WEBVTT 00:00.640 --> 00:07.360 In this laboratory lesson, we will develop a simple service server in C plus plus that will provide 00:07.360 --> 00:10.660 the functionality of calculating the sum of two integers. 00:10.930 --> 00:16.840 Then we will also develop a client that will use this service within another Ros two node. 00:17.470 --> 00:23.770 This will help us to understand how services works practically and how to use the Ros to command line 00:23.770 --> 00:25.780 interface to interact with them. 00:26.660 --> 00:30.920 Let's start by creating a new Cplusplus script inside the Arduino. 00:31.190 --> 00:32.390 CPP examples. 00:32.390 --> 00:34.160 So inside the source folder. 00:34.780 --> 00:39.340 And let's call this script simple service. 00:40.300 --> 00:41.980 Server dot cpp. 00:42.340 --> 00:49.090 Here, as always, let's start by importing the CPP library. 00:49.090 --> 00:53.110 And so let's include the CPP dot PHP. 00:53.470 --> 00:58.420 And then from this library, let's use the node class to create a new Ros2 node. 00:58.960 --> 01:12.460 So let's call this one simple service server that inherits from the CPP library and so from the node 01:12.460 --> 01:13.120 class. 01:13.420 --> 01:22.570 So let's define this class and among the public methods of this class, let's start as always by declaring 01:22.570 --> 01:24.210 the constructor of this class. 01:24.220 --> 01:30.310 So the function simple service server and here, as we did in the previous lesson. 01:30.310 --> 01:34.460 Also, let's start by initializing the node class. 01:34.460 --> 01:41.210 So the base class and we need to provide as input of the constructor the name of the node, let's call 01:41.210 --> 01:46.910 it, for example, simple service server. 01:47.710 --> 01:51.070 Now among the private variables of this class. 01:51.070 --> 01:56.680 So here let's create a new object of type service. 01:56.680 --> 02:01.840 So from RCL, CP, let's create a new service. 02:02.110 --> 02:10.420 And this is a template class and we take a shared pointer to this class and let's call this variable 02:11.140 --> 02:12.100 service. 02:12.460 --> 02:24.280 Now let's also remember to include here include the memory library from C plus plus in order to be able 02:24.280 --> 02:28.600 to use the shared pointer and now the service template class. 02:28.600 --> 02:31.180 So this one here needs as input. 02:31.180 --> 02:35.350 So among the angular parentheses, the name of the message interface. 02:35.350 --> 02:41.170 So the one that contains the request and response message that should be used in order to communicate 02:41.170 --> 02:42.730 with the service server. 02:43.400 --> 02:44.120 To do this. 02:44.150 --> 02:47.900 If you haven't followed me in the Python laboratory lessons. 02:47.900 --> 02:53.720 We need to create a new message interface for the communication with the server that we are going to 02:53.720 --> 02:55.640 create by convention. 02:55.640 --> 03:02.510 And also as a general rule in Ros2, it is recommended that all the new message types, both those for 03:02.510 --> 03:08.240 interaction with topics and those for the communication with services are placed in a different package 03:08.240 --> 03:11.630 than the ones that contains instead the robots functionalities. 03:11.750 --> 03:18.890 So if you haven't done so, let's open a new terminal and let's go to the Arduino Bot workspace and 03:18.890 --> 03:20.300 then to the source folder. 03:20.300 --> 03:22.310 And here let's create a new package. 03:22.310 --> 03:33.860 So to package, create and let's use as a build type, amend CMake and let's call this package Arduino 03:33.860 --> 03:39.650 bot messages as it will contain just message interface for the communication in Ros2. 03:40.220 --> 03:45.510 I have already created this package in my workspace, so I'm not going to run this command again. 03:45.510 --> 03:49.050 But anyway, you can see it created here. 03:49.170 --> 03:56.520 So now you need to go back to your workspace and build it again with the command called build so that 03:56.520 --> 04:01.050 the new package is recognized and is ready to use in Cplusplus. 04:01.860 --> 04:04.210 So go back in Visual Studio code. 04:04.210 --> 04:10.920 And now here we can define the new message interface that the service server must use for the communication 04:10.920 --> 04:12.390 with the service server. 