add charset support to ctx.type=

docs/api.md

@@ -275,12 +275,16 @@ var ct = this.type;
   Set response `Content-Type` via mime string or file extension.
 
 ```js
+this.type = 'text/plain; charset=utf-8';
 this.type = 'image/png';
 this.type = '.png';
 this.type = 'png';
 ```
 
-  __NOTE__: when `ctx.body` is an object the content-type is set for you.
+  Note: when appropriate a `charset` is selected for you, for
+  example `ctx.type = 'html'` will default to "utf-8", however
+  when explicitly defined in full as `ctx.type = 'text/html'`
+  no charset is assigned.
 
 ### ctx.url
 

lib/context.js

@@ -743,7 +743,12 @@ module.exports = {
    */
 
   set type(type){
-    if (!~type.indexOf('/')) type = mime.lookup(type);
+    if (!~type.indexOf('/')) {
+      type = mime.lookup(type);
+      var cs = mime.charsets.lookup(type);
+      if (cs) type += '; charset=' + cs.toLowerCase();
+    }
+
     this.set('Content-Type', type);
   },
 

test/application.js

@@ -177,7 +177,7 @@ describe('app.respond', function(){
 
       request(server)
       .get('/')
-      .expect('Content-Type', 'text/plain')
+      .expect('Content-Type', 'text/plain; charset=utf-8')
       .expect(404)
       .end(done);
     })