chore: fix README, remove dead code, centralise constants, extract tracer types

README.md

@@ -23,7 +23,7 @@ It respects negative caching and TTL. Security features include: bailiwick check
 
 ## Benchmarking
 
-`make bench` runs `scripts/bench.sh` (uses `dnsperf`; optionally compares against `kresd`). The script:
+`make bench` runs `scripts/bench.py` (uses `dnsperf`; optionally compares against `kresd`). The script:
 
 - builds with `make build-perf`
 - runs PicoDNS with `-stats` and writes a perf JSON report to `perf/picodns-perf.json`

internal/cache/ttl.go

@@ -155,10 +155,6 @@ func (c *TTL[K, V]) Clear() {
 	c.items = make(map[K]ttlEntry[V])
 }
 
-// Permanent is a special TTL value that indicates the entry should never expire.
-// Use this for addrCache where addresses don't change.
-const Permanent = time.Duration(0)
-
 // PermanentCache is a cache that never expires entries.
 // It's a thin wrapper around TTL with a permanent TTL.
 type PermanentCache[K comparable, V any] struct {

internal/obs/tracer.go

@@ -9,7 +9,6 @@ import (
 	"math"
 	"math/bits"
 	"os"
-	"runtime"
 	"sort"
 	"strconv"
 	"strings"
@@ -393,11 +392,6 @@ func Enabled() bool {
 	return true
 }
 
-// GoVersion returns the Go version for build info.
-func GoVersion() string {
-	return runtime.Version()
-}
-
 func formatDuration(d time.Duration) string {
 	if d < time.Microsecond {
 		return fmt.Sprintf("%dns", d.Nanoseconds())

internal/obs/tracer_noop.go

@@ -75,8 +75,3 @@ func (r *Registry) ReportJSON() ([]byte, error) {
 func Enabled() bool {
 	return false
 }
-
-// GoVersion returns empty string for non-perf builds.
-func GoVersion() string {
-	return ""
-}

internal/pool/bytes.go

@@ -1,3 +1,4 @@
+// Package pool provides reusable byte slice pools for DNS message buffers.
 package pool
 
 import "sync"

internal/resolver/cache.go

@@ -15,6 +15,23 @@ import (
 	"picodns/internal/types"
 )
 
+// cachedTracers holds performance tracing instrumentation for the Cached resolver.
+type cachedTracers struct {
+	resolveFromCache *obs.FuncTracer
+	resolve          *obs.FuncTracer
+	resolveFastPath  *obs.FuncTracer
+	resolveParseReq  *obs.FuncTracer
+	resolveInflight  *obs.FuncTracer
+	resolveUpstream  *obs.FuncTracer
+	resolveValidate  *obs.FuncTracer
+	resolveCacheSet  *obs.FuncTracer
+	getCachedWithKey *obs.FuncTracer
+	acquireInflight  *obs.FuncTracer
+	releaseInflight  *obs.FuncTracer
+	setCache         *obs.FuncTracer
+	maybePrefetch    *obs.FuncTracer
+}
+
 // Cached wraps a Resolver with a read-through cache, inflight deduplication,
 // stale-while-revalidate, and optional prefetch.
 type Cached struct {
@@ -31,21 +48,7 @@ type Cached struct {
 	CacheHits  atomic.Uint64
 	CacheMiss  atomic.Uint64
 
-	tracers struct {
-		resolveFromCache *obs.FuncTracer
-		resolve          *obs.FuncTracer
-		resolveFastPath  *obs.FuncTracer
-		resolveParseReq  *obs.FuncTracer
-		resolveInflight  *obs.FuncTracer
-		resolveUpstream  *obs.FuncTracer
-		resolveValidate  *obs.FuncTracer
-		resolveCacheSet  *obs.FuncTracer
-		getCachedWithKey *obs.FuncTracer
-		acquireInflight  *obs.FuncTracer
-		releaseInflight  *obs.FuncTracer
-		setCache         *obs.FuncTracer
-		maybePrefetch    *obs.FuncTracer
-	}
+	tracers cachedTracers
 }
 
 // NewCached creates a Cached resolver that fronts the given upstream with a cache layer.

internal/resolver/constants.go

@@ -87,6 +87,15 @@ const (
 
 	// EDNS0 settings
 	ednsUDPSize = 1232 // Common safe UDP size to avoid fragmentation
+
+	// Query concurrency
+	maxConcurrentQueries = 1024 // Maximum in-flight queries (semaphore size)
+
+	// CNAME resolution
+	maxCNAMEChainLength = 16 // Maximum CNAME chain depth for TTL computation
+
+	// Referral defaults
+	defaultReferralTTL = 3600 // Default TTL (seconds) for referral NS records when no TTL is present
 )
 
