures::{SinkExt, StreamExt};
+use futures::SinkExt;
 use std::collections::HashMap;
 use std::env;
 use std::error::Error;

examples/tinyhttp.rs

@@ -14,13 +14,14 @@
 #![warn(rust_2018_idioms)]
 
 use bytes::BytesMut;
-use futures::{SinkExt, StreamExt};
+use futures::SinkExt;
 use http::{header::HeaderValue, Request, Response, StatusCode};
 #[macro_use]
 extern crate serde_derive;
 use serde_json;
 use std::{env, error::Error, fmt, io};
 use tokio::net::{TcpListener, TcpStream};
+use tokio::stream::StreamExt;
 use tokio_util::codec::{Decoder, Encoder, Framed};
 
 #[tokio::main]

examples/udp-codec.rs

@@ -9,12 +9,13 @@
 #![warn(rust_2018_idioms)]
 
 use tokio::net::UdpSocket;
+use tokio::stream::StreamExt;
 use tokio::{io, time};
 use tokio_util::codec::BytesCodec;
 use tokio_util::udp::UdpFramed;
 
 use bytes::Bytes;
-use futures::{FutureExt, SinkExt, StreamExt};
+use futures::{FutureExt, SinkExt};
 use std::env;
 use std::error::Error;
 use std::net::SocketAddr;