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internal/server was the last package whose shutdown was tested by assumption: four transports, three shutdown shapes, and every one of them can strand a goroutine that a client is holding open. Both bugs below were live in the tree as handed over and neither had a test. An idle client could hold the whole shutdown open. The stream accept loop waits for its connections before Stop returns, and a connection parked in ReadMsg with no deadline in front of it only ends when the client goes away — ctx.Err() is checked between reads, so cancelling the context cannot reach a read that is already blocked. One connection that connected and said nothing was enough to make Stop sit there for the caller's entire grace period (15s in main) and then return context.DeadlineExceeded, which the app reports as "shutdown completed with errors"; and the cache snapshot the app takes right after Stop never happened, because the orchestrator had given up first. It is a shutdown DoS that costs the attacker one connection. The fix is a read deadline in the past on every accepted connection when the context is cancelled, and deliberately not a close: a query already inside the pipeline is past its read, so its answer still goes out, which is the invariant TestInFlightQueryIsAnsweredAcrossStop pins. The accept loop keeps a small registry of live connections for this — the accept path, not the query path, and no query ever takes that mutex. A UDP query in flight at Stop was lost and nothing waited for it. The stream paths register their connections with s.wait; servePacket did not register at all, so a UDP query already inside the pipeline was gone twice over: nothing waited for it, and the answer had nowhere to go once it was ready, because a datagram is written to the very socket the query arrived on. The visible damage was not the lost answer (the client retries) but the app, which snapshots the cache and closes the store the moment Stop returns — a query still in the pipeline could be writing to a store on its way out. Packets are now counted in s.wait, and the UDP listener's close wakes the read loop with an expired deadline and then waits, bounded by udpDrainGrace (250ms), for the loop and the packets it spawned before closing the socket. The bound is deliberate: a shutdown may not spend its grace period on one slow upstream, and past the bound the answer is dropped, which is what the client would see anyway. Stop returning did not mean the process was done, so nothing could tell a leaking shutdown from a clean one. TestStopLeavesNoGoroutineRunningServerCode counts goroutines whose stack still has a frame in the package — not runtime.NumGoroutine(), which in a test binary is net/http, crypto/tls and the race detector talking over each other — and it found the idle-connection bug above. TestStopIsNotBlockedByAnIdleStreamConnection sets a 60s DoT idle timeout on purpose so a config value cannot hide the regression behind a lucky tick, and TestInFlightQueryIsAnsweredAcrossStop now covers all four transports. harness.idleStream exists because a test that only dials a stream transport races the accept loop: Stop can close the listener while the connection is still in the backlog, the server never accepts it, and a shutdown assertion that needs a live server-side goroutine passes for the wrong reason. AGENTS.md gains the two durable invariants (no step in the shutdown may wait for a client; every query goroutine is registered with s.wait, UDP included) and the two test-hygiene traps. STATUS.md drops the UDP query lost at Stop from its pinned list, since it is now a test rather than an accident, and the plan starts at the pinned decisions that are actually left.
555 lines
35 KiB
Markdown
555 lines
35 KiB
Markdown
# fancy-dns — development status and continuation plan
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Last updated after the round that finished the **server shutdown paths**:
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every transport's ordering with a query in flight is now a test, and it found
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two real bugs — an idle client could hold a shutdown for the whole grace
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period, and a UDP query in flight was neither waited for nor answered. The
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round before that brought the console onto the Go side of the API contract, so
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both halves of that are done. `AGENTS.md` holds the decisions, invariants and
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working rules; this file holds state and the plan.
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## Goal
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A lightweight, high-performance recursive DNS server with:
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- **Go backend** — sharded LRU cache backed by bbolt, blocklist replication from
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multiple formats, per-client ACLs, query logging, Prometheus metrics.
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- **Secure DNS** — DNS-over-TLS (RFC 7858) and DNS-over-HTTPS (RFC 8484).
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DNSSEC validation was explicitly scoped **out**; AD/CD/extended-RCODE are
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passed through only.
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- **React + Tailwind admin console** embedded in the binary.
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- **Config as zone files + YAML**, hot-reloadable, with **Valkey/Redis** for
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cross-instance sync (chosen over AMQP).
