Peer-to-Peer Replication (beta)

This plugin allows you to replicate data between your clients devices fully P2P, without a backend server. It uses WebRTC to create a connection between the devices and then establishes a replication with the normal RxDB replication protocol.

Usage

Before you use this plugin, make sure that you understand how WebRTC works.

First you have to add the plugin, then you can call RxCollection.syncP2P() to start the replication. As options you have to provide a topic and a connection handler function that implements the P2PConnectionHandlerCreator interface. As default you should start with the getConnectionHandlerSimplePeer method which uses the simple-peer library.

In difference to the other replication plugins, the P2P replication returns a replicationPool instead of a single replication state. The replicationPool contains all replication states of the connected peers in the network.

import {
    addRxPlugin
} from 'rxdb/';
import {
    RxDBReplicationP2PPlugin,
    getConnectionHandlerSimplePeer
} from 'rxdb/plugins/replication-p2p';
addRxPlugin(RxDBReplicationP2PPlugin);


const replicationPool = await myRxCollection.syncP2P({
    // The topic is like a 'room-name'. All clients with the same topic
    // will replicate with each other. In most cases you want to use
    // a different topic string per user.
    topic: 'my-users-pool',
    /**
     * You need a collection handler to be able to create WebRTC connections.
     * Here we use the simple peer handler which uses the 'simple-peer' npm library.
     * To learn how to create a custom connection handler, read the source code,
     * it is pretty simple.
     */
    connectionHandlerCreator: getConnectionHandlerSimplePeer(
        'wss://example.com:8080',
        // only in Node.js, we need the wrtc library
        // because Node.js does not contain the WebRTC API.
        require('wrtc')
    ),
    pull: {},
    push: {}
});
replicationPool.error$.subscribe(err => { /* ... */ });
replicationPool.cancel();

Live replications

P2P replication is always live because there can not be a one-time sync when it is always possible to have new Peers that join the pool. Therefore you cannot set the live option like in the other replication plugins.

Signaling Server

The simple-peer connection handler needs a signaling server. Creating a signaling server is pretty easy and can be done in a few lines of code, like in the following example:

export async function startSignalingServer(port: number): Promise<string> {
    const server = require('http').createServer();
    const io = require('socket.io')(server);
    const socketByPeerId = new Map();
    const socketsByRoom = new Map();
    io.on('connection', function (socket: any) {
        socket.on('signal', (message: any) => {
            socketByPeerId.get(message.to).emit('signal', message);
        });
        socket.on('join', (message: any) => {
            if (!socketsByRoom.has(message.room)) {
                console.log('START NEW ROOM: ' + message.room);
                socketsByRoom.set(message.room, []);
            }
            socketsByRoom.get(message.room).push({
                socket,
                peerId: message.peerId
            });
            socketByPeerId.set(message.peerId, socket);
            const roomPeerIds = socketsByRoom.get(message.room).map((row: any) => row.peerId);
            socketsByRoom.get(message.room).forEach((row: any) => {
                row.socket.emit('joined', roomPeerIds);
            });
        });
    });
    return new Promise(res => {
        server.listen(port, () => {
            res('ws://localhost:' + port);
        });
    });
}

In production you might not want to use that and instead create your custom signaling server with authentication and a different logic.

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