Fiddler doesn't capture traffic from my C# app

Question

I've tried using Fiddler on Windows 10 x64 and on Windows 7 Ultimate x86 in Oracle VM as a guest, and on the Win 10 as well, with Fiddler2 and Fiddler4, FiddlerCore and Charles proxy.

Those (Fiddler2, 4, Core, and Charles proxy) capture all the traffic from my browsers, including even Visual Studio update requests (or some microsoft servers VS talks to), but all of the above mentioned setups fail miserably to capture traffic from my app - ran from debug or released folder, or directly from VS debugger, both in x64 and x86.

I use VS 2015, targeting .net 4.5 Also I don't have full admin rights on the host OS (win 10), which might be an issue.

Starting Fiddler first and/or as admin won't work. Starting my app or VS as admin won't work either.

Editing machine.config won't work, there isn't even .net section (in win10 probably), I modified the .web one.

Is there a library that will log requests and responses on app level instead of OS level?

Possible duplicate of [Fiddler Not Capturing Traffic from my C# Application in Windows 8](http://stackoverflow.com/questions/18482769/fiddler-not-capturing-traffic-from-my-c-sharp-application-in-windows-8) — Prabhat Sinha, Apr 21 '16 at 17:44
You still didn't answered my first question. What kind of app is that? Winforms/Wpf/Console/Windows Store App? — Sriram Sakthivel, Apr 21 '16 at 17:48
If you're using https then you need to trust the fiddler certificate. Otherwise I'm done with my guesses. — Sriram Sakthivel, Apr 21 '16 at 17:55
What are you using to generate traffic (as in, which classes)? It needs to go through the system proxy for fiddler to catch it: if you are generating direct traffic to the host, Fiddler won't be able to capture it — Jcl, Apr 21 '16 at 18:13
Don't quite understand your question but I'm sending Http requests to websites, using .net Httpwebrequest class. I've done this a hundred times before and fiddler works like a charm. Too bad I don't have another PC to test on — codingcoder, Apr 21 '16 at 18:18
Just as a test, can you set your request's `Proxy` property, something like `request.Proxy = new WebProxy ("127.0.0.1", 8888);` and see if it works? — Jcl, Apr 21 '16 at 18:21

score 7 · Answer 1 · answered Apr 21 '16 at 22:16

Your requests are not going through the system's proxy (which Fiddler modifies, and that's how it intercepts your traffic). There are several ways you can configure your .NET apps to go through one. Fiddler documentation specifies it.

But basically:

Specify a proxy in your exe config:

<configuration>
 <system.net>
  <defaultProxy>
   <proxy bypassonlocal="false" usesystemdefault="true" />
  </defaultProxy>
 </system.net>
</configuration>

Manually specify it on the requests:

    objRequest = (HttpWebRequest)WebRequest.Create(url);
    objRequest.Proxy= new WebProxy("127.0.0.1", 8888);

Also, most .NET classes bypass the proxy if accessing localhost. In this case, use ip4.fiddler as a host instead of localhost (or ipv6.fiddle for IPv6)

Fiddler doesn't capture traffic from my C# app

1 Answers1