Improve caching

thumb_image_test.go

@@ -4,6 +4,8 @@ import (
 	"bytes"
 	"image"
 	"image/jpeg"
+	"os"
+	"path/filepath"
 	"testing"
 )
 
@@ -54,3 +56,34 @@ func BenchmarkResizeBox(b *testing.B) {
 		}
 	})
 }
+
+// After a restart (empty memory cache) the digest comes from the on-disk index
+// without reading the source file.
+func TestSourceDigestPersists(t *testing.T) {
+	old := thumbCacheDir
+	thumbCacheDir = t.TempDir()
+	t.Cleanup(func() { thumbCacheDir = old })
+
+	src := filepath.Join(t.TempDir(), "a.jpg")
+	if err := os.WriteFile(src, []byte("photo"), 0644); err != nil {
+		t.Fatal(err)
+	}
+	info, _ := os.Stat(src)
+	h1, data, err := sourceDigest(src, info)
+	if err != nil || data == nil {
+		t.Fatalf("first call: %v, data=%v", err, data)
+	}
+
+	digestCacheMu.Lock()
+	delete(digestCache, src)
+	digestCacheMu.Unlock()
+	// Removing the source proves the second call does not read it again.
+	if err := os.Remove(src); err != nil {
+		t.Fatal(err)
+	}
+
+	h2, data, err := sourceDigest(src, info)
+	if err != nil || data != nil || h2 != h1 {
+		t.Fatalf("after restart: h=%s data=%v err=%v, want %s from index", h2, data, err, h1)
+	}
+}