fix: dispatch transport calls to network thread instead of worker thread

WebRTC's SctpTransport, DtlsTransport, and IceTransport are all
constructed on the network thread and assert owner_thread_->IsCurrent()
(or creator_thread_->IsCurrent()) on methods like dtls_transport(),
RegisterObserver(), UnregisterObserver(), and internal(). See the
RTC_DCHECK_RUN_ON assertions in the WebRTC source:

  - pc/sctp_transport.cc lines 59, 66, 105
  - pc/dtls_transport.cc lines 55, 61
  - pc/ice_transport.cc line 27

The node-webrtc code was dispatching these calls to WorkerThread, which
is the wrong thread and causes a crash in debug builds:

  Fatal error in: pc/sctp_transport.cc, line 105
  Check failed: (owner_thread_)->IsCurrent()

Additionally, PeerConnection::GetSctpTransport() requires the network
thread (pc/peer_connection.cc line 1817).

Change all call sites to use NetworkThread(). For Stop() methods that
may be called from network-thread callbacks (e.g. OnStateChange), use
IsCurrent() to avoid a redundant BlockingCall.

Author: kevindhanna

src/interfaces/rtc_data_channel.cc

@@ -125,6 +125,9 @@ void RTCDataChannel::OnPeerConnectionClosed() {
 }
 
 void RTCDataChannel::OnStateChange() {
+  if (_jingleDataChannel == nullptr) {
+    return;
+  }
   auto state = _jingleDataChannel->state();
   if (state == webrtc::DataChannelInterface::kClosed) {
     CleanupInternals();

src/interfaces/rtc_dtls_transport.cc

@@ -76,7 +76,7 @@ RTCDtlsTransport::RTCDtlsTransport(const Napi::CallbackInfo &info)
   // NOTE(mroberts): Ensure we create this.
   _transport_wrap.GetOrCreate(_factory, _transport->ice_transport());
 
-  _factory->WorkerThread()->BlockingCall([this]() {
+  _factory->NetworkThread()->BlockingCall([this]() {
     _transport->RegisterObserver(this);
     auto information = _transport->Information();
     _state = information.state();
@@ -94,7 +94,12 @@ RTCDtlsTransport::~RTCDtlsTransport() {
 }
 
 void RTCDtlsTransport::Stop() {
-  _transport->UnregisterObserver();
+  if (_factory->NetworkThread()->IsCurrent()) {
+    _transport->UnregisterObserver();
+  } else {
+    _factory->NetworkThread()->BlockingCall(
+        [this]() { _transport->UnregisterObserver(); });
+  }
   auto ice_transport = _transport_wrap.Get(_transport->ice_transport());
   if (ice_transport) {
     ice_transport->OnRTCDtlsTransportStopped();

src/interfaces/rtc_ice_transport.cc

@@ -38,7 +38,7 @@ RTCIceTransport::RTCIceTransport(const Napi::CallbackInfo &info)
 
   _transport = std::move(transport);
 
-  _factory->WorkerThread()->BlockingCall([this]() {
+  _factory->NetworkThread()->BlockingCall([this]() {
     auto internal = _transport->internal();
     if (internal) {
       internal->SignalIceTransportStateChanged.connect(

src/interfaces/rtc_peer_connection.cc

@@ -938,12 +938,13 @@ RTCPeerConnection::GetPendingRemoteDescription(const Napi::CallbackInfo &info) {
 }
 
 Napi::Value RTCPeerConnection::GetSctp(const Napi::CallbackInfo &info) {
-  return _jinglePeerConnection && _jinglePeerConnection->GetSctpTransport()
-             ? _transport_wrap
-                   .GetOrCreate(_factory,
-                                _jinglePeerConnection->GetSctpTransport())
-                   ->Value()
-             : info.Env().Null();
+  auto transport = _jinglePeerConnection
+                       ? _factory->NetworkThread()->BlockingCall([this]() {
+                           return _jinglePeerConnection->GetSctpTransport();
+                         })
+                       : nullptr;
+  return transport ? _transport_wrap.GetOrCreate(_factory, transport)->Value()
+                   : info.Env().Null();
 }
 
 Napi::Value

src/interfaces/rtc_sctp_transport.cc

@@ -38,7 +38,7 @@ RTCSctpTransport::RTCSctpTransport(const Napi::CallbackInfo &info)
 
   _transport = std::move(transport);
 
-  _factory->WorkerThread()->BlockingCall([this]() {
+  _factory->NetworkThread()->BlockingCall([this]() {
     _dtls_transport = _transport->dtls_transport();
     _transport->RegisterObserver(this);
   });
@@ -54,7 +54,12 @@ RTCSctpTransport::RTCSctpTransport(const Napi::CallbackInfo &info)
 RTCSctpTransport::~RTCSctpTransport() { wrap()->Release(this); }
 
 void RTCSctpTransport::Stop() {
-  _transport->UnregisterObserver();
+  if (_factory->NetworkThread()->IsCurrent()) {
+    _transport->UnregisterObserver();
+  } else {
+    _factory->NetworkThread()->BlockingCall(
+        [this]() { _transport->UnregisterObserver(); });
+  }
   AsyncObjectWrapWithLoop<RTCSctpTransport>::Stop();
 }