rtc-link/lib/establishSignalStream.js

A library for managing WebRTC connections with multiplexed streams, anti-glare handling, and streamlined data channel setup.

import {asPlex, connectAndSend, listenAndConnectionAndRead$} from "rxprotoplex";
import {ReplaySubject, switchMap, take, tap, timeout, EMPTY} from "rxjs";
import {CHANNEL} from "./constants.js";

/**
 * Establishes a signaling connection between two streams, enabling WebRTC offer, answer, and ICE message
 * exchange via multiplexed channels.
 *
 * @param {Stream} stream1 - The first data stream to be connected.
 * @param {Stream} stream2 - The second data stream to be connected.
 * @param {Object} [config={}] - Optional configuration object.
 * @param {number} [config.iceCandidateTimeout=30000] - The timeout duration in milliseconds for ICE candidate messages. The timeout only starts after an offer or answer has been received.
 *
 * @description
 * The function uses the provided streams to create multiplexed (`plex`) connections that listen for
 * specific WebRTC signaling messages (offer, answer, and ICE candidates) on designated channels.
 * When a message is received on one channel, it is forwarded to the corresponding channel on the
 * target stream, effectively establishing a bi-directional signaling pipeline between the two streams.
 *
 * A close event from either stream triggers the closure of both signaling channels to avoid
 * unexpected behavior.
 *
 * - **Channels Used**:
 *   - `CHANNEL.WEBRTC_OFFER` - For WebRTC offer messages.
 *   - `CHANNEL.WEBRTC_ANSWER` - For WebRTC answer messages.
 *   - `CHANNEL.WEBRTC_ICE` - For WebRTC ICE candidates.
 *
 * @example
 * establishSignalStream(stream1, stream2, { iceCandidateTimeout: 20000 });
 *
 * @returns {Function} - A function that, when called, closes the signaling streams.
 */
const establishSignalStream = (stream1, stream2, config = {}) => {
    const { iceCandidateTimeout = 30000 } = config;
    const plex1 = asPlex(stream1);
    const plex2 = asPlex(stream2);
    const cleanups = [];

    [[plex1, plex2], [plex2, plex1]].forEach(([from, target]) => {
        const triggered = new ReplaySubject(1);
        cleanups.push(
            listenAndConnectionAndRead$(from, CHANNEL.WEBRTC_OFFER)
                .pipe(take(1), tap(() => triggered.next()))
                .subscribe(connectAndSend(target, CHANNEL.WEBRTC_OFFER)),
            listenAndConnectionAndRead$(from, CHANNEL.WEBRTC_ANSWER)
                .pipe(take(1), tap(() => triggered.next()))
                .subscribe(connectAndSend(target, CHANNEL.WEBRTC_ANSWER)),
            triggered.pipe(
                take(1),
                switchMap(() =>
                    listenAndConnectionAndRead$(from, CHANNEL.WEBRTC_ICE)
                        .pipe(
                            timeout({
                                each: iceCandidateTimeout, // Configurable timeout for ICE candidates
                                with: () => EMPTY
                            })
                        )
                )
            ).subscribe(connectAndSend(target, CHANNEL.WEBRTC_ICE))
        );
    });

    return () => cleanups.forEach((obs) => obs.unsubscribe());
}

export {establishSignalStream};