RPC-Broker (WIP)

RPC-Broker is a transport-layer-agnostic RPC communication library. Additionally to routing RPC calls it supports transmitting Preact Signals between the clients.

It is built on WebStreams, MessagePack and Zod. It is developed using Deno.js, but also runs in Node.js and Browsers.

Adapters for WebSockets are builtin, but it works over any transport layer that is able to transmit binary data (raw TCP streams, serial/RS232, WebRTC DataChannels, ...). If the transport layer directly supports JS object cloning (e.g worker processes) the binary serialization can be skipped.

Usage

RPC-Broker does not implement the classic client/server concept. It does not distinguish between RPC callers and RPC provider, between signal source and signal sink. The classic RPC provider is just a regular client of the broker server.

If the RPC provider and the broker server run in the same process, RPCServer.client can be used. It is an automatically connected RPCClient, without any intermediary serialization.

The following examples use the simplest API possible, for more detailed information, please refer to the API section.

RPC Client

const client = new WebsocketClient(new RPCClient(), new URL(`ws://example.com/socket`));

For custom transport layers, please refer to the API section

RPC Calls

RPC calls consist of three parts: mod (to which you can subscribe, equivalent the the HTTP path), sub (equivalent to the HTTP method) and (optionally) arg. mod and sub are strings, arg is any object MessagePack can handle. It is HIGHLY RECOMMENDED to ALWAYS validate the arg. When using TypeScript, DO NOT USE the as operator, this is UNSAFE. Use FULL type checks. Do this either manually (not recommended) or using a library like zod (recommended, internally used) or TypeBox

client.subscribe(`my.api`, (sub: string, arg: unknown) => {
    // validate and handle the call
});

client.call(`my.api`, "delete", { id: 5 });

RPC Signals

1. Use RPCClient.signal to obtain a RPCSignal handle.
2. Use the RPCSignal.transmit method to transmit a signal
3. Use the RPCSignal.request method to start receiving value updates
4. Access the current value with RPCSignal.value
5. Call release when you do not need the signal anymore (saves resources and bandwidth)

It is HIGHLY RECOMMENDED to ALWAYS validate the signal value. When using TypeScript, DO NOT USE the as operator, this is UNSAFE. Use FULL type checks. Do this either manually (not recommended) or using a library like zod (recommended, internally used) or TypeBox. The Signal can become SIGNAL_INVALID at any time (no signal sender, network connection lost, ...)

const mySignal = signal("foo");
client.signal(`my.signal`).transmit(mySignal);

const myReceivedSignal = client.signal(`my.signal`);
const release = myReceivedSignal.request();
effect(() => {
    console.log(myReceivedSignal.value);
});

The library provides wrapper functions to easily access signals from Preact Components (React support is underway). These include type checks and data fallbacks.

function MyComponent() {
    const value = client.useStringSignal("my.signal", "loading...");
    return (
        <div>
            {value}
        </div>
    );
}

RPCServer

To build a WebSocket RPCServer, use serve_websocket from helpers/websocket_server.ts. If you need more granular control, use upgrade_websocket. If you want to use a custom transport layer, refer to the API Section.

API

// TODO

License

Copyright (C) 2024 Hans Schallmoser

This program is free software: you can redistribute it and/or modify it under the terms of the GNU General Public License as published by the Free Software Foundation, either version 3 of the License, or (at your option) any later version.

This program is distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License for more details. You should have received a copy of the GNU General Public License along with this program. If not, see https://www.gnu.org/licenses/.