Remove the unused cache lifetime setting (closes #69)

CacheConfig.CacheTTL was set to DefaultCacheTTL (24 hours) and never
read, so cached images never expired. Remove the field, the constant
and the line that set it. Cached source and transformed images stay
until eviction removes them to keep the cache within cache_max_bytes.

A new test checks that a source and a transformed image cached two
days ago are still served from the cache without a new upstream fetch.

Existing tests lose only the CacheTTL line of their cache config; no
test's checks change.

Model: opus-5-5

TODO.md

@@ -30,6 +30,11 @@ P2: security: per-origin rate limiting
 
 # Completed Steps
 
+- 2026-10-13 the unused cache lifetime is removed (closes #69):
+  `CacheConfig.CacheTTL`, which pixad set to `DefaultCacheTTL` (24 hours), was
+  never read, so cached images never expired. The field and the constant are
+  removed. Cached source and transformed images stay until eviction removes them
+  to keep the cache within `cache_max_bytes`.
 - 2026-10-12 per-client limit on the image routes (closes #236): the new setting
   `image_requests_per_minute` (`PIXA_IMAGE_REQUESTS_PER_MINUTE`), default 600,
   is how many `GET` and `HEAD` requests one client may send to `/v1/image/` and

internal/handlers/handlers.go

@@ -106,7 +106,6 @@ func (s *Handlers) WaitForProcessing(ctx context.Context) int {
 func newCacheConfig(cfg *config.Config, log *slog.Logger) imgcache.CacheConfig {
 	return imgcache.CacheConfig{
 		StateDir:           cfg.StateDir,
-		CacheTTL:           imgcache.DefaultCacheTTL,
 		NegativeTTL:        imgcache.DefaultNegativeTTL,
 		MaxBytes:           cfg.CacheMaxBytes,
 		UseDefaultMaxBytes: !cfg.CacheMaxBytesExplicit,

internal/handlers/handlers_internal_test.go

@@ -47,7 +47,6 @@ func setupTestHandler(t *testing.T) *testFixtures {
 
 	cache, err := imgcache.NewCache(db, imgcache.CacheConfig{
 		StateDir:    tmpDir,
-		CacheTTL:    time.Hour,
 		NegativeTTL: 5 * time.Minute,
 	})
 	if err != nil {

internal/handlers/image_cache_control_internal_test.go

@@ -31,7 +31,6 @@ func newSignedHostServer(
 
 	cache, err := imgcache.NewCache(setupTestDB(t), imgcache.CacheConfig{
 		StateDir:    t.TempDir(),
-		CacheTTL:    time.Hour,
 		NegativeTTL: 5 * time.Minute,
 	})
 	if err != nil {

internal/handlers/image_errors_internal_test.go

@@ -29,7 +29,6 @@ func newImageRoute(t *testing.T, fetcher httpfetcher.Fetcher) http.Handler {
 
 	cache, err := imgcache.NewCache(setupTestDB(t), imgcache.CacheConfig{
 		StateDir:    t.TempDir(),
-		CacheTTL:    time.Hour,
 		NegativeTTL: 5 * time.Minute,
 	})
 	if err != nil {

internal/handlers/referer_blocklist_internal_test.go

@@ -49,7 +49,6 @@ func newRefererRoutes(t *testing.T) (http.Handler, *Handlers, *countingFetcher)
 
 	cache, err := imgcache.NewCache(setupTestDB(t), imgcache.CacheConfig{
 		StateDir:    t.TempDir(),
-		CacheTTL:    time.Hour,
 		NegativeTTL: 5 * time.Minute,
 	})
 	if err != nil {

internal/imgcache/cache.go

@@ -35,7 +35,6 @@ const metaCacheSize = 10000
 // CacheConfig holds cache configuration.
 type CacheConfig struct {
 	StateDir    string
-	CacheTTL    time.Duration
 	NegativeTTL time.Duration
 
