WEBVTT 00:00.230 --> 00:06.560 Now that we know how to create and use an action server and also how to interact with it through the 00:06.560 --> 00:14.480 Ros2 command line interface, let's see how we can create a Python action client node that use the Fibonacci 00:14.480 --> 00:18.380 action server that we created in the last laboratory lesson. 00:19.080 --> 00:24.990 If you are only interested in the C plus plus development, then you can skip directly to the next lesson 00:24.990 --> 00:27.330 in which we are going to implement the same node. 00:27.330 --> 00:30.060 So the same action client in C plus plus. 00:30.860 --> 00:33.440 Just as we did with the server node. 00:33.470 --> 00:39.270 Let's also place the client node inside the Arduino board Pi examples and so inside the Arduino board 00:39.320 --> 00:40.790 by example sub folder. 00:40.790 --> 00:48.710 And here let's create a new file called Simple Action Client Dot Pi. 00:49.250 --> 00:49.760 Here. 00:49.760 --> 01:00.050 Let's start by importing the Pi library and also from the Pi library and from the node modules. 01:00.560 --> 01:03.590 Let's import the node class. 01:03.800 --> 01:14.540 And then in order to create a Ros two node, let's create a new class called Simple Action Client that 01:14.540 --> 01:18.470 inherits from the node class that is defined in the node module. 01:18.470 --> 01:24.050 So the simple action client inherits from the node class. 01:24.050 --> 01:26.270 And now let's define the constructor. 01:28.580 --> 01:32.780 So this is a member of the Simple Action Client class. 01:32.780 --> 01:38.270 And within the constructor, let's start by initializing the object of the node class. 01:38.270 --> 01:40.190 So of the base class. 01:42.500 --> 01:49.250 So let's call the init function on the object of the base class and let's pass a string as input. 01:49.250 --> 01:51.560 That is the name that we want to give to the node. 01:51.590 --> 01:57.440 So let's call it simple action client. 01:58.570 --> 02:02.670 Next, let's initialize and create the actual action client. 02:02.680 --> 02:07.570 And so in order to do this, let's import another library. 02:07.570 --> 02:16.900 So still from the Pi library, this time from the action module, let's import the definition of the 02:16.900 --> 02:21.160 action client class, and now let's use it to create a new object. 02:21.160 --> 02:30.040 So here, still within the constructor, let's create a new object and let's call this one action client. 02:30.040 --> 02:35.410 And this is an instance of the action client class. 02:36.210 --> 02:42.540 The constructor of this class takes the instance of the Ros2 node where the action client is implemented, 02:42.540 --> 02:45.750 which is the current simple action client class. 02:45.750 --> 02:49.440 So we can refer to this one with the self variable. 02:49.800 --> 02:54.810 It also takes as input the type of the interface that we want to use for the communication with the 02:54.810 --> 02:55.830 action server. 02:55.830 --> 03:00.210 And we define this interface in the Arduino bot messages package. 03:00.420 --> 03:12.360 So from this package, from the Arduino bot messages and from the action module, let's import the Fibonacci 03:12.360 --> 03:13.110 interface. 03:13.110 --> 03:18.810 And now let's use this interface, the Fibonacci for the communication with the action server. 03:18.810 --> 03:23.880 So basically we are saying that we want to create an action client which communicates with a certain 03:23.880 --> 03:26.970 action server using the Fibonacci interface. 03:27.090 --> 03:33.660 And also finally, let's specify the name of the action server that is the Fibonacci. 03:34.050 --> 03:39.640 At this point, we could already use the action client to send the goals to the server. 03:39.790 --> 03:45.730 However, before doing that, let's first verify that the action server is actually running using the 03:45.730 --> 03:46.540 function. 03:46.720 --> 03:52.870 So on the action client object, let's use the function, wait for server. 03:52.870 --> 03:55.690 And so this function will block the execution of the client. 03:55.690 --> 04:02.410 So of this script until an action server that is called Fibonacci and that uses the Fibonacci interface 04:02.410 --> 04:03.460 is available. 04:03.460 --> 04:05.110 So it becomes available in Ros2. 04:05.590 --> 04:13.060 So after this function, if we insert any instruction after this function, we are sure that an action 04:13.060 --> 04:14.560 server exists. 04:14.560 --> 04:17.380 And so it means that we can send a goal to this action server. 04:17.380 --> 04:19.720 So requesting its execution. 04:19.840 --> 04:22.540 So let's start by creating a new goal variable. 04:23.110 --> 04:31.630 Let's call this one goal and this is an instance of the Fibonacci interface and of the goal message. 04:31.630 --> 04:37.600 And now let's, for example, request the calculation of the Fibonacci sequence up to the order ten. 04:38.350 --> 04:43.750 So let's access to the goal message and then to the order variable. 