how to "save world as" programatically with c++

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Pressing "Save world as" invokes the MainWindow::Save function, which creates a "world_sdf" request message that is fulfilled by the gazebo server. The following is a paraphrase of the code in MainWindow::Save that places sdf file as a string in msgData:

  // Get the latest world in SDF.
  boost::shared_ptr<msgs::response> response =
    transport::request(get_world(), "world_sdf");

  msgs::GzString msg;

  // Make sure the response is correct
  if (response->response() != "error" && response->type() == msg.GetTypeName())
  {
    // Parse the response message
    msg.ParseFromString(response->serialized_data());
  }
  std::string msgData = msg.data();

I say it's a paraphrase because MainWindow::Save, as part of the gui, also tries to parse the sdf file and insert a <gui> element with information about the gui state (primarily camera position).

There is also a World::Save function that I think can be called from the same process as the server (WorldPlugin's and ModelPlugin's), but I'm not exactly sure how thread-safe it is.