WEBVTT 00:00.450 --> 00:08.070 In this laboratory lesson, we will create a service client in Ros2 using Python that requires the usage 00:08.070 --> 00:14.250 of the functionalities offered by the service server that we developed in the previous laboratory lessons. 00:14.790 --> 00:20.430 If you are only interested in the cplusplus development, then you can skip directly to the next lesson 00:20.430 --> 00:24.660 in which we are going to develop the same service client in Cplusplus. 00:25.310 --> 00:31.070 In practice, we are going to create a python node that use the service for the sum of two integers, 00:31.070 --> 00:33.350 which we called Adjoints. 00:33.350 --> 00:38.750 And so based on what we have learned in the theoretical lesson, the client will send a request to the 00:38.750 --> 00:42.350 service according to the format defined by the service. 00:42.350 --> 00:49.310 So following its interface and it will be notified with a response message when the service has finished 00:49.310 --> 00:50.720 its execution. 00:50.900 --> 00:56.570 So let's start by creating a new script within our Arduino Pi examples. 00:56.570 --> 01:08.420 So within the Arduino Pi example sub folder and let's call this one simple service client dot pi. 01:08.870 --> 01:21.050 As always, let's start by importing the Pi library and also from the Pi library, RCL pi library, 01:21.050 --> 01:22.730 and from the node modules. 01:23.090 --> 01:28.490 Let's import the node class which we can use to define a new ros2 node. 01:29.010 --> 01:38.460 And so let's call this one simple service client that inherits from the node class. 01:38.730 --> 01:49.470 As always, let's start by defining the constructor of this class so the init function in it as a member, 01:49.740 --> 01:53.790 so self as a member of the simple Service class. 01:54.030 --> 01:59.400 And here now, let's start also by calling the constructor of the base class. 02:00.030 --> 02:07.560 So let's call the init function of the node class which takes as input the name that we want to provide 02:07.560 --> 02:08.310 to the node. 02:08.340 --> 02:13.770 For example, let's call this one simple service. 02:15.530 --> 02:16.220 Client. 02:16.490 --> 02:19.010 We make the constructor of this class. 02:19.010 --> 02:24.380 So this variable here, this function here to receive two numbers in input. 02:24.380 --> 02:30.950 So two variables that we call A and B, and these are the two numbers that we want to sum. 02:30.950 --> 02:35.960 So these are the two numbers that we want to send in the request message to the server, and we want 02:35.960 --> 02:38.090 this service to add together. 02:38.420 --> 02:44.150 So now in order to send a request to our service server, let's create a new object. 02:44.150 --> 02:48.830 So let's create a new variable and call this one client. 02:48.830 --> 02:55.880 And as you can certainly imagine, just like we used the create service function from the Node class 02:55.880 --> 03:03.980 to initialize a service server here, we can use the create client function to create the service client 03:04.280 --> 03:06.800 similarly to the create service function. 03:06.800 --> 03:14.000 Also, the create client function requires as input the message interface type that is to be used in 03:14.000 --> 03:16.650 order to contact with the service server. 03:16.740 --> 03:24.540 So within this script let's import from the Arduino both messages and from the services that we have 03:24.540 --> 03:25.320 defined. 03:25.830 --> 03:35.310 Let's import the add to its interface and let's use this interface to contact the action server. 03:35.790 --> 03:42.420 Also, this function requires another parameter as input that is the name of the service, namely the 03:42.420 --> 03:52.530 name by which the server is recognized in Ros2 and we named it Add two ints when we initialized the 03:52.530 --> 03:54.720 service server in the previous lesson. 03:55.570 --> 04:01.960 Now that we have our client before actually using it to send the request to the server, let's first 04:01.960 --> 04:06.610 verify that the server is running and so is available to receive new requests. 