fix(node): ignore req.body that express 4's body-parser assigns without parsing

package.json

@@ -34,6 +34,7 @@
     "@standard-server/peer": "workspace:*",
     "@standard-server/shared": "workspace:*",
     "@types/express": "^5.0.6",
+    "@types/express4": "npm:@types/express@^4.17.25",
     "@types/node": "^26.4.1",
     "@types/ws": "^8.18.1",
     "@vitest/coverage-v8": "^4.1.10",
@@ -43,6 +44,7 @@
     "eslint-plugin-ban": "^2.0.0",
     "eslint-plugin-format": "^2.0.1",
     "express": "^5.2.1",
+    "express4": "npm:express@^4.22.3",
     "fastify": "^5.11.0",
     "h3": "2.0.1-rc.26",
     "lint-staged": "^17.3.0",

packages/node/src/body.test.ts

@@ -4,6 +4,7 @@ import type { NodeHttpRequest } from './types'
 import { Buffer } from 'node:buffer'
 import http2 from 'node:http2'
 import { Readable } from 'node:stream'
+import { text } from 'node:stream/consumers'
 import * as StandardServerModule from '@standard-server/core'
 import { toFetchHeaders } from '@standard-server/fetch'
 import { isAsyncIteratorObject } from '@standard-server/shared'
@@ -151,7 +152,9 @@ describe('toStandardBody', () => {
       let standardBody: StandardBody = {} as any
 
       await request(async (req: IncomingMessage, res: ServerResponse) => {
-      // @ts-expect-error fake body is parsed
+        // fake an upstream parser: consume the stream, then assign the parsed body
+        await text(req)
+        // @ts-expect-error fake body is parsed
         req.body = { value: 123 }
         standardBody = await toStandardBody(req)
         res.end()
@@ -162,6 +165,34 @@ describe('toStandardBody', () => {
 
       expect(standardBody).toEqual({ value: 123 })
     })
+
+    // body-parser 1.x (express 4) assigns `{}` to every request, even the ones it leaves unread
+    it('ignore body assigned without consuming the stream', async () => {
+      let standardBody: any
+
+      await request(async (req: IncomingMessage, res: ServerResponse) => {
+        // @ts-expect-error fake body is assigned
+        req.body = {}
+        standardBody = await toStandardBody(req)
+        res.end()
+      })
+        .post('/')
+        .set('standard-server', 'file')
+        .send(Buffer.from('foo'))
+
+      expect(standardBody).toBeInstanceOf(File)
+      expect(await standardBody.text()).toBe('foo')
+
+      await request(async (req: IncomingMessage, res: ServerResponse) => {
+        // @ts-expect-error fake body is assigned
+        req.body = {}
+        standardBody = await toStandardBody(req)
+        res.end()
+      })
+        .get('/')
+
+      expect(standardBody).toBe(undefined)
+    })
   })
 
   describe('handle utf-8 characters split across stream chunks', () => {

packages/node/src/body.ts

@@ -23,7 +23,7 @@ export async function toStandardBody(
   options: ToStandardBodyOptions = {},
 ): Promise<StandardBody> {
   // body's already parsed by upstream framework like express, ...
-  if (req.body !== undefined) {
+  if (req.body !== undefined && !req.readable) {
     return req.body
   }
 

packages/node/src/types.ts

@@ -9,6 +9,7 @@ export type NodeHttpRequest = (IncomingMessage | Http2ServerRequest) & {
 
   /**
    * Body might already parsed by upstream framework like express.js, ...
+   * Only used once the request stream has been consumed.
    */
   body?: unknown
 }