When  I tried to update fiddler i get this .net exception:

See the end of this message for details on invoking
just-in-time (JIT) debugging instead of this dialog box.

************** Exception Text **************
System.ComponentModel.Win32Exception (0x80004005): The operation was canceled by the user
at System.Diagnostics.Process.StartWithShellExecuteEx(ProcessStartInfo startInfo)
at „‡.ˆ.‡(Object , AsyncCompletedEventArgs ) in C:\JenkinsHome\jobs\FiddlerReleaseBuild\workspace\Fiddler2\v4\Common\Application\AutoUpdate\DownloadUpdateForm.cs:line 155
at System.Net.WebClient.OnDownloadFileCompleted(AsyncCompletedEventArgs e)


************** Loaded Assemblies **************
mscorlib
Assembly Version: 4.0.0.0
Win32 Version: 4.6.1586.0 built by: NETFXREL2
CodeBase: file:///C:/Windows/Microsoft.NET/Framework64/v4.0.30319/mscorlib.dll
----------------------------------------
Fiddler
Assembly Version: 4.6.20171.14978
Win32 Version: 4.6.20171.14978
CodeBase: file:///C:/Program%20Files%20(x86)/Fiddler2/Fiddler.exe
----------------------------------------
System
Assembly Version: 4.0.0.0
Win32 Version: 4.6.1586.0 built by: NETFXREL2
CodeBase: file:///C:/Windows/Microsoft.Net/assembly/GAC_MSIL/System/v4.0_4.0.0.0__b77a5c561934e089/System.dll
----------------------------------------
System.Core
Assembly Version: 4.0.0.0
Win32 Version: 4.6.1586.0 built by: NETFXREL2
CodeBase: file:///C:/Windows/Microsoft.Net/assembly/GAC_MSIL/System.Core/v4.0_4.0.0.0__b77a5c561934e089/System.Core.dll
----------------------------------------
System.Windows.Forms
Assembly Version: 4.0.0.0
Win32 Version: 4.6.1586.0 built by: NETFXREL2
CodeBase: file:///C:/Windows/Microsoft.Net/assembly/GAC_MSIL/System.Windows.Forms/v4.0_4.0.0.0__b77a5c561934e089/System.Windows.Forms.dll
----------------------------------------
System.Drawing
Assembly Version: 4.0.0.0
Win32 Version: 4.6.1586.0 built by: NETFXREL2
CodeBase: file:///C:/Windows/Microsoft.Net/assembly/GAC_MSIL/System.Drawing/v4.0_4.0.0.0__b03f5f7f11d50a3a/System.Drawing.dll
----------------------------------------
Xceed.Zip.v5.4
Assembly Version: 5.4.13572.13590
Win32 Version: 5.4.13572.13590
CodeBase: file:///C:/Program%20Files%20(x86)/Fiddler2/Xceed.Zip.v5.4.DLL
----------------------------------------
Xceed.Compression.Formats.v5.4
Assembly Version: 5.4.13572.13590
Win32 Version: 5.4.13572.13590
CodeBase: file:///C:/Program%20Files%20(x86)/Fiddler2/Xceed.Compression.Formats.v5.4.DLL
----------------------------------------
Xceed.FileSystem.v5.4
Assembly Version: 5.4.13572.13590
Win32 Version: 5.4.13572.13590
CodeBase: file:///C:/Program%20Files%20(x86)/Fiddler2/Xceed.FileSystem.v5.4.DLL
----------------------------------------
Xceed.Compression.v5.4
Assembly Version: 5.4.13572.13590
Win32 Version: 5.4.13572.13590
CodeBase: file:///C:/Program%20Files%20(x86)/Fiddler2/Xceed.Compression.v5.4.DLL
----------------------------------------
System.Configuration
Assembly Version: 4.0.0.0
Win32 Version: 4.6.1586.0 built by: NETFXREL2
CodeBase: file:///C:/Windows/Microsoft.Net/assembly/GAC_MSIL/System.Configuration/v4.0_4.0.0.0__b03f5f7f11d50a3a/System.Configuration.dll
----------------------------------------
System.Xml
Assembly Version: 4.0.0.0
Win32 Version: 4.6.1586.0 built by: NETFXREL2
CodeBase: file:///C:/Windows/Microsoft.Net/assembly/GAC_MSIL/System.Xml/v4.0_4.0.0.0__b77a5c561934e089/System.Xml.dll
----------------------------------------
Telerik.Analytics
Assembly Version: 4.0.104.0
Win32 Version: 4.0.104
CodeBase: file:///C:/Program%20Files%20(x86)/Fiddler2/Telerik.Analytics.DLL
----------------------------------------
Standard
Assembly Version: 2.6.2.0
Win32 Version: 2.6.2.0
CodeBase: file:///C:/Program%20Files%20(x86)/Fiddler2/Inspectors/Standard.dll
----------------------------------------
SyntaxView
Assembly Version: 2.6.2.0
Win32 Version: 2.6.2.0
CodeBase: file:///C:/Program%20Files%20(x86)/Fiddler2/Inspectors/SyntaxView.dll
----------------------------------------
Geoedge
Assembly Version: 1.2.5.0
Win32 Version: 1.2.5.0
CodeBase: file:///C:/Program%20Files%20(x86)/Fiddler2/Scripts/Geoedge.dll
----------------------------------------
RulesTab2
Assembly Version: 2.6.2.0
Win32 Version: 2.6.2.0
CodeBase: file:///C:/Program%20Files%20(x86)/Fiddler2/Scripts/RulesTab2.dll
----------------------------------------
SimpleFilter
Assembly Version: 2.6.2.0
Win32 Version: 2.6.2.0
CodeBase: file:///C:/Program%20Files%20(x86)/Fiddler2/Scripts/SimpleFilter.dll
----------------------------------------
Timeline
Assembly Version: 2.6.0.3
Win32 Version: 2.6.0.3
CodeBase: file:///C:/Program%20Files%20(x86)/Fiddler2/Scripts/Timeline.dll
----------------------------------------
Microsoft.JScript
Assembly Version: 10.0.0.0
Win32 Version: 14.6.1586.0 built by: NETFXREL2
CodeBase: file:///C:/Windows/Microsoft.Net/assembly/GAC_MSIL/Microsoft.JScript/v4.0_10.0.0.0__b03f5f7f11d50a3a/Microsoft.JScript.dll
----------------------------------------
System.Windows
Assembly Version: 4.0.0.0
Win32 Version: 4.6.1586.0
CodeBase: file:///C:/Windows/Microsoft.Net/assembly/GAC_MSIL/System.Windows/v4.0_4.0.0.0__b03f5f7f11d50a3a/System.Windows.dll
----------------------------------------
JScript Thunk Assembly
Assembly Version: 0.0.0.0
Win32 Version: 14.6.1586.0 built by: NETFXREL2
CodeBase: file:///C:/Windows/Microsoft.Net/assembly/GAC_MSIL/Microsoft.JScript/v4.0_10.0.0.0__b03f5f7f11d50a3a/Microsoft.JScript.dll
----------------------------------------
8IBw0-81
Assembly Version: 0.0.0.0
Win32 Version: 14.6.1586.0 built by: NETFXREL2
CodeBase: file:///C:/Windows/Microsoft.Net/assembly/GAC_MSIL/Microsoft.JScript/v4.0_10.0.0.0__b03f5f7f11d50a3a/Microsoft.JScript.dll
----------------------------------------
Microsoft.mshtml
Assembly Version: 7.0.3300.0
Win32 Version: 7.0.3300.0
CodeBase: file:///C:/Windows/assembly/GAC/Microsoft.mshtml/7.0.3300.0__b03f5f7f11d50a3a/Microsoft.mshtml.dll
----------------------------------------