04:06.910 --> 04:12.460 So we can use the function on the client object. 04:12.490 --> 04:19.120 We can use the function, wait for service, and also we can specify a certain amount of time that we 04:19.120 --> 04:21.030 want to wait for the service. 04:21.040 --> 04:25.190 So let's set a timeout of 1.0 second. 04:25.210 --> 04:32.260 So let's wait until this call is not correctly executed. 04:32.260 --> 04:37.510 So let's wait until the wait for service is not executed correctly. 04:37.510 --> 04:44.110 And so every time, if, for example, the service is not ready yet, in one second, we will wait again. 04:44.110 --> 04:48.070 So we will wait again infinitely until the server is not ready. 04:48.070 --> 04:49.240 And every time. 04:49.240 --> 04:54.510 So every time that we are waiting and the server is not ready, let's print an informative message. 04:54.520 --> 05:07.940 So with the get logger function and the informative message says service not available, waiting more. 05:09.830 --> 05:10.310 Okay. 05:10.790 --> 05:18.830 And now once we are out of this function, it means that actually the client was able to find a service 05:18.830 --> 05:21.980 with this name and it is using this interface. 05:21.980 --> 05:28.070 And so now we can actually create the request message and send it to the service server. 05:28.190 --> 05:33.740 So let's create a new variable and let's call this one request. 05:33.920 --> 05:37.520 And this is from the interface Add joins. 05:37.730 --> 05:41.210 This is of type request. 05:41.840 --> 05:46.130 And here we can assign the values to the request message. 05:46.250 --> 05:54.980 So to the request variable, let's assign a value to the variable A That is the number A that we received 05:54.980 --> 05:58.100 as input of the constructor and let's do the same. 05:58.730 --> 06:02.930 So the request B takes as input. 06:02.960 --> 06:07.010 The B variable that was received as input by the constructor. 06:07.840 --> 06:14.040 Now we can send these requests or this message to the service by using the function. 06:14.050 --> 06:22.300 So on the client, let's use the function call async and we need to pass to this function the request 06:22.300 --> 06:24.010 message that we just created. 06:24.010 --> 06:31.510 So the variable that we called request, the output of this function is a future variable. 06:31.660 --> 06:39.670 So let's store this one within the variable future, a new variable that we are defining now. 06:40.060 --> 06:47.320 And basically this function immediately returns a result that we are storing within the future function 06:47.320 --> 06:54.430 and that we can use in the future to add a callback function that can be executed as soon as the server 06:54.430 --> 06:58.120 finishes the calculation and returns a response message. 06:58.330 --> 07:00.730 So let's use this future variable. 07:03.010 --> 07:04.870 And let's add a callback function. 07:04.870 --> 07:07.720 So add done callback. 07:07.960 --> 07:13.200 And let's execute the function response callback. 07:13.210 --> 07:19.870 So basically here we are saying that after calling the service server, we have a future variable. 07:19.870 --> 07:25.840 And here let's add the done callback function that we called the response callback that will be executed 07:25.840 --> 07:28.550 once we get the response from the server. 07:28.570 --> 07:35.340 So now let's define this function still within the simple service client class. 07:35.350 --> 07:44.200 So let's define this one as a member of this class, which takes as input the future variable that we 07:44.200 --> 07:44.980 are following. 07:44.980 --> 07:49.000 So the future variable that returns from the call async. 07:49.650 --> 07:51.270 And now we can use these variables. 07:51.270 --> 07:54.980 So the future variable to access to the result of the service. 07:54.990 --> 07:58.710 So let's print an informative message into the terminal. 08:00.240 --> 08:09.300 And this message says service response, followed by the value that the service returned that we can 08:09.300 --> 08:12.090 take from the future. 08:12.480 --> 08:16.200 Then let's take the result. 08:16.380 --> 08:20.010 And from the result, let's take the sum variable. 