 // Resolver errors
@@ -95,5 +104,4 @@ var (
 	ErrNoNameservers = errors.New("recursive resolver: no nameservers found")
 	ErrNoGlueRecords = errors.New("recursive resolver: no glue records for NS")
 	ErrCnameLoop     = errors.New("recursive resolver: CNAME loop detected")
-	ErrNoRootServers = errors.New("recursive resolver: no root servers available")
 )

internal/resolver/recursive.go

@@ -23,6 +23,20 @@ type inflightRecursive struct {
 	err  error
 }
 
+// recursiveTracers holds performance tracing instrumentation for the Recursive resolver.
+type recursiveTracers struct {
+	resolve          *obs.FuncTracer
+	resolveIterative *obs.FuncTracer
+	iterHopWait      *obs.FuncTracer
+	iterParseMsg     *obs.FuncTracer
+	iterMinimize     *obs.FuncTracer
+	iterReferral     *obs.FuncTracer
+	iterResolveNS    *obs.FuncTracer
+	resolveNSNames   *obs.FuncTracer
+	warmup           *obs.FuncTracer
+	warmupRTT        *obs.FuncTracer
+}
+
 // Recursive performs full iterative DNS resolution starting from the root servers.
 // It maintains a connection pool, RTT tracker, NS cache, and delegation cache.
 type Recursive struct {
@@ -40,18 +54,7 @@ type Recursive struct {
 	inflightMu sync.Mutex
 	inflight   map[uint64]*inflightRecursive
 
-	tracers struct {
-		resolve          *obs.FuncTracer
-		resolveIterative *obs.FuncTracer
-		iterHopWait      *obs.FuncTracer
-		iterParseMsg     *obs.FuncTracer
-		iterMinimize     *obs.FuncTracer
-		iterReferral     *obs.FuncTracer
-		iterResolveNS    *obs.FuncTracer
-		resolveNSNames   *obs.FuncTracer
-		warmup           *obs.FuncTracer
-		warmupRTT        *obs.FuncTracer
-	}
+	tracers recursiveTracers
 }
 
 // NewRecursive creates a new recursive DNS resolver.
@@ -63,7 +66,7 @@ func NewRecursive(opts ...Option) *Recursive {
 		logger:          slog.Default(),
 		nsCache:         cache.NewTTL[string, []string](nil),
 		delegationCache: newDelegationCache(),
-		querySem:        make(chan struct{}, 1024),
+		querySem:        make(chan struct{}, maxConcurrentQueries),
 		inflight:        make(map[uint64]*inflightRecursive),
 	}
 	r.nsCache.MaxLen = maxNSCacheEntries
@@ -516,7 +519,7 @@ func (r *Recursive) resolveIterative(ctx context.Context, reqHeader dns.Header,
 
 		if len(respMsg.Authorities) > 0 {
 			childZone := zone
-			minTTL := uint32(3600)
+			minTTL := uint32(defaultReferralTTL)
 			for _, auth := range respMsg.Authorities {
 				if auth.Type == dns.TypeNS {
 					authZone := auth.Name

internal/resolver/utils.go

@@ -102,7 +102,7 @@ func servfailFromRequest(req []byte) ([]byte, bool) {
 	hdr.ANCount = 0
 	hdr.NSCount = 0
 	hdr.ARCount = 0
-	_ = dns.WriteHeader(resp, hdr)
+	_ = dns.WriteHeader(resp, hdr) // cannot fail: buffer validated above
 
 	return resp, true
 }
@@ -169,7 +169,7 @@ func cacheTTLForResponse(fullResp []byte, msg dns.Message, q dns.Question) (time
 	current := q.Name
 	seen := make(map[string]struct{}, 4)
 	seen[current] = struct{}{}
-	for i := 0; i < 16; i++ {
+	for i := 0; i < maxCNAMEChainLength; i++ {
 		var next string
 		var ttl uint32
 		found := false

internal/server/utils.go

@@ -35,7 +35,7 @@ func servfailFromRequestInPlace(req []byte) ([]byte, bool) {
 	hdr.ANCount = 0
 	hdr.NSCount = 0
 	hdr.ARCount = 0
-	_ = dns.WriteHeader(req, hdr)
+	_ = dns.WriteHeader(req, hdr) // cannot fail: buffer validated above
 
 	return req[:qEnd], true
 }