UI files prevent cache by response headers (#2159)

pkg/api/ui_handler.go

@@ -6,6 +6,7 @@ import (
 	"os"
 	"path"
 	"strings"
+	"time"
 
 	"github.com/rakyll/statik/fs"
 	"github.com/treeverse/lakefs/pkg/auth"
@@ -15,13 +16,51 @@ import (
 	"github.com/treeverse/lakefs/pkg/webui"
 )
 
+// Taken from https://github.com/mytrile/nocache
+var noCacheHeaders = map[string]string{
+	"Expires":         time.Unix(0, 0).Format(time.RFC1123),
+	"Cache-Control":   "no-cache, private, max-age=0",
+	"Pragma":          "no-cache",
+	"X-Accel-Expires": "0",
+}
+
+var etagHeaders = []string{
+	"ETag",
+	"If-Modified-Since",
+	"If-Match",
+	"If-None-Match",
+	"If-Range",
+	"If-Unmodified-Since",
+}
+
 func NewUIHandler(authService auth.Service, gatewayDomains []string) http.Handler {
 	mux := http.NewServeMux()
 	staticFiles, _ := fs.NewWithNamespace(webui.Webui)
-	mux.Handle("/", NewHandlerWithDefault(staticFiles, http.FileServer(staticFiles), "/", gatewayDomains))
+	fileServer := http.FileServer(staticFiles)
+	noCacheFileServer := NoCacheHandler(fileServer)
+	mux.Handle("/", NewHandlerWithDefault(staticFiles, noCacheFileServer, "/", gatewayDomains))
 	return mux
 }
 
+// NoCacheHandler based on github.com/zenazn/goji's NoCache
+func NoCacheHandler(handler http.Handler) http.Handler {
+	return http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
+		// Delete any ETag headers that may have been set
+		for _, v := range etagHeaders {
+			if r.Header.Get(v) != "" {
+				r.Header.Del(v)
+			}
+		}
+
+		// Set our NoCache headers
+		for k, v := range noCacheHeaders {
+			w.Header().Set(k, v)
+		}
+
+		handler.ServeHTTP(w, r)
+	})
+}
+
 func NewHandlerWithDefault(root http.FileSystem, handler http.Handler, defaultPath string, gatewayDomains []string) http.Handler {
 	return http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
 		if isGatewayRequest(r) {