08:20.920 --> 08:23.230 With this, the simple service client. 08:23.230 --> 08:25.180 So this class is completed. 08:25.180 --> 08:28.900 And now what is missing is just to define the main function. 08:29.500 --> 08:30.160 So. 08:38.190 --> 08:38.610 Here. 08:38.610 --> 08:43.290 Let's execute the main function and let's also define it. 08:45.660 --> 08:46.890 And in the main function. 08:46.890 --> 08:54.990 Let's start by initializing Ros two so the ros two node with rcl pi dot init. 08:55.560 --> 08:59.520 And then let's create a new instance of the simple service client class. 08:59.520 --> 09:08.430 So let's call this one simple service client as an instance of the simple service client. 09:08.670 --> 09:14.700 And however, since we are automatically executing the constructor of the Simple Service class, when 09:14.700 --> 09:21.420 we instantiate the new object, we also need to pass the two integers so the two numbers that will be 09:21.420 --> 09:23.160 contained in the request message. 09:23.160 --> 09:30.660 So the one that will be here in the request message the value A and B, So to the constructor here, 09:30.840 --> 09:35.190 we cannot pass an empty constructor, but we have to pass two numbers. 09:35.550 --> 09:41.760 We can take these two numbers from the parameters of the script that we are creating, specifically 09:41.760 --> 09:44.490 from the parameters of the main function. 09:44.490 --> 09:49.020 And to do so we need to import the system library of Python. 09:49.020 --> 09:53.610 So let's import the system library from Python. 09:53.760 --> 09:55.960 And then after the init. 09:55.960 --> 09:58.570 So here let's check if the script. 09:58.570 --> 10:04.210 So the node, the simple service client node has been started with the correct number of arguments. 10:04.240 --> 10:10.600 So let's check that the length of the system argument. 10:11.320 --> 10:14.320 Is different than three. 10:14.320 --> 10:21.520 So we expect the script to be started with three parameters because the main function always receives 10:21.550 --> 10:27.700 an argument as input, so that one is by default and we want to be passed two more arguments. 10:27.700 --> 10:33.940 So apart from the automatic argument that is always passed, we need this script to be started with 10:33.940 --> 10:40.030 two additional arguments, which are the two integers that we want to add together and if these two 10:40.030 --> 10:40.810 are not provided. 10:40.810 --> 10:47.290 So for example, if we are starting this script with a wrong number of parameters, let's print a message 10:47.290 --> 10:55.480 in the console that says wrong number of arguments. 10:55.480 --> 11:06.070 And so we complain about this one and we specify that the usage is simple service client. 11:06.070 --> 11:13.460 So this script has to be started as simple service client followed by a and B, so followed by two numbers. 11:13.460 --> 11:16.400 That will be the two numbers that will be added together. 11:16.490 --> 11:22.460 And in this case, so if the user who started this note has not provided the correct number of parameters, 11:22.490 --> 11:24.920 let's just return minus one. 11:24.920 --> 11:26.810 So let's return an error. 11:27.500 --> 11:28.370 Alternatively. 11:28.550 --> 11:32.540 So out of this, if if the script has been started correctly. 11:32.540 --> 11:38.330 So with the correct number of arguments, we can pass the first and the second of these argument as 11:38.330 --> 11:40.040 input to the constructor. 11:40.130 --> 11:44.440 So here we can pass the first one. 11:44.450 --> 11:56.510 So system argument in the first position and the system argument in the second position as input to 11:56.510 --> 11:57.290 the service client. 11:57.290 --> 12:02.420 So this will be the two numbers that then we will pass to the service server. 12:02.960 --> 12:10.910 As always, let's keep this node up and running with the RCL pi dot spin function. 12:10.910 --> 12:14.480 So let's keep the simple service client node up and running. 12:14.480 --> 12:18.820 And then if we stop the execution with Control-c, let's destroy the node. 12:18.830 --> 12:20.840 So simple service client. 