📝 Advanced tutorial for recording a bag from your own node is incorrect on Humble

[JustASimpleCoder]

Issue Type

• 🐛 Bug / Problem
• ✏️ Typo / Grammar
• 📖 Outdated Content
• 🚀 Enhancement

Generated by Generative AI

Not Generated by AI

Distribution

Humble

Description

I could not build the first example for Recording a Bag From Your Own Node CPP, where I kept getting error message:

$ colcon build --packages-select

Starting >>> bag_recorder_nodes
--- stderr: bag_recorder_nodes                             
/home/j/ros2_ws/src/bag_recorder_nodes/src/simple_bag_recorder.cpp: In member function ‘void SimpleBagRecorder::topic_callback(std::shared_ptr<const rclcpp::SerializedMessage>) const’:
/home/j/ros2_ws/src/bag_recorder_nodes/src/simple_bag_recorder.cpp:27:19: error: no matching function for call to ‘rosbag2_cpp::Writer::write(std::shared_ptr<const rclcpp::SerializedMessage>&, const char [8], const char [20], rclcpp::Time&)’
   27 |     writer_->write(msg, "chatter", "std_msgs/msg/String", time_stamp);
      |     ~~~~~~~~~~~~~~^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

Further investigation shows that the humble branch indeed does not include an overloaded method in the rosbag2_cpp::Writer class (located in writer.cpp); although later branches do include it:

void Writer::write(
  std::shared_ptr<const rclcpp::SerializedMessage>
  const std::string & topic_name,
  const std::string & type_name,
  const rclcpp::Time & time)

It just has the non-const case on the humble branch:

void Writer::write(
  std::shared_ptr<rclcpp::SerializedMessage> message,
  const std::string & topic_name,
  const std::string & type_name,
  const rclcpp::Time & time)
{
  auto serialized_bag_message = std::make_shared<rosbag2_storage::SerializedBagMessage>();
  serialized_bag_message->topic_name = topic_name;
  serialized_bag_message->time_stamp = time.nanoseconds();

  serialized_bag_message->serialized_data = std::shared_ptr<rcutils_uint8_array_t>(
    new rcutils_uint8_array_t,
    [](rcutils_uint8_array_t * msg) {
      auto fini_return = rcutils_uint8_array_fini(msg);
      delete msg;
      if (fini_return != RCUTILS_RET_OK) {
        RCLCPP_ERROR_STREAM(
          rclcpp::get_logger("rosbag2_cpp"),
          "Failed to destroy serialized message: " << rcutils_get_error_string().str);
      }
    });

  *serialized_bag_message->serialized_data = message->release_rcl_serialized_message();

  return write(serialized_bag_message, topic_name, type_name, rmw_get_serialization_format());
}

The package will build sucessfully if we change the topic_callback to the non-const version:

  void topic_callback(std::shared_ptr<rclcpp::SerializedMessage> msg) const
  {
    rclcpp::Time time_stamp = this->now();

    writer_->write(msg, "chatter", "std_msgs/msg/String", time_stamp);
  }

It looks like this was an oversight from when issue #6113 (or backport from #6005) was merged.

Affected Pages/Sections

https://docs.ros.org/en/humble/Tutorials/Advanced/Recording-A-Bag-From-Your-Own-Node-CPP.html

Screenshots or Examples (if applicable)

Suggested Fix

Either remove the const from the rclcpp::SerializedMessage in the documentation for topic_callback:

  void topic_callback(std::shared_ptr<rclcpp::SerializedMessage> msg) const
  {
    rclcpp::Time time_stamp = this->now();

    writer_->write(msg, "chatter", "std_msgs/msg/String", time_stamp);
  }

Or we can update the humble branch for rosbag2's rosbag2_cpp package to include the write method that has the std::shared_ptr<const rclcpp::SerializedMessage> and leave the documentation as is.

I already did a test on a local ros2 humble build where I copied the the write method for const rclcpp::SerializedMessage from older branches (iron, jazzy, etc) and added it to the rosbag2_cpp package. I was able to sucessfully build and run ros2 simple_bag _recorder node using that write method. Here is my fork for it: const SerializedMessage add to humble branch.

I will create a pull request for the rosbag2 repo on the humble branch after this post in case other users want to utilize std::shared_ptr<const rclcpp::SerializedMessage> when writing to rosbag outside of this tutorial.

Additional Context

This was tested on Ubuntu Jammy (22.04.5 LTS) on an AMD64 machine

[fujitatomoya]

@JustASimpleCoder thanks for reporting the issue. could you consider the contribution to fix the ros2_documentation? i am happy to review!

[JustASimpleCoder]

Sure, I will contribute to remove the const in the ros2_documentation.

I also opened a contribution on the ros2bag humble branch here so we may be able to leave const after all:

Adding Writer for Const SerialesMessage

[JustASimpleCoder]

Here is the contribution to ros2_docmuentation that removes the const in relevant section. Thanks for all your hard work!

[fujitatomoya]

Either remove the const from the rclcpp::SerializedMessage in the documentation for topic_callback:

i believe what needs to be done is this approach. #6113 breaks this tutorial for humble. CC: @mini-1235