HttpClient class is not thread safe, we should protect it as we only have one socket

ixwebsocket/IXHttpClient.cpp

@@ -109,6 +109,10 @@ namespace ix
         HttpRequestArgsPtr args,
         int redirects)
     {
+        // We only have one socket connection, so we cannot 
+        // make multiple requests concurrently.
+        std::lock_guard<std::mutex> lock(_mutex);
+
         uint64_t uploadSize = 0;
         uint64_t downloadSize = 0;
         int code = 0;

ixwebsocket/IXHttpClient.h

@@ -156,5 +156,6 @@ namespace ix
         std::thread _thread;
 
         std::shared_ptr<Socket> _socket;
+        std::mutex _mutex; // to protect accessing the _socket (only one socket per client)
     };
 } // namespace ix