WEBVTT 00:00.260 --> 00:07.520 In this laboratory lesson, we will develop a simple Python service server that will provide the functionality 00:07.520 --> 00:10.430 of calculating the sum of two integers. 00:10.640 --> 00:17.210 Then we will also develop a client that will use this service within another Ros two node. 00:17.780 --> 00:25.130 This will help us to understand how services work from a practical perspective and how to use the command 00:25.130 --> 00:27.860 line interface to interact with them. 00:28.220 --> 00:34.190 If you are only interested in the C plus plus development, then you can directly move to the next lesson 00:34.190 --> 00:40.190 where we will implement a service server that offers the same functionalities of summing two numbers 00:40.190 --> 00:41.780 but in C plus plus. 00:42.520 --> 00:48.850 Let's start by opening Visual Studio code and by creating a new Python script within the Arduino Pi 00:48.850 --> 00:53.710 example package and within the Arduino Pi Examples app folder. 00:53.860 --> 01:01.390 And let's call this one simple service server dot pi. 01:01.930 --> 01:09.740 As usual, let's begin by importing the Pi library, which allows us to use all the tools of the two 01:09.820 --> 01:11.080 in the Python script. 01:11.440 --> 01:17.920 So let's import rcl pi and let's also import. 01:17.920 --> 01:26.560 So from RCL pi and from the node module, let's import the node class. 01:26.560 --> 01:29.860 And now we can use the node class to create a new class. 01:29.860 --> 01:40.780 So to create a new node, let's call this one simple service server that inherits from the node class 01:40.990 --> 01:41.560 here. 01:41.560 --> 01:44.840 Let's start by defining the constructor of the class. 01:44.840 --> 01:52.880 So let's define the init function that is a member of the Simple Service server class. 01:53.120 --> 01:57.020 And then we also need to call the constructor of the base class. 01:57.020 --> 02:02.810 So basically with the super function, let's call the init. 02:04.010 --> 02:06.080 Init function. 02:06.080 --> 02:09.800 So the constructor of the base class of the node class. 02:09.800 --> 02:12.230 And let's provide a name to the node. 02:12.230 --> 02:19.400 So for example, let's call it a simple service, a server. 02:20.300 --> 02:24.650 Next, let's create a new variable so a new member of the class. 02:24.860 --> 02:28.490 And let's call this one service. 02:29.840 --> 02:37.070 Just as we used the Create publisher function to create a publisher object and the create subscription 02:37.070 --> 02:39.410 function to create a subscriber object. 02:39.440 --> 02:49.490 Similarly, to create a service server, we use the create service function that we inherited from the 02:49.490 --> 02:50.480 node class. 02:51.170 --> 02:57.650 This function requires the message interface to be provided as input for the communication with the 02:57.650 --> 02:58.760 service server. 02:58.760 --> 03:05.570 And so the interface that specifies how the request and response messages are done for interacting with 03:05.570 --> 03:06.860 the service server. 03:07.250 --> 03:14.120 To do this, we need to create a new message interface for the communication with this new service server. 03:14.420 --> 03:22.280 As a convention and as a general rule in Ros2, it is advisable to place all the new message types so 03:22.280 --> 03:28.580 all the user defined message types in a different package from the ones in which we have developed the 03:28.580 --> 03:29.880 robots functionalities. 03:30.500 --> 03:36.710 So let's open our new terminal and here let's go to the workspace and to the source folder. 03:36.710 --> 03:38.720 And here let's create a new package. 03:38.720 --> 03:51.560 So Ros, to package create, let's use as build type, amend, see make, and let's call this new package 03:51.560 --> 03:53.210 that will just contain messages. 03:53.210 --> 03:58.610 So Ros to interfaces, Arduino bot messages. 03:58.610 --> 04:00.560 And so let's press enter. 04:00.590 --> 04:08.420 Now let's go back to the workspace and let's build it so that the new package is recognized. 04:08.690 --> 04:15.260 Now back in Visual Studio code, we can define an interface for the communication with the service server 04:15.380 --> 04:20.290 within the newly created Arduino bot messages for convention. 04:20.300 --> 04:26.450 The messages that define the interface for the communication with the service are placed within the 04:26.570 --> 04:28.020 serve folder. 