WEBVTT 00:00.080 --> 00:02.600 This is the second step for this activity. 00:02.630 --> 00:08.420 In this step, we are going to improve this LED panel node with a service server. 00:08.420 --> 00:15.230 And this service server will allow us to modify the state of an LED from the outside of the node. 00:15.230 --> 00:19.400 So basically by using a service client from another node. 00:19.400 --> 00:25.370 And now if we think about what kind of data we need to send, well we will need to send the number of 00:25.370 --> 00:27.380 the LED and then the state. 00:27.410 --> 00:30.920 The question is do we have an existing interface that does that. 00:30.920 --> 00:34.910 If yes, we might use it, but if not we will need to create it. 00:34.910 --> 00:36.980 And here we're going to create a new interface. 00:36.980 --> 00:41.270 So a new service interface for that new service server. 00:41.300 --> 00:41.900 All right. 00:41.900 --> 00:49.250 So let's go here and let's go to our source folder my robot interfaces. 00:49.250 --> 00:52.100 And let's go to the service folder. 00:52.100 --> 00:54.950 We already have one service I'm going to create another one. 00:54.950 --> 00:59.450 Let's just name it set led.sv. 00:59.450 --> 01:03.430 RV, just like for the example we used in the real life analogy. 01:03.460 --> 01:03.850 Okay. 01:03.880 --> 01:10.060 And let's edit that file which is in the my robot interfaces. 01:10.060 --> 01:13.060 So in SV set LED. 01:13.180 --> 01:19.420 So I have the three dashes for the separation between the request and the response. 01:19.450 --> 01:22.900 First I want to give an LED number. 01:22.930 --> 01:24.610 LED number is going to be an integer. 01:24.610 --> 01:26.140 So int 64. 01:26.170 --> 01:30.190 Let's call it LED number which can be one, two, three etc.. 01:30.190 --> 01:36.760 And then after we have provided the LED number, we also want to provide the state, which I have decided 01:36.760 --> 01:39.670 that the state is going to be an integer number also. 01:39.670 --> 01:42.130 So it's going to be 0 or 1. 01:42.670 --> 01:44.110 Let's call it state. 01:44.140 --> 01:44.380 Okay. 01:44.410 --> 01:46.030 So led number and state. 01:46.030 --> 01:48.700 That's what we send from the client to the server. 01:48.700 --> 01:51.640 And then the server is going to execute this. 01:51.640 --> 01:55.210 And it could be nice to know if it worked or not. 01:55.210 --> 02:03.180 So I'm going to add a bool success here there's going to be a flag that we can return to the client. 02:03.210 --> 02:07.500 You could also add, for example, a string message if you want to. 02:07.530 --> 02:09.210 I'm just going to keep it like this. 02:09.210 --> 02:10.800 So I save the file. 02:10.830 --> 02:12.690 I go to Cmakelists.txt. 02:12.690 --> 02:15.360 And then you see we already have three interfaces. 02:15.390 --> 02:16.980 I'm going to add another one. 02:16.980 --> 02:25.500 Here's RV set LED dot s RV and save. 02:25.500 --> 02:26.670 And that's it. 02:26.700 --> 02:27.570 Super quick. 02:27.600 --> 02:27.900 Okay. 02:27.960 --> 02:34.200 So make sure you have created the service in the right folder here that you have saved all the files 02:34.200 --> 02:37.110 and that you have this line in the Cmakelists.txt. 02:37.470 --> 02:43.770 Now we can go back here and build the package. 02:43.800 --> 02:49.110 Package is select with my robot interfaces. 02:52.110 --> 02:52.920 Okay. 02:52.920 --> 02:57.780 So because I have built a new interface that I'm going to use directly in my code. 02:57.780 --> 03:00.120 Let's close this code. 03:00.420 --> 03:03.600 Let's close everything like here. 03:03.600 --> 03:06.060 And let's reopen terminals. 03:07.020 --> 03:12.150 Okay, it might seem that it takes some time, but you're going to actually save more time doing this 03:12.150 --> 03:20.220 than trying to debug stuff when you have weird errors in the future and you see it's actually very quick. 03:21.360 --> 03:21.810 Great. 