WEBVTT 00:00.050 --> 00:00.470 Great. 00:00.470 --> 00:04.610 We have a service server and we are even able to call it from the terminal. 00:04.640 --> 00:11.060 Now let's create a Python service client so we can actually call this new service from your code directly. 00:11.060 --> 00:17.900 And we will start with a non OOP example that you can use later as a template to test any service quite 00:17.900 --> 00:18.530 quickly. 00:18.530 --> 00:23.870 So here in this lesson we are going to see the mechanisms and the different steps to create a service 00:23.870 --> 00:24.560 client. 00:24.560 --> 00:26.570 Send a request and get the response. 00:26.570 --> 00:32.540 And we're going to create a very simple script that then you can use to test any server. 00:32.540 --> 00:36.590 For example, here you could see that we could call the service from the terminal. 00:36.590 --> 00:41.210 But I told you that it's only going to work for very simple requests. 00:41.210 --> 00:44.210 If you have a more complex request, you will need to write some code. 00:44.210 --> 00:47.030 And so you can use what we do now as a template. 00:47.030 --> 00:54.200 And then in the next video, we will integrate the service client inside an existing node that uses 00:54.230 --> 00:55.970 object oriented programming. 00:55.970 --> 00:59.870 So you can integrate service clients inside any node in your application. 00:59.900 --> 01:01.490 All right let's get started. 01:01.490 --> 01:04.660 So I'm going to just open any terminal. 01:04.660 --> 01:15.400 Let's go to our Python package and let's create a new file add to ins client. 01:15.400 --> 01:19.630 I'm going to name that one no oop.py. 01:19.630 --> 01:22.300 And let's make it executable. 01:24.850 --> 01:25.480 Okay. 01:25.480 --> 01:27.010 So now let's go back to VS. 01:27.010 --> 01:29.410 Code was already open here. 01:29.620 --> 01:34.390 And let's open that one I'm going to use a template. 01:34.450 --> 01:35.740 Yes I'm going to use a template. 01:35.740 --> 01:37.390 But I'm going to modify this. 01:37.390 --> 01:41.860 So here what I'm going to keep is this. 01:41.860 --> 01:42.910 So we're going to import. 01:42.910 --> 01:45.310 So we have the Python three interpreter line. 01:45.340 --> 01:48.460 We're going to import CLP and import the node. 01:48.460 --> 01:50.590 But then I'm going to remove the class okay. 01:50.620 --> 01:54.130 I'm just going to do a simple script with a main function. 01:54.130 --> 01:57.430 So here we're going to initialize Ros to communications. 01:57.460 --> 02:00.490 Then we are going to create a node. 02:00.490 --> 02:05.430 And let's give it a name add to its clients. 02:05.460 --> 02:07.080 No oop. 02:07.170 --> 02:08.640 And then we make the node spin. 02:08.670 --> 02:10.980 Actually no I'm going to remove that line. 02:10.980 --> 02:15.600 So the three lines we keep is the initialization of Rosetta communication. 02:15.600 --> 02:16.770 We create a node. 02:16.770 --> 02:19.020 And at the end we're going to shut it down. 02:19.050 --> 02:19.470 Okay. 02:19.500 --> 02:22.800 So the structure is a bit different than what we've done previously. 02:22.830 --> 02:27.090 Now let's see how to create a client and then send a request. 02:27.090 --> 02:31.980 So I'm going to create a client I'm going to store it in a client variable. 02:31.980 --> 02:36.150 And I'm going to use the node okay that I've created. 02:36.150 --> 02:39.810 So we still need the node I'm going to do node dot. 02:39.810 --> 02:42.300 So in the node in the class you would do self. 02:42.300 --> 02:44.250 But here I name it node. 02:44.250 --> 02:51.150 So that's going to be node in my main function node dot create client okay. 02:51.150 --> 02:56.070 And I need to give of course the service type and the service name. 02:56.070 --> 03:02.160 So if I want to call this service I've created here I need to use the add to hints. 03:02.160 --> 03:05.780 And I also need to use that exact same name. 03:05.780 --> 03:17.990 So I'm going to import from example interfaces dot csv import add to int I provide it here add to int 03:17.990 --> 03:23.960 and then let's make sure we use the same name add to int. 03:24.020 --> 03:24.590 Great. 