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## Architecture decisions (settled with the user)
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| Decision | Choice | Why |
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|---|---|---|
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| Scope | Full production | clustering, metrics, ACLs, query logs, hot reload, Docker, k8s, CI |
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| Config store | YAML + DNS master files | reviewable/diffable in git |
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| Cluster sync | Valkey (Redis protocol) | simple, mature Go client, easy local dev |
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| Secure DNS | DoT + DoH, no DNSSEC validation | avoids signer/anchor machinery; pass-through only |
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| Hot cache | Sharded LRU in memory, bbolt for snapshots | no I/O on the hot path; warm restart |
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| k8s networking | No hostNetwork, LoadBalancer Service | the server never sets SO_REUSEPORT, so two host-network pods cannot share :53 |
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| Memory | Soft GOMEMLIMIT, cache byte budget | a cgroup kill is an outage; a cache miss is not |
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| Scale-out | StatefulSet, no HPA | an HPA cannot drive a StatefulSet |
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| Unknown YAML keys | Ignore, loudly documented | `KnownFields(true)` was considered and rejected as a behaviour change for anyone carrying extra keys. Pinned by `TestLoadIgnoresUnknownKeys`. |
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## Package layout
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```
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cmd/fancy-dns/main.go entrypoint: flags, signals, SIGHUP reload
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internal/
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config/ Config struct, Duration, Size, Validate, atomic Store + hooks,
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${VAR} environment expansion in Load
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zonefile/ RFC 1035 master-file parser ($TTL/$ORIGIN, parens, serial math)
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blocklist/ Set (exact/sub/root maps), 4 parsers, Manager (fetch+compile+swap)
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cache/ Key, Entry, sharded LRU, TTL policy, serve-stale, bbolt Store
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resolver/ Upstream pool: health, circuit breakers, parallel/failover/random
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acl/ compiled groups, CIDR/PTR/tag matching, per-group domain policy
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localzone/ authoritative data from master files, wildcards, delegations
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engine/ THE QUERY PIPELINE (see below), reverse-PTR cache
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server/ UDP, TCP, DoT, DoH listeners; all funnel into one handler
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qlog/ bbolt query-log ring + live in-memory ring + SSE fanout
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metrics/ Prometheus collectors + rolling time-series rings
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cluster/ Valkey pub/sub, leader lease, divergence detection
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api/ admin REST + SSE, auth, CORS, rate limiting
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app/ wiring, lifecycle, API hook implementations, memory envelope,
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and the response contract the console is written against
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web/ go:embed of the built console
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web/ Vite + React + TS + Tailwind console
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deploy/ example config, example zones, k8s manifests
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```
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### Query pipeline order (engine.Handle)
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```
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validate → ACL deny → per-client concurrency → global concurrency → rate limit
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→ group allow/deny domains → local zone → blocklist → cache → upstream
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→ cache put → finalize (EDNS0, UDP truncation) → metrics + qlog
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```
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Cache is a single shard-local lookup; only a miss touches the network.
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## Status
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### Green, end to end
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`gofmt` clean, `go build ./...` clean, `go vet ./...` clean, and
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`go test -race -count=1 -timeout 300s ./...` green across every package.
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| Package | top-level tests | notes |
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|---|---|---|
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| `internal/acl` | 26 | group compilation, matching, first-group-wins |
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| `internal/api` | 55 (156 cases) | the whole route table, three auth modes, CORS, rate limiting, SSE, settings, error branches, pinned limitations |
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| `internal/app` | 30 (incl. the contract suite) | wiring, hooks, **the API response contract**, integration |
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| `internal/blocklist` | 28 | four parsers, the set, the manager, the shipped example zone |
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| `internal/cache` | 27 | LRU, TTL policy, serve-stale, bbolt round-trip |
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| `internal/cluster` | 20 | Valkey lease, pub/sub, divergence, dead-peer reaping |
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| `internal/config` | 22 | Duration/Size, `${VAR}`, unknown keys, the JSON wire form, the shipped example configs |
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| `internal/engine` | 26 | the pipeline end to end, plus the pins |
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| `internal/localzone` | 18 | wildcards, delegation, CNAME following |
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| `internal/metrics` | 10 | the metric names, which are the contract with the dashboards |
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| `internal/qlog` | 18 | ring, bbolt, top domains, sampling |
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| `internal/resolver` | 10 | pool, breakers, health, policies |
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| `internal/server` | 57 | four listeners, UDP deadline reset, truncation, DoH limits, identity, counters, **shutdown and leak** |
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| `internal/zonefile` | 29 | the master-file parser and the shipped example zone |
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| `web` | 0 | typecheck and `oxlint` clean (0 errors), no test runner |
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| `cmd/fancy-dns` | 0 | exercised by `make smoke` and the CI smoke job instead |
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### The commands that matter
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- `make check-go` — the inner loop (~1.3 s): gofmt check, vet, compile. Uses
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`go-build`, not `build`, because `build` depends on `web` and shells out to npm.
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- `make check` — `check-go` + the suite. What CI runs.
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- `make smoke` — **new.** Boots the real binary with the console embedded on
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unprivileged ports (the same `sed` rewrite CI uses), then checks `-check`,
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`/api/healthz`, the embedded console, the unauthenticated 401, an
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authenticated `whoami` and `/api/metrics`. Catches a broken embed, a bad
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default and an auth regression in one command.
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- `make web-check` — console typecheck and production build.
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- `make bench` — cache and blocklist benchmarks.
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### The contract gap is closed on both sides
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The API **response contract** used to be the interesting gap. The console's
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types are hand-written and `apiFetch` ends in `JSON.parse(text) as T`, so
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nothing in the toolchain compared them with the Go structs; a field that lost
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its `json` tag, or a response a struct never had, showed up as an empty table in
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a browser and nowhere else. `internal/app` now has contract tests that assert
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the exact JSON key set of every admin endpoint (see the fix list), and the
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console has been brought onto them — so the two sides agree *today*, but only
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because someone compared them once. The durable fix is still open: see plan
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item 2.
