Split internal/imgcache into the image proxy and the cache (closes #317)

The new package internal/imageproxy holds Proxy, which was imgcache.Service,
with its Config, ImageResponse, CacheStatus and errors. NewProxy makes and
registers the counters of upstream fetches and transforms. internal/imgcache
holds the cache only, with its hit and miss counters, and imgcache.CacheConfig
is imgcache.Config. The cache reads and writes each kind it keeps with one pair
of methods: Variant and PutVariant, Source and PutSource, Failure and
PutFailure. Source replaces LookupSource followed by GetSourceContent.
imgcache.go and module.go are gone. The proxy's tests moved with it. They reach
the cache through its database, its state directory and its metrics registry,
and run its reconciliation pass with a second cache, as pixad does at startup.

Model: opus-5-5

TODO.md

@@ -30,6 +30,34 @@ P2: security: per-origin rate limiting
 
 # Completed Steps
 
+- 2026-10-26 `internal/imgcache` holds the cache only (closes #317). The new
+  package `internal/imageproxy` fetches, transforms, caches and serves images.
+  It imports `imgcache`, and `imgcache` does not import it.
+    - `imgcache.Service` is `imageproxy.Proxy`, built by `imageproxy.NewProxy`
+      from an `imageproxy.Config`.
+    - `ImageResponse`, `CacheStatus`, `ErrNegativeCached` and
+      `ErrProcessingTimedOut` moved with it, under their names.
+    - `imgcache.CacheConfig` is `imgcache.Config`.
+    - The cache has one read and one write for each kind it keeps. Each takes
+      the place of an earlier method:
+        - `Variant`, of `GetVariant`
+        - `PutVariant`, of `StoreVariant`
+        - `Source`, of `LookupSource` followed by `GetSourceContent`
+        - `PutSource`, of `StoreSource`
+        - `Failure`, of `checkNegativeCache`
+        - `PutFailure`, of `StoreNegative`
+    - `Variant` and `Source` each open the file and hand its access time to the
+      background writer. A cache hit still makes no database call.
+    - `imgcache.go` and `module.go` are gone.
+    - `NewProxy` makes the counters of upstream fetches and transforms, and
+      registers them on the registry it is given. The cache keeps only the hit
+      and miss counters.
+    - A cached source whose row cannot be read is logged as "failed to load
+      cached source, fetching". It was logged as "source lookup failed".
+    - The proxy's tests moved to `internal/imageproxy`. They reach the cache
+      through its database, its state directory and its metrics registry.
+    - Those tests run the reconciliation pass as pixad does when it starts: with
+      a second cache over the same database and directory.
 - 2026-10-26 both image routes serve an image with one function, `serveImage`,
   and answer its errors with one, `respondImageError` (closes #316).
   `HandleImage` parses the path and verifies the signature, and `HandleImageEnc`

internal/handlers/cache_hit_internal_test.go

@@ -23,6 +23,7 @@ import (
 	"sneak.berlin/go/pixa/internal/database"
 	"sneak.berlin/go/pixa/internal/encurl"
 	"sneak.berlin/go/pixa/internal/imageprocessor"
+	"sneak.berlin/go/pixa/internal/imageproxy"
 	"sneak.berlin/go/pixa/internal/imagerequest"
 	"sneak.berlin/go/pixa/internal/imgcache"
 	"sneak.berlin/go/pixa/internal/seal"
@@ -122,7 +123,7 @@ func newCountingDatabaseServer(
 		tb.Fatalf("encoding the photo: %v", err)
 	}
 
-	cache, err := imgcache.NewCache(db, imgcache.CacheConfig{
+	cache, err := imgcache.NewCache(db, imgcache.Config{
 		StateDir:    tb.TempDir(),
 		NegativeTTL: 5 * time.Minute,
 		MaxBytes:    1 << 30,
@@ -131,7 +132,7 @@ func newCountingDatabaseServer(
 		tb.Fatalf("imgcache.NewCache() error = %v", err)
 	}
 
-	svc, err := imgcache.NewService(&imgcache.ServiceConfig{
+	svc, err := imageproxy.NewProxy(&imageproxy.Config{
 		Cache: cache,
 		Fetcher: newMockFetcher(fstest.MapFS{
 			countingHost + photoPath: &fstest.MapFile{Data: photo.Bytes()},
@@ -142,9 +143,9 @@ func newCountingDatabaseServer(
 		}),
 		MaxResponseSize: 50 << 20,
 		Logger:          slog.New(slog.DiscardHandler),
-	})
+	}, prometheus.NewRegistry())
 	if err != nil {
-		tb.Fatalf("imgcache.NewService() error = %v", err)
+		tb.Fatalf("imageproxy.NewProxy() error = %v", err)
 	}
 
 	keys, err := seal.DeriveKeys(testSigningKey)
@@ -228,9 +229,9 @@ func TestImageRoutes_CacheHitsMakeNoDatabaseCall(t *testing.T) {
 			rec := serveImage(t, srv, target)
 
 			cacheStatus := rec.Header().Get("X-Pixa-Cache")
-			if cacheStatus != string(imgcache.CacheHit) {
+			if cacheStatus != string(imageproxy.CacheHit) {
 				t.Errorf("GET %s: X-Pixa-Cache = %q, want %s",
-					target, cacheStatus, imgcache.CacheHit)
+					target, cacheStatus, imageproxy.CacheHit)
 			}
 		}
 
@@ -260,9 +261,9 @@ func BenchmarkHandleImage_CacheHits(b *testing.B) {
 			rec := serveImage(b, srv, target)
 
 			cacheStatus := rec.Header().Get("X-Pixa-Cache")
-			if cacheStatus != string(imgcache.CacheHit) {
+			if cacheStatus != string(imageproxy.CacheHit) {
 				b.Errorf("GET %s: X-Pixa-Cache = %q, want %s",
-					target, cacheStatus, imgcache.CacheHit)
+					target, cacheStatus, imageproxy.CacheHit)
 
 				return
 			}

internal/handlers/first_bytes_internal_test.go

@@ -17,6 +17,7 @@ import (
 	"sneak.berlin/go/pixa/internal/encurl"
 	"sneak.berlin/go/pixa/internal/httpfetcher"
 	"sneak.berlin/go/pixa/internal/imageprocessor"
+	"sneak.berlin/go/pixa/internal/imageproxy"
 	"sneak.berlin/go/pixa/internal/imagerequest"
 	"sneak.berlin/go/pixa/internal/imgcache"
 	"sneak.berlin/go/pixa/internal/seal"
@@ -38,7 +39,7 @@ func newRoutesFetchingThrough(
 ) (*Handlers, http.Handler) {
 	t.Helper()
 
-	cache, err := imgcache.NewCache(setupTestDB(t), imgcache.CacheConfig{
+	cache, err := imgcache.NewCache(setupTestDB(t), imgcache.Config{
 		StateDir:    t.TempDir(),
 		NegativeTTL: 5 * time.Minute,
 		MaxBytes:    1 << 30,
@@ -47,7 +48,7 @@ func newRoutesFetchingThrough(
 		t.Fatalf("imgcache.NewCache() error = %v", err)
 	}
 
-	svc, err := imgcache.NewService(&imgcache.ServiceConfig{
+	svc, err := imageproxy.NewProxy(&imageproxy.Config{
 		Cache:   cache,
 		Fetcher: fetcher,
 		Processor: imageprocessor.New(imageprocessor.Params{
@@ -56,9 +57,9 @@ func newRoutesFetchingThrough(
 		}),
 		MaxResponseSize: 50 << 20,
 		Logger:          log,
-	})
+	}, prometheus.NewRegistry())
 	if err != nil {
-		t.Fatalf("imgcache.NewService() error = %v", err)
+		t.Fatalf("imageproxy.NewProxy() error = %v", err)
 	}
 
 	keys, err := seal.DeriveKeys(testSigningKey)

internal/handlers/handlers.go

@@ -13,7 +13,7 @@ import (
 	"sneak.berlin/go/pixa/internal/config"
 	"sneak.berlin/go/pixa/internal/encurl"
 	"sneak.berlin/go/pixa/internal/healthcheck"
-	"sneak.berlin/go/pixa/internal/imgcache"
+	"sneak.berlin/go/pixa/internal/imageproxy"
 	"sneak.berlin/go/pixa/internal/logger"
 	"sneak.berlin/go/pixa/internal/seal"
 	"sneak.berlin/go/pixa/internal/session"
@@ -29,7 +29,7 @@ type Params struct {
 	Config      *config.Config
 	Keys        seal.Keys
 
-	ImageService          *imgcache.Service
+	ImageService          *imageproxy.Proxy
 	SessionManager        *session.Manager
 	EncryptedURLGenerator *encurl.Generator
 }
@@ -39,7 +39,7 @@ type Handlers struct {
 	log         *slog.Logger
 	hc          *healthcheck.Healthcheck
 	config      *config.Config
-	imgSvc      *imgcache.Service
+	imgSvc      *imageproxy.Proxy
 	sessMgr     *session.Manager
 	encGen      *encurl.Generator
 	csrfProtect func(http.Handler) http.Handler

internal/handlers/handlers_internal_test.go

@@ -23,6 +23,7 @@ import (
 	"sneak.berlin/go/pixa/internal/database"
 	"sneak.berlin/go/pixa/internal/httpfetcher"
 	"sneak.berlin/go/pixa/internal/imageprocessor"
+	"sneak.berlin/go/pixa/internal/imageproxy"
 	"sneak.berlin/go/pixa/internal/imagerequest"
 	"sneak.berlin/go/pixa/internal/imgcache"
 	"sneak.berlin/go/pixa/internal/signature"
@@ -49,7 +50,7 @@ func setupTestHandler(t *testing.T) *testFixtures {
 	tmpDir := t.TempDir()
 	db := setupTestDB(t)
 
-	cache, err := imgcache.NewCache(db, imgcache.CacheConfig{
+	cache, err := imgcache.NewCache(db, imgcache.Config{
 		StateDir:    tmpDir,
 		NegativeTTL: 5 * time.Minute,
 		MaxBytes:    1 << 30,
@@ -58,7 +59,7 @@ func setupTestHandler(t *testing.T) *testFixtures {
 		t.Fatalf("failed to create cache: %v", err)
 	}
 
-	svc, err := imgcache.NewService(&imgcache.ServiceConfig{
+	svc, err := imageproxy.NewProxy(&imageproxy.Config{
 		Cache:   cache,
 		Fetcher: newMockFetcher(mockFS),
 		Processor: imageprocessor.New(imageprocessor.Params{
@@ -66,9 +67,9 @@ func setupTestHandler(t *testing.T) *testFixtures {
 			MaxConcurrentProcessing: 2,
 		}),
 		MaxResponseSize: 50 << 20,
-	})
+	}, prometheus.NewRegistry())
 	if err != nil {
-		t.Fatalf("failed to create service: %v", err)
+		t.Fatalf("failed to create proxy: %v", err)
 	}
 
 	h := &Handlers{

internal/handlers/image.go

@@ -14,8 +14,8 @@ import (
 	"sneak.berlin/go/pixa/internal/encurl"
 	"sneak.berlin/go/pixa/internal/httpfetcher"
 	"sneak.berlin/go/pixa/internal/imageprocessor"
+	"sneak.berlin/go/pixa/internal/imageproxy"
 	"sneak.berlin/go/pixa/internal/imagerequest"
-	"sneak.berlin/go/pixa/internal/imgcache"
 	"sneak.berlin/go/pixa/internal/magic"
 )
 
@@ -253,7 +253,7 @@ func (s *Handlers) respondImageError(
 		status, message = http.StatusGatewayTimeout, "upstream timeout"
 	case errors.Is(err, httpfetcher.ErrTooManyConnections),
 		errors.Is(err, imageprocessor.ErrTooManyImages),
-		errors.Is(err, imgcache.ErrProcessingTimedOut):
+		errors.Is(err, imageproxy.ErrProcessingTimedOut):
 		status = http.StatusServiceUnavailable
 		message = "server busy, try again later"
 	case errors.Is(err, httpfetcher.ErrInvalidContentType),

internal/handlers/image_cache_control_internal_test.go

@@ -17,6 +17,7 @@ import (
 	"sneak.berlin/go/pixa/internal/allowlist"
 	"sneak.berlin/go/pixa/internal/encurl"
 	"sneak.berlin/go/pixa/internal/imageprocessor"
+	"sneak.berlin/go/pixa/internal/imageproxy"
 	"sneak.berlin/go/pixa/internal/imagerequest"
 	"sneak.berlin/go/pixa/internal/imgcache"
 	"sneak.berlin/go/pixa/internal/seal"
@@ -35,7 +36,7 @@ func newSignedHostServer(
 ) (*Handlers, http.Handler) {
 	t.Helper()
 
-	cache, err := imgcache.NewCache(setupTestDB(t), imgcache.CacheConfig{
+	cache, err := imgcache.NewCache(setupTestDB(t), imgcache.Config{
 		StateDir:    t.TempDir(),
 		NegativeTTL: 5 * time.Minute,
 		MaxBytes:    1 << 30,
@@ -46,7 +47,7 @@ func newSignedHostServer(
 
 	jpegData := generateTestJPEG(t, 100, 100, color.RGBA{255, 0, 0, 255})
 
-	svc, err := imgcache.NewService(&imgcache.ServiceConfig{
+	svc, err := imageproxy.NewProxy(&imageproxy.Config{
 		Cache: cache,
 		Fetcher: newMockFetcher(fstest.MapFS{
 			signedHost + photoPath: &fstest.MapFile{Data: jpegData},
@@ -57,9 +58,9 @@ func newSignedHostServer(
 		}),
 		MaxResponseSize: 50 << 20,
 		Logger:          log,
-	})
+	}, prometheus.NewRegistry())
 	if err != nil {
-		t.Fatalf("imgcache.NewService() error = %v", err)
+		t.Fatalf("imageproxy.NewProxy() error = %v", err)
 	}
 
 	keys, err := seal.DeriveKeys(testSigningKey)

internal/handlers/image_errors_internal_test.go

@@ -22,6 +22,7 @@ import (
 	"sneak.berlin/go/pixa/internal/allowlist"
 	"sneak.berlin/go/pixa/internal/httpfetcher"
 	"sneak.berlin/go/pixa/internal/imageprocessor"
+	"sneak.berlin/go/pixa/internal/imageproxy"
 	"sneak.berlin/go/pixa/internal/imagerequest"
 	"sneak.berlin/go/pixa/internal/imgcache"
 	"sneak.berlin/go/pixa/internal/signature"
@@ -36,7 +37,7 @@ const allowlistedHost = "allowed.example.com"
 func newImageRoute(t *testing.T, fetcher httpfetcher.Fetcher) http.Handler {
 	t.Helper()
 
-	cache, err := imgcache.NewCache(setupTestDB(t), imgcache.CacheConfig{
+	cache, err := imgcache.NewCache(setupTestDB(t), imgcache.Config{
 		StateDir:    t.TempDir(),
 		NegativeTTL: 5 * time.Minute,
 		MaxBytes:    1 << 30,
@@ -45,7 +46,7 @@ func newImageRoute(t *testing.T, fetcher httpfetcher.Fetcher) http.Handler {
 		t.Fatalf("failed to create cache: %v", err)
 	}
 
-	svc, err := imgcache.NewService(&imgcache.ServiceConfig{
+	svc, err := imageproxy.NewProxy(&imageproxy.Config{
 		Cache:   cache,
 		Fetcher: fetcher,
 		Processor: imageprocessor.New(imageprocessor.Params{
@@ -53,9 +54,9 @@ func newImageRoute(t *testing.T, fetcher httpfetcher.Fetcher) http.Handler {
 			MaxConcurrentProcessing: 2,
 		}),
 		MaxResponseSize: 50 << 20,
-	})
+	}, prometheus.NewRegistry())
 	if err != nil {
-		t.Fatalf("failed to create service: %v", err)
+		t.Fatalf("failed to create proxy: %v", err)
 	}
 
 	h := &Handlers{

internal/handlers/referer_blocklist_internal_test.go

@@ -15,6 +15,7 @@ import (
 	"sneak.berlin/go/pixa/internal/encurl"
 	"sneak.berlin/go/pixa/internal/httpfetcher"
 	"sneak.berlin/go/pixa/internal/imageprocessor"
+	"sneak.berlin/go/pixa/internal/imageproxy"
 	"sneak.berlin/go/pixa/internal/imagerequest"
 	"sneak.berlin/go/pixa/internal/imgcache"
 	"sneak.berlin/go/pixa/internal/seal"
@@ -52,7 +53,7 @@ func newRefererRoutes(t *testing.T) (http.Handler, *Handlers, *countingFetcher)
 		Fetcher: newPhotoFetcher(t, allowlistedHost, signedHost),
 	}
 
-	cache, err := imgcache.NewCache(setupTestDB(t), imgcache.CacheConfig{
+	cache, err := imgcache.NewCache(setupTestDB(t), imgcache.Config{
 		StateDir:    t.TempDir(),
 		NegativeTTL: 5 * time.Minute,
 		MaxBytes:    1 << 30,
@@ -61,7 +62,7 @@ func newRefererRoutes(t *testing.T) (http.Handler, *Handlers, *countingFetcher)
 		t.Fatalf("imgcache.NewCache() error = %v", err)
 	}
 
-	svc, err := imgcache.NewService(&imgcache.ServiceConfig{
+	svc, err := imageproxy.NewProxy(&imageproxy.Config{
 		Cache:   cache,
 		Fetcher: fetcher,
 		Processor: imageprocessor.New(imageprocessor.Params{
@@ -69,9 +70,9 @@ func newRefererRoutes(t *testing.T) (http.Handler, *Handlers, *countingFetcher)
 			MaxConcurrentProcessing: 2,
 		}),
 		MaxResponseSize: 50 << 20,
-	})
+	}, prometheus.NewRegistry())
 	if err != nil {
-		t.Fatalf("imgcache.NewService() error = %v", err)
+		t.Fatalf("imageproxy.NewProxy() error = %v", err)
 	}
 
 	keys, err := seal.DeriveKeys(testSigningKey)

internal/handlers/server_busy_internal_test.go

@@ -11,8 +11,8 @@ import (
 
 	"sneak.berlin/go/pixa/internal/httpfetcher"
 	"sneak.berlin/go/pixa/internal/imageprocessor"
+	"sneak.berlin/go/pixa/internal/imageproxy"
 	"sneak.berlin/go/pixa/internal/imagerequest"
-	"sneak.berlin/go/pixa/internal/imgcache"
 )
 
 // TestServerBusyAnswers503 checks that respondImageError, which answers the
@@ -58,7 +58,7 @@ func TestProcessingTimedOutAnswers503(t *testing.T) {
 
 	h := &Handlers{log: slog.New(slog.DiscardHandler)}
 	err := fmt.Errorf("%w: failed to encode: %w",
-		imgcache.ErrProcessingTimedOut, context.DeadlineExceeded)
+		imageproxy.ErrProcessingTimedOut, context.DeadlineExceeded)
 
 	rec := httptest.NewRecorder()
 	h.respondImageError(rec, &imagerequest.Request{}, err)

internal/imageproxy/cache_hit_internal_test.go

@@ -0,0 +1,100 @@
+package imageproxy
+
+import (
+	"bytes"
+	"os"
+	"testing"
+	"time"
+
+	"sneak.berlin/go/pixa/internal/imagerequest"
+	"sneak.berlin/go/pixa/internal/imgcache"
+)
+
+// TestProxy_Get_MakesAgainVariantOfNoOutputFormat replaces a cached
+// variant's file with text, and checks that the next request is a miss
+// answered with the variant made again, and the one after a hit.
+func TestProxy_Get_MakesAgainVariantOfNoOutputFormat(t *testing.T) {
+	t.Parallel()
+
+	svc, fixtures := setupTestProxy(t)
+	req := photoVariant(fixtures, 85, imagerequest.FitCover)
+
+	want, _ := getImage(t, svc, req)
+
+	path := variantFilePath(svc, imagerequest.CacheKey(req))
+
+	err := os.WriteFile(path, []byte("this is text, not an image"),
+		imgcache.StorageFilePerm)
+	if err != nil {
+		t.Fatalf("replacing the variant file: %v", err)
+	}
+
+	got, status := getImage(t, svc, req)
+	t.Logf("after the replacement: %d bytes, %s", len(got), status)
+
+	if status != CacheMiss || !bytes.Equal(got, want) {
+		t.Errorf("after the replacement: Get() = %d bytes, %s; want the %d bytes "+
+			"made again, %s", len(got), status, len(want), CacheMiss)
+	}
+
+	got, status = getImage(t, svc, req)
+
+	if status != CacheHit || !bytes.Equal(got, want) {
+		t.Errorf("next request: Get() = %d bytes, %s; want the %d bytes, %s",
+			len(got), status, len(want), CacheHit)
+	}
+}
+
+// TestProxy_Get_HitWaitsForNoDatabaseWrite holds the database's one
+// connection while a cached variant is requested. The hit must be answered
+// while the connection is still held, and its access time must reach the
+// database once it is free.
+func TestProxy_Get_HitWaitsForNoDatabaseWrite(t *testing.T) {
+	t.Parallel()
+
+	svc, fixtures := setupTestProxy(t)
+	req := photoVariant(fixtures, 85, imagerequest.FitCover)
+	key := imagerequest.CacheKey(req)
+
+	getImage(t, svc, req)
+
+	// Each connection to an in-memory SQLite database opens a new, empty one,
+	// so the goroutine that writes the access times must share the
+	// connection that holds the schema.
+	svc.db.SetMaxOpenConns(1)
+	svc.cache.StartPendingAccessTimeWrites()
+
+	defer func() { _ = svc.cache.StopPendingAccessTimeWrites(t.Context()) }()
+
+	anHourAgo := time.Now().Add(-time.Hour)
+	setVariantLastAccessed(t, svc.db, key, anHourAgo)
+
+	releaseDatabase := holdDatabase(t, svc.db)
+	defer releaseDatabase()
+
+	results := startGet(t.Context(), svc, req)
+
+	select {
+	case got := <-results:
+		if got.err != nil {
+			t.Fatalf("Get() of the cached variant error = %v", got.err)
+		}
+	case <-time.After(pendingAccessTimesWait):
+		t.Fatal("the cache hit waited for the database")
+	}
+
+	releaseDatabase()
+
+	deadline := time.Now().Add(pendingAccessTimesWait)
+
+	for countRows(t, svc.db, `
+		SELECT COUNT(*) FROM variant_content
+		WHERE cache_key = ? AND last_accessed_at > ?
+	`, string(key), anHourAgo.UTC().Format(sqliteTimestampFormat)) == 0 {
+		if time.Now().After(deadline) {
+			t.Fatal("the hit's access time was not written")
+		}
+
+		time.Sleep(10 * time.Millisecond)
+	}
+}

internal/imageproxy/concurrent_misses_internal_test.go

@@ -1,4 +1,4 @@
-package imgcache
+package imageproxy
 
 import (
 	"bytes"
@@ -56,15 +56,15 @@ func (f *heldFetcher) releaseFetches() {
 	f.releaseOnce.Do(func() { close(f.release) })
 }
 
