fix: allow multiple body parser coexist

lib/form.js

@@ -37,11 +37,9 @@ module.exports = function(req, opts){
   opts.qs = opts.qs || qs;
 
   // raw-body returns a Promise when no callback is specified
-  return Promise.resolve()
-    .then(function() {
-      return raw(inflate(req), opts);
-    })
-    .then(function(str){
+  return new Promise(function (resolve, reject){
+      resolve(raw(inflate(req), opts));
+    }).then(function(str){
       try {
         var parsed = opts.qs.parse(str, queryString);
         return opts.returnRawBody ? { parsed: parsed, raw: str } : parsed;

lib/json.js

@@ -36,11 +36,9 @@ module.exports = function(req, opts){
   var strict = opts.strict !== false;
 
   // raw-body returns a promise when no callback is specified
-  return Promise.resolve()
-    .then(function() {
-      return raw(inflate(req), opts);
-    })
-    .then(function(str) {
+  return new Promise(function (resolve, reject){
+      resolve(raw(inflate(req), opts));
+    }).then(function(str) {
       try {
         var parsed = parse(str);
         return opts.returnRawBody ? { parsed: parsed, raw: str } : parsed;

lib/text.js

@@ -30,11 +30,9 @@ module.exports = function(req, opts){
   opts.limit = opts.limit || '1mb';
 
   // raw-body returns a Promise when no callback is specified
-  return Promise.resolve()
-    .then(function() {
-      return raw(inflate(req), opts);
-    })
-    .then(str => {
+  return new Promise(function (resolve, reject){
+      resolve(raw(inflate(req), opts));
+    }).then(str => {
       // ensure return the same format with json / form
       return opts.returnRawBody ? { parsed: str, raw: str } : str;
     });

test/any.js

@@ -228,4 +228,47 @@ describe('parse(req, opts)', function(){
     })
   })
 
+  describe('multiple parser coexist', function(){
+    var app = koa();
+
+    app.use(function *(next){
+      this.request.bodyParser = parse(this);
+      yield next;
+    });
+    app.use(function *(next){
+      this.body = yield parse(this);
+      yield next;
+    });
+    app.use(function *(next){
+      this.body = [this.body, yield this.request.bodyParser];
+      yield next;
+    });
+
+    it('should parse json', function(done){
+      request(app.listen())
+      .post('/')
+      .set('content-type', 'application/json')
+      .send({foo:'bar'})
+      .expect(200)
+      .expect([{foo:'bar'}, {foo:'bar'}], done);
+    })
+
+    it('should parse text', function(done){
+      request(app.listen())
+      .post('/')
+      .set('content-type', 'text/plain')
+      .send('plain text')
+      .expect(200)
+      .expect(['plain text', 'plain text'], done);
+    })
+
+    it('should parse form', function(done){
+      request(app.listen())
+      .post('/')
+      .type('form')
+      .send({foo: 'bar'})
+      .expect(200)
+      .expect([{foo: 'bar'}, {foo: 'bar'}], done);
+    })
+  })
 })