common_shim.js

/*
 *  Copyright (c) 2017 The WebRTC project authors. All Rights Reserved.
 *
 *  Use of this source code is governed by a BSD-style license
 *  that can be found in the LICENSE file in the root of the source
 *  tree.
 */
/* eslint-env node */
'use strict';

import SDPUtils from 'sdp';
import * as utils from './utils';

export function shimRTCIceCandidate(window) {
  // foundation is arbitrarily chosen as an indicator for full support for
  // https://w3c.github.io/webrtc-pc/#rtcicecandidate-interface
  if (!window.RTCIceCandidate || (window.RTCIceCandidate && 'foundation' in
      window.RTCIceCandidate.prototype)) {
    return;
  }

  const NativeRTCIceCandidate = window.RTCIceCandidate;
  window.RTCIceCandidate = function RTCIceCandidate(args) {
    // Remove the a= which shouldn't be part of the candidate string.
    if (typeof args === 'object' && args.candidate &&
        args.candidate.indexOf('a=') === 0) {
      args = JSON.parse(JSON.stringify(args));
      args.candidate = args.candidate.substring(2);
    }

    if (args.candidate && args.candidate.length) {
      // Augment the native candidate with the parsed fields.
      const nativeCandidate = new NativeRTCIceCandidate(args);
      const parsedCandidate = SDPUtils.parseCandidate(args.candidate);
      for (const key in parsedCandidate) {
        if (!(key in nativeCandidate)) {
          Object.defineProperty(nativeCandidate, key,
            {value: parsedCandidate[key]});
        }
      }

      // Override serializer to not serialize the extra attributes.
      nativeCandidate.toJSON = function toJSON() {
        return {
          candidate: nativeCandidate.candidate,
          sdpMid: nativeCandidate.sdpMid,
          sdpMLineIndex: nativeCandidate.sdpMLineIndex,
          usernameFragment: nativeCandidate.usernameFragment,
        };
      };
      return nativeCandidate;
    }
    return new NativeRTCIceCandidate(args);
  };
  window.RTCIceCandidate.prototype = NativeRTCIceCandidate.prototype;

  // Hook up the augmented candidate in onicecandidate and
  // addEventListener('icecandidate', ...)
  utils.wrapPeerConnectionEvent(window, 'icecandidate', e => {
    if (e.candidate) {
      Object.defineProperty(e, 'candidate', {
        value: new window.RTCIceCandidate(e.candidate),
        writable: 'false'
      });
    }
    return e;
  });
}

export function shimRTCIceCandidateRelayProtocol(window) {
  if (!window.RTCIceCandidate || (window.RTCIceCandidate && 'relayProtocol' in
      window.RTCIceCandidate.prototype)) {
    return;
  }

  // Hook up the augmented candidate in onicecandidate and
  // addEventListener('icecandidate', ...)
  utils.wrapPeerConnectionEvent(window, 'icecandidate', e => {
    if (e.candidate) {
      const parsedCandidate = SDPUtils.parseCandidate(e.candidate.candidate);
      if (parsedCandidate.type === 'relay') {
        // This is a libwebrtc-specific mapping of local type preference
        // to relayProtocol.
        e.candidate.relayProtocol = {
          0: 'tls',
          1: 'tcp',
          2: 'udp',
        }[parsedCandidate.priority >> 24];
      }
    }
    return e;
  });
}

export function shimMaxMessageSize(window, browserDetails) {
  if (!window.RTCPeerConnection) {
    return;
  }

  if (!('sctp' in window.RTCPeerConnection.prototype)) {
    Object.defineProperty(window.RTCPeerConnection.prototype, 'sctp', {
      get() {
        return typeof this._sctp === 'undefined' ? null : this._sctp;
      }
    });
  }

  const sctpInDescription = function(description) {
    if (!description || !description.sdp) {
      return false;
    }
    const sections = SDPUtils.splitSections(description.sdp);
    sections.shift();
    return sections.some(mediaSection => {
      const mLine = SDPUtils.parseMLine(mediaSection);
      return mLine && mLine.kind === 'application'
          && mLine.protocol.indexOf('SCTP') !== -1;
    });
  };

