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

internal/imgcache/service_internal_test.go

@@ -433,22 +433,9 @@ func TestService_Get_Caching(t *testing.T) {
 }
 
 // TestService_Get_ServesSourceAndVariantCachedTwoDaysAgo caches a source and
-// a variant of it and sets back two days every time pixa stored for them.
-// For the source: fetched_at in source_metadata and in source_content, the
-// fetched_at in its metadata file, and the access and modification times of
-// its file and of its metadata file. For the variant: created_at in
-// variant_content, the created_at in its .meta file, and the access and
-// modification times of its file and of its .meta file. It then 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.
-//
-// Left at the present: last_accessed_at in source_content and variant_content,
-// which is when eviction last saw the entry used, not when it was cached; the
-// files' status change and birth times, which a program cannot set; and the
-// times of the directories holding the files, which other entries share. The
-// source's stored response headers are empty, as the mock fetcher sends none.
-// expires_at, etag and last_modified in source_metadata and in the metadata
-// file are never written, nor are the request_cache and output_content tables.
+// 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()
 
@@ -462,9 +449,45 @@ func TestService_Get_ServesSourceAndVariantCachedTwoDaysAgo(t *testing.T) {
 
 	_ = 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)
-	backdateSource(t, svc.cache, variant, twoDaysAgo)
-	backdateVariant(t, svc.cache, variant, twoDaysAgo)
+	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 {
@@ -492,110 +515,6 @@ func TestService_Get_ServesSourceAndVariantCachedTwoDaysAgo(t *testing.T) {
 	}
 }
 
-// backdateSource sets every time pixa stored for req's cached source to when,
-// as listed on TestService_Get_ServesSourceAndVariantCachedTwoDaysAgo.
-func backdateSource(
-	t *testing.T, cache *Cache, req *ImageRequest, when time.Time,
-) {
-	t.Helper()
-
-	pathHash := HashPath(req.SourcePath + "?" + req.SourceQuery)
-
-	meta, err := cache.srcMetadata.Load(req.SourceHost, pathHash)
-	if err != nil {
-		t.Fatalf("reading the source's metadata file: %v", err)
-	}
-
-	meta.FetchedAt = when.Unix()
-
-	err = cache.srcMetadata.Store(req.SourceHost, pathHash, meta)
-	if err != nil {
-		t.Fatalf("writing the source's metadata file: %v", err)
-	}
-
-	dbTime := when.UTC().Format(sqliteTimestampFormat)
-
-	updateOneRow(t, cache, `
-		UPDATE source_metadata SET fetched_at = ?
-		WHERE source_host = ? AND source_path = ? AND source_query = ?
-	`, dbTime, req.SourceHost, req.SourcePath, req.SourceQuery)
-	updateOneRow(t, cache,
-		`UPDATE source_content SET fetched_at = ? WHERE content_hash = ?`,
-		dbTime, meta.ContentHash)
-
-	for _, path := range []string{
-		cache.srcContent.hashToPath(ContentHash(meta.ContentHash)),
-		cache.srcMetadata.metaPath(req.SourceHost, pathHash),
-	} {
-		err = os.Chtimes(path, when, when)
-		if err != nil {
-			t.Fatalf("setting back the times of %s: %v", path, err)
-		}
-	}
-}
-
-// backdateVariant sets every time pixa stored for the cached variant req asks
-// for to when, as listed on
-// TestService_Get_ServesSourceAndVariantCachedTwoDaysAgo.
-func backdateVariant(
-	t *testing.T, cache *Cache, req *ImageRequest, when time.Time,
-) {
-	t.Helper()
-
-	key := CacheKey(req)
-
-	content, size, contentType, err := cache.variants.LoadWithMeta(key)
-	if err != nil || contentType == "" {
-		t.Fatalf("reading the variant's .meta file: content type %q, error %v",
-			contentType, err)
-	}
-
-	_ = content.Close()
-
-	meta, err := json.Marshal(VariantMeta{
-		ContentType: contentType,
-		Size:        size,
-		CreatedAt:   when.Unix(),
-	})
-	if err != nil {
-		t.Fatalf("encoding the variant's .meta file: %v", err)
-	}
-
-	path := cache.variants.keyToPath(key)
-
-	err = os.WriteFile(path+variantMetaSuffix, meta, StorageFilePerm)
-	if err != nil {
-		t.Fatalf("writing the variant's .meta file: %v", err)
-	}
-
-	updateOneRow(t, cache,
-		`UPDATE variant_content SET created_at = ? WHERE cache_key = ?`,
-		when.UTC().Format(sqliteTimestampFormat), string(key))
-
-	for _, file := range []string{path, path + variantMetaSuffix} {
-		err = os.Chtimes(file, when, when)
-		if err != nil {
-			t.Fatalf("setting back the times of %s: %v", file, err)
-		}
-	}
-}
-
-// updateOneRow runs the UPDATE statement query and fails the test unless it
-// changed exactly one row.
-func updateOneRow(t *testing.T, cache *Cache, query string, args ...any) {
-	t.Helper()
-
-	result, err := cache.db.ExecContext(t.Context(), query, args...)
-	if err != nil {
-		t.Fatalf("%s: %v", query, err)
-	}
-
-	rows, err := result.RowsAffected()
-	if err != nil || rows != 1 {
-		t.Fatalf("%s: rows = %d, error = %v, want 1 row", query, rows, err)
-	}
-}
-
 func TestService_Get_DifferentSizes(t *testing.T) {
 	t.Parallel()