internal/engine, internal/config and internal/metrics had no test file at all,
and writing them turned up five real bugs.
internal/engine (23 tests, new harness_test.go): a wired engine over a fake
upstream on loopback, a local zone, a blocklist, a cache, a query log and an
injectable clock. It pins the pipeline order end to end -- ACL deny before the
local zone, local zone before blocklist, blocklist before cache, drop sends
nothing, the concurrency and rate-limit refusals, serve-stale served with TTL 1
and refreshed once per key, truncation against a 512-byte client, and exactly
one metrics record and one query-log entry per query.
Five fixes:
- config.ParseSize ignored the unit multiplier, so 512MiB parsed as 512 bytes
and the whole memory envelope was inert for anyone who wrote a unit.
- finalize (EDNS0 and the UDP size) ran only on the cache-hit path, so a large
uncached answer left oversized for a 512-byte client. It now runs on the
upstream, local-zone and blocklist paths too.
- The upstream UDP client read buffer was hard-coded to 1232 while we advertise
dns.max_udp_size, so with a larger buffer configured every answer above 1232
bytes was read truncated and became SERVFAIL. The pool takes the size now.
- LRU.prefetchGate was a 64-slot global cap, not the single flight its comment
promised: a burst of stale hits launched up to 64 duplicate refreshes of one
name. It is a per-key latch now; distinct names still refresh in parallel.
- metrics.RecordMiss and RecordStaleHit moved only the Prometheus collector, so
the Cache page's misses and stale hits read 0 for the life of the process.
AGENTS.md gains the trap that cost the most time: this version of miekg/dns
reports a character-string over 255 bytes as zero length, so such a message
silently fails to pack, and the write failure looks like a client timeout.
developer
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