Publishing pre-serialized Bytes

[stelzo]

I have a use case where I need to send CDR-serialized bytes to a topic. I looked into the implementation and found a lot of DDS specific wording I am not familiar yet. I would think that adding alternatives in the pub/sub/etc. API that bypasses CDR serialization is not too hard when these types are familiar?

This issue is mainly a question what I would need to change for sending raw bytes to a topic. Afterwards I could also add it to the other APIs and make a PR out of it if that feature is interesting to anyone.

[jhelovuo]

The ros2-client Publisher is a fairly thin wrapper around a RustDDS DataWriter, or more specifically no_key variant specialized to CDR encoding. Please see https://github.com/Atostek/ros2-client/blob/master/src/pubsub.rs#L22 and the following impl block.

You would need to make a new version of the Publisher that is not locked to CDR encoding (as in https://github.com/Atostek/RustDDS/blob/master/src/dds/no_key/datawriter.rs#L23 ), but instead takes a SerializerAdapter that just "serializes" by passing through a pre-serialized bytestring. This dummy SerializerAdapter you would need to craft by yourself.

Additionally, you would need to rework the create_publisher functions in Node and Context. Even though you are sending raw bytestrings, you still need to announce the correct data type name over the wire, i.e. the Topic object used to create the DataWriter must still have the same data type name that the other end expects.

This is how I would approach the task, but of course have not tried it.

[stelzo]

Thank you for the quick reply!
It was quite easy to implement with your answer. Right now it is publisher-only and hacked together for a deadline of mine but maybe it can help anyone. Or it could be feature of the crate for dynamic topics? In that case I will try to find a better way to merge it into the existing API.

stelzo@087a4f6