  const getRemoteFirefoxVersion = function(description) {
    // TODO: Is there a better solution for detecting Firefox?
    const match = description.sdp.match(/mozilla...THIS_IS_SDPARTA-(\d+)/);
    if (match === null || match.length < 2) {
      return -1;
    }
    const version = parseInt(match[1], 10);
    // Test for NaN (yes, this is ugly)
    return version !== version ? -1 : version;
  };

  const getCanSendMaxMessageSize = function(remoteIsFirefox) {
    // Every implementation we know can send at least 64 KiB.
    // Note: Although Chrome is technically able to send up to 256 KiB, the
    //       data does not reach the other peer reliably.
    //       See: https://bugs.chromium.org/p/webrtc/issues/detail?id=8419
    let canSendMaxMessageSize = 65536;
    if (browserDetails.browser === 'firefox') {
      if (browserDetails.version < 57) {
        if (remoteIsFirefox === -1) {
          // FF < 57 will send in 16 KiB chunks using the deprecated PPID
          // fragmentation.
          canSendMaxMessageSize = 16384;
        } else {
          // However, other FF (and RAWRTC) can reassemble PPID-fragmented
          // messages. Thus, supporting ~2 GiB when sending.
          canSendMaxMessageSize = 2147483637;
        }
      } else if (browserDetails.version < 60) {
        // Currently, all FF >= 57 will reset the remote maximum message size
        // to the default value when a data channel is created at a later
        // stage. :(
        // See: https://bugzilla.mozilla.org/show_bug.cgi?id=1426831
        canSendMaxMessageSize =
          browserDetails.version === 57 ? 65535 : 65536;
      } else {
        // FF >= 60 supports sending ~2 GiB
        canSendMaxMessageSize = 2147483637;
      }
    }
    return canSendMaxMessageSize;
  };

  const getMaxMessageSize = function(description, remoteIsFirefox) {
    // Note: 65536 bytes is the default value from the SDP spec. Also,
    //       every implementation we know supports receiving 65536 bytes.
    let maxMessageSize = 65536;

    // FF 57 has a slightly incorrect default remote max message size, so
    // we need to adjust it here to avoid a failure when sending.
    // See: https://bugzilla.mozilla.org/show_bug.cgi?id=1425697
    if (browserDetails.browser === 'firefox'
         && browserDetails.version === 57) {
      maxMessageSize = 65535;
    }

    const match = SDPUtils.matchPrefix(description.sdp,
      'a=max-message-size:');
    if (match.length > 0) {
      maxMessageSize = parseInt(match[0].substring(19), 10);
    } else if (browserDetails.browser === 'firefox' &&
                remoteIsFirefox !== -1) {
      // If the maximum message size is not present in the remote SDP and
      // both local and remote are Firefox, the remote peer can receive
      // ~2 GiB.
      maxMessageSize = 2147483637;
    }
    return maxMessageSize;
  };

  const origSetRemoteDescription =
      window.RTCPeerConnection.prototype.setRemoteDescription;
  window.RTCPeerConnection.prototype.setRemoteDescription =
    function setRemoteDescription() {
      this._sctp = null;
      // Chrome decided to not expose .sctp in plan-b mode.
      // As usual, adapter.js has to do an 'ugly worakaround'
      // to cover up the mess.
      if (browserDetails.browser === 'chrome' && browserDetails.version >= 76) {
        const {sdpSemantics} = this.getConfiguration();
        if (sdpSemantics === 'plan-b') {
          Object.defineProperty(this, 'sctp', {
            get() {
              return typeof this._sctp === 'undefined' ? null : this._sctp;
            },
            enumerable: true,
            configurable: true,
          });
        }
      }

      if (sctpInDescription(arguments[0])) {
        // Check if the remote is FF.
        const isFirefox = getRemoteFirefoxVersion(arguments[0]);

        // Get the maximum message size the local peer is capable of sending
        const canSendMMS = getCanSendMaxMessageSize(isFirefox);

        // Get the maximum message size of the remote peer.
        const remoteMMS = getMaxMessageSize(arguments[0], isFirefox);

        // Determine final maximum message size
        let maxMessageSize;
        if (canSendMMS === 0 && remoteMMS === 0) {
          maxMessageSize = Number.POSITIVE_INFINITY;
        } else if (canSendMMS === 0 || remoteMMS === 0) {
          maxMessageSize = Math.max(canSendMMS, remoteMMS);
        } else {
          maxMessageSize = Math.min(canSendMMS, remoteMMS);
        }

