.NET WebClient post request not appearing in Fiddler

[Tony]

I have an ASP.NET WebForms app (sender) which sends a WebClient post request to another ASP.NET app (receiver) on the same dev machine. The WebClient post is initiated by clicking a button in the sender app. It's a test app and the form has only the button. I can see the post from the button in Fiddler but I don't see the post request from the WebClient method. Why?

I know the WebClient post runs successfully because the breakpoint is hit in the receiver app and the Forms collection has the value of the input field from the WebClient request from the sender app. (Using Windows 8.1)

This is the call:

using (var client = new WebClient())
{
client.Headers[HttpRequestHeader.ContentType] = "application/x-www-form-urlencoded";
var data = "FirstName=John";
var result = client.UploadString("http://localhost/testform/default.aspx", "POST", data);
Console.WriteLine(result);
}

[Tony]

I am not using any filters

[Eric Lawrence]

1. Traffic from applications running in different user accounts (e.g. the ASP.NET service account) isn't automatically captured by Fiddler running in the logon user's account. See http://blogs.telerik.com/fiddler/posts/13-01-08/capturing-traffic-from-.net-services-with-fiddler for details.

2. The .NET Framework is hardcoded to bypass proxies when making requests to "localhost." The workaround is to use the machine name, or "localhost.fiddler" instead. 

Regards,
Eric Lawrence
Telerik

 

 

[Tony]

It's still not working. I made the changes to the two v4. mahine.config files. When I use 'localhost.fiddler' in the WebClient url, I get this error "The remote name could not be resolved: 'localhost.fiddler". When I use the machine name, I don't get any errors but the request is not in Fiddler. If I use 'localhost.fiddler' in the browser to bring up the page, the page comes up. I don't why when it's used in WebClient, WebClient can't resolve it while the browser can.

[Eric Lawrence]

Howdy, Tony--

Fear not-- thousands of people use Fiddler to capture WebClient traffic every day, so we'll get this working.

If using "localhost.fiddler" results in a DNS failure, that means that your client is not using the proper proxy settings. I assume that you've confirmed that your application is using .NET4 and not an earlier version? Do you have any web.config or app.config files that may be overriding the default machine.config proxy settings?

If you're debugging locally, you can also temporarily debug by simply assigning the WebClient's Proxy property directly.

Regards,
Eric Lawrence
Telerik

 

 

[Tony]

I am using 4.5 on a new empty WebForms app. There's nothing added to web.config. I modified the code now so that WebClient uses a proxy.   WebProxy proxy = new WebProxy();
                proxy.Address = new Uri("http://127.0.0.1:8888");
                client.Proxy = proxy;
                ......

Now I see the WebClient post in Fiddler but the final result is this error:  The remote server returned an error: (502) Bad Gateway. I get the same result with or without the machine.config changes.

[Eric Lawrence]

Hi, Tony--

I'm afraid that I don't know what "the final result is this error" means.

Where do you see that error, and what exactly do you see in Fiddler? If the URL is HTTPS, have you configured Windows to trust the Fiddler Root certificate on a machine-wide basis?

1. In Fiddler’s Tools > Fiddler Options > HTTPS tab, click Export Root Certificate to Desktop.

2. Launch mmc.exe.

3. Click File > Add/Remove Snap-In.

4. Select the Certificates snap-in and press Add.

5. When prompted This snap-in will always manage certificates for: choose Computer Account

6. Click Local Computer, then Finish, then OK.

7. Open the Certificates (Local Computer) node.

8. Right-click the Trusted Root Certificate Authorities folder and choose All Tasks > Import.

9. Choose the file you exported in step #1 and import it.

Regards,
Eric Lawrence
Telerik

 

 

[Tony]

"The remote server returned an error: (502) Bad Gateway" is what shows in the browser after I click the button. 

I got it working now. It didn't work if localhost or 127.0.0.1 or the machine name were used in WebClient. ipv4.fiddler or localhost.fiddler worked. Thanks for your help.