[BUG] Etag makes external rewrite fail

[lauri865]

Describe the bug

We have an external rewrite (beforeFiles):

{
          source: "/client/:path*",
          destination: `${CDN_URL}/client/:path*`,
},

It works fine on first invocation, but fails on every subsequent invocation:

"exceptions": [
    {
      "stack": "    at Object.convertTo (worker.js:287862:16)\n    at worker.js:287909:40\n    at async worker.js:293333:25",
      "name": "TypeError",
      "message": "Response with null body status (101, 204, 205, or 304) cannot have a body.",
      "timestamp": 1748374222550
    }
  ],

I have traced the issue down to Etag, the presence of if-none-match header will make the subsequent rewrite fail (I guess the status code is 304, and there's no body if Etag matches).

Not sure if it's a Cloudflare issue, opennext issue or something else, as I'm struggling to trace down the stack trace. If anyone else has encountered it, would appreciate any help. We didn't have this issue with next-on-pages at least, with the equivalent rewrites setup.

Steps to reproduce

N/A (

Expected behavior

Rewrites with Etag should work

@opennextjs/cloudflare version

1.0.4

Wrangler version

4.17.0

next info output

Operating System:
  Platform: darwin
  Arch: arm64
  Version: Darwin Kernel Version 24.4.0: Fri Apr 11 18:33:39 PDT 2025; root:xnu-11417.101.15~117/RELEASE_ARM64_T6020
  Available memory (MB): 32768
  Available CPU cores: 10
Binaries:
  Node: 22.15.0
  npm: 10.9.2
  Yarn: N/A
  pnpm: 10.11.0
Relevant Packages:
  next: 15.3.2 // Latest available version is detected (15.3.2).
  eslint-config-next: 15.3.2
  react: 19.1.0
  react-dom: 19.1.0
  typescript: 5.8.3
Next.js Config:
  output: N/A

Additional context

No response

[lauri865]

Managed to reproduce this locally now.

Correct way to handle this:
https://github.com/opennextjs/opennextjs-aws/blob/ab492ca53d4494aa81234c7d6c0cdaf42cd05ba6/packages/open-next/src/overrides/wrappers/cloudflare-node.ts#L60

Root cause seems to be in that this proxy handler doesn't handle it the same way:
https://github.com/opennextjs/opennextjs-aws/blob/ab492ca53d4494aa81234c7d6c0cdaf42cd05ba6/packages/open-next/src/adapters/middleware.ts#L87

Empty readable stream is inserted into the body here for all proxied requests for whatever reason:
https://github.com/opennextjs/opennextjs-aws/blob/ab492ca53d4494aa81234c7d6c0cdaf42cd05ba6/packages/open-next/src/overrides/proxyExternalRequest/fetch.ts#L2

[sommeeeer]

This might be stem from this issue we have seen in AWS. This should probably be handled differently in Cloudflare.

[sommeeeer]

You could try with a custom override for the proxyExternalRequest. Look here for an example to do it. Just copy the fetch one and don't return a body on those statuses.

[lauri865]

Thanks! I did initially try to do this, but then I would have had to inherit whatever functionality defineCloudflareConfig also does, since it doesn't allow extensibility directly within that. Hence I went with the pnpm-patch route for now, and just removed the empty readable stream fallback. Deployed to production and the core issue is fixed at least.

[sommeeeer]

Thanks! I did initially try to do this, but then I would have had to inherit whatever functionality defineCloudflareConfig also does, since it doesn't allow extensibility directly within that.

Something like this would do the trick aswell:

import {
  defineCloudflareConfig,
  type OpenNextConfig,
} from '@opennextjs/cloudflare/config';

const cloudflareConfig = defineCloudflareConfig({});

export default {
  ...cloudflareConfig,
  cloudflare: {
    dangerousDisableConfigValidation: true,
  },
  default: {
    ...cloudflareConfig.default,
    override: {
      ...cloudflareConfig.default.override,
      proxyExternalRequest: () =>
        import('./customProxyExternalRequest').then((mod) => mod.default),
    },
  },
} satisfies OpenNextConfig;

[vicb]

Thanks for the investigation.

Do you have a minimal repro to share?

I think this is something we should be able to handle in the edge converter.

[sommeeeer]

@lauri865

Could you try with this opennextjs/opennextjs-aws#906 (comment) ?

You probably need to override it in package.json before building.