Fiddler not capturing traffic from .Net Core

Question

I have a console app that calls a number of 3rd party services via HTTP/HTTPS that was originally written to run under the .Net Framework. Fiddler works fine with that version of the app, capturing all of the HTTP and HTTPS traffic.

I ported the app to .net Core 2.1 and now Fiddler does not capture any of the HTTP/HTTPS traffic from the app.

Any suggestions as to why Fiddler (v5.0) is not working to capture traffic from the .Net Core app?

Answer 1

In my office environment, Fiddler still does not intercept requests that are issued by .NET Core 2.2 against external resources. I guess this is due to our local proxy setup.

My workaround is to capture requests from .NET Core 2.2 by explicitly defining Fiddler as a proxy to be used by the HttpClient class:

        var httpClient = new HttpClient(
           handler: new HttpClientHandler
           {
               // 8888 = Fiddler standard port
               Proxy = new WebProxy(new Uri("http://localhost:8888")),  
               UseProxy = true
           }
        );

This reliably tunnels all requests coming from Core through Fiddler.