Stateroom

Stateroom is a minimalist framework for building lightweight, single-threaded services that send and receive messages through WebSockets.

Services can either be native Rust code that runs in the server process, or be compiled into WebAssembly modules and loaded dynamically.

Usage

To create a Stateroom service, implement the SimpleStateroomService trait. There's only one function that you must implement, the constructor new.

Let's implement a simple shared counter. Any connected client will be able to increment or decrement it by sending increment or decrement messages (other messages will be ignored). Whenever the value is changed, we'll broadcast it to every connected client.

impl SimpleStateroomService for SharedCounterServer {
    fn new(_: &str,
           _: &impl StateroomContext) -> Self {
        SharedCounterServer(0)
    }

    fn message(&mut self, _: ClientId,
               message: &str,
               ctx: &impl StateroomContext) {
        match message {
            "increment" => self.0 += 1,
            "decrement" => self.0 -= 1,
            _ => (),
        }

        ctx.send_message(
            MessageRecipient::Broadcast,
            &format!("new value: {}", self.0));
    }
}

To serve this service, we will compile it into a WebAssembly module. We import the #[stateroom_wasm] annotation macro and apply it to the existing SharedCounterServer declaration.

use stateroom_wasm::stateroom_wasm;

#[stateroom_wasm]
struct SharedCounterServer(i32);

Then, install the stateroom command-line tool and the wasm32-wasi target, and run stateroom dev:

$ cargo install stateroom-cli
$ rustup target add wasm32-wasi
$ stateroom dev

stateroom dev will build your app and serve it on port :8080. Then, open http://localhost:8080/status in your browser -- if all went well, you should see the status message ok. Open up developer tools in your browser and type:

let ws = new WebSocket('ws://localhost:8080/ws');
ws.onmessage = (c) => console.log(c.data);

This connects to your service, creating a new room with the id 1 if one doesn't exist (under default server settings, any string is a vaild room ID and connecting to a non-existant room will create it).

Now, you can increment the counter by sending the increment message using the ws handle:

ws.send('increment')

If everything is set up correctly, the result will be printed out:

new value: 1

If multiple clients are connected, each one will receive this message. Just like that, we have a mechanism for sharing some (very basic) application state between clients.

Using without WebAssembly

If you don't want to compile your service to WebAssembly (for example, if you want to use capabilities that are not exposed by WASI), you can use stateroom-server.

use stateroom_server::*;

fn main() -> std::io::Result<()> {
    serve::<SharedCounterServer>()?;

    Ok(())
}

Modules

Stateroom has a modular architecture. If all you want to do is generate a Stateroom service to be served with an existing Stateroom WebAssembly server, the main crates you will interact with will probably be stateroom-cli, which provides a command-line tool, and stateroom-wasm, the main Cargo dependency for building services.

• stateroom is the core, minimal implementation of the service interface.
• stateroom-cli is a command-line interface for interacting with WebAssembly-compiled Stateroom services.
• stateroom-server provides Actix actors to facilitate serving Stateroom services in a WebSocket server.
• stateroom-wasm provides a macro for generating WebAssembly modules from Stateroom services.
• stateroom-wasm-host provides a way to import Stateroom services from WebAssembly modules.

See Also

Aper is a state synchronization library which works with Stateroom.