Special case ExtensionApp that starts the ServerApp

docs/source/developers/extensions.rst

@@ -128,7 +128,7 @@ The basic structure of an ExtensionApp is shown below:
 
         # -------------- Required traits --------------
         name = "myextension"
-        extension_url = "/myextension"
+        default_url = "/myextension"
         load_other_extensions = True
 
         # --- ExtensionApp traits you can configure ---
@@ -167,7 +167,7 @@ Methods
 Properties
 
 * ``name``: the name of the extension
-* ``extension_url``: the default url for this extension—i.e. the landing page for this extension when launched from the CLI.
+* ``default_url``: the default url for this extension—i.e. the landing page for this extension when launched from the CLI.
 * ``load_other_extensions``: a boolean enabling/disabling other extensions when launching this extension directly.
 
 ``ExtensionApp`` request handlers
@@ -302,13 +302,13 @@ To make your extension executable from anywhere on your system, point an entry-p
 ``ExtensionApp`` as a classic Notebook server extension
 -------------------------------------------------------
 
-An extension that extends ``ExtensionApp`` should still work with the old Tornado server from the classic Jupyter Notebook. The ``ExtensionApp`` class 
+An extension that extends ``ExtensionApp`` should still work with the old Tornado server from the classic Jupyter Notebook. The ``ExtensionApp`` class
 provides a method, ``load_classic_server_extension``, that handles the extension initialization. Simply  define a ``load_jupyter_server_extension`` reference
-pointing at the ``load_classic_server_extension`` method: 
+pointing at the ``load_classic_server_extension`` method:
 
 .. code-block:: python
 
-    # This is typically defined in the root `__init__.py` 
+    # This is typically defined in the root `__init__.py`
     # file of the extension package.
     load_jupyter_server_extension = MyExtensionApp.load_classic_server_extension
 
@@ -483,7 +483,7 @@ There are a few key steps to make this happen:
     .. code-block:: python
 
         def load_jupyter_server_extension(nb_server_app):
-            
+
             web_app = nb_server_app.web_app
             host_pattern = '.*$'
             base_url = web_app.settings['base_url']
@@ -495,50 +495,50 @@ There are a few key steps to make this happen:
 
             # Favicon redirects.
             favicon_redirects = [
-                (   
-                    url_path_join(base_url, "/static/favicons/favicon.ico"), 
+                (
+                    url_path_join(base_url, "/static/favicons/favicon.ico"),
                     RedirectHandler,
                     {"url": url_path_join(serverapp.base_url, "static/base/images/favicon.ico")
                 ),
                 (
-                    url_path_join(base_url, "/static/favicons/favicon-busy-1.ico"), 
+                    url_path_join(base_url, "/static/favicons/favicon-busy-1.ico"),
                     RedirectHandler,
                     {"url": url_path_join(serverapp.base_url, "static/base/images/favicon-busy-1.ico")}
                 ),
                 (
-                    url_path_join(base_url, "/static/favicons/favicon-busy-2.ico"), 
+                    url_path_join(base_url, "/static/favicons/favicon-busy-2.ico"),
                     RedirectHandler,
                     {"url": url_path_join(serverapp.base_url, "static/base/images/favicon-busy-2.ico")}
                 ),
                 (
-                    url_path_join(base_url, "/static/favicons/favicon-busy-3.ico"), 
+                    url_path_join(base_url, "/static/favicons/favicon-busy-3.ico"),
                     RedirectHandler,
                     {"url": url_path_join(serverapp.base_url, "static/base/images/favicon-busy-3.ico")}
                 ),
                 (
-                    url_path_join(base_url, "/static/favicons/favicon-file.ico"), 
+                    url_path_join(base_url, "/static/favicons/favicon-file.ico"),
                     RedirectHandler,
                     {"url": url_path_join(serverapp.base_url, "static/base/images/favicon-file.ico")}
                 ),
                 (
-                    url_path_join(base_url, "/static/favicons/favicon-notebook.ico"), 
+                    url_path_join(base_url, "/static/favicons/favicon-notebook.ico"),
                     RedirectHandler,
                     {"url": url_path_join(serverapp.base_url, "static/base/images/favicon-notebook.ico")}
                 ),
                 (
-                    url_path_join(base_url, "/static/favicons/favicon-terminal.ico"), 
+                    url_path_join(base_url, "/static/favicons/favicon-terminal.ico"),
                     RedirectHandler,
                     {"url": url_path_join(serverapp.base_url, "static/base/images/favicon-terminal.ico")}
                 ),
                 (
-                    url_path_join(base_url, "/static/logo/logo.png"), 
+                    url_path_join(base_url, "/static/logo/logo.png"),
                     RedirectHandler,
                     {"url": url_path_join(serverapp.base_url, "static/base/images/logo.png")}
                 ),
             ]
 