-// setupHeldFetchService returns a test service whose fetches go through a
+// setupHeldFetchProxy returns a test proxy whose fetches go through a
 // heldFetcher. Its database is limited to one connection: each connection to
 // an in-memory SQLite database opens a new, empty one, so requests running at
 // once must share the connection that holds the schema.
-func setupHeldFetchService(t *testing.T) (*Service, *TestFixtures, *heldFetcher) {
+func setupHeldFetchProxy(t *testing.T) (*testProxy, *TestFixtures, *heldFetcher) {
 	t.Helper()
 
-	svc, fixtures := SetupTestService(t)
-	svc.cache.db.SetMaxOpenConns(1)
+	svc, fixtures := setupTestProxy(t)
+	svc.db.SetMaxOpenConns(1)
 
 	fetcher := &heldFetcher{
 		upstream: svc.fetcher,
@@ -107,7 +107,7 @@ type getResult struct {
 // startGet calls Get in a goroutine of its own and delivers what it returned
 // on the channel.
 func startGet(
-	ctx context.Context, svc *Service, req *imagerequest.Request,
+	ctx context.Context, svc *testProxy, req *imagerequest.Request,
 ) <-chan getResult {
 	results := make(chan getResult, 1)
 
@@ -139,14 +139,14 @@ func jpegSize(data []byte) (int, int) {
 	return config.Width, config.Height
 }
 
-// TestService_Get_ConcurrentMissesShareOneFetch starts several requests for
+// TestProxy_Get_ConcurrentMissesShareOneFetch starts several requests for
 // one uncached variant while the first one's fetch is held. Between them they
 // must fetch the source once and transcode it once, every one must be answered
 // with the same 50x25 JPEG, and each must count one miss.
-func TestService_Get_ConcurrentMissesShareOneFetch(t *testing.T) {
+func TestProxy_Get_ConcurrentMissesShareOneFetch(t *testing.T) {
 	t.Parallel()
 
-	svc, fixtures, fetcher := setupHeldFetchService(t)
+	svc, fixtures, fetcher := setupHeldFetchProxy(t)
 
 	const requests = 8
 
@@ -183,7 +183,7 @@ func TestService_Get_ConcurrentMissesShareOneFetch(t *testing.T) {
 		t.Errorf("%d requests made %d upstream fetches, want 1", requests, fetches)
 	}
 
-	// NewTestFS builds the same files the test service's fetcher serves.
+	// NewTestFS builds the same files the test proxy's fetcher serves.
 	testFS, _ := NewTestFS(t)
 
 	photo, err := fs.ReadFile(testFS, fixtures.GoodHostJPEG)
@@ -193,18 +193,18 @@ func TestService_Get_ConcurrentMissesShareOneFetch(t *testing.T) {
 
 	want := counterValues{0, requests, 1, int64(len(photo)), 1}
 
-	if got := readCounters(svc.cache); got != want {
+	if got := readCounters(t, svc); got != want {
 		t.Errorf("counters = %+v, want %+v", got, want)
 	}
 }
 
-// TestService_Get_ConcurrentVariantsStayApart requests three variants of the
+// TestProxy_Get_ConcurrentVariantsStayApart requests three variants of the
 // test photo at once that differ only in quality or fit. Each must be made by
 // a fetch and a transcode of its own, and each answer must be its own variant.
-func TestService_Get_ConcurrentVariantsStayApart(t *testing.T) {
+func TestProxy_Get_ConcurrentVariantsStayApart(t *testing.T) {
 	t.Parallel()
 
-	svc, fixtures, fetcher := setupHeldFetchService(t)
+	svc, fixtures, fetcher := setupHeldFetchProxy(t)
 
 	cover := startGet(t.Context(), svc, photoVariant(fixtures, 85, imagerequest.FitCover))
 	lowQuality := startGet(t.Context(), svc,
@@ -253,14 +253,14 @@ func TestService_Get_ConcurrentVariantsStayApart(t *testing.T) {
 	}
 }
 
-// TestService_Get_WaiterStopsWhenItsContextEnds has a second request for a
+// TestProxy_Get_WaiterStopsWhenItsContextEnds has a second request for a
 // variant join the first one's held fetch, then ends the second request's
 // context. The second request must return at once with the context's error,
 // while the fetch is still held, and the first must still be answered.
-func TestService_Get_WaiterStopsWhenItsContextEnds(t *testing.T) {
+func TestProxy_Get_WaiterStopsWhenItsContextEnds(t *testing.T) {
 	t.Parallel()
 
-	svc, fixtures, fetcher := setupHeldFetchService(t)
+	svc, fixtures, fetcher := setupHeldFetchProxy(t)
 
 	first := startGet(t.Context(), svc, photoVariant(fixtures, 85, imagerequest.FitCover))
 
@@ -298,15 +298,15 @@ func TestService_Get_WaiterStopsWhenItsContextEnds(t *testing.T) {
 	}
 }
 
-// TestService_Get_FirstRequestLeavingKeepsTheWork ends the context of the
+// TestProxy_Get_FirstRequestLeavingKeepsTheWork ends the context of the
 // request whose fetch is held, after a second request has joined it. The fetch
 // and transcode must go on and answer the second request. The first request
 // waits for its own work, as every request did before misses were shared, and
 // is answered too.
-func TestService_Get_FirstRequestLeavingKeepsTheWork(t *testing.T) {
+func TestProxy_Get_FirstRequestLeavingKeepsTheWork(t *testing.T) {
 	t.Parallel()
 
-	svc, fixtures, fetcher := setupHeldFetchService(t)
+	svc, fixtures, fetcher := setupHeldFetchProxy(t)
 
 	firstCtx, cancelFirst := context.WithCancel(t.Context())
 	first := startGet(firstCtx, svc, photoVariant(fixtures, 85, imagerequest.FitCover))
@@ -337,11 +337,11 @@ func TestService_Get_FirstRequestLeavingKeepsTheWork(t *testing.T) {
 	}
 }
 
-// TestService_Get_ConcurrentMissesShareAFailure has several requests for an
+// TestProxy_Get_ConcurrentMissesShareAFailure has several requests for an
 // image that cannot be served arrive while its fetch is held: the one fetch
 // answers all of them with its error. The request after them is answered from
 // the negative cache, where the failure is kept.
-func TestService_Get_ConcurrentMissesShareAFailure(t *testing.T) {
+func TestProxy_Get_ConcurrentMissesShareAFailure(t *testing.T) {
 	t.Parallel()
 
 	tests := []struct {
@@ -362,7 +362,7 @@ func TestService_Get_ConcurrentMissesShareAFailure(t *testing.T) {
 		t.Run(tc.name, func(t *testing.T) {
 			t.Parallel()
 
-			svc, fixtures, fetcher := setupHeldFetchService(t)
+			svc, fixtures, fetcher := setupHeldFetchProxy(t)
 
 			request := func() *imagerequest.Request {
 				req := photoVariant(fixtures, 85, imagerequest.FitCover)
@@ -398,12 +398,12 @@ func TestService_Get_ConcurrentMissesShareAFailure(t *testing.T) {
 	}
 }
 
-// TestService_Get_EndedRequestFetchesNothing checks that a request whose
+// TestProxy_Get_EndedRequestFetchesNothing checks that a request whose
 // context has already ended when it misses the cache starts no fetch.
-func TestService_Get_EndedRequestFetchesNothing(t *testing.T) {
+func TestProxy_Get_EndedRequestFetchesNothing(t *testing.T) {
 	t.Parallel()
 
-	svc, fixtures, fetcher := setupHeldFetchService(t)
+	svc, fixtures, fetcher := setupHeldFetchProxy(t)
 
 	ctx, cancel := context.WithCancel(t.Context())
 	cancel()
@@ -418,14 +418,14 @@ func TestService_Get_EndedRequestFetchesNothing(t *testing.T) {
 	}
 }
 
-// TestService_Get_ReturnsByItsDeadline gives a request a deadline and holds
+// TestProxy_Get_ReturnsByItsDeadline gives a request a deadline and holds
 // its fetch until the fetch's context ends, as the fetcher does while it waits
 // for a free connection to the host. The request must return by its deadline
 // with the deadline's error.
-func TestService_Get_ReturnsByItsDeadline(t *testing.T) {
+func TestProxy_Get_ReturnsByItsDeadline(t *testing.T) {
 	t.Parallel()
 
-	svc, fixtures, _ := setupHeldFetchService(t)
+	svc, fixtures, _ := setupHeldFetchProxy(t)
 
 	const timeout = 200 * time.Millisecond
 
@@ -444,16 +444,16 @@ func TestService_Get_ReturnsByItsDeadline(t *testing.T) {
 	}
 }
 
-// TestService_Get_WaiterGetsProcessingTimedOut has a request with no deadline
+// TestProxy_Get_WaiterGetsProcessingTimedOut has a request with no deadline
 // join the held fetch of a first request with a short one. With the only
 // processing slot held, the first request's transcode waits for it until the
 // first request's deadline ends, and stops then. The waiting request, whose
 // own context has not ended, must get ErrProcessingTimedOut, which the image
 // routes answer 503 as when pixa is busy.
-func TestService_Get_WaiterGetsProcessingTimedOut(t *testing.T) {
+func TestProxy_Get_WaiterGetsProcessingTimedOut(t *testing.T) {
 	t.Parallel()
 
-	svc, fixtures, fetcher := setupHeldFetchService(t)
+	svc, fixtures, fetcher := setupHeldFetchProxy(t)
 	svc.processor = imageprocessor.New(
 		imageprocessor.Params{MaxInputBytes: 50 << 20, MaxConcurrentProcessing: 1},
 	)
@@ -494,13 +494,13 @@ func (panickingFetcher) Fetch(
 	panic("upstream fetcher panicked")
 }
 
-// TestService_Get_PanicBecomesAnError checks that a panic while a variant is
+// TestProxy_Get_PanicBecomesAnError checks that a panic while a variant is
 // being made reaches its request as an error naming the panic, instead of
 // being raised again.
-func TestService_Get_PanicBecomesAnError(t *testing.T) {
+func TestProxy_Get_PanicBecomesAnError(t *testing.T) {
 	t.Parallel()
 
-	svc, fixtures := SetupTestService(t)
+	svc, fixtures := setupTestProxy(t)
 	svc.fetcher = panickingFetcher{}
 
 	var err error
@@ -520,13 +520,13 @@ func TestService_Get_PanicBecomesAnError(t *testing.T) {
 	}
 }
 
-// TestService_Get_PanicIsReportedToSentry checks that a panic while a variant
+// TestProxy_Get_PanicIsReportedToSentry checks that a panic while a variant
 // is being made is reported through the Sentry hub on the request's context,
 // where the Sentry middleware puts one when sentry_dsn is set.
-func TestService_Get_PanicIsReportedToSentry(t *testing.T) {
+func TestProxy_Get_PanicIsReportedToSentry(t *testing.T) {
 	t.Parallel()
 
-	svc, fixtures := SetupTestService(t)
+	svc, fixtures := setupTestProxy(t)
 	svc.fetcher = panickingFetcher{}
 
 	transport := &sentry.MockTransport{}

internal/imageproxy/counters_internal_test.go

@@ -0,0 +1,78 @@
+package imageproxy
+
+import (
+	"errors"
+	"testing"
+
+	"github.com/prometheus/client_golang/prometheus"
+	"github.com/prometheus/client_golang/prometheus/testutil"
+	"sneak.berlin/go/pixa/internal/imgcache"
+)
+
+// TestNewProxy_RegistersItsCountersOnItsRegistry checks that NewProxy
+// registers the proxy's counters on the registry it is given, under the
+// names README.md gives them. The cache registers its own counters on
+// another registry.
+func TestNewProxy_RegistersItsCountersOnItsRegistry(t *testing.T) {
+	t.Parallel()
+
+	cache, err := imgcache.NewCache(setupTestDB(t),
+		imgcache.Config{StateDir: t.TempDir(), MaxBytes: 1 << 30},
+		prometheus.NewRegistry())
+	if err != nil {
+		t.Fatalf("imgcache.NewCache() error = %v", err)
+	}
+
+	registry := prometheus.NewRegistry()
+
+	_, err = NewProxy(&Config{Cache: cache}, registry)
+	if err != nil {
+		t.Fatalf("NewProxy() error = %v", err)
+	}
+
+	names := []string{
+		"pixa_upstream_fetches_total",
+		"pixa_upstream_fetch_bytes_total",
+		"pixa_transforms_total",
+	}
+
+	count, err := testutil.GatherAndCount(registry, names...)
+	if err != nil {
+		t.Fatalf("testutil.GatherAndCount() error = %v", err)
+	}
+
+	if count != len(names) {
+		t.Errorf("%d of the counters %v are on the registry, want %d",
+			count, names, len(names))
+	}
+}
+
+// TestNewProxy_FailsWhenItsCountersCannotBeRegistered makes a second proxy
+// on the registry of a first. Its counters have the same names, so the
+// registry refuses them, and NewProxy must return that error.
+func TestNewProxy_FailsWhenItsCountersCannotBeRegistered(t *testing.T) {
+	t.Parallel()
+
+	cache, err := imgcache.NewCache(setupTestDB(t),
+		imgcache.Config{StateDir: t.TempDir(), MaxBytes: 1 << 30},
+		prometheus.NewRegistry())
+	if err != nil {
+		t.Fatalf("imgcache.NewCache() error = %v", err)
+	}
+
+	registry := prometheus.NewRegistry()
+
+	_, err = NewProxy(&Config{Cache: cache}, registry)
+	if err != nil {
+		t.Fatalf("NewProxy() of the first proxy error = %v", err)
+	}
+
+	_, err = NewProxy(&Config{Cache: cache}, registry)
+	t.Logf("NewProxy() of the second proxy error = %v", err)
+
+	var alreadyRegistered prometheus.AlreadyRegisteredError
+	if !errors.As(err, &alreadyRegistered) {
+		t.Errorf("NewProxy() of the second proxy error = %v, want %T",
+			err, alreadyRegistered)
+	}
+}

internal/imageproxy/divzero_internal_test.go

@@ -1,4 +1,4 @@
-package imgcache
+package imageproxy
 
 import (
 	"fmt"

internal/imageproxy/imageproxy.go

@@ -1,4 +1,7 @@
-package imgcache
+// Package imageproxy fetches, transforms, caches and serves images. Its
+// Proxy serves an image from the cache when it can, and otherwise makes it
+// from the cached or fetched source image.
+package imageproxy
 
 import (
 	"bytes"
@@ -13,16 +16,18 @@ import (
 	"github.com/dustin/go-humanize"
 	"github.com/getsentry/sentry-go"
 	"github.com/go-chi/chi/v5/middleware"
+	"github.com/prometheus/client_golang/prometheus"
 	"golang.org/x/sync/singleflight"
 	"sneak.berlin/go/pixa/internal/httpfetcher"
 	"sneak.berlin/go/pixa/internal/imageprocessor"
 	"sneak.berlin/go/pixa/internal/imagerequest"
+	"sneak.berlin/go/pixa/internal/imgcache"
 	"sneak.berlin/go/pixa/internal/magic"
 )
 
-// Service orchestrates the cache, fetcher, and processor.
-type Service struct {
-	cache           *Cache
+// Proxy orchestrates the cache, fetcher, and processor.
+type Proxy struct {
+	cache           *imgcache.Cache
 	fetcher         httpfetcher.Fetcher
 	processor       *imageprocessor.ImageProcessor
 	log             *slog.Logger
@@ -30,12 +35,18 @@ type Service struct {
 	// variantsInProgress lets the requests that miss the same variant at the
 	// same time share one fetch and one transcode.
 	variantsInProgress singleflight.Group
+
+	// The counts of upstream fetches and transforms, made and registered by
+	// NewProxy. They are kept in memory, so adding to one waits for nothing.
+	upstreamFetches    prometheus.Counter
+	upstreamFetchBytes prometheus.Counter
+	transforms         prometheus.Counter
 }
 
-// ServiceConfig holds configuration for the image service.
-type ServiceConfig struct {
+// Config holds the proxy's configuration.
+type Config struct {
 	// Cache is the cache instance
-	Cache *Cache
+	Cache *imgcache.Cache
 	// Fetcher fetches source images from upstream hosts
 	Fetcher httpfetcher.Fetcher
 	// Processor converts and resizes the images
@@ -47,11 +58,16 @@ type ServiceConfig struct {
 	Logger *slog.Logger
 }
 
-// errCacheRequired is returned when the service is built without a cache.
+// errCacheRequired is returned when the proxy is built without a cache.
 var errCacheRequired = errors.New("cache is required")
 
-// NewService creates a new image service.
-func NewService(cfg *ServiceConfig) (*Service, error) {
+// NewProxy creates a new image proxy and registers its counters on
+// metricsRegistry. pixad passes Prometheus' default registry, the one
+// /metrics serves. It fails when metricsRegistry already holds counters of
+// the same names.
+func NewProxy(
+	cfg *Config, metricsRegistry prometheus.Registerer,
+) (*Proxy, error) {
 	if cfg.Cache == nil {
 		return nil, errCacheRequired
 	}
@@ -68,13 +84,36 @@ func NewService(cfg *ServiceConfig) (*Service, error) {
 		return nil, err
 	}
 
-	return &Service{
+	p := &Proxy{
 		cache:           cfg.Cache,
 		fetcher:         cfg.Fetcher,
 		processor:       cfg.Processor,
 		log:             log,
 		maxResponseSize: cfg.MaxResponseSize,
-	}, nil
+		upstreamFetches: prometheus.NewCounter(prometheus.CounterOpts{
+			Name: "pixa_upstream_fetches_total",
+			Help: "Fetches of a source image from upstream that read any bytes.",
+		}),
+		upstreamFetchBytes: prometheus.NewCounter(prometheus.CounterOpts{
+			Name: "pixa_upstream_fetch_bytes_total",
+			Help: "Bytes read from upstream by fetches of source images.",
+		}),
+		transforms: prometheus.NewCounter(prometheus.CounterOpts{
+			Name: "pixa_transforms_total",
+			Help: "Images the image processor transformed.",
+		}),
+	}
+
+	for _, counter := range []prometheus.Counter{
+		p.upstreamFetches, p.upstreamFetchBytes, p.transforms,
+	} {
+		err = metricsRegistry.Register(counter)
+		if err != nil {
+			return nil, fmt.Errorf("failed to register the proxy's counters: %w", err)
+		}
+	}
+
+	return p, nil
 }
 
 // ErrNegativeCached is returned when a URL is in the negative cache (recently failed).
@@ -86,25 +125,49 @@ var ErrNegativeCached = errors.New("request is in negative cache (recently faile
 var ErrProcessingTimedOut = errors.New(
 	"image processing stopped at the deadline of the request doing it")
 
+// ImageResponse represents a processed image ready to serve
+type ImageResponse struct {
+	// Content is the image data reader
+	Content io.ReadCloser
+	// ContentLength is the size in bytes (-1 if unknown)
+	ContentLength int64
+	// ContentType is the MIME type of the response
+	ContentType string
+	// ETag is the entity tag for caching
+	ETag string
+	// CacheStatus indicates HIT or MISS
+	CacheStatus CacheStatus
+	// FetchedBytes is the number of bytes fetched from upstream (0 if cache hit)
+	FetchedBytes int64
+}
+
+// CacheStatus indicates whether the response was served from cache.
+type CacheStatus string
+
+// Cache status values for response headers.
+const (
+	CacheHit  CacheStatus = "HIT"
+	CacheMiss CacheStatus = "MISS"
+)
+
 // Get retrieves a processed image, fetching and processing if necessary.
 // While its source URL is in the negative cache, a cached variant is still
 // served and a variant not in the cache is still made from a cached source;
 // only a request that needs the source fetched is refused.
 //
-// A cache hit opens the variant file and makes no database call: its access
-// time is handed to the goroutine that StartPendingAccessTimeWrites starts,
-// without waiting for it, and its hit is counted in memory. A variant file
-// that cannot be served, such as one whose first bytes are not those of an
-// output format, is a miss, and the variant is made again.
-func (s *Service) Get(
+// A cache hit opens the variant file and makes no database call: the cache
+// hands its access time to the goroutine that writes access times, without
+// waiting for it, and its hit is counted in memory. A variant file that
+// cannot be served, such as one whose first bytes are not those of an output
+// format, is a miss, and the variant is made again.
+func (p *Proxy) Get(
 	ctx context.Context, req *imagerequest.Request,
 ) (*ImageResponse, error) {
 	cacheKey := imagerequest.CacheKey(req)
 
