🔥set a Cache Control header for static ressources

Right now, each static request returns the file without any cache control
header. If you are using `app.Static` to serve your assets, the
browser shouldn't cache it. This PR introduces a way to set the cache
control header (if the file was found) on the file response to set a
custom max-age to e.g. cache it 1 year.

app.go

@@ -261,6 +261,12 @@ type Static struct {
 	// The name of the index file for serving a directory.
 	// Optional. Default value "index.html".
 	Index string `json:"index"`
+
+	// The value for the Cache-Control HTTP-header
+	// that is set on the file response. MaxAge is defined in seconds.
+	//
+	// Optional. Default value 0.
+	MaxAge int `json:"max_age"`
 }
 
 // Default Config values

app_test.go

@@ -562,12 +562,30 @@ func Test_App_Static_Direct(t *testing.T) {
 	utils.AssertEqual(t, nil, err, "app.Test(req)")
 	utils.AssertEqual(t, 200, resp.StatusCode, "Status code")
 	utils.AssertEqual(t, false, resp.Header.Get(HeaderContentLength) == "")
-	utils.AssertEqual(t, "text/plain; charset=utf-8", resp.Header.Get(HeaderContentType))
+	utils.AssertEqual(t, "text/plain; charset=utf-8", resp.Header.Get("Content-Type"))
+	utils.AssertEqual(t, "", resp.Header.Get(HeaderCacheControl), "CacheControl Control")
+
 
 	body, err = ioutil.ReadAll(resp.Body)
 	utils.AssertEqual(t, nil, err)
 	utils.AssertEqual(t, true, strings.Contains(string(body), "gofiber.io/support"))
 }
+
+// go test -run Test_App_Static_MaxAge
+func Test_App_Static_MaxAge(t *testing.T) {
+	app := New()
+
+	app.Static("/", "./.github", Static{MaxAge: 100})
+
+	resp, err := app.Test(httptest.NewRequest("GET", "/index.html", nil))
+	utils.AssertEqual(t, nil, err, "app.Test(req)")
+	utils.AssertEqual(t, 200, resp.StatusCode, "Status code")
+	utils.AssertEqual(t, false, resp.Header.Get(HeaderContentLength) == "")
+	utils.AssertEqual(t, "text/html; charset=utf-8", resp.Header.Get(HeaderContentType))
+	utils.AssertEqual(t, "public, max-age=100", resp.Header.Get(HeaderCacheControl), "CacheControl Control")
+}
+
+// go test -run Test_App_Static_Group
 func Test_App_Static_Group(t *testing.T) {
 	app := New()
 

router.go

@@ -7,6 +7,7 @@ package fiber
 import (
 	"fmt"
 	"sort"
+	"strconv"
 	"strings"
 	"time"
 
@@ -338,8 +339,15 @@ func (app *App) registerStatic(prefix, root string, config ...Static) Router {
 			fctx.Response.SetStatusCode(StatusNotFound)
 		},
 	}
+
 	// Set config if provided
+	var cacheControlValue string
 	if len(config) > 0 {
+		maxAge := config[0].MaxAge
+		if maxAge > 0 {
+			cacheControlValue = "public, max-age=" + strconv.Itoa(maxAge)
+		}
+
 		fs.Compress = config[0].Compress
 		fs.AcceptByteRange = config[0].ByteRange
 		fs.GenerateIndexPages = config[0].Browse
@@ -354,6 +362,9 @@ func (app *App) registerStatic(prefix, root string, config ...Static) Router {
 		// Return request if found and not forbidden
 		status := c.fasthttp.Response.StatusCode()
 		if status != StatusNotFound && status != StatusForbidden {
+			if len(cacheControlValue) > 0 {
+				c.fasthttp.Response.Header.Set(HeaderCacheControl, cacheControlValue)
+			}
 			return nil
 		}
 		// Reset response to default