fix: revert back support for legacy middleware

src/handler.ts

@@ -18,10 +18,23 @@ export function promisifyHandler (handler: Handler | Middleware): PromisifiedHan
 export const promisifyHandle = promisifyHandler
 
 export function callHandler (handler: Middleware, req: IncomingMessage, res: ServerResponse) {
+  const isMiddleware = handler.length > 2
   return new Promise((resolve, reject) => {
-    const next = (err?: Error) => err ? reject(err) : resolve(undefined)
+    const next = (err?: Error) => {
+      if (isMiddleware) {
+        res.off('close', next)
+        res.off('error', next)
+      }
+      return err ? reject(err) : resolve(undefined)
+    }
     try {
-      return resolve(handler(req, res, next))
+      const returned = handler(req, res, next)
+      if (isMiddleware && returned === undefined) {
+        res.once('close', next)
+        res.once('error', next)
+      } else {
+        resolve(returned)
+      }
     } catch (err) {
       next(err as Error)
     }

test/app.test.ts

@@ -1,7 +1,7 @@
 import { Readable, Transform } from 'stream'
 import supertest, { SuperTest, Test } from 'supertest'
 import { describe, it, expect, beforeEach } from 'vitest'
-import { createApp, App } from '../src'
+import { createApp, defineMiddleware, App } from '../src'
 
 describe('app', () => {
   let app: App
@@ -174,4 +174,15 @@ describe('app', () => {
     const res = await request.get('/test')
     expect(res.text).toBe('valid')
   })
+
+  it('wait for middleware (req, res, next)', async () => {
+    app.use('/', (_req, res, _next) => {
+      setTimeout(() => {
+        res.setHeader('Content-Type', 'application/json')
+        res.end(JSON.stringify({ works: 1 }))
+      }, 10)
+    })
+    const res = await request.get('/')
+    expect(res.body).toEqual({ works: 1 })
+  })
 })