Bug 1907726 - Make sure WebTransportSessionProxy::NotifyDatagramReceived is...

Bug 1907726 - Make sure WebTransportSessionProxy::NotifyDatagramReceived is called after OnStopRequest,  a=RyanVM

The crash occurs because WebTransportSessionProxy::OnDatagramReceivedInternal is called before WebTransportSessionProxy::OnStopRequest.
When this happens, WebTransportSessionProxy::mTarget is the main thread, so a task is dispatched to the main thread. This causes WebTransportSessionProxy::NotifyDatagramReceived to be called on the main thread.

If WebTransportSessionProxy::NotifyDatagramReceived is invoked while WebTransportSessionProxy::mStopRequestCalled is true, it can lead to OnDatagramReceived being called on the main thread (instead of the socket thread), resulting in a crash.

Original Revision: https://phabricator.services.mozilla.com/D220013

Differential Revision: https://phabricator.services.mozilla.com/D221661

netwerk/protocol/webtransport/WebTransportSessionProxy.cpp

@@ -1042,15 +1042,6 @@ void WebTransportSessionProxy::NotifyDatagramReceived(
     MutexAutoLock lock(mMutex);
     MOZ_ASSERT(mTarget->IsOnCurrentThread());
 
-    if (!mStopRequestCalled) {
-      CopyableTArray<uint8_t> copied(aData);
-      mPendingEvents.AppendElement(
-          [self = RefPtr{this}, data = std::move(copied)]() mutable {
-            self->NotifyDatagramReceived(std::move(data));
-          });
-      return;
-    }
-
     if (mState != WebTransportSessionProxyState::ACTIVE || !mListener) {
       return;
     }
@@ -1066,6 +1057,15 @@ NS_IMETHODIMP WebTransportSessionProxy::OnDatagramReceivedInternal(
 
   {
     MutexAutoLock lock(mMutex);
+    if (!mStopRequestCalled) {
+      CopyableTArray<uint8_t> copied(aData);
+      mPendingEvents.AppendElement(
+          [self = RefPtr{this}, data = std::move(copied)]() mutable {
+            self->OnDatagramReceivedInternal(std::move(data));
+          });
+      return NS_OK;
+    }
+
     if (!mTarget->IsOnCurrentThread()) {
       return mTarget->Dispatch(NS_NewRunnableFunction(
           "WebTransportSessionProxy::OnDatagramReceived",