04:43.840 --> 04:46.030 And let's set this 1 to 10. 04:46.150 --> 04:50.950 And now in order to send the goal to the action server, we can use the function. 04:51.220 --> 05:00.160 So still using the action client, let's use the function, send goal async and this receives as input 05:00.160 --> 05:02.440 the goal that we want to send to the server. 05:03.040 --> 05:06.790 And so basically the variable goal that we have just created. 05:07.360 --> 05:14.440 And also here in this end goal async function, we need also to pass the name of the function that we 05:14.440 --> 05:18.600 want to execute when a new feedback message is received by the client. 05:18.610 --> 05:24.910 So every time the action server will send a feedback message, the client will execute a certain function 05:24.910 --> 05:27.970 in order to inform about the progress of the action. 05:28.060 --> 05:30.370 And for example, let's call this function. 05:30.370 --> 05:39.010 So the feedback callback function, let's call this one again feedback callback. 05:39.010 --> 05:45.340 And we are going to define this feedback callback function still within the simple action client node. 05:45.440 --> 05:48.670 Now the send goal async function. 05:48.670 --> 05:54.790 This one will send a goal to the action server and returns a future variable. 05:54.790 --> 06:04.570 And so let's store this one within a variable called future that takes the output of the send goal async. 06:05.320 --> 06:06.190 This variable. 06:06.190 --> 06:12.310 So the future variable provides a mechanism to access the result of an asynchronous operation. 06:12.310 --> 06:17.920 And so, for example, we can also add a callback to this variable in order to be notified when the 06:17.920 --> 06:20.380 action server completes its execution. 06:20.500 --> 06:23.110 So on the future variable. 06:24.140 --> 06:30.050 Let's add a new callback function by using the add done callback function. 06:30.050 --> 06:36.410 And so when the server is done, so basically when the action client gets notified that the server completed 06:36.410 --> 06:43.460 its execution, we want to execute the response callback function. 06:43.460 --> 06:46.400 And so now we need to define this function. 06:46.400 --> 06:55.040 So we need to define the response callback function and let's define it as a member still of the simple 06:55.040 --> 06:56.300 action client node. 06:56.570 --> 06:59.030 And so it receives the self variable. 06:59.030 --> 07:04.040 And also this function receives as input the future variable. 07:04.040 --> 07:10.490 So the future mechanism that allows to access to the result of the action server once it is done. 07:11.030 --> 07:17.120 So first of all, let's save the result of the future variable into a new variable that we can call 07:17.150 --> 07:19.370 goal handle. 07:19.550 --> 07:29.610 And so let's take the future and let's use the function result in order to get the result of this server. 07:29.880 --> 07:35.910 Now we can check if the goal that we sent has been accepted or not by the action server. 07:35.910 --> 07:42.060 So let's check if not the goal handle variable. 07:43.140 --> 07:47.700 So the goal handle is accepted. 07:47.940 --> 07:51.780 So if this is not accepted, let's print an informative message. 07:52.440 --> 08:03.270 So with the get logger function, let's print an informative message that says goal rejected. 08:03.690 --> 08:09.660 And in this case, let's print a sad face and then let's also return. 08:09.660 --> 08:16.310 So let's terminate the execution of the action client with the return statement otherwise. 08:16.320 --> 08:24.980 So if we go here, if the goal was accepted, let's print again a new log message. 08:24.980 --> 08:32.360 So an informative message that says goal accepted. 08:32.660 --> 08:35.960 And in this case, let's print an face. 08:36.770 --> 08:43.220 Then, since the goal was accepted and the action server has started its execution, we can use the 08:43.250 --> 08:44.750 goal and all variable. 08:44.750 --> 08:49.400 So this one here to get the result of the action server execution. 08:49.820 --> 08:51.380 And so let's use this function. 08:51.380 --> 08:59.420 So the goal endl and the function get result async. 08:59.450 --> 09:06.320 So the response callback function, this one will be executed when we receive a response from the action 09:06.320 --> 09:06.980 server. 09:06.980 --> 09:14.930 And this basically informs us just if the server has accepted or not, our goal and now with this other 09:14.930 --> 09:15.440 function. 09:15.440 --> 09:22.040 So with the get result async, we are basically at the point in which we are sure we know that the action 09:22.040 --> 09:25.850 server accepted our goal and now we want the result. 09:25.850 --> 09:29.900 So we want the result of the execution of the logic of the action server. 09:30.440 --> 09:37.290 So as this is also an asynchronous function, as you can say from the name, it also returns a future 09:37.290 --> 09:38.040 variable. 