LOG4J2-3627: PatternLayout: %xEx{ [ "short" | depth ] } not working

[theit]

This change restores the feature to limit the number of lines of a stack trace that is logged and adds a couple of test methods for the corresponding JUnit test class.

[vy]

@theit! Thanks so much for the bug report and fix! Much appreciated! I have requested some changes, would you mind checking them out, please? Also a changes.xml entry would be handy too.

[theit]

Sorry the very late reply. I couldn't work earlier on the ticket because of $DAYJOB and several sick days... :-/
I reworked the patch and added the stack trace stripping as requested. This is basically done in the formatXXX methods in ThrowableProxyRenderer. Can you please have a look and review the changes?

[ppkarwasz]

This was closed automatically by Github because we renamed the release-2.x branch to 2.x. Feel free to resubmit to the 2.x branch.

[hein4daddel]

Will this fix be available in the next release? (haven't found it in 2.20.0)

[vy]

I am picking this up. I first need to wrap my mind around the changes.

[vy]

@theit, sorry for the late response. I was just able to pick this up.

Both ThrowablePatternConverter (%ex) and RootThrowablePatternConverter (%rEx), which delegates back to ThrowablePatternConverter (%xEx), simply do a String#split("\\n") and retain the first N lines. On the other hand, your ThrowableProxyRenderer changes count and, if necessary, limit the number of lines along the rendering process. This diligent work (which I am thankful that you took time to implement) is pretty sophisticated (and error-prone?) compared to its %ex counterpart. I would be in favor of a simpler approach: simply truncate the lines in StringBuilder just before the exit in package-private methods of ThrowableProxyRenderer. If you can implement this, I would be more than happy to accept your PR.

Ideally, we should wrap the StringBuilder with a LineLimitedStringBuilder wrapper, and pass that to Throwable rendering routines. But that will probably necessitate changes in dozens of files. Hence, let's try to keep it simple for now.