docs: def main(_):
    """Run the main test harness."""
  
    if flags.FLAGS.version:
      print("GRR Admin UI {}".format(config_server.VERSION["packageversion"]))
      return
  
    config.CONFIG.AddContext(
        contexts.ADMIN_UI_CONTEXT,
        "Context applied when running the admin user interface GUI.")
    server_startup.Init()
  
    if not config.CONFIG["AdminUI.headless"] and (not os.path.exists(
        os.path.join(config.CONFIG["AdminUI.document_root"],
                     "dist/grr-ui.bundle.js")) or not os.path.exists(
                         os.path.join(config.CONFIG["AdminUI.document_root"],
                                      "dist/grr-ui.bundle.css"))):
      raise RuntimeError("Can't find compiled JS/CSS bundles. "
                         "Please reinstall the PIP package using "
                         "\"pip install -e .\" to rebuild the bundles.")
  
    # Start up a server in another thread
    bind_address = config.CONFIG["AdminUI.bind"]
    ip = ipaddress.ip_address(bind_address)
    if ip.version == 4:
      # Address looks like an IPv4 address.
      ThreadedServer.address_family = socket.AF_INET
  
    max_port = config.CONFIG.Get("AdminUI.port_max",
                                 config.CONFIG["AdminUI.port"])
  
    for port in range(config.CONFIG["AdminUI.port"], max_port + 1):
      # Make a simple reference implementation WSGI server
      try:
        server = simple_server.make_server(
            bind_address,
            port,
            wsgiapp.AdminUIApp().WSGIHandler(),
            server_class=ThreadedServer)
        break
      except socket.error as e:
        if e.errno == socket.errno.EADDRINUSE and port < max_port:
          logging.info("Port %s in use, trying %s", port, port + 1)
        else:
          raise
  
    proto = "HTTP"
  
    if config.CONFIG["AdminUI.enable_ssl"]:
      cert_file = config.CONFIG["AdminUI.ssl_cert_file"]
      if not cert_file:
        raise ValueError("Need a valid cert file to enable SSL.")
  
      key_file = config.CONFIG["AdminUI.ssl_key_file"]
      server.socket = ssl.wrap_socket(
          server.socket, certfile=cert_file, keyfile=key_file, server_side=True)
      proto = "HTTPS"
  
      # SSL errors are swallowed by the WSGIServer so if your configuration does
      # not work, uncomment the line below, point your browser at the gui and look
      # at the log file to see why SSL complains:
      # server.socket.accept()
  
    sa = server.socket.getsockname()
    logging.info("Serving %s on %s port %d ...", proto, sa[0], sa[1])
    server_startup.DropPrivileges()
  
    server.serve_forever()