Header propagation with Flurl and DotNetCore

Question

I've really enjoyed using Flurl the last year but have encountered a problem that Im hoping I can solve using Flurl if possible and not resort ripping it out and using IHttpClientFactory and HttpClient from System.Net.Http

I've got a DotNetCore 3.1 API and our client is calling these APIs with custom headers. "x-activityid" as an example. My API calls out to an external API and so I've created a separate Client class where im calling the endpoints on the external API using Flurl.

I need to propagate some of the headers from the requests incomming to my API to the requests I make to the external API that Im calling using Flurl.

Some related links:

• Header propagation using ASP.NET Core
• Make HTTP requests using IHttpClientFactory in ASP.NET Core

Answer 1

The whole idea of header propagation depends on awareness of some HTTP server context from which to grab the incoming headers, which is why ASP.NET Core can support such a feature directly while Flurl, a stand-alone library that often gets embedded in things like Xamarin apps, cannot.

But all is not lost, because Flurl is really just a wrapper around HttpClient. To get this feature to work without giving up Flurl, just wire up header propagation in ASP.NET Core exactly as prescribed, allow it to inject HttpClient instances into your service classes, then wrap those instances with Flurl inside those classes. Note that you'll need to adapt the pattern of using FlurlClient directly, as opposed to building calls off URL strings, if you're not doing that already.