Add service node

[daveconger]

It would be nice if roslibjs had a way to create service nodes in addition to being able to call them.

It appears this may be dependent on rosbridge, but is there any possibility of this in the future?

[rctoris]

Currently the ROSBRIDGE 2.0 protocol does not support the advertisement of services. The current protocol itself can be found at http://kforge.ros.org/rosbridge/trac/raw-attachment/wiki/WikiStart/rosbridge%20protocol%20specification.pdf

The problem really lies in the way rosbridge is currently thought of. Since it is really based on a server/client model, having clients act as a 'service' to a ROS system begins to get tricky. For topics and messages, there is a many-to-many relationship. Many nodes/clients can subscribe to a particular topic (e.g., /rosout) and many nodes/clients can also publish to the same topic (e.g., /cmd_vel). Services, on the other hand, have a many-to-one relationship. For example, if I am a node and I advertise /do_something, many nodes/clients can make a request to /do_something. However, no other nodes/clients can advertise /do_something since then you would not know where to forward the request. In a simple case, if rosbridge server only had one client, this problem does not matter. However, if you have multiple clients, you have to have a way of ensuring this does not get violated.

[rctoris]

Moving discussion to https://github.com/RobotWebTools/rosbridge_suite to get some more discussion going! 👍

[rctoris]

Moved to RobotWebTools/rosbridge_suite#34