Custom Server with bodyParser, don't parse body again in API Route

packages/next/next-server/server/api-utils.ts

@@ -56,7 +56,7 @@ export async function apiResolver(
     )
 
     // Parsing of body
-    if (bodyParser) {
+    if (bodyParser && !apiReq.body) {
       apiReq.body = await parseBody(
         apiReq,
         config.api && config.api.bodyParser && config.api.bodyParser.sizeLimit

test/integration/api-body-parser/pages/api/index.js

@@ -0,0 +1,5 @@
+export default ({ method, body }, res) => {
+  if (method === 'POST') {
+    res.status(200).json(body)
+  }
+}

test/integration/api-body-parser/server.js

@@ -0,0 +1,28 @@
+const next = require('next')
+const bodyParser = require('body-parser')
+const express = require('express')
+
+const dev = process.env.NODE_ENV !== 'production'
+const dir = __dirname
+const port = process.env.PORT || 3000
+
+const app = next({ dev, dir })
+const handleNextRequests = app.getRequestHandler()
+
+app.prepare().then(() => {
+  const server = express()
+
+  server.use(bodyParser.json({ limit: '5mb' }))
+
+  server.all('*', (req, res) => {
+    handleNextRequests(req, res)
+  })
+
+  server.listen(port, (err) => {
+    if (err) {
+      throw err
+    }
+
+    console.log(`> Ready on http://localhost:${port}`)
+  })
+})

test/integration/api-body-parser/test/index.test.js

@@ -0,0 +1,72 @@
+/* eslint-env jest */
+
+import { join } from 'path'
+import {
+  killApp,
+  findPort,
+  launchApp,
+  fetchViaHTTP,
+  initNextServerScript,
+} from 'next-test-utils'
+import clone from 'clone'
+import getPort from 'get-port'
+
+jest.setTimeout(1000 * 60 * 2)
+const appDir = join(__dirname, '../')
+let appPort
+
+let app
+let server
+jest.setTimeout(1000 * 60 * 2)
+
+const context = {}
+
+function runTests() {
+  it('should parse JSON body', async () => {
+    appPort = await findPort()
+    app = await launchApp(appDir, appPort, {})
+    const data = await makeRequest()
+    expect(data).toEqual([{ title: 'Nextjs' }])
+    killApp(app)
+  })
+
+  it('should not throw if request body is already parsed in custom middleware', async () => {
+    await startServer()
+    const data = await makeRequest()
+    expect(data).toEqual([{ title: 'Nextjs' }])
+    killApp(server)
+  })
+}
+
+async function makeRequest() {
+  const data = await fetchViaHTTP(appPort, '/api', null, {
+    method: 'POST',
+    headers: {
+      'Content-Type': 'application/json; charset=utf-8',
+    },
+    body: JSON.stringify([{ title: 'Nextjs' }]),
+  }).then((res) => res.ok && res.json())
+
+  return data
+}
+
+const startServer = async (optEnv = {}, opts) => {
+  const scriptPath = join(appDir, 'server.js')
+  context.appPort = appPort = await getPort()
+  const env = Object.assign(
+    {},
+    clone(process.env),
+    { PORT: `${appPort}` },
+    optEnv
+  )
+
+  server = await initNextServerScript(
+    scriptPath,
+    /ready on/i,
+    env,
+    /ReferenceError: options is not defined/,
+    opts
+  )
+}
+
+runTests()