 	// MaxBytes is the disk cache size limit in bytes that eviction

internal/imgcache/cache_internal_test.go

@@ -102,7 +102,6 @@ func setupTestCache(t *testing.T) *Cache {
 
 	cache, err := NewCache(db, CacheConfig{
 		StateDir:    tmpDir,
-		CacheTTL:    time.Hour,
 		NegativeTTL: 5 * time.Minute,
 	})
 	if err != nil {
@@ -241,7 +240,6 @@ func TestCache_NegativeCacheExpiry(t *testing.T) {
 	// Very short negative TTL for testing
 	cache, err := NewCache(db, CacheConfig{
 		StateDir:    tmpDir,
-		CacheTTL:    time.Hour,
 		NegativeTTL: 1 * time.Millisecond,
 	})
 	if err != nil {

internal/imgcache/eviction_internal_test.go

@@ -70,7 +70,6 @@ func newEvictionTestCache(t *testing.T, maxBytes int64) (*Cache, string) {
 	// backwards compatibility with existing fixtures.
 	cache, err := NewCache(db, CacheConfig{
 		StateDir:         tmpDir,
-		CacheTTL:         time.Hour,
 		NegativeTTL:      5 * time.Minute,
 		MaxBytes:         maxBytes,
 		DisableDiskCache: maxBytes == 0,

internal/imgcache/module.go

@@ -4,6 +4,5 @@ import "time"
 
 // CacheConfig defaults.
 const (
-	DefaultCacheTTL    = 24 * time.Hour
 	DefaultNegativeTTL = 5 * time.Minute
 )

internal/imgcache/negative_cache_internal_test.go

@@ -15,7 +15,6 @@ func TestNegativeCache_StoreAndCheck(t *testing.T) {
 
 	cache, err := NewCache(db, CacheConfig{
 		StateDir:    dir,
-		CacheTTL:    time.Hour,
 		NegativeTTL: 5 * time.Minute,
 	})
 	if err != nil {
@@ -63,7 +62,6 @@ func TestNegativeCache_Expired(t *testing.T) {
 
 	cache, err := NewCache(db, CacheConfig{
 		StateDir:    dir,
-		CacheTTL:    time.Hour,
 		NegativeTTL: 1 * time.Millisecond, // very short TTL
 	})
 	if err != nil {

internal/imgcache/service_internal_test.go

@@ -2,7 +2,9 @@ package imgcache
 
 import (
 	"context"
+	"encoding/json"
 	"io"
+	"os"
 	"testing"
 	"time"
 
