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ASP.NET Core gives you a chance to gracefully shutdown your background services (such as cleaning up and/or finishing in-progress work). By default, you’re given a grand total of 5 seconds to shutdown all background services. If you need more time than this, there are a few ways to control the graceful shutdown time, which I’ll … Read more
When you’re using the Visual Studio debugger to step through your code, sometimes it’s useful to be able to step into the .NET source code. I had to do this recently to figure out why my ASP.NET Core code wasn’t behaving as expected. You can enable .NET source code debugging with the following steps: Now … Read more
The simplest way to delete a directory is by using Directory.Delete() (in System.IO). Here are a few examples: You have to specify the path of the directory to delete. This can be an absolute or relative path. You can pass in a recursive flag, which tells it to delete everything in the directory (files and … Read more
There are two ways to receive CSV data in a web API: In this article, I’ll show examples of both of these approaches. I’ll be using the CsvHelper library to parse CSV data into model objects and then do model validation. Note: To use CsvHelper, install the CsvHelper package (Install-Package CsvHelper). Or use whichever parser … Read more
When you use HttpClient to make requests, you can directly get the status code from the HttpResponseMessage object, like this: The main reason for checking the status code is to determine if the request was successful and then reacting to error status codes (usually by throwing an exception). The HttpResponseMessage class has two helpers that … Read more
It’s a good idea to provide users with a way to cancel a HttpClient request that’s taking too long. To be able to cancel an HttpClient request, you can pass in a CancellationToken: To get a CancellationToken, you have to create a CancellationTokenSource: To actually cancel the request, you have to call CancellationTokenSource.Cancel(): This means … Read more
In an electrical system, a circuit breaker detects electrical problems and opens the circuit, which blocks electricity from flowing. To get electricity flowing again, you have to close the circuit. The same approach can be implemented in software when you’re sending requests to an external service. This is especially important when you’re sending lots of … Read more
There are two global exception events available in all .NET applications: You wire up these event handlers in Main() (before anything else has executed), like this: Note: If you’re using top-level statements, put these statements at the top of the ‘entry point’ file. This outputs the following before crashing: Notice the FirstChanceException event fired first. … Read more
You can use Microsoft Extensibility Framework (MEF) to load assemblies at runtime. This is an alternative to implementing dynamic assembly loading with a more manual approach (like using AssemblyLoadContext). Here’s an example of using MEF to load an instance of IMessageProcessorPlugin from some assembly located in the C:\Plugins directory: MEF looks for exported types in … Read more
Whenever you’re dealing with code that can run into transient errors, it’s a good idea to implement retries. Transient errors, by definition, are temporary and subsequent attempts should succeed. When you retry with a delay, it means you think the the transient error will go away by itself after a short period of time. When … Read more
EF Core has built-in retry functionality. To use it, you can call options.EnableRetryOnFailure(), like this: The retry logic is contained in execution strategy classes. The above code is using the default execution strategy class (SqlServerRetryingExecutionStrategy). When you execute a query, it goes through the execution strategy class. It executes the query and checks for transient … Read more
I was reading about logging in ASP.NET when I came across this statement about logging to the database: When logging to SQL Server, don’t do so directly. Instead, add log messages to an in-memory queue and have a background worker dequeue and insert data to SQL Server. Paraphrased from Microsoft – No asynchronous logger methods … Read more
When a background service throws an unhandled exception in ExecuteAsync(), you have two options: You can change the behavior if the default isn’t what you want (notice the default behavior changed in .NET 6). In .NET 6+, you can configure the behavior in the initialization code. Here’s an example of making it ignore crashed background … Read more
There are three requirements for unit testing a middleware class: Here’s an example: This is a simple test that only checks the response status code. By passing in DefaultHttpContext, you have control over the request and response objects. You can set the request to whatever you need, and then verify the response. I’ll show examples … Read more
When you’re using the same HttpClient instance to send multiple requests, and you want to change the timeout per request, you can pass in a CancellationToken, like this: You can’t change HttpClient.Timeout after the instance has been used. You have to pass in a CancellationToken instead. There are other key points to know when trying … Read more
The key to unit testing an ApiController class is to mock out all of its dependencies, including the controller’s HttpContext property, like this: If the controller method you’re testing uses anything from the HttpContext, then you’ll want to swap in your own value. Otherwise HttpContext will be null and you’ll get a NullReferenceException. Fortunately Microsoft … Read more
Try/finally blocks are useful for when you are required to do something at the end of a method no matter what. The finally block always executes, even if there’s an exception (there is one case where this isn’t true, which I’ll explain in the Unhandled exception section below). There are a few common scenarios where … Read more
When you use System.Text.Json.JsonSerializer to serialize an object that has a cycle, you get the following exception: System.Text.Json.JsonException: A possible object cycle was detected which is not supported. This can either be due to a cycle or if the object depth is larger than the maximum allowed depth of 0. In .NET 6+, you can … Read more
When a Task throws an exception and stops running, it has faulted. The question is, how do you get the exception that was thrown from the faulted Task? This depends on if you’re awaiting the Task or not. This article shows how to handle a faulted Task’s exception in two scenarios: when you’re awaiting the … Read more
When you have code that calls an endpoint, you need to make sure it’s resilient and can handle error scenarios, such as timeouts. One way to prove your code is resilient is by using toxiproxy to simulate bad behavior. Toxiproxy sits between your client code and the endpoint. It receives requests from your client, applies … Read more
This article shows code for converting a hex string to a byte array, unit tests, and a speed comparison. First, this diagram shows the algorithm for converting a hex string to a byte array. To convert a hex string to a byte array, you need to loop through the hex string and convert two characters … Read more
You can use exception filtering to conditionally catch exceptions, like this: Note: This feature was added in C# 6. Any SqlException that doesn’t meet the condition specified in the when clause will not be caught. Previously, without exception filtering, you’d have to handle that scenario in the catch block and rethrow, like this: Exception filtering … Read more
You can use a hosted BackgroundService in ASP.NET Core for two purposes: In this article, I’ll show how to create and register a hosted BackgroundService. In this example, it periodically pings a URL and logs the results. 1 – Subclass BackgroundService The first step is to subclass BackgroundService: In this example, we’ll create a background … Read more
Server-Sent Events (SSE) allow a client to subscribe to messages on a server. The server pushes new messages to the client as they happen. This is an alternative to the client polling the server for new messages. In this article I’ll show how to implement the messaging system shown in the diagram below. This uses … Read more
Server-Sent Events (SSE) allow a client to subscribe to messages from the server. It creates a one-way stream from the server to the client. When the server has new messages for the client, it writes them to the stream. This is an alternative to the client polling the server for updates. Use the following to … Read more