HTTP headers that may be added

[LiviaMedeiros]

Some HTTP mechanisms that may be added:

• Accept / Content-Type
  Implemented for errors.
  Easy to implement for arbitrary files by checking extension and/or using libmagic, but it's a guessing game.
• Accept-Encoding / Content-Encoding
  Compression. This would be fun to have and it should be implemented, but the practical benefit too questionable.
• Accept-Language / Content-Language
  The former is not applicable, the latter can be implemented but it's a guessing game.
• Accept-Ranges / Range / Content-Range
  Implemented, with deviations from standard. Responses with multipart/byteranges are absurd to implement here.
• Authorization
  Theoretically speaking, this can be used to access files that don't belong to current user. Feasible as is, but how to avoid horrid security implications?
• Cache-Control
  Not really applicable. Caching local files should be done by OS.
• Connection / Keep-Alive
  For some methods, it's somewhat possible to implement aborting with TimeoutError and closing file descriptors if the response body state happens to be stalling. Fun, but not very useful and probably not very robust.
• Expect / request Content-Length
  This can be applicable as in "is there enough of free space on device" or "does FS support files this big". Unfortunately, we don't always know request body size, free space can vary, and 100 is not the most convenient thing in HTTP.
• Cookie / Set-Cookie
  Maybe there will be a brilliant idea. Someday.
• Host / Origin / Referer
  Maybe there should be some value that will be ignored internally anyway.
• If-Match / If-None-Match / ETag
  Implemented.
• If-Modified-Since / If-Unmodified-Since / Last-Modified
  Implemented.
• Client Hints
  There are lots of interesting things like Downlink, but usability is questionable even if it was simple to implement.