03:24.590 --> 03:25.250 And that's it. 03:25.250 --> 03:26.870 You just create a client like that. 03:26.870 --> 03:28.490 So the client is not going to do anything. 03:28.490 --> 03:31.670 Then you need to use it to send a request. 03:31.700 --> 03:36.650 Now there is one thing we can do is to first wait for the service to be up. 03:36.650 --> 03:40.280 Because if you try to send a request but the service is not up. 03:40.280 --> 03:46.100 So basically the node containing the service is not running, then you're going to get an error. 03:46.100 --> 03:53.120 So what we can do and that's a common structure we can do while not client wait for service. 03:53.120 --> 03:55.880 So you have the wait for service method inside the client. 03:55.880 --> 04:00.920 And we can give a timeout of one second for example. 04:00.980 --> 04:03.050 And then do a print. 04:03.050 --> 04:06.150 So node dot get logger. 04:06.480 --> 04:11.910 And this time, well, instead of info, I'm going to use one. 04:11.940 --> 04:12.180 Okay. 04:12.210 --> 04:15.000 Because that's more like a warning message. 04:15.000 --> 04:26.430 The server is not up and we can say waiting for server waiting for for example add to insert server. 04:26.970 --> 04:31.710 So what's going to happen is this is going to wait for the service indefinitely. 04:31.710 --> 04:33.360 But you can also provide a timeout. 04:33.360 --> 04:36.120 So it's going to return after one second. 04:36.120 --> 04:39.060 If the service is not found it's going to return false. 04:39.060 --> 04:40.380 And so you put a not. 04:40.410 --> 04:45.870 And so basically as long as the service is not found we say waiting for the server. 04:45.870 --> 04:47.460 And then we keep waiting. 04:47.460 --> 04:52.950 Then when the service is found we're going to go out of the loop because this is going to return true. 04:52.980 --> 04:53.520 Okay. 04:53.520 --> 05:01.680 We can already test this code just to make sure that we can create a client and we can find the service 05:01.680 --> 05:02.370 server. 05:02.370 --> 05:09.410 So I'm going to save that and I'm going to create a new executable here comma. 05:09.410 --> 05:13.640 And then let's name it add to insert client. 05:13.670 --> 05:14.390 No. 05:14.780 --> 05:15.440 OOP. 05:15.470 --> 05:17.180 So it starts to be quite long. 05:17.450 --> 05:26.390 My pi pkg and then add to int client. 05:27.080 --> 05:27.950 No. 05:27.980 --> 05:28.610 OOP. 05:29.330 --> 05:31.250 And that's the main function. 05:31.280 --> 05:32.900 It's always the main function here. 05:34.520 --> 05:35.480 The main. 05:35.480 --> 05:36.890 So we call the main function. 05:37.220 --> 05:38.120 Okay. 05:38.150 --> 05:40.460 Let's save that. 05:40.670 --> 05:41.180 All right. 05:41.180 --> 05:46.040 So what's going to happen very simply is that we initialize rose to communications. 05:46.040 --> 05:47.570 We create a node. 05:47.570 --> 05:49.760 Then we create a client inside the node. 05:49.760 --> 05:51.950 And we just wait for the service. 05:51.950 --> 05:54.020 Let's build. 05:55.670 --> 06:02.780 Let's go back to the Ros2 workspace Qualcomm build packages. 06:02.810 --> 06:10.480 Select with my pi pkg E.g. and let's use Simulink install so we don't need to build again to modify 06:10.480 --> 06:11.380 this code. 06:12.760 --> 06:13.540 Okay. 06:13.540 --> 06:23.470 And then I'm just gonna stop the terminals here, open new ones so everything is correctly sourced. 06:23.890 --> 06:25.750 And let's start here. 06:25.750 --> 06:34.360 The node we have just created Ros to run my pi pkg add to mint client. 06:34.390 --> 06:35.380 No OOP. 06:35.560 --> 06:36.760 Let's run that. 06:36.910 --> 06:43.120 And you can see waiting for the server because the server is not up. 06:43.150 --> 06:52.270 Now here I'm going to run Ros to run with my Pi pkg add to its server. 06:52.270 --> 06:56.560 And you see add to server has been started. 