12:22.370 --> 12:26.440 Destroy the node and then also shut down Ros. 12:26.450 --> 12:30.090 So rcl dot shut down. 12:31.310 --> 12:38.120 With this, the simple service client is complete and now we can proceed to install it alongside all 12:38.120 --> 12:44.240 the other nodes, all the other executable that we have already created for the Arduino Pi examples. 12:44.240 --> 12:52.460 So in the setup.py, let's copy this line that we used for installing the simple service server and 12:52.460 --> 12:57.530 let's just change the name of the executable into simple service client. 12:57.830 --> 13:04.910 And the name of the script also is the simple service client from which still we want the main function 13:04.910 --> 13:06.050 to be executed. 13:07.030 --> 13:07.780 For this node. 13:07.810 --> 13:14.230 We don't need to modify the package dot XML since we don't have introduced any new dependency so we 13:14.230 --> 13:17.650 can directly proceed to run this node and see how it works. 13:18.100 --> 13:26.140 So let's open a new terminal and let's go to the workspace and here we can build it. 13:28.000 --> 13:36.760 Now the build is successful so we can split the terminal and here we can source the file setup dot bash 13:36.850 --> 13:40.000 and finally we can run our client node. 13:40.890 --> 13:43.320 So first let's start the server. 13:43.320 --> 13:55.020 So with Ros to run and from the Arduino board by examples, let's start the simple service server node. 13:55.260 --> 13:59.730 So let's press enter and this will start the simple service server. 13:59.730 --> 14:06.300 And now we can contact this server so we can send a request to this server in a new terminal. 14:06.300 --> 14:15.810 Let's again source the workspace and let's run the simple service client with Ros to run and from the 14:15.810 --> 14:18.450 Arduino bot by examples. 14:18.690 --> 14:22.680 Let's start the simple service client node. 14:22.800 --> 14:29.610 If you remember, we need to provide two additional arguments to this script, which are the two numbers 14:29.610 --> 14:30.540 that we want to send. 14:30.870 --> 14:34.380 For example, let's add together five entry. 14:34.470 --> 14:37.350 So let's press enter here. 14:37.350 --> 14:40.990 We can see that there is an error since we need to cast. 14:41.410 --> 14:42.910 In the simple service. 14:42.910 --> 14:49.960 So here, by default, the arguments that we pass to the main are treated as string. 14:50.290 --> 14:54.730 So we need first to cast them to integers. 14:55.700 --> 14:58.790 And now we can build again the workspace. 15:00.520 --> 15:03.160 And we can execute again our script. 15:03.400 --> 15:05.590 And now we can see that correctly. 15:05.590 --> 15:06.520 The node. 15:06.520 --> 15:09.190 So the client is correctly calling. 15:09.280 --> 15:11.830 So it's sending a request to this service. 15:11.830 --> 15:18.010 And this service is receiving the request and is returning a response that contains the sum. 15:18.520 --> 15:24.820 If now, for example, we restart this same node so the simple service client with a wrong number of 15:24.820 --> 15:25.660 parameters. 15:25.810 --> 15:28.360 Let's say that we don't pass any number. 15:28.810 --> 15:35.830 Now we can see that of course the node is stopped so the node fails as we are not passing the A and 15:35.830 --> 15:38.440 B, So the two numbers that we need to add together. 15:39.130 --> 15:45.610 We can also try to stop the service server and to start this time only the service client. 15:45.640 --> 15:47.920 So let's start the correct version of it. 15:47.920 --> 15:52.210 So let's start the service client passing the numbers five and three. 15:52.210 --> 15:55.360 So let's say that we want to add together five and three. 15:55.600 --> 15:57.250 So let's press enter. 15:57.340 --> 16:01.600 And as you can see, the service client is not doing anything. 16:01.600 --> 16:05.860 So it's just printing the message service not available, waiting more. 16:05.860 --> 16:12.820 So basically because we stopped the service server and as soon as we restart the server, actually we 16:12.820 --> 16:17.530 can see that it received the request and also returns the response.