Cannot display a SocketAddr returned by peer_addr()

Question

I'm trying to print the address returned by peer_addr() of a TcpStream but Rust gives the error:

error: the trait core::fmt::Display is not implemented for the type core::result::Result<std::net::addr::SocketAddr, std::io::error::Error> [E0277] src/main.rs:29 format!("New client {}", stream.peer_addr());

According to the documentation Display is implemented.

Code is as follows:

use std::net::{TcpListener, TcpStream};
use std::thread;

fn main()
{
    let listener = TcpListener::bind("127.0.0.1:80").unwrap();

    for stream in listener.incoming() {
        match stream {
            Ok(stream) => {
                thread::spawn(move|| {
                    // connection succeeded
                    handle_client(stream)
                });
            }
            Err(e) => {
                println!("Accept err {}", e);
            }
        }
    }

    // close the socket server
    drop(listener);
}

fn handle_client(stream: TcpStream) {
    println!("New client {}", stream.peer_addr());
}

Lukas Kalbertodt Lukas Kalbertodt · Accepted Answer · 2015-10-07T21:56:50

If you read the compiler error carefully you can see, that your variable is of the type core::result::Result<std::net::addr::SocketAddr, std::io::error::Error>. You need to get the SocketAddr out of there. Sadly, the documentation does not specify when an Err value is returned. The easiest solution:

println!("New client {}", stream.peer_addr().unwrap());

Of course unwrap() is evil and you should do proper error handling here!

Cannot display a SocketAddr returned by peer_addr()

1 Answers