code: public static Message buildFileReceived(String fullPath) {
      ZabMessage.FileReceived received = ZabMessage.FileReceived
                                                   .newBuilder()
                                                   .setFullPath(fullPath)
                                                   .build();
      return Message.newBuilder().setType(MessageType.FILE_RECEIVED)
                                 .setFileReceived(received).build();
    }
docs: Creates a FILE_RECEIVED message.
  
  @param fullPath the path of the received file.
  @return a protobuf message.