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//! A "print-each-packet" server with Tokio
//! This server will create a TCP listener, accept connections in a loop, and
//! put down in the stdout everything that's read off of each TCP connection.
//! Because the Tokio runtime uses a thread pool, each TCP connection is
//! processed concurrently with all other TCP connections across multiple
//! threads.
//! To see this server in action, you can run this in one terminal:
//! cargo run --example print\_each\_packet
//! and in another terminal you can run:
//! cargo run --example connect
//! Each line you type in to the `connect` terminal should be written to terminal!
//! Minimal js example:
//! ```js
//! var net = require("net");
//! var listenPort = 8080;
//! var server = net.createServer(function (socket) {
//! socket.on("data", function (bytes) {
//! console.log("bytes", bytes);
//! });
//! socket.on("end", function() {
//! console.log("Socket received FIN packet and closed connection");
//! });
//! socket.on("error", function (error) {
//! console.log("Socket closed with error", error);
//! });
//! socket.on("close", function (with_error) {
//! if (with_error) {
//! console.log("Socket closed with result: Err(SomeError)");
//! } else {
//! console.log("Socket closed with result: Ok(())");
//! }
//! });
//! });
//! server.listen(listenPort);
//! console.log("Listening on:", listenPort);
//! ```
extern crate tokio;
extern crate tokio_codec;
use tokio_codec::BytesCodec;
use tokio::net::TcpListener;
use tokio::prelude::*;
use tokio::codec::Decoder;
use std::env;
use std::net::SocketAddr;
fn main() -> Result<(), Box<std::error::Error>> {
// 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
// for connections.
let addr = env::args().nth(1).unwrap_or("".to_string());
let addr = addr.parse::<SocketAddr>()?;
// 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)?;
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
.map_err(|e| println!("failed to accept socket; error = {:?}", e))
.for_each(move |socket| {
// Once we're inside this closure this represents an accepted client
// from our server. The `socket` is the client connection (similar to
// how the standard library operates).
// We're parsing each socket with the `BytesCodec` included in `tokio_io`,
// and then we `split` each codec into the reader/writer halves.
// See
let framed = BytesCodec::new().framed(socket);
let (_writer, reader) = framed.split();
let processor = reader
.for_each(|bytes| {
println!("bytes: {:?}", bytes);
// After our copy operation is complete we just print out some helpful
// information.
.and_then(|()| {
println!("Socket received FIN packet and closed connection");
.or_else(|err| {
println!("Socket closed with error: {:?}", err);
// We have to return the error to catch it in the next ``.then` call
.then(|result| {
println!("Socket closed with result: {:?}", result);
// 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
// `tokio::spawn` function to execute the work in the background.
// This function will transfer ownership of the future (`msg` in this
// case) to the Tokio runtime thread pool that. The thread pool will
// drive the future to completion.
// Essentially here we're executing a new task to run concurrently,
// which will allow all of our clients to be processed concurrently.
// And finally now that we've define what our server is, we run it!
// This starts the Tokio runtime, spawns the server task, and blocks the
// current thread until all tasks complete execution. Since the `done` task
// never completes (it just keeps accepting sockets), `tokio::run` blocks
// forever (until ctrl-c is pressed).