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#!/usr/bin/env python
"""This server runs an XMLRPC server that can be submitted code and tests
and returns the output. It *should* be run as root and will run as the user
'nobody' so as to minimize any damange by errant code.
"""
import sys
import traceback
from SimpleXMLRPCServer import SimpleXMLRPCServer
import pwd
import os
from os.path import isdir
import signal
# Timeout for the code to run in seconds.
TIMEOUT = 2
def run_as_nobody():
# Set the effective uid
nobody = pwd.getpwnam('nobody')
os.setegid(nobody.pw_gid)
os.seteuid(nobody.pw_uid)
# Raised when the code times-out.
# c.f. http://pguides.net/python/timeout-a-function
class TimeoutException(Exception):
pass
def timeout_handler(signum, frame):
raise TimeoutException('Code took too long to run.')
def run_code(answer, test_code, in_dir=None):
"""Tests given Python function (`answer`) with the `test_code` supplied.
If the optional `in_dir` keyword argument is supplied it changes the
directory to that directory (it does not change it back to the original when
done). This function also timesout when the function takes more than
TIMEOUT seconds to run to prevent runaway code.
Returns
-------
A tuple: (success, error message).
"""
if in_dir is not None and isdir(in_dir):
os.chdir(in_dir)
# Add a new signal handler for the execution of this code.
old_handler = signal.signal(signal.SIGALRM, timeout_handler)
signal.alarm(TIMEOUT)
success = False
tb = None
try:
submitted = compile(answer, '<string>', mode='exec')
g = {}
exec submitted in g
_tests = compile(test_code, '<string>', mode='exec')
exec _tests in g
except TimeoutException:
err = 'Code took more than %s seconds to run.'%TIMEOUT
except AssertionError:
type, value, tb = sys.exc_info()
info = traceback.extract_tb(tb)
fname, lineno, func, text = info[-1]
text = str(test_code).splitlines()[lineno-1]
err = "{0} {1} in: {2}".format(type.__name__, str(value), text)
except:
type, value = sys.exc_info()[:2]
err = "Error: {0}".format(repr(value))
else:
success = True
err = 'Correct answer'
finally:
del tb
# Set back any original signal handler.
signal.signal(signal.SIGALRM, old_handler)
# Cancel the signal if any, see signal.alarm documentation.
signal.alarm(0)
return success, err
def main():
run_as_nobody()
server = SimpleXMLRPCServer(("localhost", 8001))
server.register_function(run_code)
server.serve_forever()
if __name__ == '__main__':
main()
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