04:28.070 --> 04:32.250 So let's create this folder that is called serve. 04:32.610 --> 04:41.310 And within this one, let's create a new file that is called Add to insert Serve. 04:43.300 --> 04:47.500 In this file, we need to define the structure of the request message. 04:47.500 --> 04:50.530 That is the one that has to be sent to the server. 04:50.680 --> 04:59.200 So the request message and this request message will consists of the two integers for which we want 04:59.200 --> 05:00.850 the server to calculate the sum. 05:01.210 --> 05:10.330 So these are two integers that we call A and B, And then we also need to define the structure of the 05:10.330 --> 05:11.380 response message. 05:11.380 --> 05:16.720 That is the one that is returned by the server when it has completed its calculation. 05:16.720 --> 05:26.560 So we can use three dashes to separate the response message from the request one and the server will 05:26.560 --> 05:33.280 simply return an integer that will contain the sum of the two integers that it received as input. 05:33.370 --> 05:35.560 So let's call this one sum. 05:37.060 --> 05:43.570 With this, we have completed the definition of the ad joints interface and now we can proceed to declare 05:43.570 --> 05:51.250 its existence to the compiler so that it can correctly build and compile this message so that other 05:51.250 --> 05:53.770 Ros two nodes and packages can use it. 05:54.010 --> 05:56.730 So let's open the file CMake list. 05:56.740 --> 06:08.380 And here let's add the dependency from the library standard messages and also let's add another find 06:08.380 --> 06:15.270 package instruction and here to compile and generate all the necessary file for using the new message, 06:15.280 --> 06:19.210 let's declare the usage of the Ros Idle. 06:21.880 --> 06:22.810 Default. 06:25.260 --> 06:26.850 Generators library. 06:27.060 --> 06:32.530 And then let's also add here before the build testing a new Ros. 06:33.190 --> 06:40.260 Idle generate interfaces instruction. 06:40.260 --> 06:46.140 And so here we say that we are generating an interface for the package Arduino bot messages. 06:46.260 --> 06:57.390 So let's use the variable project name and then let's declare the name of the service that we are using. 06:57.390 --> 07:04.180 So among the double quotes, let's declare that we have a new service within the service folder and 07:04.180 --> 07:08.570 this called Add to dot Serve. 07:09.710 --> 07:15.680 Now we are only missing to declare the dependencies of the Arduino bot messages package also in the 07:15.680 --> 07:17.390 package dot XML file. 07:17.720 --> 07:25.250 So here, let's add a dependency from the standard messages library. 07:25.460 --> 07:28.730 Then let's also add another build dependency. 07:28.880 --> 07:37.880 So here a build dependency from the Ros IDL default 07:39.980 --> 07:41.240 generators. 07:42.230 --> 07:45.350 Also declare another execution dependency. 07:45.380 --> 07:54.590 So execution dependency from the Ros IDL default runtime. 07:56.330 --> 08:04.840 And then for the generation of the service interface messages, we also need the tag member of group. 08:04.880 --> 08:14.300 And here we need to insert the ros IDL interface packages. 08:14.630 --> 08:17.470 So let's save this file. 08:17.480 --> 08:23.510 And now we can proceed to build our workspace so that the new message interface with the service. 08:23.510 --> 08:30.890 So the add to interface is recognized and we can start using it within the simple service server. 08:31.130 --> 08:32.870 So let's open a new terminal. 08:33.140 --> 08:37.070 Let's go into the workspace and let's build it. 08:40.420 --> 08:46.090 This has compiled the workspace and so it has generated also the interface with the service. 08:46.240 --> 08:53.410 And now we can go back to the simple service server here and still within the Create service function, 08:53.410 --> 08:59.050 we need to insert the interface so the message type that the service needs to use. 08:59.050 --> 09:00.520 So let's import it. 09:00.550 --> 09:12.310 So from the Arduino board messages from the services, let's import the add to insert interface. 09:13.320 --> 09:18.750 And then now let's use this interface within the create service function. 09:18.750 --> 09:25.440 So here to declare that the type of the service object that needs to be initialized should be the request 09:25.440 --> 09:30.600 and response message interface as defined in the Add joins interface. 