fix: handle multiple x-forwarded-proto headers (#58824)

### What?
This PR changes how protocol is determined.
A change was recently made (in [PR
57815](1caa58087a (diff-c49c4767e6ed8627e6e1b8f96b141ee13246153f5e9142e1da03450c8e81e96fR1744)))
that did not take into account cases where there are multiple
`x-forwarded-proto` headers. In such cases, the protocol becomes e.g
"https, https".

### Why?
An error will occur in parseUrl on line 1616, since its not a valid url
(e.g. `https, https://localhost:3000`).

### How?
Reverted part of the changes in [PR
57815](https://github.com/vercel/next.js/pull/57815).

Fixes #58764 and fixes #59031

Closes NEXT-2437

---------

Co-authored-by: Balázs Orbán <info@balazsorban.com>

packages/next/src/server/lib/router-utils/resolve-routes.ts

@@ -136,7 +136,7 @@ export function getResolveRoutes(
     // TODO: inherit this from higher up
     const protocol =
       (req?.socket as TLSSocket)?.encrypted ||
-      req.headers['x-forwarded-proto'] === 'https'
+      req.headers['x-forwarded-proto']?.includes('https')
         ? 'https'
         : 'http'
 

packages/next/src/server/next-server.ts

@@ -1785,7 +1785,9 @@ export default class NextNodeServer extends BaseServer {
     isUpgradeReq?: boolean
   ) {
     // Injected in base-server.ts
-    const protocol = req.headers['x-forwarded-proto'] as 'https' | 'http'
+    const protocol = req.headers['x-forwarded-proto']?.includes('https')
+      ? 'https'
+      : 'http'
 
     // When there are hostname and port we build an absolute URL
     const initUrl =

test/e2e/app-dir/x-forwarded-headers/x-forwarded-headers.test.ts

@@ -63,5 +63,16 @@ createNextDescribe('x-forwarded-headers', { files: __dirname }, ({ next }) => {
       expect(headers['middleware-x-forwarded-port']).toBe(reqHeaders.port)
       expect(headers['middleware-x-forwarded-proto']).toBe(reqHeaders.proto)
     })
+
+    it('should work with multiple x-forwarded-* headers', async () => {
+      const res = await next.fetch('/', {
+        headers: { 'x-forwarded-proto': 'https, https' },
+      })
+
+      expect(res.status).toBe(200)
+
+      const headers = await res.json()
+      expect(headers['x-forwarded-proto']).toBe('https, https')
+    })
   })
 })