rtsp-simple-server/internal/servers/webrtc/reader.js

'use strict';

(() => {

  const supportsNonAdvertisedCodec = (codec, fmtp) => (
    new Promise((resolve) => {
      const payloadType = 118; // TODO: dynamic
      const pc = new RTCPeerConnection({ iceServers: [] });
      const mediaType = 'audio';
      pc.addTransceiver(mediaType, { direction: 'recvonly' });
      pc.createOffer()
        .then((offer) => {
          if (offer.sdp.includes(' ' + codec)) { // codec is advertised, there's no need to add it manually
            throw new Error('already present');
          }
          const sections = offer.sdp.split(`m=${mediaType}`);
          const lines = sections[1].split('\r\n');
          lines[0] += ` ${payloadType}`;
          lines.splice(lines.length - 1, 0, `a=rtpmap:${payloadType} ${codec}`);
          if (fmtp !== undefined) {
            lines.splice(lines.length - 1, 0, `a=fmtp:${payloadType} ${fmtp}`);
          }
          sections[1] = lines.join('\r\n');
          offer.sdp = sections.join(`m=${mediaType}`);
          return pc.setLocalDescription(offer);
        })
        .then(() => {
          return pc.setRemoteDescription(new RTCSessionDescription({
            type: 'answer',
            sdp: 'v=0\r\n'
            + 'o=- 6539324223450680508 0 IN IP4 0.0.0.0\r\n'
            + 's=-\r\n'
            + 't=0 0\r\n'
            + 'a=fingerprint:sha-256 0D:9F:78:15:42:B5:4B:E6:E2:94:3E:5B:37:78:E1:4B:54:59:A3:36:3A:E5:05:EB:27:EE:8F:D2:2D:41:29:25\r\n'
            + `m=${mediaType} 9 UDP/TLS/RTP/SAVPF ${payloadType}` + '\r\n'
            + 'c=IN IP4 0.0.0.0\r\n'
            + 'a=ice-pwd:7c3bf4770007e7432ee4ea4d697db675\r\n'
            + 'a=ice-ufrag:29e036dc\r\n'
            + 'a=sendonly\r\n'
            + 'a=rtcp-mux\r\n'
            + `a=rtpmap:${payloadType} ${codec}` + '\r\n'
            + ((fmtp !== undefined) ? `a=fmtp:${payloadType} ${fmtp}` + '\r\n' : ''),
          }));
        })
        .then(() => {
          resolve(true);
        })
        .catch(() => {
          resolve(false);
        })
        .finally(() => {
          pc.close();
        });
    })
  );

  const unquoteCredential = (v) => (
    JSON.parse(`"${v}"`)
  );

  const linkToIceServers = (links) => (
    (links !== null) ? links.split(', ').map((link) => {
      const m = link.match(/^<(.+?)>; rel="ice-server"(; username="(.*?)"; credential="(.*?)"; credential-type="password")?/i);
      const ret = {
        urls: [m[1]],
      };

      if (m[3] !== undefined) {
        ret.username = unquoteCredential(m[3]);
        ret.credential = unquoteCredential(m[4]);
        ret.credentialType = 'password';
      }

      return ret;
    }) : []
  );

  const parseOffer = (sdp) => {
    const ret = {
      iceUfrag: '',
      icePwd: '',
      medias: [],
    };

    for (const line of sdp.split('\r\n')) {
      if (line.startsWith('m=')) {
        ret.medias.push(line.slice('m='.length));
      } else if (ret.iceUfrag === '' && line.startsWith('a=ice-ufrag:')) {
        ret.iceUfrag = line.slice('a=ice-ufrag:'.length);
      } else if (ret.icePwd === '' && line.startsWith('a=ice-pwd:')) {
        ret.icePwd = line.slice('a=ice-pwd:'.length);
      }
    }

    return ret;
  };

  const findFreePayloadType = (firstLine) => {
    const payloadTypes = firstLine.split(' ').slice(3);
    for (let i = 96; i <= 127; i++) {
      if (!payloadTypes.includes(i.toString())) {
        return i.toString();
      }
    }
    throw Error('unable to find a free payload type');
  };

  const enableStereoPcmau = (section) => {
    let lines = section.split('\r\n');

