C# – How to read problem details JSON with HttpClient

Problem details (RFC7807) is a standardized error response format that has a Content-Type of application/problem+json, an error response code (i.e. 400 – Bad Request), and has a response body that looks like this: This can be extended to include any number of properties. The example shown above comes from the default way ASP.NET Core returns … Read more

C# – The performance gains of HttpClient reusing connections

When you use the same instance of HttpClient for multiple requests (sequential and concurrent) to the same URL, it’ll reuse connections. Requests that get to reuse a connection are 5.5-8.5x faster than requests that have to open a new connection. There are a few scenarios that benefit from this connection reuse: Measuring the performance gains … Read more

C# – Disposing the request HttpContent when using HttpClient

In versions before .NET Core 3.0 (including .NET Framework), HttpClient disposes the request HttpContent object for you. This is surprising default behavior (a violation of the principle of least surprise for sure). This causes multiple problems, but one of the main problems is it prevents you from reusing the HttpContent object (you’re greeted with an … Read more

C# – How to send a file with HttpClient

In order to send a file in a request with HttpClient, add the file into a MultipartFormDataContent object, and send this object as the request content. Here’s an example: This sends the following multipart/form-data POST request: In this article, I’ll explain a few details about MultipartFormDataContent, and show a few other file-sending scenarios. MultipartFormDataContent Add() … Read more

C# – Circuit breaker with Polly

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

C# – How to use Polly to do retries

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

C# – How to change the HttpClient timeout per request

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

How to use toxiproxy to simulate web API error scenarios

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

C# – How to unit test code that uses HttpClient

When you want to unit test code that uses HttpClient, you’ll want to treat HttpClient like any other dependency: pass it into the code (aka dependency injection) and then mock it out in the unit tests. There are two approaches to mocking it out: In this article I’ll show examples of these two approaches. Untested … Read more

C# – Fixing the Sync over Async antipattern

The Sync over Async antipattern is when you’re using a blocking wait on an async method, instead of awaiting the results asynchronously. This wastes the thread, causes unresponsiveness (if called from the UI), and exposes you to potential deadlocks. There are two causes: In this article I’ll show an example of the Sync over Async … Read more