             web_app.add_handlers(
-                host_pattern, 
+                host_pattern,
                 custom_handlers + favicon_redirects
             )
 

jupyter_server/extension/application.py

@@ -4,6 +4,7 @@
 
 from jinja2 import Environment, FileSystemLoader
 
+from traitlets.config import Config
 from traitlets import (
     HasTraits,
     Unicode,
@@ -12,7 +13,6 @@
     Bool,
     default
 )
-from traitlets.config import Config
 from tornado.log import LogFormatter
 from tornado.web import RedirectHandler
 
@@ -186,6 +186,9 @@ def get_extension_point(cls):
     def _default_url(self):
         return self.extension_url
 
+    # Is this linked to a serverapp yet?
+    _linked = Bool(False)
+
     # Extension can configure the ServerApp from the command-line
     classes = [
         ServerApp,
@@ -196,9 +199,6 @@ def _default_url(self):
 
     _log_formatter_cls = LogFormatter
 
-    # Whether this app is the starter app
-    _is_starter_app = False
-
     @default('log_level')
     def _default_log_level(self):
         return logging.INFO
@@ -333,14 +333,14 @@ def _prepare_templates(self):
             })
         self.initialize_templates()
 
-    @classmethod
-    def _jupyter_server_config(cls):
+    def _jupyter_server_config(self):
         base_config = {
             "ServerApp": {
-                "jpserver_extensions": {cls.get_extension_package(): True},
+                "default_url": self.default_url,
+                "open_browser": self.open_browser
             }
         }
-        base_config["ServerApp"].update(cls.serverapp_config)
+        base_config["ServerApp"].update(self.serverapp_config)
         return base_config
 
     def _link_jupyter_server_extension(self, serverapp):
@@ -351,6 +351,10 @@ def _link_jupyter_server_extension(self, serverapp):
         the command line contains traits for the ExtensionApp
         or the ExtensionApp's config files have server
         settings.
+
+        Note, the ServerApp has not initialized the Tornado
+        Web Application yet, so do not try to affect the
+        `web_app` attribute.
         """
         self.serverapp = serverapp
         # Load config from an ExtensionApp's config files.
@@ -370,23 +374,8 @@ def _link_jupyter_server_extension(self, serverapp):
         # ServerApp, do it here.
         # i.e. ServerApp traits <--- ExtensionApp config
         self.serverapp.update_config(self.config)
-
-    @classmethod
-    def initialize_server(cls, argv=[], load_other_extensions=True, **kwargs):
-        """Creates an instance of ServerApp where this extension is enabled
-        (superceding disabling found in other config from files).
-
-        This is necessary when launching the ExtensionApp directly from
-        the `launch_instance` classmethod.
-        """
-        # The ExtensionApp needs to add itself as enabled extension
-        # to the jpserver_extensions trait, so that the ServerApp
-        # initializes it.
-        config = Config(cls._jupyter_server_config())
-        serverapp = ServerApp.instance(**kwargs, argv=[], config=config)
-        cls._is_starter_app = True
-        serverapp.initialize(argv=argv, find_extensions=load_other_extensions)
-        return serverapp
+        # Acknowledge that this extension has been linked.
+        self._linked = True
 
     def initialize(self):
         """Initialize the extension app. The
@@ -440,12 +429,7 @@ def _load_jupyter_server_extension(cls, serverapp):
         except KeyError:
             extension = cls()
             extension._link_jupyter_server_extension(serverapp)
-        if cls._is_starter_app:
-            serverapp._starter_app = extension
         extension.initialize()
-        # Set the serverapp's default url to the extension's url.
-        if cls._is_starter_app:
-            serverapp.default_url = extension.default_url
         return extension
 
     @classmethod
@@ -478,6 +462,24 @@ def load_classic_server_extension(cls, serverapp):
         ])
         extension.initialize()
 
