Handle UDP responses that overflow with TC bit

[SriHarsha001]

1. Why is this pull request needed and what does it do?

Description in this PR - #6003
Code changes in plugin/pkg/proxy/connect.go file is copied from above PR - #6003

This PR - #6100 was closed by mistake. So submitting a new PR here with the same code changes.

Getting this PR miekg/dns#1475 reviewed is taking time. Can we get the bug fix merged here with "overflow" string comparison. And we can address this "To accurately identify the error by type rather than string compares" as a follow up PR while I work with maintainers of miekg package.

2. Which issues (if any) are related?

#5953
#5998

3. Which documentation changes (if any) need to be made?

Not sure.

4. Does this introduce a backward incompatible change or deprecation?

No.

[SriHarsha001]

@chrisohaver - I apologize, I had accidently deleted my fork which closed this PR - #6100 , hence submitted this PR with the same code changes.

As trying to get this PR miekg/dns#1475 reviewed and merged is taking a long time, can we get the bug fix merged here with "overflow" string comparison.

Can we address this comment "To accurately identify the error by type rather than string compares" as a follow up PR while I work with maintainers of miekg package.

[SriHarsha001]

@chrisohaver - When you get a chance, I kindly request you to take a look at this request.

[chrisohaver]

Is there anything new to review here vs where #6100 was left off?

[SriHarsha001]

@chrisohaver - Thank you for your reply. I wanted to check if we get the bug fix merged here with "overflow" string comparison. And we can address this "To accurately identify the error by type rather than string compares" as a follow up PR while I work with maintainers of miekg package on this PR - miekg/dns#1475

[codecov]

Codecov Report

Merging #6277 (a89212e) into master (93c57b6) will increase coverage by 2.77%.
Report is 1035 commits behind head on master.
The diff coverage is 55.36%.

@@            Coverage Diff             @@
##           master    #6277      +/-   ##
==========================================
+ Coverage   55.70%   58.47%   +2.77%     
==========================================
  Files         224      252      +28     
  Lines       10016    16537    +6521     
==========================================
+ Hits         5579     9670    +4091     
- Misses       3978     6278    +2300     
- Partials      459      589     +130     

Files Changed	Coverage Δ
core/dnsserver/config.go	0.00% <ø> (ø)
core/dnsserver/register.go	13.27% <0.00%> (-4.71%)	⬇️
plugin/auto/auto.go	0.00% <0.00%> (ø)
plugin/auto/xfr.go	0.00% <0.00%> (ø)
plugin/auto/zone.go	78.94% <ø> (+0.68%)	⬆️
plugin/autopath/autopath.go	73.61% <ø> (-1.39%)	⬇️
plugin/azure/azure.go	10.61% <0.00%> (-0.57%)	⬇️
plugin/azure/setup.go	56.36% <0.00%> (-4.14%)	⬇️
plugin/backend_lookup.go	0.00% <0.00%> (ø)
plugin/bind/bind.go	50.00% <0.00%> (-50.00%)	⬇️
... and 77 more

... and 170 files with indirect coverage changes

📣 We’re building smart automated test selection to slash your CI/CD build times. Learn more

[chrisohaver]

@chrisohaver - Thank you for your reply. I wanted to check if we get the bug fix merged here with "overflow" string comparison. And we can address this "To accurately identify the error by type rather than string compares" as a follow up PR while I work with maintainers of miekg package on this PR - miekg/dns#1475

Aside from that, were there other outstanding issues that needed to be addressed? It looks like there were ... relating to AA bit? Maybe elsewhere? Can you review the feedback and requested changes in #6100?

[SriHarsha001]

@chrisohaver - yes yes, we had discussed about setting AA bit to false here - #6100 (comment)

Please let me know, if there is anything outstanding that needs to be address.

[chrisohaver]

I couldn't find any specific RFC that directly addresses the handling of the authorization bit (AA) in truncated DNS responses. There is no specific handling or interpretation defined for the authorization bit (AA) in truncated responses

I think in that case we should not alter the AA bit from the original.

[chrisohaver]

requested changes may be confusing... I think all the error/overflow/truncation logic can be moved into the if proto == "udp" { ... } block.