WebRTC - Failed to set remote answer sdp: Called in wrong state: STATE_INPROGRESS - webrtc

Question

I'm following the example here: https://www.w3.org/TR/webrtc/#simple-peer-to-peer-example
I've modified the code because I only need one-way streaming:
var configuration = null; //{ "iceServers": [{ "urls": "stuns:stun.example.org" }] };
var peerConnection;
var outboundPeerStream = null;
var outboundPeerStreamSessionId = null;
var createPeerConnection = function () {
if (peerConnection)
return;
peerConnection = new RTCPeerConnection(configuration);
// send any ice candidates to the other peer
peerConnection.onicecandidate = function (event) {
signalrModule.sendClientNotification(JSON.stringify({ "candidate": event.candidate }));
};
// let the "negotiationneeded" event trigger offer generation
peerConnection.onnegotiationneeded = peerStreamingModule.sendOfferToPeers;
// once remote track arrives, show it in the remote video element
peerConnection.ontrack = function (event) {
var inboundPeerStream = event.streams[0];
remoteStreamHelper.pushStreamToDom(inboundPeerStream, foo);
}
}
// this gets called either on negotiationNeeded and every 30s to ensure all peers have the offer from the stream originator
peerStreamingModule.sendOfferToPeers = function () {
peerConnection.createOffer().then(function (offer) {
return peerConnection.setLocalDescription(offer);
}).then(function () {
// send the offer to the other peer
signalrModule.sendClientNotification(JSON.stringify({ "desc": peerConnection.localDescription}));
}).catch(logger.internalLog);
};
// this gets called by the stream originator when the stream is available to initiate streaming to peers
peerStreamingModule.initializeWithStream = function (outboundStream, sessionId) {
outboundPeerStream = outboundStream;
outboundPeerStreamSessionId = sessionId;
createPeerConnection();
peerConnection.addStream(outboundStream);
//peerStreamingModule.sendOfferToPeers(); I don't think I need this...
}
peerStreamingModule.handleP2PEvent = function (notification) {
if (!peerConnection)
createPeerConnection();
if (notification.desc) {
var desc = notification.desc;
// if we get an offer, we need to reply with an answer
if (desc.type == "offer") {
peerConnection.setRemoteDescription(desc).then(function () {
return peerConnection.createAnswer();
}).then(function (answer) {
return peerConnection.setLocalDescription(answer);
}).then(function () {
signalrModule.sendClientNotification(JSON.stringify({ "desc": peerConnection.localDescription, "sessionId": sessionManager.thisSession().deviceSessionId() }), app.username());
}).catch(logger.internalLog);
} else if (desc.type == "answer") {
peerConnection.setRemoteDescription(desc).catch(logger.internalLog);
} else {
logger.internalLog("Unsupported SDP type. Your code may differ here.");
}
} else
pc.addIceCandidate(notification.candidate).catch(logger.internalLog);
}
This seems to be working, but I'm stumped with two parts:
1) WebRTC - Failed to set remote answer sdp: Called in wrong state: STATE_INPROGRESS - this is appearing in my logs from time to time - am I doing something wrong in the above that is causing this?
2) Am I correctly implementing sendOfferToPeers and initializeWithStream? I'm afraid that the sendOfferToPeers getting triggered on interval from the originator isn't how the spec is intended to be used; my goal is to ensure that all peers eventually receive an offer no matter when they join or whether or not they're facing connectivity issues that drop the original offer / negotiation.

Answer 1

// this gets called either on negotiationNeeded and every 30s to ensure all peers have the offer
You can't send the same offer to multiple peers. It's peer-to-peer, not peer-to-peers. One-to-many requires at minimum a connection per participant, and probably a media server to scale.
Also, SDP is not for discovery. The offer/answer exchange is a fragile state-machine negotiation between two end-points only, to set up a single connection.
You should solve who's connecting with whom ahead of establishing the WebRTC connection.