Outdated spec implementation. "fetch" spec changed in 2017 - Does not lowercase headers

[ameliabradley]

This polyfill is an outdated implementation of the fetch standard.

See this change to the fetch standard in 2017: whatwg/fetch#476

To come back in compliance with the standard, the polyfill needs to stop lowercasing headers, regardless how headers are meant to be interpreted in RFC2616.

Browser implementations such as Chrome are already in compliance and do not lowercase headers for fetch calls.

[naclcaleb]

Are you primarily speaking of this function?
https://github.com/github/fetch/blob/7232090c04e1ddefb806910bbd0a756bc8aac2f0/fetch.js#L43-L51

[ameliabradley]

@naclcaleb Sort of? But we can't just remove the lowercasing in normalization. I'm guessing we also need to implement a byte-insensitive match like annevk created in his whatwg PR.

[ameliabradley]

The reason why this spec update is important is while a server might be expected to handle headers a certain way (as outlined in RFC2616), they do not always comply. I recently came across such an issue.

[JakeChampion]

Headers look to not be lowercase when declared via an object but are lowercased when declared via the Header class.

[JakeChampion]

PR to resolve this --> #798