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### The server's shutdown is now pinned behaviour, not folklore
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It was the last part of `internal/server` tested by assumption. Four
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transports, three shutdown shapes (a datagram socket, a stream accept loop with
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configurable idle timeouts, and an `http.Server` that drains politely), and
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every one of them can strand a goroutine a client is holding open. The
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invariants that came out of it are in AGENTS.md; the two bugs it found are in
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the fix list below.
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### Decided this round (behaviour changed on purpose, each with a test)
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- **An RPZ record did not cover the name it names.** `rpzRule` gave a bare
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owner name the subdomain form (`*.name`), so `analytics.example.org.` in a
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policy zone blocked `cdn.analytics.example.org.` and left
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`analytics.example.org.` resolving normally, and an `rpz-passthru.` record
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did not allowlist its own domain either. RPZ semantics say the record applies
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to the domain and everything under it, so a bare owner now takes the apex
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form `**.name`; an owner written with an explicit `*.` is still strict, so a
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zone that wants subdomain-only behaviour can ask for it. This changes which
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queries get blocked for an existing policy zone — re-read your zones if they
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relied on the old behaviour. `TestExampleRPZZoneCoversTheApexItNames` pins
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both halves, `TestParseRPZ` pins the compiled forms, and the example zone now
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says which half it relies on.
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- **`metrics.OutcomeLocal` had no producer.** The engine reported a local-zone
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answer as `qlog.ActionAllow`, which `outcomeFor` mapped to
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`OutcomeUpstream`, so every locally answered query was counted as an upstream
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one and the dashboard's local column was permanently empty. `Response.Local`
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is now set on the local-zone path and `outcomeFor` consults it first, so a
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local answer publishes `outcome="local"` and is *not* counted as upstream.
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This moved published counters, which is why it was a decision: the README's
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metrics section and the dashboard notes are updated in the same change.
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`TestLocallyAnsweredQueryIsCountedAsLocal` replaces the pin.
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## Fixed this round
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- **A client that connected and said nothing held the whole shutdown open.**
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The stream accept loop waits for its connections before `Stop` returns, and a
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connection parked in `ReadMsg` with no deadline in front of it only ends when
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the client goes away — `ctx.Err()` is checked *between* reads, so cancelling
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the context cannot reach a read that is already blocked. One idle TCP
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connection (or one DoT connection, with `timeouts.tls` set high) was enough to
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make `Stop` sit there for the caller's entire grace period — 15s in `main` —
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and then return `context.DeadlineExceeded`, which the app reports as
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"shutdown completed with errors". Worse, the cache snapshot the app takes
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right after `Stop` never happened: the orchestrator had already given up. It
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is a shutdown DoS that costs the attacker one connection, and nothing tested
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it. The fix is a read deadline in the past on every accepted connection when
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the context is cancelled, and deliberately *not* a close: a query already
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inside the pipeline is past its read, so its answer still goes out, which is
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the invariant `TestInFlightQueryIsAnsweredAcrossStop` pins.
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`TestStopIsNotBlockedByAnIdleStreamConnection` sets a 60s DoT idle timeout on
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purpose, so a config value cannot hide the regression behind a lucky tick.
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- **A UDP query in flight at `Stop` was lost, and nothing waited for it.** The
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stream paths register their connections with `s.wait`, so `Stop` waits for
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them; `servePacket` did not register at all, so a UDP query already inside
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the pipeline when the socket closed was gone twice over — nothing waited for
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it, and the answer had nowhere to go even once it was ready, because a
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datagram is written to the very socket the query arrived on. The visible
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damage was not the lost answer (the client retries) but the app: it snapshots
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the cache and closes the store the moment `Stop` returns, so a query still in
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the pipeline could be writing to a store that was about to close. Packets are
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now counted in `s.wait`, and the UDP listener's close waits (bounded by
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`udpDrainGrace`, 250ms) for the read loop and the packets it spawned before it
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closes the socket. A shutdown must not spend its grace period on one slow
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upstream, hence the bound: past it the answer is dropped, which is what the
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client would see anyway. Pinned on all four transports by
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`TestInFlightQueryIsAnsweredAcrossStop/{tcp,dot,udp,doh}`.
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- **`Stop` returning did not mean the process was done.** Nothing asserted that
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the server's goroutines were gone, so a shutdown that leaked one was
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indistinguishable from one that did not. `TestStopLeavesNoGoroutineRunningServerCode`
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counts goroutines whose stack still has a frame in this package — not
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`runtime.NumGoroutine()`, which in a test binary is net/http, crypto/tls and
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the race detector talking over each other — and it found the idle-connection
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bug above, since the check is the only way to see a goroutine that has no
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client left to answer.
