Capturing traffic by fiddler in .net 4.5 - httpwebrequest

Question

I wrote simple application on VS2010 that send httpwebrequest and without any configurations fiddler is captures this request. But after, I installed VS2012 and run fiddler, and when i send request i have exception "Operation timed out" and request is no captured. When i close fiddler all requests are sends.
I delete VS2012 and .net framework 4.5. After that request are sends and fiddler capturing them.
Why fiddler dont't capture traffic when .net4.5 installed?

Answer 1

Did you by any chance try to set the Host property of the HttpWebRequest?
This may be the cause of your problem.
I have also .NET 4.5 installed and experience the same situation.
I get the same error when fiddler is running and is acting as a proxy. The error is:
System.Net.WebException: The operation has timed out at
System.Net.HttpWebRequest.GetResponse()
Here is a trivial sample that reproduces the problem:
using System;
using System.IO;
using System.Net;
namespace WebRequestTest
{
class Program
{
static void Main(string[] args)
{
HttpWebRequest request = (HttpWebRequest)WebRequest.Create("http://www.microsoft.com");
request.Host = "www.microsoft.com";//If I comment this line, capturing with fiddler works OK.
request.Method = "GET";
request.UserAgent = "Mozilla/5.0 (Windows NT 6.1; WOW64; rv:18.0) Gecko/20100101 Firefox/18.0";
using (HttpWebResponse response = (HttpWebResponse)request.GetResponse())
using (Stream stream = response.GetResponseStream())
using (StreamReader sr = new StreamReader(stream))
{
string content = sr.ReadToEnd();
Console.WriteLine(content);
}
}
}
}
In my case I just had to comment the request.Host="www.microsoft.com" line and everything worked OK.
I suspect same behavior will occur when using an HTTP proxy other than fiddler, but I have not tested it though.