FiddlerCore Without Registering As A System Proxy - fiddlercore

Question

I have a .NET Application that I need to alter some WCF traffic headers on. The Microsoft folks told me there is no way to really inject the headers I need in the request and pick them up out of the response with the current framework. What I would like to do is just add FiddlerCore to the application, and if the header isn't there on the outgoing request from my application, then I would like to add it. (Real simple).
I can get everything to work, however the events only fire if I register the FiddlerApplication as a system proxy. I would like this transparent to the user so that it doesn't screw up their proxy settings in the OS.
private void Form1_Load(object sender, EventArgs e)
{
Fiddler.FiddlerApplication.SetAppDisplayName("FiddlerCoreTester");
Fiddler.FiddlerApplication.RequestHeadersAvailable += this.RequestHeadersAvailable;
Fiddler.FiddlerApplication.BeforeRequest += this.BeforeRequest;
Fiddler.FiddlerApplication.AfterSessionComplete += this.SessionComplete;
FiddlerApplication.OnNotification += this.OnNotification;
Fiddler.FiddlerApplication.ResponseHeadersAvailable += this.ResponseHeadersAvailable;
Fiddler.URLMonInterop.SetProxyInProcess("127.0.0.1:80", "<-loopback>");
Fiddler.FiddlerApplication.Startup(80, false, false);
WebClient wc = new WebClient();
string s = wc.DownloadString("http://www.google.com");
System.Windows.Forms.MessageBox.Show(s);
Fiddler.FiddlerApplication.Shutdown();
}
private void ResponseHeadersAvailable(Session oSession)
{
}
private void OnNotification(object sender, NotificationEventArgs e)
{
}
private void SessionComplete(Session oSession)
{
}
private void RequestHeadersAvailable()
{
}
private void BeforeRequest(Fiddler.Session oSession)
{
if (oSession.RequestHeaders.Exists("TESTHEADER") == false) {
oSession.RequestHeaders.Add("TESTHEADER", "TEST");
}
}
The events never get called in this case, however if I change this over to the below it does:
Fiddler.FiddlerApplication.Startup(80, true, false);
Does anyone know how to get this working?
Thanks so much

Answer 1

You should let your webclient use FiddlerCore as the proxy. You need to do this by setting the proxy of the webclient equal to proxy url that Fiddler listens to. Now your webclient loads the string through http://127.0.0.1:80 and Fiddler can capture your request.
WebClient wc = new WebClient();
wc.Proxy = new WebProxy(new Uri("http://127.0.0.1:80"));
string s = wc.DownloadString("http://www.google.com");
Fiddler.FiddlerApplication.Shutdown();