call

Connect to a ROS network.

rosinit

Launching ROS Core...
.Done in 1.2771 seconds.
Initializing ROS master on http://172.20.220.163:57900.
Initializing global node /matlab_global_node_01450 with NodeURI http://dcc821001glnxa64:32977/ and MasterURI http://localhost:57900.

Set up a service server. Use structures for the ROS message data format.

server = rossvcserver('/test', 'std_srvs/Empty', @exampleHelperROSEmptyCallback,...
                      'DataFormat','struct');
client = rossvcclient('/test','DataFormat','struct');

Check whether the service server is available. If it is, wait for the service client to connect to the server.

if(isServerAvailable(client))
    [connectionStatus,connectionStatustext] = waitForServer(client)
end

connectionStatus = logical
   1

connectionStatustext = 
'success'

Call service server with default message.

response = call(client)

response = struct with fields:
    MessageType: 'std_srvs/EmptyResponse'

If the call function above fails, it results in an error. Instead of an error, if you would prefer to react to a call failure using conditionals, return the status and statustext outputs from the call function. The status output indicates if the call succeeded, while statustext provides additional information.

numCallFailures = 0;
[response,status,statustext] = call(client,"Timeout",3);
if ~status
    numCallFailures = numCallFailues + 1;
    fprintf("Call failure number %d. Error cause: %s\n",numCallFailures,statustext)
else
    disp(response)
end

    MessageType: 'std_srvs/EmptyResponse'

Shut down the ROS network.

rosshutdown

Shutting down global node /matlab_global_node_01450 with NodeURI http://dcc821001glnxa64:32977/ and MasterURI http://localhost:57900.
Shutting down ROS master on http://172.20.220.163:57900.

Connect to a ROS network.

rosinit

Launching ROS Core...
Done in 0.70072 seconds.
Initializing ROS master on http://172.20.220.163:52789.
Initializing global node /matlab_global_node_64166 with NodeURI http://dcc821001glnxa64:43527/ and MasterURI http://localhost:52789.

Set up a service server and client. This server calculates the sum of two integers and is based on a ROS service tutorial.

sumserver = rossvcserver('/sum','roscpp_tutorials/TwoInts',@exampleHelperROSSumCallback);
sumclient = rossvcclient('/sum');

Get the request message for the client and modify the parameters.

reqMsg = rosmessage(sumclient);
reqMsg.A = 2;
reqMsg.B = 1;

Call service and get a response. The response should be the sum of the two integers given in the request message. Wait 5 seconds for the service to time out.

response = call(sumclient,reqMsg,'Timeout',5)

response = 
  ROS TwoIntsResponse message with properties:

    MessageType: 'roscpp_tutorials/TwoIntsResponse'
            Sum: 3

  Use showdetails to show the contents of the message

Shut down the ROS network.

rosshutdown

Shutting down global node /matlab_global_node_64166 with NodeURI http://dcc821001glnxa64:43527/ and MasterURI http://localhost:52789.
Shutting down ROS master on http://172.20.220.163:52789.

Create a sample ROS 2 network with two nodes.

node_1 = ros2node('node_1_service_client');
node_2 = ros2node('node_2_service_client');

Set up a service server and attach it to a ROS 2 node. Specify the callback function flipstring, which flips the input string. The callback function is defined at the end of this example.

server = ros2svcserver(node_1,'/test','test_msgs/BasicTypes',@flipString);

Set up a service client of the same service type and attach it to a different node.

client = ros2svcclient(node_2,'/test','test_msgs/BasicTypes');

Wait for the service client to connect to the server.

[connectionStatus,connectionStatustext] = waitForServer(client)

connectionStatus = logical
   1

connectionStatustext = 
'success'

Create a request message based on the client. Assign the string to the corresponding field in the message, string_value.

request = ros2message(client);
request.string_value = 'hello world';

Check whether the service server is available. If it is, send a service request and wait for a response. Specify that the service waits 3 seconds for a response.

if(isServerAvailable(client))
    response = call(client,request,'Timeout',3);
end

The response is a flipped string from the request message which you see in the string_value field.

response.string_value

ans = 
'dlrow olleh'

If the call function above fails, it results in an error. Instead of an error, if you would prefer to react to a call failure using conditionals, return the status and statustext outputs from the call function. The status output indicates if the call succeeded, while statustext provides additional information.

numCallFailures = 0;
[response,status,statustext] = call(client,request,"Timeout",3);
if ~status
    numCallFailures = numCallFailues + 1;
    fprintf("Call failure number %d. Error cause: %s\n",numCallFailures,statustext)
else
    disp(response.string_value)
end

dlrow olleh

The callback function used to flip the string is defined below.

function resp = flipString(req,resp)
% FLIPSTRING Reverses the order of a string in REQ and returns it in RESP.
resp.string_value = fliplr(req.string_value);
end