Non-existent topic silent failure

[davidtaddei]

Description
When a client requests a topic through the bridge but the topic does not yet exist the bridge will silently fail the request and return success to the requesting client. If the topic then appears at a later time the data not relayed to the requesting client.

• Library Version: 3.0.2
• ROS Version: Jazzy
• Platform / OS: Ubuntu 22.04

Steps To Reproduce

1. Run the rosbridge
2. Perform a topic subscription for a topic which does not exist
3. Observe the returned success (or lack of error)
4. Publish to the requested topic using ros2
5. Observe that data is not relayed to the subscriber

Expected Behavior

1. Rosbridge returns a warning that the topic does not yet exist
2. Rosbridge retains the subscription request and waits for the topic to exist

Actual Behavior

1. Rosbridge returns a success / no error/warning message
2. Topic subscription silently failed