API: Take multiple values into account for the query (#9196)

* Take multiple values into account

* make typescript happy

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

@@ -119,7 +119,15 @@ export function getQueryParser({ url }: IncomingMessage) {
 
     const query: { [key: string]: string | string[] } = {}
     for (const [key, value] of params) {
-      query[key] = value
+      if (query[key]) {
+        if (Array.isArray(query[key])) {
+          ;(query[key] as string[]).push(value)
+        } else {
+          query[key] = [query[key], value]
+        }
+      } else {
+        query[key] = value
+      }
     }
 
     return query

test/integration/api-support/pages/api/query.js

@@ -0,0 +1,3 @@
+export default (req, res) => {
+  res.status(200).send(req.query)
+}

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

@@ -180,6 +180,23 @@ function runTests (serverless = false) {
     expect(data).toEqual({ message: 'Parsed body' })
   })
 
+  it('should return empty query object', async () => {
+    const data = await fetchViaHTTP(appPort, '/api/query', null, {}).then(
+      res => res.ok && res.json()
+    )
+    expect(data).toEqual({})
+  })
+
+  it('should parse query correctly', async () => {
+    const data = await fetchViaHTTP(
+      appPort,
+      '/api/query?a=1&b=2&a=3',
+      null,
+      {}
+    ).then(res => res.ok && res.json())
+    expect(data).toEqual({ a: ['1', '3'], b: '2' })
+  })
+
   it('should return empty cookies object', async () => {
     const data = await fetchViaHTTP(appPort, '/api/cookies', null, {}).then(
       res => res.ok && res.json()