[cloudflare adapter] Can't set multiple cookies

[half2me]

Describe the bug

When setting multiple cookies from hooks in the handle function, I have the following code:

return {
  // rest of response
  headers: {
    'set-cookie': ['cookie1', 'cookie2'],
  },
}

When using the node adapter, it correctly uses separate entries in the returned headers for each cookie.

set-cookie: cookie1
set-cookie: cookie2

However when running on cloudflare workers, with the cloudflare adapter, the cookies are merged into a single entry:

set-cookie: cookie1,cookie2

This results in only one cookie being set.

Reproduction

Return multiple cookies and use the @sveltejs/adapter-cloudflare-workers adapter

Logs

No response

System Info

System:
    OS: macOS 11.5.2
    CPU: (12) x64 Intel(R) Core(TM) i7-9750H CPU @ 2.60GHz
    Memory: 407.40 MB / 16.00 GB
    Shell: 5.8 - /bin/zsh
  Binaries:
    Node: 16.7.0 - /usr/local/bin/node
    npm: 7.21.0 - /usr/local/bin/npm
  Browsers:
    Chrome: 92.0.4515.159
    Safari: 14.1.2
  npmPackages:
    @sveltejs/adapter-cloudflare-workers: ^1.0.0-next.19 => 1.0.0-next.19 
    @sveltejs/adapter-node: ^1.0.0-next.43 => 1.0.0-next.43 
    @sveltejs/kit: next => 1.0.0-next.158 
    svelte: ^3.34.0 => 3.42.3

Severity

blocking all usage of SvelteKit

Additional Information

No response

[benmccann]

I'm not sure that the Cloudflare adapter changes this. If it did, then it'd probably happen here:

kit/packages/adapter-cloudflare-workers/files/entry.js

Line 37 in 8f67e46

headers: Object.fromEntries(request.headers),

I guess Cloudflare itself does it and the solution would be to make SvelteKit split apart the header into two when setting cookies

[JeanJPNM]

Maybe this can work:

/**
 * @param {Record<string, string | string[]>} headers
 */
function makeHeaders(headers) {
	const result = new Headers();
	for (const header in headers) {
		const value = headers[header];
		if (typeof value === 'string') {
			result.set(header, value);
			continue;
		}
		for (const sub of value) {
			result.append(header, sub);
		}
	}
	return result;
}

[half2me]

Thanks @JeanJPNM this works perfectly. I'll be using this as a workaround for now. Reckon this behaviour could be made default?

[JeanJPNM]

Ok, I will make a pull request

[benmccann]

Won't result.append(header, sub); make it so that there's just a single header for Set-Cookie? I thought that's what @half2me was complaining about in the issue description

[JeanJPNM]

Yes, it technically does the same thing, but for some reason it works

[benmccann]

I guess it's because headers takes a bytestring and not a string[]: https://developer.mozilla.org/en-US/docs/Web/API/Headers/Headers#parameters