    let payloadType = findFreePayloadType(lines[0]);
    lines[0] += ` ${payloadType}`;
    lines.splice(lines.length - 1, 0, `a=rtpmap:${payloadType} PCMU/8000/2`);
    lines.splice(lines.length - 1, 0, `a=rtcp-fb:${payloadType} transport-cc`);

    payloadType = findFreePayloadType(lines[0]);
    lines[0] += ` ${payloadType}`;
    lines.splice(lines.length - 1, 0, `a=rtpmap:${payloadType} PCMA/8000/2`);
    lines.splice(lines.length - 1, 0, `a=rtcp-fb:${payloadType} transport-cc`);

    return lines.join('\r\n');
  };

  const enableMultichannelOpus = (section) => {
    let lines = section.split('\r\n');

    let payloadType = findFreePayloadType(lines[0]);
    lines[0] += ` ${payloadType}`;
    lines.splice(lines.length - 1, 0, `a=rtpmap:${payloadType} multiopus/48000/3`);
    lines.splice(lines.length - 1, 0, `a=fmtp:${payloadType} channel_mapping=0,2,1;num_streams=2;coupled_streams=1`);
    lines.splice(lines.length - 1, 0, `a=rtcp-fb:${payloadType} transport-cc`);

    payloadType = findFreePayloadType(lines[0]);
    lines[0] += ` ${payloadType}`;
    lines.splice(lines.length - 1, 0, `a=rtpmap:${payloadType} multiopus/48000/4`);
    lines.splice(lines.length - 1, 0, `a=fmtp:${payloadType} channel_mapping=0,1,2,3;num_streams=2;coupled_streams=2`);
    lines.splice(lines.length - 1, 0, `a=rtcp-fb:${payloadType} transport-cc`);

    payloadType = findFreePayloadType(lines[0]);
    lines[0] += ` ${payloadType}`;
    lines.splice(lines.length - 1, 0, `a=rtpmap:${payloadType} multiopus/48000/5`);
    lines.splice(lines.length - 1, 0, `a=fmtp:${payloadType} channel_mapping=0,4,1,2,3;num_streams=3;coupled_streams=2`);
    lines.splice(lines.length - 1, 0, `a=rtcp-fb:${payloadType} transport-cc`);

    payloadType = findFreePayloadType(lines[0]);
    lines[0] += ` ${payloadType}`;
    lines.splice(lines.length - 1, 0, `a=rtpmap:${payloadType} multiopus/48000/6`);
    lines.splice(lines.length - 1, 0, `a=fmtp:${payloadType} channel_mapping=0,4,1,2,3,5;num_streams=4;coupled_streams=2`);
    lines.splice(lines.length - 1, 0, `a=rtcp-fb:${payloadType} transport-cc`);

    payloadType = findFreePayloadType(lines[0]);
    lines[0] += ` ${payloadType}`;
    lines.splice(lines.length - 1, 0, `a=rtpmap:${payloadType} multiopus/48000/7`);
    lines.splice(lines.length - 1, 0, `a=fmtp:${payloadType} channel_mapping=0,4,1,2,3,5,6;num_streams=4;coupled_streams=4`);
    lines.splice(lines.length - 1, 0, `a=rtcp-fb:${payloadType} transport-cc`);

    payloadType = findFreePayloadType(lines[0]);
    lines[0] += ` ${payloadType}`;
    lines.splice(lines.length - 1, 0, `a=rtpmap:${payloadType} multiopus/48000/8`);
    lines.splice(lines.length - 1, 0, `a=fmtp:${payloadType} channel_mapping=0,6,1,4,5,2,3,7;num_streams=5;coupled_streams=4`);
    lines.splice(lines.length - 1, 0, `a=rtcp-fb:${payloadType} transport-cc`);

    return lines.join('\r\n');
  };

  const enableL16 = (section) => {
    let lines = section.split('\r\n');

    let payloadType = findFreePayloadType(lines[0]);
    lines[0] += ` ${payloadType}`;
    lines.splice(lines.length - 1, 0, `a=rtpmap:${payloadType} L16/8000/2`);
    lines.splice(lines.length - 1, 0, `a=rtcp-fb:${payloadType} transport-cc`);

    payloadType = findFreePayloadType(lines[0]);
    lines[0] += ` ${payloadType}`;
    lines.splice(lines.length - 1, 0, `a=rtpmap:${payloadType} L16/16000/2`);
    lines.splice(lines.length - 1, 0, `a=rtcp-fb:${payloadType} transport-cc`);