04:12.390 --> 04:18.330 So within the Arduino bot messages still, if you haven't followed me in the Python lessons, you need 04:18.330 --> 04:20.700 to create the serve folder. 04:20.700 --> 04:26.850 That by convention is where we place all the message interface with the service servers. 04:26.850 --> 04:31.590 And so here you need to create the add joints.sv file. 04:31.650 --> 04:37.890 And inside this file we need to define the structure of the request message that is the one that the 04:37.890 --> 04:40.110 client sends to the server. 04:40.110 --> 04:45.840 And this one contains just two integers, two numbers that are the two numbers that we want the server 04:45.840 --> 04:49.200 to send and then separated by three dashes. 04:49.230 --> 04:55.800 We also need to declare the response message and this server will simply return another integer, which 04:55.800 --> 05:00.840 is the sum of the two integers received as inputs or received in the request. 05:01.140 --> 05:07.740 With this we have completed the definition of the add joints and so in order to use it, we need also 05:07.740 --> 05:15.960 to declare it inside the cmakelists.txt so that the compiler is aware of the existence of this message 05:15.960 --> 05:19.440 interface here in the previous lesson. 05:19.440 --> 05:24.510 First of all, we declared the usage of the standard message library, which contains the definition 05:24.510 --> 05:26.450 of the integer message. 05:26.460 --> 05:32.520 Then we also define the usage of the Ros IDL Default Generators library. 05:32.520 --> 05:37.230 That is the one in charge of compiling our SV files. 05:37.230 --> 05:43.080 So in general our Ros to interface messages and make them available to the node. 05:43.080 --> 05:46.110 So to the scripts both Cplusplus and Python. 05:46.640 --> 05:54.620 Then also we used the instruction Ros generate interfaces in order to generate the interface for the 05:54.620 --> 05:55.580 current project. 05:55.580 --> 06:02.720 So for the current package that is the Arduino board messages and we declared the existence of the Arduino 06:03.110 --> 06:06.950 dot SVG file within the SVG folder. 06:08.380 --> 06:08.950 Next. 06:08.950 --> 06:16.270 We need to also to modify the package dot XML file and here we need to add the dependency still from 06:16.270 --> 06:18.010 the standard message library. 06:18.040 --> 06:24.780 Also, we need to add a build dependency from the Ros IDL Default Generators library. 06:24.790 --> 06:28.570 That is the one that we are going to use to build our messages. 06:28.600 --> 06:34.750 Then we also need an execution dependency from the Ros IDL default runtime. 06:34.900 --> 06:41.620 And finally, we also need to use this tag so the member of group in order to declare and so in order 06:41.620 --> 06:45.400 to use the ros IDL interface packages. 06:45.700 --> 06:50.920 And this is all we need in order to define and declare this interface. 06:50.920 --> 06:56.770 So the Add joins interface that from now on we can use within our script. 06:56.770 --> 07:00.690 So both within our Python and our C plus plus script. 07:00.700 --> 07:07.720 But before doing so, so after you create this interface in the Arduino board messages in order for 07:07.820 --> 07:15.800 it to be recognized by Roscoe, let's go back again in the workspace and let's build it with the command 07:15.800 --> 07:16.820 called build. 07:18.960 --> 07:26.220 Now the interface is compiled and we can go back to our simple service server here and we can start 07:26.220 --> 07:27.870 using this interface. 07:27.870 --> 07:36.390 So let's include and from the Arduino board messages here, if you don't have the autocompletion of 07:36.390 --> 07:43.110 the text, you need to press Ctrl shift P and then look for Ros. 07:43.140 --> 07:45.450 Update Cplusplus properties. 07:45.600 --> 07:51.630 So this will scan again the workspace and will enable the Autocompletion for Ros two. 07:51.960 --> 07:58.710 And so then from the Arduino bot messages, we have the Autocompletion now from the SR folder, let's 07:58.710 --> 08:05.130 import the Add joints interface and now we can use this interface within the angular brackets. 08:05.130 --> 08:12.210 So here inside the service to declare that the service server that we are going to use is using the 08:12.210 --> 08:18.910 interface from the Arduino board messages from the service and that is called add to INS. 08:20.120 --> 08:27.800 Now here in the body of the constructor of the Simple Service Server class, let's initialize the service 08:27.800 --> 08:28.540 variable. 