Fix URL error failure mode

[gisborne]

Describe the bug

Seeing this error when trying to create a channel:

MissingPluginException(No implementation found for method listen on channel)

To Reproduce

Create new Flutter app. Delete chrome and variables from default app.

Replace build method with:

  @override
  Widget build(BuildContext context) {
    return Scaffold(
      appBar: AppBar(
        backgroundColor: Theme.of(context).colorScheme.inversePrimary,
        title: const Text("WebRTC Demo"),
      ),
      body: Center(
        child: Column(
          mainAxisAlignment: MainAxisAlignment.center,
          children: <Widget>[
            ElevatedButton(
              onPressed: () async {
                _peerConnection ??= await createPeerConnection({
                  "iceServers": [
                    {"url": "stun.l.google.com:19302"},
                    {"url": "stun1.l.google.com:19302"},
                    {"url": "stun2.l.google.com:19302"},
                    {"url": "stun3.l.google.com:19302"},
                    {"url": "stun4.l.google.com:19302"},
                  ],
                });
                _peerConnection!.onIceCandidate = (candidate) {
                  if (_peerConnection!.iceConnectionState ==
                      RTCIceConnectionState.RTCIceConnectionStateCompleted) {
                    print("Sending ${candidate.toMap()}");
                  }
                };
              },
              child: const Text("Start WebRTC"),
            ),
            ElevatedButton(
              onPressed: () {
                _peerConnection?.close();
                _peerConnection = null;
              },
              child: const Text("Stop WebRTC"),
            ),
          ],
        ),
      ),
    );
  }

Run app in MacOS and click Start WebRTC button. Observe error in console.

Expected behavior

Should create peer connection and print "Sending" message to console.

Platform information
Dart 3.3.3

• Flutter version:
  Flutter 3.29.5

• Plugin version:

• OS:
  MacOS

• OS version:
  M1 MacOS 14.2.1.

[gisborne]

Commenting out the ice servers removes the problem.

Also occurs in iOS Simulator 17.4 iPhone SE (3rd generation)

[gisborne]

Found the answer. I had this for the iceServers argument:

"iceServers": [
  {'url': 'stun.l.google.com:19302'},
…

This should be:

"iceServers": [
  {'url': 'stun:stun.l.google.com:19302'},

This is an abominable failure mode and should be fixed.