Add a no blob option to skip storing response body.

Some usecases may require an ETag cache without actually storing
the response body. This patch introduces a `NoBlob` option which when
set skips caching the response blob but creates a cache entry with
an ETag.

fastcache.go

@@ -37,6 +37,11 @@ type Options struct {
 	// Process ETags and send 304s?
 	ETag bool
 
+	// By default, handler response bodies are cached and served. If this is
+	// enabled, only ETags are cached and for response bodies, the original
+	// handler is invoked.
+	NoBlob bool
+
 	// Logger is the optional logger to which errors will be written.
 	Logger *log.Logger
 
@@ -210,10 +215,15 @@ func (f *FastCache) cache(r *fastglue.Request, namespace, group string, o *Optio
 	}
 	uri := hex.EncodeToString(hash[:])
 
+	var blob []byte
+	if !o.NoBlob {
+		blob = r.RequestCtx.Response.Body()
+	}
+
 	err := f.s.Put(namespace, group, uri, Item{
 		ETag:        etag,
 		ContentType: r.RequestCtx.Response.Header.ContentType(),
-		Blob:        r.RequestCtx.Response.Body(),
+		Blob:        blob,
 	}, o.TTL)
 	if err != nil && o.Logger != nil {
 		return fmt.Errorf("error writing cache to store: %v", err)

fastcache_test.go

@@ -42,6 +42,14 @@ func init() {
 			Logger:       log.New(os.Stdout, "", log.Ldate|log.Ltime|log.Lshortfile),
 		}
 
+		noBlob = &fastcache.Options{
+			NamespaceKey: namespaceKey,
+			ETag:         true,
+			TTL:          time.Second * 60,
+			NoBlob:       true,
+			Logger:       log.New(os.Stdout, "", log.Ldate|log.Ltime|log.Lshortfile),
+		}
+
 		fc = fastcache.New(cachestore.New("CACHE:", redis.NewClient(&redis.Options{
 			Addr: rd.Addr(),
 		})))
@@ -62,6 +70,10 @@ func init() {
 		return r.SendBytes(200, "text/plain", []byte("ok"))
 	}, ttlShort, group))
 
+	srv.GET("/no-blob", fc.Cached(func(r *fastglue.Request) error {
+		return r.SendBytes(200, "text/plain", []byte("ok"))
+	}, noBlob, group))
+
 	srv.GET("/clear-group", fc.ClearGroup(func(r *fastglue.Request) error {
 		return r.SendBytes(200, "text/plain", []byte("ok"))
 	}, ttlShort, group))
@@ -158,3 +170,22 @@ func TestNoCache(t *testing.T) {
 		}
 	}
 }
+
+func TestNoBlob(t *testing.T) {
+	// All requests should return 200.
+	eTag := ""
+	for n := 0; n < 3; n++ {
+		r, _ := getReq(srvRoot+"/no-blob", eTag, t)
+		if n == 0 {
+			eTag = r.Header.Get("Etag")
+			if r.StatusCode != 200 {
+				t.Fatalf("expected 200 but got %v", r.StatusCode)
+			}
+			continue
+		}
+
+		if r.StatusCode != 304 {
+			t.Fatalf("expected 304 but got %v", r.StatusCode)
+		}
+	}
+}