Allow a session to connect to an existing kernel

notebook/services/sessions/handlers.py

@@ -42,10 +42,13 @@ def post(self):
             path = model['notebook']['path']
         except KeyError:
             raise web.HTTPError(400, "Missing field in JSON data: notebook.path")
-        try:
-            kernel_name = model['kernel']['name']
-        except KeyError:
-            self.log.debug("No kernel name specified, using default kernel")
+
+        kernel = model.get('kernel', {})
+        kernel_name = kernel.get('name') or None
+        kernel_id = kernel.get('id') or None
+
+        if not kernel_id and not kernel_name:
+            self.log.debug("No kernel specified, using default kernel")
             kernel_name = None
 
         # Check to see if session exists
@@ -55,7 +58,8 @@ def post(self):
         else:
             try:
                 model = yield gen.maybe_future(
-                    sm.create_session(path=path, kernel_name=kernel_name))
+                    sm.create_session(path=path, kernel_name=kernel_name,
+                                      kernel_id=kernel_id))
             except NoSuchKernel:
                 msg = ("The '%s' kernel is not available. Please pick another "
                        "suitable kernel instead, or install that kernel." % kernel_name)

notebook/services/sessions/sessionmanager.py

@@ -64,10 +64,14 @@ def new_session_id(self):
         return unicode_type(uuid.uuid4())
 
     @gen.coroutine
-    def create_session(self, path=None, kernel_name=None):
+    def create_session(self, path=None, kernel_name=None, kernel_id=None):
         """Creates a session and returns its model"""
         session_id = self.new_session_id()
-        kernel_id = yield self.start_kernel_for_session(session_id, path, kernel_name)
+        if kernel_id is not None and kernel_id in self.kernel_manager:
+            pass
+        else:
+            kernel_id = yield self.start_kernel_for_session(session_id, path,
+                                                            kernel_name)
         result = yield gen.maybe_future(
             self.save_session(session_id, path=path, kernel_id=kernel_id)
         )

notebook/services/sessions/tests/test_sessions_api.py

@@ -39,9 +39,10 @@ def list(self):
     def get(self, id):
         return self._req('GET', id)
 
-    def create(self, path, kernel_name='python'):
+    def create(self, path, kernel_name='python', kernel_id=None):
         body = json.dumps({'notebook': {'path':path},
-                           'kernel': {'name': kernel_name}})
+                           'kernel': {'name': kernel_name,
+                                      'id': kernel_id}})
         return self._req('POST', '', body)
 
     def modify_path(self, id, path):
@@ -110,6 +111,28 @@ def test_create(self):
         got = self.sess_api.get(sid).json()
         self.assertEqual(got, newsession)
 
+    def test_create_with_kernel_id(self):
+        # create a new kernel
+        r = requests.post(url_path_join(self.base_url(), 'api/kernels'))
+        r.raise_for_status()
+        kernel = r.json()
+
+        resp = self.sess_api.create('foo/nb1.ipynb', kernel_id=kernel['id'])
+        self.assertEqual(resp.status_code, 201)
+        newsession = resp.json()
+        self.assertIn('id', newsession)
+        self.assertEqual(newsession['notebook']['path'], 'foo/nb1.ipynb')
+        self.assertEqual(newsession['kernel']['id'], kernel['id'])
+        self.assertEqual(resp.headers['Location'], self.url_prefix + 'api/sessions/{0}'.format(newsession['id']))
+
+        sessions = self.sess_api.list().json()
+        self.assertEqual(sessions, [newsession])
+
+        # Retrieve it
+        sid = newsession['id']
+        got = self.sess_api.get(sid).json()
+        self.assertEqual(got, newsession)
+
     def test_delete(self):
         newsession = self.sess_api.create('foo/nb1.ipynb').json()
         sid = newsession['id']