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.
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.