From 190bca6bc74d4cf80ad8d49eb5e8662f9494f0e4 Mon Sep 17 00:00:00 2001
From: Matt Silverlock <matt@eatsleeprepeat.net>
Date: Fri, 23 May 2014 17:13:28 +0800
Subject: [PATCH] NoCache middleware - prevents proxies/clients from caching
 content.

---
 web/middleware/nocache.go      | 56 ++++++++++++++++++++++++++++++++++
 web/middleware/nocache_test.go | 29 ++++++++++++++++++
 2 files changed, 85 insertions(+)
 create mode 100644 web/middleware/nocache.go
 create mode 100644 web/middleware/nocache_test.go

diff --git a/web/middleware/nocache.go b/web/middleware/nocache.go
new file mode 100644
index 0000000..54ead3b
--- /dev/null
+++ b/web/middleware/nocache.go
@@ -0,0 +1,56 @@
+package middleware
+
+import (
+	"fmt"
+	"net/http"
+	"time"
+)
+
+// Unix epoch time
+var epoch = fmt.Sprintf("%s", time.Unix(0, 0).Format(time.RFC1123))
+
+// Taken from https://github.com/mytrile/nocache
+var noCacheHeaders = map[string]string{
+	"Expires":         epoch,
+	"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",
+}
+
+// NoCache is a simple piece of middleware that sets a number of HTTP headers to prevent
+// a router (or subrouter) from being cached by an upstream proxy and/or client.
+//
+// As per http://wiki.nginx.org/HttpProxyModule - NoCache sets:
+//      Expires: Thu, 01 Jan 1970 00:00:00 UTC
+//      Cache-Control: no-cache, private, max-age=0
+//      X-Accel-Expires: 0
+//      Pragma: no-cache (for HTTP/1.0 proxies/clients)
+func NoCache(h http.Handler) http.Handler {
+	fn := 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)
+		}
+
+		h.ServeHTTP(w, r)
+	}
+
+	return http.HandlerFunc(fn)
+}
diff --git a/web/middleware/nocache_test.go b/web/middleware/nocache_test.go
new file mode 100644
index 0000000..1fb71f6
--- /dev/null
+++ b/web/middleware/nocache_test.go
@@ -0,0 +1,29 @@
+package middleware
+
+import (
+	"net/http"
+	"net/http/httptest"
+	"testing"
+
+	"github.com/zenazn/goji/web"
+)
+
+func TestNoCache(t *testing.T) {
+
+	rr := httptest.NewRecorder()
+	s := web.New()
+
+	s.Use(NoCache)
+	r, err := http.NewRequest("GET", "/", nil)
+	if err != nil {
+		t.Fatal(err)
+	}
+
+	s.ServeHTTP(rr, r)
+
+	for k, v := range noCacheHeaders {
+		if rr.HeaderMap[k][0] != v {
+			t.Errorf("%s header not set by middleware.", k)
+		}
+	}
+}