feat(backend): set caching headers for all static files

Those should improve browser caching so we avoid fetching all css/js files on every page load

assets.go

@@ -7,6 +7,7 @@ import (
 	"net/http"
 	"os"
 	"strings"
+	"time"
 
 	assetfs "github.com/elazarl/go-bindata-assetfs"
 	"github.com/gin-gonic/gin"
@@ -87,3 +88,13 @@ func serverFileOrEmpty(path string, contentType string, c *gin.Context) {
 	}
 	c.File(path)
 }
+
+func staticHeaders(prefix string) gin.HandlerFunc {
+	return func(c *gin.Context) {
+		if strings.HasPrefix(c.Request.URL.Path, prefix) {
+			c.Header("Cache-Control", "public, max-age=2592000")
+			expiresTime := time.Now().AddDate(0, 0, 30).Format(http.TimeFormat)
+			c.Header("Expires", expiresTime)
+		}
+	}
+}

main.go

@@ -19,11 +19,11 @@ import (
 	"github.com/gin-contrib/static"
 	"github.com/gin-gonic/contrib/sentry"
 	"github.com/gin-gonic/gin"
-	"github.com/patrickmn/go-cache"
 	"github.com/spf13/pflag"
 
 	raven "github.com/getsentry/raven-go"
 	ginprometheus "github.com/mcuadros/go-gin-prometheus"
+	cache "github.com/patrickmn/go-cache"
 	log "github.com/sirupsen/logrus"
 )
 
@@ -55,6 +55,7 @@ func getViewURL(sub string) string {
 
 func setupRouter(router *gin.Engine) {
 	router.Use(gzip.Gzip(gzip.DefaultCompression))
+	router.Use(staticHeaders(getViewURL("/static/")))
 	router.Use(static.Serve(getViewURL("/"), staticBuildFileSystem))
 	// next 2 lines are to allow service raw sources so sentry can fetch source maps
 	router.Use(static.Serve(getViewURL("/static/js/"), staticSrcFileSystem))