static: support setting "Cache-Control" (#143)

Co-authored-by: Phil Harris <phil@harris-family.info>
Co-authored-by: Joe Chen <jc@unknwon.io>

static.go

@@ -37,6 +37,9 @@ type StaticOptions struct {
 	// EnableLogging indicates whether to print "[Static]" log messages whenever a
 	// static file is served.
 	EnableLogging bool
+	// CacheControl is used to set the "Cache-Control" response header for every
+	// static file that is served. Default is not set.
+	CacheControl func() string
 }
 
 func generateETag(size int64, name string, modtime time.Time) string {
@@ -141,6 +144,9 @@ func Static(opts ...StaticOptions) Handler {
 		if opt.Expires != nil {
 			c.ResponseWriter().Header().Set("Expires", opt.Expires())
 		}
+		if opt.CacheControl != nil {
+			c.ResponseWriter().Header().Set("Cache-Control", opt.CacheControl())
+		}
 
 		if opt.SetETag {
 			etag := generateETag(fi.Size(), fi.Name(), fi.ModTime())

static_test.go

@@ -173,6 +173,28 @@ func TestStatic_Options(t *testing.T) {
 		assert.Equal(t, "2830", resp.Header().Get("Expires"))
 	})
 
+	t.Run("cache-control", func(t *testing.T) {
+		const cacheControl = "public, max-age=60"
+		f := NewWithLogger(&bytes.Buffer{})
+		f.Use(Static(
+			StaticOptions{
+				Directory: ".",
+				CacheControl: func() string {
+					return cacheControl
+				},
+			},
+		))
+
+		resp := httptest.NewRecorder()
+		req, err := http.NewRequest(http.MethodHead, "/.editorconfig", http.NoBody)
+		assert.Nil(t, err)
+
+		f.ServeHTTP(resp, req)
+
+		assert.Equal(t, http.StatusOK, resp.Code)
+		assert.Equal(t, cacheControl, resp.Header().Get("Cache-Control"))
+	})
+
 	t.Run("etag", func(t *testing.T) {
 		f := NewWithLogger(&bytes.Buffer{})
 		f.Use(Static(