fix(cookie): add docs & expose in node v16

[KhafraDev]

Since the cookie handling uses some stuff from the fetch spec, it can only be exposed in node v16+.

[codecov-commenter]

Codecov Report

Base: 90.32% // Head: 90.31% // Decreases project coverage by -0.01% ⚠️

Coverage data is based on head (b5c6ab8) compared to base (7ee93b2).
Patch coverage: 100.00% of modified lines in pull request are covered.

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #1849      +/-   ##
==========================================
- Coverage   90.32%   90.31%   -0.02%     
==========================================
  Files          70       70              
  Lines        6027     6028       +1     
==========================================
  Hits         5444     5444              
- Misses        583      584       +1     

Impacted Files	Coverage Δ
index.js	100.00% <100.00%> (ø)
lib/fetch/file.js	89.65% <0.00%> (-1.15%)	⬇️

Help us with your feedback. Take ten seconds to tell us how you rate us. Have a feature suggestion? Share it here.

☔ View full report at Codecov.
📢 Do you have feedback about the report comment? Let us know in this issue.

[mcollina]

How will we expose those in Node.js core?

[KhafraDev]

I'm not sure, there's a few way I could think of.

1. with the rest of undici. I know there's an issue open somewhere asking to expose other parts of undici in node core.
2. As http.cookies/https.cookies/http2.cookies, or somewhere in util?
3. Recommend using undici in node docs for cookie handling with Headers.

I also need to note that it doesn't currently work with the global Headers because we need to access internals (set-cookie headers are stored in an array rather than being joined together).

[mcollina]

Once undici is updated in core, will it work with the global headers?

[mcollina]

lgtm

[KhafraDev]

will it work with the global headers

For deleteCookie, getCookies, and setCookie yes, but getSetCookies is handled differently, unlike Deno, to be more correct & not introduce a breaking change. Deno stores set-cookie headers in an array, and when getting them, will return an array. The spec tells us to return a concatenated string though.

To bypass this, I added a property to HeadersList that stores set-cookie headers in an array, and we use the value of that rather than doing headers.get('set-cookie'), which wouldn't be possible to parse (using headers.get('set-cookie') still returns a string). Since we can guarantee that node won't add in their own symbols to Headers (etc), I could add support for it, but I wasn't keen on implementing such a dirty hack.