Add root access check to cns server.

media/tools/constrained_network_server/cns.py

 #!/usr/bin/env python
 # Copyright (c) 2012 The Chromium Authors. All rights reserved.
 # Use of this source code is governed by a BSD-style license that can be
 # found in the LICENSE file.
 
 """Constrained Network Server. Serves files with supplied network constraints.
 
 The CNS exposes a web based API allowing network constraints to be imposed on
 file serving.
 
@@ skipping 309 matching lines @@
   log_level = _DEFAULT_LOG_LEVEL
   if verbose:
     log_level = logging.DEBUG
   logging.basicConfig(level=log_level, format='[%(threadName)s] %(message)s')
 
 
 def Main():
   """Configure and start the ConstrainedNetworkServer."""
   options = ParseArgs()
 
+  try:
+    traffic_control.CheckRequirements()
+  except traffic_control.TrafficControlError as e:
+    cherrypy.log(e.msg)
+    return
+
   cherrypy.config.update(
       {'server.socket_host': '::', 'server.socket_port': options.port})
 
   if options.threads:
     cherrypy.config.update({'server.thread_pool': options.threads})
 
   # Setup port allocator here so we can call cleanup on failures/exit.
   pa = PortAllocator(options.port_range, expiry_time_secs=options.expiry_time)
 
   try:
     cherrypy.quickstart(ConstrainedNetworkServer(options, pa))
   finally:
     # Disable Ctrl-C handler to prevent interruption of cleanup.
     signal.signal(signal.SIGINT, lambda signal, frame: None)
     pa.Cleanup(options.interface, all_ports=True)
 
 
 if __name__ == '__main__':
   Main()