class Rack::URLMap

def call(env)
  path        = env[PATH_INFO]
  script_name = env[SCRIPT_NAME]
  http_host   = env[HTTP_HOST]
  server_name = env[SERVER_NAME]
  server_port = env[SERVER_PORT]
  is_same_server = casecmp?(http_host, server_name) ||
                   casecmp?(http_host, "#{server_name}:#{server_port}")
  is_host_known = @known_hosts.include? http_host
  @mapping.each do |host, location, match, app|
    unless casecmp?(http_host, host) \
        || casecmp?(server_name, host) \
        || (!host && is_same_server) \
        || (!host && !is_host_known) # If we don't have a matching host, default to the first without a specified host
      next
    end
    next unless m = match.match(path.to_s)
    rest = m[1]
    next unless !rest || rest.empty? || rest[0] == ?/
    env[SCRIPT_NAME] = (script_name + location)
    env[PATH_INFO] = rest
    return app.call(env)
  end
  [404, { CONTENT_TYPE => "text/plain", "x-cascade" => "pass" }, ["Not Found: #{path}"]]
ensure
  env[PATH_INFO]   = path
  env[SCRIPT_NAME] = script_name
end