Backport PR #6105: only set allow_origin_pat if defined

fixes the default behavior to be as intended (require Origin == Host)

IPython/html/notebookapp.py

@@ -1,882 +1,883 b''
 # coding: utf-8
 """A tornado based IPython notebook server.
 
 Authors:
 
 * Brian Granger
 """
 from __future__ import print_function
 #-----------------------------------------------------------------------------
 #  Copyright (C) 2013  The IPython Development Team
 #
 #  Distributed under the terms of the BSD License.  The full license is in
 #  the file COPYING, distributed as part of this software.
 #-----------------------------------------------------------------------------
 
 #-----------------------------------------------------------------------------
 # Imports
 #-----------------------------------------------------------------------------
 
 # stdlib
 import errno
 import io
 import json
 import logging
 import os
 import random
 import re
 import select
 import signal
 import socket
 import sys
 import threading
 import time
 import webbrowser
 
 
 # Third party
 # check for pyzmq 2.1.11
 from IPython.utils.zmqrelated import check_for_zmq
 check_for_zmq('2.1.11', 'IPython.html')
 
 from jinja2 import Environment, FileSystemLoader
 
 # Install the pyzmq ioloop. This has to be done before anything else from
 # tornado is imported.
 from zmq.eventloop import ioloop
 ioloop.install()
 
 # check for tornado 3.1.0
 msg = "The IPython Notebook requires tornado >= 3.1.0"
 try:
     import tornado
 except ImportError:
     raise ImportError(msg)
 try:
     version_info = tornado.version_info
 except AttributeError:
     raise ImportError(msg + ", but you have < 1.1.0")
 if version_info < (3,1,0):
     raise ImportError(msg + ", but you have %s" % tornado.version)
 
 from tornado import httpserver
 from tornado import web
 
 # Our own libraries
 from IPython.html import DEFAULT_STATIC_FILES_PATH
 from .base.handlers import Template404
 from .log import log_request
 from .services.kernels.kernelmanager import MappingKernelManager
 from .services.notebooks.nbmanager import NotebookManager
 from .services.notebooks.filenbmanager import FileNotebookManager
 from .services.clusters.clustermanager import ClusterManager
 from .services.sessions.sessionmanager import SessionManager
 
 from .base.handlers import AuthenticatedFileHandler, FileFindHandler
 
 from IPython.config import Config
 from IPython.config.application import catch_config_error, boolean_flag
 from IPython.core.application import BaseIPythonApplication
 from IPython.core.profiledir import ProfileDir
 from IPython.consoleapp import IPythonConsoleApp
 from IPython.kernel import swallow_argv
 from IPython.kernel.zmq.session import default_secure
 from IPython.kernel.zmq.kernelapp import (
     kernel_flags,
     kernel_aliases,
 )
 from IPython.nbformat.sign import NotebookNotary
 from IPython.utils.importstring import import_item
 from IPython.utils import submodule
 from IPython.utils.traitlets import (
     Dict, Unicode, Integer, List, Bool, Bytes,
     DottedObjectName, TraitError,
 )
 from IPython.utils import py3compat
 from IPython.utils.path import filefind, get_ipython_dir
 
 from .utils import url_path_join
 
 #-----------------------------------------------------------------------------
 # Module globals
 #-----------------------------------------------------------------------------
 
 _examples = """
 ipython notebook                       # start the notebook
 ipython notebook --profile=sympy       # use the sympy profile
 ipython notebook --certfile=mycert.pem # use SSL/TLS certificate
 """
 
 #-----------------------------------------------------------------------------
 # Helper functions
 #-----------------------------------------------------------------------------
 
 def random_ports(port, n):
     """Generate a list of n random ports near the given port.
 
