Visual Studio 2012, IIS Express, and Fiddler

From the mail bag… Q:When I use IE10 on Windows 8 to visit an IIS Express instance using the following URL http://ipv4.fiddler:2468/, I get an unexpected error message. HTTP/1.1 400 Bad RequestContent-Type: text/html;charset=us-asciiServer: Microsoft-HTTPAPI/2.0Date: Wed, 22 Aug 2012 19:59:52 GMTConnection: closeContent-Length: 334 <!DOCTYPE HTML PUBLIC “-//W3C//DTD HTML 4.01//EN”””><HTML><HEAD><TITLE>Bad Request</TITLE><META HTTP-EQUIV=”Content-Type” Content=”text/html; charset=us-ascii”></HEAD><BODY><h2>Bad Request – Invalid Hostname</h2><hr><p>HTTP Error 400….


My book “Debugging with Fiddler”, is now available

I’m delighted to announce that my new full-length book on Fiddler is now available. Weighing in at 330 pages, it covers every feature in Fiddler, and provides the most comprehensive available documentation of how to develop Fiddler extensions (including Inspectors, Transcoders, and IFiddlerExtensions) and build on the FiddlerCore class library. The book is available in…


.NET HTTPS connections timeout on SNI TLS Warning

Recently, a handful of folks have emailed me complaining that some HTTPS sites cannot be reached by their .NET programs or from any program when Fiddler is configured to decrypt traffic. Notably, these users only have problems when running on Windows Vista or later. So, what’s going on? When I need to troubleshoot issues that…


New Tricks in Fiddler

The new Fiddler Beta has a few useful tricks. First, you can copy a DataURI to your clipboard (from Fiddler itself, or anywhere else): and use the new Edit > Paste Files as Sessions command: … to instruct Fiddler to parse the DataURI and create a new Session for it. You can then use Fiddler’s…


News on Fiddler Surveys and Telemetry

For this morning’s post, I wanted to give everyone a quick picture of some of the data I’ve collected about Fiddler usage, how I plan to respond, and how I will continue to learn more. I’ve recently had the chance to run some surveys and spend some time with developers who are using Fiddler, and…


Generating HTML5 AppCache Manifests with Fiddler

HTML5 introduces the concept of an Application Cache, which allows a web developer to provide a manifest of pages that should be cached to permit offline use. You can see an instance of AppCache over on the IETestDrive site; if you examine the markup, you can find that the HTML tag contains a manifest attribute…


Fiddler and Windows 8 Metro-style applications

Over on StackOverflow, a new Windows 8 user asked how to get Fiddler working with new Windows 8 Metro-style applications. These applications work somewhat differently than classic desktop applications, and require a bit of special configuration work to get Fiddler to work properly. Fear not, however, Windows 8 and Fiddler get along just fine after…


Fiddler and Channel Binding Tokens Revisited

Just under a year ago, I wrote a blog post about how the new “Extended Protection” feature (also known as Channel Binding Tokens or CBT) prevented seamless decryption of certain authenticated HTTPS traffic when Fiddler is running. The quick recap is that CBT binds a set of NTLM or Kerberos authentication credentials to the “channel”…


Swapping out JQuery with Fiddler

This morning, someone asked me to look into a site-compatibility problem on a HTML5 demo site. When loading the site into IE9 and IE10, the F12 Developer Tools’ Script Debugger showed the following error: Now, obviously, IE does support getElementsByTagName, and I confirmed that the page is running in IE9 and IE10 Standards Modes in…


Debugging Windows Phone 7 device traffic with Fiddler

Back in October, I showed how to debug Windows Phone emulator traffic with Fiddler . Since then, I’ve acquired the LG Quantum phone, and naturally, one of my first goals was to start looking at the traffic from mobile Internet Explorer and some of my WP7 applications. The process for capturing traffic from a phone…