return value for the start of the range
return value for the end of the range
return value for the total length of the resource, or %NULL if you don't care.
%TRUE if @hdrs contained a "Content-Range" header containing a byte range which could be parsed, %FALSE otherwise.
2.26
Parses @hdrs's Content-Range header and returns it in @start, @end, and @total_length. If the total length field in the header was specified as "*", then @total_length will be set to -1.