06:56.560 --> 06:58.300 And then you see we return here. 06:58.300 --> 06:59.410 So what does it mean. 06:59.410 --> 07:02.500 It means that it's currently working on the client side. 07:02.500 --> 07:03.790 We create a client. 07:03.790 --> 07:08.250 And then as long as the server is not up we are waiting for the server. 07:08.280 --> 07:16.680 Now, look, if I start the service client again, it's going to return immediately because the service 07:16.680 --> 07:18.810 server is already running. 07:18.840 --> 07:19.230 Okay. 07:19.260 --> 07:22.980 So this mechanism here is just in case. 07:22.980 --> 07:24.180 It's like a safety. 07:24.180 --> 07:30.180 So if you start both nodes around the same time, but if the client is up before the server then you 07:30.180 --> 07:32.100 make sure that you wait for the server. 07:32.130 --> 07:32.460 Okay. 07:32.460 --> 07:32.730 Good. 07:32.730 --> 07:34.410 So now we have created our client. 07:34.410 --> 07:40.530 And at this point of the execution here, we know that the service server has been found. 07:40.530 --> 07:46.050 So what we can do is we can create a request and send that request. 07:46.080 --> 07:47.910 Let's create a request. 07:47.910 --> 07:54.900 So we do request is equal to add to int dot request okay. 07:54.900 --> 07:57.300 So it's basically like creating a message. 07:57.300 --> 08:01.680 You create a request and then you do request dot a. 08:02.070 --> 08:03.420 So y dot a. 08:03.450 --> 08:10.850 Because if you remember in this interface we have a and B as the request and then some as the response. 08:11.480 --> 08:12.650 Let's say three. 08:12.650 --> 08:14.210 So let's give some number here. 08:14.240 --> 08:17.930 Request dot b is equal to eight. 08:17.960 --> 08:19.790 So the sum should be 11. 08:19.790 --> 08:26.690 And then we are going to use this request with the client to send where to send the request. 08:26.720 --> 08:28.160 How do we do this. 08:28.160 --> 08:30.410 We are going to do client dot. 08:30.410 --> 08:33.380 And then we have call and call async. 08:33.380 --> 08:36.290 So call is going to be synchronous call. 08:36.290 --> 08:40.910 But it's not recommended because you might end up in a deadlock situation. 08:40.940 --> 08:41.150 Okay. 08:41.180 --> 08:43.310 It's going to block the execution. 08:43.310 --> 08:47.810 And then actually to get the response you need to have the node that's spinning. 08:47.810 --> 08:50.060 But if you block here the node is not going to be spinning. 08:50.060 --> 08:53.360 Well that's a bit more complex for you to understand right now. 08:53.360 --> 08:59.510 But basically if you write call here just like that, you might have some issues and you may never get 08:59.510 --> 09:00.170 the response. 09:00.170 --> 09:04.940 So we are going to do a call async, which means that we are going to call. 09:04.940 --> 09:06.290 So to send the request. 09:06.290 --> 09:07.880 And then that's going to return. 09:07.880 --> 09:13.130 And we need to do something else to get the response, and we send the request here. 09:13.760 --> 09:14.750 Request. 09:15.830 --> 09:18.860 So client dot call async with the request. 09:18.890 --> 09:22.190 This is going to return a future. 09:22.220 --> 09:23.150 Object. 09:23.570 --> 09:24.110 Okay. 09:24.140 --> 09:28.820 No need to really understand future objects in Python. 09:28.820 --> 09:29.570 Just need to. 09:29.600 --> 09:30.740 Know that it's a future. 09:30.740 --> 09:33.800 So it's something that's going to return in the future. 09:33.830 --> 09:40.550 And then what I'm going to do here is I'm going to make the node spin until the future is complete. 09:40.550 --> 09:47.510 For that I can do CLP dot spin until future complete. 09:47.510 --> 09:49.970 So you see we are now using the normal spin. 09:49.970 --> 09:51.920 We are using a different spin. 09:51.920 --> 09:55.610 And I put the node that's the one we've created here. 09:55.610 --> 09:59.330 And I put the future that we have here. 09:59.360 --> 09:59.690 All right. 