09:31.050 --> 09:37.680 Still in the create service function, we also need to assign a name to the service, the name by which 09:37.680 --> 09:41.220 the service will be recognized in the Ros environment. 09:41.370 --> 09:47.220 For example, let's call it add two ins. 09:48.520 --> 09:55.390 Then we also need to provide a callback function, namely a function that will be executed by the service 09:55.390 --> 09:59.050 server whenever a new message request is received. 09:59.050 --> 10:06.970 So whenever a client requests the server to calculate the sum of two integers and let's call this function 10:07.990 --> 10:17.320 service callback that still we are going to define as a member of the simple service server class. 10:18.180 --> 10:22.440 To conclude the constructor of this class, let's also print a message in the terminal. 10:22.440 --> 10:28.260 So a log message using the get logger function. 10:28.410 --> 10:39.420 And then let's print an informative message that says service at the joints is ready. 10:39.900 --> 10:47.640 And now still the constructor is done, but still inside the simple service server we are missing to 10:47.640 --> 10:50.580 declare the service callback function. 10:50.580 --> 10:52.740 So let's declare this function. 10:54.490 --> 10:58.960 And let's declare it as a member of the simple service server. 10:59.770 --> 11:06.190 And as this is a callback function, it receives as input the message interface that is used for the 11:06.190 --> 11:09.550 communication and the data exchange with the server. 11:09.580 --> 11:16.630 Therefore, it receives the request and the response message for the communication with the client. 11:16.630 --> 11:22.840 So the request that was the one received from the client and the response, that is the one that we 11:22.840 --> 11:25.570 are going to return to provide to the client. 11:26.390 --> 11:30.570 First in this function, let's log an informative message in the terminal. 11:30.590 --> 11:45.020 So still with the get logger function, let's print an informative message that says new message received. 11:45.020 --> 11:50.630 And then let's print the two numbers, the two integers that we received in the request message. 11:50.630 --> 11:58.760 And so the variable A and then the variable B, So let's print both of them. 12:00.050 --> 12:03.350 And these are contained in the request message. 12:04.070 --> 12:10.640 So in the request message, let's access to the variable A and to the variable B. 12:11.150 --> 12:17.630 Now actually we can perform the logic of this service, which in this case is just to calculate the 12:17.630 --> 12:21.620 sum of the two integers that are received in the request message. 12:21.620 --> 12:30.980 And so let's calculate the sum between the variable A and the variable B, and let's store their value. 12:30.980 --> 12:34.010 So the value of the sum in the response message. 12:34.010 --> 12:41.660 So in the sum variable, so in the variable that we called sum in the response message at the end of 12:41.660 --> 12:45.560 this calculation, let's also print another informative message in the terminal. 12:51.060 --> 12:56.400 And this message says returning some. 12:56.760 --> 13:04.470 And then the value of the sum that is basically the one that we stored in the response message. 13:05.310 --> 13:10.620 Finally, to conclude this function, let's also return the response variable. 13:10.620 --> 13:16.680 So let's return the response message to the client that requested the execution of the service. 13:17.680 --> 13:22.500 This covers the definition of all the components of the simple service server. 13:22.510 --> 13:27.640 And now we can move on to define the main function, which is the one that is automatically executed 13:27.640 --> 13:29.140 when the node starts. 13:35.790 --> 13:38.250 So here, let's execute the main function. 13:38.670 --> 13:40.800 And now let's define. 13:43.180 --> 13:44.260 The main function. 13:44.260 --> 13:50.320 And let's start by initializing Ros with the function init. 13:50.350 --> 13:54.220 Then let's create a new instance of the simple service server class. 13:59.770 --> 14:01.990 And then let's keep this node up and running. 14:01.990 --> 14:11.020 So with the rcl py, let's use the spin function to keep the simple service server up and running. 14:11.200 --> 14:16.630 And finally, if we terminate the execution of the node with control Z, let's destroy the node. 14:16.960 --> 14:18.970 So simple service server. 