08:28.550 --> 08:36.680 So this shared pointer and as we used the create publisher function to initialize our Ros to publisher 08:36.680 --> 08:43.490 and the create subscription function to initialize our subscriber, we can use the Create service function. 08:43.490 --> 08:50.450 So create service function to initialize our service server. 08:50.600 --> 08:57.320 This is a template function that requires, again among the angular parentheses the type of the interface 08:57.320 --> 09:03.980 used for the communication with the service server, which once again is this one is the one that we 09:03.980 --> 09:08.600 declared in the Arduino board messages and that is called Add joins. 09:09.620 --> 09:11.260 Inside the parentheses instead. 09:11.270 --> 09:16.790 So here, as the input of the function, we need to pass the name to give to this service. 09:16.790 --> 09:25.010 So the name by which this service will be recognized in Russia, for example, let's call it add two 09:25.880 --> 09:26.690 ins. 09:27.110 --> 09:31.640 Then also as input, we need to provide a callback function. 09:31.640 --> 09:38.510 So namely a function that has to be executed by the service server every time it receives a new request. 09:38.510 --> 09:42.920 So every time a new client requests the execution of the server. 09:42.920 --> 09:50.600 And so the execution of this of the two integers to do so, we can use the bind function of the C plus 09:50.600 --> 09:59.690 plus standard library and let's call the function service callback, which we are going to declare still 09:59.750 --> 10:02.390 within the simple service server class. 10:02.720 --> 10:09.930 So let's say that this service callback function will be a member of the simple service server class 10:09.930 --> 10:14.130 and that we want to use the one declared in the current instance. 10:14.130 --> 10:15.720 So in the current object. 10:15.720 --> 10:19.350 And then also let's use the placeholder namespace. 10:19.470 --> 10:31.530 So using from the standard library, the namespace STD placeholders. 10:31.980 --> 10:40.740 And so from this namespace, let's use the placeholders one and two to indicate that this callback function. 10:40.740 --> 10:44.700 So the service callback function will require two inputs. 10:44.700 --> 10:47.550 So we require two variables as input. 10:47.550 --> 10:52.560 That will be exactly the two messages contained in the interface with the server. 10:52.560 --> 10:55.530 So the request and the response message. 10:56.140 --> 11:01.970 To finish the constructor of this class, let's just print an informative message in the terminal. 11:01.990 --> 11:09.460 So with the CP info and let's print the message. 11:09.580 --> 11:18.460 Let's take the reference to the logger with the get logger function and let's print the message. 11:18.640 --> 11:20.470 So service. 11:21.790 --> 11:29.200 And then the name of the service that is at two ends is ready. 11:30.440 --> 11:35.450 So that we can confirm that the service has been correctly instantiated. 11:35.720 --> 11:43.220 Now, still here, among the private attributes of the simple service class, we can define the service 11:43.220 --> 11:44.490 callback function. 11:44.510 --> 11:49.130 So let's copy this one and let's define this function. 11:49.850 --> 11:51.440 So it returns void. 11:51.440 --> 11:53.630 So it returns no parameters. 11:53.630 --> 11:59.960 And as this is a callback function, as we said previously, it requires a input the message interface 11:59.960 --> 12:01.790 to be used for the communication. 12:01.790 --> 12:09.440 And so for the data exchange with the service server, therefore it receives a shared pointer to a request 12:09.440 --> 12:10.160 message. 12:10.160 --> 12:13.250 So it receives a constant 12:15.740 --> 12:26.810 shared pointer of type Arduino, both messages and then from the service from the Arduino interface 12:26.870 --> 12:27.650 of. 12:28.070 --> 12:33.270 So it receives a request message and let's call this variable request. 12:33.510 --> 12:40.680 And then the second input of this, one of this function is still another constant pointer. 12:40.680 --> 12:43.500 So another shared pointer. 12:46.670 --> 12:53.390 And this time still from the Arduino bot messages. 12:54.080 --> 13:03.470 Let's take from these services the add to into service and let's take the response and let's call this 13:03.470 --> 13:05.060 one response. 