-	reader, size, contentType, err := s.cache.GetVariant(cacheKey)
+	reader, size, contentType, err := p.cache.Variant(cacheKey)
 	if err == nil {
-		s.cache.touchVariant(cacheKey)
-		s.cache.IncrementStats(true, 0)
+		p.cache.IncrementStats(true)
 
 		return &ImageResponse{
 			Content:       reader,
@@ -115,17 +178,17 @@ func (s *Service) Get(
 		}, nil
 	}
 
-	if !errors.Is(err, ErrNotFound) {
-		s.log.Warn("cached variant not served, making it again",
+	if !errors.Is(err, imgcache.ErrNotFound) {
+		p.log.Warn("cached variant not served, making it again",
 			"cache_key", cacheKey, "error", err)
 	}
 
 	// Cache miss - get the variant, processed once for all the requests that
 	// miss it at the same time, then count this request's miss, also when it
 	// failed or the request context has ended meanwhile
-	response, err := s.processOrWait(ctx, req)
+	response, err := p.processOrWait(ctx, req)
 
-	s.cache.IncrementStats(false, 0)
+	p.cache.IncrementStats(false)
 
 	if err != nil {
 		return nil, err
@@ -138,8 +201,8 @@ func (s *Service) Get(
 
 // WaitForProcessing waits until no image is being processed, or until ctx
 // ends, and returns how many images were still being processed then.
-func (s *Service) WaitForProcessing(ctx context.Context) int {
-	return s.processor.WaitForProcessing(ctx)
+func (p *Proxy) WaitForProcessing(ctx context.Context) int {
+	return p.processor.WaitForProcessing(ctx)
 }
 
 // errPanicked is returned when processing a variant panicked.
@@ -151,7 +214,7 @@ var errPanicked = errors.New("panic while processing image")
 // and take no upstream connection or processing slot. The processing ignores
 // the first request's cancellation, so the others are still served if that
 // client goes away, but keeps its deadline.
-func (s *Service) processOrWait(
+func (p *Proxy) processOrWait(
 	ctx context.Context, req *imagerequest.Request,
 ) (*ImageResponse, error) {
 	// A request that has already ended starts no processing
@@ -165,7 +228,7 @@ func (s *Service) processOrWait(
 	// only when no other request is processing the variant
 	processing := make(chan struct{})
 
-	results := s.variantsInProgress.DoChan(string(cacheKey),
+	results := p.variantsInProgress.DoChan(string(cacheKey),
 		func() (_ any, err error) {
 			close(processing)
 
@@ -176,7 +239,7 @@ func (s *Service) processOrWait(
 			defer func() {
 				recovered := recover()
 				if recovered != nil {
-					s.log.Error("panic while processing image",
+					p.log.Error("panic while processing image",
 						"host", req.Source.Host, "path", req.Source.Path,
 						"panic", recovered, "stack", string(debug.Stack()))
 
@@ -191,7 +254,7 @@ func (s *Service) processOrWait(
 			processingCtx, cancel := withoutCancelKeepingDeadline(ctx)
 			defer cancel()
 
-			return s.processFromSourceOrFetch(processingCtx, req, cacheKey)
+			return p.processFromSourceOrFetch(processingCtx, req, cacheKey)
 		})
 
 	var result singleflight.Result
@@ -240,25 +303,31 @@ func withoutCancelKeepingDeadline(
 	return context.WithDeadline(context.WithoutCancel(ctx), deadline)
 }
 
-// loadCachedSource opens source content from cache, without reading it, and
-// returns it with its size; nil if the cached data is unavailable, empty or
-// exceeds maxResponseSize.
-func (s *Service) loadCachedSource(
-	sourceKey imagerequest.SourceKey,
+// loadCachedSource opens src's cached source, without reading it, and
+// returns it with its size; nil if it is not in the cache, cannot be read,
+// is empty or exceeds maxResponseSize.
+func (p *Proxy) loadCachedSource(
+	ctx context.Context, src imagerequest.Source,
 ) (io.ReadCloser, int64) {
-	reader, size, err := s.cache.GetSourceContent(sourceKey)
+	reader, size, err := p.cache.Source(ctx, src)
+	if errors.Is(err, imgcache.ErrNotFound) {
+		return nil, 0
+	}
+
 	if err != nil {
-		s.log.Warn("failed to load cached source, fetching", "error", err)
+		p.log.Warn("failed to load cached source, fetching", "error", err)
 
 		return nil, 0
 	}
 
-	if size > s.maxResponseSize {
+	p.log.Debug("using cached source", "source_key", src.Key())
+
+	if size > p.maxResponseSize {
 		_ = reader.Close()
 
-		s.log.Warn("cached source exceeds max response size, discarding",
-			"source_key", sourceKey,
-			"max_bytes", s.maxResponseSize,
+		p.log.Warn("cached source exceeds max response size, discarding",
+			"source_key", src.Key(),
+			"max_bytes", p.maxResponseSize,
 		)
 
 		return nil, 0
@@ -275,30 +344,16 @@ func (s *Service) loadCachedSource(
 
 // processFromSourceOrFetch processes an image, using cached source content
 // if available.
-func (s *Service) processFromSourceOrFetch(
+func (p *Proxy) processFromSourceOrFetch(
 	ctx context.Context,
 	req *imagerequest.Request,
 	cacheKey imagerequest.VariantKey,
 ) (*processedVariant, error) {
-	// Check if we have cached source content
-	sourceKey, err := s.cache.LookupSource(ctx, req)
-	if err != nil {
-		s.log.Warn("source lookup failed", "error", err)
-	}
-
-	var (
-		source     io.ReadCloser
-		sourceSize int64
-	)
-
-	if sourceKey != "" {
-		s.log.Debug("using cached source", "source_key", sourceKey)
-		source, sourceSize = s.loadCachedSource(sourceKey)
-	}
+	source, sourceSize := p.loadCachedSource(ctx, req.Source)
 
 	// Fetch from upstream if we don't have source data or it's empty
 	if source == nil {
-		return s.fetchAndProcess(ctx, req, cacheKey)
+		return p.fetchAndProcess(ctx, req, cacheKey)
 	}
 
 	defer func() { _ = source.Close() }()
@@ -306,26 +361,26 @@ func (s *Service) processFromSourceOrFetch(
 	// Process using cached source; nothing was fetched from upstream. The
 	// image processor reads the source only once it has a processing slot,
 	// so a request waiting for one holds none of it in memory.
-	return s.processAndStore(ctx, req, cacheKey, source, sourceSize)
+	return p.processAndStore(ctx, req, cacheKey, source, sourceSize)
 }
 
 // fetchAndProcess fetches from upstream, processes, and caches the result.
 // It counts the fetch with the bytes read from upstream, including when
 // reading the response or a later step fails. It fetches nothing while the
 // source URL is in the negative cache.
-func (s *Service) fetchAndProcess(
+func (p *Proxy) fetchAndProcess(
 	ctx context.Context,
 	req *imagerequest.Request,
 	cacheKey imagerequest.VariantKey,
 ) (*processedVariant, error) {
 	// Check negative cache - skip fetching for recently-failed URLs
-	negHit, err := s.cache.checkNegativeCache(ctx, req)
+	negHit, err := p.cache.Failure(ctx, req.Source)
 	if err != nil {
-		s.log.Warn("negative cache check failed", "error", err)
+		p.log.Warn("negative cache check failed", "error", err)
 	}
 
 	if negHit {
-		s.log.Debug("negative cache hit",
+		p.log.Debug("negative cache hit",
 			"host", req.Source.Host,
 			"path", req.Source.Path,
 		)
@@ -334,14 +389,14 @@ func (s *Service) fetchAndProcess(
 	}
 
 	// Fetch from upstream
-	s.log.Debug("fetching from upstream", "host", req.Source.Host,
+	p.log.Debug("fetching from upstream", "host", req.Source.Host,
 		"path", req.Source.Path, "query", req.Source.Query)
 
-	fetchResult, err := s.fetcher.Fetch(ctx, req.Source)
+	fetchResult, err := p.fetcher.Fetch(ctx, req.Source)
 	if err != nil {
 		// Store negative cache for certain errors
 		if isNegativeCacheable(err) {
-			s.storeNegative(ctx, req)
+			p.storeNegative(ctx, req)
 		}
 
 		return nil, fmt.Errorf("upstream fetch failed: %w", err)
@@ -358,7 +413,7 @@ func (s *Service) fetchAndProcess(
 	fetchBytes := int64(len(sourceData))
 
 	// Counted also when the request context has ended meanwhile
-	s.cache.IncrementUpstreamFetch(fetchBytes)
+	p.incrementUpstreamFetch(fetchBytes)
 
 	if err != nil {
 		return nil, fmt.Errorf("failed to read upstream response: %w", err)
@@ -374,7 +429,7 @@ func (s *Service) fetchAndProcess(
 	}
 
 	// Log upstream fetch details
-	s.log.Info("upstream fetched",
+	p.log.Info("upstream fetched",
 		"request_id", middleware.GetReqID(ctx),
 		"host", req.Source.Host,
 		"path", req.Source.Path,
@@ -392,33 +447,44 @@ func (s *Service) fetchAndProcess(
 	// error status does.
 	err = magic.ValidateMagicBytes(sourceData, fetchResult.ContentType)
 	if err != nil {
-		s.log.Warn("source refused", "request_id", middleware.GetReqID(ctx),
+		p.log.Warn("source refused", "request_id", middleware.GetReqID(ctx),
 			"host", req.Source.Host, "path", req.Source.Path,
 			"content_type", fetchResult.ContentType, "error", err)
-		s.storeNegative(ctx, req)
+		p.storeNegative(ctx, req)
 
 		return nil, fmt.Errorf("content validation failed: %w", err)
 	}
 
 	// Store source content
-	_, err = s.cache.StoreSource(ctx, req, bytes.NewReader(sourceData))
+	_, err = p.cache.PutSource(ctx, req.Source, bytes.NewReader(sourceData))
 	if err != nil {
-		s.log.Warn("failed to store source content", "error", err)
+		p.log.Warn("failed to store source content", "error", err)
 		// Continue even if caching fails
 	}
 
-	return s.processAndStore(
+	return p.processAndStore(
 		ctx, req, cacheKey, bytes.NewReader(sourceData), fetchBytes,
 	)
 }
 
+// incrementUpstreamFetch counts one upstream fetch that read fetchBytes bytes.
+// A fetch that read no bytes is not counted.
+func (p *Proxy) incrementUpstreamFetch(fetchBytes int64) {
+	if fetchBytes <= 0 {
+		return
+	}
+
+	p.upstreamFetches.Inc()
+	p.upstreamFetchBytes.Add(float64(fetchBytes))
+}
+
 // storeNegative stores a negative cache entry for req's source, whose fetch
 // failed, so the source is not fetched again until the entry expires. A
 // failure to store the entry is only logged.
-func (s *Service) storeNegative(ctx context.Context, req *imagerequest.Request) {
-	err := s.cache.StoreNegative(ctx, req)
+func (p *Proxy) storeNegative(ctx context.Context, req *imagerequest.Request) {
+	err := p.cache.PutFailure(ctx, req.Source)
 	if err != nil {
-		s.log.Warn("failed to store negative cache entry",
+		p.log.Warn("failed to store negative cache entry",
 			"host", req.Source.Host, "path", req.Source.Path, "error", err)
 	}
 }
@@ -433,7 +499,7 @@ type processedVariant struct {
 
 // processAndStore processes the image read from source and stores the
 // result.
-func (s *Service) processAndStore(
+func (p *Proxy) processAndStore(
 	ctx context.Context,
 	req *imagerequest.Request,
 	cacheKey imagerequest.VariantKey,
@@ -445,7 +511,7 @@ func (s *Service) processAndStore(
 
 	// ctx has the deadline of the request doing the processing, which can
 	// end while a request waiting for its image has time left
-	processResult, err := s.processor.Process(ctx, source, &req.Transform)
+	processResult, err := p.processor.Process(ctx, source, &req.Transform)
 	if errors.Is(err, context.DeadlineExceeded) {
 		return nil, fmt.Errorf("%w: %w", ErrProcessingTimedOut, err)
 	}
@@ -457,7 +523,7 @@ func (s *Service) processAndStore(
 	processDuration := time.Since(processStart)
 
 	// Counted also when the request context has ended meanwhile
-	s.cache.IncrementTransformCount()
+	p.transforms.Inc()
 
 	// Read processed content
 	processedData, err := io.ReadAll(processResult.Content)
@@ -476,7 +542,7 @@ func (s *Service) processAndStore(
 		sizePercent = float64(outputSize) / float64(fetchBytes) * 100.0
 	}
 
-	s.log.Info("image converted",
+	p.log.Info("image converted",
 		"request_id", middleware.GetReqID(ctx),
 		"host", req.Source.Host,
 		"path", req.Source.Path,
@@ -495,9 +561,9 @@ func (s *Service) processAndStore(
 	)
 
 	// Store variant to cache
-	err = s.cache.StoreVariant(ctx, cacheKey, bytes.NewReader(processedData))
+	err = p.cache.PutVariant(ctx, cacheKey, bytes.NewReader(processedData))
 	if err != nil {
-		s.log.Warn("failed to store variant", "error", err)
+		p.log.Warn("failed to store variant", "error", err)
 		// Continue even if caching fails
 	}
 

internal/imageproxy/imageproxy_internal_test.go

@@ -1,4 +1,4 @@
-package imgcache
+package imageproxy
 
 import (
 	"context"
@@ -17,10 +17,10 @@ const (
 	testPathUpload = "/uploads/image.jpg"
 )
 
-func TestService_Get_GoodHost(t *testing.T) {
+func TestProxy_Get_GoodHost(t *testing.T) {
 	t.Parallel()
 
-	svc, fixtures := SetupTestService(t)
+	svc, fixtures := setupTestProxy(t)
 	ctx := context.Background()
 
 	req := &imagerequest.Request{
@@ -58,12 +58,12 @@ func TestService_Get_GoodHost(t *testing.T) {
 	}
 }
 
-// TestService_Get_OtherHost checks that the image service serves a second host
-// as it serves GoodHost.
-func TestService_Get_OtherHost(t *testing.T) {
+// TestProxy_Get_OtherHost checks that the proxy serves a second host as it
+// serves GoodHost.
+func TestProxy_Get_OtherHost(t *testing.T) {
 	t.Parallel()
 
-	svc, fixtures := SetupTestService(t)
+	svc, fixtures := setupTestProxy(t)
 	ctx := context.Background()
 
 	req := &imagerequest.Request{
@@ -97,10 +97,10 @@ func TestService_Get_OtherHost(t *testing.T) {
 	}
 }
 
-func TestService_Get_InvalidFile(t *testing.T) {
+func TestProxy_Get_InvalidFile(t *testing.T) {
 	t.Parallel()
 
-	svc, fixtures := SetupTestService(t)
+	svc, fixtures := setupTestProxy(t)
 	ctx := context.Background()
 
 	req := photoVariant(fixtures, 85, imagerequest.FitCover)
@@ -114,10 +114,10 @@ func TestService_Get_InvalidFile(t *testing.T) {
 	}
 }
 
-func TestService_Get_NotFound(t *testing.T) {
+func TestProxy_Get_NotFound(t *testing.T) {
 	t.Parallel()
 
-	svc, fixtures := SetupTestService(t)
+	svc, fixtures := setupTestProxy(t)
 	ctx := context.Background()
 
 	req := photoVariant(fixtures, 85, imagerequest.FitCover)
@@ -130,10 +130,10 @@ func TestService_Get_NotFound(t *testing.T) {
 	}
 }
 
-func TestService_Get_FormatConversion(t *testing.T) {
+func TestProxy_Get_FormatConversion(t *testing.T) {
 	t.Parallel()
 
-	svc, fixtures := SetupTestService(t)
+	svc, fixtures := setupTestProxy(t)
 	ctx := context.Background()
 
 	tests := []struct {
@@ -213,10 +213,10 @@ func TestService_Get_FormatConversion(t *testing.T) {
 	}
 }
 
-func TestService_Get_Caching(t *testing.T) {
+func TestProxy_Get_Caching(t *testing.T) {
 	t.Parallel()
 
-	svc, fixtures := SetupTestService(t)
+	svc, fixtures := setupTestProxy(t)
 	ctx := context.Background()
 
 	req := &imagerequest.Request{
@@ -272,7 +272,7 @@ func TestService_Get_Caching(t *testing.T) {
 	}
 }
 
-// TestService_Get_ServesSourceAndVariantCachedTwoDaysAgo caches a source and
+// TestProxy_Get_ServesSourceAndVariantCachedTwoDaysAgo caches a source and
 // a variant of it and sets back two days every time pixa stored for them.
 // For the source: last_accessed_at in source_content, and the access and
 // modification times of its file. For the variant: last_accessed_at in
@@ -283,10 +283,10 @@ func TestService_Get_Caching(t *testing.T) {
 // Left at the present: 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.
-func TestService_Get_ServesSourceAndVariantCachedTwoDaysAgo(t *testing.T) {
+func TestProxy_Get_ServesSourceAndVariantCachedTwoDaysAgo(t *testing.T) {
 	t.Parallel()
 
-	svc, fixtures := SetupTestService(t)
+	svc, fixtures := setupTestProxy(t)
 	variant := photoVariant(fixtures, 85, imagerequest.FitCover)
 
 	resp, err := svc.Get(t.Context(), variant)
@@ -297,8 +297,8 @@ func TestService_Get_ServesSourceAndVariantCachedTwoDaysAgo(t *testing.T) {
 	_ = resp.Content.Close()
 
 	twoDaysAgo := time.Now().AddDate(0, 0, -2)
-	backdateSource(t, svc.cache, variant, twoDaysAgo)
-	backdateVariant(t, svc.cache, variant, twoDaysAgo)
+	backdateSource(t, svc, variant, twoDaysAgo)
+	backdateVariant(t, svc, variant, twoDaysAgo)
 
 	resp, err = svc.Get(t.Context(), variant)
 	if err != nil {
@@ -320,23 +320,23 @@ func TestService_Get_ServesSourceAndVariantCachedTwoDaysAgo(t *testing.T) {
 
 	_ = resp.Content.Close()
 
-	fetches := readCounters(svc.cache).upstreamFetchCount
+	fetches := readCounters(t, svc).upstreamFetchCount
 	if fetches != 1 {
 		t.Errorf("upstream fetches = %d, want 1", fetches)
 	}
 }
 
 // backdateSource sets every time pixa stored for req's cached source to when,
-// as listed on TestService_Get_ServesSourceAndVariantCachedTwoDaysAgo.
+// as listed on TestProxy_Get_ServesSourceAndVariantCachedTwoDaysAgo.
 func backdateSource(
-	t *testing.T, cache *Cache, req *imagerequest.Request, when time.Time,
+	t *testing.T, svc *testProxy, req *imagerequest.Request, when time.Time,
 ) {
 	t.Helper()
 
 	key := req.Source.Key()
-	setSourceLastAccessed(t, cache, key, when)
+	setSourceLastAccessed(t, svc.db, key, when)
 
-	path := cache.srcContent.keyToPath(key)
+	path := sourceFilePath(svc, key)
 
 	err := os.Chtimes(path, when, when)
 	if err != nil {
@@ -346,16 +346,16 @@ func backdateSource(
 
 // backdateVariant sets every time pixa stored for the cached variant req asks
 // for to when, as listed on
-// TestService_Get_ServesSourceAndVariantCachedTwoDaysAgo.
+// TestProxy_Get_ServesSourceAndVariantCachedTwoDaysAgo.
 func backdateVariant(
-	t *testing.T, cache *Cache, req *imagerequest.Request, when time.Time,
+	t *testing.T, svc *testProxy, req *imagerequest.Request, when time.Time,
 ) {
 	t.Helper()
 
 	key := imagerequest.CacheKey(req)
-	path := cache.variants.keyToPath(key)
+	path := variantFilePath(svc, key)
 
-	setVariantLastAccessed(t, cache, key, when)
+	setVariantLastAccessed(t, svc.db, key, when)
 
 	err := os.Chtimes(path, when, when)
 	if err != nil {
@@ -363,10 +363,10 @@ func backdateVariant(
 	}
 }
 
-func TestService_Get_DifferentSizes(t *testing.T) {
+func TestProxy_Get_DifferentSizes(t *testing.T) {
 	t.Parallel()
 
-	svc, fixtures := SetupTestService(t)
+	svc, fixtures := setupTestProxy(t)
 	ctx := context.Background()
 
 	// Request same image at different sizes
@@ -417,10 +417,10 @@ func TestService_Get_DifferentSizes(t *testing.T) {
 	}
 }
 
-func TestService_Get_ContextCancellation(t *testing.T) {
+func TestProxy_Get_ContextCancellation(t *testing.T) {
 	t.Parallel()
 
-	svc, fixtures := SetupTestService(t)
+	svc, fixtures := setupTestProxy(t)
 
 	ctx, cancel := context.WithCancel(context.Background())
 	cancel() // Cancel immediately
@@ -444,10 +444,10 @@ func TestService_Get_ContextCancellation(t *testing.T) {
 	}
 }
 
-func TestService_Get_ReturnsETag(t *testing.T) {
+func TestProxy_Get_ReturnsETag(t *testing.T) {
 	t.Parallel()
 
