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# Copyright 2009 Canonical Ltd. This software is licensed under the
# GNU Affero General Public License version 3 (see the file LICENSE).
# Explicit is better than implicit.
# pylint: disable-msg=W0602,W0603
"""Helpers to time out external operations."""
__metaclass__ = type
__all__ = [
"get_default_timeout_function",
"SafeTransportWithTimeout",
"set_default_timeout_function",
"TimeoutError",
"TransportWithTimeout",
"urlfetch",
"with_timeout",
]
import httplib
import socket
import sys
from threading import Thread
import urllib2
from xmlrpclib import (
SafeTransport,
Transport,
)
default_timeout_function = None
def get_default_timeout_function():
"""Return the function returning the default timeout value to use."""
global default_timeout_function
return default_timeout_function
def set_default_timeout_function(timeout_function):
"""Change the function returning the default timeout value to use."""
global default_timeout_function
default_timeout_function = timeout_function
class TimeoutError(Exception):
"""Exception raised when a function doesn't complete within time."""
class ThreadCapturingResult(Thread):
"""Thread subclass that saves the return value of its target.
It also saves exceptions raised when invoking the target.
"""
def __init__(self, target, args, kwargs, **opt):
super(ThreadCapturingResult, self).__init__(**opt)
self.target = target
self.args = args
self.kwargs = kwargs
def run(self):
"""See `Thread`."""
try:
self.result = self.target(*self.args, **self.kwargs)
except (SystemExit, KeyboardInterrupt):
# Don't trap those.
raise
except Exception:
self.exc_info = sys.exc_info()
class DefaultTimeout:
"""Descriptor returning the timeout computed by the default function."""
def __get__(self, obj, type=None):
global default_timeout_function
if default_timeout_function is None:
raise AssertionError(
"no timeout set and there is no default timeout function.")
return default_timeout_function()
class with_timeout:
"""Make sure the decorated function doesn't exceed a time out.
This will execute the function in a separate thread. If the function
doesn't complete in the timeout, a TimeoutError is raised. The clean-up
function will be called to "stop" the thread. (If it's possible to do so.)
"""
timeout = DefaultTimeout()
def __init__(self, cleanup=None, timeout=None):
"""Creates the function decorator.
:param cleanup: That may be a callable or a string. If it's a string,
a method under that name will be looked up. That callable will
be called if the timeout is exceeded.
:param timeout: The number of seconds to wait for.
"""
# If the cleanup function is specified by name, the function but be a
# method, so defined in a class definition context.
if isinstance(cleanup, basestring):
frame = sys._getframe(1)
f_locals = frame.f_locals
# Try to make sure we were called from a class def.
if f_locals is frame.f_globals or '__module__' not in f_locals:
raise TypeError(
"when not wrapping a method, cleanup must be a callable.")
self.cleanup = cleanup
if timeout is not None:
self.timeout = timeout
def __call__(self, f):
"""Wraps the method."""
def call_with_timeout(*args, **kwargs):
t = ThreadCapturingResult(f, args, kwargs)
t.start()
t.join(self.timeout)
if t.isAlive():
if self.cleanup is not None:
if isinstance(self.cleanup, basestring):
# 'self' will be first positional argument.
getattr(args[0], self.cleanup)()
else:
self.cleanup()
# Collect cleaned-up worker thread.
t.join()
raise TimeoutError("timeout exceeded.")
if getattr(t, 'exc_info', None) is not None:
exc_info = t.exc_info
# Remove the cyclic reference for faster GC.
del t.exc_info
raise exc_info[0], exc_info[1], exc_info[2]
return t.result
return call_with_timeout
class CleanableHTTPHandler(urllib2.HTTPHandler):
"""Subclass of `urllib2.HTTPHandler` that can be cleaned-up."""
def http_open(self, req):
"""See `urllib2.HTTPHandler`."""
def connection_factory(*args, **kwargs):
"""Save the created connection so that we can clean it up."""
self.__conn = httplib.HTTPConnection(*args, **kwargs)
return self.__conn
return self.do_open(connection_factory, req)
def reset_connection(self):
"""Reset the underlying HTTP connection."""
try:
self.__conn.sock.shutdown(socket.SHUT_RDWR)
except AttributeError:
# It's possible that the other thread closed the socket
# beforehand.
pass
self.__conn.close()
class URLFetcher:
"""Object fetching remote URLs with a time out."""
@with_timeout(cleanup='cleanup')
def fetch(self, url, data=None):
"""Fetch the URL using a custom HTTP handler supporting timeout."""
assert url.startswith('http://'), "only http is supported."
self.handler = CleanableHTTPHandler()
opener = urllib2.build_opener(self.handler)
return opener.open(url, data).read()
def cleanup(self):
"""Reset the connection when the operation timed out."""
self.handler.reset_connection()
def urlfetch(url, data=None):
"""Wrapper for `urllib2.urlopen()` that times out."""
return URLFetcher().fetch(url, data)
class TransportWithTimeout(Transport):
"""Create a HTTP transport for XMLRPC with timeouts."""
def make_connection(self, host):
"""Create the connection for the transport and save it."""
self.conn = Transport.make_connection(self, host)
return self.conn
@with_timeout(cleanup='cleanup')
def request(self, host, handler, request_body, verbose=0):
"""Make the request but using the with_timeout decorator."""
return Transport.request(
self, host, handler, request_body, verbose)
def cleanup(self):
"""In the event of a timeout cleanup by closing the connection."""
try:
self.conn._conn.sock.shutdown(socket.SHUT_RDWR)
except AttributeError:
# It's possible that the other thread closed the socket
# beforehand.
pass
self.conn._conn.close()
class SafeTransportWithTimeout(SafeTransport):
"""Create a HTTPS transport for XMLRPC with timeouts."""
def make_connection(self, host):
"""Create the connection for the transport and save it."""
self.conn = SafeTransport.make_connection(self, host)
return self.conn
@with_timeout(cleanup='cleanup')
def request(self, host, handler, request_body, verbose=0):
"""Make the request but using the with_timeout decorator."""
return SafeTransport.request(
self, host, handler, request_body, verbose)
def cleanup(self):
"""In the event of a timeout cleanup by closing the connection."""
try:
self.conn._conn.sock.shutdown(socket.SHUT_RDWR)
except AttributeError:
# It's possible that the other thread closed the socket
# beforehand.
pass
self.conn._conn.close()
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