fix: match .json method responses in API routes/Middleware

packages/next/server/api-utils.ts

@@ -89,7 +89,7 @@ export async function apiResolver(
     }
     apiRes.status = (statusCode) => sendStatusCode(apiRes, statusCode)
     apiRes.send = (data) => sendData(apiReq, apiRes, data)
-    apiRes.json = (data) => sendJson(apiRes, data)
+    apiRes.json = apiRes.send
     apiRes.redirect = (statusOrUrl: number | string, url?: string) =>
       redirect(apiRes, statusOrUrl, url)
     apiRes.setPreviewData = (data, options = {}) =>
@@ -266,7 +266,7 @@ export function sendData(
   res: NextApiResponse,
   body: any
 ): void {
-  if (body === null || body === undefined) {
+  if (body === undefined) {
     res.end()
     return
   }
@@ -297,7 +297,10 @@ export function sendData(
     return
   }
 
-  const isJSONLike = ['object', 'number', 'boolean'].includes(typeof body)
+  const isJSONLike = ['object', 'number', 'boolean', 'string'].includes(
+    typeof body
+  )
+
   const stringifiedBody = isJSONLike ? JSON.stringify(body) : body
   const etag = generateETag(stringifiedBody)
   if (sendEtagResponse(req, res, etag)) {
@@ -321,19 +324,6 @@ export function sendData(
   res.end(stringifiedBody)
 }
 
-/**
- * Send `JSON` object
- * @param res response object
- * @param jsonBody of data
- */
-export function sendJson(res: NextApiResponse, jsonBody: any): void {
-  // Set header to application/json
-  res.setHeader('Content-Type', 'application/json; charset=utf-8')
-
-  // Use send to handle request
-  res.send(jsonBody)
-}
-
 const COOKIE_NAME_PRERENDER_BYPASS = `__prerender_bypass`
 const COOKIE_NAME_PRERENDER_DATA = `__next_preview_data`
 

test/integration/api-support/pages/api/json-null.js

@@ -0,0 +1,3 @@
+export default (req, res) => {
+  res.json(null)
+}

test/integration/api-support/pages/api/json-string.js

@@ -0,0 +1,3 @@
+export default (req, res) => {
+  res.json('Hello world!')
+}

test/integration/api-support/test/index.test.js

@@ -94,7 +94,7 @@ function runTests(dev = false) {
     const text = await fetchViaHTTP(appPort, '/api', null, {}).then(
       (res) => res.ok && res.text()
     )
-    expect(text).toEqual('Index should work')
+    expect(text).toEqual('"Index should work"')
   })
 
   it('should return custom error', async () => {
@@ -162,8 +162,28 @@ function runTests(dev = false) {
     expect(body).toBe(true)
   })
 
+  it('should support string for JSON in api page', async () => {
+    const res = await fetchViaHTTP(appPort, '/api/json-string')
+    const body = res.ok ? await res.json() : 'Some error'
+    expect(res.status).toBe(200)
+    expect(res.headers.get('content-type')).toBe(
+      'application/json; charset=utf-8'
+    )
+    expect(body).toBe('Hello world!')
+  })
+
+  it('should support null for JSON in api page', async () => {
+    const res = await fetchViaHTTP(appPort, '/api/json-null')
+    const body = res.ok ? await res.json() : 'Not null'
+    expect(res.status).toBe(200)
+    expect(res.headers.get('content-type')).toBe(
+      'application/json; charset=utf-8'
+    )
+    expect(body).toBe(null)
+  })
+
   it('should support undefined response body', async () => {
-    const res = await fetchViaHTTP(appPort, '/api/undefined', null, {})
+    const res = await fetchViaHTTP(appPort, '/api/json-undefined', null, {})
     const body = res.ok ? await res.text() : null
     expect(body).toBe('')
   })
@@ -501,7 +521,7 @@ function runTests(dev = false) {
       expect(stderr).toContain(
         `API resolved without sending a response for ${apiURL}, this may result in stalled requests.`
       )
-      expect(await req.text()).toBe('hello world')
+      expect(await req.text()).toBe('"hello world"')
     })
 
     it('should not show warning if using externalResolver flag', async () => {
@@ -511,7 +531,7 @@ function runTests(dev = false) {
       expect(stderr.substr(startIdx)).not.toContain(
         `API resolved without sending a response for ${apiURL}`
       )
-      expect(await req.text()).toBe('hello world')
+      expect(await req.text()).toBe('"hello world"')
     })
   } else {
     it('should show warning with next export', async () => {