//! A "hello world" echo server with tokio-core
//!
//! This server will create a TCP listener, accept connections in a loop, and
//! simply write back everything that's read off of each TCP connection. Each
//! TCP connection is processed concurrently with all other TCP connections, and
//! each connection will have its own buffer that it's reading in/out of.
//!
//! To see this server in action, you can run this in one terminal:
//!
//! cargo run --example echo
//!
//! and in another terminal you can run:
//!
//! cargo run --example connect 127.0.0.1:8080
//!
//! Each line you type in to the `connect` terminal should be echo'd back to
//! you! If you open up multiple terminals running the `connect` example you
//! should be able to see them all make progress simultaneously.
extern crate futures;
extern crate tokio_core;
extern crate tokio_io;
use std::env;
use std::net::SocketAddr;
use futures::Future;
use futures::stream::Stream;
use tokio_io::AsyncRead;
use tokio_io::io::copy;
use tokio_core::net::TcpListener;
use tokio_core::reactor::Core;
fn main() {
// Allow passing an address to listen on as the first argument of this
// program, but otherwise we'll just set up our TCP listener on
// 127.0.0.1:8080 for connections.
let addr = env::args().nth(1).unwrap_or("127.0.0.1:8080".to_string());
let addr = addr.parse::<SocketAddr>().unwrap();
// First up we'll create the event loop that's going to drive this server.
// This is done by creating an instance of the `Core` type, tokio-core's
// event loop. Most functions in tokio-core return an `io::Result`, and
// `Core::new` is no exception. For this example, though, we're mostly just
// ignoring errors, so we unwrap the return value.
//
// After the event loop is created we acquire a handle to it through the
// `handle` method. With this handle we'll then later be able to create I/O
// objects and spawn futures.
let mut core = Core::new().unwrap();
let handle = core.handle();
// Next up we create a TCP listener which will listen for incoming
// connections. This TCP listener is bound to the address we determined
// above and must be associated with an event loop, so we pass in a handle
// to our event loop. After the socket's created we inform that we're ready
// to go and start accepting connections.
let socket = TcpListener::bind(&addr, &handle).unwrap();
println!("Listening on: {}", addr);
// Here we convert the `TcpListener` to a stream of incoming connections
// with the `incoming` method. We then define how to process each element in
// the stream with the `for_each` method.
//
// This combinator, defined on the `Stream` trait, will allow us to define a
// computation to happen for all items on the stream (in this case TCP
// connections made to the server). The return value of the `for_each`
// method is itself a future representing processing the entire stream of
// connections, and ends up being our server.
let done = socket.incoming().for_each(move |(socket, addr)| {
// Once we're inside this closure this represents an accepted client
// from our server. The `socket` is the client connection and `addr` is
// the remote address of the client (similar to how the standard library
// operates).
//
// We just want to copy all data read from the socket back onto the
// socket itself (e.g. "echo"). We can use the standard `io::copy`
// combinator in the `tokio-core` crate to do precisely this!
//
// The `copy` function takes two arguments, where to read from and where
// to write to. We only have one argument, though, with `socket`.
// Luckily there's a method, `Io::split`, which will split an Read/Write
// stream into its two halves. This operation allows us to work with
// each stream independently, such as pass them as two arguments to the
// `copy` function.
//
// The `copy` function then returns a future, and this future will be
// resolved when the copying operation is complete, resolving to the
// amount of data that was copied.
let (reader, writer) = socket.split();
let amt = copy(reader, writer);
// After our copy operation is complete we just print out some helpful
// information.
let msg = amt.then(move |result| {
match result {
Ok((amt, _, _)) => println!("wrote {} bytes to {}", amt, addr),
Err(e) => println!("error on {}: {}", addr, e),
}
Ok(())
});
// And this is where much of the magic of this server happens. We
// crucially want all clients to make progress concurrently, rather than
// blocking one on completion of another. To achieve this we use the
// `spawn` function on `Handle` to essentially execute some work in the
// background.
//
// This function will transfer ownership of the future (`msg` in this
// case) to the event loop that `handle` points to. The event loop will
// then drive the future to completion.
//
// Essentially here we're spawning a new task to run concurrently, which
// will allow all of our clients to be processed concurrently.
handle.spawn(msg);
Ok(())
});
// And finally now that we've define what our server is, we run it! We
// didn't actually do much I/O up to this point and this `Core::run` method
// is responsible for driving the entire server to completion.
//
// The `run` method will return the result of the future that it's running,
// but in our case the `done` future won't ever finish because a TCP
// listener is never done accepting clients. That basically just means that
// we're going to be running the server until it's killed (e.g. ctrl-c).
core.run(done).unwrap();
}