Making ROS action/service server compatible with GRIP
This page provides non-exhaustive explanations about what are ROS service and action servers and how to create them.
ROS services
In addition to ROS topics, that provide a one-to-many way to communicate between different ROS nodes (i.e. process performing computations), ROS also supports request / reply communications, through services. A ROS service is defined using srv files that describe the type of ROS message is expected as request and as reply. The computations performed by the service are gathered in a server (i.e. ROS node), and a client calls this service by sending the request message and awaiting the reply.
If you don’t understand the details, no worries, you don’t have to master these notions to successfully create your service! In fact, you can just follow our step-by-step guide to create ROS services fully compatible with GRIP!
ROS actions
Similarly to services, actions provide a request / reply type of communication between a server and a client. However, in some cases, the operations performed by the server can take a long time to execute. In such scenarios, it can be interesting to cancel the request during execution or to get periodic feedback about the current progress. That’s what actions do.
If you are not sure about how to create ROS actions, you can just follow our step-by-step guide to create ROS actions fully compatible with GRIP!
Compatibility with GRIP
If you want your ROS action and/or service to be properly integrated to GRIP, then your srv and/or action files must follow a specific format.
For ROS servers, your srv files must follow this format:
<msg_type> input
---
int8 outcome
<msg_type> returned_object
For ROS action, your action files must follow this format:
# Goal definition
<msg_type> input
---
# Result definition
<msg_type> returned_object
int8 outcome
---
# Feedback definition
<msg_type> <field_name>
<msg_type> is left to your preference, i.e. it’s implementation-dependent. As a result, when specified to GRIP’s GUI, the framework will automatically create a state running your code in the task editor!