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- **A dead peer stayed in the cluster peer list forever.** `Cluster.seen` was
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only ever added to and deleted from on an explicit `bye`, so a node that
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crashed — or whose Valkey connection died — was reported as a live peer for
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the life of the process, and its stale blocklist digest was flagged as
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divergence forever. `Peers()` now reaps peers unheard for `peer_ttl * 4`
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(four missed heartbeats) and stamps each state with the receiver's own clock,
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so clock skew between two machines can neither reap a healthy peer nor keep a
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dead one. `Discover()` ages out the same way on the publisher's own
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`last_seen` stamp, because the keyed Valkey record outlives a crash: a live
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node keeps refreshing the key's TTL, so a dead node's field stayed readable
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for the life of the fleet. `TestDeadPeerAgesOutOfPeers` (which was failing on
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the tree as handed over — the reaping it asked for did not exist) now passes.
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- **`peer_ttl: 0` would have crashed the process.** `time.NewTicker(PeerTTL/2)`
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panics on a non-positive period, and `EXPIRE key 0` *deletes* the heartbeat
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key, so a config that left `peer_ttl` unset would have taken the process down
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at `Start` (or made every instance believe it is alone in the fleet). Both go
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through `peerTTL()`/`peerDeadline()`, which fall back to the default.
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- **Two cluster tests raced on the wire, not on the product.** A node that
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joined after another's heartbeat was in flight hears about it on the next
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tick, so "b does not see a", read immediately after "a sees b", is a coin
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flip; and `TestStatusReportsDivergentPeers` waited for a digest on the wrong
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node's view of the fleet. Both tests were wrong, not the code.
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- **The partial-bind test only worked unprivileged.**
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`TestStartReportsAPartialFailureButServes` used `127.0.0.1:1` as a port that
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cannot be bound, which is not true in any container with
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`net.ipv4.ip_unprivileged_port_start=0` — it binds, and the test failed with
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both transports up. It now occupies a port with a live listener in the test
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process, which is a deterministic `EADDRINUSE` on every machine and every
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uid.
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- **Four API/console contract breaks, all found by the new contract test:**
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`blocklist.Source` and `SourceMeta` had no `json` tags at all, so the Sources
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table rendered blank rows and its per-row toggle posted `name: undefined`;
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`acl.GroupSummary` was flat where the console reads a nested `match`, so every
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group card read "matches nothing"; `PUT /api/clients` answered 400
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`json: unknown field "ptr_suffixes"` to the payload the console sends, because
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`config.Group` and `config.Match` had yaml tags only; and `PUT /api/upstreams`
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answered 400 `json: unknown field "health"`, because the console round-trips
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the whole server object it read, runtime health fields included. The write
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structs now carry json tags, the health fields are accepted and ignored (the
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server owns them), and `acl.Match` is nested.
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- **A duration on the wire was a nanosecond count.** `config.Duration` had a
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`MarshalYAML` but no `MarshalJSON`, so `bootstraps[].refresh` arrived as
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`30000000000` while the console typed the field as a string, and
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`healthcheck_interval` was a float of seconds in one place and a string in
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another. Durations on the wire are duration strings everywhere now, which is
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the same spelling config.yaml uses; a bare JSON number is still accepted and
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means **seconds**, not nanoseconds. `TestDurationJSONForm` pins all of it and
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says the old behaviour was the bug.
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- **A log row's key set depended on the row.** `api.LogEntry` was `omitempty`
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on `client_group`, `response`, `upstream` and `list`, so a query with no ACL
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group arrived without the key and the console rendered "undefined" where the
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column should be empty. The contract test can only pin one shape if the
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server emits one, so nothing on that struct is `omitempty` any more.
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- **Every query from a client that asks for EDNS0 NSID got SERVFAIL.**
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`dns.EDNS0_NSID.Nsid` is a *hex string* in miekg/dns v1.1.73 — `pack`
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hex-decodes it, `unpack` hex-encodes it — and the engine put the literal
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`"fancy-dns"` in it. `hex.DecodeString("fancy-dns")` fails, so the forwarded
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upstream query could not be built, the exchange failed, and the client got
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SERVFAIL. A one-line bug with total blast radius on a documented feature.
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Fixed with `hex.EncodeToString`, and pinned from both sides:
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`TestClientNSIDIsAnswered` (a client asking for NSID gets a real answer, the
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option we forward upstream decodes to our own name, and `dns.hide_identity`
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drops it) and `TestPinnedEDNS0NSIDIsHex` (the library contract, so a future
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bump that changes `Nsid` to raw bytes fails here with an explanation instead
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of silently breaking the feature).
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- **The login rate limiter was applied to every route except the one it exists
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for.** `allowRequest` is the only reader of `limitState.lockedTill` and it ran
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behind `authed`, while the login route was registered through `public`. So N
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bad API keys gave N × 401 and never a 429, and the lockout instead locked the
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caller out of the *rest* of the API — brute-force protection is the one thing
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the auth surface most needs, and it was the one thing that did not work. There
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is now a `limited()` wrapper (the limiter only, no auth) on the login route;
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`allowRequest` stays the single reader of the lockout state. Pinned by
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`TestLoginBruteForceEventuallyHitsTheRateLimiter`,
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`TestLoginLockoutExpiresWithTheClock`, `TestLoginLockoutIsPerIP`,
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`TestLoginLockoutDisabledWithoutFailures` and the `TestAuthedRouteRateLimit*`
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family, so both routes stay honest.
