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//! An example of hooking up stdin/stdout to either a TCP or UDP stream.
//! This example will connect to a socket address specified in the argument list
//! and then forward all data read on stdin to the server, printing out all data
//! received on stdout. An optional `--udp` argument can be passed to specify
//! that the connection should be made over UDP instead of TCP, translating each
//! line entered on stdin to a UDP packet to be sent to the remote address.
//! Note that this is not currently optimized for performance, especially
//! around buffer management. Rather it's intended to show an example of
//! working with a client.
//! This example can be quite useful when interacting with the other examples in
//! this repository! Many of them recommend running this as a simple "hook up
//! stdin/stdout to a server" to get up and running.
extern crate futures;
extern crate tokio_core;
extern crate tokio_io;
extern crate bytes;
use std::env;
use std::io::{self, Read, Write};
use std::net::SocketAddr;
use std::thread;
use futures::sync::mpsc;
use futures::{Sink, Future, Stream};
use tokio_core::reactor::Core;
fn main() {
// Determine if we're going to run in TCP or UDP mode
let mut args = env::args().skip(1).collect::<Vec<_>>();
let tcp = match args.iter().position(|a| a == "--udp") {
Some(i) => {
None => true,
// Parse what address we're going to connect to
let addr = args.first().unwrap_or_else(|| {
panic!("this program requires at least one argument")
let addr = addr.parse::<SocketAddr>().unwrap();
// Create the event loop and initiate the connection to the remote server
let mut core = Core::new().unwrap();
let handle = core.handle();
// Right now Tokio doesn't support a handle to stdin running on the event
// loop, so we farm out that work to a separate thread. This thread will
// read data (with blocking I/O) from stdin and then send it to the event
// loop over a standard futures channel.
let (stdin_tx, stdin_rx) = mpsc::channel(0);
thread::spawn(|| read_stdin(stdin_tx));
let stdin_rx = stdin_rx.map_err(|_| panic!()); // errors not possible on rx
// Now that we've got our stdin read we either set up our TCP connection or
// our UDP connection to get a stream of bytes we're going to emit to
// stdout.
let stdout = if tcp {
tcp::connect(&addr, &handle, Box::new(stdin_rx))
} else {
udp::connect(&addr, &handle, Box::new(stdin_rx))
// And now with our stream of bytes to write to stdout, we execute that in
// the event loop! Note that this is doing blocking I/O to emit data to
// stdout, and in general it's a no-no to do that sort of work on the event
// loop. In this case, though, we know it's ok as the event loop isn't
// otherwise running anything useful.
let mut out = io::stdout();|chunk| {
mod tcp {
use std::io;
use std::net::SocketAddr;
use bytes::{BufMut, BytesMut};
use futures::{Future, Stream};
use tokio_core::net::TcpStream;
use tokio_core::reactor::Handle;
use tokio_io::AsyncRead;
use tokio_io::codec::{Encoder, Decoder};
pub fn connect(addr: &SocketAddr,
handle: &Handle,
stdin: Box<Stream<Item = Vec<u8>, Error = io::Error>>)
-> Box<Stream<Item = BytesMut, Error = io::Error>>
let tcp = TcpStream::connect(addr, handle);
let handle = handle.clone();
// After the TCP connection has been established, we set up our client
// to start forwarding data.
// First we use the `Io::framed` method with a simple implementation of
// a `Codec` (listed below) that just ships bytes around. We then split
// that in two to work with the stream and sink separately.
// Half of the work we're going to do is to take all data we receive on
// `stdin` and send that along the TCP stream (`sink`). The second half
// is to take all the data we receive (`stream`) and then write that to
// stdout. We'll be passing this handle back out from this method.
// You'll also note that we *spawn* the work to read stdin and write it
// to the TCP stream. This is done to ensure that happens concurrently
// with us reading data from the stream.
Box::new( |stream| {
let (sink, stream) = stream.framed(Bytes).split();
handle.spawn(stdin.forward(sink).then(|result| {
if let Err(e) = result {
panic!("failed to write to socket: {}", e)
/// A simple `Codec` implementation that just ships bytes around.
/// This type is used for "framing" a TCP stream of bytes but it's really
/// just a convenient method for us to work with streams/sinks for now.
/// This'll just take any data read and interpret it as a "frame" and
/// conversely just shove data into the output location without looking at
/// it.
struct Bytes;
impl Decoder for Bytes {
type Item = BytesMut;
type Error = io::Error;
fn decode(&mut self, buf: &mut BytesMut) -> io::Result<Option<BytesMut>> {
if buf.len() > 0 {
let len = buf.len();
} else {
fn decode_eof(&mut self, buf: &mut BytesMut) -> io::Result<Option<BytesMut>> {
impl Encoder for Bytes {
type Item = Vec<u8>;
type Error = io::Error;
fn encode(&mut self, data: Vec<u8>, buf: &mut BytesMut) -> io::Result<()> {
mod udp {
use std::io;
use std::net::SocketAddr;
use bytes::BytesMut;
use futures::{Future, Stream};
use tokio_core::net::{UdpCodec, UdpSocket};
use tokio_core::reactor::Handle;
pub fn connect(&addr: &SocketAddr,
handle: &Handle,
stdin: Box<Stream<Item = Vec<u8>, Error = io::Error>>)
-> Box<Stream<Item = BytesMut, Error = io::Error>>
// We'll bind our UDP socket to a local IP/port, but for now we
// basically let the OS pick both of those.
let addr_to_bind = if addr.ip().is_ipv4() {
} else {
let udp = UdpSocket::bind(&addr_to_bind, handle)
.expect("failed to bind socket");
// Like above with TCP we use an instance of `UdpCodec` to transform
// this UDP socket into a framed sink/stream which operates over
// discrete values. In this case we're working with *pairs* of socket
// addresses and byte buffers.
let (sink, stream) = udp.framed(Bytes).split();
// All bytes from `stdin` will go to the `addr` specified in our
// argument list. Like with TCP this is spawned concurrently
handle.spawn( |chunk| {
(addr, chunk)
}).forward(sink).then(|result| {
if let Err(e) = result {
panic!("failed to write to socket: {}", e)
// With UDP we could receive data from any source, so filter out
// anything coming from a different address
Box::new(stream.filter_map(move |(src, chunk)| {
if src == addr {
} else {
struct Bytes;
impl UdpCodec for Bytes {
type In = (SocketAddr, Vec<u8>);
type Out = (SocketAddr, Vec<u8>);
fn decode(&mut self, addr: &SocketAddr, buf: &[u8]) -> io::Result<Self::In> {
Ok((*addr, buf.to_vec()))
fn encode(&mut self, (addr, buf): Self::Out, into: &mut Vec<u8>) -> SocketAddr {
// Our helper method which will read data from stdin and send it along the
// sender provided.
fn read_stdin(mut tx: mpsc::Sender<Vec<u8>>) {
let mut stdin = io::stdin();
loop {
let mut buf = vec![0; 1024];
let n = match buf) {
Err(_) |
Ok(0) => break,
Ok(n) => n,
tx = match tx.send(buf).wait() {
Ok(tx) => tx,
Err(_) => break,