     The first 5 ports will be sequential, and the remaining n-5 will be
     randomly selected in the range [port-2*n, port+2*n].
     """
     for i in range(min(5, n)):
         yield port + i
     for i in range(n-5):
         yield max(1, port + random.randint(-2*n, 2*n))
 
 def load_handlers(name):
     """Load the (URL pattern, handler) tuples for each component."""
     name = 'IPython.html.' + name
     mod = __import__(name, fromlist=['default_handlers'])
     return mod.default_handlers
 
 #-----------------------------------------------------------------------------
 # The Tornado web application
 #-----------------------------------------------------------------------------
 
 class NotebookWebApplication(web.Application):
 
     def __init__(self, ipython_app, kernel_manager, notebook_manager,
                  cluster_manager, session_manager, log, base_url,
                  settings_overrides, jinja_env_options):
 
         settings = self.init_settings(
             ipython_app, kernel_manager, notebook_manager, cluster_manager,
             session_manager, log, base_url, settings_overrides, jinja_env_options)
         handlers = self.init_handlers(settings)
 
         super(NotebookWebApplication, self).__init__(handlers, **settings)
 
     def init_settings(self, ipython_app, kernel_manager, notebook_manager,
                       cluster_manager, session_manager, log, base_url,
                       settings_overrides, jinja_env_options=None):
         # Python < 2.6.5 doesn't accept unicode keys in f(**kwargs), and
         # base_url will always be unicode, which will in turn
         # make the patterns unicode, and ultimately result in unicode
         # keys in kwargs to handler._execute(**kwargs) in tornado.
         # This enforces that base_url be ascii in that situation.
         # 
         # Note that the URLs these patterns check against are escaped,
         # and thus guaranteed to be ASCII: 'héllo' is really 'h%C3%A9llo'.
         base_url = py3compat.unicode_to_str(base_url, 'ascii')
         template_path = settings_overrides.get("template_path", os.path.join(os.path.dirname(__file__), "templates"))
         jenv_opt = jinja_env_options if jinja_env_options else {}
         env = Environment(loader=FileSystemLoader(template_path),**jenv_opt )
         settings = dict(
             # basics
             log_function=log_request,
             base_url=base_url,
             template_path=template_path,
             static_path=ipython_app.static_file_path,
             static_handler_class = FileFindHandler,
             static_url_prefix = url_path_join(base_url,'/static/'),
             
             # authentication
             cookie_secret=ipython_app.cookie_secret,
             login_url=url_path_join(base_url,'/login'),
             password=ipython_app.password,
             
             # managers
             kernel_manager=kernel_manager,
             notebook_manager=notebook_manager,
             cluster_manager=cluster_manager,
             session_manager=session_manager,
 
             # IPython stuff
             nbextensions_path = ipython_app.nbextensions_path,
             mathjax_url=ipython_app.mathjax_url,
             config=ipython_app.config,
             jinja2_env=env,
         )
 
         # allow custom overrides for the tornado web app.
         settings.update(settings_overrides)
         return settings
 
     def init_handlers(self, settings):
         # Load the (URL pattern, handler) tuples for each component.
         handlers = []
         handlers.extend(load_handlers('base.handlers'))
         handlers.extend(load_handlers('tree.handlers'))
         handlers.extend(load_handlers('auth.login'))
         handlers.extend(load_handlers('auth.logout'))
         handlers.extend(load_handlers('notebook.handlers'))
         handlers.extend(load_handlers('nbconvert.handlers'))
         handlers.extend(load_handlers('services.kernels.handlers'))
         handlers.extend(load_handlers('services.notebooks.handlers'))
         handlers.extend(load_handlers('services.clusters.handlers'))
         handlers.extend(load_handlers('services.sessions.handlers'))
         handlers.extend(load_handlers('services.nbconvert.handlers'))
         # FIXME: /files/ should be handled by the Contents service when it exists
         nbm = settings['notebook_manager']
         if hasattr(nbm, 'notebook_dir'):
             handlers.extend([
             (r"/files/(.*)", AuthenticatedFileHandler, {'path' : nbm.notebook_dir}),
             (r"/nbextensions/(.*)", FileFindHandler, {'path' : settings['nbextensions_path']}),
         ])
         # prepend base_url onto the patterns that we match
         new_handlers = []
         for handler in handlers:
             pattern = url_path_join(settings['base_url'], handler[0])
             new_handler = tuple([pattern] + list(handler[1:]))
             new_handlers.append(new_handler)
         # add 404 on the end, which will catch everything that falls through
         new_handlers.append((r'(.*)', Template404))
         return new_handlers
 
 
 class NbserverListApp(BaseIPythonApplication):
     
     description="List currently running notebook servers in this profile."
     