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- **A successful login reset the attacker's request budget.**
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`clearLoginFailures` deleted the whole per-IP `limitState`, which also reset
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the per-minute window, so one valid key in the middle of a brute-force burst
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handed back a fresh budget. It now clears only `failures` and `lockedTill`,
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and `TestSuccessfulLoginDoesNotResetTheRequestWindow` /
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`TestSuccessfulLoginClearsTheFailureCounter` pin both halves.
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- **DoH GET had no size cap.** The POST path is capped by `readCapped` at
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`dns.MaxMsgSize`; the GET path handed `?dns=` straight to a base64 decode and an
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`Unpack`, so the only limit was net/http's `MaxHeaderBytes` — roughly a
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megabyte of attacker-chosen base64 decoded per request, unauthenticated,
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against a 64 KiB cap on the neighbouring path. A DNS message cannot exceed
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65535 bytes, so the cap is `base64.RawURLEncoding.EncodedLen(dns.MaxMsgSize)`
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and cannot refuse a conforming client. Pinned by
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`TestDoHGETQueryStringOverTheCapIsRefused` (413) and
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`TestDoHServesALargeButLegalQuery` (a message just under the wire limit is
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still served, so the cap cannot be tightened carelessly).
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- **A clean `Stop` sometimes returned "use of closed network connection".** The
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DoH listener has two owners: `Stop`'s close list, and `http.Server.Shutdown`,
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which tracks the same `net.Listener` because `serveDoH` hands it to
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`srv.Serve`. Whichever lost that race made an orderly shutdown look like a
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failed one. Closing an already-closed listener is not a failure, so `Stop` now
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ignores `net.ErrClosed` and only reports a real close error. It reproduced 3
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times in 3 runs with DoH enabled and never with it disabled, which is what
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made it findable; `TestStopIsIdempotent` is the pin.
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- **A per-transport `dropped` counter did not exist.** The DoH drop fix above
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was invisible in the UI: `HandlerStats.Dropped` is an aggregate that cannot
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say which transport dropped, and `TransportStats` had no `Dropped` field at
|
||
all, even though all four transports bump the counter. Added, with the
|
||
reasoning in the field's comment.
|
||
- **A DoH drop was not counted as a drop.**
|
||
`dropped` when `res.Drop`; the DoH path only reached `classify`, which maps
|
||
`drop` to `errors`, so `HandlerStats.Dropped` under-counted DoH. One line, in
|
||
the same position as the other two.
|
||
- **Both shipped zone files matched nothing.** `blocklist.local_zones` and the
|
||
`rpz`-format list source are read with the origin taken from the file's base
|
||
name (`zonefile.OriginFromPath`: `local.example.zone` → `local.`), so the
|
||
relative owner names in the examples were being qualified with that — a
|
||
`*.doubleclick.net` rule blocked `*.doubleclick.net.local.`, and the local
|
||
zone mixed relative owners with absolute ones. An operator copying either file
|
||
got a server that answered nothing and blocked nothing. Both examples now
|
||
spell every name out in full, and
|
||
`TestExampleLocalZoneIsOriginIndependent` (zonefile) plus
|
||
`TestExampleRPZZoneBlocksWhatItSays` (blocklist, through the real
|
||
`parseRPZFiles` path) fail if they are "tidied up" back to relative names.
|
||
- **The shipped configs were never loaded by anything.**
|
||
`deploy/config.example.yaml` and the ConfigMap in `deploy/k8s/00-config.yaml`
|
||
are now loaded through `config.Load` (which ends in `Validate`) and
|
||
spot-checked, including that the k8s `${FANCYDNS_API_KEY}` still expands and
|
||
still *fails* when the Secret is missing, and that the memory envelope matches
|
||
the StatefulSet's 1Gi limit.
|
||
- **The admin API's response shapes had drifted from the console's types** —
|
||
verified against a running binary, not inferred. `blocklist.Source` has no
|
||
`json` tags at all, so the Sources table rendered blank rows and its
|
||
per-row toggle posted `name: undefined`; `acl.GroupSummary` is flat where the
|
||
console expects a nested `match`, so every group card read "matches nothing";
|
||
and **both write endpoints answered 400 to the payload the console actually
|
||
sends** (`json: unknown field "ptr_suffixes"` on `PUT /api/clients`,
|
||
`unknown field "health"` on `PUT /api/upstreams`). The Go side is being fixed
|
||
with contract tests that assert the exact key set of every endpoint; the
|
||
console side is the next piece of work.
