Build the request body for one upload part: the server's content_range_start
/ content_range_end (inclusive, zero-based) select the slice of fileBytes
this part carries, and when the instruction carries multipart_form_data
the slice is wrapped with the server-supplied prefix/suffix bytes — the
Documents API spec's way of letting a server ask for a
multipart/form-data body without the client having to know its boundary
scheme.
Build the request body for one upload part: the server's
content_range_start/content_range_end(inclusive, zero-based) select the slice offileBytesthis part carries, and when the instruction carriesmultipart_form_datathe slice is wrapped with the server-suppliedprefix/suffixbytes — the Documents API spec's way of letting a server ask for amultipart/form-databody without the client having to know its boundary scheme.