     flags = dict(
         json=({'NbserverListApp': {'json': True}},
               "Produce machine-readable JSON output."),
     )
     
     json = Bool(False, config=True,
           help="If True, each line of output will be a JSON object with the "
                   "details from the server info file.")
 
     def start(self):
         if not self.json:
             print("Currently running servers:")
         for serverinfo in list_running_servers(self.profile):
             if self.json:
                 print(json.dumps(serverinfo))
             else:
                 print(serverinfo['url'], "::", serverinfo['notebook_dir'])
 
 #-----------------------------------------------------------------------------
 # Aliases and Flags
 #-----------------------------------------------------------------------------
 
 flags = dict(kernel_flags)
 flags['no-browser']=(
     {'NotebookApp' : {'open_browser' : False}},
     "Don't open the notebook in a browser after startup."
 )
 flags['no-mathjax']=(
     {'NotebookApp' : {'enable_mathjax' : False}},
     """Disable MathJax
     
     MathJax is the javascript library IPython uses to render math/LaTeX. It is
     very large, so you may want to disable it if you have a slow internet
     connection, or for offline use of the notebook.
     
     When disabled, equations etc. will appear as their untransformed TeX source.
     """
 )
 
 # Add notebook manager flags
 flags.update(boolean_flag('script', 'FileNotebookManager.save_script',
                'Auto-save a .py script everytime the .ipynb notebook is saved',
                'Do not auto-save .py scripts for every notebook'))
 
 # the flags that are specific to the frontend
 # these must be scrubbed before being passed to the kernel,
 # or it will raise an error on unrecognized flags
 notebook_flags = ['no-browser', 'no-mathjax', 'script', 'no-script']
 
 aliases = dict(kernel_aliases)
 
 aliases.update({
     'ip': 'NotebookApp.ip',
     'port': 'NotebookApp.port',
     'port-retries': 'NotebookApp.port_retries',
     'transport': 'KernelManager.transport',
     'keyfile': 'NotebookApp.keyfile',
     'certfile': 'NotebookApp.certfile',
     'notebook-dir': 'NotebookApp.notebook_dir',
     'browser': 'NotebookApp.browser',
 })
 
 # remove ipkernel flags that are singletons, and don't make sense in
 # multi-kernel evironment:
 aliases.pop('f', None)
 
 notebook_aliases = [u'port', u'port-retries', u'ip', u'keyfile', u'certfile',
                     u'notebook-dir', u'profile', u'profile-dir', 'browser']
 
 #-----------------------------------------------------------------------------
 # NotebookApp
 #-----------------------------------------------------------------------------
 
 class NotebookApp(BaseIPythonApplication):
 
     name = 'ipython-notebook'
     
     description = """
         The IPython HTML Notebook.
         
         This launches a Tornado based HTML Notebook Server that serves up an
         HTML5/Javascript Notebook client.
     """
     examples = _examples
     
     classes = IPythonConsoleApp.classes + [MappingKernelManager, NotebookManager,
         FileNotebookManager, NotebookNotary]
     flags = Dict(flags)
     aliases = Dict(aliases)
     
     subcommands = dict(
         list=(NbserverListApp, NbserverListApp.description.splitlines()[0]),
     )
 
     kernel_argv = List(Unicode)
 
     def _log_level_default(self):
         return logging.INFO
 
     def _log_format_default(self):
         """override default log format to include time"""
         return u"%(asctime)s.%(msecs).03d [%(name)s]%(highlevel)s %(message)s"
 
     # create requested profiles by default, if they don't exist:
     auto_create = Bool(True)
 
     # file to be opened in the notebook server
     file_to_run = Unicode('', config=True)
     def _file_to_run_changed(self, name, old, new):
         path, base = os.path.split(new)
         if path:
             self.file_to_run = base
             self.notebook_dir = path
 
     # Network related information
 
     allow_origin = Unicode('', config=True,
         help="""Set the Access-Control-Allow-Origin header
 
         Use '*' to allow any origin to access your server.
 
