def set_range(r, e = nil)
    unless r
      @header.delete 'range'
      return r
    end
    r = (r...r+e) if e
    case r
    when Numeric
      n = r.to_i
      rangestr = (n > 0 ? "0-#{n-1}" : "-#{-n}")
    when Range
      first = r.first
      last = r.last
      last -= 1 if r.exclude_end?
      if last == -1
        rangestr = (first > 0 ? "#{first}-" : "-#{-first}")
      else
        raise Net::HTTPHeaderSyntaxError, 'range.first is negative' if first < 0
        raise Net::HTTPHeaderSyntaxError, 'range.last is negative' if last < 0
        raise Net::HTTPHeaderSyntaxError, 'must be .first < .last' if first > last
        rangestr = "#{first}-#{last}"
      end
    else
      raise TypeError, 'Range/Integer is required'
    end
    @header['range'] = ["bytes=#{rangestr}"]
    r
  end
Sets the HTTP Range: header.
Accepts either a Range object as a single argument,
or a beginning index and a length from that index.
Example:

req.range = (0..1023)
req.set_range 0, 1023