Support sending is_eof for online websocket server. (#2204)

is_final=true means an endpoint is detected.

is_eof=true means all received samples have been processed
by the server.

@@ -77,7 +77,8 @@ std::string OnlineRecognizerResult::AsJsonString() const {
   os << "\"words\": " << VecToString(words, 0) << ", ";
   os << "\"start_time\": " << std::fixed << std::setprecision(2) << start_time
      << ", ";
-  os << "\"is_final\": " << (is_final ? "true" : "false");
+  os << "\"is_final\": " << (is_final ? "true" : "false") << ", ";
+  os << "\"is_eof\": " << (is_eof ? "true" : "false");
   os << "}";
   return os.str();
 }

@@ -53,9 +53,14 @@ struct OnlineRecognizerResult {
   /// When an endpoint is detected, it will change
   float start_time = 0;
 
-  /// True if the end of this segment is reached
+  /// True if the end of this segment is reached, i.e., an endpoint is detected
+  /// used only in ./online-websocket-server-impl.cc
   bool is_final = false;
 
+  /// used only in ./online-websocket-server-impl.cc
+  /// If it is true, it means the server has processed all received samples
+  bool is_eof = false;
+
   /** Return a json string.
    *
    * The returned string contains:
@@ -69,6 +74,7 @@ struct OnlineRecognizerResult {
    *     "segment": x,
    *     "start_time": x,
    *     "is_final": true|false
+   *     "is_eof": true|false
    *   }
    */
   std::string AsJsonString() const;

@@ -210,6 +210,7 @@ void OnlineWebsocketDecoder::Decode() {
 
     if (!recognizer_->IsReady(c->s.get()) && c->eof) {
       result.is_final = true;
+      result.is_eof = true;
     }
 
     asio::post(server_->GetConnectionContext(),