webserver.cc: try to pass exception text with 500 errors

[Habbie]

Short description

fixes #14637 -if- the client sends Accept: application/json

Checklist

I have:

• read the CONTRIBUTING.md document
• compiled this code
• tested this code
• included documentation (including possible behaviour changes)
• documented the code
• added or modified regression test(s)
• added or modified unit test(s)
• checked that this code was merged to master

[coveralls]

Pull Request Test Coverage Report for Build 10850324716

Details

• 0 of 2 (0.0%) changed or added relevant lines in 1 file are covered.
• 42 unchanged lines in 12 files lost coverage.
• Overall coverage increased (+0.03%) to 64.7%

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Changes Missing Coverage	Covered Lines	Changed/Added Lines	%
pdns/webserver.cc	0	2	0.0%

Files with Coverage Reduction	New Missed Lines	%
pdns/pollmplexer.cc	1	83.66%
pdns/recursordist/sortlist.cc	2	74.12%
pdns/recursordist/aggressive_nsec.cc	2	66.1%
modules/lmdbbackend/lmdbbackend.cc	2	73.54%
pdns/iputils.cc	3	55.45%
pdns/misc.hh	3	87.62%
pdns/tsigverifier.cc	3	77.22%
pdns/packethandler.cc	4	72.69%
pdns/recursordist/syncres.cc	4	79.62%
pdns/signingpipe.cc	5	86.86%

Totals
Change from base Build 10850027583:	0.03%
Covered Lines:	124861
Relevant Lines:	162277

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💛 - Coveralls

[omoerbeek]

A potential issue here is that the exception message might reveal info we do not want to share.

[Habbie]

A potential issue here is that the exception message might reveal info we do not want to share.

to somebody who has an API token, right?

I'll give it a good ponder, it's a good question (yours, not mine :) )

[zeha]

The thing I'm vaguely concerned about is clients starting to parse the error messages. But I hope its clear that they are not contractual.

[Habbie]

The thing I'm vaguely concerned about is clients starting to parse the error messages. But I hope its clear that they are not contractual.

I actually intended to not have JSON, or perhaps Internal Server Error\n\n{json goes here} but it turns out we had the JSON so ready to go, so I took the easy way out. I agree we should decide that these texts are not contractual (while I bet some of the constraints, content checks etc. are treated this way now by clients)

[zeha]

For content checks etc I'm less concerned; IOW I hope its easier to preserve the messages there.
For "internal server error" it's a different story.

[Habbie]

A potential issue here is that the exception message might reveal info we do not want to share.

after pondering over the weekend, this does not worry me

[omoerbeek]

A potential issue here is that the exception message might reveal info we do not want to share.

after pondering over the weekend, this does not worry me

Agreed, it's build into my system to be weary about these things, but in this case it's ok.