Add an example simple announcement service

examples/service-announcement/README.md

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+
+# Simple Announcement Service Example
+
+This is a simple service that allows administrators to manage announcements
+that appear when JupyterHub renders pages.
+
+To run the service as a hub-managed service simply include in your JupyterHub
+configuration file something like:
+
+    c.JupyterHub.services = [
+            {
+                'name': 'announcement',
+                'url': 'http://127.0.0.1:8888',
+                'command': ["python", "-m", "announcement"],
+            }
+    ]
+
+This starts the announcements service up at `/services/announcement` when
+JupyterHub launches.  By default the announcement text is empty.
+
+The `announcement` module has a configurable port (default 8888) and an API
+prefix setting.  By default the API prefix is `JUPYTERHUB_SERVICE_PREFIX` if
+that environment variable is set or `/` if it is not.
+
+## Managing the Announcement
+
+Admin users can set the announcement text with an API token:
+
+    $ curl -X POST -H "Authorization: token <token>"                        \
+        -d "{'announcement':'JupyterHub will be upgraded on August 14!'}"   \
+        https://.../services/announcement
+
+Anyone can read the announcement:
+
+    $ curl https://.../services/announcement | python -m json.tool
+    {
+        announcement: "JupyterHub will be upgraded on August 14!",
+        timestamp: "...",
+        user: "..."
+    }
+
+The time the announcement was posted is recorded in the `timestamp` field and
+the user who posted the announcement is recorded in the `user` field.
+
+To clear the announcement text, just DELETE.  Only admin users can do this.
+
+    $ curl -X POST -H "Authorization: token <token>"                        \
+        https://.../services/announcement
+
+## Seeing the Announcement in JupyterHub
+
+To be able to render the announcement, include the provide `page.html` template
+that extends the base `page.html` template.  Set `c.JupyterHub.template_paths`
+in JupyterHub's configuration to include the path to the extending template.
+The template changes the `announcement` element and does a JQuery `$.get()` call
+to retrieve the announcement text.
+
+JupyterHub's configurable announcement template variables can be set for various
+pages like login, logout, spawn, and home.  Including the template provided in
+this example overrides all of those.

examples/service-announcement/announcement.py

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+
+import argparse
+import datetime
+import json
+import os
+
+from jupyterhub.services.auth import HubAuthenticated
+from tornado import escape, gen, ioloop, web
+
+
+class AnnouncementRequestHandler(HubAuthenticated, web.RequestHandler):
+    """Dynamically manage page announcements"""
+
+    def initialize(self, storage):
+        """Create storage for announcement text"""
+        self.storage = storage
+
+    @web.authenticated
+    def post(self):
+        """Update announcement"""
+        user = self.get_current_user()
+        if user is None or not user.get("admin", False):
+            raise web.HTTPError(403)
+        doc = escape.json_decode(self.request.body)
+        self.storage["announcement"] = doc["announcement"]
+        self.storage["timestamp"] = datetime.datetime.now().isoformat()
+        self.storage["user"] = user["name"]
+        self.write_to_json(self.storage)
+
+    def get(self):
+        """Retrieve announcement"""
+        self.write_to_json(self.storage)
+
+    @web.authenticated
+    def delete(self):
+        """Clear announcement"""
+        user = self.get_current_user()
+        if user is None or not user.get("admin", False):
+            raise web.HTTPError(403)
+        self.storage["announcement"] = ""
+        self.write_to_json(self.storage)
+
+    def write_to_json(self, doc):
+        """Write dictionary document as JSON"""
+        self.set_header("Content-Type", "application/json; charset=UTF-8")
+        self.write(escape.utf8(json.dumps(doc)))
+
+
+def main():
+    args = parse_arguments()
+    application = create_application(**vars(args))
+    application.listen(args.port)
+    ioloop.IOLoop.current().start()
+
+
+def parse_arguments():
+    parser = argparse.ArgumentParser()
+    parser.add_argument("--api-prefix", "-a",
+            default=os.environ.get("JUPYTERHUB_SERVICE_PREFIX", "/"),
+            help="application API prefix")
+    parser.add_argument("--port", "-p",
+            default=8888,
+            help="port for API to listen on",
+            type=int)
+    return parser.parse_args()
+
+
+def create_application(api_prefix="/", 
+        handler=AnnouncementRequestHandler,
+        **kwargs):
+    storage = dict(announcement="", timestamp="", user="")
+    return web.Application([(api_prefix, handler, dict(storage=storage))])
+
+
+if __name__ == "__main__":
+    main()

examples/service-announcement/jupyterhub_config.py

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+
+c.JupyterHub.services = [
+        {
+            'name': 'announcement',
+            'url': 'http://127.0.0.1:8888',
+            'command': ["python", "-m", "announcement"],
+        }
+]
+
+c.JupyterHub.template_paths = ["templates"]

examples/service-announcement/templates/page.html

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+{% extends "templates/page.html" %}
+{% block announcement %}
+<div class="container text-center announcement">
+</div>
+{% endblock %}
+
+{% block script %}
+{{ super() }}
+<script>
+$.get("/services/announcement/", function(data) {
+    $(".announcement").html(data["announcement"]);
+});
+</script>
+{% endblock %}