Using Range headers for more than just bytes

[mrjoops]

Hi all!

This is a feature request.

As an API designer and Oak user, I was looking for the HTTP Range header support in Oak and was pleased to see it is actually supported... with some limitation: it can only accept bytes ranges, as cruelly written in the parseRange function in range.ts:

  if (unit !== "bytes") {
    throw createHttpError(Status.RequestedRangeNotSatisfiable);
  }

However the RFC is a bit less limiting on this particular subject (see https://datatracker.ietf.org/doc/html/rfc9110/#section-14.1) as it notes "Range units are intended to be extensible".
I often use "items" and "pages" units myself for example.

I'm not a particularly talented Typescript developer but it doesn't seem to be such a big deal to implement and if we could agree on the approach, I could surely help.

We could introduce a GenericRange interface that ByteRange could extend, and update parseRange to return either GenericRange[] or ByteRange[], using the same condition you used to throw the exception. The rest of the code could be left untouched, to start.

Thank you for reading!