Identify a FastDDS example topic on ROS2 [13775]

[Nir-Az]

Hi,

If I take a FastDDS example (like HelloWorldSharedMem) and run a publisher,
What need to be changed in order for ROS2 to identify this message? (let say see it in ros2 topic list command)
Thanks

[EduPonz]

Hi @Nir-Az ,

I think you may take this as an starting point to get communication going. The idea is to:

1. Transform the ROS 2 msg file into an IDL
2. Use Fast DDS-Gen with -typeros2 flag to generate the type support
3. Include the new type support into the example

However, for your publisher to appear in the ROS 2 CLI, you'd have to publish data into the ros_discovery_info topic, which ROS 2 uses for distributing discovery information. You can read more about the ROS 2 introspection tools here.

[Nir-Az]

Thanks @EduPonz ,

I took the example https://github.com/eProsima/Fast-DDS/tree/master/examples/C%2B%2B/DDS/HelloWorldExample
And rerun fastddsgen on the example idl file with -typeros2 flag,
It didn't change anything except some comment of GUID, so I think it did nothing.

1. Does the step of creating a .msg file and converting him is necessary? can't I just run it on an idl file?
   How fastddsgen HelloWorld.idl -typeros2 is different than the msg-> idl process?
2. I will read further on the introspection tools.

Thanks

[Nir-Az]

Hey @EduPonz ,

I tried doing to "proper" way and to create a .msg file according to the guide you attached.

I created devices.msg containing a single line:
string device_name

Now according to the guide I should use fastddsgen to convert this message into an IDL file?
Generate a ROS 2 compatible IDL from the ROS 2 .msg using Fast DDS-gen

How Do I do it?
I don't see this kind of option in the fastddsgen tool..
If I try -typeros2 I get this:

devices.msg:1:0: error: mismatched input 'string' expecting {'@', 'typedef', 'custom', 'import', 'struct', 'native', 'eventtype', 'enum', 'home', 'exception', 'const', 'valuetype', 'module', 'union', 'abstract', 'typeprefix', 'typeid', 'local', 'interface', 'component', 'bitset', 'bitmask', '@annotation'}
Exception in thread "main" java.lang.NullPointerException
        at com.eprosima.fastdds.fastddsgen.execute(fastddsgen.java:401)
        at com.eprosima.fastdds.fastddsgen.main(fastddsgen.java:1474)

Any help?

I also tried using fastddsgen with / without the -typeros2 flag for an OMG style idl file and the output was identical.
What am I missing?

I created also a ticket on fastddsgen repo (eProsima/Fast-DDS-Gen#92) hoping to get an answer quickly so I can progress with it..

Thanks.

[EduPonz]

Hi @Nir-Az ,

It seems there have been changes in ROS 2 since I wrote that small guide that break it. We are writing a more complete guide in Fast DDS documentation. We're still working on the text, but it should be enough for you to complete your task (see here, we'll updated it today or tomorrow). The thing is that sadly, the data type and type name need to meet a specific criteria in order for ROS 2 to detect them.