The recursor cache needs to check stale when updating the ns type cache.

[zjs604381586]

Short description

When an NS record already exists in the recursor cache and the NS record is replaced again, the TTD setting of the NS record should check the stale flag of CacheEntry. Otherwise, the TTL of the NS cache will always be s_serveStaleExtensionPeriod(30s). Then the new NS cache will expires quickly, causing delays in iterative DNS resolution

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 8864635806

Details

• 1 of 1 (100.0%) changed or added relevant line in 1 file are covered.
• 41 unchanged lines in 10 files lost coverage.
• Overall coverage increased (+0.01%) to 59.464%

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Files with Coverage Reduction	New Missed Lines	%
pdns/iputils.hh	1	74.8%
pdns/pollmplexer.cc	1	82.39%
pdns/dnsdistdist/dnsdist.cc	2	68.36%
pdns/communicator.cc	3	71.85%
modules/gpgsqlbackend/spgsql.cc	3	67.46%
pdns/auth-secondarycommunicator.cc	3	64.59%
pdns/dnsdistdist/dnsdist-tcp.cc	5	76.05%
pdns/rcpgenerator.cc	5	89.5%
pdns/recursordist/test-syncres_cc1.cc	8	89.46%
pdns/tcpiohandler.cc	10	66.67%

Totals
Change from base Build 8830304531:	0.01%
Covered Lines:	114204
Relevant Lines:	159427

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💛 - Coveralls

[rgacogne]

Thanks! I see the issue, but I'm a bit concerned that this exact fix would make it possible for a child zone to stay alive forever, even if the parent disagrees, as long as serve-stale is enabled. We might have to be a bit smarter and only bypass the check when we are actually refreshing a staled entry. Let's see what Otto thinks about it.

[omoerbeek]

I think not capping on cacheEntry.d_servedStale == 0 is not right.
The capping needs take into account the remaining serve stale time. Look at MemRecursorCache::updateStaleEntry for inspiration.