-	svc, fixtures := SetupTestService(t)
+	svc, fixtures := setupTestProxy(t)
 	ctx := context.Background()
 
 	req := &imagerequest.Request{
@@ -481,10 +481,10 @@ func TestService_Get_ReturnsETag(t *testing.T) {
 	}
 }
 
-func TestService_Get_ETagConsistency(t *testing.T) {
+func TestProxy_Get_ETagConsistency(t *testing.T) {
 	t.Parallel()
 
-	svc, fixtures := SetupTestService(t)
+	svc, fixtures := setupTestProxy(t)
 	ctx := context.Background()
 
 	req := &imagerequest.Request{
@@ -526,10 +526,10 @@ func TestService_Get_ETagConsistency(t *testing.T) {
 	}
 }
 
-func TestService_Get_DifferentETagsForDifferentContent(t *testing.T) {
+func TestProxy_Get_DifferentETagsForDifferentContent(t *testing.T) {
 	t.Parallel()
 
-	svc, fixtures := SetupTestService(t)
+	svc, fixtures := setupTestProxy(t)
 	ctx := context.Background()
 
 	// Request same image at different sizes - should get different ETags

internal/imageproxy/max_concurrent_processing_internal_test.go

@@ -1,4 +1,4 @@
-package imgcache
+package imageproxy
 
 import (
 	"image/color"
@@ -55,16 +55,16 @@ func holdProcessingSlot(
 	return release
 }
 
-// TestService_Get_WaitsForSlotBeforeReadingCachedSource checks that a
+// TestProxy_Get_WaitsForSlotBeforeReadingCachedSource checks that a
 // request whose source is cached holds none of it while it waits for a
 // processing slot: it reads the cached file only once it has a slot. With
 // the only slot held, a request for a new width of the cached 100x100 photo
 // waits; the cached file is then rewritten as a 100x50 image before the slot
 // is freed, so the request must answer with that image scaled to 40x20.
-func TestService_Get_WaitsForSlotBeforeReadingCachedSource(t *testing.T) {
+func TestProxy_Get_WaitsForSlotBeforeReadingCachedSource(t *testing.T) {
 	t.Parallel()
 
-	svc, fixtures := SetupTestService(t)
+	svc, fixtures := setupTestProxy(t)
 	svc.processor = imageprocessor.New(
 		imageprocessor.Params{MaxInputBytes: 50 << 20, MaxConcurrentProcessing: 1},
 	)
@@ -77,13 +77,15 @@ func TestService_Get_WaitsForSlotBeforeReadingCachedSource(t *testing.T) {
 
 	_ = resp.Content.Close()
 
-	sourceKey, err := svc.cache.LookupSource(t.Context(),
-		widthOnlyRequest(fixtures, 50))
-	if err != nil || sourceKey == "" {
-		t.Fatalf("LookupSource() = %q, %v; want the cached source",
-			sourceKey, err)
+	cachedSource := widthOnlyRequest(fixtures, 50).Source
+
+	reader, _, err := svc.cache.Source(t.Context(), cachedSource)
+	if err != nil {
+		t.Fatalf("Source() error = %v; want the cached source", err)
 	}
 
+	_ = reader.Close()
+
 	release := holdProcessingSlot(t, svc.processor)
 
 	var (
@@ -103,7 +105,7 @@ func TestService_Get_WaitsForSlotBeforeReadingCachedSource(t *testing.T) {
 	// before waiting, it would have read it by now.
 	time.Sleep(100 * time.Millisecond)
 
-	err = os.WriteFile(svc.cache.srcContent.keyToPath(sourceKey),
+	err = os.WriteFile(sourceFilePath(svc, cachedSource.Key()),
 		generateTestJPEG(t, 100, 50, color.RGBA{0, 0, 255, 255}), 0o600)
 	if err != nil {
 		t.Fatalf("failed to rewrite the cached source: %v", err)

internal/imageproxy/negative_cache_internal_test.go

@@ -0,0 +1,96 @@
+package imageproxy
+
+import (
+	"errors"
+	"os"
+	"testing"
+
+	"sneak.berlin/go/pixa/internal/imagerequest"
+)
+
+// TestProxy_Get_ServesCachedVariantOfNegativeCachedURL caches a variant of
+// the test photo, then keeps a failed fetch of the photo's URL in the negative
+// cache, as a failed fetch for another variant does once the source has been
+// evicted. The cached variant is still served, and a variant not in the cache
+// is made from the cached source. Once the source is evicted, a variant not in
+// the cache needs a fetch and is refused.
+func TestProxy_Get_ServesCachedVariantOfNegativeCachedURL(t *testing.T) {
+	t.Parallel()
+
+	svc, fixtures := setupTestProxy(t)
+
+	resp, err := svc.Get(t.Context(), photoVariant(fixtures, 85, imagerequest.FitCover))
+	if err != nil {
+		t.Fatalf("Get() first request error = %v", err)
+	}
+
+	_ = resp.Content.Close()
+
+	err = svc.cache.PutFailure(t.Context(),
+		photoVariant(fixtures, 85, imagerequest.FitCover).Source)
+	if err != nil {
+		t.Fatalf("PutFailure() error = %v", err)
+	}
+
+	resp, err = svc.Get(t.Context(), photoVariant(fixtures, 85, imagerequest.FitCover))
+	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)
+	}
+
+	resp, err = svc.Get(t.Context(), photoVariant(fixtures, 40, imagerequest.FitCover))
+	t.Logf("Get() of a variant made from the cached source: error = %v", err)
+
+	if err != nil {
+		t.Fatalf("Get() of a variant made from the cached source error = %v", err)
+	}
+
+	_ = resp.Content.Close()
+
+	source := photoVariant(fixtures, 85, imagerequest.FitCover).Source
+
+	reader, _, err := svc.cache.Source(t.Context(), source)
+	if err != nil {
+		t.Fatalf("Source() error = %v, want the cached source", err)
+	}
+
+	_ = reader.Close()
+
+	// Evicts the source as the cache's eviction does: its row, then its file
+	_, err = svc.db.ExecContext(t.Context(),
+		`DELETE FROM source_content WHERE source_key = ?`, string(source.Key()))
+	if err != nil {
+		t.Fatalf("deleting the source's row: %v", err)
+	}
+
+	err = os.Remove(sourceFilePath(svc, source.Key()))
+	if err != nil {
+		t.Fatalf("removing the source's file: %v", err)
+	}
+
+	_, err = svc.Get(t.Context(), photoVariant(fixtures, 60, imagerequest.FitCover))
+	t.Logf("Get() of a variant whose source was evicted: error = %v", err)
+
+	if !errors.Is(err, ErrNegativeCached) {
+		t.Errorf("Get() of a variant whose source was evicted error = %v, want %v",
+			err, ErrNegativeCached)
+	}
+}
+
+func TestProxy_Get_ReturnsErrorForNegativeCachedURL(t *testing.T) {
+	t.Parallel()
+
+	// This test verifies that Proxy.Get() checks the negative cache
+	// We can't easily test the full pipeline without vips, but we can
+	// verify the error type
+	err := ErrNegativeCached
+	if !errors.Is(err, ErrNegativeCached) {
+		t.Error("ErrNegativeCached should be identifiable with errors.Is")
+	}
+}

internal/imageproxy/partial_cache_files_internal_test.go

@@ -0,0 +1,273 @@
+package imageproxy
+
+import (
+	"bytes"
+	"errors"
+	"io"
+	"io/fs"
+	"log/slog"
+	"os"
+	"path/filepath"
+	"strings"
+	"testing"
+	"time"
+
+	"github.com/prometheus/client_golang/prometheus"
+	"sneak.berlin/go/pixa/internal/imagerequest"
+	"sneak.berlin/go/pixa/internal/imgcache"
+)
+
+// getImage calls Get for req and returns the image it answered with and
+// its cache status.
+func getImage(
+	t *testing.T, svc *testProxy, req *imagerequest.Request,
+) ([]byte, CacheStatus) {
+	t.Helper()
+
+	resp, err := svc.Get(t.Context(), req)
+	if err != nil {
+		t.Fatalf("Get() of quality %d error = %v", req.Transform.Quality, err)
+	}
+
+	defer func() { _ = resp.Content.Close() }()
+
+	body, err := io.ReadAll(resp.Content)
+	if err != nil {
+		t.Fatalf("reading the image of quality %d: %v", req.Transform.Quality, err)
+	}
+
+	return body, resp.CacheStatus
+}
+
+// fileSize returns the size of the file at path.
+func fileSize(t *testing.T, path string) int64 {
+	t.Helper()
+
+	info, err := os.Stat(path)
+	if err != nil {
+		t.Fatalf("stat %s: %v", path, err)
+	}
+
+	return info.Size()
+}
+
+// truncateFile cuts the file at path down to size bytes.
+func truncateFile(t *testing.T, path string, size int64) {
+	t.Helper()
+
+	t.Logf("cutting %s from %d to %d bytes",
+		filepath.Base(path), fileSize(t, path), size)
+
+	err := os.Truncate(path, size)
+	if err != nil {
+		t.Fatalf("truncating %s: %v", path, err)
+	}
+}
+
+// cachedSourcePath returns the path of the cached source file req uses.
+func cachedSourcePath(
+	t *testing.T, svc *testProxy, req *imagerequest.Request,
+) string {
+	t.Helper()
+
+	reader, _, err := svc.cache.Source(t.Context(), req.Source)
+	if err != nil {
+		t.Fatalf("Source() error = %v; want the cached source", err)
+	}
+
+	_ = reader.Close()
+
+	return sourceFilePath(svc, req.Source.Key())
+}
+
+// reconcileAsAtStartup runs the reconciliation pass of a second cache over
+// the database and the state directory of svc's cache, as pixad does when it
+// starts. It waits for the pass to remove the file at path, stops the second
+// cache, and returns what that cache logged.
+//
+// The database is limited to one connection, the one that holds the
+// in-memory schema. A statement cancelled while it runs can close that
+// connection, and the database with it. The test therefore takes the
+// connection before it stops the second cache, so that the stop only cancels
+// a wait for the connection.
+func reconcileAsAtStartup(t *testing.T, svc *testProxy, path string) string {
+	t.Helper()
+
+	var logBuf bytes.Buffer
+
+	cache, err := imgcache.NewCache(svc.db, imgcache.Config{
+		StateDir: svc.stateDir,
+		MaxBytes: 1 << 30,
+		Logger:   slog.New(slog.NewJSONHandler(&logBuf, nil)),
+	}, prometheus.NewRegistry())
+	if err != nil {
+		t.Fatalf("failed to create the second cache: %v", err)
+	}
+
+	svc.db.SetMaxOpenConns(1)
+	cache.StartEviction(imgcache.DefaultEvictionInterval)
+
+	deadline := time.Now().Add(5 * time.Second)
+
+	_, statErr := os.Stat(path)
+	for statErr == nil && time.Now().Before(deadline) {
+		time.Sleep(10 * time.Millisecond)
+
+		_, statErr = os.Stat(path)
+	}
+
+	releaseDatabase := holdDatabase(t, svc.db)
+	err = cache.StopEviction(t.Context())
+
+	releaseDatabase()
+
+	if err != nil {
+		t.Fatalf("StopEviction() error = %v", err)
+	}
+
+	t.Logf("reconciliation log: %s", logBuf.String())
+
+	if !errors.Is(statErr, fs.ErrNotExist) {
+		t.Fatalf("the reconciliation pass did not remove %s: %v", path, statErr)
+	}
+
+	return logBuf.String()
+}
+
+// assertWarningNames checks that logs hold a warning naming the file at
+// path.
+func assertWarningNames(t *testing.T, logs, path string) {
+	t.Helper()
+
+	for line := range strings.Lines(logs) {
+		if strings.Contains(line, `"level":"WARN"`) &&
+			strings.Contains(line, `"path":"`+path+`"`) {
+			return
+		}
+	}
+
+	t.Errorf("reconciliation logged no warning naming %s", path)
+}
+
+// TestProxy_Get_FetchesAgainForEmptyCachedSource empties the cached source
+// file, as a crash or a restored snapshot could, and runs the reconciliation
+// pass, which must remove it with a warning naming it. It then asks for two
+// new sizes of the source: the first must fetch it again and cache it whole,
+// so that the second is made from the cache without a third fetch.
+func TestProxy_Get_FetchesAgainForEmptyCachedSource(t *testing.T) {
+	t.Parallel()
+
+	svc, fixtures := setupTestProxy(t)
+
+	getImage(t, svc, photoVariant(fixtures, 85, imagerequest.FitCover))
+
+	path := cachedSourcePath(t, svc, photoVariant(fixtures, 85, imagerequest.FitCover))
+	wholeSize := fileSize(t, path)
+
+	truncateFile(t, path, 0)
+	assertWarningNames(t, reconcileAsAtStartup(t, svc, path), path)
+
+	getImage(t, svc, photoVariant(fixtures, 40, imagerequest.FitCover))
+	getImage(t, svc, photoVariant(fixtures, 30, imagerequest.FitCover))
+
+	fetches := readCounters(t, svc).upstreamFetchCount
+	t.Logf("upstream fetches = %d", fetches)
+
+	if fetches != 2 {
+		t.Errorf("upstream fetches = %d, want 2: the empty cached source "+
+			"was kept and fetched again on every new size", fetches)
+	}
+
+	size := fileSize(t, path)
+	if size != wholeSize {
+		t.Errorf("cached source is %d bytes, want %d", size, wholeSize)
+	}
+}
+
+// TestProxy_Get_FetchesAgainForPartialCachedSource cuts the cached source
+// file to half its size, as a crash or a restored snapshot could, and runs
+// the reconciliation pass, which must remove it with a warning naming it.
+// It then asks for two new sizes of the source: the first must fetch it
+// again rather than fail to decode the partial file, and the second is
+// made from the cache.
+func TestProxy_Get_FetchesAgainForPartialCachedSource(t *testing.T) {
+	t.Parallel()
+
+	svc, fixtures := setupTestProxy(t)
+
+	getImage(t, svc, photoVariant(fixtures, 85, imagerequest.FitCover))
+
+	path := cachedSourcePath(t, svc, photoVariant(fixtures, 85, imagerequest.FitCover))
+	wholeSize := fileSize(t, path)
+
+	truncateFile(t, path, wholeSize/2)
+	assertWarningNames(t, reconcileAsAtStartup(t, svc, path), path)
+
+	getImage(t, svc, photoVariant(fixtures, 40, imagerequest.FitCover))
+	getImage(t, svc, photoVariant(fixtures, 30, imagerequest.FitCover))
+
+	fetches := readCounters(t, svc).upstreamFetchCount
+	t.Logf("upstream fetches = %d", fetches)
+
+	if fetches != 2 {
+		t.Errorf("upstream fetches = %d, want 2", fetches)
+	}
+
+	size := fileSize(t, path)
+	if size != wholeSize {
+		t.Errorf("cached source is %d bytes, want %d", size, wholeSize)
+	}
+}
+
+// assertConvertedAgain caches a variant of the photo, cuts its file to size
+// bytes and runs the reconciliation pass, which must remove it with a
+// warning naming it. It then checks that Get converts the image again
+// instead of serving the file, and that the next Get serves the whole
+// variant from the cache.
+func assertConvertedAgain(t *testing.T, size int64) {
+	t.Helper()
+
+	svc, fixtures := setupTestProxy(t)
+	req := photoVariant(fixtures, 85, imagerequest.FitCover)
+
+	want, _ := getImage(t, svc, req)
+
+	path := variantFilePath(svc, imagerequest.CacheKey(req))
+
+	truncateFile(t, path, size)
+	assertWarningNames(t, reconcileAsAtStartup(t, svc, path), path)
+
+	got, status := getImage(t, svc, req)
+	t.Logf("after the cut: %d bytes, %s", len(got), status)
+
+	if status != CacheMiss || !bytes.Equal(got, want) {
+		t.Errorf("after the cut: Get() = %d bytes, %s; want the %d bytes "+
+			"converted again, %s", len(got), status, len(want), CacheMiss)
+	}
+
+	got, status = getImage(t, svc, req)
+	t.Logf("next request: %d bytes, %s", len(got), status)
+
+	if status != CacheHit || !bytes.Equal(got, want) {
+		t.Errorf("next request: Get() = %d bytes, %s; want the %d bytes, %s",
+			len(got), status, len(want), CacheHit)
+	}
+}
+
+// TestProxy_Get_ConvertsAgainForEmptyCachedVariant empties a cached
+// variant file, as a crash or a restored snapshot could, and checks that it
+// is converted again rather than served empty.
+func TestProxy_Get_ConvertsAgainForEmptyCachedVariant(t *testing.T) {
+	t.Parallel()
+
+	assertConvertedAgain(t, 0)
+}
+
+// TestProxy_Get_ConvertsAgainForPartialCachedVariant cuts a cached
+// variant file to ten bytes, as a crash or a restored snapshot could, and
+// checks that it is converted again rather than served cut short.
+func TestProxy_Get_ConvertsAgainForPartialCachedVariant(t *testing.T) {
+	t.Parallel()
+
+	assertConvertedAgain(t, 10)
+}

internal/imageproxy/pendingaccesstimes_internal_test.go

@@ -0,0 +1,78 @@
+package imageproxy
+
+import (
+	"context"
+	"database/sql"
+	"errors"
+	"testing"
+	"time"
+
+	"sneak.berlin/go/pixa/internal/imagerequest"
+)
+
+// pendingAccessTimesWait is how long a test waits for the database's
+// connection, for a cache hit to be answered, for an access time to reach
+// the database, or for a request to return past its deadline.
+const pendingAccessTimesWait = 5 * time.Second
+
+// holdDatabase takes the one connection of db, so that every other query
+// waits for it, and returns the func that frees it.
+func holdDatabase(t *testing.T, db *sql.DB) func() {
+	t.Helper()
+
+	ctx, cancel := context.WithTimeout(t.Context(), pendingAccessTimesWait)
+	defer cancel()
+
+	conn, err := db.Conn(ctx)
+	if err != nil {
+		t.Fatalf("failed to take the database connection: %v", err)
+	}
+
+	return func() { _ = conn.Close() }
+}
+
+// TestProxy_Get_ReturnsByItsDeadlineWhileTheDatabaseIsBusy holds the
+// database's one connection while a request whose fetch is held reaches its
+// deadline. The request must return with the deadline's error while the
+// connection is still held, as it waits for no database write past its
+// deadline.
+func TestProxy_Get_ReturnsByItsDeadlineWhileTheDatabaseIsBusy(t *testing.T) {
+	t.Parallel()
+
+	svc, fixtures, fetcher := setupHeldFetchProxy(t)
+
+	svc.cache.StartPendingAccessTimeWrites()
+	defer func() { _ = svc.cache.StopPendingAccessTimeWrites(t.Context()) }()
+
+	// Room for the request to reach its fetch on a busy host
+	const timeout = 2 * time.Second
+
+	ctx, cancel := context.WithTimeout(t.Context(), timeout)
+	defer cancel()
+
+	deadline, _ := ctx.Deadline()
+
+	results := startGet(ctx, svc, photoVariant(fixtures, 85, imagerequest.FitCover))
+
+	// The request has made its database reads by the time it fetches.
+	select {
+	case <-fetcher.started:
+	case <-time.After(timeout):
+		t.Fatal("request did not reach its fetch by its deadline")
+	}
+
+	releaseDatabase := holdDatabase(t, svc.db)
+	defer releaseDatabase()
+
+	select {
+	case got := <-results:
+		t.Logf("Get() returned %v after its deadline, error = %v",
+			time.Since(deadline), got.err)
+
+		if !errors.Is(got.err, context.DeadlineExceeded) {
+			t.Errorf("Get() error = %v, want %v", got.err, context.DeadlineExceeded)
+		}
+	case <-time.After(time.Until(deadline) + pendingAccessTimesWait):
+		t.Fatal("request did not return while the database was busy")
+	}
+}

internal/imageproxy/stats_internal_test.go

@@ -1,4 +1,4 @@
-package imgcache
+package imageproxy
 
 import (
 	"bytes"
@@ -12,15 +12,16 @@ import (
 	"sneak.berlin/go/pixa/internal/imagerequest"
 )
 
-// TestService_Get_CountsStats walks Get through a miss that fetches the
+// TestProxy_Get_CountsStats walks Get through a miss that fetches the
 // source, a hit, a miss that reuses the cached source, and two misses whose
-// source cannot be used, checking every counter of the cache after each.
-func TestService_Get_CountsStats(t *testing.T) {
+// source cannot be used, checking every counter of the proxy and its cache
+// after each.
+func TestProxy_Get_CountsStats(t *testing.T) {
 	t.Parallel()
 
-	svc, fixtures := SetupTestService(t)
+	svc, fixtures := setupTestProxy(t)
 
-	// NewTestFS builds the same files the test service's fetcher serves.
+	// NewTestFS builds the same files the test proxy's fetcher serves.
 	testFS, _ := NewTestFS(t)
 
 	photo, err := fs.ReadFile(testFS, fixtures.GoodHostJPEG)
@@ -76,7 +77,7 @@ func TestService_Get_CountsStats(t *testing.T) {
 			_ = resp.Content.Close()
 		}
 
-		got := readCounters(svc.cache)
+		got := readCounters(t, svc)
 		if got != step.want {
 			t.Fatalf("after the %s: counters = %+v, want %+v", step.name, got, step.want)
 		}
@@ -114,10 +115,11 @@ func (u *fakeUpstream) Read(p []byte) (int, error) {
 	return 0, u.err
 }
 