|
||
- **The GitHub Actions image job could never tag an image.** It used
|
||
`${{ gitea.sha }}` in a workflow under `.github/`, and the `gitea` context
|
||
only exists on Gitea; the image is also published by
|
||
`.gitea/workflows/build.yaml`, which is the pipeline with registry access. It
|
||
now tags with `github.sha` and only logs in and pushes when this repository
|
||
actually has a registry token, so a GitHub runner builds and stops instead of
|
||
failing.
|
||
- **`api.constantTimeEqual` had no callers**, and the `authenticator` doc
|
||
comment described a constant-time "API key scan" that does not exist. The real
|
||
design is better than the comment (API keys are compared as SHA-256 digests
|
||
through a hash-keyed map, so the plaintext is never stored) — the dead
|
||
function is gone and the comment now describes the code.
|
||
- **`maxGETResponse` was dead code** whose comment claimed a guarantee the
|
||
handler did not provide. Deleted; the DoH response is written as packed.
|
||
|
||
## Pinned, not fixed (each one has a test that says so out loud)
|
||
|
||
The standing decision for the round after this one was: **pin, do not change**.
|
||
Every item below is behaviour someone may want to change deliberately; each has
|
||
a test that fails when it changes, and says what to do when it does.
|
||
|
||
- **Unknown config keys are silently ignored** (a settled decision, see the
|
||
table above). `TestLoadIgnoresUnknownKeys` in `internal/config` also pins the
|
||
asymmetry that makes this surprising: a typo is invisible, while a known key
|
||
with a bad *type* is a startup failure.
|
||
- **Auth configuration is frozen at `New`.** `api.base_path`,
|
||
`api.trusted_proxies` and the authenticator (`auth.mode`, `api_keys`) are
|
||
captured once; a reload re-reads CORS only. Writing a new API key through
|
||
`PUT /api/settings` answers `ok` while the running server keeps the old key.
|
||
`TestPinnedWrittenAuthConfigIsNotAppliedUntilRestart` and
|
||
`TestCORSOriginsAreReadAtHandlerBuild` hold this in place until someone decides
|
||
whether a reload should re-apply it.
|
||
- **DoH clients behind an Ingress all present as the proxy.** `httpRemoteAddr`
|
||
uses the raw `RemoteAddr` and never consults `trusted_proxies`, so every DoH
|
||
client lands in the Ingress's ACL group: fail-closed if that group is
|
||
restrictive, fail-open if it is permissive.
|
||
`TestDoHClientIdentityIsTheProxyNotTheForwardedForHeader` pins it, with the
|
||
reason honouring `X-Forwarded-For` without `trusted_proxies` would break the
|
||
ACL and rate-limit invariants.
|
||
- **`api.cors_origins: ["*"]` echoes the request's `Origin` and sets
|
||
`Access-Control-Allow-Credentials: true`.** Deliberate (a literal `*` is
|
||
ignored by browsers when credentials are involved), but it does mean any
|
||
website can drive the admin API with whatever the browser has cached for that
|
||
host. The preflight also answers 204 for any origin and any path.
|
||
`TestCORSWildcardEchoesTheOrigin` and `TestCORSPreflight` pin all of it.
|
||
- **A partial bind failure is invisible.** `serveDoT`/`serveDoH` record a failed
|
||
bind in an error list only, so `ListenerInfo.Err` is never set and the admin
|
||
API cannot show which address failed.
|
||
`TestStartReportsAPartialFailureButServes` pins that `Start` returns nil
|
||
whenever any listener came up.
|
||
- **A question-less message is answered on UDP and kills the connection on
|
||
TCP/DoT.** `TestUDPQuestionlessMessageReachesTheEngine` pins the UDP half (the
|
||
engine turns it into a FORMERR); the stream path returns instead. Probably
|
||
right for both, but it is an asymmetry worth knowing about.
|
||
- **`doh.sent` is never bumped.** The DoH handler writes its answer through
|
||
`net/http`, so the `sent` counter is only meaningful on UDP/TCP/DoT, and the
|
||
console's transport table shows `sent: 0` for DoH. Pinned as current
|
||
behaviour by `TestCountersFollowTheEngineOutcome` with a comment saying why.
|
||
- **`api.metrics.path` is ignored**
|
||
always `${base_path}/metrics`); `POST /api/blocklists/refresh` returned
|
||
`{"names": null}`; an empty `config_yaml` in the settings form is not valid (it
|
||
decodes onto `Default()`, which enables a blocklist with no sources); `"1Gi"`
|
||
is not a valid size — only `GiB`, `G`, `GB` — even though that is how k8s
|
||
spells it.
|
||
|
||
## Continuation plan, in order
|
||
|
||
1. **Decide the rest of the pinned list**, one at a time, each with a changelog
|
||
note: the frozen auth config, the DoH client identity, CORS wildcards, the
|
||
question-less message asymmetry, `doh.sent` never bumped. (The UDP query lost
|
||
at `Stop` left this list when it was fixed.)
