Merge pull request #7083 from takluyver/server-extensions

Add support for notebook server extensions

IPython/html/notebookapp.py

@@ -1,1052 +1,1077 b''
 # coding: utf-8
 """A tornado based IPython notebook server."""
 
 # Copyright (c) IPython Development Team.
 # Distributed under the terms of the Modified BSD License.
 
 from __future__ import print_function
 
 import base64
 import datetime
 import errno
+import importlib
 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
 
 
 # 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 >= 4.0"
 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 < (4,0):
     raise ImportError(msg + ", but you have %s" % tornado.version)
 
 from tornado import httpserver
 from tornado import web
 from tornado.log import LogFormatter, app_log, access_log, gen_log
 
 from IPython.html import (
     DEFAULT_STATIC_FILES_PATH,
     DEFAULT_TEMPLATE_PATH_LIST,
 )
 from .base.handlers import Template404
 from .log import log_request
 from .services.kernels.kernelmanager import MappingKernelManager
 from .services.contents.manager import ContentsManager
 from .services.contents.filemanager import FileContentsManager
 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, base_flags, base_aliases,
 )
 from IPython.core.profiledir import ProfileDir
 from IPython.kernel import KernelManager
 from IPython.kernel.kernelspec import KernelSpecManager
 from IPython.kernel.zmq.session import default_secure, Session
 from IPython.nbformat.sign import NotebookNotary
 from IPython.utils.importstring import import_item
 from IPython.utils import submodule
 from IPython.utils.process import check_pid
 from IPython.utils.traitlets import (
     Dict, Unicode, Integer, List, Bool, Bytes, Instance,
     DottedObjectName, TraitError,
 )
 from IPython.utils import py3compat
 from IPython.utils.path import filefind, get_ipython_dir
 from IPython.utils.sysinfo import get_sys_info
 
 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, contents_manager,
                  cluster_manager, session_manager, kernel_spec_manager,
                  config_manager, log,
                  base_url, default_url, settings_overrides, jinja_env_options):
 
         settings = self.init_settings(
             ipython_app, kernel_manager, contents_manager, cluster_manager,
             session_manager, kernel_spec_manager, config_manager, log, base_url,
             default_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, contents_manager,
                       cluster_manager, session_manager, kernel_spec_manager,
                       config_manager,
                       log, base_url, default_url, settings_overrides,
                       jinja_env_options=None):
 
         _template_path = settings_overrides.get(
             "template_path",
             ipython_app.template_file_path,
         )
         if isinstance(_template_path, str):
             _template_path = (_template_path,)
         template_path = [os.path.expanduser(path) for path in _template_path]
 
         jenv_opt = jinja_env_options if jinja_env_options else {}
         env = Environment(loader=FileSystemLoader(template_path), **jenv_opt)
         
         sys_info = get_sys_info()
         if sys_info['commit_source'] == 'repository':
             # don't cache (rely on 304) when working from master
             version_hash = ''
         else:
             # reset the cache on server restart
             version_hash = datetime.datetime.now().strftime("%Y%m%d%H%M%S")
 
         settings = dict(
             # basics
             log_function=log_request,
             base_url=base_url,
             default_url=default_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/'),
             static_handler_args = {
                 # don't cache custom.js
                 'no_cache_paths': [url_path_join(base_url, 'static', 'custom')],
             },
             version_hash=version_hash,
             
             # authentication
             cookie_secret=ipython_app.cookie_secret,
             login_url=url_path_join(base_url,'/login'),
             login_handler_class=ipython_app.login_handler_class,
             logout_handler_class=ipython_app.logout_handler_class,
             password=ipython_app.password,
 
             # managers
             kernel_manager=kernel_manager,
             contents_manager=contents_manager,
             cluster_manager=cluster_manager,
             session_manager=session_manager,
             kernel_spec_manager=kernel_spec_manager,
             config_manager=config_manager,
 
             # IPython stuff
             nbextensions_path=ipython_app.nbextensions_path,
             websocket_url=ipython_app.websocket_url,
             mathjax_url=ipython_app.mathjax_url,
             config=ipython_app.config,
             jinja2_env=env,
             terminals_available=False,  # Set later if terminals are available
         )
 