-// TestService_Get_CountsInterruptedMisses checks every counter of the cache
-// after a miss whose request context ends during or after the upstream
-// fetch, and after a miss whose upstream body is over the size limit.
-func TestService_Get_CountsInterruptedMisses(t *testing.T) {
+// TestProxy_Get_CountsInterruptedMisses checks every counter of the proxy
+// and its cache after a miss whose request context ends during or after the
+// upstream fetch, and after a miss whose upstream body is over the size
+// limit.
+func TestProxy_Get_CountsInterruptedMisses(t *testing.T) {
 	t.Parallel()
 
 	photo := generateTestJPEG(t, 100, 100, color.RGBA{255, 0, 0, 255})
@@ -145,7 +147,7 @@ func TestService_Get_CountsInterruptedMisses(t *testing.T) {
 		t.Run(tc.name, func(t *testing.T) {
 			t.Parallel()
 
-			svc, fixtures := SetupTestService(t)
+			svc, fixtures := setupTestProxy(t)
 
 			ctx, cancel := context.WithCancel(t.Context())
 			defer cancel()
@@ -182,7 +184,7 @@ func TestService_Get_CountsInterruptedMisses(t *testing.T) {
 				_ = resp.Content.Close()
 			}
 
-			got := readCounters(svc.cache)
+			got := readCounters(t, svc)
 			if got != tc.want {
 				t.Errorf("counters = %+v, want %+v", got, tc.want)
 			}
@@ -190,13 +192,13 @@ func TestService_Get_CountsInterruptedMisses(t *testing.T) {
 	}
 }
 
-// TestService_Get_CountsHitAfterRequestEnds checks every counter of the
-// cache after a hit served with a request context that has already ended:
-// only the hit count moves.
-func TestService_Get_CountsHitAfterRequestEnds(t *testing.T) {
+// TestProxy_Get_CountsHitAfterRequestEnds checks every counter of the
+// proxy and its cache after a hit served with a request context that has
+// already ended: only the hit count moves.
+func TestProxy_Get_CountsHitAfterRequestEnds(t *testing.T) {
 	t.Parallel()
 
-	svc, fixtures := SetupTestService(t)
+	svc, fixtures := setupTestProxy(t)
 
 	req := &imagerequest.Request{
 		Source: imagerequest.Source{
@@ -219,7 +221,7 @@ func TestService_Get_CountsHitAfterRequestEnds(t *testing.T) {
 
 	_ = resp.Content.Close()
 
-	want := readCounters(svc.cache)
+	want := readCounters(t, svc)
 	want.hitCount++
 
 	ctx, cancel := context.WithCancel(t.Context())
@@ -236,7 +238,7 @@ func TestService_Get_CountsHitAfterRequestEnds(t *testing.T) {
 		t.Fatalf("CacheStatus = %v, want %v", resp.CacheStatus, CacheHit)
 	}
 
-	got := readCounters(svc.cache)
+	got := readCounters(t, svc)
 	if got != want {
 		t.Errorf("counters = %+v, want %+v", got, want)
 	}

internal/imageproxy/testutil_internal_test.go

@@ -0,0 +1,355 @@
+package imageproxy
+
+import (
+	"bytes"
+	"context"
+	"database/sql"
+	"image"
+	"image/color"
+	"image/gif"
+	"image/jpeg"
+	"image/png"
+	"io/fs"
+	"path/filepath"
+	"testing"
+	"testing/fstest"
+	"time"
+
+	"github.com/prometheus/client_golang/prometheus"
+	"sneak.berlin/go/pixa/internal/database"
+	"sneak.berlin/go/pixa/internal/httpfetcher"
+	"sneak.berlin/go/pixa/internal/imageprocessor"
+	"sneak.berlin/go/pixa/internal/imagerequest"
+	"sneak.berlin/go/pixa/internal/imgcache"
+)
+
+// Shared test data literals, extracted as constants for goconst.
+const (
+	testContentTypeJPEG = "image/jpeg"
+)
+
+// sqliteTimestampFormat matches the format SQLite's CURRENT_TIMESTAMP
+// produces, so injected timestamps compare correctly against ones the
+// cache writes.
+const sqliteTimestampFormat = "2006-01-02 15:04:05"
+
+// TestFixtures contains paths to test files in the mock filesystem.
+type TestFixtures struct {
+	// Valid image files
+	GoodHostJPEG  string // valid JPEG on GoodHost
+	GoodHostPNG   string // valid PNG on GoodHost
+	GoodHostGIF   string // valid GIF on GoodHost
+	OtherHostJPEG string // valid JPEG on OtherHost
+	OtherHostPNG  string // valid PNG on OtherHost
+
+	// Invalid/edge case files
+	InvalidFile string // file with wrong magic bytes
+	EmptyFile   string // zero-byte file
+	TextFile    string // text file masquerading as image
+
+	// Hostnames
+	GoodHost  string // a host the mock fetcher serves
+	OtherHost string // a second host the mock fetcher serves
+}
+
+// DefaultFixtures returns the standard test fixture paths.
+func DefaultFixtures() *TestFixtures {
+	return &TestFixtures{
+		GoodHostJPEG:  "goodhost.example.com/images/photo.jpg",
+		GoodHostPNG:   "goodhost.example.com/images/logo.png",
+		GoodHostGIF:   "goodhost.example.com/images/animation.gif",
+		OtherHostJPEG: "otherhost.example.com/uploads/image.jpg",
+		OtherHostPNG:  "otherhost.example.com/uploads/icon.png",
+		InvalidFile:   "goodhost.example.com/images/fake.jpg",
+		EmptyFile:     "goodhost.example.com/images/empty.jpg",
+		TextFile:      "goodhost.example.com/images/text.png",
+		GoodHost:      "goodhost.example.com",
+		OtherHost:     "otherhost.example.com",
+	}
+}
+
+// NewTestFS creates a mock filesystem with test images.
+func NewTestFS(t *testing.T) (fs.FS, *TestFixtures) {
+	t.Helper()
+
+	fixtures := DefaultFixtures()
+
+	// Generate test images
+	jpegData := generateTestJPEG(t, 100, 100, color.RGBA{255, 0, 0, 255})
+	pngData := generateTestPNG(t, 100, 100, color.RGBA{0, 255, 0, 255})
+	gifData := generateTestGIF(t, 100, 100, color.RGBA{0, 0, 255, 255})
+
+	// Create the mock filesystem
+	mockFS := fstest.MapFS{
+		// Good host files
+		fixtures.GoodHostJPEG: &fstest.MapFile{Data: jpegData},
+		fixtures.GoodHostPNG:  &fstest.MapFile{Data: pngData},
+		fixtures.GoodHostGIF:  &fstest.MapFile{Data: gifData},
+
+		// Other host files
+		fixtures.OtherHostJPEG: &fstest.MapFile{Data: jpegData},
+		fixtures.OtherHostPNG:  &fstest.MapFile{Data: pngData},
+
+		// Invalid files
+		fixtures.InvalidFile: &fstest.MapFile{Data: []byte("not a real image file content")},
+		fixtures.EmptyFile:   &fstest.MapFile{Data: []byte{}},
+		fixtures.TextFile:    &fstest.MapFile{Data: []byte("This is just text, not a PNG")},
+	}
+
+	return mockFS, fixtures
+}
+
+// generateTestJPEG creates a minimal valid JPEG image.
+func generateTestJPEG(t *testing.T, width, height int, c color.Color) []byte {
+	t.Helper()
+
+	img := image.NewRGBA(image.Rect(0, 0, width, height))
+	for y := range height {
+		for x := range width {
+			img.Set(x, y, c)
+		}
+	}
+
+	var buf bytes.Buffer
+
+	err := jpeg.Encode(&buf, img, &jpeg.Options{Quality: 85})
+	if err != nil {
+		t.Fatalf("failed to encode test JPEG: %v", err)
+	}
+
+	return buf.Bytes()
+}
+
+// generateTestPNG creates a minimal valid PNG image.
+func generateTestPNG(t *testing.T, width, height int, c color.Color) []byte {
+	t.Helper()
+
+	img := image.NewRGBA(image.Rect(0, 0, width, height))
+	for y := range height {
+		for x := range width {
+			img.Set(x, y, c)
+		}
+	}
+
+	var buf bytes.Buffer
+
+	err := png.Encode(&buf, img)
+	if err != nil {
+		t.Fatalf("failed to encode test PNG: %v", err)
+	}
+
+	return buf.Bytes()
+}
+
+// generateTestGIF creates a minimal valid GIF image.
+func generateTestGIF(t *testing.T, width, height int, c color.Color) []byte {
+	t.Helper()
+
+	img := image.NewPaletted(
+		image.Rect(0, 0, width, height),
+		[]color.Color{c, color.White},
+	)
+	for y := range height {
+		for x := range width {
+			img.SetColorIndex(x, y, 0)
+		}
+	}
+
+	var buf bytes.Buffer
+
+	err := gif.Encode(&buf, img, nil)
+	if err != nil {
+		t.Fatalf("failed to encode test GIF: %v", err)
+	}
+
+	return buf.Bytes()
+}
+
+// testProxy is a Proxy with the database and the state directory of its
+// cache, through which a test reads and changes the cache behind the proxy.
+// registry is the metrics registry the proxy and its cache share.
+type testProxy struct {
+	*Proxy
+
+	db       *sql.DB
+	stateDir string
+	registry *prometheus.Registry
+}
+
+// setupTestProxy creates a Proxy with mock fetcher for testing.
+func setupTestProxy(t *testing.T) (*testProxy, *TestFixtures) {
+	t.Helper()
+
+	mockFS, fixtures := NewTestFS(t)
+
+	// Create temp directory for cache
+	tmpDir := t.TempDir()
+
+	// Create in-memory database
+	db := setupTestDB(t)
+
+	registry := prometheus.NewRegistry()
+
+	cache, err := imgcache.NewCache(db, imgcache.Config{
+		StateDir:    tmpDir,
+		NegativeTTL: 5 * time.Minute,
+		MaxBytes:    1 << 30,
+	}, registry)
+	if err != nil {
+		t.Fatalf("failed to create cache: %v", err)
+	}
+
+	proxy, err := NewProxy(&Config{
+		Cache:   cache,
+		Fetcher: httpfetcher.NewMock(mockFS),
+		Processor: imageprocessor.New(imageprocessor.Params{
+			MaxInputBytes:           50 << 20,
+			MaxConcurrentProcessing: 2,
+		}),
+		MaxResponseSize: 50 << 20,
+	}, registry)
+	if err != nil {
+		t.Fatalf("failed to create proxy: %v", err)
+	}
+
+	return &testProxy{
+		Proxy:    proxy,
+		db:       db,
+		stateDir: tmpDir,
+		registry: registry,
+	}, fixtures
+}
+
+// counterValues holds the values of the counters of a proxy and its cache.
+type counterValues struct {
+	hitCount           int64
+	missCount          int64
+	upstreamFetchCount int64
+	upstreamFetchBytes int64
+	transformCount     int64
+}
+
+// readCounters reads the counters of svc and its cache from their metrics
+// registry.
+func readCounters(t *testing.T, svc *testProxy) counterValues {
+	t.Helper()
+
+	families, err := svc.registry.Gather()
+	if err != nil {
+		t.Fatalf("failed to gather the counters: %v", err)
+	}
+
+	values := make(map[string]int64, len(families))
+
+	for _, family := range families {
+		values[family.GetName()] = int64(family.GetMetric()[0].GetCounter().GetValue())
+	}
+
+	return counterValues{
+		hitCount:           values["pixa_cache_hits_total"],
+		missCount:          values["pixa_cache_misses_total"],
+		upstreamFetchCount: values["pixa_upstream_fetches_total"],
+		upstreamFetchBytes: values["pixa_upstream_fetch_bytes_total"],
+		transformCount:     values["pixa_transforms_total"],
+	}
+}
+
+// sourceFilePath returns the path of the file of the source key in svc's
+// cache, as README.md gives it: <state_dir>/cache/sources/<ab>/<cd>/<key>.
+func sourceFilePath(svc *testProxy, key imagerequest.SourceKey) string {
+	name := string(key)
+
+	return filepath.Join(svc.stateDir, "cache", "sources", name[0:2], name[2:4], name)
+}
+
+// variantFilePath returns the path of the file of the variant key in svc's
+// cache, as README.md gives it: <state_dir>/cache/variants/<ab>/<cd>/<key>.
+func variantFilePath(svc *testProxy, key imagerequest.VariantKey) string {
+	name := string(key)
+
+	return filepath.Join(svc.stateDir, "cache", "variants", name[0:2], name[2:4], name)
+}
+
+// setVariantLastAccessed backdates the last access time of a tracked
+// variant.
+func setVariantLastAccessed(
+	t *testing.T, db *sql.DB, key imagerequest.VariantKey, when time.Time,
+) {
+	t.Helper()
+
+	res, err := db.ExecContext(t.Context(),
+		`UPDATE variant_content SET last_accessed_at = ? WHERE cache_key = ?`,
+		when.UTC().Format(sqliteTimestampFormat), string(key),
+	)
+	if err != nil {
+		t.Fatalf("failed to set variant last_accessed_at: %v", err)
+	}
+
+	affected, err := res.RowsAffected()
+	if err != nil {
+		t.Fatalf("failed to read affected rows: %v", err)
+	}
+
+	if affected != 1 {
+		t.Fatalf("variant %s has no accounting row (affected=%d); "+
+			"stores must track variants in the database", key, affected)
+	}
+}
+
+// setSourceLastAccessed backdates the last access time of a tracked
+// source content blob.
+func setSourceLastAccessed(
+	t *testing.T, db *sql.DB, key imagerequest.SourceKey, when time.Time,
+) {
+	t.Helper()
+
+	res, err := db.ExecContext(t.Context(),
+		`UPDATE source_content SET last_accessed_at = ? WHERE source_key = ?`,
+		when.UTC().Format(sqliteTimestampFormat), string(key),
+	)
+	if err != nil {
+		t.Fatalf("failed to set source last_accessed_at: %v", err)
+	}
+
+	affected, err := res.RowsAffected()
+	if err != nil {
+		t.Fatalf("failed to read affected rows: %v", err)
+	}
+
+	if affected != 1 {
+		t.Fatalf("source %s has no accounting row (affected=%d)", key, affected)
+	}
+}
+
+// countRows returns the number of rows the given query yields.
+func countRows(t *testing.T, db *sql.DB, query string, args ...any) int {
+	t.Helper()
+
+	var n int
+
+	err := db.QueryRowContext(t.Context(), query, args...).Scan(&n)
+	if err != nil {
+		t.Fatalf("count query %q failed: %v", query, err)
+	}
+
+	return n
+}
+
+// setupTestDB creates an in-memory SQLite database for testing
+// using the production schema.
+func setupTestDB(t *testing.T) *sql.DB {
+	t.Helper()
+
+	db, err := sql.Open("sqlite", ":memory:")
+	if err != nil {
+		t.Fatalf("failed to open test db: %v", err)
+	}
+
+	// Use the real production schema via migrations
+	err = database.ApplyMigrations(context.Background(), db, nil)
+	if err != nil {
+		t.Fatalf("failed to apply migrations: %v", err)
+	}
+
+	return db
+}

internal/imgcache/cache.go

@@ -1,3 +1,10 @@
+// Package imgcache is the image cache. It keeps:
+//   - the source images fetched from upstream
+//   - the variants made from them
+//   - the negative cache: the source URLs whose fetch failed recently
+//
+// Each image is a file with a row in the database. Eviction removes the
+// least recently used images to keep the cache under its size limit.
 package imgcache
 
 import (
@@ -26,8 +33,12 @@ const maxPendingAccessTimes = 10000
 // have expired.
 const cleanExpiredBatchSize = 1000
 
-// CacheConfig holds cache configuration.
-type CacheConfig struct {
+// DefaultNegativeTTL is how long pixad keeps a failed fetch in the negative
+// cache.
+const DefaultNegativeTTL = 5 * time.Minute
+
+// Config holds cache configuration.
+type Config struct {
 	StateDir    string
 	NegativeTTL time.Duration
 
@@ -48,7 +59,7 @@ type Cache struct {
 	db         *sql.DB
 	srcContent *ContentStorage // source images by source key
 	variants   *VariantStorage // processed variants by cache key
-	config     CacheConfig
+	config     Config
 	log        *slog.Logger
 
 	// Eviction machinery. The channels are created in NewCache so
@@ -73,13 +84,10 @@ type Cache struct {
 	pendingAccessTimesDone    chan struct{}
 	pendingAccessTimesCancel  context.CancelFunc
 
-	// The counts of what the cache does, made and registered by
+	// The counts of cache hits and misses, made and registered by
 	// registerCounters (see counters.go)
-	cacheHits          prometheus.Counter
-	cacheMisses        prometheus.Counter
-	upstreamFetches    prometheus.Counter
-	upstreamFetchBytes prometheus.Counter
-	transforms         prometheus.Counter
+	cacheHits   prometheus.Counter
+	cacheMisses prometheus.Counter
 
 	// reconciliationPageSize is the most rows one read of a content table
 	// returns in the reconciliation pass. NewCache sets it to
@@ -97,7 +105,7 @@ type Cache struct {
 // metricsRegistry. pixad passes Prometheus' default registry, the one
 // /metrics serves. It makes no database call.
 func NewCache(
-	db *sql.DB, config CacheConfig, metricsRegistry prometheus.Registerer,
+	db *sql.DB, config Config, metricsRegistry prometheus.Registerer,
 ) (*Cache, error) {
 	log := config.Logger
 	if log == nil {
@@ -147,75 +155,35 @@ func NewCache(
 	return c, nil
 }
 
-// GetVariant opens a cached variant and returns a reader, its size and its
+// Variant opens a cached variant and returns a reader, its size and its
 // content type, read from the variant file's first bytes. It opens that one
-// file and makes no database call. A variant not in the cache, or any
-// variant of a disabled cache, is ErrNotFound; a variant file whose first
-// bytes are not those of an output format is another error.
-func (c *Cache) GetVariant(
+// file and makes no database call. A variant it opens has its access time
+// handed to the background writer without waiting (see touchVariant). A
+// variant not in the cache, or any variant of a disabled cache, is
+// ErrNotFound; a variant file whose first bytes are not those of an output
+// format is another error.
+func (c *Cache) Variant(
 	cacheKey imagerequest.VariantKey,
 ) (io.ReadCloser, int64, string, error) {
 	if c.config.MaxBytes == 0 {
 		return nil, 0, "", ErrNotFound
 	}
 
-	return c.variants.LoadWithContentType(cacheKey)
+	reader, size, contentType, err := c.variants.LoadWithContentType(cacheKey)
+	if err != nil {
+		return nil, 0, "", err
+	}
+
+	c.touchVariant(cacheKey)
+
+	return reader, size, contentType, nil
 }
 
-// StoreSource stores fetched source content: it writes the file named by
-// the source's key, then the source's row. When the row cannot be written
-// the file is removed and the store fails, as a file with no row is never
-// served or evicted; if that removal fails too, the next reconciliation
-// pass removes the file. On a disabled cache it is a no-op returning an
-// empty key.
-func (c *Cache) StoreSource(
-	ctx context.Context,
-	req *imagerequest.Request,
-	content io.Reader,
-) (imagerequest.SourceKey, error) {
-	if c.config.MaxBytes == 0 {
-		return "", nil
-	}
-
-	data, err := io.ReadAll(content)
-	if err != nil {
-		return "", fmt.Errorf("failed to read source content: %w", err)
-	}
-
-	key := req.Source.Key()
-
-	size, err := c.srcContent.Store(key, data)
-	if err != nil {
-		return "", fmt.Errorf("failed to store source content: %w", err)
-	}
-
-	_, err = c.db.ExecContext(ctx, `
-		INSERT INTO source_content (source_key, size_bytes)
-		VALUES (?, ?)
-		ON CONFLICT(source_key) DO UPDATE SET
-			size_bytes = excluded.size_bytes,
-			last_accessed_at = CURRENT_TIMESTAMP
-	`, string(key), size)
-	if err != nil {
-		deleteErr := c.srcContent.Delete(key)
-		if deleteErr != nil {
-			c.log.Warn("failed to remove source file whose row was not written",
-				"source_key", key, "error", deleteErr)
-		}
-
-		return "", fmt.Errorf("failed to insert source content: %w", err)
-	}
-
-	c.notifyWritePressure()
-
-	return key, nil
-}
-
-// StoreVariant stores a processed variant by its cache key and records
+// PutVariant stores a processed variant by its cache key and records
 // it in the size accounting. On a disabled cache it is a no-op. The
 // accounting insert is best-effort (the startup reconciliation pass
 // adopts any variant file that misses its accounting row).
-func (c *Cache) StoreVariant(
+func (c *Cache) PutVariant(
 	ctx context.Context, cacheKey imagerequest.VariantKey, content io.Reader,
 ) error {
 	if c.config.MaxBytes == 0 {
@@ -244,19 +212,18 @@ func (c *Cache) StoreVariant(
 	return nil
 }
 
-// LookupSource checks if we have cached source content for a request.
-// Returns the source key if found, or an empty key if not; a row whose
-// file is missing is not found. A source found has its access time
-// handed to the background writer without waiting (see
-// touchSourceContent); a disabled cache always reports no cached source.
-func (c *Cache) LookupSource(
-	ctx context.Context, req *imagerequest.Request,
-) (imagerequest.SourceKey, error) {
+// Source opens the cached source of src and returns a reader and its size
+// in bytes. A source whose row or file is missing is ErrNotFound, as is any
+// source of a disabled cache. A source it opens has its access time handed
+// to the background writer without waiting (see touchSourceContent).
+func (c *Cache) Source(
+	ctx context.Context, src imagerequest.Source,
+) (io.ReadCloser, int64, error) {
 	if c.config.MaxBytes == 0 {
-		return "", nil
+		return nil, 0, ErrNotFound
 	}
 
