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//! A "hello world" echo server with Tokio
//!
//! This server will create a TCP listener, accept connections in a loop, and
//! write back 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 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.
#![warn(rust_2018_idioms)]
use tokio::io::{AsyncReadExt, AsyncWriteExt};
use tokio::net::TcpListener;
use std::env;
use std::error::Error;
#[tokio::main]
async fn main() -> Result<(), Box<dyn 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
// 127.0.0.1:8080 for connections.
let addr = env::args()
.nth(1)
.unwrap_or_else(|| "127.0.0.1:8080".to_string());
// 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.
let listener = TcpListener::bind(&addr).await?;
println!("Listening on: {}", addr);
loop {
// Asynchronously wait for an inbound socket.
let (mut socket, _) = listener.accept().await?;
// 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.
//
// Essentially here we're executing a new task to run concurrently,
// which will allow all of our clients to be processed concurrently.
tokio::spawn(async move {
let mut buf = [0; 1024];
// In a loop, read data from the socket and write the data back.
loop {
let n = socket
.read(&mut buf)
.await
.expect("failed to read data from socket");
if n == 0 {
return;
}
socket
.write_all(&buf[0..n])
.await
.expect("failed to write data to socket");
}
});
}
}
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