The response to a HEAD request for a upload SHOULD NOT contain the Upload-Offset header unless the
concatenation has been successfully finished. After successful concatenation, the Upload-Offset and
Upload-Length MUST be set and their values MUST be equal. The value of the Upload-Offset header before
concatenation is not defined for a upload.
The response to a HEAD request for a partial upload MUST contain the Upload-Offset header. Response to HEAD
request against partial or upload MUST include the Upload-Concat header and its value as received in
the upload creation request.