Crash Fiddler on Linux and lost all the internet connection

[Takayoshi]

I installed Fiddler on Fedora 24. After running Fiddler for a while, Fiddler crashed suddenly with this error.

$ cat /etc/fedora-release
Fedora release 24 (Twenty Four)
$ mono Fiddler.exe
can not parse as value of type 'i':
  ""
  ^^
can not parse as value of type 'i':
  ""
  ^^

After this error, I can't see Fiddler Window and I found all the internet connection are lost. I can't connect internet page on Chrome browser even though the Fiddler and mono process . The workaround is launching Fiddler again and exit from the menu.

[Tsviatko Yovtchev]

Hi Takayoshi,

Could you reproduce the crash?

The internet connection behavior after the crash is not unexpected. Fiddler sets itself as the system proxy on startup and restores the previous settings on exit. When it crashes the previous settings are not restored. It's on the next startup/exit they get restored.

Regards,
Tsviatko Yovtchev
Telerik by Progress

[JoKi]

Hi,

same observation on Ubuntu 16.04 during (first) start of Fiddler:

$ mono Fiddler.exe
can not parse as value of type 'i':
  ""
  ^^
can not parse as value of type 'i':
  ""
  ^^

 

The output is generated while switching from splash screen to main window.

Fiddler is then operational as expected.

Regards, JoKi

[Kevin Dietrich]

I am experiencing the same problem. However, I don't think the lines listed above ("can not parse") are the error because they appear immediately upon running the executable (those lines were there even when Fiddler was working for me). But I did lose my internet connectivity, and can't seem to get it back, even after disabling/enabling networking.

My crash happened after I had set up HTTPS to decrypt all. When I closed Fiddler then opened it again, it started popping up tons of dialogs about bad certs (?) and then crashed with this:

[xcb] Too much data requested from _XRead
[xcb] This is most likely caused by a broken X extension library
[xcb] Aborting, sorry about that.
mono: ../../src/xcb_io.c:736: _XRead: Assertion `!xcb_xlib_too_much_data_requested' failed.
Stacktrace:

  at <unknown> <0xffffffff>
  at (wrapper managed-to-native) System.Windows.Forms.X11Keyboard.XCreateFontSet (intptr,string,intptr&,int&,intptr) <0xffffffff>
  at System.Windows.Forms.X11Keyboard.CreateOverTheSpotXic (intptr,intptr) <0x000af>
  at System.Windows.Forms.X11Keyboard.CreateXic (intptr,intptr) <0x000d7>
  at System.Windows.Forms.X11Keyboard.CreateXicForWindow (intptr) <0x00037>
  at System.Windows.Forms.X11Keyboard.FocusIn (intptr) <0x00087>
  at System.Windows.Forms.XplatUIX11.SetFocus (intptr) <0x000b3>
  at System.Windows.Forms.XplatUI.SetFocus (intptr) <0x0001f>
  at System.Windows.Forms.ContainerControl.SendControlFocus (System.Windows.Forms.Control) <0x00083>
  at System.Windows.Forms.Form.SetVisibleCore (bool) <0x0071f>
  at System.Windows.Forms.Control.set_Visible (bool) <0x00032>
  at (wrapper remoting-invoke-with-check) System.Windows.Forms.Control.set_Visible (bool) <0xffffffff>
  at System.Windows.Forms.Application.RunLoop (bool,System.Windows.Forms.ApplicationContext) <0x002ef>
  at System.Windows.Forms.Form.ShowDialog (System.Windows.Forms.IWin32Window) <0x008a3>
  at (wrapper remoting-invoke-with-check) System.Windows.Forms.Form.ShowDialog (System.Windows.Forms.IWin32Window) <0xffffffff>
  at Fiddler.frmViewer.GetDecision (Fiddler.frmAlert) <0x00037>
  at (wrapper runtime-invoke) <Module>.runtime_invoke_DialogResult__this___object (object,intptr,intptr,intptr) <0xffffffff>
  at <unknown> <0xffffffff>
  at (wrapper managed-to-native) System.Reflection.MonoMethod.InternalInvoke (System.Reflection.MonoMethod,object,object[],System.Exception&) <0xffffffff>
  at System.Reflection.MonoMethod.Invoke (object,System.Reflection.BindingFlags,System.Reflection.Binder,object[],System.Globalization.CultureInfo) <0x000d7>
  at System.Reflection.MethodBase.Invoke (object,object[]) <0x00032>
  at System.Delegate.DynamicInvokeImpl (object[]) <0x00203>
  at System.MulticastDelegate.DynamicInvokeImpl (object[]) <0x0003b>
  at System.Delegate.DynamicInvoke (object[]) <0x00020>
  at System.Windows.Forms.XplatUIDriverSupport.ExecutionCallback (object) <0x0006b>
  at System.Threading.ExecutionContext/<Run>c__AnonStorey0.<>m__0 (object) <0x00055>
  at System.Security.SecurityContext.Run (System.Security.SecurityContext,System.Threading.ContextCallback,object) <0x00107>
  at System.Threading.ExecutionContext.Run (System.Threading.ExecutionContext,System.Threading.ContextCallback,object) <0x00223>
  at System.Windows.Forms.XplatUIDriverSupport.ExecuteClientMessage (System.Runtime.InteropServices.GCHandle) <0x000d3>
  at System.Windows.Forms.XplatUIX11.GetMessage (object,System.Windows.Forms.MSG&,intptr,int,int) <0x02c8b>
  at System.Windows.Forms.XplatUI.GetMessage (object,System.Windows.Forms.MSG&,intptr,int,int) <0x00047>
  at System.Windows.Forms.Application.RunLoop (bool,System.Windows.Forms.ApplicationContext) <0x00db7>
  at System.Windows.Forms.Form.ShowDialog (System.Windows.Forms.IWin32Window) <0x008a3>
  at (wrapper remoting-invoke-with-check) System.Windows.Forms.Form.ShowDialog (System.Windows.Forms.IWin32Window) <0xffffffff>
  at Fiddler.frmViewer.GetDecision (Fiddler.frmAlert) <0x00037>
  at (wrapper runtime-invoke) <Module>.runtime_invoke_DialogResult__this___object (object,intptr,intptr,intptr) <0xffffffff>
  at <unknown> <0xffffffff>
  at (wrapper managed-to-native) System.Reflection.MonoMethod.InternalInvoke (System.Reflection.MonoMethod,object,object[],System.Exception&) <0xffffffff>
  at System.Reflection.MonoMethod.Invoke (object,System.Reflection.BindingFlags,System.Reflection.Binder,object[],System.Globalization.CultureInfo) <0x000d7>
  at System.Reflection.MethodBase.Invoke (object,object[]) <0x00032>
  at System.Delegate.DynamicInvokeImpl (object[]) <0x00203>
  at System.MulticastDelegate.DynamicInvokeImpl (object[]) <0x0003b>
  at System.Delegate.DynamicInvoke (object[]) <0x00020>
  at System.Windows.Forms.XplatUIDriverSupport.ExecutionCallback (object) <0x0006b>
  at System.Threading.ExecutionContext/<Run>c__AnonStorey0.<>m__0 (object) <0x00055>
  at System.Security.SecurityContext.Run (System.Security.SecurityContext,System.Threading.ContextCallback,object) <0x00107>
  at System.Threading.ExecutionContext.Run (System.Threading.ExecutionContext,System.Threading.ContextCallback,object) <0x00223>
  at System.Windows.Forms.XplatUIDriverSupport.ExecuteClientMessage (System.Runtime.InteropServices.GCHandle) <0x000d3>
  at System.Windows.Forms.XplatUIX11.GetMessage (object,System.Windows.Forms.MSG&,intptr,int,int) <0x02c8b>
  at System.Windows.Forms.XplatUI.GetMessage (object,System.Windows.Forms.MSG&,intptr,int,int) <0x00047>
  at System.Windows.Forms.Application.RunLoop (bool,System.Windows.Forms.ApplicationContext) <0x00db7>
  at System.Windows.Forms.Form.ShowDialog (System.Windows.Forms.IWin32Window) <0x008a3>
  at (wrapper remoting-invoke-with-check) System.Windows.Forms.Form.ShowDialog (System.Windows.Forms.IWin32Window) <0xffffffff>
  at Fiddler.frmViewer.GetDecision (Fiddler.frmAlert) <0x00037>
  at (wrapper runtime-invoke) <Module>.runtime_invoke_DialogResult__this___object (object,intptr,intptr,intptr) <0xffffffff>
  at <unknown> <0xffffffff>
  at (wrapper managed-to-native) System.Reflection.MonoMethod.InternalInvoke (System.Reflection.MonoMethod,object,object[],System.Exception&) <0xffffffff>
  at System.Reflection.MonoMethod.Invoke (object,System.Reflection.BindingFlags,System.Reflection.Binder,object[],System.Globalization.CultureInfo) <0x000d7>
  at System.Reflection.MethodBase.Invoke (object,object[]) <0x00032>
  at System.Delegate.DynamicInvokeImpl (object[]) <0x00203>
  at System.MulticastDelegate.DynamicInvokeImpl (object[]) <0x0003b>
  at System.Delegate.DynamicInvoke (object[]) <0x00020>
  at System.Windows.Forms.XplatUIDriverSupport.ExecutionCallback (object) <0x0006b>
  at System.Threading.ExecutionContext/<Run>c__AnonStorey0.<>m__0 (object) <0x00055>
  at System.Security.SecurityContext.Run (System.Security.SecurityContext,System.Threading.ContextCallback,object) <0x00107>
  at System.Threading.ExecutionContext.Run (System.Threading.ExecutionContext,System.Threading.ContextCallback,object) <0x00223>
  at System.Windows.Forms.XplatUIDriverSupport.ExecuteClientMessage (System.Runtime.InteropServices.GCHandle) <0x000d3>