    payloadType = findFreePayloadType(lines[0]);
    lines[0] += ` ${payloadType}`;
    lines.splice(lines.length - 1, 0, `a=rtpmap:${payloadType} L16/48000/2`);
    lines.splice(lines.length - 1, 0, `a=rtcp-fb:${payloadType} transport-cc`);

    return lines.join('\r\n');
  };

  const enableStereoOpus = (section) => {
    let opusPayloadFormat = '';
    let lines = section.split('\r\n');

    for (let i = 0; i < lines.length; i++) {
      if (lines[i].startsWith('a=rtpmap:') && lines[i].toLowerCase().includes('opus/')) {
        opusPayloadFormat = lines[i].slice('a=rtpmap:'.length).split(' ')[0];
        break;
      }
    }

    if (opusPayloadFormat === '') {
      return section;
    }

    for (let i = 0; i < lines.length; i++) {
      if (lines[i].startsWith('a=fmtp:' + opusPayloadFormat + ' ')) {
        if (!lines[i].includes('stereo')) {
          lines[i] += ';stereo=1';
        }
        if (!lines[i].includes('sprop-stereo')) {
          lines[i] += ';sprop-stereo=1';
        }
      }
    }

    return lines.join('\r\n');
  };

  const editOffer = (sdp, nonAdvertisedCodecs) => {
    const sections = sdp.split('m=');

    for (let i = 0; i < sections.length; i++) {
      if (sections[i].startsWith('audio')) {
        sections[i] = enableStereoOpus(sections[i]);

        if (nonAdvertisedCodecs.includes('pcma/8000/2')) {
          sections[i] = enableStereoPcmau(sections[i]);
        }
        if (nonAdvertisedCodecs.includes('multiopus/48000/6')) {
          sections[i] = enableMultichannelOpus(sections[i]);
        }
        if (nonAdvertisedCodecs.includes('L16/48000/2')) {
          sections[i] = enableL16(sections[i]);
        }

        break;
      }
    }

    return sections.join('m=');
  };

  const generateSdpFragment = (od, candidates) => {
    const candidatesByMedia = {};
    for (const candidate of candidates) {
      const mid = candidate.sdpMLineIndex;
      if (candidatesByMedia[mid] === undefined) {
        candidatesByMedia[mid] = [];
      }
      candidatesByMedia[mid].push(candidate);
    }

    let frag = 'a=ice-ufrag:' + od.iceUfrag + '\r\n'
      + 'a=ice-pwd:' + od.icePwd + '\r\n';

    let mid = 0;

    for (const media of od.medias) {
      if (candidatesByMedia[mid] !== undefined) {
        frag += 'm=' + media + '\r\n'
          + 'a=mid:' + mid + '\r\n';

        for (const candidate of candidatesByMedia[mid]) {
          frag += 'a=' + candidate.candidate + '\r\n';
        }
      }
      mid++;
    }

    return frag;
  };

  const retryPause = 2000;

  class MediaMTXWebRTCReader {
    constructor(conf) {
      this.conf = conf;
      this.state = 'initializing';
      this.restartTimeout = null;
      this.pc = null;
      this.offerData = null;
      this.sessionUrl = null;
      this.queuedCandidates = [];

      this.getNonAdvertisedCodecs()
        .then(() => this.start())
        .catch((err) => {
          this.handleError(err);
        });
    }

    handleError = (err) => {
      if (this.state === 'restarting' || this.state === 'error') {
        return;
      }

      if (this.pc !== null) {
        this.pc.close();
        this.pc = null;
      }

      this.offerData = null;

      if (this.sessionUrl !== null) {
        fetch(this.sessionUrl, {
          method: 'DELETE',
        });
        this.sessionUrl = null;
      }

      this.queuedCandidates = [];

      if (this.state === 'running') {
        this.state = 'restarting';

        this.restartTimeout = window.setTimeout(() => {
          this.restartTimeout = null;
          this.start();
        }, retryPause);

        if (this.conf.onError !== undefined) {
          this.conf.onError(err + ', retrying in some seconds');
        }
      } else {
        this.state = 'error';

        if (this.conf.onError !== undefined) {
          this.conf.onError(err);
        }
      }
    };