03:21.810 --> 03:25.800 So now I'm going to go to I don't need all of that. 03:25.800 --> 03:30.630 I'm going to go back to my LED panel, Dot Pi, and here I will. 03:30.660 --> 03:34.050 So let's wait that it's initialized okay. 03:34.050 --> 03:36.270 We have the auto completion and all that stuff. 03:36.300 --> 03:47.100 Now how do we add simply my new interface my robot interfaces, dot CSV import set LED. 03:47.400 --> 03:53.250 And because we have used the My Robot interfaces package before here, we don't need to add anything 03:53.250 --> 03:54.900 else in the package dot XML. 03:54.900 --> 03:56.600 You see it's already there. 03:56.690 --> 03:57.230 All right. 03:57.260 --> 03:59.630 And now let's create a service server. 03:59.660 --> 04:05.690 Before I create the service server I'm just going to create the callback here. 04:05.780 --> 04:07.580 That's going to be callback. 04:07.580 --> 04:10.190 So the service name is going to be set LED. 04:10.520 --> 04:11.270 Okay. 04:11.420 --> 04:19.670 We get self and then we get request which is set LED dot request. 04:19.700 --> 04:21.200 Okay I provide the type. 04:21.200 --> 04:24.440 This is optional but it's a best practice to do so. 04:24.770 --> 04:31.880 Response which is a set LED dot response. 04:33.380 --> 04:34.670 Okay so what do we do. 04:34.700 --> 04:39.170 We will need to take from that request. 04:39.200 --> 04:39.500 Okay. 04:39.530 --> 04:41.690 We have two things in the request. 04:41.720 --> 04:43.880 We have so I can see it here. 04:43.880 --> 04:45.830 We have the LED number and the state. 04:45.830 --> 04:53.300 So we need to modify the elements of the list that corresponds to the LED number and apply the state. 04:53.300 --> 05:01.030 But before we do this It could be nice to actually validate the data, because what if you send an LED 05:01.030 --> 05:06.220 number that is negative or that is outside of the list? 05:06.430 --> 05:10.450 Well, you're going to try then to modify an element outside of the list and you're going to get an 05:10.450 --> 05:11.950 exception in your code. 05:12.010 --> 05:15.970 Or what if you get a state that is not 0 or 1? 05:16.000 --> 05:21.100 Well, we have decided that the state is only 0 or 1, so that's specific to the application. 05:21.130 --> 05:22.960 Now what if I give you three? 05:22.990 --> 05:25.660 Are you going to put three inside the array. 05:25.690 --> 05:26.800 No you will not. 05:26.800 --> 05:29.860 So for that you need to validate the data. 05:29.890 --> 05:30.460 Okay. 05:30.490 --> 05:33.310 First what I'm going to do is just create some variables here. 05:33.340 --> 05:38.230 And the number is equal to request dot led number. 05:38.230 --> 05:41.140 So we don't have to write the whole thing every time. 05:41.140 --> 05:45.790 And state request dot state. 05:46.630 --> 05:50.860 And then first let's validate the LED number. 05:50.860 --> 05:54.330 And so actually because in programming we start to count from zero. 05:54.330 --> 05:57.660 So we're going to have index zero one and two. 05:57.690 --> 06:00.210 Well let's use that in our code. 06:00.210 --> 06:05.160 You could decide to just say that the LED number is one two and three. 06:05.160 --> 06:10.650 And then you could do minus one in your code to get access to the corresponding array. 06:10.650 --> 06:16.410 But because this service is going to be used by a client from another node, and basically that person 06:16.410 --> 06:18.690 writing the other node is a developer. 06:18.690 --> 06:21.390 So they know we start to count from zero. 06:21.420 --> 06:21.720 Okay. 06:21.750 --> 06:25.320 You could put it explicitly in the service here. 06:25.320 --> 06:32.670 You could add a comment for example here LED number or just maybe a comment here okay LED number starting 06:32.700 --> 06:34.170 at zero something like that. 06:34.170 --> 06:47.730 So if LED number is greater or equal than the length of a self led state. 06:48.540 --> 06:48.990 All right. 06:48.990 --> 06:52.790 So if we provide three so One, two, three. 06:52.820 --> 07:00.650 We are outside of the array or if LED number is strictly lower than zero. 07:00.650 --> 07:05.630 Basically, if we are going before I mean there is nothing before zero in the list. 07:05.630 --> 07:09.110 So in this case we know that we have a wrong LED number. 