-	key := req.Source.Key()
+	key := src.Key()
 
 	var rowExists bool
 
@@ -264,25 +231,100 @@ func (c *Cache) LookupSource(
 		SELECT EXISTS(SELECT 1 FROM source_content WHERE source_key = ?)
 	`, string(key)).Scan(&rowExists)
 	if err != nil {
-		return "", fmt.Errorf("failed to lookup source: %w", err)
+		return nil, 0, fmt.Errorf("failed to lookup source: %w", err)
 	}
 
 	if !rowExists {
-		return "", nil
+		return nil, 0, ErrNotFound
 	}
 
-	// Verify the content file exists
-	if !c.srcContent.Exists(key) {
-		return "", nil
+	reader, size, err := c.srcContent.LoadWithSize(key)
+	if err != nil {
+		return nil, 0, err
 	}
 
 	c.touchSourceContent(key)
 
+	return reader, size, nil
+}
+
+// PutSource stores fetched source content: it writes the file named by
+// the source's key, then the source's row. When the row cannot be written
+// the file is removed and the store fails, as a file with no row is never
+// served or evicted; if that removal fails too, the next reconciliation
+// pass removes the file. On a disabled cache it is a no-op returning an
+// empty key.
+func (c *Cache) PutSource(
+	ctx context.Context,
+	src imagerequest.Source,
+	content io.Reader,
+) (imagerequest.SourceKey, error) {
+	if c.config.MaxBytes == 0 {
+		return "", nil
+	}
+
+	data, err := io.ReadAll(content)
+	if err != nil {
+		return "", fmt.Errorf("failed to read source content: %w", err)
+	}
+
+	key := src.Key()
+
+	size, err := c.srcContent.Store(key, data)
+	if err != nil {
+		return "", fmt.Errorf("failed to store source content: %w", err)
+	}
+
+	_, err = c.db.ExecContext(ctx, `
+		INSERT INTO source_content (source_key, size_bytes)
+		VALUES (?, ?)
+		ON CONFLICT(source_key) DO UPDATE SET
+			size_bytes = excluded.size_bytes,
+			last_accessed_at = CURRENT_TIMESTAMP
+	`, string(key), size)
+	if err != nil {
+		deleteErr := c.srcContent.Delete(key)
+		if deleteErr != nil {
+			c.log.Warn("failed to remove source file whose row was not written",
+				"source_key", key, "error", deleteErr)
+		}
+
+		return "", fmt.Errorf("failed to insert source content: %w", err)
+	}
+
+	c.notifyWritePressure()
+
 	return key, nil
 }
 
-// StoreNegative stores a negative cache entry for a failed fetch.
-func (c *Cache) StoreNegative(ctx context.Context, req *imagerequest.Request) error {
+// Failure reports whether src is in the negative cache. It only reads: a
+// row past its expiry is not a hit, and the eviction goroutine deletes it
+// with the other expired rows (see CleanExpired).
+func (c *Cache) Failure(
+	ctx context.Context, src imagerequest.Source,
+) (bool, error) {
+	var expiresAt time.Time
+
+	err := c.db.QueryRowContext(ctx, `
+		SELECT expires_at FROM negative_cache
+		WHERE source_host = ? AND source_path = ? AND source_query = ?
+	`, src.Host, src.Path, src.Query).Scan(&expiresAt)
+
+	if errors.Is(err, sql.ErrNoRows) {
+		return false, nil
+	}
+
+	if err != nil {
+		return false, fmt.Errorf("failed to check negative cache: %w", err)
+	}
+
+	expired := time.Now().After(expiresAt)
+
+	return !expired, nil
+}
+
+// PutFailure stores a negative cache entry for src, whose fetch failed.
+func (c *Cache) PutFailure(ctx context.Context, src imagerequest.Source) error {
 	expiresAt := time.Now().UTC().Add(c.config.NegativeTTL)
 
 	_, err := c.db.ExecContext(ctx, `
@@ -291,7 +333,7 @@ func (c *Cache) StoreNegative(ctx context.Context, req *imagerequest.Request) er
 		VALUES (?, ?, ?, ?)
 		ON CONFLICT(source_host, source_path, source_query) DO UPDATE SET
 			expires_at = excluded.expires_at
-	`, req.Source.Host, req.Source.Path, req.Source.Query, expiresAt)
+	`, src.Host, src.Path, src.Query, expiresAt)
 	if err != nil {
 		return fmt.Errorf("failed to insert negative cache: %w", err)
 	}
@@ -299,18 +341,6 @@ func (c *Cache) StoreNegative(ctx context.Context, req *imagerequest.Request) er
 	return nil
 }
 
-// GetSourceContent returns a reader for cached source content by its key,
-// and the content's size in bytes.
-func (c *Cache) GetSourceContent(
-	key imagerequest.SourceKey,
-) (io.ReadCloser, int64, error) {
-	if c.config.MaxBytes == 0 {
-		return nil, 0, ErrNotFound
-	}
-
-	return c.srcContent.LoadWithSize(key)
-}
-
 // CleanExpired removes the negative cache rows past their expiry, one
 // batch per statement, until none is left. Once ctx ends it starts no
 // further batch and returns ctx's error. The eviction goroutine calls it
@@ -334,34 +364,15 @@ func (c *Cache) CleanExpired(ctx context.Context) error {
 	}
 }
 
-// IncrementStats counts a cache hit or miss, and an upstream fetch that read
-// fetchBytes bytes, as IncrementUpstreamFetch does. Like the other Increment
-// methods, it only adds to the cache's Prometheus counters in memory (see
-// counters.go), so it never waits for the database or fails.
-func (c *Cache) IncrementStats(hit bool, fetchBytes int64) {
+// IncrementStats counts a cache hit or miss. It only adds to the cache's
+// Prometheus counters in memory (see counters.go), so it never waits for the
+// database or fails.
+func (c *Cache) IncrementStats(hit bool) {
 	if hit {
 		c.cacheHits.Inc()
 	} else {
 		c.cacheMisses.Inc()
 	}
-
-	c.IncrementUpstreamFetch(fetchBytes)
-}
-
-// IncrementUpstreamFetch counts one upstream fetch that read fetchBytes bytes.
-// A fetch that read no bytes is not counted.
-func (c *Cache) IncrementUpstreamFetch(fetchBytes int64) {
-	if fetchBytes <= 0 {
-		return
-	}
-
-	c.upstreamFetches.Inc()
-	c.upstreamFetchBytes.Add(float64(fetchBytes))
-}
-
-// IncrementTransformCount counts one image transcoded by the image processor.
-func (c *Cache) IncrementTransformCount() {
-	c.transforms.Inc()
 }
 
 // touchVariant hands the access time of a variant served from the cache to
@@ -388,32 +399,6 @@ func (c *Cache) touchSourceContent(key imagerequest.SourceKey) {
 	}
 }
 
-// checkNegativeCache checks if a request is in the negative cache. It only
-// reads: a row past its expiry is not a hit, and the eviction goroutine
-// deletes it with the other expired rows (see CleanExpired).
-func (c *Cache) checkNegativeCache(
-	ctx context.Context, req *imagerequest.Request,
-) (bool, error) {
-	var expiresAt time.Time
-
-	err := c.db.QueryRowContext(ctx, `
-		SELECT expires_at FROM negative_cache
-		WHERE source_host = ? AND source_path = ? AND source_query = ?
-	`, req.Source.Host, req.Source.Path, req.Source.Query).Scan(&expiresAt)
-
-	if errors.Is(err, sql.ErrNoRows) {
-		return false, nil
-	}
-
-	if err != nil {
-		return false, fmt.Errorf("failed to check negative cache: %w", err)
-	}
-
-	expired := time.Now().After(expiresAt)
-
-	return !expired, nil
-}
-
 // cleanExpiredBatch deletes up to cleanExpiredBatchSize negative cache
 // rows past their expiry in one statement, and returns how many it
 // deleted. DELETE ... LIMIT needs a SQLite build option, so the subquery

internal/imgcache/cache_hit_internal_test.go

@@ -6,7 +6,6 @@ import (
 	"fmt"
 	"image/color"
 	"io"
-	"os"
 	"testing"
 	"time"
 
@@ -15,10 +14,10 @@ import (
 	"sneak.berlin/go/pixa/internal/magic"
 )
 
-// TestGetVariant_ContentTypeFromFirstBytes stores an image in each output
-// format as a variant and checks that GetVariant serves it whole with the
+// TestVariant_ContentTypeFromFirstBytes stores an image in each output
+// format as a variant and checks that Variant serves it whole with the
 // content type of its format, read from the file.
-func TestGetVariant_ContentTypeFromFirstBytes(t *testing.T) {
+func TestVariant_ContentTypeFromFirstBytes(t *testing.T) {
 	t.Parallel()
 
 	cache, _ := newEvictionTestCache(t, 1<<30)
@@ -50,14 +49,14 @@ func TestGetVariant_ContentTypeFromFirstBytes(t *testing.T) {
 
 		key := imagerequest.VariantKey("aabbccdd10" + string(format))
 
-		err = cache.StoreVariant(t.Context(), key, bytes.NewReader(image))
+		err = cache.PutVariant(t.Context(), key, bytes.NewReader(image))
 		if err != nil {
-			t.Fatalf("StoreVariant(%s) error = %v", format, err)
+			t.Fatalf("PutVariant(%s) error = %v", format, err)
 		}
 
-		reader, size, contentType, err := cache.GetVariant(key)
+		reader, size, contentType, err := cache.Variant(key)
 		if err != nil {
-			t.Fatalf("GetVariant(%s) error = %v", format, err)
+			t.Fatalf("Variant(%s) error = %v", format, err)
 		}
 
 		served, err := io.ReadAll(reader)
@@ -80,11 +79,11 @@ func TestGetVariant_ContentTypeFromFirstBytes(t *testing.T) {
 	}
 }
 
-// TestGetVariant_RefusesFileOfNoOutputFormat checks that GetVariant refuses
+// TestVariant_RefusesFileOfNoOutputFormat checks that Variant refuses
 // a variant file whose first bytes are not those of an output format, with
 // an error other than ErrNotFound, and that a variant with no file, or any
 // variant of a disabled cache, is ErrNotFound.
-func TestGetVariant_RefusesFileOfNoOutputFormat(t *testing.T) {
+func TestVariant_RefusesFileOfNoOutputFormat(t *testing.T) {
 	t.Parallel()
 
 	cache, _ := newEvictionTestCache(t, 1<<30)
@@ -110,118 +109,30 @@ func TestGetVariant_RefusesFileOfNoOutputFormat(t *testing.T) {
 			t.Fatalf("%s: storing the variant file: %v", tt.name, err)
 		}
 
-		reader, _, contentType, err := cache.GetVariant(key)
-		t.Logf("%s: GetVariant() error = %v", tt.name, err)
+		reader, _, contentType, err := cache.Variant(key)
+		t.Logf("%s: Variant() error = %v", tt.name, err)
 
 		if reader != nil || contentType != "" || !errors.Is(err, tt.wantErr) {
-			t.Errorf("%s: GetVariant() = reader %v, content type %q, error %v; "+
+			t.Errorf("%s: Variant() = reader %v, content type %q, error %v; "+
 				"want no reader and %v", tt.name, reader, contentType, err, tt.wantErr)
 		}
 	}
 
-	reader, _, _, err := cache.GetVariant(testVariantKeyFour)
+	reader, _, _, err := cache.Variant(testVariantKeyFour)
 	if reader != nil || !errors.Is(err, ErrNotFound) {
-		t.Errorf("GetVariant() of a variant with no file = reader %v, error %v; "+
+		t.Errorf("Variant() of a variant with no file = reader %v, error %v; "+
 			"want no reader and %v", reader, err, ErrNotFound)
 	}
 
 	disabled, _ := newEvictionTestCache(t, 0)
 
-	reader, _, _, err = disabled.GetVariant(testVariantKeyOne)
+	reader, _, _, err = disabled.Variant(testVariantKeyOne)
 	if reader != nil || !errors.Is(err, ErrNotFound) {
-		t.Errorf("GetVariant() on a disabled cache = reader %v, error %v; "+
+		t.Errorf("Variant() on a disabled cache = reader %v, error %v; "+
 			"want no reader and %v", reader, err, ErrNotFound)
 	}
 }
 
-// TestService_Get_MakesAgainVariantOfNoOutputFormat replaces a cached
-// variant's file with text, and checks that the next request is a miss
-// answered with the variant made again, and the one after a hit.
-func TestService_Get_MakesAgainVariantOfNoOutputFormat(t *testing.T) {
-	t.Parallel()
-
-	svc, fixtures := SetupTestService(t)
-	req := photoVariant(fixtures, 85, imagerequest.FitCover)
-
-	want, _ := getImage(t, svc, req)
-
-	path := svc.cache.variants.keyToPath(imagerequest.CacheKey(req))
-
-	err := os.WriteFile(path, []byte("this is text, not an image"), StorageFilePerm)
-	if err != nil {
-		t.Fatalf("replacing the variant file: %v", err)
-	}
-
-	got, status := getImage(t, svc, req)
-	t.Logf("after the replacement: %d bytes, %s", len(got), status)
-
-	if status != CacheMiss || !bytes.Equal(got, want) {
-		t.Errorf("after the replacement: Get() = %d bytes, %s; want the %d bytes "+
-			"made again, %s", len(got), status, len(want), CacheMiss)
-	}
-
-	got, status = getImage(t, svc, req)
-
-	if status != CacheHit || !bytes.Equal(got, want) {
-		t.Errorf("next request: Get() = %d bytes, %s; want the %d bytes, %s",
-			len(got), status, len(want), CacheHit)
-	}
-}
-
-// TestService_Get_HitWaitsForNoDatabaseWrite holds the database's one
-// connection while a cached variant is requested. The hit must be answered
-// while the connection is still held, and its access time must reach the
-// database once it is free.
-func TestService_Get_HitWaitsForNoDatabaseWrite(t *testing.T) {
-	t.Parallel()
-
-	svc, fixtures := SetupTestService(t)
-	req := photoVariant(fixtures, 85, imagerequest.FitCover)
-	key := imagerequest.CacheKey(req)
-
-	getImage(t, svc, req)
-
-	// Each connection to an in-memory SQLite database opens a new, empty one,
-	// so the goroutine that writes the access times must share the
-	// connection that holds the schema.
-	svc.cache.db.SetMaxOpenConns(1)
-	svc.cache.StartPendingAccessTimeWrites()
-
-	defer func() { _ = svc.cache.StopPendingAccessTimeWrites(t.Context()) }()
-
-	anHourAgo := time.Now().Add(-time.Hour)
-	setVariantLastAccessed(t, svc.cache, key, anHourAgo)
-
-	releaseDatabase := holdDatabase(t, svc.cache)
-	defer releaseDatabase()
-
-	results := startGet(t.Context(), svc, req)
-
-	select {
-	case got := <-results:
-		if got.err != nil {
-			t.Fatalf("Get() of the cached variant error = %v", got.err)
-		}
-	case <-time.After(pendingAccessTimesWait):
-		t.Fatal("the cache hit waited for the database")
-	}
-
-	releaseDatabase()
-
-	deadline := time.Now().Add(pendingAccessTimesWait)
-
-	for countRows(t, svc.cache, `
-		SELECT COUNT(*) FROM variant_content
-		WHERE cache_key = ? AND last_accessed_at > ?
-	`, string(key), anHourAgo.UTC().Format(sqliteTimestampFormat)) == 0 {
-		if time.Now().After(deadline) {
-			t.Fatal("the hit's access time was not written")
-		}
-
-		time.Sleep(10 * time.Millisecond)
-	}
-}
-
 // TestTouchVariantAndTouchSourceContent_DropAccessTimesPastTheLimit hands one
 // more access time of a variant, and one more of a source, than may wait to
 // be written. touchVariant and touchSourceContent must return each time

internal/imgcache/cache_internal_test.go

@@ -50,7 +50,7 @@ func TestCache_CleanExpired(t *testing.T) {
 	tmpDir := t.TempDir()
 	db := setupTestDB(t)
 
-	cache, _ := NewCache(db, CacheConfig{
+	cache, _ := NewCache(db, Config{
 		StateDir:    tmpDir,
 		NegativeTTL: 1 * time.Millisecond,
 		MaxBytes:    1 << 30,
@@ -103,7 +103,7 @@ func TestCache_StorageDirectoriesCreated(t *testing.T) {
 	tmpDir := t.TempDir()
 	db := setupTestDB(t)
 
-	_, err := NewCache(db, CacheConfig{
+	_, err := NewCache(db, Config{
 		StateDir: tmpDir,
 		MaxBytes: 1 << 30,
 	}, prometheus.NewRegistry())

internal/imgcache/counters.go

@@ -19,22 +19,8 @@ func (c *Cache) registerCounters(metricsRegistry prometheus.Registerer) error {
 		Name: "pixa_cache_misses_total",
 		Help: "Image requests not served from the cache.",
 	})
-	c.upstreamFetches = prometheus.NewCounter(prometheus.CounterOpts{
-		Name: "pixa_upstream_fetches_total",
-		Help: "Fetches of a source image from upstream that read any bytes.",
-	})
-	c.upstreamFetchBytes = prometheus.NewCounter(prometheus.CounterOpts{
-		Name: "pixa_upstream_fetch_bytes_total",
-		Help: "Bytes read from upstream by fetches of source images.",
-	})
-	c.transforms = prometheus.NewCounter(prometheus.CounterOpts{
-		Name: "pixa_transforms_total",
-		Help: "Images the image processor transformed.",
-	})
 
-	for _, counter := range []prometheus.Counter{
-		c.cacheHits, c.cacheMisses, c.upstreamFetches, c.upstreamFetchBytes, c.transforms,
-	} {
+	for _, counter := range []prometheus.Counter{c.cacheHits, c.cacheMisses} {
 		err := metricsRegistry.Register(counter)
 		if err != nil {
 			return fmt.Errorf("failed to register the cache's counters: %w", err)

internal/imgcache/counters_internal_test.go

@@ -8,26 +8,6 @@ import (
 	"github.com/prometheus/client_golang/prometheus/testutil"
 )
 
-// counterValues holds the values of a cache's counters.
-type counterValues struct {
-	hitCount           int64
-	missCount          int64
-	upstreamFetchCount int64
-	upstreamFetchBytes int64
-	transformCount     int64
-}
-
-// readCounters reads cache's counters.
-func readCounters(cache *Cache) counterValues {
-	return counterValues{
-		hitCount:           int64(testutil.ToFloat64(cache.cacheHits)),
-		missCount:          int64(testutil.ToFloat64(cache.cacheMisses)),
-		upstreamFetchCount: int64(testutil.ToFloat64(cache.upstreamFetches)),
-		upstreamFetchBytes: int64(testutil.ToFloat64(cache.upstreamFetchBytes)),
-		transformCount:     int64(testutil.ToFloat64(cache.transforms)),
-	}
-}
-
 // TestNewCache_RegistersItsCountersOnItsRegistry checks that NewCache
 // registers the cache's counters on the registry it is given, under the
 // names README.md gives them.
@@ -37,7 +17,7 @@ func TestNewCache_RegistersItsCountersOnItsRegistry(t *testing.T) {
 	registry := prometheus.NewRegistry()
 
 	_, err := NewCache(evictionTestDB(t),
-		CacheConfig{StateDir: t.TempDir(), MaxBytes: 1 << 30}, registry)
+		Config{StateDir: t.TempDir(), MaxBytes: 1 << 30}, registry)
 	if err != nil {
 		t.Fatalf("NewCache() error = %v", err)
 	}
@@ -45,9 +25,6 @@ func TestNewCache_RegistersItsCountersOnItsRegistry(t *testing.T) {
 	names := []string{
 		"pixa_cache_hits_total",
 		"pixa_cache_misses_total",
-		"pixa_upstream_fetches_total",
-		"pixa_upstream_fetch_bytes_total",
-		"pixa_transforms_total",
 	}
 
 	count, err := testutil.GatherAndCount(registry, names...)
@@ -70,13 +47,13 @@ func TestNewCache_FailsWhenItsCountersCannotBeRegistered(t *testing.T) {
 	registry := prometheus.NewRegistry()
 
 	_, err := NewCache(evictionTestDB(t),
-		CacheConfig{StateDir: t.TempDir(), MaxBytes: 1 << 30}, registry)
+		Config{StateDir: t.TempDir(), MaxBytes: 1 << 30}, registry)
 	if err != nil {
 		t.Fatalf("NewCache() of the first cache error = %v", err)
 	}
 
 	_, err = NewCache(evictionTestDB(t),
-		CacheConfig{StateDir: t.TempDir(), MaxBytes: 1 << 30}, registry)
+		Config{StateDir: t.TempDir(), MaxBytes: 1 << 30}, registry)
 	t.Logf("NewCache() of the second cache error = %v", err)
 
 	var alreadyRegistered prometheus.AlreadyRegisteredError

internal/imgcache/eviction.go

@@ -317,7 +317,7 @@ func (c *Cache) evictVariant(
 // evictSourceBlob removes one source: its row first, then its file, as
 // evictVariant does for a variant. It holds no lock: a store of the same
 // source in between can leave the source's row with no file, which
-// LookupSource treats as a miss.
+// Source treats as a miss.
 func (c *Cache) evictSourceBlob(ctx context.Context, key imagerequest.SourceKey) error {
 	_, err := c.db.ExecContext(ctx,
 		`DELETE FROM source_content WHERE source_key = ?`, string(key))
@@ -479,7 +479,7 @@ func (c *Cache) runCleanExpired(ctx context.Context) {
 // then on the first periodic eviction tick that comes at least ten times
 // as long after the last pass ended as that pass took, off the request
 // hot path: it adopts variant files that predate the accounting table
-// (or whose accounting insert failed, e.g. StoreVariant's best-effort
+// (or whose accounting insert failed, e.g. PutVariant's best-effort
 // insert under transient DB contention), drops variant accounting rows
 // whose files are missing, removes source blob files the database does
 // not know, removes source and variant files that are empty or not the

internal/imgcache/eviction_internal_test.go

@@ -67,7 +67,7 @@ func newEvictionTestCache(t *testing.T, maxBytes int64) (*Cache, string) {
 	db := evictionTestDB(t)
 