         Takes precedence over allow_origin_pat.
         """
     )
 
     allow_origin_pat = Unicode('', config=True,
         help="""Use a regular expression for the Access-Control-Allow-Origin header
 
         Requests from an origin matching the expression will get replies with:
 
             Access-Control-Allow-Origin: origin
 
         where `origin` is the origin of the request.
 
         Ignored if allow_origin is set.
         """
     )
 
     allow_credentials = Bool(False, config=True,
         help="Set the Access-Control-Allow-Credentials: true header"
     )
 
     ip = Unicode('localhost', config=True,
         help="The IP address the notebook server will listen on."
     )
 
     def _ip_changed(self, name, old, new):
         if new == u'*': self.ip = u''
 
     port = Integer(8888, config=True,
         help="The port the notebook server will listen on."
     )
     port_retries = Integer(50, config=True,
         help="The number of additional ports to try if the specified port is not available."
     )
 
     certfile = Unicode(u'', config=True, 
         help="""The full path to an SSL/TLS certificate file."""
     )
     
     keyfile = Unicode(u'', config=True, 
         help="""The full path to a private key file for usage with SSL/TLS."""
     )
     
     cookie_secret = Bytes(b'', config=True,
         help="""The random bytes used to secure cookies.
         By default this is a new random number every time you start the Notebook.
         Set it to a value in a config file to enable logins to persist across server sessions.
         
         Note: Cookie secrets should be kept private, do not share config files with
         cookie_secret stored in plaintext (you can read the value from a file).
         """
     )
     def _cookie_secret_default(self):
         return os.urandom(1024)
 
     password = Unicode(u'', config=True,
                       help="""Hashed password to use for web authentication.
 
                       To generate, type in a python/IPython shell:
 
                         from IPython.lib import passwd; passwd()
 
                       The string should be of the form type:salt:hashed-password.
                       """
     )
 
     open_browser = Bool(True, config=True,
                         help="""Whether to open in a browser after starting.
                         The specific browser used is platform dependent and
                         determined by the python standard library `webbrowser`
                         module, unless it is overridden using the --browser
                         (NotebookApp.browser) configuration option.
                         """)
 
     browser = Unicode(u'', config=True,
                       help="""Specify what command to use to invoke a web
                       browser when opening the notebook. If not specified, the
                       default browser will be determined by the `webbrowser`
                       standard library module, which allows setting of the
                       BROWSER environment variable to override it.
                       """)
     
     webapp_settings = Dict(config=True,
             help="Supply overrides for the tornado.web.Application that the "
                  "IPython notebook uses.")
 
     jinja_environment_options = Dict(config=True, 
             help="Supply extra arguments that will be passed to Jinja environment.")
 
     
     enable_mathjax = Bool(True, config=True,
         help="""Whether to enable MathJax for typesetting math/TeX
 
         MathJax is the javascript library IPython uses to render math/LaTeX. It is
         very large, so you may want to disable it if you have a slow internet
         connection, or for offline use of the notebook.
 
         When disabled, equations etc. will appear as their untransformed TeX source.
         """
     )
     def _enable_mathjax_changed(self, name, old, new):
         """set mathjax url to empty if mathjax is disabled"""
         if not new:
             self.mathjax_url = u''
 
     base_url = Unicode('/', config=True,
                                help='''The base URL for the notebook server.
 
