SetRemoteDescription called with no ice-ufrag

[chinatsm]

Hello, I just learned webrtc recently, this is great, I’m a little confused, please help me answer
The remote client Javascript generates the following SDP
{
sdp: "v=0
↵o=- 3430854848718527786 2 IN IP4 127.0.0.1
↵s=-
↵t=0 0
↵a=msid-semantic: WMS
↵",
type: "offer",
}

Through SetRemoteDescription to handle the error as follows, may I ask what went wrong
SetRemoteDescription called with no ice-ufrag

[Sean-Der]

Hey @chinatsm

You need to add at least one track on create one datachannel before generating an Offer. This is true for establing a WebRTC connection between any implementation.

thanks for using Pion!

[chinatsm]

Thank you for your help
Now I can receive ice-ufrag, but the Answer received in Pion cannot be used, and the error "invalid proposed signaling state transition: stable->SetRemote(answer)->stable" is reported.
The following is the code：
go

func (this *Peer) Offer(id string) (info ConnectInfo, err error) {

	offer, err := this.Pc.CreateOffer(nil)
	if err != nil {
		log.Println("offer create offer error:", err)
		this.Close()
		return
	}
	if err = this.Pc.SetLocalDescription(offer); err != nil {
		log.Println("offer rtc error:", err)
		this.Close()
		return
	}
	info = ConnectInfo{
		Description: Description{
			Type: "offer",
			Sdp:  offer.SDP,
		},
		From: "server",
		To:   id,
	}
	return
}

javascript

if (description) {
                try {
                    await pc.setRemoteDescription(description);
                } catch(err) {
                    await Promise.all([
                        pc.setLocalDescription({type: "rollback"}),
                        pc.setRemoteDescription(description)
                    ]);
                } finally {
                    if (description.type == "offer") {
                        await pc.setLocalDescription(await pc.createAnswer());
                        signaler.send({description: pc.localDescription, from: to , to: from});
                    }
                }
            } else if (candidate) {
                await pc.addIceCandidate(candidate);
            }

go

case "answer":
   	anser := webrtc.SessionDescription{}
   	if err = json.Unmarshal([]byte(tojson(msg.Description)), &anser); err != nil {
   		return
   	}
   	err = this.Pc.SetRemoteDescription(anser)
   	if err != nil {
   		return
   	}

[Sean-Der]

That error happens with CreateOffer and SetLocalDescription hasn't been called.

Is it possible that you have multiple PeerConnections and are setting the answer on one that hasn't been used yet? I am happy to help, but would you prefer to discuss this here or on Stackoverflow just don't want to duplicate the effort.

[chinatsm]

Okay, I'm very sorry, I have been deleted from StackOverflow, thank you very much for your help, there are now two PEERs
One is PION and the other is a browser.
PION is used to read the local stream, and the browser can watch it through websocket communication
Is this possible?

[chinatsm]

func (this *Peer) Offer() (offer webrtc.SessionDescription, err error) {

	offer, err = this.Pc.CreateOffer(nil)
	if err != nil {
		log.Println("offer create offer error:", err)
		this.Close()
		return
	}
	err = this.Pc.SetLocalDescription(offer)
	if err != nil {
		log.Println("offer rtc error:", err)
		this.Close()
		return
	}
	return
}

Hello, I carefully checked the code according to your suggestion, and still reported an error after using SetLocalDescription: InvalidModificationError: The suggested signaling state transition is invalid: stable-> SetRemote(answer)-> stable
The current situation is:
There is no problem sending the Offer from the browser -> Pion receives and sends the Answer and the created Offer to the browser. That is, at the end Pion received the browser's Answer signal and reported an error when setting the RemoteDescription.
I haven’t solved it after testing for a long time, please help me, thank you

[Sean-Der]

Hey @chinatsm

Sorry I am not sure exatly. I would maybe start with sfu-ws and modify it.