session-timers fix (#545)

Author: eschmidbauer

lib/src/rtc_session.dart

@@ -3281,19 +3281,20 @@ class RTCSession extends EventManager implements Owner {
 
     // I'm the refresher.
     if (_sessionTimers.refresher) {
-      _sessionTimers.timer = setTimeout(() {
-        if (_state == RtcSessionState.terminated) {
-          return;
-        }
-
-        logger.d('runSessionTimer() | sending session refresh request');
-
-        if (_sessionTimers.refreshMethod == SipMethod.UPDATE) {
-          _sendUpdate();
-        } else {
-          _sendReinvite();
-        }
-      }, expires! * 500); // Half the given interval (as the RFC states).
+      final int delayMs = expires! * 500;
+      _sessionTimers.timer = Timer.periodic(
+        Duration(milliseconds: delayMs),
+        (_) {
+          if (_state == RtcSessionState.terminated) return;
+          logger.d(
+              'runSessionTimer() | sending session refresh request with expires=$expires, delayMs=$delayMs');
+          if (_sessionTimers.refreshMethod == SipMethod.UPDATE) {
+            _sendUpdate();
+          } else {
+            _sendReinvite();
+          }
+        },
+      );
     }
     // I'm not the refresher.
     else {

lib/src/sip_ua_helper.dart

@@ -182,7 +182,7 @@ class SIPUAHelper extends EventManager {
     _settings.session_timers = uaSettings.sessionTimers;
     _settings.ice_gathering_timeout = uaSettings.iceGatheringTimeout;
     _settings.session_timers_refresh_method =
-        uaSettings.sessionTimersRefreshMethod;
+        uaSettings.sessionTimersRefreshMethodEnum;
     _settings.instance_id = uaSettings.instanceId;
     _settings.registrar_server = uaSettings.registrarServer;
     _settings.contact_uri = uaSettings.contact_uri != null
@@ -921,5 +921,14 @@ class UaSettings {
   /// Controls which kind of messages are to be sent to keep a SIP session
   /// alive.
   /// Defaults to "UPDATE"
-  DartSIP_C.SipMethod sessionTimersRefreshMethod = DartSIP_C.SipMethod.UPDATE;
+  String sessionTimersRefreshMethod = 'UPDATE';
+  DartSIP_C.SipMethod get sessionTimersRefreshMethodEnum {
+    switch (sessionTimersRefreshMethod.toUpperCase()) {
+      case 'INVITE':
+        return DartSIP_C.SipMethod.INVITE;
+      case 'UPDATE':
+      default:
+        return DartSIP_C.SipMethod.UPDATE;
+    }
+  }
 }