module Rack::Utils

def get_byte_ranges(http_range, size)
  # See <http://www.w3.org/Protocols/rfc2616/rfc2616-sec14.html#sec14.35>
  return nil unless http_range && http_range =~ /bytes=([^;]+)/
  ranges = []
  $1.split(/,\s*/).each do |range_spec|
    return nil unless range_spec.include?('-')
    range = range_spec.split('-')
    r0, r1 = range[0], range[1]
    if r0.nil? || r0.empty?
      return nil if r1.nil?
      # suffix-byte-range-spec, represents trailing suffix of file
      r0 = size - r1.to_i
      r0 = 0  if r0 < 0
      r1 = size - 1
    else
      r0 = r0.to_i
      if r1.nil?
        r1 = size - 1
      else
        r1 = r1.to_i
        return nil  if r1 < r0  # backwards range is syntactically invalid
        r1 = size - 1  if r1 >= size
      end
    end
    ranges << (r0..r1)  if r0 <= r1
  end
  ranges
end