Add x-forward headers to external rewrites

packages/next/server/image-optimizer.ts

@@ -244,6 +244,7 @@ export async function imageOptimizer(
         mockRes.setHeader = (name: string, value: string | string[]) =>
           (mockHeaders[name.toLowerCase()] = value)
         mockRes._implicitHeader = () => {}
+        mockRes.connection = res.connection
         mockRes.finished = false
         mockRes.statusCode = 200
 
@@ -258,6 +259,7 @@ export async function imageOptimizer(
         mockReq.headers = req.headers
         mockReq.method = req.method
         mockReq.url = href
+        mockReq.connection = req.connection
 
         await server.getRequestHandler()(
           mockReq,

packages/next/server/next-server.ts

@@ -963,6 +963,7 @@ export default class Server {
               target,
               changeOrigin: true,
               ignorePath: true,
+              xfwd: true,
               proxyTimeout: 30_000, // limit proxying to 30 seconds
             })
 

test/integration/custom-routes/test/index.test.js

@@ -646,7 +646,9 @@ const runTests = (isDev = false) => {
         },
       },
     ])
-    expect(await res.text()).toContain('hi from external')
+    const nextHost = `localhost:${appPort}`
+    const externalHost = `localhost:${externalServerPort}`
+    expect(await res.text()).toContain(`hi ${nextHost} from ${externalHost}`)
   })
 
   it('should support unnamed parameters correctly', async () => {
@@ -1911,7 +1913,9 @@ describe('Custom routes', () => {
     externalServerPort = await findPort()
     externalServer = http.createServer((req, res) => {
       externalServerHits.add(req.url)
-      res.end('hi from external')
+      const nextHost = req.headers['x-forwarded-host']
+      const externalHost = req.headers['host']
+      res.end(`hi ${nextHost} from ${externalHost}`)
     })
     await new Promise((resolve, reject) => {
       externalServer.listen(externalServerPort, (error) => {