From b0898cd1f3cd29d3c4fb8ddcc4df370bbb7278d7 Mon Sep 17 00:00:00 2001
From: Umputun <umputun@gmail.com>
Date: Wed, 15 Jan 2020 15:07:45 -0600
Subject: [PATCH] add cache control for frontend assets

---
 backend/app/rest/api/rest.go      | 51 ++++++++++++++++++++++++-------
 backend/app/rest/api/rest_test.go | 33 ++++++++++++++++++++
 2 files changed, 73 insertions(+), 11 deletions(-)

diff --git a/backend/app/rest/api/rest.go b/backend/app/rest/api/rest.go
index 65eb353c..5dbec418 100644
--- a/backend/app/rest/api/rest.go
+++ b/backend/app/rest/api/rest.go
@@ -6,6 +6,7 @@ import (
 	"encoding/json"
 	"fmt"
 	"net/http"
+	"strconv"
 	"strings"
 	"sync"
 	"time"
@@ -338,7 +339,7 @@ func (s *Rest) routes() chi.Router {
 	})
 
 	// file server for static content from /web
-	addFileServer(router, "/web", http.Dir(s.WebRoot))
+	addFileServer(router, "/web", http.Dir(s.WebRoot), s.Version)
 	return router
 }
 
@@ -444,7 +445,7 @@ func (s *Rest) configCtrl(w http.ResponseWriter, r *http.Request) {
 }
 
 // serves static files from /web or embedded by statik
-func addFileServer(r chi.Router, path string, root http.FileSystem) {
+func addFileServer(r chi.Router, path string, root http.FileSystem, version string) {
 
 	var webFS http.Handler
 
@@ -466,15 +467,17 @@ func addFileServer(r chi.Router, path string, root http.FileSystem) {
 	}
 	path += "*"
 
-	r.With(tollbooth_chi.LimitHandler(tollbooth.NewLimiter(20, nil)), middleware.Timeout(10*time.Second)).
-		Get(path, func(w http.ResponseWriter, r *http.Request) {
-			// don't show dirs, just serve files
-			if strings.HasSuffix(r.URL.Path, "/") && len(r.URL.Path) > 1 && r.URL.Path != (origPath+"/") {
-				http.NotFound(w, r)
-				return
-			}
-			webFS.ServeHTTP(w, r)
-		})
+	r.With(tollbooth_chi.LimitHandler(tollbooth.NewLimiter(20, nil)),
+		middleware.Timeout(10*time.Second),
+		cacheControl(time.Hour*24, version),
+	).Get(path, func(w http.ResponseWriter, r *http.Request) {
+		// don't show dirs, just serve files
+		if strings.HasSuffix(r.URL.Path, "/") && len(r.URL.Path) > 1 && r.URL.Path != (origPath+"/") {
+			http.NotFound(w, r)
+			return
+		}
+		webFS.ServeHTTP(w, r)
+	})
 }
 
 func encodeJSONWithHTML(v interface{}) ([]byte, error) {
@@ -566,6 +569,32 @@ func matchSiteID(next http.Handler) http.Handler {
 	return http.HandlerFunc(fn)
 }
 
+// cacheControl is a middleware setting cache expiration. Using url+version as etag
+func cacheControl(expiration time.Duration, version string) func(http.Handler) http.Handler {
+
+	etag := func(r *http.Request, version string) string {
+		s := version + ":" + r.URL.String()
+		return store.EncodeID(s)
+	}
+
+	return func(h http.Handler) http.Handler {
+		fn := func(w http.ResponseWriter, r *http.Request) {
+			e := `"` + etag(r, version) + `"`
+			w.Header().Set("Etag", e)
+			w.Header().Set("Cache-Control", "max-age="+strconv.Itoa(int(expiration.Seconds())))
+
+			if match := r.Header.Get("If-None-Match"); match != "" {
+				if strings.Contains(match, e) {
+					w.WriteHeader(http.StatusNotModified)
+					return
+				}
+			}
+			h.ServeHTTP(w, r)
+		}
+		return http.HandlerFunc(fn)
+	}
+}
+
 func parseError(err error, defaultCode int) (code int) {
 	code = defaultCode
 
diff --git a/backend/app/rest/api/rest_test.go b/backend/app/rest/api/rest_test.go
index 42710de5..c7092800 100644
--- a/backend/app/rest/api/rest_test.go
+++ b/backend/app/rest/api/rest_test.go
@@ -293,6 +293,39 @@ func TestRest_parseError(t *testing.T) {
 	}
 }
 
+func TestRest_cacheControl(t *testing.T) {
+
+	tbl := []struct {
+		url     string
+		version string
+		exp     time.Duration
+		etag    string
+		maxAge  int
+	}{
+		{"http://example.com/foo", "v1", time.Hour, "b433be1ea19edaee9dc92ca4b895b6bdf3c058cb", 3600},
+		{"http://example.com/foo2", "v1", 10 * time.Hour, "6d8466aef3246c1057452561acddf7ad9d0d99e0", 36000},
+		{"http://example.com/foo", "v2", time.Hour, "481700c52aab0dfbca99f3ffc2a4fbb27884c114", 3600},
+		{"https://example.com/foo", "v2", time.Hour, "bebd4f1b87f474792c4e75e5affe31fbf67f5778", 3600},
+	}
+
+	for i, tt := range tbl {
+		t.Run(strconv.Itoa(i), func(t *testing.T) {
+			req := httptest.NewRequest("GET", tt.url, nil)
+			w := httptest.NewRecorder()
+
+			h := cacheControl(tt.exp, tt.version)(http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {}))
+			h.ServeHTTP(w, req)
+			resp := w.Result()
+			assert.Equal(t, http.StatusOK, resp.StatusCode)
+			t.Logf("%+v", resp.Header)
+			assert.Equal(t, `"`+tt.etag+`"`, resp.Header.Get("Etag"))
+			assert.Equal(t, `max-age=`+strconv.Itoa(int(tt.exp.Seconds())), resp.Header.Get("Cache-Control"))
+
+		})
+	}
+
+}
+
 func startupT(t *testing.T) (ts *httptest.Server, srv *Rest, teardown func()) {
 	log.Setup(log.CallerFile, log.CallerFunc, log.Msec, log.LevelBraces)