Debugging your Extensions

• Extension developers should set the fiddler.debug.extensions.showerrors preference to True ensure that exceptions and other extension-related errors are not silently caught.

• Extension developers should set the fiddler.debug.extensions.verbose preference to True to spew logging information to the Log tab.

If you write to me complaining that your extension doesn't work and you have not first set these preferences before testing, I will tease you mercilessly.

Step-by-step Sample Extension

using System;
using System.IO;
using System.Text;
using System.Windows.Forms;
using Fiddler;
using System.Diagnostics;
using System.Reflection;
[assembly: AssemblyVersion("1.0.0.0")]
[assembly: Fiddler.RequiredVersion("2.4.0.0")]


[ProfferFormat("TAB-Separated Values", "Session List in Tab-Delimited Format")]
[ProfferFormat("Comma-Separated Values",
    "Session List in Comma-Delimited Format; import into Excel or other tools")]

public class CSVTranscoder: ISessionExporter  // Ensure class is public, or Fiddler won't see it!
{
  public bool ExportSessions(string sFormat, Session[] oSessions, Dictionary<string, object> dictOptions,
      EventHandler<ProgressCallbackEventArgs> evtProgressNotifications)
  {
    bool bResult = false;
    string chSplit;

    // Determine if we already have a filename from the dictOptions collection
    string sFilename = null;
    if (null != dictOptions && dictOptions.ContainsKey("Filename"))
    {
      sFilename = dictOptions["Filename"] as string;
    }

    if (sFormat == "Comma-Separated Values")
    {
      chSplit = ",";
      if (string.IsNullOrEmpty(sFilename)) sFilename = Fiddler.Utilities.ObtainSaveFilename("Export As " + sFormat, "CSV Files (*.csv)|*.csv");
    }
    else
    {
      chSplit = "\t";
      if (string.IsNullOrEmpty(sFilename)) sFilename = Fiddler.Utilities.ObtainSaveFilename("Export As " + sFormat, "TSV Files (*.tsv)|*.tsv");
    }

    if (String.IsNullOrEmpty(sFilename)) return false;

    try
    {
      StreamWriter swOutput = new StreamWriter(sFilename, false, Encoding.UTF8);
      int iCount = 0;
      int iMax = oSessions.Length;

      #region WriteColHeaders
      bool bFirstCol = true;
      foreach (ColumnHeader oLVCol in FiddlerApplication.UI.lvSessions.Columns)
      {
        if (!bFirstCol)
        {
        swOutput.Write(chSplit);
        }
        else
        {
        bFirstCol = false;
        }
        swOutput.Write(oLVCol.Text.Replace(chSplit, ""));
        }
        swOutput.WriteLine();
        #endregion WriteColHeaders

        #region WriteEachSession
        foreach (Session oS in oSessions)
        {
        iCount++;
        if (null != oS.ViewItem)
        {
        bFirstCol = true;
        ListViewItem oLVI = (oS.ViewItem as ListViewItem);
        if (null == oLVI) continue;
        foreach (ListViewItem.ListViewSubItem oLVC in oLVI.SubItems)
        {
          if (!bFirstCol)
        {
          swOutput.Write(chSplit);
        }
        else
        {
          bFirstCol = false;
        }

          swOutput.Write(oLVC.Text.Replace(chSplit, ""));
        }

        swOutput.WriteLine();
      }

      if (null != evtProgressNotifications)
      {
        evtProgressNotifications(null, new ProgressCallbackEventArgs(, ));
        ProgressCallbackEventArgs PCEA = new ProgressCallbackEventArgs((iCount/(float)iMax), "wrote " + iCount.ToString() + " records.");
        evtProgressNotifications(null, PCEA);
        if (PCEA.Cancel) { swOutput.Close(); return false; }
      }
    }
    #endregion WriteEachSession

    swOutput.Close();
    bResult = true;
    }
    catch (Exception eX)
    {
      MessageBox.Show(eX.Message, "Failed to export");
      bResult = false;
     }
  }
  return bResult;
  }

  public void Dispose()
  {
  }
}

Other Examples and Information

Passing arguments to the Transcoder

Transcoders may be passed arguments in a dictionary object.  For instance, FiddlerScript can invoke the HTTPArchive transcoder, passing in the filename string and maximum response size integers thusly:

var oSessions = FiddlerApplication.UI.GetAllSessions();
var oExportOptions = FiddlerObject.createDictionary();
oExportOptions.Add("Filename", "C:\\users\\ericlaw\\desktop\\out1.har");
oExportOptions.Add("MaxTextBodyLength", 1024);
oExportOptions.Add("MaxBinaryBodyLength", 16384);
FiddlerApplication.DoExport("HTTPArchive v1.2", oSessions, oExportOptions, null);

Your Transcoder extension may collect these options like so:

 public bool ExportSessions(string sFormat, Session[] oSessions,
      Dictionary<string, object> dictOptions, EventHandler<ProgressCallbackEventArgs> evtProgressNotifications)
{

//...

  if (null != dictOptions)
  {
    if (dictOptions.ContainsKey("Filename"))
    {
    sFilename = dictOptions["Filename"] as string;
    }

    if (dictOptions.ContainsKey("MaxTextBodyLength"))
    {
      iMaxTextBodyLength = (int)dictOptions["MaxTextBodyLength"];
    }

    if (dictOptions.ContainsKey("MaxBinaryBodyLength"))
    {
       iMaxBinaryBodyLength = (int)dictOptions["MaxBinaryBodyLength"];
    }
  }

Almost done...

• Compile your project.

• Drop your assembly .DLL in your \Documents\Fiddler2\ImportExport\ folder (or use \Program Files\Fiddler2\ImportExport\to make available to all users on the machine)

• Restart Fiddler2.

• Click File > Import or File > Export

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

Change Log
6/21/10 - Created
6/28/10 - Updated with Cancel flag
6/29/10 - Updated Interface signatures with dictOptions collection introduced in Fiddler 2.2.9.7
4/04/11 - Updated with additional information about passing parameters via Options dictionary