Update to not show API not ended warning when response is piped to

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

@@ -55,9 +55,17 @@ export async function apiResolver(
     apiRes.json = data => sendJson(apiRes, data)
 
     const resolver = interopDefault(resolverModule)
+    let wasPiped = false
+
+    if (process.env.NODE_ENV !== 'production') {
+      // listen for pipe event and don't show resolve warning
+      res.once('pipe', () => (wasPiped = true))
+    }
+
+    // Call API route method
     await resolver(req, res)
 
-    if (process.env.NODE_ENV !== 'production' && !isResSent(res)) {
+    if (process.env.NODE_ENV !== 'production' && !isResSent(res) && !wasPiped) {
       console.warn(
         `API resolved without sending a response for ${req.url}, this may result in stalled requests.`
       )

test/integration/api-support/pages/api/test-res-pipe.js

@@ -0,0 +1,10 @@
+import fetch from 'node-fetch'
+
+export default async (req, res) => {
+  const dataRes = await fetch(
+    `http://localhost:${req.query.port}/api/query?hello=from-pipe`
+  )
+
+  res.status(dataRes.status)
+  dataRes.body.pipe(res)
+}

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

@@ -363,6 +363,14 @@ function runTests(dev = false) {
         `API resolved without sending a response for /api/test-no-end, this may result in stalled requests.`
       )
     })
+
+    it('should not show warning when the API resolves and the response is piped', async () => {
+      const startIdx = stderr.length > 0 ? stderr.length - 1 : stderr.length
+      await fetchViaHTTP(appPort, `/api/test-res-pipe`, { port: appPort })
+      expect(stderr.substr(startIdx)).not.toContain(
+        `API resolved without sending a response for /api/test-res-pipe`
+      )
+    })
   } else {
     it('should build api routes', async () => {
       const pagesManifest = JSON.parse(