Building Fiddler Inspectors

Building custom Inspector objects for Fiddler is easy!  You can use any .NET language, although I'll present my examples in C#.

Fiddler v2.x loads only .NET CLR v2.0 assemblies; use Visual Studio 2005+ to compile your extension. If you use Visual Studio 2010 or later, you must change your project to target the .NET2.0/3.5 framework or Fiddler will not load your extension.

Fiddler itself requires only that the user have .NET Framework 2.0 SP1 installed. You may have your extensions target the .NET Framework 3.5 (which includes Linq) since that framework also (confusingly) runs on the v2.0 CLR, but you MUST yourself ensure that the user has the required Framework version installed BEFORE you install your extension, or a user with only the older Framework will crash on boot.

You should also ensure your project targets AnyCPU to ensure that it works properly with 64bit Fiddler.

Building for Fiddler v2 and v4

Learn more about Building assemblies to run in both Fiddler v2 and v4.

Step-by-Step

1. File | New Project

2. Pick VC# Projects | Class Library

3. Type a name, e.g. WebBrowser

4. Hit OK.

5. In Solution Explorer, right-click References and choose Add Reference

6. Hit Browse and find Fiddler.exe

7. On the .NET tab, you probably want to add a reference to System.Windows.Forms as well.

8. Ensure both libraries are in the Selected Components List and hit OK.

In Solution Explorer, rename Class1.cs to whatever, e.g. WebViewer.cs

Change the code to derive from the Inspector2 class.  Also, implement either IResponseInspector2 or IRequestInspector2.

using Fiddler;

[assembly: Fiddler.RequiredVersion("2.3.0.0")]

public class WebViewer: Inspector2, IResponseInspector2
{
   public Viewers()
   {
   //
   // TODO: Add constructor logic here
  //
   }
}

Inside the class, create a new method. By typing public override, you'll get an autocomplete list of the methods you need to write.

In Solution Explorer, right-click on the project and choose Add | User Control

Use the Toolbox to add controls to your user control-- these will show the data about the HTTP message under Inspection.

In the body{ set } and headers{ set } properties, you should update your control's visual representation of the request or response. 

Almost done...

• Compile your project.

• Drop your assembly .DLL in the \Fiddler2\Inspectors folder

• Restart Fiddler2

If you need help or have questions, please email me using the Contact link above.

TextViewer.cs

using System;
using System.IO;
using System.Drawing;
using System.Windows.Forms;
using System.Collections;
using Fiddler;

[assembly: Fiddler.RequiredVersion("2.2.7.0")]

namespace Standard
{
 public class RequestTextViewer: Inspector2, IRequestInspector2
 {
 TextView myControl;
 private byte[] m_entityBody;
 private bool m_bDirty;

 private bool m_bReadOnly;

 public bool bReadOnly{
 get {
   return m_bReadOnly;
 }
 set{
   m_bReadOnly = value;   // TODO: You probably also want to turn your visible control CONFIG.colorDisabledEdit (false) or WHITE (true) here depending on the value being passed in.  
  }
 }

public void Clear(){
  m_entityBody = null;
  m_bDirty = false;
  myControl.txtBody.Clear();
}

public RequestTextViewer()
{
  // TODO: Add constructor logic here
}

public HTTPRequestHeaders headers{
 get {
  return null;    // Return null if your control doesn't allow header editing.
  }
 set{
  }
}

public byte[] body
{
 get
 {
   return m_entityBody;
 }
 set
 {    // Here's where the action is.  It's time to update the visible display of the text
  m_entityBody = value;
 
  if (null!=m_entityBody){
   myControl.txtBody.Text = System.Text.Encoding.UTF8.GetString(m_entityBody); // TODO: Use correct encoding based on content header.
  }
  else {
   myControl.txtBody.Text = "";
  }
  m_bDirty = false;   // Note: Be sure to have an OnTextChanged handler for the textbox which sets m_bDirty to true!
}

public bool bDirty
{
 get
  {
    return m_bDirty;
  }
}

public override int GetOrder()
{
 return 0;
}

public override void AddToTab(System.Windows.Forms.TabPage o)
{
  myControl = new TextView(this);   // Essentially the TextView class is simply a usercontrol containing a textbox.
  o.Text = "TextView";
  o.Controls.Add(myControl);
  o.Controls[0].Dock= DockStyle.Fill;
}

}
}