Enabled TCP candidates to improve connectivity (#132)

Author: davidzhao

Sources/LiveKit/Core/Engine.swift

@@ -671,7 +671,14 @@ extension Engine: TransportDelegate {
             self.log("subscriberPrimary: \(joinResponse.subscriberPrimary)")
 
             // update iceServers from joinResponse
-            self._state.mutate { $0.connectOptions.rtcConfiguration.set(iceServers: joinResponse.iceServers) }
+            self._state.mutate {
+                $0.connectOptions.rtcConfiguration.set(iceServers: joinResponse.iceServers)
+                if joinResponse.clientConfiguration.forceRelay == .enabled {
+                    $0.connectOptions.rtcConfiguration.iceTransportPolicy = .relay
+                } else {
+                    $0.connectOptions.rtcConfiguration.iceTransportPolicy = .all
+                }
+            }
 
             self.subscriber = try Transport(config: self._state.connectOptions.rtcConfiguration,
                                             target: .subscriber,

Sources/LiveKit/Extensions/RTCConfiguration.swift

@@ -27,8 +27,7 @@ extension RTCConfiguration {
         result.sdpSemantics = .unifiedPlan
         result.continualGatheringPolicy = .gatherContinually
         result.candidateNetworkPolicy = .all
-        // don't send TCP candidates, they are passive and only server should be sending
-        result.tcpCandidatePolicy = .disabled
+        result.tcpCandidatePolicy = .enabled
         result.iceTransportPolicy = .all
 
         result.iceServers = [ DispatchQueue.webRTC.sync { RTCIceServer(urlStrings: defaultIceServers) } ]