         # 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."""
         
         # Order matters. The first handler to match the URL will handle the request.
         handlers = []
         handlers.extend(load_handlers('tree.handlers'))
         handlers.extend([(r"/login", settings['login_handler_class'])])
         handlers.extend([(r"/logout", settings['logout_handler_class'])])
         handlers.extend(load_handlers('files.handlers'))
         handlers.extend(load_handlers('notebook.handlers'))
         handlers.extend(load_handlers('nbconvert.handlers'))
         handlers.extend(load_handlers('kernelspecs.handlers'))
         handlers.extend(load_handlers('edit.handlers'))
         handlers.extend(load_handlers('services.config.handlers'))
         handlers.extend(load_handlers('services.kernels.handlers'))
         handlers.extend(load_handlers('services.contents.handlers'))
         handlers.extend(load_handlers('services.clusters.handlers'))
         handlers.extend(load_handlers('services.sessions.handlers'))
         handlers.extend(load_handlers('services.nbconvert.handlers'))
         handlers.extend(load_handlers('services.kernelspecs.handlers'))
         handlers.extend(load_handlers('services.security.handlers'))
         handlers.append(
             (r"/nbextensions/(.*)", FileFindHandler, {
                 'path': settings['nbextensions_path'],
                 'no_cache_paths': ['/'], # don't cache anything in nbextensions
             }),
         )
         # register base handlers last
         handlers.extend(load_handlers('base.handlers'))
         # set the URL that will be redirected from `/`
         handlers.append(
             (r'/?', web.RedirectHandler, {
                 'url' : url_path_join(settings['base_url'], settings['default_url']),
                 'permanent': False, # want 302, not 301
             })
         )
         # 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(base_flags)
 flags['no-browser']=(
     {'NotebookApp' : {'open_browser' : False}},
     "Don't open the notebook in a browser after startup."
 )
 flags['pylab']=(
     {'NotebookApp' : {'pylab' : 'warn'}},
     "DISABLED: use %pylab or %matplotlib in the notebook to enable matplotlib."
 )
 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', 'FileContentsManager.save_script',
                'DEPRECATED, IGNORED',
                'DEPRECATED, IGNORED'))
 
 aliases = dict(base_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',
     'pylab': 'NotebookApp.pylab',
 })
 
 #-----------------------------------------------------------------------------
 # 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
     aliases = aliases
     flags = flags
     
     classes = [
         KernelManager, ProfileDir, Session, MappingKernelManager,
         ContentsManager, FileContentsManager, NotebookNotary,
     ]
     flags = Dict(flags)
     aliases = Dict(aliases)
     
     subcommands = dict(
         list=(NbserverListApp, NbserverListApp.description.splitlines()[0]),
     )
 
     ipython_kernel_argv = List(Unicode)
     
     _log_formatter_cls = LogFormatter
 
     def _log_level_default(self):
         return logging.INFO
 
     def _log_datefmt_default(self):
         """Exclude date from default date format"""
         return "%H:%M:%S"
     
     def _log_format_default(self):
         """override default log format to include time"""
         return u"%(color)s[%(levelname)1.1s %(asctime)s.%(msecs).03d %(name)s]%(end_color)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)
 
     # 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"
     )
     
     default_url = Unicode('/tree', config=True,
         help="The default URL to redirect to from `/`"
     )
     
     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_file = Unicode(config=True,
         help="""The file where the cookie secret is stored."""
     )
     def _cookie_secret_file_default(self):
         if self.profile_dir is None:
             return ''
         return os.path.join(self.profile_dir.security_dir, 'notebook_cookie_secret')
     
     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):
         if os.path.exists(self.cookie_secret_file):
             with io.open(self.cookie_secret_file, 'rb') as f:
                 return f.read()
         else:
             secret = base64.encodestring(os.urandom(1024))
             self._write_cookie_secret_file(secret)
             return secret
     
     def _write_cookie_secret_file(self, secret):
         """write my secret to my secret_file"""
         self.log.info("Writing notebook server cookie secret to %s", self.cookie_secret_file)
         with io.open(self.cookie_secret_file, 'wb') as f:
             f.write(secret)
         try:
             os.chmod(self.cookie_secret_file, 0o600)
         except OSError:
             self.log.warn(
                 "Could not set permissions on %s",
                 self.cookie_secret_file
             )
 
     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="DEPRECATED, use tornado_settings"
     )
     def _webapp_settings_changed(self, name, old, new):
         self.log.warn("\n    webapp_settings is deprecated, use tornado_settings.\n")
         self.tornado_settings = new
     
     tornado_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]
 
     extra_template_paths = List(Unicode, config=True,
         help="""Extra paths to search for serving jinja templates.
 
