Add x-forward headers to external rewrites

[thomasmarshall]

I'd like to be able to use external rewrites to proxy requests to a Rails app. However, the changeOrigin: true proxy setting switches out the requested host for the target origin, which means the Rails app doesn't know it's being proxied to and will generate URLs and perform redirects to the wrong host.

For example: if I rewrite next.test/foo to rails.test/foo, any links or redirects on the proxied site will use the host rails.test instead of the requested next.test and break out of the proxy.

Rather than changing or removing the changeOrigin setting, this commit configures the proxy to include x-forward headers 1. Rails can then use the X-Forwarded-Host header to determine which host to use for URL generation and redirects 2.

[thomasmarshall]

We're currently using an API route with a custom proxy to handle this:

// next.config.js

module.exports = {
  rewrites: async () => [
    {
      source: '/:path*',
      destination: '/:path*',
    },
    {
      source: '/:path*',
      destination: '/api/proxy/:path*',
    },
  ],
};

// pages/api/proxy/[[...path]].js

import { createProxyMiddleware } from 'http-proxy-middleware';

export default createProxyMiddleware({
  target: process.env.PROXY_HOST,
  changeOrigin: true,
  pathRewrite: { '^/api': '/' },
  xfwd: true,
});

[focux]

Any thoughts on this @timneutkens? My use case is similar to the OP's but in PHP.

[minusfive]

Yeah, would love to see this feature make it in soon — we're hacking around a similar use case. Any feedback @Timer , @lfades , @timneutkens ?

[vwatel]

Any update on this one?
After upgrading to version 10, we are missing lot of headers when being behind a Proxy such as Application Gateway on Azure.
For example, here are few HTTP headers that are not part of the request anymore:

• "x-original-host": custom HTTP header set by Azure Application Gateway
• "x-forwarded-host"
• "cache-control"
• etc

Thank you for your help 👍

[thomasmarshall]

Hey @timneutkens @ijjk – is there any possibility of getting this reviewed? If so, I'll rebase and resolve the conflict – otherwise I can just close the PR.

[adrienharnay]

Hello, I just noticed that the x-forwarded-for header does not contain the correct IP address while using the rewrites feature in next.config.js (e.g. for incremental adoption). Could someone please review this small PR?

[ijjk]

Thanks for the PR!

[ijjk]

Stats from current PR

Default Build (Decrease detected ✓)

General Overall increase ⚠️

	vercel/next.js canary	thomasmarshall/next.js rewrite-proxy-xfwd	Change
buildDuration	17.2s	16.8s	-385ms
buildDurationCached	3.8s	4s	⚠️ +167ms
nodeModulesSize	49.4 MB	49.4 MB	⚠️ +369 B

Page Load Tests Overall decrease ⚠️

	vercel/next.js canary	thomasmarshall/next.js rewrite-proxy-xfwd	Change
/ failed reqs	0	0	✓
/ total time (seconds)	2.882	2.838	-0.04
/ avg req/sec	867.33	880.98	+13.65
/error-in-render failed reqs	0	0	✓
/error-in-render total time (seconds)	1.715	1.763	⚠️ +0.05
/error-in-render avg req/sec	1457.41	1418.44	⚠️ -38.97

Client Bundles (main, webpack, commons)

	vercel/next.js canary	thomasmarshall/next.js rewrite-proxy-xfwd	Change
359.HASH.js gzip	2.96 kB	2.96 kB	✓
framework-HASH.js gzip	42 kB	42 kB	✓
main-HASH.js gzip	20.9 kB	20.9 kB	✓
webpack-HASH.js gzip	1.49 kB	1.49 kB	✓
Overall change	67.4 kB	67.4 kB	✓

Legacy Client Bundles (polyfills)

	vercel/next.js canary	thomasmarshall/next.js rewrite-proxy-xfwd	Change
polyfills-HASH.js gzip	31.1 kB	31.1 kB	✓
Overall change	31.1 kB	31.1 kB	✓

