Function
downstream-original-header-names
Returns the client request's header names exactly as they were originally received.
This includes both the original header name characters' cases, as well as the original order of the received headers.
The first cursor names are skipped. The remaining names are encoded successively with
a NUL byte after each into a list of bytes at most max-len long. If any of the remaining
names don't fit, the returned option<u32> is the index of the first name that didn't fit,
or none if all the remaining names fit. If max-len is too small to fit any name,
an error.buffer-len error is returned, providing a recommended buffer size.