09:38.040 --> 09:40.980 So let's store this one in the variable future. 09:43.920 --> 09:49.530 And now, as we did previously, let's also add a callback function to this future variable. 09:49.530 --> 09:54.480 In order to be notified whenever the server completes the execution of the goal. 09:54.930 --> 10:06.060 So still on the future variable, let's call the function add then callback and this receives the name 10:06.060 --> 10:06.840 of the function. 10:06.840 --> 10:12.210 So of the callback function that we want to execute when the server finishes its execution. 10:12.210 --> 10:19.140 In this case, let's execute the function result callback. 10:19.690 --> 10:24.090 So here is self result callback. 10:24.100 --> 10:29.530 And so still we are going to define this function as a member of the simple action client node. 10:30.190 --> 10:34.900 So let's define this function and it receives the self. 10:35.200 --> 10:42.730 And also this function receives the future variable that contains the mechanism to access the response. 10:42.730 --> 10:45.130 And so the result of the action server. 10:45.250 --> 10:52.450 So let's start with this one with taking the result of the action server and let's store it in a new 10:52.450 --> 10:54.190 variable called result. 10:54.280 --> 11:00.900 And so this takes the future variable and then the result function. 11:00.910 --> 11:04.240 And from this one, let's take the result. 11:04.240 --> 11:08.020 So here we are accessing to the result of the future variable. 11:08.020 --> 11:14.140 And here we are accessing to the result of the message interface of with the action server. 11:15.160 --> 11:16.570 Now this variable here. 11:16.570 --> 11:20.350 So the result variable contains the result of the action server. 11:20.350 --> 11:22.540 So the full Fibonacci sequence. 11:22.720 --> 11:25.930 Now let's print this sequence within the terminal. 11:26.710 --> 11:38.260 So with the get logger function, let's print an informative message that says result and then let's 11:38.260 --> 11:39.730 print the full vector. 11:40.180 --> 11:48.880 So let's format this string and let's print basically the result sequence. 11:48.880 --> 11:53.830 So let's print the full Fibonacci sequence that was calculated by the action server. 11:54.310 --> 11:58.330 Once we have received correctly the result from the action server. 11:58.420 --> 12:00.610 Now our simple example node. 12:00.610 --> 12:07.150 So the action client has finished basically its execution, so it doesn't need to execute any more actions 12:07.150 --> 12:14.960 and so we can actually shut down completely the node with the Pi shutdown function. 12:15.230 --> 12:19.340 Now, as you can see, we are only missing to declare one function. 12:19.340 --> 12:22.820 So to define the feedback callback function. 12:22.940 --> 12:25.640 Let's also declare this one as a member. 12:26.420 --> 12:29.720 So here of the simple action client. 12:30.170 --> 12:35.990 And so let's pass the self in order to indicate that this belongs to the simple action client class. 12:35.990 --> 12:41.990 And also this function receives as input the feedback message that was sent by the action server. 12:42.140 --> 12:47.210 So let's call this variable feedback message. 12:48.430 --> 12:49.750 Now when this happens. 12:49.750 --> 12:55.120 So when this function is executed, it means that we received a new feedback message from the action 12:55.120 --> 12:55.630 server. 12:55.630 --> 12:59.140 And so let's simply print in the terminal its content. 12:59.410 --> 13:09.820 So let's use the get logger function and then let's print an informative message that says received 13:10.690 --> 13:15.030 feedback and then followed by the content of the feedback message. 13:15.040 --> 13:20.650 So let's format this string and let's print from the feedback message. 13:20.770 --> 13:25.030 So let's access to the feedback variable. 13:25.030 --> 13:26.620 And here let's print the. 13:28.030 --> 13:30.970 Partial sequence. 13:31.330 --> 13:37.690 With this, the simple action client class is completed and now, since we have defined several callback 13:37.690 --> 13:41.260 function, let's quickly recap the purpose of each of them. 13:41.710 --> 13:43.930 The response callback function. 13:43.930 --> 13:51.580 So this one is executed after we send the goal to the action server and basically it checks whether 13:51.580 --> 13:55.360 or not the action server accepted our goal. 13:55.450 --> 14:01.930 Then the result callback function is executed at the end of the action server execution. 14:01.930 --> 14:06.460 So after the server has accepted and completed the action. 14:06.760 --> 14:12.550 And finally this one, this last one, the feedback callback function is executed repeatedly. 14:12.550 --> 14:18.490 So each time we receive a new feedback message from the action server during its execution. 14:19.000 --> 14:22.420 Now we only need to declare also the main function. 