Service return array of arrays

edit

Hi @sisko,

You cannot do that since the definition is not well formed. As well as you cannot do string[][] topic since only one dimension is supported in msg definition. What you can do to achieve what you want can split into several approaches:

• Either you define a custom message containing a String array:

StringArray.msg

string[] topic

And then use it in your srv file like:

TopicList.srv

StringArray topic
---
StringArray[] topics

List item

• Or just implement a custom msg Multiarray like Float32Multiarray but StringMultiarray that let you declare a multi dimensional variable. It would be something like:

StringMultiarray.msg

std_msgs/MultiArrayLayout layout
string[] data

and TopicList.srv

string[] topic
---
StringMultiArray topics

Hope that can help you solving the problem.

Regards.

EDIT:

@sisko, I had implemented a client and service nodes to test your set up and I was able to make it work without errors. I used the follosing code:

For the server_node:

#!/usr/bin/env python

from topics_lister.srv import FetchTopics, FetchTopicsResponse
from topics_lister.msg import Topic
import rospy

def sendTopics(request):
    print("_________________________")
    msg_topic_1 = Topic('/turtle1/color_sensor', 'turtlesim/Color')
    msg_topic_2 = Topic('/client_count', 'std_msgs/Int32')

    response = FetchTopicsResponse()
    response.topics = [msg_topic_1, msg_topic_2]

    return response


def fetch_topics_server():
    rospy.init_node('fetch_topics_server')
    s = rospy.Service('fetch_topics', FetchTopics, sendTopics)
    print ("Serving topics ...")
    rospy.spin()

if __name__ == "__main__":
    fetch_topics_server()

And for the client_node:

#!/usr/bin/env python

import sys
import rospy
from topics_lister.srv import *
from topics_lister.msg import *

def fetch_topic_client(data):
    rospy.wait_for_service('fetch_topics')
    try:
        fetch_topics = rospy.ServiceProxy('fetch_topics', FetchTopics)
        resp1 = fetch_topics(data)
        return resp1.topics
    except rospy.ServiceException as e:
        print("Service call failed: %s"%e)

def usage():
    return "%s [data]"%sys.argv[0]

if __name__ == "__main__":
    if len(sys.argv) == 2:
        data = sys.argv[1]
    else:
        print(usage())
        sys.exit(1)
    print("Requesting topics...")
    print(fetch_topic_client("place_holder"))

Since yu only provided the response of the srv I assume the full definition is:

string req_data
---
Topic[] topics

But you can change that easily.