************** JIT Debugging **************
To enable just-in-time (JIT) debugging, the .config file for this
application or computer (machine.config) must have the
jitDebugging value set in the system.windows.forms section.
The application must also be compiled with debugging
enabled.

For example:

<configuration>
<system.windows.forms jitDebugging="true" />
</configuration>

When JIT debugging is enabled, any unhandled exception
will be sent to the JIT debugger registered on the computer
rather than be handled by this dialog box.

Basic fix should be a one-liner.

More interesting optimizations include dropping StreamAndForget to ~262mb for all users (not just 32bit) and replace MemoryStream in PipeReadBuffer with a RecyclableMemoryStream or similar data structure.

When viewing an average-size request (few dozens of KB, or hundrers of KB), display performance is just horrible.

The Raw Inspectors take several seconds to display the request (plus they redraw multiple times uselessly, which slows down even more).

This is extremely painful when scrolling thru a capture session, searching for or deleting items... a large request will sometimes get the focus and freeze Fiddler for several seconds. Given the number of times the UI is redrawn, it can easily take 20 or 30 seconds to skip a single request.

Please improve display performance for average-size or large requests (or at the very least eliminate useless redraws, and make the slowdown asynchronous, so that the user can switch to another request if they clicked a large one by mistake).

https://groups.google.com/forum/#!topic/httpfiddler/NnrWVBoym4Y

If you have auto save turned on and a web socket initiates inbetween the save interval, messages captured during the interval are saved to the "_w" files in the saz file.

After the autosave is triggered, captures that happen on the same session are no saved in subsequent autosaved saz files.

The Raw Inspectors try to avoid spewing a bunch of junk into the display if the MIME type is binary. But because of how the assignment happens today, switching sessions can temporarily cause a mixed state where the headers from a new (text) session are evaluated in parallel with an old session's binary body, resulting in a momentary garbage rendering.

This is a performance bug that should be really easy to fix.

Steps to reproduce:

1. Open Fiddler

2. Go to Tools > Telerik Fiddler Options > HTTPS

3. Click the TLS Protocols

4. Fiddler hangs and after a minute or so crashes

Fiddler Version: 4.6.3.44161 macOS

Recently Fiddler has taken to flooding OutputDebugString with the message (from DebugView):
[5936] Telerik Analytics Monitor ***** ERROR *****: Recovered session data could not be sent: 0 Request failed: NameResolutionFailure: No se puede resolver el nombre remoto: '27006a8622544e43b0da60db63bd66ba.monitor-telerik.com (http://27006a8622544e43b0da60db63bd66ba.monitor-telerik.com/) '
There seem to be about 8 messages a second. This makes debugging other applications that use OutputDebugString almost impossible if Fiddler is running.

Otherwise, the response is illegal, because you MUST not send a C-L if you're sending Transfer-Encoding:Chunked

I'm running the latest Fiddler's mono version and it would be great to be able to capture WebSockets traffic on this version. I know it is possible on the Windows version.

I use McAfee Web Gateway proxies that only support Kerberos authentication. When trying to use these devices as an upstream proxy fiddler first tries NTLMSSP and then NTLMSSP2 and then prompts for credentials. It never tries Kerberos in the request header section "Proxy-Authorization: Negotiate"