rsp2k/coredns-rfc2136
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L1/L2/L4: cleanup + README operational guide

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L1 — Replace hand-rolled atoi/parseUint with strconv.ParseUint wrapped
in mustParseUint. Hamilton's reasoning: the comment "strconv adds
overhead we don't need" is the Lauren-Bug shape — we already validated
the input. Until we hadn't, on a path we couldn't predict. Stdlib's
edge-case coverage is the safer default; the wrapper panics on
malformed input so any future regression surfaces in CI, not as a
silent 0 serial.

L2 — applyUpdate no longer mutates the caller's RR header TTL. miekg/
dns parses the UPDATE message into RRs the caller still owns; silently
rewriting hdr.Ttl was a hygiene smell with no current functional
consequence but a clear documentation issue. Now we dns.Copy() the RR
before any header mutation.

L4 — README expanded with an "Operational constraints" section
documenting the contracts and limits operators should understand
before relying on this in production:
  - Single-process atomicity only (with rsync-race mitigation)
  - Process-global MsgAcceptFunc override
  - No-op UPDATE doesn't bump SOA (with touch-UPDATE workaround)
  - SOA invariants enforced strictly (zero, multi, non-apex SOA all
    refused)
  - Serial counter NNNN=9999 rollover semantics
  - TSIG replay window dependency on miekg/dns default
  - Git commit failure logged at ERROR, not rolled back
  - Per-key rate limit knobs

Every constraint maps to a Hamilton review finding; documenting the
contract in operator-facing prose closes the gap between code and
expectation that the review identified.
This commit is contained in:
Ryan Malloy 2026-05-22 21:33:37 -06:00
parent 8d1477350a
commit 89993ca207
3 changed files with 120 additions and 28 deletions
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7
update.go
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@ -297,8 +297,13 @@ func applyUpdate(zone string, defaultTTL uint32, rrs []dns.RR, rr dns.RR) ([]dns
log.Debugf("apex %s add refused", dns.TypeToString[hdr.Rrtype])
return rrs, dns.RcodeRefused, false
}
// Hamilton L2: don't mutate the caller's RR header. miekg/dns
// parses the UPDATE message into RRs the caller still owns;
// silently rewriting their TTL is a hygiene smell. Copy first,
// then apply our default if needed.
if hdr.Ttl == 0 {
hdr.Ttl = defaultTTL
rr = dns.Copy(rr)
rr.Header().Ttl = defaultTTL
}
before := len(rrs)
rrs = addRRTo(rrs, rr)