# File lib/rack/utils.rb, line 395
    def byte_ranges(env, size)
      # See <http://www.w3.org/Protocols/rfc2616/rfc2616-sec14.html#sec14.35>
      http_range = env['HTTP_RANGE']
      return nil unless http_range && http_range =~ /bytes=([^;]+)/
      ranges = []
      $1.split(/,\s*/).each do |range_spec|
        return nil  unless range_spec =~ /(\d*)-(\d*)/
        r0,r1 = $1, $2
        if r0.empty?
          return nil  if r1.empty?
          # 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.empty?
            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