 	// maxBytes zero turns the disk cache off, as cache_max_bytes: 0 does.
-	cache, err := NewCache(db, CacheConfig{
+	cache, err := NewCache(db, Config{
 		StateDir:    tmpDir,
 		NegativeTTL: 5 * time.Minute,
 		MaxBytes:    maxBytes,
@@ -98,11 +98,11 @@ func storeEvictionTestSource(
 		},
 	}
 
-	key, err := cache.StoreSource(
-		context.Background(), req, bytes.NewReader(content),
+	key, err := cache.PutSource(
+		context.Background(), req.Source, bytes.NewReader(content),
 	)
 	if err != nil {
-		t.Fatalf("StoreSource(%s%s) failed: %v", host, path, err)
+		t.Fatalf("PutSource(%s%s) failed: %v", host, path, err)
 	}
 
 	return key
@@ -115,9 +115,9 @@ func storeEvictionTestVariant(
 ) {
 	t.Helper()
 
-	err := cache.StoreVariant(t.Context(), key, bytes.NewReader(content))
+	err := cache.PutVariant(t.Context(), key, bytes.NewReader(content))
 	if err != nil {
-		t.Fatalf("StoreVariant(%s) failed: %v", key, err)
+		t.Fatalf("PutVariant(%s) failed: %v", key, err)
 	}
 }
 
@@ -423,20 +423,20 @@ func assertDisabledCacheWritesAreNoOps(
 
 	ctx := t.Context()
 
-	err := cache.StoreVariant(
+	err := cache.PutVariant(
 		ctx, imagerequest.CacheKey(req), bytes.NewReader([]byte("data")),
 	)
 	if err != nil {
-		t.Fatalf("StoreVariant on disabled cache must be a no-op, got error: %v", err)
+		t.Fatalf("PutVariant on disabled cache must be a no-op, got error: %v", err)
 	}
 
-	key, err := cache.StoreSource(ctx, req, bytes.NewReader([]byte("data")))
+	key, err := cache.PutSource(ctx, req.Source, bytes.NewReader([]byte("data")))
 	if err != nil {
-		t.Fatalf("StoreSource on disabled cache must be a no-op, got error: %v", err)
+		t.Fatalf("PutSource on disabled cache must be a no-op, got error: %v", err)
 	}
 
 	if key != "" {
-		t.Errorf("StoreSource on disabled cache returned key %q, want empty", key)
+		t.Errorf("PutSource on disabled cache returned key %q, want empty", key)
 	}
 }
 
@@ -449,13 +449,13 @@ func assertDisabledCacheReadsAlwaysMiss(
 
 	ctx := t.Context()
 
-	key, err := cache.LookupSource(ctx, req)
-	if err != nil {
-		t.Fatalf("LookupSource on disabled cache failed: %v", err)
+	reader, _, err := cache.Source(ctx, req.Source)
+	if !errors.Is(err, ErrNotFound) {
+		t.Fatalf("Source on disabled cache error = %v, want %v", err, ErrNotFound)
 	}
 
-	if key != "" {
-		t.Errorf("LookupSource on disabled cache = %q, want empty", key)
+	if reader != nil {
+		t.Errorf("Source on disabled cache = reader %v, want none", reader)
 	}
 }
 
@@ -544,7 +544,7 @@ func TestEvictionRunsUnderWritePressure(t *testing.T) {
 }
 
 // TestEvictionRunsOnPeriodicSchedule writes three variant files straight
-// to disk, bypassing StoreVariant, so they have no accounting rows and no
+// to disk, bypassing PutVariant, so they have no accounting rows and no
 // write-pressure notification fires. Only a periodic reconciliation pass
 // can then adopt them, and only the eviction pass that follows it can
 // evict them.
@@ -697,7 +697,7 @@ func TestStartEvictionReconcilesAccountingWithDisk(t *testing.T) {
 // TestPeriodicReconciliationAdoptsFileThatAppearsAfterStartup proves
 // reconciliation is not a one-shot startup-only pass: it must also run
 // on the periodic ticker, so a variant file that lands on disk with no
-// accounting row well after startup (e.g. because StoreVariant's
+// accounting row well after startup (e.g. because PutVariant's
 // best-effort accounting insert failed under transient contention, or
 // any other cause of an untracked file appearing during steady-state
 // operation) is still adopted into accounting eventually, rather than
@@ -733,7 +733,7 @@ func TestPeriodicReconciliationAdoptsFileThatAppearsAfterStartup(t *testing.T) {
 
 	// Simulate a variant whose accounting insert failed after the
 	// process was already running and serving requests: the content
-	// file is written directly, bypassing StoreVariant's (and thus its
+	// file is written directly, bypassing PutVariant's (and thus its
 	// accounting insert) entirely, exactly as would happen if that
 	// insert had failed and only the file write had succeeded.
 	untracked := bytes.Repeat([]byte{0x41}, 900)

internal/imgcache/imgcache.go

@@ -1,29 +0,0 @@
-// Package imgcache provides types for the image caching proxy.
-package imgcache
-
-import "io"
-
-// ImageResponse represents a processed image ready to serve
-type ImageResponse struct {
-	// Content is the image data reader
-	Content io.ReadCloser
-	// ContentLength is the size in bytes (-1 if unknown)
-	ContentLength int64
-	// ContentType is the MIME type of the response
-	ContentType string
-	// ETag is the entity tag for caching
-	ETag string
-	// CacheStatus indicates HIT or MISS
-	CacheStatus CacheStatus
-	// FetchedBytes is the number of bytes fetched from upstream (0 if cache hit)
-	FetchedBytes int64
-}
-
-// CacheStatus indicates whether the response was served from cache.
-type CacheStatus string
-
-// Cache status values for response headers.
-const (
-	CacheHit  CacheStatus = "HIT"
-	CacheMiss CacheStatus = "MISS"
-)

internal/imgcache/module.go

@@ -1,8 +0,0 @@
-package imgcache
-
-import "time"
-
-// CacheConfig defaults.
-const (
-	DefaultNegativeTTL = 5 * time.Minute
-)

internal/imgcache/negative_cache_internal_test.go

@@ -17,7 +17,7 @@ func TestNegativeCache_StoreAndCheck(t *testing.T) {
 	db := setupTestDB(t)
 	dir := t.TempDir()
 
-	cache, err := NewCache(db, CacheConfig{
+	cache, err := NewCache(db, Config{
 		StateDir:    dir,
 		NegativeTTL: 5 * time.Minute,
 		MaxBytes:    1 << 30,
@@ -35,7 +35,7 @@ func TestNegativeCache_StoreAndCheck(t *testing.T) {
 	}
 
 	// Initially should not be in negative cache
-	hit, err := cache.checkNegativeCache(ctx, req)
+	hit, err := cache.Failure(ctx, req.Source)
 	if err != nil {
 		t.Fatal(err)
 	}
@@ -45,13 +45,13 @@ func TestNegativeCache_StoreAndCheck(t *testing.T) {
 	}
 
 	// Store a negative entry
-	err = cache.StoreNegative(ctx, req)
+	err = cache.PutFailure(ctx, req.Source)
 	if err != nil {
 		t.Fatal(err)
 	}
 
 	// Now should be in negative cache
-	hit, err = cache.checkNegativeCache(ctx, req)
+	hit, err = cache.Failure(ctx, req.Source)
 	if err != nil {
 		t.Fatal(err)
 	}
@@ -67,7 +67,7 @@ func TestNegativeCache_Expired(t *testing.T) {
 	db := setupTestDB(t)
 	dir := t.TempDir()
 
-	cache, err := NewCache(db, CacheConfig{
+	cache, err := NewCache(db, Config{
 		StateDir:    dir,
 		NegativeTTL: 1 * time.Millisecond, // very short TTL
 		MaxBytes:    1 << 30,
@@ -85,7 +85,7 @@ func TestNegativeCache_Expired(t *testing.T) {
 	}
 
 	// Store a negative entry with very short TTL
-	err = cache.StoreNegative(ctx, req)
+	err = cache.PutFailure(ctx, req.Source)
 	if err != nil {
 		t.Fatal(err)
 	}
@@ -94,7 +94,7 @@ func TestNegativeCache_Expired(t *testing.T) {
 	time.Sleep(10 * time.Millisecond)
 
 	// Should no longer be in negative cache
-	hit, err := cache.checkNegativeCache(ctx, req)
+	hit, err := cache.Failure(ctx, req.Source)
 	if err != nil {
 		t.Fatal(err)
 	}
@@ -104,71 +104,6 @@ func TestNegativeCache_Expired(t *testing.T) {
 	}
 }
 
-// TestService_Get_ServesCachedVariantOfNegativeCachedURL caches a variant of
-// the test photo, then keeps a failed fetch of the photo's URL in the negative
-// cache, as a failed fetch for another variant does once the source has been
-// evicted. The cached variant is still served, and a variant not in the cache
-// is made from the cached source. Once the source is evicted, a variant not in
-// the cache needs a fetch and is refused.
-func TestService_Get_ServesCachedVariantOfNegativeCachedURL(t *testing.T) {
-	t.Parallel()
-
-	svc, fixtures := SetupTestService(t)
-
-	resp, err := svc.Get(t.Context(), photoVariant(fixtures, 85, imagerequest.FitCover))
-	if err != nil {
-		t.Fatalf("Get() first request error = %v", err)
-	}
-
-	_ = resp.Content.Close()
-
-	err = svc.cache.StoreNegative(t.Context(),
-		photoVariant(fixtures, 85, imagerequest.FitCover))
-	if err != nil {
-		t.Fatalf("StoreNegative() error = %v", err)
-	}
-
-	resp, err = svc.Get(t.Context(), photoVariant(fixtures, 85, imagerequest.FitCover))
-	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)
-	}
-
-	resp, err = svc.Get(t.Context(), photoVariant(fixtures, 40, imagerequest.FitCover))
-	t.Logf("Get() of a variant made from the cached source: error = %v", err)
-
-	if err != nil {
-		t.Fatalf("Get() of a variant made from the cached source error = %v", err)
-	}
-
-	_ = resp.Content.Close()
-
-	sourceKey, err := svc.cache.LookupSource(t.Context(),
-		photoVariant(fixtures, 85, imagerequest.FitCover))
-	if err != nil || sourceKey == "" {
-		t.Fatalf("LookupSource() = %q, %v, want the cached source", sourceKey, err)
-	}
-
-	err = svc.cache.evictSourceBlob(t.Context(), sourceKey)
-	if err != nil {
-		t.Fatalf("evictSourceBlob() error = %v", err)
-	}
-
-	_, err = svc.Get(t.Context(), photoVariant(fixtures, 60, imagerequest.FitCover))
-	t.Logf("Get() of a variant whose source was evicted: error = %v", err)
-
-	if !errors.Is(err, ErrNegativeCached) {
-		t.Errorf("Get() of a variant whose source was evicted error = %v, want %v",
-			err, ErrNegativeCached)
-	}
-}
-
 // TestEvictionLoopRemovesExpiredNegativeCacheRows stores a failed fetch
 // that expires a second later and starts the eviction loop with a short
 // interval: a later tick must remove its row although its URL is never
@@ -190,7 +125,7 @@ func TestEvictionLoopRemovesExpiredNegativeCacheRows(t *testing.T) {
 		t.Run(tt.name, func(t *testing.T) {
 			t.Parallel()
 
-			cache, err := NewCache(evictionTestDB(t), CacheConfig{
+			cache, err := NewCache(evictionTestDB(t), Config{
 				StateDir:    t.TempDir(),
 				NegativeTTL: time.Second,
 				MaxBytes:    tt.maxBytes,
@@ -203,9 +138,9 @@ func TestEvictionLoopRemovesExpiredNegativeCacheRows(t *testing.T) {
 				Source: imagerequest.Source{Host: testHostExample, Path: "/gone.jpg"},
 			}
 
-			err = cache.StoreNegative(t.Context(), expired)
+			err = cache.PutFailure(t.Context(), expired.Source)
 			if err != nil {
-				t.Fatalf("StoreNegative failed: %v", err)
+				t.Fatalf("PutFailure failed: %v", err)
 			}
 
 			const notExpiredPath = "/later.jpg"
@@ -269,7 +204,7 @@ func TestCleanExpiredDeletesInBatches(t *testing.T) {
 	t.Parallel()
 
 	cache, err := NewCache(evictionTestDB(t),
-		CacheConfig{StateDir: t.TempDir(), MaxBytes: 1 << 30},
+		Config{StateDir: t.TempDir(), MaxBytes: 1 << 30},
 		prometheus.NewRegistry())
 	if err != nil {
 		t.Fatalf("failed to create cache: %v", err)
@@ -325,7 +260,7 @@ func TestCleanExpiredRemovesMoreThanOneBatch(t *testing.T) {
 	t.Parallel()
 
 	cache, err := NewCache(evictionTestDB(t),
-		CacheConfig{StateDir: t.TempDir(), MaxBytes: 1 << 30},
+		Config{StateDir: t.TempDir(), MaxBytes: 1 << 30},
 		prometheus.NewRegistry())
 	if err != nil {
 		t.Fatalf("failed to create cache: %v", err)
@@ -357,7 +292,7 @@ func TestCleanExpiredStopsOnceContextEnds(t *testing.T) {
 	t.Parallel()
 
 	cache, err := NewCache(evictionTestDB(t),
-		CacheConfig{StateDir: t.TempDir(), MaxBytes: 1 << 30},
+		Config{StateDir: t.TempDir(), MaxBytes: 1 << 30},
 		prometheus.NewRegistry())
 	if err != nil {
 		t.Fatalf("failed to create cache: %v", err)
@@ -410,15 +345,3 @@ func negativeCacheTableRowCount(tb testing.TB, cache *Cache) int {
 
 	return count
 }
-
-func TestService_Get_ReturnsErrorForNegativeCachedURL(t *testing.T) {
-	t.Parallel()
-
-	// This test verifies that Service.Get() checks the negative cache
-	// We can't easily test the full pipeline without vips, but we can
-	// verify the error type
-	err := ErrNegativeCached
-	if !errors.Is(err, ErrNegativeCached) {
-		t.Error("ErrNegativeCached should be identifiable with errors.Is")
-	}
-}

internal/imgcache/partial_cache_files_internal_test.go

@@ -12,67 +12,6 @@ import (
 	"sneak.berlin/go/pixa/internal/imagerequest"
 )
 
-// getImage calls Get for req and returns the image it answered with and
-// its cache status.
-func getImage(
-	t *testing.T, svc *Service, req *imagerequest.Request,
-) ([]byte, CacheStatus) {
-	t.Helper()
-
-	resp, err := svc.Get(t.Context(), req)
-	if err != nil {
-		t.Fatalf("Get() of quality %d error = %v", req.Transform.Quality, err)
-	}
-
-	defer func() { _ = resp.Content.Close() }()
-
-	body, err := io.ReadAll(resp.Content)
-	if err != nil {
-		t.Fatalf("reading the image of quality %d: %v", req.Transform.Quality, err)
-	}
-
-	return body, resp.CacheStatus
-}
-
-// fileSize returns the size of the file at path.
-func fileSize(t *testing.T, path string) int64 {
-	t.Helper()
-
-	info, err := os.Stat(path)
-	if err != nil {
-		t.Fatalf("stat %s: %v", path, err)
-	}
-
-	return info.Size()
-}
-
-// truncateFile cuts the file at path down to size bytes.
-func truncateFile(t *testing.T, path string, size int64) {
-	t.Helper()
-
-	t.Logf("cutting %s from %d to %d bytes",
-		filepath.Base(path), fileSize(t, path), size)
-
-	err := os.Truncate(path, size)
-	if err != nil {
-		t.Fatalf("truncating %s: %v", path, err)
-	}
-}
-
-// cachedSourcePath returns the path of the cached source file req uses.
-func cachedSourcePath(
-	t *testing.T, svc *Service, req *imagerequest.Request,
-) string {
-	t.Helper()
-
-	sourceKey, err := svc.cache.LookupSource(t.Context(), req)
-	if err != nil || sourceKey == "" {
-		t.Fatalf("LookupSource() = %q, %v; want the cached source", sourceKey, err)
-	}
-
-	return svc.cache.srcContent.keyToPath(sourceKey)
-}
-
 // reconcileAsAtStartup runs the cache's reconciliation pass, as pixa does
 // when it starts, and returns what the pass logged.
 func reconcileAsAtStartup(t *testing.T, cache *Cache) string {
@@ -107,129 +46,6 @@ func assertWarningNames(t *testing.T, logs, path string) {
 	t.Errorf("reconciliation logged no warning naming %s", path)
 }
 
-// TestService_Get_FetchesAgainForEmptyCachedSource empties the cached source
-// file, as a crash or a restored snapshot could, and runs the reconciliation
-// pass, which must remove it with a warning naming it. It then asks for two
-// new sizes of the source: the first must fetch it again and cache it whole,
-// so that the second is made from the cache without a third fetch.
-func TestService_Get_FetchesAgainForEmptyCachedSource(t *testing.T) {
-	t.Parallel()
-
-	svc, fixtures := SetupTestService(t)
-
-	getImage(t, svc, photoVariant(fixtures, 85, imagerequest.FitCover))
-
-	path := cachedSourcePath(t, svc, photoVariant(fixtures, 85, imagerequest.FitCover))
-	wholeSize := fileSize(t, path)
-
-	truncateFile(t, path, 0)
-	assertWarningNames(t, reconcileAsAtStartup(t, svc.cache), path)
-
-	getImage(t, svc, photoVariant(fixtures, 40, imagerequest.FitCover))
-	getImage(t, svc, photoVariant(fixtures, 30, imagerequest.FitCover))
-
-	fetches := readCounters(svc.cache).upstreamFetchCount
-	t.Logf("upstream fetches = %d", fetches)
-
-	if fetches != 2 {
-		t.Errorf("upstream fetches = %d, want 2: the empty cached source "+
-			"was kept and fetched again on every new size", fetches)
-	}
-
-	size := fileSize(t, path)
-	if size != wholeSize {
-		t.Errorf("cached source is %d bytes, want %d", size, wholeSize)
-	}
-}
-
-// TestService_Get_FetchesAgainForPartialCachedSource cuts the cached source
-// file to half its size, as a crash or a restored snapshot could, and runs
-// the reconciliation pass, which must remove it with a warning naming it.
-// It then asks for two new sizes of the source: the first must fetch it
-// again rather than fail to decode the partial file, and the second is
-// made from the cache.
-func TestService_Get_FetchesAgainForPartialCachedSource(t *testing.T) {
-	t.Parallel()
-
-	svc, fixtures := SetupTestService(t)
-
-	getImage(t, svc, photoVariant(fixtures, 85, imagerequest.FitCover))
-
-	path := cachedSourcePath(t, svc, photoVariant(fixtures, 85, imagerequest.FitCover))
-	wholeSize := fileSize(t, path)
-
-	truncateFile(t, path, wholeSize/2)
-	assertWarningNames(t, reconcileAsAtStartup(t, svc.cache), path)
-
-	getImage(t, svc, photoVariant(fixtures, 40, imagerequest.FitCover))
-	getImage(t, svc, photoVariant(fixtures, 30, imagerequest.FitCover))
-
-	fetches := readCounters(svc.cache).upstreamFetchCount
-	t.Logf("upstream fetches = %d", fetches)
-
-	if fetches != 2 {
-		t.Errorf("upstream fetches = %d, want 2", fetches)
-	}
-
-	size := fileSize(t, path)
-	if size != wholeSize {
-		t.Errorf("cached source is %d bytes, want %d", size, wholeSize)
-	}
-}
-
-// assertConvertedAgain caches a variant of the photo, cuts its file to size
-// bytes and runs the reconciliation pass, which must remove it with a
-// warning naming it. It then checks that Get converts the image again
-// instead of serving the file, and that the next Get serves the whole
-// variant from the cache.
-func assertConvertedAgain(t *testing.T, size int64) {
-	t.Helper()
-
-	svc, fixtures := SetupTestService(t)
-	req := photoVariant(fixtures, 85, imagerequest.FitCover)
-
-	want, _ := getImage(t, svc, req)
-
-	path := svc.cache.variants.keyToPath(imagerequest.CacheKey(req))
-
-	truncateFile(t, path, size)
-	assertWarningNames(t, reconcileAsAtStartup(t, svc.cache), path)
-
-	got, status := getImage(t, svc, req)
-	t.Logf("after the cut: %d bytes, %s", len(got), status)
-
-	if status != CacheMiss || !bytes.Equal(got, want) {
-		t.Errorf("after the cut: Get() = %d bytes, %s; want the %d bytes "+
-			"converted again, %s", len(got), status, len(want), CacheMiss)
-	}
-
-	got, status = getImage(t, svc, req)
-	t.Logf("next request: %d bytes, %s", len(got), status)
-
-	if status != CacheHit || !bytes.Equal(got, want) {
-		t.Errorf("next request: Get() = %d bytes, %s; want the %d bytes, %s",
-			len(got), status, len(want), CacheHit)
-	}
-}
-
-// TestService_Get_ConvertsAgainForEmptyCachedVariant empties a cached
-// variant file, as a crash or a restored snapshot could, and checks that it
-// is converted again rather than served empty.
-func TestService_Get_ConvertsAgainForEmptyCachedVariant(t *testing.T) {
-	t.Parallel()
-
-	assertConvertedAgain(t, 0)
-}
-
-// TestService_Get_ConvertsAgainForPartialCachedVariant cuts a cached
-// variant file to ten bytes, as a crash or a restored snapshot could, and
-// checks that it is converted again rather than served cut short.
-func TestService_Get_ConvertsAgainForPartialCachedVariant(t *testing.T) {
-	t.Parallel()
-
-	assertConvertedAgain(t, 10)
-}
-
 // TestReconciliationRemovesEmptyVariantFileWithoutRow checks that the
 // reconciliation pass removes an empty variant file that has no
 // accounting row, with a warning naming it, instead of adding a row for

internal/imgcache/pendingaccesstimes_internal_test.go

@@ -5,6 +5,7 @@ import (
 	"context"
 	"database/sql"
 	"errors"
+	"io"
 	"log/slog"
 	"strings"
 	"testing"
@@ -15,8 +16,7 @@ import (
 
