Server

Listen on unused port TCP/IP

In this example, the port is displayed on the console, and the program will listen until a request is made. SocketAddrV4 assigns a random port when setting port to 0.

use std::net::{SocketAddrV4, Ipv4Addr, TcpListener};
use std::io::{Read, Error};

fn main() -> Result<(), Error> {
    let loopback = Ipv4Addr::new(127, 0, 0, 1);
    let socket = SocketAddrV4::new(loopback, 0);
    let listener = TcpListener::bind(socket)?;
    let port = listener.local_addr()?;
    println!("Listening on {}, access this port to end the program", port);
    let (mut tcp_stream, addr) = listener.accept()?; //block  until requested
    println!("Connection received! {:?} is sending data.", addr);
    let mut input = String::new();
    let _ = tcp_stream.read_to_string(&mut input)?;
    println!("{:?} says {}", addr, input);
    Ok(())
}

From the cookbook repository, run this example:

cargo run --example listen_unused

The listening port number will be printed, as in this example run:

Listening on 127.0.0.1:34337, access this port to end the program

Then, in another terminal window, use the netcat command to connect to the example program, specifing the listening port number printed, and send it some data:

echo "hi there" | nc -N localhost 34337

The example program should then print out what was sent over the TCP socket and then exit:

Connection received! 127.0.0.1:36500 is sending data.
127.0.0.1:36500 says hi there