Client Pages

	vercel/next.js canary	thomasmarshall/next.js rewrite-proxy-xfwd	Change
_app-HASH.js gzip	803 B	803 B	✓
_error-HASH.js gzip	3.06 kB	3.06 kB	✓
amp-HASH.js gzip	554 B	554 B	✓
css-HASH.js gzip	329 B	329 B	✓
hooks-HASH.js gzip	903 B	903 B	✓
image-HASH.js gzip	5.6 kB	5.6 kB	✓
index-HASH.js gzip	261 B	261 B	✓
link-HASH.js gzip	1.66 kB	1.66 kB	✓
routerDirect..HASH.js gzip	319 B	319 B	✓
withRouter-HASH.js gzip	320 B	320 B	✓
bb14e60e810b..30f.css gzip	125 B	125 B	✓
Overall change	13.9 kB	13.9 kB	✓

Client Build Manifests

	vercel/next.js canary	thomasmarshall/next.js rewrite-proxy-xfwd	Change
_buildManifest.js gzip	417 B	417 B	✓
Overall change	417 B	417 B	✓

Rendered Page Sizes

	vercel/next.js canary	thomasmarshall/next.js rewrite-proxy-xfwd	Change
index.html gzip	529 B	529 B	✓
link.html gzip	543 B	543 B	✓
withRouter.html gzip	523 B	523 B	✓
Overall change	1.59 kB	1.59 kB	✓

---

Webpack 4 Mode (Increase detected ⚠️)

General Overall increase ⚠️

	vercel/next.js canary	thomasmarshall/next.js rewrite-proxy-xfwd	Change
buildDuration	14s	13.6s	-422ms
buildDurationCached	5.7s	5.3s	-376ms
nodeModulesSize	49.4 MB	49.4 MB	⚠️ +369 B

Page Load Tests Overall increase ✓

	vercel/next.js canary	thomasmarshall/next.js rewrite-proxy-xfwd	Change
/ failed reqs	0	0	✓
/ total time (seconds)	3.044	3.056	⚠️ +0.01
/ avg req/sec	821.2	817.95	⚠️ -3.25
/error-in-render failed reqs	0	0	✓
/error-in-render total time (seconds)	1.852	1.756	-0.1
/error-in-render avg req/sec	1349.69	1423.58	+73.89

Client Bundles (main, webpack, commons)

	vercel/next.js canary	thomasmarshall/next.js rewrite-proxy-xfwd	Change
14.HASH.js gzip	2.98 kB	2.98 kB	✓
677f882d2ed8..HASH.js gzip	13.7 kB	13.7 kB	✓
framework.HASH.js gzip	41.8 kB	41.8 kB	✓
main-HASH.js gzip	8.39 kB	8.39 kB	✓
webpack-HASH.js gzip	1.19 kB	1.19 kB	✓
Overall change	68 kB	68 kB	✓

Legacy Client Bundles (polyfills)

	vercel/next.js canary	thomasmarshall/next.js rewrite-proxy-xfwd	Change
polyfills-HASH.js gzip	31.3 kB	31.3 kB	✓
Overall change	31.3 kB	31.3 kB	✓

Client Pages

	vercel/next.js canary	thomasmarshall/next.js rewrite-proxy-xfwd	Change
_app-HASH.js gzip	791 B	791 B	✓
_error-HASH.js gzip	3.76 kB	3.76 kB	✓
amp-HASH.js gzip	552 B	552 B	✓
css-HASH.js gzip	333 B	333 B	✓
hooks-HASH.js gzip	910 B	910 B	✓
index-HASH.js gzip	230 B	230 B	✓
link-HASH.js gzip	1.64 kB	1.64 kB	✓
routerDirect..HASH.js gzip	297 B	297 B	✓
withRouter-HASH.js gzip	293 B	293 B	✓
e025d2764813..52f.css gzip	125 B	125 B	✓
Overall change	8.93 kB	8.93 kB	✓

Client Build Manifests

	vercel/next.js canary	thomasmarshall/next.js rewrite-proxy-xfwd	Change
_buildManifest.js gzip	420 B	420 B	✓
Overall change	420 B	420 B	✓

Rendered Page Sizes

	vercel/next.js canary	thomasmarshall/next.js rewrite-proxy-xfwd	Change
index.html gzip	576 B	576 B	✓
link.html gzip	590 B	590 B	✓
withRouter.html gzip	569 B	569 B	✓
Overall change	1.74 kB	1.74 kB	✓

Commit: 8810ba7