07:09.110 --> 07:16.130 And so we are going to do response dot success is equal to false. 07:16.130 --> 07:20.120 So we fill the response with what we have here. 07:20.120 --> 07:24.800 And then we return the response okay. 07:24.830 --> 07:29.120 So if we don't pass this test we're just going to return right away. 07:29.150 --> 07:30.740 We don't do anything else. 07:30.920 --> 07:32.540 Then I'm going to do another test. 07:32.540 --> 07:39.920 If state let's say state not in zero one okay. 07:39.950 --> 07:42.110 So state must be 0 or 1. 07:42.110 --> 07:44.510 If not same thing we do. 07:44.540 --> 07:52.820 Response dot success false and return The response. 07:52.820 --> 07:58.670 If you had added a message, for example, a string, you could add a different string message here 07:58.670 --> 08:00.620 to explain what was the issue. 08:00.620 --> 08:08.390 And now if I reach this line of code, I know that we have a correct LED number that corresponds to 08:08.420 --> 08:12.380 an index of that list and the state is correct. 08:12.380 --> 08:22.220 So I can just do self led state and reach the LED number index. 08:22.370 --> 08:29.180 And I can just say that that becomes the state, because now I know all the data is correct. 08:29.180 --> 08:38.120 And if I do this I can also do response dot success is equal to true and return. 08:38.120 --> 08:40.790 Let's not forget to return the response okay? 08:41.270 --> 08:42.680 It's a very common mistake. 08:42.710 --> 08:43.340 Great. 08:43.340 --> 08:47.030 And that's going to be the end for this callback right. 08:47.030 --> 08:50.380 So we first get the different elements of the request. 08:50.380 --> 08:58.390 If needed, we might want to validate the data, and then we do the action and we return a response. 08:58.780 --> 09:06.400 So let's actually create a service because this callback is not going to be called if we don't create 09:06.430 --> 09:07.330 a service. 09:07.330 --> 09:19.960 So here for example after the timer we can do self set LED service is equal to self dot create service. 09:20.470 --> 09:25.000 We need to provide the service type which is set LED. 09:25.570 --> 09:28.360 We need to provide a name which we decide here. 09:28.360 --> 09:36.610 So I gave you set LED before and then the callback self dot callback set LED. 09:38.740 --> 09:39.130 All right. 09:39.130 --> 09:40.000 And that's it. 09:40.000 --> 09:44.950 So you see in this node we have one publisher one timer and one service. 09:45.130 --> 09:47.140 So in the end we have two callbacks. 09:47.140 --> 09:50.730 You see we have one callback for the timer. 09:50.760 --> 09:55.980 There's going to be triggered every five seconds, and then we have one callback for the service that's 09:55.980 --> 10:00.900 going to be triggered whenever we get an incoming request from a client. 10:01.380 --> 10:03.750 So let's save that. 10:03.840 --> 10:05.340 Let's go back to the terminal. 10:05.340 --> 10:12.330 And I have used Simulink install, so I should be able to run it without building again. 10:12.360 --> 10:16.320 Let's just do a source bashrc still just in case. 10:17.940 --> 10:25.770 And just to run my Python package with LED panel. 10:27.300 --> 10:31.260 Okay, so you can see we have reached the end of the constructor. 10:31.290 --> 10:40.440 Now if I do rust to service list, you see I have my set LED and so I can already test it. 10:40.440 --> 10:43.950 And because this is quite easy. 10:43.950 --> 10:45.840 So the request actually is quite easy. 10:45.870 --> 10:47.280 It's just two integers. 10:47.280 --> 10:50.240 We can easily test it from the terminal. 10:50.270 --> 10:56.900 Okay, so I can do ros2 service call and then set LED. 10:57.260 --> 11:02.720 Then I need to provide the interface so my I can just press tab here. 11:02.720 --> 11:03.830 It's going to find it. 11:03.860 --> 11:06.200 My robot interface is set LED. 11:06.380 --> 11:10.730 And then I can build the request. 