Add caching to web assets (#22137)

lib/httplib/httpheaders.go

@@ -22,6 +22,7 @@ import (
 	"fmt"
 	"net/http"
 	"strings"
+	"time"
 )
 
 // SetNoCacheHeaders tells proxies and browsers do not cache the content
@@ -31,6 +32,11 @@ func SetNoCacheHeaders(h http.Header) {
 	h.Set("Expires", "0")
 }
 
+// SetCacheHeaders tells proxies and browsers to cache the content
+func SetCacheHeaders(h http.Header, maxAge time.Duration) {
+	h.Set("Cache-Control", fmt.Sprintf("max-age=%.f, immutable", maxAge.Seconds()))
+}
+
 // SetDefaultSecurityHeaders adds headers that should generally be considered safe defaults.  It is expected that all
 // responses should be able to add these headers without negative impact.
 func SetDefaultSecurityHeaders(h http.Header) {

lib/web/apiserver.go

@@ -402,7 +402,12 @@ func NewHandler(cfg Config, opts ...HandlerOption) (*APIHandler, error) {
 
 		// serve Web UI:
 		if strings.HasPrefix(r.URL.Path, "/web/app") {
-			http.StripPrefix("/web", makeGzipHandler(http.FileServer(cfg.StaticFS))).ServeHTTP(w, r)
+			fs := http.FileServer(cfg.StaticFS)
+
+			fs = makeGzipHandler(fs)
+			fs = makeCacheHandler(fs)
+
+			http.StripPrefix("/web", fs).ServeHTTP(w, r)
 		} else if strings.HasPrefix(r.URL.Path, "/web/") || r.URL.Path == "/web" {
 			csrfToken, err := csrf.AddCSRFProtection(w, r)
 			if err != nil {

lib/web/cachehandler.go

@@ -0,0 +1,33 @@
+/*
+Copyright 2023 Gravitational, Inc.
+
+Licensed under the Apache License, Version 2.0 (the "License");
+you may not use this file except in compliance with the License.
+You may obtain a copy of the License at
+
+    http://www.apache.org/licenses/LICENSE-2.0
+
+Unless required by applicable law or agreed to in writing, software
+distributed under the License is distributed on an "AS IS" BASIS,
+WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+See the License for the specific language governing permissions and
+limitations under the License.
+*/
+
+package web
+
+import (
+	"net/http"
+	"time"
+
+	"github.com/gravitational/teleport/lib/httplib"
+)
+
+// makeCacheHandler adds support for gzip compression for given handler.
+func makeCacheHandler(handler http.Handler) http.Handler {
+	return http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
+		httplib.SetCacheHeaders(w.Header(), time.Hour*24*365 /* one year */)
+
+		handler.ServeHTTP(w, r)
+	})
+}