https://pkg.go.dev/net/http#ServeContent - this is what you are looking for (it will handle partial byte ranges and all mentioned headers).
this worked wonders! I'll keep testing it and submit a pull request by tomorrow.
the changes were a little more complex than just adding a call to ServeContent (they always are) but i think i managed to get everything right. see here: https://github.com/fiatjaf/khatru/compare/master...girino:khatru:master
(there is still some debug "prints" in there, i'll remove them before the pull request)
Looking good! If you’re open to a small suggestion, and if fiatjaf doesn’t mind introducing some early-stage backwards-incompatible changes to khatru's Blossom’s API, I think you could simplify things by changing the return type here https://github.com/fiatjaf/khatru/blob/76ecf4f7914a93b7ec4f0cc0c823304a7402adab/blossom/server.go#L18 to `io.ReadSeeker`. This would allow you to eliminate the `io.Copy` fallback code and the `Content-Type` handling, as `http.ServeContent` also takes care of that for you. It even handles ETags and cache-related headers, so I’d expect your patch to significantly improve things for all clients—not just iOS. Well done!