11:10.730 --> 11:22.520 So if you don't remember Ros2 interface show my robot interfaces solve set LED okay. 11:22.520 --> 11:26.510 So we need to provide LED number. 11:27.470 --> 11:29.060 Let's say zero. 11:29.090 --> 11:30.110 That's the first one. 11:30.110 --> 11:32.960 And state let's say one. 11:32.960 --> 11:39.890 We want to turn on the LED and to verify that so we can run it and see if it's working. 11:40.010 --> 11:45.770 But to double check we can also see what's going to happen on the topic. 11:45.830 --> 11:46.780 So Series two. 11:46.810 --> 11:47.290 Topic. 11:47.320 --> 11:50.740 Eco led panel. 11:50.740 --> 11:51.820 State. 11:52.780 --> 11:55.780 Let's see for the first message to arrive. 11:56.350 --> 11:56.860 Okay. 11:56.860 --> 11:58.570 And then let's run that. 11:59.590 --> 12:00.940 You see it's working. 12:00.940 --> 12:02.020 We have response success. 12:02.020 --> 12:07.000 And the next time that we have the topic the first LED here is turned on. 12:07.270 --> 12:07.840 Okay. 12:07.870 --> 12:10.900 Now I can turn it off with zero. 12:12.370 --> 12:12.940 Okay. 12:12.940 --> 12:16.270 But what you can see is when I do this, it's working. 12:16.660 --> 12:21.280 But then we receive the topic because we publish every five seconds. 12:21.280 --> 12:26.500 So we might wait as long as five seconds to receive the new data on the topic. 12:26.500 --> 12:29.350 And how can we kind of solve that? 12:29.380 --> 12:30.490 Well, there are two ways. 12:30.490 --> 12:38.260 First, you could increase the frequency a lot and say that, for example, you publish every 0.1 second 12:38.290 --> 12:42.790 or something like that, but then you're going to publish a lot of messages and still you will not get 12:42.790 --> 12:45.910 exactly immediately the new data on the topic. 12:45.910 --> 12:54.310 So what we can do is that directly after we set the new state here, and before we return the response, 12:54.310 --> 12:56.500 we could publish here. 12:56.500 --> 13:02.560 From there we could do self-publish led state. 13:02.620 --> 13:03.400 All right. 13:03.430 --> 13:10.150 I told you that you could publish on a topic from anywhere so you can publish from a timer callback. 13:10.180 --> 13:12.310 You can publish from a subscriber callback. 13:12.310 --> 13:13.540 We have done that previously. 13:13.540 --> 13:17.710 You can also publish from a service callback. 13:17.740 --> 13:18.010 Okay. 13:18.040 --> 13:19.210 There is no problem with that. 13:19.240 --> 13:22.750 And so here what we do is we publish every five seconds. 13:22.840 --> 13:27.970 But then whenever we change the state, we publish immediately the new state. 13:27.970 --> 13:31.450 So let's save that and let's go back. 13:31.450 --> 13:35.380 Let's run everything again okay. 13:35.380 --> 13:39.610 And let's do this. 13:40.900 --> 13:41.620 Okay. 13:41.830 --> 13:44.080 Now I'm going to wait for the next one. 13:45.210 --> 13:45.510 Okay. 13:45.540 --> 13:47.220 And I'm going to run the service. 13:48.120 --> 13:54.810 And you see, as soon as we have gotten a response here, we also see the new state here. 13:55.320 --> 13:55.440 Okay. 13:55.470 --> 13:57.270 We don't have to wait five seconds. 13:57.990 --> 14:03.420 So here you see, as soon as we have that we get the new state. 14:03.420 --> 14:06.210 So there is a new message on the topic. 14:07.350 --> 14:07.740 Great. 14:07.740 --> 14:08.970 So that's currently working. 14:08.970 --> 14:13.770 And let's just test the cases where we're going to get an error. 14:13.770 --> 14:15.900 So when the success is going to be false. 14:15.900 --> 14:24.270 So for example LED number if I put four you see I should get success false. 14:24.660 --> 14:27.390 And then let's put zero. 14:27.390 --> 14:28.740 So that's the correct number. 14:28.920 --> 14:32.580 But then let's put two for the state. 14:33.300 --> 14:35.730 And you see we have success false. 14:36.090 --> 14:40.770 So we can validate that our data validation is also working great. 14:40.770 --> 14:43.680 And that's the end of the second step for this activity.