14:29.170 --> 14:38.500 And so here, let's call the main function and let's define this function here above and here. 14:38.500 --> 14:40.900 Let's start by initializing the ros2 node. 14:40.930 --> 14:45.790 So rql pi init in order to initialize the node. 14:45.820 --> 14:54.340 Then let's create a new instance of the simple action client class and let's call this one action client 14:54.670 --> 14:57.640 as an instance of the simple action client. 14:57.640 --> 15:05.410 And then also let's keep this node up and running with the Pi dot spin function. 15:05.410 --> 15:08.800 And then with this we have done with our script. 15:08.920 --> 15:14.620 Now, as usual, we also need to add this script to the setup dot pi file. 15:14.620 --> 15:19.450 So to this one in which we have already installed, for example, the simple action server. 15:19.690 --> 15:29.680 So we can copy this instruction here also for the installation of the simple action client node that 15:29.680 --> 15:38.140 is still in the Arduino Pi examples folder and is in the simple action client script. 15:38.140 --> 15:41.740 And from this one we want still to execute the main function. 15:43.030 --> 15:45.250 Now, let's also save this file. 15:45.250 --> 15:51.450 And as we haven't added any new dependencies to our package, we don't need to modify the package dot 15:51.610 --> 15:56.050 XML and so we can directly proceed to build and run our node. 15:56.470 --> 15:58.720 To do so, let's open a new terminal. 15:59.410 --> 16:03.250 Let's go to the workspace and let's build it. 16:04.660 --> 16:08.710 Once the build is done, let's open a new window of the terminal. 16:09.350 --> 16:13.880 And here, let's start by launching the Simple Action Server. 16:13.880 --> 16:19.970 So let's start the action server by sourcing the workspace setup bash. 16:20.180 --> 16:26.150 And then we click on Ros to run from the Arduino Pi examples. 16:26.360 --> 16:29.300 Let's start the simple Action server. 16:29.300 --> 16:31.160 So let's press Enter. 16:31.550 --> 16:35.570 And now that the action server is running, we can also start the client. 16:35.570 --> 16:39.410 So in a new terminal, let's source the workspace. 16:39.410 --> 16:48.140 So if I set up Bash and here in order to launch the client node, let's use the command Ros to run and 16:48.140 --> 16:49.430 steal from the Arduino board. 16:49.730 --> 16:51.530 Pi Examples package. 16:51.560 --> 16:56.030 Let's start the simple action client node. 16:56.030 --> 16:57.980 So let's press enter. 16:59.280 --> 17:08.310 Here, we can see that there is an error as we need here in this function, to pass the name of the 17:08.310 --> 17:09.720 node that we want to spin. 17:09.990 --> 17:14.400 So here there was a small error, so let's save this one. 17:14.700 --> 17:19.620 But anyway, we can see that we were able to send the goal to the server. 17:19.710 --> 17:21.600 Now let's run this again. 17:21.600 --> 17:26.130 So let's build it and let's see again how it works. 17:26.520 --> 17:32.700 So now the node should remain in execution, so the actual client should remain in execution and also 17:32.700 --> 17:36.600 receive the feedback messages and the result messages from the server. 17:36.840 --> 17:40.890 Now let's start the client again and now correctly. 17:40.890 --> 17:44.880 As soon as we start the client, we see the message Goal accepted. 17:44.880 --> 17:49.710 So it means that we correctly send the goal and it was accepted by the server. 17:49.710 --> 17:57.360 And also we can see that we are starting to receive all the feedback messages that are sent by the action 17:57.380 --> 18:00.640 server and also at the end of the action. 18:00.640 --> 18:07.150 So here we can see that the last message that the action client receives before terminating its execution 18:07.150 --> 18:08.950 is the full Fibonacci sequence. 18:08.950 --> 18:11.350 So it's the result message. 18:11.350 --> 18:15.940 And here this is the result of the execution of the action server. 18:17.080 --> 18:22.210 Now if, for example, we terminate the execution of the action server. 18:22.360 --> 18:30.190 So now we can see that there is no action server with the command Ros2 action list. 18:30.880 --> 18:31.210 Okay. 18:31.210 --> 18:35.890 Now actually there aren't any action servers available in Ros2. 18:36.220 --> 18:41.530 And if, for example, we restart the action client, we can see that nothing happens. 18:41.530 --> 18:47.920 And so basically that this node is doing nothing, is idle and is waiting for an action server named 18:47.920 --> 18:50.080 Fibonacci to become available. 18:50.080 --> 18:55.840 And so this happened because here we use the function wait for server. 18:55.840 --> 19:03.430 So basically now our script is blocked, is stuck at this instruction until a Fibonacci action server 19:03.430 --> 19:06.790 that uses the Fibonacci interface becomes available. 19:07.000 --> 19:15.880 And so as soon as we restart the action server, actually the client is able to send the goal and also 19:15.880 --> 19:22.520 then to receive feedback messages and then at the end also to receive the result from the action server.