code: private void writeToNetwork(EngineConnection engineConnection) {
        final String methodName = "writeToNetwork";
        logger.entry(this, methodName, engineConnection);
  
          if (engineConnection.transport.pending() > 0) {
              ByteBuffer head = engineConnection.transport.head();
              int amount = head.remaining();
              engineConnection.channel.write(head, new NetworkWritePromiseImpl(this, amount, engineConnection));
              engineConnection.transport.pop(amount);
              engineConnection.transport.tick(System.currentTimeMillis());
          }
  
          logger.exit(this, methodName);
      }
docs: Drains any pending data from a Proton transport object onto the network