Solution proposed to implementing sim clock feature in ros2 bag play

[scoopySHI]

ros2 bag play with sim time (current time) as time stamper in header

As mentioned in issue #99, there is no proper way to play the rosbag file with sim colock (current time) as the time stamper. Therefore the rosbag file cannot be properly handled with some packages like robot_localization.
@kikass13 and i managed to find a solution to implementing this feature. We figured out the exact position of "Header" in Fastrtps serialized data and memcpy the current sim time into it as the new time stamper.
This feature is triggered with-cas argument in ros2 bag play. Otherwise ros2bag play performs as default.

Example:

ros2 bag play -c yourbagfiles.db3

Fork + branch:
https://github.com/scoopySHI/rosbag2/tree/time_fix


Test instances:
Originally it was tested with sensor_msgs/Imu and sensor_msgs/NavSatFix. In order to test the feature more comprehensively, multiple custom ros messages are also used to generate the testing rosbag files. The header is not required to be always at the first place inside the message. These custom messages are meaningless but cover thoroughly the types of messages including string, wide string, array etc. There can also be custom messages in front of the header.
Rosbags and custom messages tested:
https://github.com/scoopySHI/msg_ws

We would like to hear any feedback plus test results of this feature. @Karsten1987 @dirk-thomas @ivanpauno

[kikass13]

👍

[emersonknapp]

Closing this issue as there is already #99 tracking the feature, and this approach was decided against