Fix NPE in SimpleResolver

[PhroZenOne]

When reading a response that is REFUSED with no more data. The code could crash while comparing the DNS query with the response.

This change skips the comparison if the response is denied.

[codecov-commenter]

Codecov Report

Base: 64.18% // Head: 64.17% // Decreases project coverage by -0.02% ⚠️

Coverage data is based on head (f348300) compared to base (442fff4).
Patch coverage: 100.00% of modified lines in pull request are covered.

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Additional details and impacted files

@@             Coverage Diff              @@
##             master     #277      +/-   ##
============================================
- Coverage     64.18%   64.17%   -0.02%     
- Complexity     2766     2770       +4     
============================================
  Files           178      178              
  Lines         12536    12540       +4     
  Branches       1911     1912       +1     
============================================
+ Hits           8046     8047       +1     
- Misses         4001     4003       +2     
- Partials        489      490       +1     

Impacted Files	Coverage Δ
src/main/java/org/xbill/DNS/SimpleResolver.java	34.05% <100.00%> (+2.56%)	⬆️
src/main/java/org/xbill/DNS/NioTcpClient.java	65.38% <0.00%> (-2.57%)	⬇️
src/main/java/org/xbill/DNS/DohResolver.java	50.51% <0.00%> (-0.69%)	⬇️
src/main/java/org/xbill/DNS/Message.java	78.35% <0.00%> (+0.37%)	⬆️

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[ibauersachs]

Hi, thanks for your contribution!

I'm very hesitant to accept this as is, as I'm currently considering the answer you received from the server is invalid. Specifically, the DNS specification requires the validation on all of id/name/class/type (see RFC 5452, 9.1). However, you're right that the missing name shouldn't cause a NPE: the response from SimpleResolver (and for that matter, the other implementations too) should be failed otherwise.

Can you please share some details about the setup where you got this, especially the name and version of the server?

[PhroZenOne]

The DNS server is something I'm accessing as a third party so I have no info about the server itself. I have notified them and hope that they fix stuff on their side.

However, I changed the fix to throw an WireParseException instead. Only issue I have with this solution is that the DENIED flag might be a good indicator on what is wrong and that is hidden right now.

Maybe returning the message with the exception is a solution?

[PhroZenOne]

@ibauersachs have you had time to think about this? :)

[ibauersachs]

No, not yet. I'll might get to it on Sunday, but I can't make any promises.

[ibauersachs]

It's fine like this, thank you!