                                Leading and trailing slashes can be omitted,
                                and will automatically be added.
                                ''')
     def _base_url_changed(self, name, old, new):
         if not new.startswith('/'):
             self.base_url = '/'+new
         elif not new.endswith('/'):
             self.base_url = new+'/'
     
     base_project_url = Unicode('/', config=True, help="""DEPRECATED use base_url""")
     def _base_project_url_changed(self, name, old, new):
         self.log.warn("base_project_url is deprecated, use base_url")
         self.base_url = new
 
     extra_static_paths = List(Unicode, config=True,
         help="""Extra paths to search for serving static files.
         
         This allows adding javascript/css to be available from the notebook server machine,
         or overriding individual files in the IPython"""
     )
     def _extra_static_paths_default(self):
         return [os.path.join(self.profile_dir.location, 'static')]
     
     @property
     def static_file_path(self):
         """return extra paths + the default location"""
         return self.extra_static_paths + [DEFAULT_STATIC_FILES_PATH]
     
     nbextensions_path = List(Unicode, config=True,
         help="""paths for Javascript extensions. By default, this is just IPYTHONDIR/nbextensions"""
     )
     def _nbextensions_path_default(self):
         return [os.path.join(get_ipython_dir(), 'nbextensions')]
 
     mathjax_url = Unicode("", config=True,
         help="""The url for MathJax.js."""
     )
     def _mathjax_url_default(self):
         if not self.enable_mathjax:
             return u''
         static_url_prefix = self.webapp_settings.get("static_url_prefix",
                          url_path_join(self.base_url, "static")
         )
         
         # try local mathjax, either in nbextensions/mathjax or static/mathjax
         for (url_prefix, search_path) in [
             (url_path_join(self.base_url, "nbextensions"), self.nbextensions_path),
             (static_url_prefix, self.static_file_path),
         ]:
             self.log.debug("searching for local mathjax in %s", search_path)
             try:
                 mathjax = filefind(os.path.join('mathjax', 'MathJax.js'), search_path)
             except IOError:
                 continue
             else:
                 url = url_path_join(url_prefix, u"mathjax/MathJax.js")
                 self.log.info("Serving local MathJax from %s at %s", mathjax, url)
                 return url
         
         # no local mathjax, serve from CDN
         if self.certfile:
             # HTTPS: load from Rackspace CDN, because SSL certificate requires it
             host = u"https://c328740.ssl.cf1.rackcdn.com"
         else:
             host = u"http://cdn.mathjax.org"
         
         url = host + u"/mathjax/latest/MathJax.js"
         self.log.info("Using MathJax from CDN: %s", url)
         return url
     
     def _mathjax_url_changed(self, name, old, new):
         if new and not self.enable_mathjax:
             # enable_mathjax=False overrides mathjax_url
             self.mathjax_url = u''
         else:
             self.log.info("Using MathJax: %s", new)
 
     notebook_manager_class = DottedObjectName('IPython.html.services.notebooks.filenbmanager.FileNotebookManager',
         config=True,
         help='The notebook manager class to use.')
 
     trust_xheaders = Bool(False, config=True,
         help=("Whether to trust or not X-Scheme/X-Forwarded-Proto and X-Real-Ip/X-Forwarded-For headers"
               "sent by the upstream reverse proxy. Necessary if the proxy handles SSL")
     )
     
     info_file = Unicode()
 
     def _info_file_default(self):
         info_file = "nbserver-%s.json"%os.getpid()
         return os.path.join(self.profile_dir.security_dir, info_file)
     
     notebook_dir = Unicode(py3compat.getcwd(), config=True,
         help="The directory to use for notebooks and kernels."
     )
 
     def _notebook_dir_changed(self, name, old, new):
         """Do a bit of validation of the notebook dir."""
         if not os.path.isabs(new):
             # If we receive a non-absolute path, make it absolute.
             self.notebook_dir = os.path.abspath(new)
             return
         if not os.path.isdir(new):
             raise TraitError("No such notebook dir: %r" % new)
         