|
||
2. **Stop hand-writing the console's types.** The contract tests make the Go
|
||
side authoritative; the cheapest durable answer is generating
|
||
`web/src/lib/types.ts` from the Go structs (or an OpenAPI document emitted by
|
||
the server) so `apiFetch` is typed against something real instead of
|
||
`JSON.parse(text) as T`. `internal/app/dump_shapes_test.go` (`DUMP_SHAPES=1`)
|
||
is the stopgap that already exists.
|
||
3. **Decide whether the shutdown grace belongs in config.** `main` hard-codes
|
||
15s for the whole `Stop`, and the drain inside it is 250ms of that. A
|
||
Kubernetes `terminationGracePeriodSeconds` and a resolver's own notion of
|
||
"long enough to answer what is in flight" are the same number, and right now
|
||
only one of them is visible. The four-transport invariant is pinned, so
|
||
changing the bound is cheap — but the knobs do not exist yet.
|
||
4. **Read the pinned "not fixed" list in this file for anything that has since
|
||
become untrue.** Each entry claims a behaviour a reader may act on; a claim
|
||
that no longer matches the code is worse than a missing one.
|
||
|
||
## Design notes worth preserving
|
||
|
||
- **Cache stores packed wire bytes, not `*dns.Msg`.** A hit costs one `Unpack`
|
||
and yields a private copy, so serving never mutates shared state and TTL
|
||
ageing is free. Same trade dnsmasq makes.
|
||
- **Everything the query path reads is behind an `atomic.Pointer` holder** — ACL,
|
||
blocklist, localzone, and now the upstream pool. Readers load the pointer once
|
||
and work against a value that cannot change under them. Prefer a new immutable
|
||
snapshot over a lock.
|
||
- **Cache invalidation on rule changes flushes the cache** rather than guessing
|
||
which subtrees are affected (`invalidateBlocklistCache` in
|
||
`internal/app/hooks.go`).
|
||
- **API responses share the field names in `internal/app/hooks.go`.** If you
|
||
rename one, grep the frontend too — and now also expect `internal/app`'s
|
||
contract test to fail, which is the point of it.
|
||
- **API keys are compared by SHA-256 hash, constant-time**, and
|
||
`X-Forwarded-For` is honoured *only* from `trusted_proxies`.
|
||
- **The UDP listener resets its read deadline every iteration.** A deadline set
|
||
once expires for good and turns the loop into a spin that never reads another
|
||
packet (caught by `TestBlocklistToggle`).
|
||
- **Shutdown order is: cancel, close every listener, then wait.** The close is
|
||
not interruptible by the caller's context, because releasing the ports is the
|
||
work the next process start needs. Everything after it is interruptible, and
|
||
a cancelled context is expected to be able to cut the *wait* short — which is
|
||
why no step in the shutdown may depend on a client doing anything.
|
||
- **Only the Valkey lease holder fetches lists**, so N instances do not hit a
|
||
mirror N times.
|
||
- **Serve-stale** answers get TTL 1; an expired upstream answer is never cached;
|
||
a truncated answer is never cached (it would be served truncated forever).
|
||
- **`PatternKind.Pattern` is the display form; `WireName` is the wildcard form.**
|
||
The internal `*.` / `**.` prefixes must not leak into the UI, but the API
|
||
needs them to re-add a rule unchanged (the domains list ships `rule` for
|
||
exactly this).
|
||
- **pprof is loopback-only by construction**, not by policy, so no config flag
|
||
can turn it into a network-reachable unauthenticated endpoint.
|
||
- **A master file's origin is its base name**, so a relative owner name in a
|
||
zone is qualified with the file's name, not with the zone you meant. Absolute
|
||
names are the only spelling that survives a rename.
|
||
|
||
## Test-hygiene traps
|
||
|
||
- `dns.NewRR` needs a TTL column: `dns.NewRR("host.example.com")` does not
|
||
parse. That is a fixture bug, not a product bug.
|
||
- A test that closes a stop channel *after* `wg.Wait()` deadlocks the whole
|
||
package and looks like "the suite hangs". Close first, then wait.
|
||
- Assert on invariants, not on what a concurrent goroutine happened to observe.
|
||
"A reader must have seen address X" is a flake; "every list a reader sees is
|
||
one of the published ones" is a real property and cannot flake.
|
||
- **A test that only dials a stream transport races the accept loop.** Stop can
|
||
close the listener while the connection is still in the backlog, the server
|
||
never accepts it, and any shutdown assertion that needs a live server-side
|
||
goroutine passes for the wrong reason. Exchange one query first, then leave
|
||
the connection alone — that is what `harness.idleStream` is for.
|
||
- **Count leaked goroutines by stack, not by `runtime.NumGoroutine()`.** A test
|
||
binary shares its process with net/http, crypto/tls and the race detector; a
|
||
baseline count is noise. "Does any goroutine still have a frame in this
|
||
package?" is a property of the product, and it needs the caller's own
|
||
goroutine filtered out by id or every run finds exactly one.
|
||
- `tsc -b` replays **cached diagnostics** from `node_modules/.tmp/*.tsbuildinfo`.
|
||
After a large edit, `rm node_modules/.tmp/*.tsbuildinfo`.
