feat: ignore response if already sent by raw level outgoing API.

README.md

@@ -212,6 +212,33 @@ type Http2Bindings = {
 }
 ```
 
+## Direct response from Node.js API
+
+You can directly respond to the client from the Node.js API.
+In that case, the response from Hono should be ignored, so return RESPONSE_ALREADY_SENT.
+
+> [!NOTE]
+> This feature can be used when migrating existing Node.js applications to Hono, but we recommend using Hono's API for new applications.
+
+```ts
+import { serve } from '@hono/node-server'
+import type { HttpBindings } from '@hono/node-server'
+import { RESPONSE_ALREADY_SENT } from '@hono/node-server/utils/response'
+import { Hono } from 'hono'
+
+const app = new Hono<{ Bindings: HttpBindings }>()
+
+app.get('/', (c) => {
+  const { outgoing } = c.env
+  outgoing.writeHead(200, { 'Content-Type': 'text/plain' })
+  outgoing.end('Hello World\n')
+
+  return RESPONSE_ALREADY_SENT
+})
+
+serve(app)
+```
+
 ## Related projects
 
 - Hono - <https://hono.dev>

package.json

@@ -22,6 +22,11 @@
       "types": "./dist/vercel.d.ts",
       "require": "./dist/vercel.js",
       "import": "./dist/vercel.mjs"
+    },
+    "./utils/*": {
+      "types": "./dist/utils/*.d.ts",
+      "require": "./dist/utils/*.js",
+      "import": "./dist/utils/*.mjs"
     }
   },
   "typesVersions": {
@@ -34,6 +39,9 @@
       ],
       "vercel": [
         "./dist/vercel.d.ts"
+      ],
+      "utils/*": [
+        "./dist/utils/*.d.ts"
       ]
     }
   },

src/listener.ts

@@ -4,6 +4,7 @@ import { getAbortController, newRequest } from './request'
 import { cacheKey, getInternalBody } from './response'
 import type { CustomErrorHandler, FetchCallback, HttpBindings } from './types'
 import { writeFromReadableStream, buildOutgoingHttpHeaders } from './utils'
+import { X_ALREADY_SENT } from './utils/response/constants'
 import './globals'
 
 const regBuffer = /^no$/i
@@ -128,6 +129,8 @@ const responseViaResponseObject = async (
       outgoing.writeHead(res.status, resHeaderRecord)
       outgoing.end(new Uint8Array(buffer))
     }
+  } else if (resHeaderRecord[X_ALREADY_SENT]) {
+    // do nothing, the response has already been sent
   } else {
     outgoing.writeHead(res.status, resHeaderRecord)
     outgoing.end()

src/utils/response.ts

@@ -0,0 +1,4 @@
+import { X_ALREADY_SENT } from './response/constants'
+export const RESPONSE_ALREADY_SENT = new Response(null, {
+  headers: { [X_ALREADY_SENT]: 'true' },
+})

src/utils/response/constants.ts

@@ -0,0 +1 @@
+export const X_ALREADY_SENT = 'x-hono-already-sent'

test/utils/response.test.ts

@@ -0,0 +1,23 @@
+import { Hono } from 'hono'
+import request from 'supertest'
+import type { HttpBindings } from '../../src/'
+import { createAdaptorServer } from '../../src/server'
+import { RESPONSE_ALREADY_SENT } from '../../src/utils/response'
+
+describe('RESPONSE_ALREADY_SENT', () => {
+  const app = new Hono<{ Bindings: HttpBindings }>()
+  app.get('/', (c) => {
+    const { outgoing } = c.env
+    outgoing.writeHead(200, { 'Content-Type': 'text/plain' })
+    outgoing.end('Hono!')
+    return RESPONSE_ALREADY_SENT
+  })
+  const server = createAdaptorServer(app)
+
+  it('Should return 200 response - GET /', async () => {
+    const res = await request(server).get('/')
+    expect(res.status).toBe(200)
+    expect(res.headers['content-type']).toMatch('text/plain')
+    expect(res.text).toBe('Hono!')
+  })
+})