rtc-link/lib/listenForOffer.js

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

import {waitForOffer} from "./waitForOffer.js";
import {extractFingerprint} from "./extractFingerprint.js";
import {connectAndSend, withEncoding} from "rxprotoplex";
import {CHANNEL} from "./constants.js";

export const listenForOffer = async (plex, rtc, close$, makeNewPeer) => {
    try {
        const offer = await waitForOffer(plex, close$);
        if (!offer) return;

        const incomingFingerprint = extractFingerprint(offer.sdp);

        // Glare handling: if we are making an offer and receive an incoming offer, we check fingerprints
        if (rtc.makingOffer || rtc.signalingState !== "stable") {
            if (rtc.localFingerprint && incomingFingerprint) {
                if (incomingFingerprint < rtc.localFingerprint) {
                    return makeNewPeer(false);
                }
            }
        }

        // Check if rtc is still open before setting remote description
        if (rtc.signalingState !== "closed") {
            await rtc.setRemoteDescription(new RTCSessionDescription(offer));
            const answer = await rtc.createAnswer();
            await rtc.setLocalDescription(answer);

            connectAndSend(plex, CHANNEL.WEBRTC_ANSWER, withEncoding("json", {unique: false}))(answer);
        }
    } catch (error) {
        close$.next();
        console.error("Error in listenForOffer:", error);
    }
};