 // pendingAccessTimesWait is how long a test waits for the database's
 // connection, for an access time to reach the database, for a write to start
-// waiting for the connection, for a request to return past its deadline, or
-// for StopPendingAccessTimeWrites to return.
+// waiting for the connection, or for StopPendingAccessTimeWrites to return.
 const pendingAccessTimesWait = 5 * time.Second
 
 // otherWritesWait is how long a test gives other writes, once one write waits
@@ -56,52 +56,6 @@ func waitForConnectionWaits(t *testing.T, db *sql.DB, waits int64) {
 	}
 }
 
-// TestService_Get_ReturnsByItsDeadlineWhileTheDatabaseIsBusy holds the
-// database's one connection while a request whose fetch is held reaches its
-// deadline. The request must return with the deadline's error while the
-// connection is still held, as it waits for no database write past its
-// deadline.
-func TestService_Get_ReturnsByItsDeadlineWhileTheDatabaseIsBusy(t *testing.T) {
-	t.Parallel()
-
-	svc, fixtures, fetcher := setupHeldFetchService(t)
-
-	svc.cache.StartPendingAccessTimeWrites()
-	defer func() { _ = svc.cache.StopPendingAccessTimeWrites(t.Context()) }()
-
-	// Room for the request to reach its fetch on a busy host
-	const timeout = 2 * time.Second
-
-	ctx, cancel := context.WithTimeout(t.Context(), timeout)
-	defer cancel()
-
-	deadline, _ := ctx.Deadline()
-
-	results := startGet(ctx, svc, photoVariant(fixtures, 85, imagerequest.FitCover))
-
-	// The request has made its database reads by the time it fetches.
-	select {
-	case <-fetcher.started:
-	case <-time.After(timeout):
-		t.Fatal("request did not reach its fetch by its deadline")
-	}
-
-	releaseDatabase := holdDatabase(t, svc.cache)
-	defer releaseDatabase()
-
-	select {
-	case got := <-results:
-		t.Logf("Get() returned %v after its deadline, error = %v",
-			time.Since(deadline), got.err)
-
-		if !errors.Is(got.err, context.DeadlineExceeded) {
-			t.Errorf("Get() error = %v, want %v", got.err, context.DeadlineExceeded)
-		}
-	case <-time.After(time.Until(deadline) + pendingAccessTimesWait):
-		t.Fatal("request did not return while the database was busy")
-	}
-}
-
 // TestStopPendingAccessTimeWrites_LetsTheWriteUnderWayFinish holds the
 // database's one connection while the goroutine that writes the pending
 // access times waits for it, hands over another access time, then stops that
@@ -242,11 +196,11 @@ func TestStopPendingAccessTimeWrites_ReturnsWhenItsContextEnds(t *testing.T) {
 	}
 }
 
-// TestLookupSource_HandsAccessTimeToTheBackgroundWriter finds a cached source
-// whose access time is an hour old. LookupSource must not write the access
+// TestSource_HandsAccessTimeToTheBackgroundWriter finds a cached source
+// whose access time is an hour old. Source must not write the access
 // time itself but hand it over to be written, and StopPendingAccessTimeWrites
 // must then write it.
-func TestLookupSource_HandsAccessTimeToTheBackgroundWriter(t *testing.T) {
+func TestSource_HandsAccessTimeToTheBackgroundWriter(t *testing.T) {
 	t.Parallel()
 
 	cache, _ := newEvictionTestCache(t, 1<<30)
@@ -261,15 +215,21 @@ func TestLookupSource_HandsAccessTimeToTheBackgroundWriter(t *testing.T) {
 	`
 	anHourAgoInDatabase := anHourAgo.UTC().Format(sqliteTimestampFormat)
 
-	found, err := cache.LookupSource(t.Context(), &imagerequest.Request{
-		Source: imagerequest.Source{Host: "example.com", Path: "/photo.jpg"},
-	})
-	if err != nil || found != key {
-		t.Fatalf("LookupSource() = %q, %v; want %q", found, err, key)
+	reader, _, err := cache.Source(t.Context(),
+		imagerequest.Source{Host: "example.com", Path: "/photo.jpg"})
+	if err != nil {
+		t.Fatalf("Source() error = %v; want the source of %q", err, key)
+	}
+
+	found, err := io.ReadAll(reader)
+	_ = reader.Close()
+
+	if err != nil || string(found) != "source bytes" {
+		t.Fatalf("Source() reads %q, %v; want the source of %q", found, err, key)
 	}
 
 	if countRows(t, cache, touchedQuery, string(key), anHourAgoInDatabase) != 0 {
-		t.Error("LookupSource wrote the source's access time itself")
+		t.Error("Source wrote the source's access time itself")
 	}
 
 	if waiting := len(cache.pendingSourceAccessTimes); waiting != 1 {

internal/imgcache/source_content_internal_test.go

@@ -10,11 +10,11 @@ import (
 	"sneak.berlin/go/pixa/internal/imagerequest"
 )
 
-// TestStoreSource_StoresIdenticalBytesOfTwoURLsTwice stores the same bytes
+// TestPutSource_StoresIdenticalBytesOfTwoURLsTwice stores the same bytes
 // for two source URLs and checks that each URL has a source_content row of
 // its own and a file of its own, named by its source key under
 // cache/sources/<ab>/<cd>/.
-func TestStoreSource_StoresIdenticalBytesOfTwoURLsTwice(t *testing.T) {
+func TestPutSource_StoresIdenticalBytesOfTwoURLsTwice(t *testing.T) {
 	t.Parallel()
 
 	cache, stateDir := newEvictionTestCache(t, 1<<30)
@@ -84,18 +84,12 @@ func TestEvictSourceBlob_LeavesSourceWithIdenticalBytesServed(t *testing.T) {
 		t.Errorf("the evicted source still has %d source_content rows", n)
 	}
 
-	kept, err := cache.LookupSource(t.Context(), &imagerequest.Request{
-		Source: imagerequest.Source{Host: testHostCDN, Path: "/kept.jpg"},
-	})
-	t.Logf("LookupSource() of the kept source = %q, error %v", kept, err)
+	reader, _, err := cache.Source(t.Context(),
+		imagerequest.Source{Host: testHostCDN, Path: "/kept.jpg"})
+	t.Logf("Source() of the kept source: error %v", err)
 
-	if err != nil || kept == "" {
-		t.Fatalf("LookupSource() of the kept source = %q, %v; want it cached", kept, err)
-	}
-
-	reader, _, err := cache.GetSourceContent(kept)
 	if err != nil {
-		t.Fatalf("GetSourceContent() of the kept source error = %v", err)
+		t.Fatalf("Source() of the kept source error = %v; want it cached", err)
 	}
 
 	defer func() { _ = reader.Close() }()
@@ -111,10 +105,10 @@ func TestEvictSourceBlob_LeavesSourceWithIdenticalBytesServed(t *testing.T) {
 	}
 }
 
-// TestStoreSource_FailedRowWriteLeavesNoFile drops source_content, so that
-// StoreSource cannot write the source's row, and checks that the store fails
+// TestPutSource_FailedRowWriteLeavesNoFile drops source_content, so that
+// PutSource cannot write the source's row, and checks that the store fails
 // and leaves no file under the source's key.
-func TestStoreSource_FailedRowWriteLeavesNoFile(t *testing.T) {
+func TestPutSource_FailedRowWriteLeavesNoFile(t *testing.T) {
 	t.Parallel()
 
 	cache, _ := newEvictionTestCache(t, 1<<30)
@@ -127,12 +121,12 @@ func TestStoreSource_FailedRowWriteLeavesNoFile(t *testing.T) {
 	req := &imagerequest.Request{
 		Source: imagerequest.Source{Host: testHostCDN, Path: testPathCat},
 	}
-	key, err := cache.StoreSource(t.Context(), req,
+	key, err := cache.PutSource(t.Context(), req.Source,
 		bytes.NewReader([]byte("source bytes")))
-	t.Logf("StoreSource() = %q, error = %v", key, err)
+	t.Logf("PutSource() = %q, error = %v", key, err)
 
 	if err == nil {
-		t.Error("StoreSource() error = nil, want the failed row write")
+		t.Error("PutSource() error = nil, want the failed row write")
 	}
 
 	if cache.srcContent.Exists(req.Source.Key()) {

internal/imgcache/testutil_internal_test.go

@@ -2,98 +2,19 @@ package imgcache
 
 import (
 	"bytes"
-	"context"
-	"database/sql"
 	"image"
 	"image/color"
-	"image/gif"
 	"image/jpeg"
-	"image/png"
-	"io/fs"
 	"testing"
-	"testing/fstest"
-	"time"
-
-	"github.com/prometheus/client_golang/prometheus"
-	"sneak.berlin/go/pixa/internal/database"
-	"sneak.berlin/go/pixa/internal/httpfetcher"
-	"sneak.berlin/go/pixa/internal/imageprocessor"
 )
 
 // Shared test data literals, extracted as constants for goconst.
 const (
-	testHostCDN         = "cdn.example.com"
-	testHostExample     = "example.com"
-	testPathCat         = "/photos/cat.jpg"
-	testContentTypeJPEG = "image/jpeg"
+	testHostCDN     = "cdn.example.com"
+	testHostExample = "example.com"
+	testPathCat     = "/photos/cat.jpg"
 )
 
-// TestFixtures contains paths to test files in the mock filesystem.
-type TestFixtures struct {
-	// Valid image files
-	GoodHostJPEG  string // valid JPEG on GoodHost
-	GoodHostPNG   string // valid PNG on GoodHost
-	GoodHostGIF   string // valid GIF on GoodHost
-	OtherHostJPEG string // valid JPEG on OtherHost
-	OtherHostPNG  string // valid PNG on OtherHost
-
-	// Invalid/edge case files
-	InvalidFile string // file with wrong magic bytes
-	EmptyFile   string // zero-byte file
-	TextFile    string // text file masquerading as image
-
-	// Hostnames
-	GoodHost  string // a host the mock fetcher serves
-	OtherHost string // a second host the mock fetcher serves
-}
-
-// DefaultFixtures returns the standard test fixture paths.
-func DefaultFixtures() *TestFixtures {
-	return &TestFixtures{
-		GoodHostJPEG:  "goodhost.example.com/images/photo.jpg",
-		GoodHostPNG:   "goodhost.example.com/images/logo.png",
-		GoodHostGIF:   "goodhost.example.com/images/animation.gif",
-		OtherHostJPEG: "otherhost.example.com/uploads/image.jpg",
-		OtherHostPNG:  "otherhost.example.com/uploads/icon.png",
-		InvalidFile:   "goodhost.example.com/images/fake.jpg",
-		EmptyFile:     "goodhost.example.com/images/empty.jpg",
-		TextFile:      "goodhost.example.com/images/text.png",
-		GoodHost:      "goodhost.example.com",
-		OtherHost:     "otherhost.example.com",
-	}
-}
-
-// NewTestFS creates a mock filesystem with test images.
-func NewTestFS(t *testing.T) (fs.FS, *TestFixtures) {
-	t.Helper()
-
-	fixtures := DefaultFixtures()
-
-	// Generate test images
-	jpegData := generateTestJPEG(t, 100, 100, color.RGBA{255, 0, 0, 255})
-	pngData := generateTestPNG(t, 100, 100, color.RGBA{0, 255, 0, 255})
-	gifData := generateTestGIF(t, 100, 100, color.RGBA{0, 0, 255, 255})
-
-	// Create the mock filesystem
-	mockFS := fstest.MapFS{
-		// Good host files
-		fixtures.GoodHostJPEG: &fstest.MapFile{Data: jpegData},
-		fixtures.GoodHostPNG:  &fstest.MapFile{Data: pngData},
-		fixtures.GoodHostGIF:  &fstest.MapFile{Data: gifData},
-
-		// Other host files
-		fixtures.OtherHostJPEG: &fstest.MapFile{Data: jpegData},
-		fixtures.OtherHostPNG:  &fstest.MapFile{Data: pngData},
-
-		// Invalid files
-		fixtures.InvalidFile: &fstest.MapFile{Data: []byte("not a real image file content")},
-		fixtures.EmptyFile:   &fstest.MapFile{Data: []byte{}},
-		fixtures.TextFile:    &fstest.MapFile{Data: []byte("This is just text, not a PNG")},
-	}
-
-	return mockFS, fixtures
-}
-
 // generateTestJPEG creates a minimal valid JPEG image.
 func generateTestJPEG(t *testing.T, width, height int, c color.Color) []byte {
 	t.Helper()
@@ -114,104 +35,3 @@ func generateTestJPEG(t *testing.T, width, height int, c color.Color) []byte {
 
 	return buf.Bytes()
 }
-
-// generateTestPNG creates a minimal valid PNG image.
-func generateTestPNG(t *testing.T, width, height int, c color.Color) []byte {
-	t.Helper()
-
-	img := image.NewRGBA(image.Rect(0, 0, width, height))
-	for y := range height {
-		for x := range width {
-			img.Set(x, y, c)
-		}
-	}
-
-	var buf bytes.Buffer
-
-	err := png.Encode(&buf, img)
-	if err != nil {
-		t.Fatalf("failed to encode test PNG: %v", err)
-	}
-
-	return buf.Bytes()
-}
-
-// generateTestGIF creates a minimal valid GIF image.
-func generateTestGIF(t *testing.T, width, height int, c color.Color) []byte {
-	t.Helper()
-
-	img := image.NewPaletted(
-		image.Rect(0, 0, width, height),
-		[]color.Color{c, color.White},
-	)
-	for y := range height {
-		for x := range width {
-			img.SetColorIndex(x, y, 0)
-		}
-	}
-
-	var buf bytes.Buffer
-
-	err := gif.Encode(&buf, img, nil)
-	if err != nil {
-		t.Fatalf("failed to encode test GIF: %v", err)
-	}
-
-	return buf.Bytes()
-}
-
-// SetupTestService creates a Service with mock fetcher for testing.
-func SetupTestService(t *testing.T) (*Service, *TestFixtures) {
-	t.Helper()
-
-	mockFS, fixtures := NewTestFS(t)
-
-	// Create temp directory for cache
-	tmpDir := t.TempDir()
-
-	// Create in-memory database
-	db := setupServiceTestDB(t)
-
-	cache, err := NewCache(db, CacheConfig{
-		StateDir:    tmpDir,
-		NegativeTTL: 5 * time.Minute,
-		MaxBytes:    1 << 30,
-	}, prometheus.NewRegistry())
-	if err != nil {
-		t.Fatalf("failed to create cache: %v", err)
-	}
-
-	svc, err := NewService(&ServiceConfig{
-		Cache:   cache,
-		Fetcher: httpfetcher.NewMock(mockFS),
-		Processor: imageprocessor.New(imageprocessor.Params{
-			MaxInputBytes:           50 << 20,
-			MaxConcurrentProcessing: 2,
-		}),
-		MaxResponseSize: 50 << 20,
-	})
-	if err != nil {
-		t.Fatalf("failed to create service: %v", err)
-	}
-
-	return svc, fixtures
-}
-
-// setupServiceTestDB creates an in-memory SQLite database for testing
-// using the production schema.
-func setupServiceTestDB(t *testing.T) *sql.DB {
-	t.Helper()
-
-	db, err := sql.Open("sqlite", ":memory:")
-	if err != nil {
-		t.Fatalf("failed to open test db: %v", err)
-	}
-
-	// Use the real production schema via migrations
-	err = database.ApplyMigrations(context.Background(), db, nil)
-	if err != nil {
-		t.Fatalf("failed to apply migrations: %v", err)
-	}
-
-	return db
-}

internal/providers/providers.go

@@ -26,6 +26,7 @@ import (
 	"sneak.berlin/go/pixa/internal/encurl"
 	"sneak.berlin/go/pixa/internal/httpfetcher"
 	"sneak.berlin/go/pixa/internal/imageprocessor"
+	"sneak.berlin/go/pixa/internal/imageproxy"
 	"sneak.berlin/go/pixa/internal/imgcache"
 	"sneak.berlin/go/pixa/internal/logger"
 	"sneak.berlin/go/pixa/internal/seal"
@@ -34,7 +35,7 @@ import (
 
 // Constructors returns the constructors of the parts this package builds,
 // for fx.Provide. The fx graph must also provide the prometheus.Registerer
-// the cache registers its counters on.
+// the cache and the image service register their counters on.
 func Constructors() []any {
 	return []any{
 		newKeys,
@@ -79,7 +80,7 @@ func newCache(lc fx.Lifecycle, params cacheParams) (*imgcache.Cache, error) {
 		return nil, err
 	}
 
-	cache, err := imgcache.NewCache(db, imgcache.CacheConfig{
+	cache, err := imgcache.NewCache(db, imgcache.Config{
 		StateDir:    cfg.StateDir,
 		NegativeTTL: imgcache.DefaultNegativeTTL,
 		MaxBytes:    maxBytes,
@@ -213,25 +214,26 @@ func newProcessor(cfg *config.Config) *imageprocessor.ImageProcessor {
 type imageServiceParams struct {
 	fx.In
 
-	Config    *config.Config
-	Cache     *imgcache.Cache
-	Fetcher   *httpfetcher.HTTPFetcher
-	Processor *imageprocessor.ImageProcessor
-	Logger    *logger.Logger
+	Config          *config.Config
+	Cache           *imgcache.Cache
+	Fetcher         *httpfetcher.HTTPFetcher
+	Processor       *imageprocessor.ImageProcessor
+	Logger          *logger.Logger
+	MetricsRegistry prometheus.Registerer
 }
 
 // newImageService builds the image service from the cache, the fetcher
 // and the processor, with the largest upstream response the config allows.
 func newImageService(
 	_ fx.Lifecycle, params imageServiceParams,
-) (*imgcache.Service, error) {
-	return imgcache.NewService(&imgcache.ServiceConfig{
+) (*imageproxy.Proxy, error) {
+	return imageproxy.NewProxy(&imageproxy.Config{
 		Cache:           params.Cache,
 		Fetcher:         params.Fetcher,
 		Processor:       params.Processor,
 		MaxResponseSize: params.Config.UpstreamMaxResponseSize,
 		Logger:          params.Logger.Get(),
-	})
+	}, params.MetricsRegistry)
 }
 
 // sessionManagerParams defines dependencies for newSessionManager.

internal/server/source_url_internal_test.go

@@ -14,8 +14,8 @@ import (
 	"time"
 
 	"sneak.berlin/go/pixa/internal/encurl"
+	"sneak.berlin/go/pixa/internal/imageproxy"
 	"sneak.berlin/go/pixa/internal/imagerequest"
-	"sneak.berlin/go/pixa/internal/imgcache"
 	"sneak.berlin/go/pixa/internal/seal"
 	"sneak.berlin/go/pixa/internal/session"
 	"sneak.berlin/go/pixa/internal/signature"
@@ -227,7 +227,7 @@ func TestSourcePathsHoldingSpaceAndPercent20AreFetchedApart(t *testing.T) {
 
 	for _, imageURL := range imageURLs {
 		cacheStatus := getImage(t, s, imageURL).Header().Get("X-Pixa-Cache")
-		if cacheStatus != string(imgcache.CacheHit) {
+		if cacheStatus != string(imageproxy.CacheHit) {
 			t.Errorf("second GET %s: X-Pixa-Cache = %q, want HIT",
 				imageURL, cacheStatus)
 		}
@@ -256,7 +256,7 @@ func TestSourceQueryWrittenTwoWaysIsOneUpstreamRequest(t *testing.T) {
 
 	second := getImage(t, s,
 		"/v1/image/"+upstreamHost+"/photo.png%3Fname=my%20cat/orig.png")
-	if got := second.Header().Get("X-Pixa-Cache"); got != string(imgcache.CacheHit) {
+	if got := second.Header().Get("X-Pixa-Cache"); got != string(imageproxy.CacheHit) {
 		t.Errorf("second X-Pixa-Cache = %q, want HIT", got)
 	}
 
@@ -365,7 +365,7 @@ func TestGeneratorMakesOneImageURLForTwoSpellingsOfASourceURL(t *testing.T) {
 			getImage(t, s, imageURLs[0])
 
 			second := getImage(t, s, imageURLs[1])
-			if got := second.Header().Get("X-Pixa-Cache"); got != string(imgcache.CacheHit) {
+			if got := second.Header().Get("X-Pixa-Cache"); got != string(imageproxy.CacheHit) {
 				t.Errorf("second X-Pixa-Cache = %q, want HIT", got)
 			}