14:21.440 --> 14:23.390 Destroy the node. 14:24.050 --> 14:26.630 And also, in this case, let's shut down Ros. 14:26.630 --> 14:27.960 So RCMP. 14:29.960 --> 14:30.920 Shut down. 14:31.960 --> 14:34.190 Here is our pie. 14:34.480 --> 14:35.440 Perfect. 14:35.590 --> 14:42.040 With this, the simple Service survey is completed, and now we can proceed to install it by modifying 14:42.040 --> 14:48.040 the file Setup.py, where we have already installed the simple publisher, subscriber and parameter 14:48.190 --> 14:53.290 so we can copy this line and we can paste it below and the new node. 14:53.290 --> 14:58.540 So the new executable will be the simple service server. 14:59.080 --> 15:04.090 And also it is in the simple service server script. 15:04.090 --> 15:08.920 As a final step since we used the Arduino bot Messages library. 15:08.920 --> 15:15.730 So since we used this library within the Arduino Pi example package, we need also to declare the usage 15:15.730 --> 15:16.660 of this library. 15:16.660 --> 15:20.230 And so we need to do this in the package dot XML. 15:20.260 --> 15:22.660 We need to add an execution dependency. 15:23.020 --> 15:29.200 So execution dependency from the Arduino bot messages. 15:29.200 --> 15:31.900 And now we can proceed to run the node. 15:31.900 --> 15:36.580 So let's open a new terminal and let's go to the workspace. 15:36.730 --> 15:43.000 And here let's first build our workspace so that the new node is installed. 15:43.720 --> 15:49.600 And now we can open a new window of the terminal, and here we can actually source the workspace. 15:50.080 --> 15:55.300 So if I set up Bash and we can run our service server node. 15:55.630 --> 16:00.370 So let's make this bigger with the command Ros to run. 16:00.400 --> 16:08.330 And from the Arduino Pi examples, let's start the simple service server node. 16:08.350 --> 16:10.540 So let's press enter. 16:10.630 --> 16:16.450 And as we do so, we can confirm that actually the node and so the server is running from the output 16:16.450 --> 16:17.200 of the terminal. 16:17.200 --> 16:20.900 So we can see that the service chewins is ready. 16:20.920 --> 16:30.190 We can also double check this if we open a new terminal and we use the command Ros two service list, 16:30.220 --> 16:37.480 we can see that actually the service Atkins is there, which is the name that we assigned to our script. 16:37.870 --> 16:41.260 Furthermore, if also in this terminal, we source the workspace. 16:41.680 --> 16:45.000 So let's source the workspace. 16:45.010 --> 16:48.580 We can also get additional information about this service. 16:48.580 --> 16:50.230 So about the communication. 16:50.230 --> 16:59.590 So the interface that it is using with the command Ros2 service type followed by the name of the service 16:59.590 --> 17:02.320 that is the Add Chewins. 17:02.320 --> 17:04.210 So let's press enter. 17:04.210 --> 17:11.890 And as we can see here, it tells us that it is using the interface the that is declared in the Arduino 17:11.890 --> 17:13.180 board messages. 17:14.050 --> 17:15.850 Now still from the terminal. 17:15.850 --> 17:21.430 We can also send our request to this service server by sending our request message. 17:21.430 --> 17:29.950 And we do this with the command rescue service call, followed by the name of the service that still 17:29.950 --> 17:34.450 is the Adkins, followed by the type of the request message. 17:34.450 --> 17:38.860 And so this is the one that belongs to the Adkins interface. 17:38.860 --> 17:43.990 So if we press tab twice, we can see that it is automatically detected. 17:44.350 --> 17:48.910 So let's insert a message of this type and then if we press tab twice. 17:48.910 --> 17:55.180 So let's insert the double quotes and let's insert the letter A and then let's press tab. 17:55.180 --> 18:00.400 We can see that it also enters an empty prototype of the request message. 18:00.400 --> 18:03.970 So the autocompletion of Ross in this is very useful. 18:04.390 --> 18:09.820 For example, let's ask the server to calculate the sum between seven. 18:10.820 --> 18:12.510 And the number five. 18:12.530 --> 18:14.300 So let's press enter. 18:14.300 --> 18:21.410 And as we can see, as soon as we do that, the server tells us that it received a new request and also 18:21.410 --> 18:23.480 it tells us that it is returning there. 18:23.780 --> 18:27.440 So 12 and also in the terminal in which we called. 18:27.440 --> 18:30.510 So we asked for the execution of this server. 18:30.530 --> 18:34.730 We see that we have the sum that was returned by the server.