class Rack::Files

def serving(request, path)
  if request.options?
    return [200, { 'allow' => ALLOW_HEADER, CONTENT_LENGTH => '0' }, []]
  end
  last_modified = ::File.mtime(path).httpdate
  return [304, {}, []] if request.get_header('HTTP_IF_MODIFIED_SINCE') == last_modified
  headers = { "last-modified" => last_modified }
  mime_type = mime_type path, @default_mime
  headers[CONTENT_TYPE] = mime_type if mime_type
  # Set custom headers
  headers.merge!(@headers) if @headers
  status = 200
  size = filesize path
  ranges = Rack::Utils.get_byte_ranges(request.get_header('HTTP_RANGE'), size)
  if ranges.nil?
    # No ranges:
    ranges = [0..size - 1]
  elsif ranges.empty?
    # Unsatisfiable. Return error, and file size:
    response = fail(416, "Byte range unsatisfiable")
    response[1]["content-range"] = "bytes */#{size}"
    return response
  else
    # Partial content
    partial_content = true
    if ranges.size == 1
      range = ranges[0]
      headers["content-range"] = "bytes #{range.begin}-#{range.end}/#{size}"
    else
      headers[CONTENT_TYPE] = "multipart/byteranges; boundary=#{MULTIPART_BOUNDARY}"
    end
    status = 206
    body = BaseIterator.new(path, ranges, mime_type: mime_type, size: size)
    size = body.bytesize
  end
  headers[CONTENT_LENGTH] = size.to_s
  if request.head?
    body = []
  elsif !partial_content
    body = Iterator.new(path, ranges, mime_type: mime_type, size: size)
  end
  [status, headers, body]
end