WEBVTT 00:00.410 --> 00:00.770 Okay. 00:00.770 --> 00:05.810 So what we're going to take a look at in this lesson is we're going to deal with how we send back an 00:05.810 --> 00:07.370 exception to our client. 00:07.370 --> 00:13.190 And the idea of this is we're just going to format the response so that we can send the exception back 00:13.190 --> 00:15.590 to the client whilst we're in developer mode. 00:15.590 --> 00:19.040 We wouldn't send this level of detail back in production mode. 00:19.040 --> 00:20.870 And that is the default behavior. 00:20.900 --> 00:26.780 In fact, in our code, if we go and take a look at the program class, it's kind of hidden now in modern 00:26.780 --> 00:27.710 versions of. 00:27.950 --> 00:34.820 Net to hide or remove some of the boilerplate that we would see in our code and what we do have here 00:34.850 --> 00:41.120 inside the middleware, although we don't actually see it, is we have this developer exception page, 00:41.120 --> 00:48.380 and that's just automatically added unless we override it with our own exception or our own exception 00:48.380 --> 00:49.040 middleware. 00:49.040 --> 00:52.250 But this is what's going on, even though we don't see it in our code. 00:52.250 --> 00:57.050 And that's responsible for sending back what we see in the response in postman. 00:57.050 --> 01:02.390 Now we're going to take a look at using middleware so that we can send back our own version of list. 01:02.420 --> 01:09.250 What I'd like it to be is a JSON formatted response, so that we can use this more easily in our client 01:09.250 --> 01:09.850 application. 01:09.850 --> 01:12.280 What we've currently got is just text that's coming back. 01:12.310 --> 01:16.000 I would like this to be JSON, so we'll take a look at how we can do that. 01:16.000 --> 01:19.240 And it gives us an opportunity to look at middleware as well. 01:19.450 --> 01:24.970 As far as the other responses goes about the other HTTP response errors, I'm okay with them. 01:24.970 --> 01:30.670 We can handle them inside our client just as they are, and then take whatever action we need to take 01:30.670 --> 01:34.600 based on what type of HTTP error response it is. 01:34.600 --> 01:40.990 But we will take a look at middleware initially, and I've just come to the ASP.Net documentation about 01:40.990 --> 01:45.280 middleware, just to discuss what this actually is and what it does for us. 01:45.280 --> 01:53.740 So as a request comes in to our API server, we have our request and it goes through a series of middleware 01:53.770 --> 01:57.070 steps in what's referred to as a pipeline. 01:57.070 --> 02:00.160 So the request comes in, it hits the first bit of middleware. 02:00.160 --> 02:05.530 And then any logic inside this middleware can be executed against that request. 02:05.530 --> 02:06.820 It can manipulate the request. 02:06.820 --> 02:08.380 It can authorize the request. 02:08.380 --> 02:11.590 It can do whatever we need to do with that request. 02:11.590 --> 02:19.240 And once that has executed, we then call the next method and it gets passed to the next piece of middleware. 02:19.630 --> 02:24.280 Logic gets executed in there, and then the next method is called again. 02:24.280 --> 02:27.130 And then we go through the middleware pipeline. 02:27.130 --> 02:32.980 And then we can do something with the middleware or the request on its way in through the pipeline, 02:32.980 --> 02:37.390 or also on its way out before getting to our response. 02:37.450 --> 02:44.140 Now, at any point during this journey, it's possible an exception can be thrown by any of the logic 02:44.140 --> 02:51.370 in any of these bits of middleware, and if an exception is thrown, then the goal of this is to have 02:51.370 --> 02:53.980 something that can catch that exception. 02:53.980 --> 02:56.950 What we have currently is the developer exception. 02:56.950 --> 03:01.840 But what we're going to do is create our own middleware, and exception handling middleware lives at 03:01.840 --> 03:09.090 the very top of the middleware tree, because when an exception happens, it will be thrown and it's 03:09.090 --> 03:14.550 going to keep being thrown back up the middleware tree until it gets to a point where something can 03:14.550 --> 03:15.480 catch it. 03:15.480 --> 03:21.630 So we're going to catch the exception at the highest possible level and then handle that exception. 03:21.630 --> 03:24.030 So that's the goal of what we're about to do. 03:24.060 --> 03:26.130 So inside VS code. 03:26.130 --> 03:33.810 Let's close all of this stuff down and we will open up in the API folder. 03:33.810 --> 03:36.810 We'll create a new folder and we'll call it middle. 03:36.840 --> 03:43.140 And inside our middleware folder we'll create a new file that's going to be a class. 03:43.140 --> 03:48.570 And we'll call it exception middleware and press return. 03:48.720 --> 03:54.900 And inside here we're going to use an interface called I middleware. 03:55.110 --> 04:00.060 And when we use an interface then we can use this to populate its required methods. 04:00.060 --> 04:01.650 And I'll just use the quick fix. 04:01.650 --> 04:05.130 And we can implement this interface. 04:05.130 --> 04:13.040 And what we use here is the invoke Async method, and what's passed into this invoke async method as 04:13.040 --> 04:15.110 an argument is the HTTP context. 04:15.140 --> 04:18.620 So we have access to that and also the request delegate. 04:18.620 --> 04:23.390 So we can call next and pass this on to the next piece of middleware. 04:23.420 --> 04:28.340 Now we'll also add a couple of parameters arguments to this as well. 04:28.340 --> 04:33.440 And we want to inject the environment that we're running in. 04:33.530 --> 04:38.150 And also a logger so we can log information to our console. 04:38.180 --> 04:42.800 So we're going to inject the host environment into this and call it env. 04:43.160 --> 04:48.590 And we're also going to inject an ilogger just so we can write stuff out to the console. 04:48.590 --> 04:54.050 And the type parameter for the logger is the name of the class that we're using this in. 04:54.050 --> 04:57.830 So I'll specify exception middleware and we'll just call it logger. 04:57.830 --> 05:01.250 And I'll just bring this down so it fits on the screen. 05:01.250 --> 05:03.860 And this is a public task. 05:03.860 --> 05:06.110 So we're going to make this method async. 05:06.410 --> 05:11.940 And inside here instead of throwing a new exception we're going to use a try catch block so we can use 05:11.940 --> 05:13.140 a snippet for that. 05:13.620 --> 05:16.080 So I'm just going to select try for try catch. 05:16.080 --> 05:16.950 And great. 05:16.980 --> 05:18.870 Now we've got our try catch block. 05:18.870 --> 05:23.280 So in the try block we're not going to do anything here apart from call the next method. 05:23.280 --> 05:27.330 So that this goes to the next piece of middleware. 05:27.330 --> 05:32.010 And we need to pass in the Httpcontext for this method. 05:32.010 --> 05:34.860 And then we're going to catch the exception. 05:34.860 --> 05:38.820 I'll remove system from there and just say exception x. 05:39.210 --> 05:44.670 And then I'm going to say await and handle exception. 05:45.090 --> 05:49.200 And we're going to pass in to this method that we don't have yet but we will do. 05:49.230 --> 05:54.510 I'm going to pass in as arguments the context and the exception to this method. 05:54.510 --> 06:00.090 Put my cursor inside here, and then I'm just going to generate the method handle exception. 06:00.090 --> 06:02.250 So I'll split this lesson into two parts. 06:02.250 --> 06:06.330 And in the next lesson we'll populate what we're doing inside the handle exception. 06:06.330 --> 06:10.950 And also take a look at the program class where we use this middleware. 06:10.950 --> 06:13.380 And we'll take a look at that next.