        // Create a dummy RTCSctpTransport object and the 'maxMessageSize'
        // attribute.
        const sctp = {};
        Object.defineProperty(sctp, 'maxMessageSize', {
          get() {
            return maxMessageSize;
          }
        });
        this._sctp = sctp;
      }

      return origSetRemoteDescription.apply(this, arguments);
    };
}

export function shimSendThrowTypeError(window) {
  if (!(window.RTCPeerConnection &&
      'createDataChannel' in window.RTCPeerConnection.prototype)) {
    return;
  }

  // Note: Although Firefox >= 57 has a native implementation, the maximum
  //       message size can be reset for all data channels at a later stage.
  //       See: https://bugzilla.mozilla.org/show_bug.cgi?id=1426831

  function wrapDcSend(dc, pc) {
    const origDataChannelSend = dc.send;
    dc.send = function send() {
      const data = arguments[0];
      const length = data.length || data.size || data.byteLength;
      if (dc.readyState === 'open' &&
          pc.sctp && length > pc.sctp.maxMessageSize) {
        throw new TypeError('Message too large (can send a maximum of ' +
          pc.sctp.maxMessageSize + ' bytes)');
      }
      return origDataChannelSend.apply(dc, arguments);
    };
  }
  const origCreateDataChannel =
    window.RTCPeerConnection.prototype.createDataChannel;
  window.RTCPeerConnection.prototype.createDataChannel =
    function createDataChannel() {
      const dataChannel = origCreateDataChannel.apply(this, arguments);
      wrapDcSend(dataChannel, this);
      return dataChannel;
    };
  utils.wrapPeerConnectionEvent(window, 'datachannel', e => {
    wrapDcSend(e.channel, e.target);
    return e;
  });
}


/* shims RTCConnectionState by pretending it is the same as iceConnectionState.
 * See https://bugs.chromium.org/p/webrtc/issues/detail?id=6145#c12
 * for why this is a valid hack in Chrome. In Firefox it is slightly incorrect
 * since DTLS failures would be hidden. See
 * https://bugzilla.mozilla.org/show_bug.cgi?id=1265827
 * for the Firefox tracking bug.
 */
export function shimConnectionState(window) {
  if (!window.RTCPeerConnection ||
      'connectionState' in window.RTCPeerConnection.prototype) {
    return;
  }
  const proto = window.RTCPeerConnection.prototype;
  Object.defineProperty(proto, 'connectionState', {
    get() {
      return {
        completed: 'connected',
        checking: 'connecting'
      }[this.iceConnectionState] || this.iceConnectionState;
    },
    enumerable: true,
    configurable: true
  });
  Object.defineProperty(proto, 'onconnectionstatechange', {
    get() {
      return this._onconnectionstatechange || null;
    },
    set(cb) {
      if (this._onconnectionstatechange) {
        this.removeEventListener('connectionstatechange',
          this._onconnectionstatechange);
        delete this._onconnectionstatechange;
      }
      if (cb) {
        this.addEventListener('connectionstatechange',
          this._onconnectionstatechange = cb);
      }
    },
    enumerable: true,
    configurable: true
  });

  ['setLocalDescription', 'setRemoteDescription'].forEach((method) => {
    const origMethod = proto[method];
    proto[method] = function() {
      if (!this._connectionstatechangepoly) {
        this._connectionstatechangepoly = e => {
          const pc = e.target;
          if (pc._lastConnectionState !== pc.connectionState) {
            pc._lastConnectionState = pc.connectionState;
            const newEvent = new Event('connectionstatechange', e);
            pc.dispatchEvent(newEvent);
          }
          return e;
        };
        this.addEventListener('iceconnectionstatechange',
          this._connectionstatechangepoly);
      }
      return origMethod.apply(this, arguments);
    };
  });
}

