From 8836cd30d140ec285e3ceadbeadeda1f1796af24 Mon Sep 17 00:00:00 2001
From: Lee Bousfield <ljbousfield@gmail.com>
Date: Thu, 27 Oct 2016 23:13:07 -0600
Subject: [PATCH 1/2] Return middleware chain promise from `callback()`

Without this, there's no way of hooking into after Koa is done with the response. This can be extremely important if used with `ctx.respond = false`, as in #846 (see there for use case). While this is technically a breaking change, I don't expect it to break anything.
---
 lib/application.js | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/lib/application.js b/lib/application.js
index 8b6a78bcc..b15b80dbd 100644
--- a/lib/application.js
+++ b/lib/application.js
@@ -133,7 +133,7 @@ app.callback = function(){
     res.statusCode = 404;
     var ctx = self.createContext(req, res);
     onFinished(res, ctx.onerror);
-    fn.call(ctx).then(function handleResponse() {
+    return fn.call(ctx).then(function handleResponse() {
       respond.call(ctx);
     }).catch(ctx.onerror);
   }

From 734a62cd88f2c2cf8b5bf91d4b5b716b619c643c Mon Sep 17 00:00:00 2001
From: Lee Bousfield <ljbousfield@gmail.com>
Date: Fri, 28 Oct 2016 09:14:32 -0600
Subject: [PATCH 2/2] Added app.usedAsMiddleware

Disables default response handler. See docs for more info.
---
 docs/api/index.md   |  6 ++++++
 lib/application.js  |  7 ++++++-
 test/application.js | 38 ++++++++++++++++++++++++++++++++++++++
 3 files changed, 50 insertions(+), 1 deletion(-)

diff --git a/docs/api/index.md b/docs/api/index.md
index e5a0614cb..cd64cb269 100644
--- a/docs/api/index.md
+++ b/docs/api/index.md
@@ -169,6 +169,12 @@ this.cookies.set('name', 'tobi', { signed: true });
 app.context.db = db();
 ```
 
+## app.usedAsMiddleware
+
+  Disables the default 404 status code and empty response.
+  This is very useful if you're using Koa as part of another framework, where Koa tries
+  to handle a request first and then falls back to the legacy framework.
+
 ## Error Handling
 
   By default outputs all errors to stderr unless __NODE_ENV__ is "test" or `app.silent` is `true`.
diff --git a/lib/application.js b/lib/application.js
index b15b80dbd..0198422d1 100644
--- a/lib/application.js
+++ b/lib/application.js
@@ -130,7 +130,10 @@ app.callback = function(){
   if (!this.listeners('error').length) this.on('error', this.onerror);
 
   return function handleRequest(req, res){
-    res.statusCode = 404;
+    // don't set the default status code if Koa is part of a larger framework
+    if (!self.usedAsMiddleware) {
+      res.statusCode = 404;
+    }
     var ctx = self.createContext(req, res);
     onFinished(res, ctx.onerror);
     return fn.call(ctx).then(function handleResponse() {
@@ -215,6 +218,8 @@ function respond() {
 
   // status body
   if (null == body) {
+    // don't send back the default empty response if Koa is part of a larger framework
+    if (this.app.usedAsMiddleware) return;
     this.type = 'text';
     body = this.message || String(code);
     this.length = Buffer.byteLength(body);
diff --git a/test/application.js b/test/application.js
index d114f2269..d9d087350 100644
--- a/test/application.js
+++ b/test/application.js
@@ -1110,3 +1110,41 @@ describe('app.response', function(){
     .expect(204, done);
   })
 })
+
+describe('app.usedAsMiddleware', function(){
+  var app = koa()
+  app.use(function *(next) {
+    if (this.url.indexOf('/koa') == 0) {
+      this.statusCode = 200
+      this.body = 'Hello from Koa!'
+    } else {
+      yield next
+    }
+  })
+  app.usedAsMiddleware = true
+  var koaHandle = app.callback()
+  function handle(req, res){
+    koaHandle(req, res).then(function(){
+      if (!res.finished) {
+        res.end('Hello from other framework!')
+      }
+    })
+  }
+  var server = http.createServer(handle).listen(0)
+
+  it('should not touch res if middleware doesn\'t', function(done){
+    request(server)
+    .get('/')
+    .expect(200)
+    .expect('Hello from other framework!')
+    .end(done)
+  })
+
+  it('should let middleware handle res', function(done){
+    request(server)
+    .get('/koa')
+    .expect(200)
+    .expect('Hello from Koa!')
+    .end(done)
+  })
+})