  at System.Windows.Forms.XplatUIX11.GetMessage (object,System.Windows.Forms.MSG&,intptr,int,int) <0x02c8b>
  at System.Windows.Forms.XplatUI.GetMessage (object,System.Windows.Forms.MSG&,intptr,int,int) <0x00047>
  at System.Windows.Forms.Application.RunLoop (bool,System.Windows.Forms.ApplicationContext) <0x00db7>
  at System.Windows.Forms.Form.ShowDialog (System.Windows.Forms.IWin32Window) <0x008a3>
  at (wrapper remoting-invoke-with-check) System.Windows.Forms.Form.ShowDialog (System.Windows.Forms.IWin32Window) <0xffffffff>
  at Fiddler.frmViewer.GetDecision (Fiddler.frmAlert) <0x00037>
  at (wrapper runtime-invoke) <Module>.runtime_invoke_DialogResult__this___object (object,intptr,intptr,intptr) <0xffffffff>
  at <unknown> <0xffffffff>
  at (wrapper managed-to-native) System.Reflection.MonoMethod.InternalInvoke (System.Reflection.MonoMethod,object,object[],System.Exception&) <0xffffffff>
  at System.Reflection.MonoMethod.Invoke (object,System.Reflection.BindingFlags,System.Reflection.Binder,object[],System.Globalization.CultureInfo) <0x000d7>
  at System.Reflection.MethodBase.Invoke (object,object[]) <0x00032>
  at System.Delegate.DynamicInvokeImpl (object[]) <0x00203>
  at System.MulticastDelegate.DynamicInvokeImpl (object[]) <0x0003b>
  at System.Delegate.DynamicInvoke (object[]) <0x00020>
  at System.Windows.Forms.XplatUIDriverSupport.ExecutionCallback (object) <0x0006b>
  at System.Threading.ExecutionContext/<Run>c__AnonStorey0.<>m__0 (object) <0x00055>
  at System.Security.SecurityContext.Run (System.Security.SecurityContext,System.Threading.ContextCallback,object) <0x00107>
  at System.Threading.ExecutionContext.Run (System.Threading.ExecutionContext,System.Threading.ContextCallback,object) <0x00223>
  at System.Windows.Forms.XplatUIDriverSupport.ExecuteClientMessage (System.Runtime.InteropServices.GCHandle) <0x000d3>
  at System.Windows.Forms.XplatUIX11.GetMessage (object,System.Windows.Forms.MSG&,intptr,int,int) <0x02c8b>
  at System.Windows.Forms.XplatUI.GetMessage (object,System.Windows.Forms.MSG&,intptr,int,int) <0x00047>
  at System.Windows.Forms.Application.RunLoop (bool,System.Windows.Forms.ApplicationContext) <0x00db7>
  at System.Windows.Forms.Form.ShowDialog (System.Windows.Forms.IWin32Window) <0x008a3>
  at (wrapper remoting-invoke-with-check) System.Windows.Forms.Form.ShowDialog (System.Windows.Forms.IWin32Window) <0xffffffff>
  at Fiddler.frmViewer.GetDecision (Fiddler.frmAlert) <0x00037>
  at (wrapper runtime-invoke) <Module>.runtime_invoke_DialogResult__this___object (object,intptr,intptr,intptr) <0xffffffff>
  at <unknown> <0xffffffff>
  at (wrapper managed-to-native) System.Reflection.MonoMethod.InternalInvoke (System.Reflection.MonoMethod,object,object[],System.Exception&) <0xffffffff>
  at System.Reflection.MonoMethod.Invoke (object,System.Reflection.BindingFlags,System.Reflection.Binder,object[],System.Globalization.CultureInfo) <0x000d7>
  at System.Reflection.MethodBase.Invoke (object,object[]) <0x00032>
  at System.Delegate.DynamicInvokeImpl (object[]) <0x00203>
  at System.MulticastDelegate.DynamicInvokeImpl (object[]) <0x0003b>
  at System.Delegate.DynamicInvoke (object[]) <0x00020>
  at System.Windows.Forms.XplatUIDriverSupport.ExecutionCallback (object) <0x0006b>
  at System.Threading.ExecutionContext/<Run>c__AnonStorey0.<>m__0 (object) <0x00055>
  at System.Security.SecurityContext.Run (System.Security.SecurityContext,System.Threading.ContextCallback,object) <0x00107>
  at System.Threading.ExecutionContext.Run (System.Threading.ExecutionContext,System.Threading.ContextCallback,object) <0x00223>
  at System.Windows.Forms.XplatUIDriverSupport.ExecuteClientMessage (System.Runtime.InteropServices.GCHandle) <0x000d3>
  at System.Windows.Forms.XplatUIX11.GetMessage (object,System.Windows.Forms.MSG&,intptr,int,int) <0x02c8b>
  at System.Windows.Forms.XplatUI.GetMessage (object,System.Windows.Forms.MSG&,intptr,int,int) <0x00047>
  at System.Windows.Forms.Application.RunLoop (bool,System.Windows.Forms.ApplicationContext) <0x00db7>
  at System.Windows.Forms.Form.ShowDialog (System.Windows.Forms.IWin32Window) <0x008a3>
  at (wrapper remoting-invoke-with-check) System.Windows.Forms.Form.ShowDialog (System.Windows.Forms.IWin32Window) <0xffffffff>
  at Fiddler.frmViewer.GetDecision (Fiddler.frmAlert) <0x00037>
  at (wrapper runtime-invoke) <Module>.runtime_invoke_DialogResult__this___object (object,intptr,intptr,intptr) <0xffffffff>
  at <unknown> <0xffffffff>
  at (wrapper managed-to-native) System.Reflection.MonoMethod.InternalInvoke (System.Reflection.MonoMethod,object,object[],System.Exception&) <0xffffffff>
  at System.Reflection.MonoMethod.Invoke (object,System.Reflection.BindingFlags,System.Reflection.Binder,object[],System.Globalization.CultureInfo) <0x000d7>
  at System.Reflection.MethodBase.Invoke (object,object[]) <0x00032>
  at System.Delegate.DynamicInvokeImpl (object[]) <0x00203>
  at System.MulticastDelegate.DynamicInvokeImpl (object[]) <0x0003b>
  at System.Delegate.DynamicInvoke (object[]) <0x00020>
  at System.Windows.Forms.XplatUIDriverSupport.ExecutionCallback (object) <0x0006b>
  at System.Threading.ExecutionContext/<Run>c__AnonStorey0.<>m__0 (object) <0x00055>
  at System.Security.SecurityContext.Run (System.Security.SecurityContext,System.Threading.ContextCallback,object) <0x00107>
  at System.Threading.ExecutionContext.Run (System.Threading.ExecutionContext,System.Threading.ContextCallback,object) <0x00223>
  at System.Windows.Forms.XplatUIDriverSupport.ExecuteClientMessage (System.Runtime.InteropServices.GCHandle) <0x000d3>
  at System.Windows.Forms.XplatUIX11.GetMessage (object,System.Windows.Forms.MSG&,intptr,int,int) <0x02c8b>
  at System.Windows.Forms.XplatUI.GetMessage (object,System.Windows.Forms.MSG&,intptr,int,int) <0x00047>
  at System.Windows.Forms.Application.RunLoop (bool,System.Windows.Forms.ApplicationContext) <0x00db7>
  at System.Windows.Forms.Application.Run (System.Windows.Forms.ApplicationContext) <0x0005f>
  at System.Windows.Forms.Application.Run (System.Windows.Forms.Form) <0x00033>
  at Fiddler.frmViewer.‹• (string[]) <0x00597>
  at Fiddler.frmViewer.ॠ(string[]) <0x0008b>
  at (wrapper runtime-invoke) <Module>.runtime_invoke_void_object (object,intptr,intptr,intptr) <0xffffffff>