13:05.890 --> 13:11.590 As a first thing in this callback function, let's print another informative message in the terminal. 13:11.590 --> 13:19.750 So with the rql cpp info stream function. 13:20.170 --> 13:26.740 And here let's use the function Rcpp get logger. 13:27.430 --> 13:29.620 And then let's print the message. 13:29.950 --> 13:35.920 New request received followed by the two numbers. 13:35.920 --> 13:39.930 So the two integers that were received in the request message. 13:39.940 --> 13:46.120 So a that is in the request message. 13:47.140 --> 13:56.260 And also let's print B and also this one is in the request message under the name of the variable B. 13:57.860 --> 14:05.000 Then after this message, we can execute the actual logic of the server that basically consists of calculating 14:05.000 --> 14:08.100 the sum of the two integers that were received as input. 14:08.120 --> 14:18.530 So it calculates the sum between the variable A plus the variable B that are in the request message. 14:18.530 --> 14:26.480 And let's store the content of this operation within the response message and within the sum variable. 14:26.690 --> 14:34.100 So within the sum variable, let's store the sum of these two and let's finally print one more message 14:34.100 --> 14:34.940 in the terminal. 14:39.600 --> 14:41.310 Still, let's use the jet logger 14:45.510 --> 14:49.920 and let's print the message returning some. 14:50.130 --> 14:51.420 Followed by the sum. 14:52.020 --> 14:54.120 So here, let's use the double quotes. 14:55.350 --> 14:56.940 And now let's print. 14:58.330 --> 15:04.540 The sum of the two numbers that is in the response message under the name of the variable sum. 15:05.920 --> 15:11.740 This is all we need for the moment, for the definition of all the components of this simple service 15:11.740 --> 15:13.020 server class. 15:13.030 --> 15:16.240 And now we can move on to create the main function. 15:26.240 --> 15:29.390 And let's return zero. 15:29.390 --> 15:32.800 And here let's initialize the node with rcl. 15:33.060 --> 15:35.690 CPP init. 15:36.200 --> 15:38.810 Then let's create a new shared pointer. 15:38.810 --> 15:42.950 So a new shared pointer to the simple service server class. 15:43.130 --> 15:54.350 So let's create a new variable called Node and then let's use the function make shared from the standard 15:54.350 --> 15:55.670 C plus plus library. 15:56.360 --> 15:59.600 And we want this one to create a pointer. 15:59.600 --> 16:04.250 So a shared pointer to an object of the simple service server class. 16:05.330 --> 16:08.660 And so let's save this one within the node variable. 16:08.780 --> 16:15.260 And now let's keep this node up and running with the CPP spin function. 16:15.260 --> 16:17.510 So let's keep the node running. 16:17.510 --> 16:23.420 And then if, for example, we terminate the execution of the node with control C, let's shut down 16:23.420 --> 16:29.450 Ross with RCL cpp shut down function. 16:30.540 --> 16:34.740 With this, we have completed also our simple service server node. 16:34.770 --> 16:41.940 So before executing this node, let's modify also the file Cmakelists.txt in order to install it. 16:41.940 --> 16:48.000 So in order to declare the missing dependencies and also to install the new executable, first, we 16:48.000 --> 16:52.470 need to declare the dependency from the Arduino board messages library. 16:52.530 --> 16:55.560 So Arduino board messages. 16:55.560 --> 17:00.780 That is the package that contains the definition of the interface with the service. 17:01.630 --> 17:08.860 Then we can add a new execute table so we can basically copy these two instructions and we can paste 17:08.860 --> 17:09.580 it below. 17:09.580 --> 17:16.360 And so let's call this new executable simple service server. 17:17.420 --> 17:18.830 So let's copy this one. 17:18.980 --> 17:20.090 The Executable. 17:20.090 --> 17:23.760 So the script is also called Simple Service Server Dot CP. 17:24.320 --> 17:33.920 And then let's also add the the target dependencies to this script that are the RCL, CP and the Arduino 17:33.920 --> 17:34.890 board messages. 17:34.910 --> 17:36.980 So let's copy this one. 17:37.280 --> 17:39.620 Finally in the install section. 17:39.620 --> 17:42.320 So here we also need to install this new node. 17:42.320 --> 17:44.140 So the simple service server. 