Add root access check to cns server.

media/tools/constrained_network_server/traffic_control.py

 # Copyright (c) 2011 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.
 
 """Traffic control library for constraining the network configuration on a port.
 
 The traffic controller sets up a constrained network configuration on a port.
 Traffic to the constrained port is forwarded to a specified server port.
 """
 
 import logging
+import os
 import re
 import subprocess
 
 # The maximum bandwidth limit.
 _DEFAULT_MAX_BANDWIDTH_KBIT = 1000000
 
 
 class TrafficControlError(BaseException):
   """Exception raised for errors in traffic control library.
 
   Attributes:
     msg: User defined error message.
     cmd: Command for which the exception was raised.
     returncode: Return code of running the command.
     stdout: Output of running the command.
     stderr: Error output of running the command.
   """
 
   def __init__(self, msg, cmd=None, returncode=None, output=None,
                error=None):
     BaseException.__init__(self, msg)
     self.msg = msg
     self.cmd = cmd
     self.returncode = returncode
     self.output = output
     self.error = error
 
 
+def CheckRequirements():
+  """Checks if permissions are available to run traffic control commands.
+
+  Raises:
+    TrafficControlError: If permissions to run traffic control commands are not
+    available.
+  """
+  if not os.geteuid() == 0:

[DaleCurtis, 2012/01/10 00:17:59]

Use != 0.

[shadi, 2012/01/10 00:36:39]

I thought (from previous CL) 'not' is preferred over '!='
On 2012/01/10 00:17:59, DaleCurtis wrote:

[DaleCurtis, 2012/01/10 00:40:01]

For objects and boolean statements, but usually not for a primitive type
comparison.

+    _Exec(['sudo', '-n', 'tc'], msg=('Cannot run traffic control commands. '

[DaleCurtis, 2012/01/10 00:17:59]

Add -help just to be sure.

Where is the iptables check? Should have a ['sudo', '-n', 'iptables', '--help'].
You need both tc and iptables.

[shadi, 2012/01/10 00:36:39]

My bad. I thought the purpose was to check if sudo -n works. I forgot this
checks if the commands exists as well :)
On 2012/01/10 00:17:59, DaleCurtis wrote:

+                                     'Please check that you have root access.'))
+
+
 def CreateConstrainedPort(config):
   """Creates a new constrained port.
 
   Imposes packet level constraints such as bandwidth, latency, and packet loss
   on a given port using the specified configuration dictionary. Traffic to that
   port is forwarded to a specified server port.
 
   Args:
     config: Constraint configuration dictionary, format:
       port: Port to constrain (integer 1-65535).
@@ skipping 278 matching lines @@
   """
   cmd_list = [str(x) for x in command]
   cmd = ' '.join(cmd_list)
   logging.debug('Running command: %s', cmd)
 
   p = subprocess.Popen(cmd_list, stdout=subprocess.PIPE, stderr=subprocess.PIPE)
   output, error = p.communicate()
   if p.returncode != 0:
     raise TrafficControlError(msg, cmd, p.returncode, output, error)
   return output.strip()