09:59.720 --> 10:08.090 So very basically put you send a request and then you just say spin the node until we receive a response. 10:08.090 --> 10:11.930 And in this case the future is going to get the result. 10:11.930 --> 10:20.630 And after that well we can do response is equal to future dot result. 10:20.960 --> 10:23.990 And that's going to be the response of the service okay. 10:23.990 --> 10:26.570 And let's do a log. 10:26.570 --> 10:35.390 So we're going to use the node here node dot get logger with info. 10:35.390 --> 10:39.410 And let's just print a plus B is equal to sum. 10:39.710 --> 10:42.050 Actually I think I've done it here already. 10:42.290 --> 10:46.670 Yes you can just get this okay. 10:46.700 --> 10:47.810 So we don't need to rewrite. 10:47.810 --> 10:51.140 Everything is one more parenthesis. 10:54.650 --> 10:54.980 Okay. 10:54.980 --> 10:57.410 So we just print the request a plus. 10:57.410 --> 11:02.360 The request b is equal to the response dot sum. 11:02.360 --> 11:04.370 And that's going to be pretty much it. 11:04.370 --> 11:06.590 So let's do a quick recap. 11:06.590 --> 11:08.720 First we initialize roster communication. 11:08.720 --> 11:09.740 We create a node. 11:09.740 --> 11:10.790 Then we create a client. 11:10.790 --> 11:13.180 We wait for the service to be up. 11:13.210 --> 11:14.770 We create a request. 11:14.800 --> 11:16.780 We send that request. 11:16.810 --> 11:22.510 We make the node spin until the future is complete, which means that we got the response from the server, 11:22.510 --> 11:25.420 and then we just get the response using the future object. 11:25.420 --> 11:29.080 And we can just print or do whatever we want with this response. 11:29.080 --> 11:33.610 And finally we shut down Rosta communications and everything is going to be shut down. 11:33.610 --> 11:37.000 So let's save that and let's go back here. 11:37.000 --> 11:40.540 I don't need to build again because we've used the Simulink install. 11:40.660 --> 11:43.240 So the server is running okay. 11:43.270 --> 11:44.830 We haven't touched anything in the server. 11:44.830 --> 11:48.190 So let's keep it that way and let's run that again. 11:49.210 --> 11:55.420 And you see now we have here a log on the server side and a log on the client side, which means that 11:55.420 --> 11:57.970 the communication was successfully done. 11:58.000 --> 11:58.480 All right. 11:58.510 --> 12:04.120 So now you have seen what are the different steps that you need to implement as a client. 12:04.120 --> 12:06.490 So to send a request and get a response. 12:06.490 --> 12:12.550 And this here this no OOP script I've written it like this because it's going to be quite useful for 12:12.550 --> 12:12.910 you. 12:12.940 --> 12:18.970 Let's say you have created a service server and the request is a bit complex. 12:18.970 --> 12:25.150 So you have created the server, but you want to quickly test it and you cannot really do a ros2 service 12:25.150 --> 12:27.820 call from the terminal because it's going to be a mess. 12:27.820 --> 12:31.030 And it's hard to build the request from the terminal. 12:31.030 --> 12:32.860 Well, you can just use that. 12:32.890 --> 12:37.540 You use that, you create a client, you just change the interface, the name, and then you create 12:37.540 --> 12:38.290 the request. 12:38.320 --> 12:41.620 Well, you fill the request with whatever you need, okay. 12:41.650 --> 12:43.570 And then basically it's the same thing. 12:43.570 --> 12:44.890 This line is the same. 12:44.890 --> 12:47.140 That line is the same, that line is the same. 12:47.140 --> 12:51.730 And then you just well, you just print something else if you want, okay. 12:51.760 --> 12:59.020 But basically you can use that as also a template for you to test any service server that you have created. 12:59.020 --> 13:03.940 And not only that, but if you have written a service server in Python or in C plus. 13:03.940 --> 13:11.740 Plus as you know that Ros is language agnostic, you can use this Python script here to test even a 13:11.740 --> 13:13.630 C plus plus service server.