Add res.append(field, val) to append headers

docs/api/context.md

@@ -190,6 +190,7 @@ koa uses [http-assert](https://github.com/jshttp/http-assert) for assertions.
   - `ctx.redirect()`
   - `ctx.attachment()`
   - `ctx.set()`
+  - `ctx.append()`
   - `ctx.remove()`
   - `ctx.lastModified=`
   - `ctx.etag=`

docs/api/response.md

@@ -151,6 +151,13 @@ var etag = this.get('ETag');
 this.set('Cache-Control', 'no-cache');
 ```
 
+### response.append(field, value)
+  Append additional header `field` with value `val`.
+
+```js
+this.append('Link', '<http://127.0.0.1/>');
+```
+
 ### response.set(fields)
 
   Set several response header `fields` with an object:

lib/context.js

@@ -147,6 +147,7 @@ delegate(proto, 'response')
   .method('remove')
   .method('vary')
   .method('set')
+  .method('append')
   .access('status')
   .access('message')
   .access('body')

lib/response.js

@@ -424,6 +424,33 @@ module.exports = {
     }
   },
 
+  /**
+   * Append additional header `field` with value `val`.
+   *
+   * Examples:
+   *
+   *    this.append('Link', ['<http://localhost/>', '<http://localhost:3000/>']);
+   *    this.append('Set-Cookie', 'foo=bar; Path=/; HttpOnly');
+   *    this.append('Warning', '199 Miscellaneous warning');
+   *
+   * @param {String} field
+   * @param {String|Array} val
+   * @api public
+   */
+
+  append: function(field, val){
+    var prev = this.get(field);
+    var value = val;
+    if (prev) {
+      // concat the new and prev vals
+      value = Array.isArray(prev) ? prev.concat(val)
+        : Array.isArray(val) ? [prev].concat(val)
+        : [prev, val];
+    }
+
+    return this.set(field, value);
+  },
+
   /**
    * Remove header `field`.
    *

test/response/append.js

@@ -0,0 +1,38 @@
+
+var context = require('../context');
+
+describe('ctx.append(name, val)', function(){
+  it('should append multiple headers', function(){
+    var ctx = context();
+    ctx.append('x-foo', 'bar1');
+    ctx.append('x-foo', 'bar2');
+    ctx.response.header['x-foo'].should.eql(['bar1', 'bar2']);
+  })
+
+ it('should accept array of values', function (){
+    var ctx = context();
+
+    ctx.append('Set-Cookie', ['foo=bar', 'fizz=buzz']);
+    ctx.response.header['set-cookie'].should.eql(['foo=bar', 'fizz=buzz']);
+  })
+
+  it('should get reset by res.set(field, val)', function (){
+    var ctx = context();
+
+    ctx.append('Link', '<http://localhost/>');
+    ctx.append('Link', '<http://localhost:80/>');
+
+    ctx.set('Link', '<http://127.0.0.1/>');
+
+    ctx.response.header.link.should.equal('<http://127.0.0.1/>');
+  })
+
+  it('should work with res.set(field, val) first', function (){
+    var ctx = context();
+
+    ctx.set('Link', '<http://localhost/>');
+    ctx.append('Link', '<http://localhost:80/>');
+
+    ctx.response.header.link.should.eql(['<http://localhost/>', '<http://localhost:80/>']);
+  })
+})