Parse multipart byte ranges mime

parse_multipart_byteranges.rb

# multipart byte ranges mime -> [[offset, content], ...]
def parse_multipart_byteranges(body, content_type)
  # match boundary=...
  match = /boundary=(.*)$/.match(content_type)
  return nil if match.nil?
  boundary = match[1]

  # (\r\n)--boundary\r\npart\r\n--boundary(--)\r\n -> [part, ..]
  parts = body.split(/(?:\r\n)?--#{boundary}(?:--)?\r\n/)
  ranges = []
  total_length = 0

  parts.each do |part|
    # filter out empty parts
    next if /\A\s*\Z/.match(part)

    # key: value\r\nkey: value\r\n\r\nbody -> [key: value, body]
    part_header, part_body = part.split("\r\n\r\n", 2)
    return nil if part_body.nil?

    # key: value\r\n -> {key: value}
    headers = Hash[part_header.lines.map do |line|
      line.strip!
      key, value = line.split(/:\s*/, 2)
      return nil if value.nil?

      [key.downcase, value]
    end]

    content_range = headers["content-range"]
    return nil if content_range.nil?

    # match bytes offset-length/total_length
    match = /^bytes (\d+)-(\d+)\/(\d+)$/.match(content_range)
    return nil if match.nil?
    offset, length, total_length = match[1].to_i, match[2].to_i, match[3].to_i

    ranges << [offset, part_body[0,length]]
  end

  return ranges, total_length
end