Can I publish a topic with type known at runtime?

[corot]

Yes:

    topic_name = rospy.get_param('~topic_name')
    topic_type = rospy.get_param('~topic_type')

    topic_class = roslib.message.get_message_class(topic_type)

    object_pub = rospy.Publisher(topic_name, topic_class, latch = True)

but.... as roslib.message import get_message_class internally imports the module containing the topic type, it must be in the Python path, what will not always be the case: the code running on the server is not supposed to have access to all the annotations' message definitions that he must handle.

Or will he??? I think this will impose a hard (but reasonable) constraint to the world canvas server use.

[jihoonl]

rosbridge_library has a dynamic message loader which you might be interested in. https://github.com/RobotWebTools/rosbridge_suite/blob/develop/rosbridge_library/src/rosbridge_library/internal/ros_loader.py#L40-L45

Forget this if it does not fit in the purpose.

[stonier]

@corot why would the server need the message definitions? I thought they would just be taking some fields and storing these in the database - e.g. relevant ones here would be

• topic_type
• a yaml string or uint8 bytearray

I can't see where it would actually need the message definition.

[stonier]

Some code that might be useful. C++ and python relaying of unknown topics at a lower level (xmlrpc/master level):

https://github.com/stonier/multimaster_experimental/tree/master/foreign_relay/src/nodes

[corot]

Yes, yes. You are right, but at some point all the solutions I have inspected import the package containing the messages. Or, as foreign_relay does, reads from the master the published topics and get topic type from there (what cannot be done in the WC server: he will publish already unpublished topics).

But I'm not worry too much about this: In most cases, the messages will be already in the server workspace, and if not, the only victim is PublishAnnotations, who will answer: "Message type not available for publishing"

[stonier]

I suspect the client library will require the message package import floating around on the ROS_PACKAGE_PATH as well. It will have to pack binary data into these message type instances.

[corot]

right. but in the client it's not a problem: if the client wants some kinds of annotations is because he knows them.

2014-06-12 3:14 GMT+02:00 Daniel Stonier notifications@github.com:

I suspect the client library will require the message package import floating around on the ROS_PACKAGE_PATH as well. It will have to pack binary data into these message type instances.

— Reply to this email directly or view it on GitHub https://github.com/corot/world_canvas/issues/5#issuecomment-45819774.

[corot]

We can close this.