How to inspect service and make a service call

In this article, we will walk through the process of service inspection and present an example of making service call.

The first step is to list available services on the network

ros2 service list
ros2 service list -t

The second command list both service name and the request type.

Suppose we have a service called /add_entity. The next step is to find out the reques type of this service. This can be done using the following command:

ros2 service type /add_entity

The output of this command is the service request type. Suppose the output is entity_management/srv/AddEntity. The next step is to find out the details of this type. This can be done using the following command:

ros2 interface show entity_management/srv/AddEntity

The interface show command produces the details of the type. For example,

AddEntity
string name
string model_filepath
geometry_msgs/Point location
	float64 x
	float64 y
	float64 z
float64 theta
---
bool result

To summarize, we have collected the following information:

Item	Description
service name	/add_entity
service request type	entity_management/srv/AddEntity
service response type	bool
fields in the request type	name, model_filepath, location, theta

The remaining question is how can we make a service call? The command to use is ros2 service call <service_name> <service_type>. Here is an example:

ros2 service call /add_entity entity_management/srv/AddEntity "{name: 'name with space', model_filepath: 'test_path', location: {x: 1, y: 2, z: 3}, theta: 1.3}"

The space in the command is significant, especially the one following the colon (:) that comes after the field name.

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