         # setting App.notebook_dir implies setting notebook and kernel dirs as well
         self.config.FileNotebookManager.notebook_dir = new
         self.config.MappingKernelManager.root_dir = new
         
 
     def parse_command_line(self, argv=None):
         super(NotebookApp, self).parse_command_line(argv)
         
         if self.extra_args:
             arg0 = self.extra_args[0]
             f = os.path.abspath(arg0)
             self.argv.remove(arg0)
             if not os.path.exists(f):
                 self.log.critical("No such file or directory: %s", f)
                 self.exit(1)
             
             # Use config here, to ensure that it takes higher priority than
             # anything that comes from the profile.
             c = Config()
             if os.path.isdir(f):
                 c.NotebookApp.notebook_dir = f
             elif os.path.isfile(f):
                 c.NotebookApp.file_to_run = f
             self.update_config(c)
 
     def init_kernel_argv(self):
         """construct the kernel arguments"""
         # Scrub frontend-specific flags
         self.kernel_argv = swallow_argv(self.argv, notebook_aliases, notebook_flags)
         if any(arg.startswith(u'--pylab') for arg in self.kernel_argv):
             self.log.warn('\n    '.join([
                 "Starting all kernels in pylab mode is not recommended,",
                 "and will be disabled in a future release.",
                 "Please use the %matplotlib magic to enable matplotlib instead.",
                 "pylab implies many imports, which can have confusing side effects",
                 "and harm the reproducibility of your notebooks.",
             ]))
         # Kernel should inherit default config file from frontend
         self.kernel_argv.append("--IPKernelApp.parent_appname='%s'" % self.name)
         # Kernel should get *absolute* path to profile directory
         self.kernel_argv.extend(["--profile-dir", self.profile_dir.location])
 
     def init_configurables(self):
         # force Session default to be secure
         default_secure(self.config)
         self.kernel_manager = MappingKernelManager(
             parent=self, log=self.log, kernel_argv=self.kernel_argv,
             connection_dir = self.profile_dir.security_dir,
         )
         kls = import_item(self.notebook_manager_class)
         self.notebook_manager = kls(parent=self, log=self.log)
         self.session_manager = SessionManager(parent=self, log=self.log)
         self.cluster_manager = ClusterManager(parent=self, log=self.log)
         self.cluster_manager.update_profiles()
 
     def init_logging(self):
         # This prevents double log messages because tornado use a root logger that
         # self.log is a child of. The logging module dipatches log messages to a log
         # and all of its ancenstors until propagate is set to False.
         self.log.propagate = False
         
         # hook up tornado 3's loggers to our app handlers
         for name in ('access', 'application', 'general'):
             logger = logging.getLogger('tornado.%s' % name)
             logger.parent = self.log
             logger.setLevel(self.log.level)
 
     def init_webapp(self):
         """initialize tornado webapp and httpserver"""
         self.webapp_settings['allow_origin'] = self.allow_origin
+        if self.allow_origin_pat:
         self.webapp_settings['allow_origin_pat'] = re.compile(self.allow_origin_pat)
         self.webapp_settings['allow_credentials'] = self.allow_credentials
 
