Errors when ICE Candidates are received before answer is sent

Question

I'm establishing WebRTC connection on Chrome 23. To attach local stream you need to allow browser to use the camera and microphone. On the caller side I'm checking if local stream can be obtained and I'm not sending offer until this moment. Then offer is sent and the browser immediately starts to send ICE candidates.

Then if remote browser didn't obtained local media stream yet I get SYNTAX_ERR: DOM Exception 12 on peerConnection.addIceCandidate(candidate) for every ICE candidate received.

I checked documentation on addIceCandidate but there is no info about prerequisites.

I think I can delay sending ICE candidates from offerer by delaying it and waiting for signal that remote client added local stream, but this is additional communication needed and doesn't look right.

Can I somehow add remote ICE candidates to webkitRTCPeerConnection before answer is sent and local media stream is attached?

Answer 1

After I wrote this question an answer came into my mind... There is no need for attaching local stream before receiving ICE candidates, but remoteDescription should be set (which should be done at the moment of receiving offer). In my code I waited with setting remoteDescription and sending answer until browser gets the local stream.

Answer 2

The solution from Episodex helped me.

First setRemoteDescription, then create own stream, then create and send the answer.

  // On read message
  if (msg.sdp.type === 'offer') {

        this.peerConnection.setRemoteDescription(new RTCSessionDescription(msg.sdp))
          .then(() => navigator.mediaDevices.getUserMedia({audio: true, video: true}))
          .then(stream => this.peerConnection.addStream(stream));
          .then(() => this.peerConnection.createAnswer())
          .then(answer => this.peerConnection.setLocalDescription(answer))
          .then(() => this.sendMessage({sdp: this.peerConnection.localDescription}))

  }