RedirectHandler cleans headers too aggressively

[joelschou]

Bug Description

Undici explicitly supports headers passed as a Headers object, but the RedirectHandler does not account for this object type in its internal cleanRequestHeaders function.

Reproducible By

1. Configure global dispatcher to use redirect interceptor

2. Use undici.request to send a request with headers constructed via new Headers(...)

   import { Headers, request } from 'undici';
   
   await request( '/local/test/url', { headers: new Headers({ 'x-my-header': true }) } );

3. Your local test server should see 'x-my-header': 'true' in the request headers

4. Your local test server should respond with a 3xx statusCode and a location: '/local/test/alt-url' header

5. Undici should follow the redirect and make a request to the new location

6. Your local test server WILL NOT see 'x-my-header': 'true' in the request headers

Compare to:

1. same as above

2. Send the request this way instead:

   await request( '/local/test/url', { headers: { 'x-my-header': true } } );

3. same as above

4. same as above

5. same as above

6. Your local test server WILL see 'x-my-header': 'true' in the request headers

Expected Behavior

1. Headers on the initial request should be repeated on the redirect request(s) for all supported ways to pass headers

Logs & Screenshots

I believe I've tracked this down to this logic inside cleanRequestHeaders:

// ...
} else if (headers && typeof headers === 'object') {
    for (const key of Object.keys(headers)) {
      if (!shouldRemoveHeader(key, removeContent, unknownOrigin)) {
        ret.push(key, headers[key])
      }
    }
  }
// ...

For headers constructed with new Headers(...), the typeof headers === 'object' condition will return true, but Object.keys(...) does not behave as expected on a Headers object. As a result, this for loop does not push any keys/values into ret.

Environment

• macOS 15.0.1 (current)
• Node v20.16.0 (LTS, but two minors behind)

Additional context

[mcollina]

Thanks for reporting! Would you like to send a Pull Request to address this issue? Remember to add unit tests.