Supports getting the connected remote address. (#177)

* chore: Supports getting the connected remote address.

* chore: Merge duplicate code.

* chore: update.

* update pub deps.

* Migrate to webrtc standard stats.

lib/src/core/engine.dart

@@ -73,6 +73,9 @@ class Engine extends Disposable with EventsEmittable<EngineEvent> {
   bool _subscriberPrimary = false;
   String? _participantSid;
 
+  String? _connectedServerAddress;
+  String? get connectedServerAddress => _connectedServerAddress;
+
   // server-provided ice servers
   List<lk_rtc.ICEServer> _serverProvidedIceServers = [];
 
@@ -367,11 +370,27 @@ class Engine extends Disposable with EventsEmittable<EngineEvent> {
       signalClient.sendIceCandidate(candidate, lk_rtc.SignalTarget.PUBLISHER);
     };
 
+    publisher?.pc.onIceConnectionState =
+        (rtc.RTCIceConnectionState state) async {
+      logger.fine('publisher iceConnectionState: $state');
+      if (state == rtc.RTCIceConnectionState.RTCIceConnectionStateConnected) {
+        await _handleGettingConnectedServerAddress(publisher!.pc);
+      }
+    };
+
     subscriber?.pc.onIceCandidate = (rtc.RTCIceCandidate candidate) {
       logger.fine('subscriber onIceCandidate');
       signalClient.sendIceCandidate(candidate, lk_rtc.SignalTarget.SUBSCRIBER);
     };
 
+    subscriber?.pc.onIceConnectionState =
+        (rtc.RTCIceConnectionState state) async {
+      logger.fine('subscriber iceConnectionState: $state');
+      if (state == rtc.RTCIceConnectionState.RTCIceConnectionStateConnected) {
+        await _handleGettingConnectedServerAddress(subscriber!.pc);
+      }
+    };
+
     publisher?.onOffer = (offer) {
       logger.fine('publisher onOffer');
       signalClient.sendOffer(offer);
@@ -529,6 +548,20 @@ class Engine extends Disposable with EventsEmittable<EngineEvent> {
     }
   }
 
+  Future<void> _handleGettingConnectedServerAddress(
+      rtc.RTCPeerConnection pc) async {
+    try {
+      var remoteAddress = await getConnectedAddress(publisher!.pc);
+      logger.fine('Connected address: $remoteAddress');
+      if (_connectedServerAddress == null ||
+          _connectedServerAddress != remoteAddress) {
+        _connectedServerAddress = remoteAddress;
+      }
+    } catch (e) {
+      logger.warning('could not get connected server address ${e.toString()}');
+    }
+  }
+
   void _onDCMessage(rtc.RTCDataChannelMessage message) {
     // always expect binary
     if (!message.isBinary) {
@@ -709,3 +742,49 @@ extension EngineInternalMethods on Engine {
         _lossyDCPub
       ].whereNotNull().map((e) => e.toLKInfoType()).toList();
 }
+
+Future<String?> getConnectedAddress(rtc.RTCPeerConnection pc) async {
+  var selectedCandidatePairId = '';
+  final candidatePairs = <String, rtc.StatsReport>{};
+  // id -> candidate ip
+  final candidates = <String, String>{};
+  final List<rtc.StatsReport> stats = await pc.getStats();
+  for (var v in stats) {
+    switch (v.type) {
+      case 'transport':
+        selectedCandidatePairId = v.values['selectedCandidatePairId'] as String;
+        break;
+      case 'candidate-pair':
+        if (selectedCandidatePairId == '') {
+          if (v.values['selected'] != null && v.values['selected'] == true) {
+            selectedCandidatePairId = v.id;
+          }
+        }
+        candidatePairs[v.id] = v;
+        break;
+      case 'remote-candidate':
+        var address = '';
+        var port = 0;
+        if (v.values['address'] != null) {
+          address = v.values['address'] as String;
+        }
+        if (v.values['port'] != null) {
+          port = v.values['port'] as int;
+        }
+        candidates[v.id] = '$address:$port';
+        break;
+      default:
+    }
+  }
+
+  if (selectedCandidatePairId == '') {
+    return null;
+  }
+
+  final report = candidatePairs[selectedCandidatePairId];
+  if (report == null) {
+    return null;
+  }
+  final selectedID = report.values['remoteCandidateId'] as String;
+  return candidates[selectedID];
+}