How do I create a TCP listening socket in Rust

Question

I am using TcpListener from the standard library

I have a public function that is supposed to start up a listening socket

pub fn start_listen(){
    let mut file = File::open("Listen.toml").unwrap();
    let mut contents = String::new();
    file.read_to_string(&mut contents).unwrap();
    let value = contents.parse::<Value>().unwrap();

    let ip = value["ip"].as_str().unwrap().to_string();
    let port = value["port"].as_str().unwrap().to_string();
    let socket_string = format!("{}:{}", &ip, &port);
    println!("socket_string -> {}", &socket_string);

    TcpListener::bind(&socket_string).unwrap();
    println!("now listening!");
}

and I call it from main.rs

    start_listen::start_listen();
    println!("waiting 30s...");
    sleep(Duration::from_secs(30));
    println!("closing program!");

The problem is the function runs for the 30 seconds and breaks without any errors, but I cannot see the listening socket when I look for it. I am on Ubuntu.

I have tried manually typing in ip and ports like "127.0.0.1:8080" but the program runs just fine without me being able to find that socket.

Does anyone know what issue I am having? Thanks!

EDIT:

The commands I am using to try and see if the listening socket exists

sudo ss -tulpn | grep LISTEN

sudo netstat -tulpn | grep 8080

I do not see anything that indicates that socket exists

EDIT2:

Adding this did nothing

    for stream in listener.incoming() {
        let stream = stream.unwrap();

        println!("Connection established!");
    }

Answer 1

The TcpListener::bind creates a new TcpListener and returns it. The socket is closed when this TcpListener is dropped.

Modify your start_listen() function like this to save the TcpListener and return it:

pub fn start_listen() -> TcpListener {
    ...
    let listener = TcpListener::bind(&socket_string).unwrap();
    println!("now listening!");
    listener
}

Then in the main.rs save the listener before you wait for 30 seconds:

let listener = start_listen::start_listen();
println!("waiting 30s...");
sleep(Duration::from_secs(30));
println!("closing program!");