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https://github.com/facontidavide/ros_type_introspection

Deserialize ROS messages that are unknown at compilation time
https://github.com/facontidavide/ros_type_introspection

deserialize ros-messages rosbag

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Deserialize ROS messages that are unknown at compilation time

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# This library will be discontinued !!!



A large refactoring has been done to create a better and simpler library. All the development effort will be moved there.



### Have a look at [ros_msg_parser](https://github.com/facontidavide/ros_msg_parser)



# Ros Message Introspection



This simple library extracts information from a ROS Message, even when its

type is unknown at compilation time. 



Have you ever wanted to build an app that can subscribe to __any__ 

`topic` and extract its content, or can read data from __any__ `rosbag`? 

What if the topic and/or the bag contains user defined ROS types ignored 

at compilation time?



The common solution in the ROS ecosystem is to use Python, that provides

the needed introspection. Tools, for instance, like __rqt_plot__ and __rqt_bag__ 

took this approach. This library implements a __C++ alternative__.



This library is particularly useful to extract data from two type-erasing classes 

provided by ROS itself:



1. [topic_tools::ShapeShifter](http://docs.ros.org/diamondback/api/topic_tools/html/classtopic__tools_1_1ShapeShifter.html):

a type used to subscribe to any topic, regardless of the original type.



2. [rosbag::MessageInstance](http://docs.ros.org/diamondback/api/rosbag/html/c++/classrosbag_1_1MessageInstance.html):

the generic type commonly used to read data from a ROS bag.



Please take a look to the [examples and unit tests](https://github.com/facontidavide/type_introspection_tests) to see how to use the library.



# Some background

The ROS Message Types can be described as 

a [Interface Description Language](https://en.wikipedia.org/wiki/Interface_description_language).

This approach is very well known and commonly used on the web and in distributed systems in general.



A [rosmsg](http://wiki.ros.org/rosmsg) is defined by the user; an "IDL compiler", i.e. 

[gencpp](http://wiki.ros.org/gencpp), 

reads this schema and generates a header file that contains the source code that the user

shall include in his/her applications.

The inclusion of this header file is needed on both the publisher *and* the subscriber sides.



This approach provides strong and type-safe contracts between the producer and the consumer 

of the message and, additionally, is needed to implements a fast 

serialization / deserialization mechanism.



The only "problem" is that in very few use cases (for instance if you want to build

a plugin to [load ROS bags in MATLAB](https://github.com/bcharrow/matlab_rosbag)) 

you don't know in advance which ROS Messages you will need to read. 

Therefore, you won't be able to include the necessary header files.



# Acknowledgements

This library is inspired by these other libraries 

[matlab_rosbag](https://github.com/bcharrow/matlab_rosbag) and 

[cpp_introspection](https://github.com/tu-darmstadt-ros-pkg/cpp_introspection).