    getNonAdvertisedCodecs = () => {
      return Promise.all([
        ['pcma/8000/2'],
        ['multiopus/48000/6', 'channel_mapping=0,4,1,2,3,5;num_streams=4;coupled_streams=2'],
        ['L16/48000/2'],
      ]
        .map((c) => supportsNonAdvertisedCodec(c[0], c[1]).then((r) => (r) ? c[0] : false)))
        .then((c) => c.filter((e) => e !== false))
        .then((codecs) => {
          this.nonAdvertisedCodecs = codecs;
        });
    };

    start = () => {
      this.state = 'running';

      this.requestICEServers()
        .then((iceServers) => this.setupPeerConnection(iceServers))
        .then((offer) => this.sendOffer(offer))
        .then((answer) => this.setAnswer(answer))
        .catch((err) => {
          this.handleError(err.toString());
        });
    };

    requestICEServers = () => {
      return fetch(this.conf.url, {
        method: 'OPTIONS',
      })
        .then((res) => linkToIceServers(res.headers.get('Link')))
    };

    setupPeerConnection = (iceServers) => {
      this.pc = new RTCPeerConnection({
        iceServers,
        // https://webrtc.org/getting-started/unified-plan-transition-guide
        sdpSemantics: 'unified-plan',
      });

      const direction = 'recvonly';
      this.pc.addTransceiver('video', { direction });
      this.pc.addTransceiver('audio', { direction });

      this.pc.onicecandidate = (evt) => this.onLocalCandidate(evt);
      this.pc.onconnectionstatechange = () => this.onConnectionState();
      this.pc.ontrack = (evt) => this.onTrack(evt);

      return this.pc.createOffer()
        .then((offer) => {
          offer.sdp = editOffer(offer.sdp, this.nonAdvertisedCodecs);
          this.offerData = parseOffer(offer.sdp);

          return this.pc.setLocalDescription(offer)
            .then(() => offer.sdp);
        });
    };

    sendOffer = (offer) => {
      return fetch(this.conf.url, {
        method: 'POST',
        headers: {'Content-Type': 'application/sdp'},
        body: offer,
      })
        .then((res) => {
          switch (res.status) {
          case 201:
            break;
          case 404:
            throw new Error('stream not found');
          case 400:
            return res.json().then((e) => { throw new Error(e.error); });
          default:
            throw new Error(`bad status code ${res.status}`);
          }

          this.sessionUrl = new URL(res.headers.get('location'), this.conf.url).toString();

          return res.text();
        });
    };

    setAnswer = (answer) => {
      if (this.state !== 'running') {
        return;
      }

      return this.pc.setRemoteDescription(new RTCSessionDescription({
        type: 'answer',
        sdp: answer,
      }))
        .then(() => {
          if (this.queuedCandidates.length !== 0) {
            this.sendLocalCandidates(this.queuedCandidates);
            this.queuedCandidates = [];
          }
        });
    };

    onLocalCandidate = (evt) => {
      if (this.state !== 'running') {
        return;
      }

      if (evt.candidate !== null) {
        if (this.sessionUrl === null) {
          this.queuedCandidates.push(evt.candidate);
        } else {
          this.sendLocalCandidates([evt.candidate]);
        }
      }
    };

    sendLocalCandidates = (candidates) => {
      fetch(this.sessionUrl, {
        method: 'PATCH',
        headers: {
          'Content-Type': 'application/trickle-ice-sdpfrag',
          'If-Match': '*',
        },
        body: generateSdpFragment(this.offerData, candidates),
      })
        .then((res) => {
          switch (res.status) {
          case 204:
            break;
          case 404:
            throw new Error('stream not found');
          default:
            throw new Error(`bad status code ${res.status}`);
          }
        })
        .catch((err) => {
          this.handleError(err.toString());
        });
    };

    onConnectionState = () => {
      if (this.state !== 'running') {
        return;
      }

      // "closed" can arrive before "failed" and without
      // the close() method being called at all.
      // It happens when the other peer sends a termination
      // message like a DTLS CloseNotify.
      if (this.pc.connectionState === 'failed'
        || this.pc.connectionState === 'closed'
      ) {
        this.handleError('peer connection closed');
      }
    };

    onTrack = (evt) => {
      if (this.conf.onTrack !== undefined) {
        this.conf.onTrack(evt);
      }
    };

  }

  window.MediaMTXWebRTCReader = MediaMTXWebRTCReader;

})();