chore: allow the compose function to be configurable

__tests__/application/compose.js

@@ -0,0 +1,71 @@
+
+'use strict'
+
+const request = require('supertest')
+const assert = require('assert')
+const Koa = require('../..')
+
+describe('app.compose', () => {
+  it('should work with default compose ', async () => {
+    const app = new Koa()
+    const calls = []
+
+    app.use((ctx, next) => {
+      calls.push(1)
+      return next().then(() => {
+        calls.push(4)
+      })
+    })
+
+    app.use((ctx, next) => {
+      calls.push(2)
+      return next().then(() => {
+        calls.push(3)
+      })
+    })
+
+    const server = app.listen()
+
+    await request(server)
+      .get('/')
+      .expect(404)
+
+    assert.deepStrictEqual(calls, [1, 2, 3, 4])
+  })
+
+  it('should work with configurable compose', async () => {
+    const calls = []
+    let count = 0
+    const app = new Koa({
+      compose (fns){
+        return async (ctx) => {
+          const dispatch = async () => {
+            count++
+            const fn = fns.shift()
+            fn && fn(ctx, dispatch)
+          }
+          dispatch()
+        }
+      }
+    })
+
+    app.use((ctx, next) => {
+      calls.push(1)
+      next()
+      calls.push(4)
+    })
+    app.use((ctx, next) => {
+      calls.push(2)
+      next()
+      calls.push(3)
+    })
+
+    const server = app.listen()
+
+    await request(server)
+      .get('/')
+
+    assert.deepStrictEqual(calls, [1, 2, 3, 4])
+    assert.equal(count, 3)
+  })
+})

__tests__/application/index.js

@@ -78,6 +78,12 @@ describe('app', () => {
     assert.strictEqual(app.subdomainOffset, subdomainOffset)
   })
 
+  it('should set compose from the constructor', () => {
+    const compose = () => (ctx) => {}
+    const app = new Koa({ compose })
+    assert.strictEqual(app.compose, compose)
+  })
+
   it('should have a static property exporting `HttpError` from http-errors library', () => {
     const CreateError = require('http-errors')
 

lib/application.js

@@ -51,6 +51,7 @@ module.exports = class Application extends Emitter {
     this.proxyIpHeader = options.proxyIpHeader || 'X-Forwarded-For'
     this.maxIpsCount = options.maxIpsCount || 0
     this.env = options.env || process.env.NODE_ENV || 'development'
+    this.compose = options.compose || compose
     if (options.keys) this.keys = options.keys
     this.middleware = []
     this.context = Object.create(context)
@@ -132,7 +133,7 @@ module.exports = class Application extends Emitter {
    */
 
   callback () {
-    const fn = compose(this.middleware)
+    const fn = this.compose(this.middleware)
 
     if (!this.listenerCount('error')) this.on('error', this.onerror)