         self.web_app = NotebookWebApplication(
             self, self.kernel_manager, self.notebook_manager,
             self.cluster_manager, self.session_manager,
             self.log, self.base_url, self.webapp_settings,
             self.jinja_environment_options
         )
         if self.certfile:
             ssl_options = dict(certfile=self.certfile)
             if self.keyfile:
                 ssl_options['keyfile'] = self.keyfile
         else:
             ssl_options = None
         self.web_app.password = self.password
         self.http_server = httpserver.HTTPServer(self.web_app, ssl_options=ssl_options,
                                                  xheaders=self.trust_xheaders)
         if not self.ip:
             warning = "WARNING: The notebook server is listening on all IP addresses"
             if ssl_options is None:
                 self.log.critical(warning + " and not using encryption. This "
                     "is not recommended.")
             if not self.password:
                 self.log.critical(warning + " and not using authentication. "
                     "This is highly insecure and not recommended.")
         success = None
         for port in random_ports(self.port, self.port_retries+1):
             try:
                 self.http_server.listen(port, self.ip)
             except socket.error as e:
                 if e.errno == errno.EADDRINUSE:
                     self.log.info('The port %i is already in use, trying another random port.' % port)
                     continue
                 elif e.errno in (errno.EACCES, getattr(errno, 'WSAEACCES', errno.EACCES)):
                     self.log.warn("Permission to listen on port %i denied" % port)
                     continue
                 else:
                     raise
             else:
                 self.port = port
                 success = True
                 break
         if not success:
             self.log.critical('ERROR: the notebook server could not be started because '
                               'no available port could be found.')
             self.exit(1)
     
     @property
     def display_url(self):
         ip = self.ip if self.ip else '[all ip addresses on your system]'
         return self._url(ip)
 
     @property
     def connection_url(self):
         ip = self.ip if self.ip else 'localhost'
         return self._url(ip)
 
     def _url(self, ip):
         proto = 'https' if self.certfile else 'http'
         return "%s://%s:%i%s" % (proto, ip, self.port, self.base_url)
 
     def init_signal(self):
         if not sys.platform.startswith('win'):
             signal.signal(signal.SIGINT, self._handle_sigint)
         signal.signal(signal.SIGTERM, self._signal_stop)
         if hasattr(signal, 'SIGUSR1'):
             # Windows doesn't support SIGUSR1
             signal.signal(signal.SIGUSR1, self._signal_info)
         if hasattr(signal, 'SIGINFO'):
             # only on BSD-based systems
             signal.signal(signal.SIGINFO, self._signal_info)
     
     def _handle_sigint(self, sig, frame):
         """SIGINT handler spawns confirmation dialog"""
         # register more forceful signal handler for ^C^C case
         signal.signal(signal.SIGINT, self._signal_stop)
         # request confirmation dialog in bg thread, to avoid
         # blocking the App
         thread = threading.Thread(target=self._confirm_exit)
         thread.daemon = True
         thread.start()
     
     def _restore_sigint_handler(self):
         """callback for restoring original SIGINT handler"""
         signal.signal(signal.SIGINT, self._handle_sigint)
     
     def _confirm_exit(self):
         """confirm shutdown on ^C
         
         A second ^C, or answering 'y' within 5s will cause shutdown,
         otherwise original SIGINT handler will be restored.
         
         This doesn't work on Windows.
         """
         # FIXME: remove this delay when pyzmq dependency is >= 2.1.11
         time.sleep(0.1)
         info = self.log.info
         info('interrupted')
         print(self.notebook_info())
         sys.stdout.write("Shutdown this notebook server (y/[n])? ")
         sys.stdout.flush()
         r,w,x = select.select([sys.stdin], [], [], 5)
         if r:
             line = sys.stdin.readline()
             if line.lower().startswith('y') and 'n' not in line.lower():
                 self.log.critical("Shutdown confirmed")
                 ioloop.IOLoop.instance().stop()
                 return
         else:
             print("No answer for 5s:", end=' ')
         print("resuming operation...")
         # no answer, or answer is no:
         # set it back to original SIGINT handler
         # use IOLoop.add_callback because signal.signal must be called
         # from main thread
         ioloop.IOLoop.instance().add_callback(self._restore_sigint_handler)
     
     def _signal_stop(self, sig, frame):
         self.log.critical("received signal %s, stopping", sig)
         ioloop.IOLoop.instance().stop()
 
     def _signal_info(self, sig, frame):
         print(self.notebook_info())
     
     def init_components(self):
         """Check the components submodule, and warn if it's unclean"""
         status = submodule.check_submodule_status()
         if status == 'missing':
             self.log.warn("components submodule missing, running `git submodule update`")
             submodule.update_submodules(submodule.ipython_parent())
         elif status == 'unclean':
             self.log.warn("components submodule unclean, you may see 404s on static/components")
             self.log.warn("run `setup.py submodule` or `git submodule update` to update")
     
     @catch_config_error
     def initialize(self, argv=None):
         super(NotebookApp, self).initialize(argv)
         self.init_logging()
         self.init_kernel_argv()
         self.init_configurables()
         self.init_components()
         self.init_webapp()
         self.init_signal()
 
     def cleanup_kernels(self):
         """Shutdown all kernels.
         
