Add Cache-Control header

Add Cache-Control response header for static files in order to improve page loading speed.
Fixes  #322

cache.go

@@ -11,6 +11,7 @@
 package writefreely
 
 import (
+	"net/http"
 	"sync"
 	"time"
 )
@@ -67,3 +68,10 @@ func GetPostsCache(userID int64) *[]PublicPost {
 	}
 	return pci.Posts
 }
+
+func cacheControl(next http.Handler) http.Handler {
+	return http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
+		w.Header().Set("Cache-Control", "public, max-age=604800, immutable")
+		next.ServeHTTP(w, r)
+	})
+}

routes.go

@@ -26,6 +26,7 @@ import (
 func (app *App) InitStaticRoutes(r *mux.Router) {
 	// Handle static files
 	fs := http.FileServer(http.Dir(filepath.Join(app.cfg.Server.StaticParentDir, staticDir)))
+	fs = cacheControl(fs)
 	app.shttp = http.NewServeMux()
 	app.shttp.Handle("/", fs)
 	r.PathPrefix("/").Handler(fs)

routes_test.go

@@ -0,0 +1,38 @@
+package writefreely
+
+import (
+	"net/http"
+	"net/http/httptest"
+	"strings"
+	"testing"
+
+	"github.com/gorilla/mux"
+)
+
+func TestCacheControlForStaticFiles(t *testing.T) {
+	app := NewApp("testdata/config.ini")
+	if err := app.LoadConfig(); err != nil {
+		t.Fatalf("Could not create an app; %v", err)
+	}
+	router := mux.NewRouter()
+	app.InitStaticRoutes(router)
+
+	rec := httptest.NewRecorder()
+	req := httptest.NewRequest("GET", "/style.css", nil)
+	router.ServeHTTP(rec, req)
+	if code := rec.Result().StatusCode; code != http.StatusOK {
+		t.Fatalf("Could not get /style.css, got HTTP status %d", code)
+	}
+	actual := rec.Result().Header.Get("Cache-Control")
+
+	expectedDirectives := []string{
+		"public",
+		"max-age",
+		"immutable",
+	}
+	for _, expected := range expectedDirectives {
+		if !strings.Contains(actual, expected) {
+			t.Errorf("Expected Cache-Control header to contain '%s', but was '%s'", expected, actual)
+		}
+	}
+}

testdata/.gitignore

@@ -0,0 +1 @@
+!config.ini

testdata/config.ini

@@ -0,0 +1,2 @@
+[server]
+static_parent_dir  = testdata

testdata/static/style.css

@@ -0,0 +1,3 @@
+body {
+    background-color: lightblue;
+}