Remove usage of res._headers private field

closes #3174

History.md

@@ -2,6 +2,8 @@ unreleased
 ==========
 
   * Add debug message when loading view engine
+  * Remove usage of `res._headers` private field
+    - Improves compatibility with Node.js 8 nightly
   * deps: debug@2.6.1
     - Allow colors in workers
     - Deprecated `DEBUG_FD` environment variable set to `3` or higher

lib/request.js

@@ -452,14 +452,18 @@ defineGetter(req, 'host', deprecate.function(function host(){
 
 defineGetter(req, 'fresh', function(){
   var method = this.method;
-  var s = this.res.statusCode;
+  var res = this.res
+  var status = res.statusCode
 
   // GET or HEAD for weak freshness validation only
   if ('GET' !== method && 'HEAD' !== method) return false;
 
   // 2xx or 304 as per rfc2616 14.26
-  if ((s >= 200 && s < 300) || 304 === s) {
-    return fresh(this.headers, (this.res._headers || {}));
+  if ((status >= 200 && status < 300) || 304 === status) {
+    return fresh(this.headers, {
+      'etag': res.get('ETag'),
+      'last-modified': res.get('Last-Modified')
+    })
   }
 
   return false;

test/req.fresh.js

@@ -36,8 +36,8 @@ describe('req', function(){
     it('should return false without response headers', function(done){
       var app = express();
 
+      app.disable('x-powered-by')
       app.use(function(req, res){
-        res._headers = null;
         res.send(req.fresh);
       });
 

test/req.stale.js

@@ -36,8 +36,8 @@ describe('req', function(){
     it('should return true without response headers', function(done){
       var app = express();
 
+      app.disable('x-powered-by')
       app.use(function(req, res){
-        res._headers = null;
         res.send(req.stale);
       });