         Can be used to override templates from IPython.html.templates."""
     )
     def _extra_template_paths_default(self):
         return []
 
     @property
     def template_file_path(self):
         """return extra paths + the default locations"""
         return self.extra_template_paths + DEFAULT_TEMPLATE_PATH_LIST
 
     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')]
 
     websocket_url = Unicode("", config=True,
         help="""The base URL for websockets,
         if it differs from the HTTP server (hint: it almost certainly doesn't).
         
         Should be in the form of an HTTP origin: ws[s]://hostname[:port]
         """
     )
     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.tornado_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
         url = u"https://cdn.mathjax.org/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)
 
     contents_manager_class = DottedObjectName('IPython.html.services.contents.filemanager.FileContentsManager',
         config=True,
         help='The notebook manager class to use.'
     )
     kernel_manager_class = DottedObjectName('IPython.html.services.kernels.kernelmanager.MappingKernelManager',
         config=True,
         help='The kernel manager class to use.'
     )
     session_manager_class = DottedObjectName('IPython.html.services.sessions.sessionmanager.SessionManager',
         config=True,
         help='The session manager class to use.'
     )
     cluster_manager_class = DottedObjectName('IPython.html.services.clusters.clustermanager.ClusterManager',
         config=True,
         help='The cluster manager class to use.'
     )
 
     config_manager_class = DottedObjectName('IPython.html.services.config.manager.ConfigManager',
         config = True,
         help='The config manager class to use'
     )
 
     kernel_spec_manager = Instance(KernelSpecManager)
 
     def _kernel_spec_manager_default(self):
         return KernelSpecManager(ipython_dir=self.ipython_dir)
 
     kernel_spec_manager_class = DottedObjectName('IPython.kernel.kernelspec.KernelSpecManager',
             config=True,
             help="""
             The kernel spec manager class to use. Should be a subclass
             of `IPython.kernel.kernelspec.KernelSpecManager`.
 
             The Api of KernelSpecManager is provisional and might change
             without warning between this version of IPython and the next stable one.
             """)
 
     login_handler = DottedObjectName('IPython.html.auth.login.LoginHandler',
         config=True,
         help='The login handler class to use.')
 
     logout_handler = DottedObjectName('IPython.html.auth.logout.LogoutHandler',
         config=True,
         help='The logout handler 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)
     
     pylab = Unicode('disabled', config=True,
         help="""
         DISABLED: use %pylab or %matplotlib in the notebook to enable matplotlib.
         """
     )
     def _pylab_changed(self, name, old, new):
         """when --pylab is specified, display a warning and exit"""
         if new != 'warn':
             backend = ' %s' % new
         else:
             backend = ''
         self.log.error("Support for specifying --pylab on the command line has been removed.")
         self.log.error(
             "Please use `%pylab{0}` or `%matplotlib{0}` in the notebook itself.".format(backend)
         )
         self.exit(1)
 
     notebook_dir = Unicode(config=True,
         help="The directory to use for notebooks and kernels."
     )
 
     def _notebook_dir_default(self):
         if self.file_to_run:
             return os.path.dirname(os.path.abspath(self.file_to_run))
         else:
             return py3compat.getcwd()
 
     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.FileContentsManager.root_dir = new
         self.config.MappingKernelManager.root_dir = new
 
+    server_extensions = List(Unicode(), config=True,
+        help=("Python modules to load as notebook server extensions. "
+              "This is an experimental API, and may change in future releases.")
+    )
+
     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):
         """add the profile-dir to arguments to be passed to IPython kernels"""
         # FIXME: remove special treatment of IPython kernels
         # Kernel should get *absolute* path to profile directory
         self.ipython_kernel_argv = ["--profile-dir", self.profile_dir.location]
 
     def init_configurables(self):
         # force Session default to be secure
         default_secure(self.config)
         kls = import_item(self.kernel_spec_manager_class)
         self.kernel_spec_manager = kls(ipython_dir=self.ipython_dir)
 
         kls = import_item(self.kernel_manager_class)
         self.kernel_manager = kls(
             parent=self, log=self.log, ipython_kernel_argv=self.ipython_kernel_argv,
             connection_dir = self.profile_dir.security_dir,
         )
         kls = import_item(self.contents_manager_class)
         self.contents_manager = kls(parent=self, log=self.log)
         kls = import_item(self.session_manager_class)
         self.session_manager = kls(parent=self, log=self.log,
                                    kernel_manager=self.kernel_manager,
                                    contents_manager=self.contents_manager)
         kls = import_item(self.cluster_manager_class)
         self.cluster_manager = kls(parent=self, log=self.log)
         self.cluster_manager.update_profiles()
         self.login_handler_class = import_item(self.login_handler)
         self.logout_handler_class = import_item(self.logout_handler)
 
         kls = import_item(self.config_manager_class)
         self.config_manager = kls(parent=self, log=self.log,
                                   profile_dir=self.profile_dir.location)
 
