Issue with undici.request and Headers Global Object

[JaoodxD]

Bug Description

Undici's request function appears to be skipping headers that are constructed using the Headers global object.

Reproducible By

1. Create an instance of Headers class.
2. Add header with set/append.
3. Pass headers instance to request.

const headers = new Headers()
headers.append('random-header', 'hello world')

const res = await request('http://localhost:3001', { headers })

Full reproducable example can be found in following repo

Expected Behavior

I expect the undici.request function to treat instances of the Headers class the same way it handles plain JavaScript objects passed to options.
Specifically, I anticipate that the headers, when constructed using the Headers class, should be seamlessly attached to the HTTP request.

Logs & Screenshots

{
  host: 'localhost:3000',
  connection: 'keep-alive',
  'random-header': 'hello world' // passed as plain object
}
{ host: 'localhost:3001', connection: 'keep-alive' } // as Headers instance

Environment

OS: Windows 10
Nodejs: v20.8.0
undici: v6.6.1

[JaoodxD]

As we can see here https://github.com/nodejs/undici/blob/main/lib/core/request.js#L159-L174 request constructor expects only Array or plain Object.

[ronag]

Headers object are not expected to work. Though I wouldn't mind adding support for it. PR welcome.

[JaoodxD]

Headers object are not expected to work. Though I wouldn't mind adding support for it. PR welcome.

I would like to implement it.

[KhafraDev]

it might be worth it to allow Map-like objects instead (ie. something that implements .get()/an iterator) instead of only Headers.

[JaoodxD]

it might be worth it to allow Map-like objects instead (ie. something that implements .get()/an iterator) instead of only Headers.

Good idea. Would it be a sufficient to implement it like it's done in fetch? (check for symbol.iterator)

undici/lib/fetch/headers.js

Lines 573 to 576 in 8e14078

	if (webidl.util.Type(V) === 'Object') {
	if (V[Symbol.iterator]) {
	return webidl.converters['sequence<sequence<ByteString>>'](V)
	}