         The kernels will shutdown themselves when this process no longer exists,
         but explicit shutdown allows the KernelManagers to cleanup the connection files.
         """
         self.log.info('Shutting down kernels')
         self.kernel_manager.shutdown_all()
 
     def notebook_info(self):
         "Return the current working directory and the server url information"
         info = self.notebook_manager.info_string() + "\n"
         info += "%d active kernels \n" % len(self.kernel_manager._kernels)
         return info + "The IPython Notebook is running at: %s" % self.display_url
 
     def server_info(self):
         """Return a JSONable dict of information about this server."""
         return {'url': self.connection_url,
                 'hostname': self.ip if self.ip else 'localhost',
                 'port': self.port,
                 'secure': bool(self.certfile),
                 'base_url': self.base_url,
                 'notebook_dir': os.path.abspath(self.notebook_dir),
                }
 
     def write_server_info_file(self):
         """Write the result of server_info() to the JSON file info_file."""
         with open(self.info_file, 'w') as f:
             json.dump(self.server_info(), f, indent=2)
 
     def remove_server_info_file(self):
         """Remove the nbserver-<pid>.json file created for this server.
         
         Ignores the error raised when the file has already been removed.
         """
         try:
             os.unlink(self.info_file)
         except OSError as e:
             if e.errno != errno.ENOENT:
                 raise
 
     def start(self):
         """ Start the IPython Notebook server app, after initialization
         
         This method takes no arguments so all configuration and initialization
         must be done prior to calling this method."""
         if self.subapp is not None:
             return self.subapp.start()
 
         info = self.log.info
         for line in self.notebook_info().split("\n"):
             info(line)
         info("Use Control-C to stop this server and shut down all kernels (twice to skip confirmation).")
 
         self.write_server_info_file()
 
         if self.open_browser or self.file_to_run:
             try:
                 browser = webbrowser.get(self.browser or None)
             except webbrowser.Error as e:
                 self.log.warn('No web browser found: %s.' % e)
                 browser = None
             
             if self.file_to_run:
                 fullpath = os.path.join(self.notebook_dir, self.file_to_run)
                 if not os.path.exists(fullpath):
                     self.log.critical("%s does not exist" % fullpath)
                     self.exit(1)
                 
                 uri = url_path_join('notebooks', self.file_to_run)
             else:
                 uri = 'tree'
             if browser:
                 b = lambda : browser.open(url_path_join(self.connection_url, uri),
                                           new=2)
                 threading.Thread(target=b).start()
         try:
             ioloop.IOLoop.instance().start()
         except KeyboardInterrupt:
             info("Interrupted...")
         finally:
             self.cleanup_kernels()
             self.remove_server_info_file()
 
 
 def list_running_servers(profile='default'):
     """Iterate over the server info files of running notebook servers.
     
     Given a profile name, find nbserver-* files in the security directory of
     that profile, and yield dicts of their information, each one pertaining to
     a currently running notebook server instance.
     """
     pd = ProfileDir.find_profile_dir_by_name(get_ipython_dir(), name=profile)
     for file in os.listdir(pd.security_dir):
         if file.startswith('nbserver-'):
             with io.open(os.path.join(pd.security_dir, file), encoding='utf-8') as f:
                 yield json.load(f)
 
 #-----------------------------------------------------------------------------
 # Main entry point
 #-----------------------------------------------------------------------------
 
 launch_new_instance = NotebookApp.launch_instance