     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
         
         for log in app_log, access_log, gen_log:
             # consistent log output name (NotebookApp instead of tornado.access, etc.)
             log.name = self.log.name
         # hook up tornado 3's loggers to our app handlers
         logger = logging.getLogger('tornado')
         logger.propagate = True
         logger.parent = self.log
         logger.setLevel(self.log.level)
     
     def init_webapp(self):
         """initialize tornado webapp and httpserver"""
         self.tornado_settings['allow_origin'] = self.allow_origin
         if self.allow_origin_pat:
             self.tornado_settings['allow_origin_pat'] = re.compile(self.allow_origin_pat)
         self.tornado_settings['allow_credentials'] = self.allow_credentials
         
         self.web_app = NotebookWebApplication(
             self, self.kernel_manager, self.contents_manager,
             self.cluster_manager, self.session_manager, self.kernel_spec_manager,
             self.config_manager,
             self.log, self.base_url, self.default_url, self.tornado_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.login_handler_class.validate_security(self, ssl_options=ssl_options)
         self.http_server = httpserver.HTTPServer(self.web_app, ssl_options=ssl_options,
                                                  xheaders=self.trust_xheaders)
 
         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_terminals(self):
         try:
             from .terminal import initialize
             initialize(self.web_app)
             self.web_app.settings['terminals_available'] = True
         except ImportError as e:
             self.log.info("Terminals not available (error was %s)", e)
 
     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.
         """
         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.current().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.current().add_callback(self._restore_sigint_handler)
     
     def _signal_stop(self, sig, frame):
         self.log.critical("received signal %s, stopping", sig)
         ioloop.IOLoop.current().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")
+
+    def init_server_extensions(self):
+        """Load any extensions specified by config.
+
+        Import the module, then call the load_jupyter_server_extension function,
+        if one exists.
+        
+        The extension API is experimental, and may change in future releases.
+        """
+        for modulename in self.server_extensions:
+            try:
+                mod = importlib.import_module(modulename)
+                func = getattr(mod, 'load_jupyter_server_extension', None)
+                if func is not None:
+                    func(self)
+            except Exception:
+                self.log.warn("Error loading server extension %s", modulename,
+                              exc_info=True)
     
     @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_terminals()
         self.init_signal()
+        self.init_server_extensions()
 
     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.contents_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),
                 'pid': os.getpid()
                }
 
     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:
                 if not os.path.exists(self.file_to_run):
                     self.log.critical("%s does not exist" % self.file_to_run)
                     self.exit(1)
 
                 relpath = os.path.relpath(self.file_to_run, self.notebook_dir)
                 uri = url_path_join('notebooks', *relpath.split(os.sep))
             else:
                 uri = 'tree'
             if browser:
                 b = lambda : browser.open(url_path_join(self.connection_url, uri),
                                           new=2)
                 threading.Thread(target=b).start()
         
         self.io_loop = ioloop.IOLoop.current()
         try:
             self.io_loop.start()
         except KeyboardInterrupt:
             info("Interrupted...")
         finally:
             self.cleanup_kernels()
             self.remove_server_info_file()
     
     def stop(self):
         def _stop():
             self.http_server.stop()
             self.io_loop.stop()
         self.io_loop.add_callback(_stop)
 
 
 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:
                 info = json.load(f)
 
             # Simple check whether that process is really still running
             # Also remove leftover files from IPython 2.x without a pid field
             if ('pid' in info) and check_pid(info['pid']):
                 yield info
             else:
                 # If the process has died, try to delete its info file
                 try:
                     os.unlink(file)
                 except OSError:
                     pass  # TODO: This should warn or log or something
 #-----------------------------------------------------------------------------
 # Main entry point
 #-----------------------------------------------------------------------------
 
 launch_new_instance = NotebookApp.launch_instance