export function removeExtmapAllowMixed(window, browserDetails) {
  /* remove a=extmap-allow-mixed for webrtc.org < M71 */
  if (!window.RTCPeerConnection) {
    return;
  }
  if (browserDetails.browser === 'chrome' && browserDetails.version >= 71) {
    return;
  }
  if (browserDetails.browser === 'safari' && browserDetails.version >= 605) {
    return;
  }
  const nativeSRD = window.RTCPeerConnection.prototype.setRemoteDescription;
  window.RTCPeerConnection.prototype.setRemoteDescription =
  function setRemoteDescription(desc) {
    if (desc && desc.sdp && desc.sdp.indexOf('\na=extmap-allow-mixed') !== -1) {
      const sdp = desc.sdp.split('\n').filter((line) => {
        return line.trim() !== 'a=extmap-allow-mixed';
      }).join('\n');
      // Safari enforces read-only-ness of RTCSessionDescription fields.
      if (window.RTCSessionDescription &&
          desc instanceof window.RTCSessionDescription) {
        arguments[0] = new window.RTCSessionDescription({
          type: desc.type,
          sdp,
        });
      } else {
        desc.sdp = sdp;
      }
    }
    return nativeSRD.apply(this, arguments);
  };
}

export function shimAddIceCandidateNullOrEmpty(window, browserDetails) {
  // Support for addIceCandidate(null or undefined)
  // as well as addIceCandidate({candidate: "", ...})
  // https://bugs.chromium.org/p/chromium/issues/detail?id=978582
  // Note: must be called before other polyfills which change the signature.
  if (!(window.RTCPeerConnection && window.RTCPeerConnection.prototype)) {
    return;
  }
  const nativeAddIceCandidate =
      window.RTCPeerConnection.prototype.addIceCandidate;
  if (!nativeAddIceCandidate || nativeAddIceCandidate.length === 0) {
    return;
  }
  window.RTCPeerConnection.prototype.addIceCandidate =
    function addIceCandidate() {
      if (!arguments[0]) {
        if (arguments[1]) {
          arguments[1].apply(null);
        }
        return Promise.resolve();
      }
      // Firefox 68+ emits and processes {candidate: "", ...}, ignore
      // in older versions.
      // Native support for ignoring exists for Chrome M77+.
      // Safari ignores as well, exact version unknown but works in the same
      // version that also ignores addIceCandidate(null).
      if (((browserDetails.browser === 'chrome' && browserDetails.version < 78)
           || (browserDetails.browser === 'firefox'
               && browserDetails.version < 68)
           || (browserDetails.browser === 'safari'))
          && arguments[0] && arguments[0].candidate === '') {
        return Promise.resolve();
      }
      return nativeAddIceCandidate.apply(this, arguments);
    };
}

// Note: Make sure to call this ahead of APIs that modify
// setLocalDescription.length
export function shimParameterlessSetLocalDescription(window, browserDetails) {
  if (!(window.RTCPeerConnection && window.RTCPeerConnection.prototype)) {
    return;
  }
  const nativeSetLocalDescription =
      window.RTCPeerConnection.prototype.setLocalDescription;
  if (!nativeSetLocalDescription || nativeSetLocalDescription.length === 0) {
    return;
  }
  window.RTCPeerConnection.prototype.setLocalDescription =
    function setLocalDescription() {
      let desc = arguments[0] || {};
      if (typeof desc !== 'object' || (desc.type && desc.sdp)) {
        return nativeSetLocalDescription.apply(this, arguments);
      }
      // The remaining steps should technically happen when SLD comes off the
      // RTCPeerConnection's operations chain (not ahead of going on it), but
      // this is too difficult to shim. Instead, this shim only covers the
      // common case where the operations chain is empty. This is imperfect, but
      // should cover many cases. Rationale: Even if we can't reduce the glare
      // window to zero on imperfect implementations, there's value in tapping
      // into the perfect negotiation pattern that several browsers support.
      desc = {type: desc.type, sdp: desc.sdp};
      if (!desc.type) {
        switch (this.signalingState) {
          case 'stable':
          case 'have-local-offer':
          case 'have-remote-pranswer':
            desc.type = 'offer';
            break;
          default:
            desc.type = 'answer';
            break;
        }
      }
      if (desc.sdp || (desc.type !== 'offer' && desc.type !== 'answer')) {
        return nativeSetLocalDescription.apply(this, [desc]);
      }
      const func = desc.type === 'offer' ? this.createOffer : this.createAnswer;
      return func.apply(this)
        .then(d => nativeSetLocalDescription.apply(this, [d]));
    };
}