@@ -430,6 +432,89 @@ func TestService_Get_Caching(t *testing.T) {
 	}
 }
 
+// TestService_Get_ServesSourceAndVariantCachedTwoDaysAgo caches a source and
+// a variant of it, sets their stored fetch and creation times back two days,
+// and checks that the variant is still served from the cache and that a new
+// variant is made from the cached source without fetching it again.
+func TestService_Get_ServesSourceAndVariantCachedTwoDaysAgo(t *testing.T) {
+	t.Parallel()
+
+	svc, fixtures := SetupTestService(t)
+	variant := photoVariant(fixtures, 85, FitCover)
+
+	resp, err := svc.Get(t.Context(), variant)
+	if err != nil {
+		t.Fatalf("Get() first request error = %v", err)
+	}
+
+	_ = resp.Content.Close()
+
+	for _, statement := range []string{
+		`UPDATE source_metadata SET fetched_at = datetime('now', '-2 days')`,
+		`UPDATE source_content SET fetched_at = datetime('now', '-2 days')`,
+		`UPDATE variant_content SET created_at = datetime('now', '-2 days')`,
+	} {
+		result, err := svc.cache.db.ExecContext(t.Context(), statement)
+		if err != nil {
+			t.Fatalf("%s: %v", statement, err)
+		}
+
+		rows, err := result.RowsAffected()
+		if err != nil || rows != 1 {
+			t.Fatalf("%s: rows = %d, error = %v, want 1 row", statement, rows, err)
+		}
+	}
+
+	// The variant's creation time is also its file's modification time
+	// and the created_at in its .meta file
+	twoDaysAgo := time.Now().AddDate(0, 0, -2)
+	variantPath := svc.cache.variants.keyToPath(CacheKey(variant))
+
+	err = os.Chtimes(variantPath, twoDaysAgo, twoDaysAgo)
+	if err != nil {
+		t.Fatalf("setting the variant file's modification time back: %v", err)
+	}
+
+	meta, err := json.Marshal(VariantMeta{
+		ContentType: resp.ContentType,
+		Size:        resp.ContentLength,
+		CreatedAt:   twoDaysAgo.Unix(),
+	})
+	if err != nil {
+		t.Fatalf("encoding .meta file: %v", err)
+	}
+
+	err = os.WriteFile(variantPath+".meta", meta, StorageFilePerm)
+	if err != nil {
+		t.Fatalf("writing .meta file: %v", err)
+	}
+
+	resp, err = svc.Get(t.Context(), variant)
+	if err != nil {
+		t.Fatalf("Get() of the cached variant error = %v", err)
+	}
+
+	_ = resp.Content.Close()
+
+	if resp.CacheStatus != CacheHit {
+		t.Errorf("cached variant CacheStatus = %q, want %q",
+			resp.CacheStatus, CacheHit)
+	}
+
+	// Another quality is a new variant, made from the cached source
+	resp, err = svc.Get(t.Context(), photoVariant(fixtures, 40, FitCover))
+	if err != nil {
+		t.Fatalf("Get() of a new variant error = %v", err)
+	}
+
+	_ = resp.Content.Close()
+
+	fetches := readCacheStatsCounters(t, svc.cache).upstreamFetchCount
+	if fetches != 1 {
+		t.Errorf("upstream fetches = %d, want 1", fetches)
+	}
+}
+
 func TestService_Get_DifferentSizes(t *testing.T) {
 	t.Parallel()
 

internal/imgcache/stats_internal_test.go

@@ -43,7 +43,6 @@ func TestStats_HitRateIsRatio(t *testing.T) {
 
 	cache, err := NewCache(db, CacheConfig{
 		StateDir:    dir,
-		CacheTTL:    time.Hour,
 		NegativeTTL: 5 * time.Minute,
 	})
 	if err != nil {
@@ -91,7 +90,6 @@ func TestStats_ZeroCounts(t *testing.T) {
 
 	cache, err := NewCache(db, CacheConfig{
 		StateDir:    dir,
-		CacheTTL:    time.Hour,
 		NegativeTTL: 5 * time.Minute,
 	})
 	if err != nil {
@@ -120,7 +118,6 @@ func TestStats_LogsFailedCountQueries(t *testing.T) {
 
 	cache, err := NewCache(db, CacheConfig{
 		StateDir:    t.TempDir(),
-		CacheTTL:    time.Hour,
 		NegativeTTL: 5 * time.Minute,
 		Logger:      slog.New(slog.NewJSONHandler(&logBuf, nil)),
 	})
@@ -162,7 +159,6 @@ func TestIncrementStats_LogsFailedUpdates(t *testing.T) {
 
 	cache, err := NewCache(db, CacheConfig{
 		StateDir:    t.TempDir(),
-		CacheTTL:    time.Hour,
 		NegativeTTL: 5 * time.Minute,
 		Logger:      slog.New(slog.NewJSONHandler(&logBuf, nil)),
 	})
@@ -232,7 +228,6 @@ func TestStats_DisabledCacheReportsNoItems(t *testing.T) {
 
 	disabled, err := NewCache(enabled.db, CacheConfig{
 		StateDir:         t.TempDir(),
-		CacheTTL:         time.Hour,
 		NegativeTTL:      5 * time.Minute,
 		DisableDiskCache: true,
 	})

internal/imgcache/testutil_internal_test.go

@@ -185,7 +185,6 @@ func SetupTestService(
 
 	cache, err := NewCache(db, CacheConfig{
 		StateDir:    tmpDir,
-		CacheTTL:    time.Hour,
 		NegativeTTL: 5 * time.Minute,
 	})
 	if err != nil {