nlog exception layout to format exception type, message and stack trace

user_940182 0
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Help me please to format exception logged with file logger I would like to have exceptions to be logged with new line separator between inner exceptions (if any) with exception type surrounded with some special sort of symbols, like [ArgumentException] to make it different from error text, and exceptions to be intended with tab just to make it easy to read stack traces

I've checked the latest NLog 4.4.12 package but the problem is that it is not so easy to parameterize default layout to get something like

2017-10-04 15:13:22.5823 NLogTest.Program starting
2017-10-04 15:13:22.5823 NLogTest.Program failed to start NLogTest
    [ArgumentException] bad try 
       at NLogTest.Classes.UnitOfWork.tryException() in d:\projects\NLogTest\Program.cs:line 62
       at NLogTest.Program.Main(String[] args) in d:\projects\NLogTest\Program.cs:line 19
    [ArgumentException] outer exception
       at NLogTest.Classes.UnitOfWork.outerException() in d:\projects\NLogTest\Program.cs:line 49
       at NLogTest.Classes.UnitOfWork.tryException() in d:\projects\NLogTest\Program.cs:line 57
    [KeyNotFoundException] innerException
       at NLogTest.Classes.UnitOfWork.innerException() in d:\projects\NLogTest\Program.cs:line 38
       at NLogTest.Classes.UnitOfWork.outerException() in d:\projects\NLogTest\Program.cs:line 45
2017-10-04 15:13:22.5823 NLogTest.Program the end

This is exception file log that I'd like to get. I've tried with layout like

layout="${longdate} ${logger} ${message}${onexception:${newline}${exception:format=tostring}}"

it uses standard tostring exception method but the result is not the same. I do not like that 

2017-10-04 15:28:52.6881 NLogTest.Program failed to start NLogTest
System.ArgumentException: bad try ---> System.ArgumentException: outer exception ---> System.Collections.Generic.KeyNotFoundException: innerException
   at NLogTest.Classes.UnitOfWork.innerException() in d:\projects\NLogTest\Program.cs:line 40
   at NLogTest.Classes.UnitOfWork.outerException() in d:\projects\NLogTest\Program.cs:line 47
   --- End of inner exception stack trace ---
   at NLogTest.Classes.UnitOfWork.outerException() in d:\projects\NLogTest\Program.cs:line 51
   at NLogTest.Classes.UnitOfWork.tryException() in d:\projects\NLogTest\Program.cs:line 59
   --- End of inner exception stack trace ---
   at NLogTest.Classes.UnitOfWork.tryException() in d:\projects\NLogTest\Program.cs:line 64
   at NLogTest.Program.Main(String[] args) in d:\projects\NLogTest\Program.cs:line 20

Inner exception messages stack trace are detached in the log (so it is hard to read log later) in case if exception is re-thrown more then twice and there is no tab (space) before exception type name.

The best result I've got was with layout below

layout="${longdate} ${logger} ${message}${onexception:${newline}${exception:maxInnerExceptionLevel=10:format=shortType,message,stacktrace:separator=*:innerExceptionSeparator=
	}}"

and it is 

2017-10-04 15:49:02.6188 NLogTest.Program failed to start NLogTest
ArgumentException*bad try*   at NLogTest.Classes.UnitOfWork.tryException() in d:\projects\NLogTest\Program.cs:line 64
   at NLogTest.Program.Main(String[] args) in d:\projects\NLogTest\Program.cs:line 20
    ArgumentException*outer exception*   at NLogTest.Classes.UnitOfWork.outerException() in d:\projects\NLogTest\Program.cs:line 51
   at NLogTest.Classes.UnitOfWork.tryException() in d:\projects\NLogTest\Program.cs:line 59
    KeyNotFoundException*innerException*   at NLogTest.Classes.UnitOfWork.innerException() in d:\projects\NLogTest\Program.cs:line 40
   at NLogTest.Classes.UnitOfWork.outerException() in d:\projects\NLogTest\Program.cs:line 47

However it is very hard to read. First stack trace line is on the same line as exception message. Inner error message is intended but inner stack trace - no.

Is there anything in layout that I've missed ? Should I create custom exception layout renderer ? Here is c# source code that I've used to raise exception

nlog exception c#
1 Answers

Writing NLog layout renderer is simple enough so I've managed to create exception layout renderer that format exception exactly as it was requested.

The latest custom layout source code version can be found on gist Sample configuration for console and file logger is available also.

UPD there is NLog.IndentException NuGet package also.

Additionally I've added stack trace filter. Sometimes exceptions are logged more than once. May be because of bad design (exception should be logged only once) or maybe because the same method can be used from external code (so exception should be logged locally before is thrown out) or by another methods in the same solution. In such case inner exception can be logged more than once. To reduce stack trace I've added a possibility to skip stack trace logging if exception was logged before. Only exception type and message are logged in such case. Like below:

[1] 2017-10-04 16:55:17.2227 Debug NLogTest.Program starting
[1] 2017-10-04 16:55:17.2527 Error NLogTest.Classes.UnitOfWork tryException failure
    [ArgumentException] outer exception
        at NLogTest.Classes.UnitOfWork.outerException() in d:\projects\NLogTest\Program.cs:line 48
        at NLogTest.Classes.UnitOfWork.tryException() in d:\projects\NLogTest\Program.cs:line 56
    [KeyNotFoundException] innerException
        at NLogTest.Classes.UnitOfWork.innerException() in d:\projects\NLogTest\Program.cs:line 37
        at NLogTest.Classes.UnitOfWork.outerException() in d:\projects\NLogTest\Program.cs:line 44
[1] 2017-10-04 16:55:17.2697 Error NLogTest.Program failed to start NLogTest
    [ArgumentException] bad try
        at NLogTest.Classes.UnitOfWork.tryException() in d:\projects\NLogTest\Program.cs:line 61
        at NLogTest.Program.Main(String[] args) in d:\projects\NLogTest\Program.cs:line 17
    [ArgumentException] outer exception
    [KeyNotFoundException] innerException

outer exception and innerException are logged twice. First time as outer exception was caught, and second when they are logged as inner exceptions. However since log contains stack trace already only exception type and message are logged.

user_9401820
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