Support IceRestart when Ice State Disconnected。 (#218)

* 网络切换后重新协商 SDP，使用IceRestart实现

* 在通话过程中持续坚挺Ice事件

* update.

* update.

Co-authored-by: cloudwebrtc <duanweiwei1982@gmail.com>

Author: zjzhang-cn

lib/src/rtc_session.dart

@@ -1139,7 +1139,8 @@ class RTCSession extends EventManager {
 
     options = options ?? <String, dynamic>{};
 
-    Map<String, dynamic> rtcOfferConstraints = options['rtcOfferConstraints'];
+    Map<String, dynamic> rtcOfferConstraints =
+        options['rtcOfferConstraints'] ?? _rtcOfferConstraints;
 
     if (_status != C.STATUS_WAITING_FOR_ACK && _status != C.STATUS_CONFIRMED) {
       return false;
@@ -1574,6 +1575,13 @@ class RTCSession extends EventManager {
     }, Timers.TIMER_H);
   }
 
+  void _iceRestart() async {
+    Map<String, dynamic> offerConstraints =
+        _rtcOfferConstraints ?? <String, dynamic>{};
+    offerConstraints['mandatory']['IceRestart'] = true;
+    renegotiate(offerConstraints);
+  }
+
   Future<void> _createRTCConnection(Map<String, dynamic> pcConfig,
       Map<String, dynamic> rtcConstraints) async {
     _connection = await createPeerConnection(pcConfig, rtcConstraints);
@@ -1585,6 +1593,9 @@ class RTCSession extends EventManager {
           'status_code': 408,
           'reason_phrase': DartSIP_C.causes.RTP_TIMEOUT
         });
+      } else if (state ==
+          RTCIceConnectionState.RTCIceConnectionStateDisconnected) {
+        _iceRestart();
       }
     };
 
@@ -1619,7 +1630,7 @@ class RTCSession extends EventManager {
   FutureOr<RTCSessionDescription> _createLocalDescription(
       String type, Map<String, dynamic> constraints) async {
     logger.debug('createLocalDescription()');
-
+    _iceGatheringState = RTCIceGatheringState.RTCIceGatheringStateNew;
     Completer<RTCSessionDescription> completer =
         Completer<RTCSessionDescription>();
 
@@ -1655,7 +1666,6 @@ class RTCSession extends EventManager {
     Future<Null> Function() ready = () async {
       _connection.onIceCandidate = null;
       _connection.onIceGatheringState = null;
-      _connection.onIceConnectionState = null;
       _iceGatheringState = RTCIceGatheringState.RTCIceGatheringStateComplete;
       finished = true;
       _rtcReady = true;