add res.vary(). Closes #1682

lib/response.js

@@ -463,7 +463,7 @@ res.format = function(obj){
 
   var key = req.accepts(keys);
 
-  this.set('Vary', 'Accept');
+  this.vary("Accept");
 
   if (key) {
     this.set('Content-Type', normalizeType(key).value);
@@ -720,6 +720,44 @@ res.redirect = function(url){
   this.end(head ? null : body);
 };
 
+/**
+ * Add `field` to Vary. If already present in the Vary set, then
+ * this call is simply ignored.
+ *
+ * @param {Array|String} field
+ * @param {ServerResponse} for chaining
+ * @api public
+ */
+
+res.vary = function(field){
+  var self = this;
+
+  // nothing
+  if (!field) return this;
+
+  // array
+  if (Array.isArray(field)) {
+    field.forEach(function(field){
+      self.vary(field);
+    });
+    return;
+  }
+
+  var vary = this.get('Vary');
+
+  // append  
+  if (vary) {
+    vary = vary.split(/ *, */);
+    if (!~vary.indexOf(field)) vary.push(field);
+    this.set('Vary', vary.join(', '));
+    return this;
+  }
+
+  // set
+  this.set('Vary', field);
+  return this;
+};
+
 /**
  * Render `view` with the given `options` and optional callback `fn`.
  * When a callback function is given a response will _not_ be made

test/res.vary.js

@@ -0,0 +1,55 @@
+
+var express = require('../')
+  , should = require('should');
+
+function response() {
+  var res = Object.create(express.response);
+  res._headers = {};
+  return res;
+}
+
+describe('res.vary()', function(){
+  describe('with no arguments', function(){
+    it('should not set Vary', function(){
+      var res = response();
+      res.vary();
+      should.not.exist(res.get('Vary'));
+    })
+  })
+
+  describe('with an empty array', function(){
+    it('should not set Vary', function(){
+      var res = response();
+      res.vary([]);
+      should.not.exist(res.get('Vary'));
+    })
+  })
+
+  describe('with an array', function(){
+    it('should set the values', function(){
+      var res = response();
+      res.vary(['Accept', 'Accept-Language', 'Accept-Encoding']);
+      res.get('Vary').should.equal('Accept, Accept-Language, Accept-Encoding');
+    })
+  })
+
+  describe('with a string', function(){
+    it('should set the value', function(){
+      var res = response();
+      res.vary('Accept');
+      res.get('Vary').should.equal('Accept');
+    })
+  })
+
+  describe('when the value is present', function(){
+    it('should not add it again', function(){
+      var res = response();
+      res.vary('Accept');
+      res.vary('Accept-Encoding');
+      res.vary('Accept-Encoding');
+      res.vary('Accept-Encoding');
+      res.vary('Accept');
+      res.get('Vary').should.equal('Accept, Accept-Encoding');
+    })
+  })
+})