Native stacktrace:

    mono() [0x4b73d8]
    /lib/x86_64-linux-gnu/libpthread.so.0(+0x10330) [0x7fbca2bf9330]
    /lib/x86_64-linux-gnu/libc.so.6(gsignal+0x37) [0x7fbca2856c37]
    /lib/x86_64-linux-gnu/libc.so.6(abort+0x148) [0x7fbca285a028]
    /lib/x86_64-linux-gnu/libc.so.6(+0x2fbf6) [0x7fbca284fbf6]
    /lib/x86_64-linux-gnu/libc.so.6(+0x2fca2) [0x7fbca284fca2]
    /usr/lib/x86_64-linux-gnu/libX11.so.6(_XRead+0xd5) [0x7fbc9f1ff925]
    /usr/lib/x86_64-linux-gnu/libX11.so.6(_XRead32+0x24) [0x7fbc9f2003b4]
    /usr/lib/x86_64-linux-gnu/libX11.so.6(XListFontsWithInfo+0x368) [0x7fbc9f1e2fc8]
    /usr/lib/x86_64-linux-gnu/libX11.so.6(+0x7358d) [0x7fbc9f23658d]
    /usr/lib/x86_64-linux-gnu/libX11.so.6(XCreateOC+0xeb) [0x7fbc9f1eed4b]
    /usr/lib/x86_64-linux-gnu/libX11.so.6(XCreateFontSet+0x5c) [0x7fbc9f1e39cc]
    [0x40dac79b]

