Cache manifests in memory when using the S3 backend.

src/backend.go

@@ -18,6 +18,8 @@ import (
 
 	"github.com/minio/minio-go/v7"
 	"github.com/minio/minio-go/v7/pkg/credentials"
+
+	"github.com/maypok86/otter/v2"
 )
 
 type Backend interface {
@@ -205,10 +207,16 @@ func (fs *FSBackend) DeleteManifest(name string) error {
 	return fs.siteRoot.Remove(name)
 }
 
+type CachedManifest struct {
+	manifest *Manifest
+	weight   uint32
+}
+
 type S3Backend struct {
 	ctx    context.Context
 	client *minio.Client
 	bucket string
+	cache  *otter.Cache[string, *CachedManifest]
 }
 
 func NewS3Backend(
@@ -244,7 +252,27 @@ func NewS3Backend(
 		}
 	}
 
-	return &S3Backend{ctx, client, bucket}, nil
+	cacheConfig := config.Backend.S3.Cache
+	var maxWeight uint64 = 134217728
+	if cacheConfig.MaxSize != 0 {
+		maxWeight = cacheConfig.MaxSize
+	}
+	var maxAge time.Duration = 5 * time.Second
+	if cacheConfig.MaxAge != "" {
+		maxAge, err = time.ParseDuration(cacheConfig.MaxAge)
+		if err != nil {
+			return nil, fmt.Errorf("max-age: %s", err)
+		}
+	}
+	cache := otter.Must[string, *CachedManifest](&otter.Options[string, *CachedManifest]{
+		MaximumWeight: maxWeight,
+		Weigher: func(key string, value *CachedManifest) uint32 {
+			return value.weight
+		},
+		ExpiryCalculator: otter.ExpiryCreating[string, *CachedManifest](maxAge),
+	})
+
+	return &S3Backend{ctx, client, bucket, cache}, nil
 }
 
 func (s3 *S3Backend) Backend() Backend {
@@ -308,20 +336,34 @@ func stagedManifestObjectName(manifestData []byte) string {
 }
 
 func (s3 *S3Backend) GetManifest(name string) (*Manifest, error) {
-	log.Printf("s3: get manifest %s\n", name)
+	loader := func(ctx context.Context, name string) (*CachedManifest, error) {
+		log.Printf("s3: get manifest %s\n", name)
 
-	object, err := s3.client.GetObject(s3.ctx, s3.bucket, manifestObjectName(name),
-		minio.GetObjectOptions{})
+		object, err := s3.client.GetObject(s3.ctx, s3.bucket, manifestObjectName(name),
+			minio.GetObjectOptions{})
+		if err != nil {
+			return nil, err
+		}
+
+		data, err := io.ReadAll(object)
+		if err != nil {
+			return nil, err
+		}
+
+		manifest, err := DecodeManifest(data)
+		if err != nil {
+			return nil, err
+		}
+
+		return &CachedManifest{manifest, uint32(len(data))}, nil
+	}
+
+	cached, err := s3.cache.Get(s3.ctx, name, otter.LoaderFunc[string, *CachedManifest](loader))
 	if err != nil {
 		return nil, err
 	}
 
-	data, err := io.ReadAll(object)
-	if err != nil {
-		return nil, err
-	}
-
-	return DecodeManifest(data)
+	return cached.manifest, err
 }
 
 func (s3 *S3Backend) StageManifest(manifest *Manifest) error {

src/config.go

@@ -6,14 +6,14 @@ import (
 	"github.com/pelletier/go-toml/v2"
 )
 
-type Listen struct {
+type ListenConfig struct {
 	Protocol string `toml:"protocol"`
 	Address  string `toml:"address"`
 }
 
 type Config struct {
-	Pages    Listen `toml:"pages"`
-	Caddy    Listen `toml:"caddy"`
+	Pages    ListenConfig `toml:"pages"`
+	Caddy    ListenConfig `toml:"caddy"`
 	Wildcard struct {
 		Domain    string `toml:"domain"`
 		CloneURL  string `toml:"clone-url"`
@@ -31,11 +31,15 @@ type Config struct {
 			SecretAccessKey string `toml:"secret-access-key"`
 			Region          string `toml:"region"`
 			Bucket          string `toml:"bucket"`
+			Cache           struct {
+				MaxSize uint64 `toml:"max-size"` // in bytes
+				MaxAge  string `toml:"max-age"`
+			} `toml:"cache"`
 		}
 	} `toml:"backend"`
 }
 
-func readConfig(path string, config *Config) error {
+func ReadConfig(path string, config *Config) error {
 	file, err := os.Open(path)
 	if err != nil {
 		return err

src/main.go

@@ -10,7 +10,7 @@ import (
 var config Config
 var backend Backend
 
-func serveHandler(name string, listen Listen, serve func(http.ResponseWriter, *http.Request)) {
+func serveHandler(name string, listen ListenConfig, serve func(http.ResponseWriter, *http.Request)) {
 	listener, err := net.Listen(listen.Protocol, listen.Address)
 	if err != nil {
 		log.Fatalf("%s: %s\n", name, err)
@@ -29,7 +29,7 @@ func main() {
 	configPath := flag.String("config", "config.toml", "path to configuration file")
 	flag.Parse()
 
-	if err = readConfig(*configPath, &config); err != nil {
+	if err = ReadConfig(*configPath, &config); err != nil {
 		log.Fatalln("configuration:", err)
 	}
 
@@ -57,7 +57,7 @@ func main() {
 
 	log.Println("ready")
 
-	if config.Caddy != (Listen{}) {
+	if config.Caddy != (ListenConfig{}) {
 		go serveHandler("caddy", config.Caddy, ServeCaddy)
 	}