Tokio Tungstenite Async Chat

I'm trying to learn how to use tokio-tungstenite and websockets in general. Right now I'm wanting to take their server example here and move the actual logic where it handles each connection into a separate function. I've tried a few ways but still I'm struggling on how to do it.

Here's what I have so far:

use std::collections::HashMap;
use std::env;
use std::io::{Error, ErrorKind};
use std::sync::{Arc, Mutex};

use futures::stream::Stream;
use futures::Future;
use tokio::net::TcpListener;
use tungstenite::protocol::Message;

use tokio_tungstenite::accept_async;

pub fn handle_connection(stream: tokio_tungstenite::WebSocket, connections: Arc<Mutex<HashMap<SocketAddr, futures::sync::mpsc::UnboundedReceiver>>>) -> Result<(), _> {
    let addr = stream
        .expect("connected streams should have a peer address");
    println!("Peer address: {}", addr);

    // We have to clone both of these values, because the `and_then`
    // function below constructs a new future, `and_then` requires
    // `FnOnce`, so we construct a move closure to move the
    // environment inside the future (AndThen future may overlive our
    // `for_each` future).
    let connections_inner = connections.clone();

        .and_then(move |ws_stream| {
            println!("New WebSocket connection: {}", addr);

            // Create a channel for our stream, which other sockets will use to
            // send us messages. Then register our address with the stream to send
            // data to us.
            let (tx, rx) = futures::sync::mpsc::unbounded();
            connections_inner.lock().unwrap().insert(addr, tx);

            // Let's split the WebSocket stream, so we can work with the
            // reading and writing halves separately.
            let (sink, stream) = ws_stream.split();

            // Whenever we receive a message from the client, we print it and
            // send to other clients, excluding the sender.
            let connections = connections_inner.clone();
            let ws_reader = stream.for_each(move |message: Message| {
                println!("Received a message from {}: {}", addr, message);

                // For each open connection except the sender, send the
                // string via the channel.
                let mut conns = connections.lock().unwrap();
                let iter = conns
                    .filter(|&(&k, _)| k != addr)
                    .map(|(_, v)| v);
                for tx in iter {

            // Whenever we receive a string on the Receiver, we write it to
            // `WriteHalf<WebSocketStream>`.
            let ws_writer = rx.fold(sink, |mut sink, msg| {
                use futures::Sink;

            // Now that we've got futures representing each half of the socket, we
            // use the `select` combinator to wait for either half to be done to
            // tear down the other. Then we spawn off the result.
            let connection = ws_reader
                .map(|_| ())
                .map_err(|_| ())
                .select(|_| ()).map_err(|_| ()));

            tokio::spawn(connection.then(move |_| {
                println!("Connection {} closed.", addr);

        .map_err(|e| {
            println!("Error during the websocket handshake occurred: {}", e);
            Error::new(ErrorKind::Other, e)

pub fn main() {
    let addr = "".to_string();
    let addr = addr.parse().unwrap();

    // Create the event loop and TCP listener we'll accept connections on.
    let socket = TcpListener::bind(&addr).unwrap();
    println!("Listening on: {}", addr);

    // Tokio Runtime uses a thread pool based executor by default, so we need
    // to use Arc and Mutex to store the map of all connections we know about.
    let connections = Arc::new(Mutex::new(HashMap::new()));

    let srv = socket.incoming().for_each(move |stream, connections| {
        handle_connection(stream, connections);

    tokio::runtime::run(srv.map_err(|_e| ()));

Currently the errors are around the futures parameter ^^^^^^^^^^^^^^^^^^^^^^^^^^^^ expected 1 type argument


^ not allowed in type signatures in reference to the Result<(), _>. Does that mean I need to specify exactly the errors that could occur? I'm also not sure what the type argument the compiler is expecting.

Any advice would be appreciated because I'm struggling on this one.