17:44.150 --> 17:50.150 So let's list it below the other executable that we have already created so far. 17:50.970 --> 17:56.310 Last but not least, since we used the Arduino bot messages in the new executable. 17:56.340 --> 18:00.900 Now we need also to declare its usage in the package dot XML. 18:00.960 --> 18:08.490 So here let's add a new dependency from the Arduino bot messages package. 18:08.670 --> 18:12.870 Now everything is set and we can proceed to run our node. 18:13.020 --> 18:19.380 So let's open a new terminal and let's go into the workspace and here let's build it. 18:19.770 --> 18:26.460 So click on Build so that the new node is compiled and we have an executable that we can run. 18:27.490 --> 18:27.910 Here. 18:27.910 --> 18:30.940 We forgot in the main function. 18:32.400 --> 18:32.940 Yes. 18:32.940 --> 18:33.300 Here. 18:33.300 --> 18:39.570 We forgot to pass the argument of the main to the cpp init. 18:39.690 --> 18:42.600 So let's save and build again. 18:43.790 --> 18:51.140 And also here we have another error because in the get logger we need to specify that we want the logger 18:51.140 --> 18:52.910 for the CP. 18:53.730 --> 18:57.930 So let's copy this one also here and here. 18:57.930 --> 19:00.930 So whenever we use the get logger function. 19:01.170 --> 19:03.690 So let's give it one more try. 19:07.710 --> 19:12.150 And now the build is finally successful so we can start using our node. 19:12.810 --> 19:14.400 So let's open a new terminal. 19:14.880 --> 19:16.890 And here let's search the workspace. 19:17.280 --> 19:20.010 So the file setup dot bash. 19:20.280 --> 19:23.700 And now we can finally run our service server. 19:23.700 --> 19:25.770 So, Ros to run. 19:26.340 --> 19:32.790 And from the Arduino bot CP examples, let's start the simple service server node. 19:33.120 --> 19:39.260 So let's press enter and as soon as we launch it, we have the confirmation that the server is ready. 19:39.270 --> 19:43.560 So the service server is ready and we can also double check it. 19:43.800 --> 19:50.670 If we open a new terminal and we launch the command Ros two service list. 19:50.880 --> 19:56.910 Actually we can see that among other services that were automatically created by Ros2, there is a word 19:56.910 --> 19:59.850 service, so the Add Chewins service. 20:00.240 --> 20:07.590 Furthermore, if we source the workspace also in this terminal, we can get additional information about 20:07.590 --> 20:14.320 the service and so about the type of the communication interface that the service Atkins is using. 20:14.320 --> 20:22.810 And we can do so with the command Ros2 service type, followed by the name of the service that is the 20:22.810 --> 20:24.250 Atkins. 20:24.400 --> 20:32.410 So let's press enter and we can see that this service is using the interface, Atkins declared in the 20:32.410 --> 20:33.790 Arduino bot messages. 20:34.770 --> 20:36.060 Also from the terminal. 20:36.060 --> 20:44.310 We can also send a request message to the service and so we can use the command rescue service call 20:44.310 --> 20:48.510 this time and then followed by the name of the service which we want to call. 20:48.720 --> 20:51.060 And this is the Add Chewins. 20:51.060 --> 20:57.270 And this is followed then by the type of the message interface that we need to use in order to contact 20:57.270 --> 20:58.400 with the server. 20:58.410 --> 21:05.400 If we press tab twice, we can see that Ross two is able to automatically detect the type of the interface. 21:05.610 --> 21:13.440 So let's type the interface and then if we use double quotes and press tab twice again, and then type 21:13.440 --> 21:18.990 the letter A and tab again, Ros two is able to autocomplete the text. 21:18.990 --> 21:22.200 And so here we have a prototype of the message. 21:22.200 --> 21:27.090 So of the request message that we can send directly to the service server. 21:27.240 --> 21:35.740 For example, let's ask the service server to calculate the sum between the number seven and five. 21:35.770 --> 21:37.300 So let's press enter. 21:37.300 --> 21:40.750 And as you can see, the request is sent to the service. 21:40.750 --> 21:47.680 So here it is, informing us that it received a new request and the request contains the numbers seven 21:47.680 --> 21:54.460 and five and also that it returned, it calculated correctly the sum and it is returning the correct 21:54.460 --> 21:58.330 sum to the client that then is receiving correctly. 21:58.450 --> 22:02.950 So here is the response that the client is receiving from the server.