Sharing mutable state between clients using async (tokio) rust-websocket

Question

I am writing a websocket server in Rust using rust-websocket and its Tokio-based asynchronous system. I can serve clients normally, but I cannot figure out how to share volatile state between clients. Here are some (partial) code demonstrating this problem:

let mut core = Core::new().unwrap();
let handle = core.handle();
let server = Server::bind("localhost:62831", &handle).unwrap();

let mut state = State{
    ...
};

let f = server.incoming()
    .map_err(|InvalidConnection {error, ..}| error)
    .for_each(|upgrade, _)| {
        let f = upgrade.accept()
            .and_then(|s, _| {
                let ctx = ClientContext{
                    // some other per-client values
                    state: &mut state,
                }
                ...
                return s.send(Message::binary(data).into())
                    .and_then(move |s| Ok(s, ctx)); // this could be the complete wrong way to insert context into the stream
            }).and_then(|s, ctx| {
                // client handling code here
            });

            handle.spawn(f
                .map_err(...)
                .map(...)
            );
            return Ok(())
    });

core.run(f).unwrap();

This error code is with this:

error[E0373]: closure may outlive the current function, but it borrows `**state`, which is owned by the current function
   --> src/main.rs:111:27
    |
111 |                 .and_then(|(s, _)| {
    |                           ^^^^^^^^ may outlive borrowed value `**state`
...
114 |                         state: &mut state,
    |                                     ----- `**state` is borrowed here
    |
help: to force the closure to take ownership of `**state` (and any other referenced variables), use the `move` keyword, as shown:
    |                 .and_then(move |(s, _)| {

When I try to suggest a compiler, I get the following:

error[E0507]: cannot move out of captured outer variable in an `FnMut` closure
   --> src/main.rs:111:27
    |
111 |                 .and_then(move |(s, _)| {
    |                           ^^^^^^^^^^^^^ cannot move out of captured outer variable in an `FnMut` closure

error: `state` does not live long enough
   --> src/main.rs:114:37
    |
114 |                         state: &mut state,
    |                                     ^^^^^ does not live long enough
...
122 |                 })
    |                 - borrowed value only lives until here
    |
    = note: borrowed value must be valid for the static lifetime...

I also tried to wrap the state in RefCell(creating RefCellimmediately after the state itself), however, the compiler gives a similar move error, as it tries to move RefCellto a closure that creates the client context.

Answer 1

RefCell. Rc , RefCell, Rc, RefCell .

let shared_state = Rc::new(RefCell::new(State::new())));
incoming().for_each(move |s, _| {
    let shared_state = shared_state.clone();  // Left uncaptured
    shared_state.borrow_mut().do_mutable_state_stuff(); // Could panic
});

, , Rc RefCell , , , ClientContext Rc > &mut State. , &mut State , &mut State RefMut, , ( , try_).

, , , , Rc Arc RefCell Mutex, , .