Unity-Robotics-Hub/tutorials/ros_unity_integration/unity_scripts/RosServiceExample.cs

using RosMessageTypes.RoboticsDemo;
using UnityEngine;
using Unity.Robotics.ROSTCPConnector;

public class RosServiceExample : MonoBehaviour
{
    ROSConnection ros;

    public string serviceName = "pos_srv";

    public GameObject cube;

    // Cube movement conditions
    public float delta = 1.0f;
    public float speed = 2.0f;
    private Vector3 destination;

    float awaitingResponseUntilTimestamp = -1;

    void Start()
    {
        ros = ROSConnection.instance;
        destination = cube.transform.position;
    }

    private void Update()
    {
        // Move our position a step closer to the target.
        float step = speed * Time.deltaTime; // calculate distance to move
        cube.transform.position = Vector3.MoveTowards(cube.transform.position, destination, step);

        if (Vector3.Distance(cube.transform.position, destination) < delta && Time.time > awaitingResponseUntilTimestamp)
        {
            Debug.Log("Destination reached.");

            MPosRot cubePos = new MPosRot(
                cube.transform.position.x,
                cube.transform.position.y,
                cube.transform.position.z,
                cube.transform.rotation.x,
                cube.transform.rotation.y,
                cube.transform.rotation.z,
                cube.transform.rotation.w
            );

            MPositionServiceRequest positionServiceRequest = new MPositionServiceRequest(cubePos);

            // Send message to ROS and return the response
            ros.SendServiceMessage<MPositionServiceResponse>(serviceName, positionServiceRequest, Callback_Destination);
            awaitingResponseUntilTimestamp = Time.time+1.0f; // don't send again for 1 second, or until we receive a response
        }
    }

    void Callback_Destination(MPositionServiceResponse response)
    {
        awaitingResponseUntilTimestamp = -1;
        destination = new Vector3(response.output.pos_x, response.output.pos_y, response.output.pos_z);
        Debug.Log("New Destination: " + destination);
    }
}