tokio/examples/connect.rs

//! A simple example of hooking up stdin/stdout to a TCP stream.
//!
//! This example will connect to a server specified in the argument list and
//! then forward all data read on stdin to the server, printing out all data
//! received on stdout.
//!
//! 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.

extern crate futures;
extern crate tokio_core;

use std::env;
use std::io::{self, Read, Write};
use std::net::SocketAddr;
use std::thread;

use futures::{Sink, Future, Stream};
use futures::sync::mpsc;
use tokio_core::reactor::Core;
use tokio_core::io::{Io, EasyBuf, Codec};
use tokio_core::net::TcpStream;

fn main() {
    // Parse what address we're going to connect to
    let addr = env::args().nth(1).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();
    let tcp = TcpStream::connect(&addr, &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 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

    // 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 (`stdin_rx`) 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. Currently we just write to stdout in a synchronous
    // fashion.
    //
    // Finally we set the client to terminate once either half of this work
    // finishes. If we don't have any more data to read or we won't receive any
    // more work from the remote then we can exit.
    let mut stdout = io::stdout();
    let client = tcp.and_then(|stream| {
        let (sink, stream) = stream.framed(Bytes).split();
        let send_stdin = stdin_rx.forward(sink);
        let write_stdout = stream.for_each(move |buf| {
            stdout.write_all(buf.as_slice())
        });

        send_stdin.map(|_| ())
                  .select(write_stdout.map(|_| ()))
                  .then(|_| Ok(()))
    });

    // And now that we've got our client, we execute it in the event loop!
    core.run(client).unwrap();
}

/// 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 Codec for Bytes {
    type In = EasyBuf;
    type Out = Vec<u8>;

    fn decode(&mut self, buf: &mut EasyBuf) -> io::Result<Option<EasyBuf>> {
        if buf.len() > 0 {
            let len = buf.len();
            Ok(Some(buf.drain_to(len)))
        } else {
            Ok(None)
        }
    }

    fn encode(&mut self, data: Vec<u8>, buf: &mut Vec<u8>) -> io::Result<()> {
        buf.extend(data);
        Ok(())
    }
}

// Our helper method which will read data from stdin and send it along the
// sender provided.
fn read_stdin(mut rx: mpsc::Sender<Vec<u8>>) {
    let mut stdin = io::stdin();
    loop {
        let mut buf = vec![0; 1024];
        let n = match stdin.read(&mut buf) {
            Err(_) |
            Ok(0) => break,
            Ok(n) => n,
        };
        buf.truncate(n);
        rx = rx.send(buf).wait().unwrap();
    }
}