|
||
- `vite build` empties `outDir` and **deletes `internal/web/dist/.gitkeep`**.
|
||
Restore it or the directory disappears from git. `//go:embed all:dist` still
|
||
builds while the directory is empty, so a console rebuild in the middle of
|
||
someone else's `go build` is not fatal.
|
||
- **A `TXT` string over 255 bytes does not pack** in miekg/dns v1.1.73 — the
|
||
error is `dns: string exceeded 255 bytes in txt`, and 255 is the exact
|
||
boundary. On a fake upstream's write path the failure is silent and presents
|
||
as a client timeout, so build a multi-kilobyte answer out of many short
|
||
strings and assert the fake's write error before blaming the client.
|
||
- **`dns.EDNS0_NSID.Nsid` is a hex string, not the bytes on the wire.** A plain
|
||
value such as `"fancy-dns"` fails with `dns: overflow packing opt`, and a long
|
||
NSID packs fine (unlike `TXT`). Always hex-encode on the way in.
|
||
- `gofmt -l internal/` is the fastest way to see that a file does not parse.
|
||
- The console has **no test runner at all** — only `tsc -b --noEmit` and
|
||
`oxlint`. A field-name drift between the API and the console is invisible to
|
||
both, which is why the Go side now has contract tests.
|
||
|
||
## Fixed earlier and worth not re-breaking
|
||
|
||
A running list, kept because each of these was invisible until it was found:
|
||
|
||
- `config.ParseSize` ignored the unit multiplier entirely (`512MiB` parsed as
|
||
512 bytes), so every memory budget in the tree was off by a factor of the
|
||
unit. `size_test.go` pins the units, the shadowing cases, the range and the
|
||
truncating rounding.
|
||
- A cache miss and a stale hit moved only the Prometheus counter and not the
|
||
atomics the console's `Totals` reads, so the Cache page read zero for the
|
||
life of the process.
|
||
- `finalize` — the EDNS0/UDP-size step that turns an oversized answer into a
|
||
question-only TC reply — ran only on the cache-hit path, so a multi-kilobyte
|
||
answer from upstream, from the local zone or from a sinkhole was left as a
|
||
datagram a 512-byte UDP client silently dropped.
|
||
- The serve-stale prefetch gate was a 64-slot channel, so a burst of stale hits
|
||
on one hot name launched up to 64 duplicate upstream exchanges instead of the
|
||
one its own comment promised. It is a per-key latch now.
|
||
- The upstream UDP client read buffer was hard-coded to 1232 while the engine
|
||
advertises `dns.max_udp_size`, so an operator who raised it got SERVFAIL for
|
||
every answer over 1232 bytes.
|
||
- Every relative RDATA name in a master file pointed at the DNS root: the
|
||
qualification pass ran *after* `dns.NewRR`, so `www CNAME host` became
|
||
`CNAME host.`. It is now a token-level pass driven by a table of which RDATA
|
||
positions hold a name.
|
||
- The cache snapshot never round-tripped: `Load` decoded the record header out of
|
||
the *key's* remainder instead of the value, so every restart was a cold cache.
|
||
There is now an `encodeRecord`/`decodeRecord` pair with a version byte and a
|
||
CRC-32C trailer, and `Load` drops expired entries and rewrites the TTL to the
|
||
time actually left.
|
||
- `${VAR}` expansion never worked inside quotes — the only form anyone writes —
|
||
because the reference check sat below the quote branches in the same switch.
|
||
The admin API key was the literal string `"${FANCYDNS_API_KEY}"`.
|
||
- ACL PTR suffix matching crossed label boundaries, so a group scoped to
|
||
`example.com.` also swallowed `ample.com.`; the ACL `*` catch-all was dropped
|
||
from the rendered domain patterns; `Upstream.Success` never closed an open
|
||
breaker; `Exchange` fanned out in parallel even under `policy: failover`; the
|
||
cache byte budget was never fed to the LRU.
|
||
- **`TestRebindUnderConcurrentQueries` was a flake** (2 runs in 10) because it
|
||
asserted a reader had to observe two specific addresses. It now pins the
|
||
copy-on-write invariant itself.
|
||
- CI could not have passed (`go.mod` requires Go 1.27.1, CI and the Dockerfile
|
||
pinned 1.23), the Dockerfile clobbered the console by copying the source tree
|
||
after the bundle, and the k8s set could not have worked (`hostNetwork: true`
|
||
with `replicas: 2` and no SO_REUSEPORT).
|
||
- `$TTL` was ignored by the zone parser; every record got the SOA minimum.
|
||
- Blocklist: leading BOM stripped, `!allow` works, `SourceMeta` exists for a
|
||
rule-only source, `Pattern()` reports the bare name while `WireName()` gives
|
||
the wildcard form, RPZ inherits the zone default TTL, hosts files complain
|
||
about a missing address, adblock handles CRLF and over-long lines.
|
||
- `serveUDP` called `net.ResolveUDPAddr` per packet; the peer already is a
|
||
`*net.UDPAddr`.
|