Debug info from gdb:

Could not attach to process.  If your uid matches the uid of the target
process, check the setting of /proc/sys/kernel/yama/ptrace_scope, or try
again as the root user.  For more details, see /etc/sysctl.d/10-ptrace.conf
ptrace: Operation not permitted.
No threads.

=================================================================
Got a SIGABRT while executing native code. This usually indicates
a fatal error in the mono runtime or one of the native libraries
used by your application.
=================================================================

Aborted (core dumped)

[Simeon]

Hi Kevin,

Sorry for the late reply. In your case it seems that you have to synchronize the Mono SSL certificate store against your OS certificate store. This could be achieved by executing the

mozroots --import --sync

command. Please, check the Fiddler for Mono HTTPS Configuration link for more information.

Fiddler for Mono runs in Mono, hence it checks in the Mono SSL certificate store if you trust the certificate of the website. However, this store is empty by default which means that Mono apps trust any websites unless the user executes the command above.

Fiddler warns the user with a popup message by default if it detects a certificate which is not trusted. Because a regular website has many resources this means that the browser makes multiple requests to get these resources and it gets multiple responses and Fiddler makes a warning for each one of them.

However, there is a bug in Mono Windows Forms and it cannot handle multiple dialog windows at once which makes the Mono Runtime to abort and Fiddler crashes. Unfortunately, it seems that Windows Forms for Mono is not supported anymore and our hands are tied.

This is one of the reasons why we created the Fiddler Orchestra whose clients run on Linux, Mac and Windows if there is .NET Core 2.0 installed. For now the clients need a running Fiddler on a Windows machine accessible by the network in order to report the captured HTTP traffic to that Fiddler instance but we are working to deliver many of the Fiddler features (and more) straight into the client.

Until then, consider using the latest version of Fiddler Orchestra if your network setup allows so.

Regards,
Simeon
Progress Telerik