Bug 1641901 - Check the type of OutboundMessage::mMsg before using r=michal,necko-reviewers

Differential Revision: https://phabricator.services.mozilla.com/D77546

netwerk/protocol/websocket/WebSocketChannel.cpp

@@ -942,14 +942,21 @@ class OutboundMessage {
 
   WsMsgType GetMsgType() const { return mMsgType; }
   int32_t Length() {
-    pString& ref = mMsg.as<pString>();
-    return ref.mValue.Length();
+    if (mMsg.is<pString>()) {
+      return mMsg.as<pString>().mValue.Length();
+    }
+
+    return mMsg.as<StreamWithLength>().mLength;
   }
   int32_t OrigLength() {
+    if (mMsg.is<pString>()) {
       pString& ref = mMsg.as<pString>();
       return mDeflated ? ref.mOrigValue.Length() : ref.mValue.Length();
     }
 
+    return mMsg.as<StreamWithLength>().mLength;
+  }
+
   uint8_t* BeginWriting() {
     MOZ_ASSERT(mMsgType != kMsgTypeStream,
                "Stream should have been converted to string by now");