tokio/examples/hello_world.rs

//! Hello world server.
//!
//! A simple client that opens a TCP stream, writes "hello world\n", and closes
//! the connection.
//!
//! You can test this out by running:
//!
//!     ncat -l 6142
//!
//! And then in another terminal run:
//!
//!     cargo run --example hello_world

#![deny(warnings)]

extern crate tokio;

use tokio::io;
use tokio::net::TcpStream;
use tokio::prelude::*;

pub fn main() -> Result<(), Box<std::error::Error>> {
    let addr = "127.0.0.1:6142".parse()?;

    // Open a TCP stream to the socket address.
    //
    // Note that this is the Tokio TcpStream, which is fully async.
    let client = TcpStream::connect(&addr).and_then(|stream| {
        println!("created stream");
        io::write_all(stream, "hello world\n").then(|result| {
            println!("wrote to stream; success={:?}", result.is_ok());
            Ok(())
        })
    })
    .map_err(|err| {
        // All tasks must have an `Error` type of `()`. This forces error
        // handling and helps avoid silencing failures.
        //
        // In our example, we are only going to log the error to STDOUT.
        println!("connection error = {:?}", err);
    });

    // Start the Tokio runtime.
    //
    // The Tokio is a pre-configured "out of the box" runtime for building
    // asynchronous applications. It includes both a reactor and a task
    // scheduler. This means applications are multithreaded by default.
    //
    // This function blocks until the runtime reaches an idle state. Idle is
    // defined as all spawned tasks have completed and all I/O resources (TCP
    // sockets in our case) have been dropped.
    println!("About to create the stream and write to it...");
    tokio::run(client);
    println!("Stream has been created and written to.");

    Ok(())
}