[Feature] Support multiple header values in Request/Response objects/Request interception

[nexcode]

browserContext.route('**', async (route, request) => {
    await route.fulfill({
        status: 200,
        headers: {'set-cookie': 'cookie'}, // headers?: {[p: string]: string}
    });
});

It is impossible to set several identical headers in the map, but cookies are set using multiple set-cookies headers.
NodeJS solves this problem like this: { [p: string]: string | string[] }

Could it be worth doing the same here too?

[nexcode]

Same in https://playwright.dev/docs/api/class-request#request-headers
returns: <Object<string, string>> must be <Object<string, string | string[]>> or <Object<string, string[]>>

[mindplay-dk]

It is impossible to set several identical headers in the map

Are you sure?

When I read from response().headers(), in the case of set-cookie, I get multiple header-values separated by \n - have you tried that?

NodeJS solves this problem like this: { [p: string]: string | string[] }

Please, not a type union - this requires if-statements and typeof checks before you can do anything.

If we're going to fix this, let's have a proper string[] with new method-names and/or a proper header collection-type of some sort, with an API with suitable semantics to add/remove/replace headers.

If adding header values is supported with \n, it would be possible to make the collection-type optional, keeping existing API and semantics. (Although, in my opinion, it's kind of messy and confusing as-is.)

[mindplay-dk]

Looks like this is landing with #8638

[nexcode]

In v1.15 you can get multiple headers, but you still can't set multiple headers on route.fulfill