class Rack::Sendfile

def map_accel_path(env, path)
  if mapping = @mappings.find { |internal, _| internal =~ path }
    path.sub(*mapping)
  elsif mapping = env['HTTP_X_ACCEL_MAPPING']
    mapping.split(',').map(&:strip).each do |m|
      internal, external = m.split('=', 2).map(&:strip)
      new_path = path.sub(/^#{internal}/i, external)
      return new_path unless path == new_path
    end
    path
  end
end