async_std::net::TcpListener does not work

[ginko]

Hello,

I try a very basic example of async_std. I probably do something wrong. Any help is welcome.

The code i am trying to do is:

    let listener = TcpListener::bind("127.0.0.1:4444").await.unwrap();
    println!("Server listening on {}", listener.local_addr().unwrap());

    listener
        .incoming()
        .for_each_concurrent(None, |tcpstream| async move {
            let tcpstream = tcpstream.unwrap();
            println!("Accepting from: {}", tcpstream.peer_addr().unwrap());
        })
        .await;

It compile well.
When i start this TCP listener, and connect to it:

nc 127.0.0.1 4444

I expect the ip:port to be prompted thanks to the println!
But there is nothing, like the code execute.
But i verify with wireshark that the TCP server responds to the nc connection.
So there is definitely something that goes wrong.

If you have an idea ... please let me know

[alice]

That's a good question. I'm not sure why yours fail, but this works.

use async_std::net::TcpListener;

#[async_std::main]
async fn main() {
    let listener = TcpListener::bind("127.0.0.1:4444").await.unwrap();
    println!("Server listening on {}", listener.local_addr().unwrap());

    loop {
        let (tcp, ip) = listener.accept().await.unwrap();
        println!("Accepting from: {}", tcp.peer_addr().unwrap());
    }

}

Your original code works fine with Tokio.

use tokio::net::TcpListener;
use futures::StreamExt;

#[tokio::main]
async fn main() {
    let mut listener = TcpListener::bind("127.0.0.1:4444").await.unwrap();
    println!("Server listening on {}", listener.local_addr().unwrap());

    listener
        .incoming()
        .for_each_concurrent(None, |tcpstream| async move {
            let tcpstream = tcpstream.unwrap();
            println!("Accepting from: {}", tcpstream.peer_addr().unwrap());
        })
        .await;
}

[yoshuawuyts]

Thanks for raising this! A report was filed in async-std#888 and we've published async-std@1.6.5 with a fix.

The root cause of this issue was that one of our dependencies (async-io) published a new version earlier today that included a change in Drop behavior. On its own it was a perfectly reasonable change, but it ended up affecting our implementation causing a regression. But we've managed to resolve this now!