+    @classmethod
+    def initialize_server(cls, argv=[], load_other_extensions=True, **kwargs):
+        """Creates an instance of ServerApp and explicitly sets
+        this extension to enabled=True (i.e. superceding disabling
+        found in other config from files).
+
+        The `launch_instance` method uses this method to initialize
+        and start a server.
+        """
+        serverapp = ServerApp.instance(
+            jpserver_extensions={cls.get_extension_package(): True}, **kwargs)
+        serverapp.initialize(
+            argv=argv,
+            starter_extension=cls.name,
+            find_extensions=cls.load_other_extensions,
+        )
+        return serverapp
+
     @classmethod
     def launch_instance(cls, argv=None, **kwargs):
         """Launch the extension like an application. Initializes+configs a stock server
@@ -489,27 +491,29 @@ def launch_instance(cls, argv=None, **kwargs):
             args = sys.argv[1:]  # slice out extension config.
         else:
             args = argv
-        # Check for subcommands
+
+        # Handle all "stops" that could happen before
+        # continuing to launch a server+extension.
         subapp = _preparse_for_subcommand(cls, args)
         if subapp:
             subapp.start()
-        else:
-            # Check for help, version, and generate-config arguments
-            # before initializing server to make sure these
-            # arguments trigger actions from the extension not the server.
-            _preparse_for_stopping_flags(cls, args)
-            # Get a jupyter server instance.
-            serverapp = cls.initialize_server(
-                argv=args,
-                load_other_extensions=cls.load_other_extensions
+            return
+
+        # Check for help, version, and generate-config arguments
+        # before initializing server to make sure these
+        # arguments trigger actions from the extension not the server.
+        _preparse_for_stopping_flags(cls, args)
+
+        serverapp = cls.initialize_server(argv=args)
+
+        # Log if extension is blocking other extensions from loading.
+        if not cls.load_other_extensions:
+            serverapp.log.info(
+                "{ext_name} is running without loading "
+                "other extensions.".format(ext_name=cls.name)
             )
-            # Log if extension is blocking other extensions from loading.
-            if not cls.load_other_extensions:
-                serverapp.log.info(
-                    "{ext_name} is running without loading "
-                    "other extensions.".format(ext_name=cls.name)
-                )
-            try:
-                serverapp.start()
-            except NoStart:
-                pass
+        # Start the server.
+        try:
+            serverapp.start()
+        except NoStart:
+            pass

jupyter_server/extension/manager.py

@@ -1,11 +1,13 @@
 import importlib
 
-from traitlets.config import LoggingConfigurable
+from traitlets.config import LoggingConfigurable, Config
+
 from traitlets import (
     HasTraits,
     Dict,
     Unicode,
     Bool,
+    Any,
     validate
 )
 
@@ -21,12 +23,10 @@ class ExtensionPoint(HasTraits):
     """A simple API for connecting to a Jupyter Server extension
     point defined by metadata and importable from a Python package.
     """
-    metadata = Dict()
+    _linked = Bool(False)
+    _app = Any(None, allow_none=True)
 
-    def __init__(self, *args, **kwargs):
-        # Store extension points that have been linked.
-        self._app = None
-        super().__init__(*args, **kwargs)
+    metadata = Dict()
 
     @validate('metadata')
     def _valid_metadata(self, proposed):
@@ -54,13 +54,30 @@ def _valid_metadata(self, proposed):
 
     @property
     def linked(self):
+        """Has this extension point been linked to the server.
+
+        Will pull from ExtensionApp's trait, if this point
+        is an instance of ExtensionApp.
+        """
+        if self.app:
+            return self.app._linked
         return self._linked
 
     @property
     def app(self):
         """If the metadata includes an `app` field"""
         return self._app
 
+    @property
+    def config(self):
+        """Return any configuration provided by this extension point."""
+        if self.app:
+            return self.app._jupyter_server_config()
+        # At some point, we might want to add logic to load config from
+        # disk when extensions don't use ExtensionApp.
+        else:
+            return {}
+
     @property
     def module_name(self):
         """Name of the Python package module where the extension's
@@ -119,8 +136,11 @@ def link(self, serverapp):
         This looks for a `_link_jupyter_server_extension` function
         in the extension's module or ExtensionApp class.
         """
-        linker = self._get_linker()
-        return linker(serverapp)
+        if not self.linked:
+            linker = self._get_linker()
+            linker(serverapp)
+            # Store this extension as already linked.
+            self._linked = True
 
     def load(self, serverapp):
         """Load the extension in a Jupyter ServerApp object.