return (ip, port) from Spawner.start

removes the need for Spawners to set db state themselves in most cases

Should be backward-compatible with warnings.

jupyterhub/spawner.py

@@ -46,6 +46,9 @@ class Spawner(LoggingConfigurable):
     ip = Unicode('127.0.0.1',
         help="The IP address (or hostname) the single-user server should listen on"
     ).tag(config=True)
+    port = Integer(0,
+        help="The port for single-user servers to listen on. New in version 0.7."
+    )
     start_timeout = Integer(60,
         help="""Timeout (in seconds) before giving up on the spawner.
         
@@ -245,7 +248,6 @@ class Spawner(LoggingConfigurable):
         """Return the arguments to be passed after self.cmd"""
         args = [
             '--user=%s' % self.user.name,
-            '--port=%i' % self.user.server.port,
             '--cookie-name=%s' % self.user.server.cookie_name,
             '--base-url=%s' % self.user.server.base_url,
             '--hub-host=%s' % self.hub.host,
@@ -254,6 +256,13 @@ class Spawner(LoggingConfigurable):
             ]
         if self.ip:
             args.append('--ip=%s' % self.ip)
+
+        if self.port:
+            args.append('--port=%i' % self.port)
+        elif self.user.server.port:
+            self.log.warning("Setting port from user.server is deprecated as of JupyterHub 0.7.")
+            args.append('--port=%i' % self.user.server.port)
+
         if self.notebook_dir:
             self.notebook_dir = self.notebook_dir.replace("%U",self.user.name)
             args.append('--notebook-dir=%s' % self.notebook_dir)
@@ -270,7 +279,15 @@ class Spawner(LoggingConfigurable):
     
     @gen.coroutine
     def start(self):
-        """Start the single-user process"""
+        """Start the single-user server
+        
+        Returns:
+        
+        (ip, port): the ip, port where the Hub can connect to the server.
+        
+        .. versionchanged:: 0.7
+            Return ip, port instead of setting on self.user.server directly.
+        """
         raise NotImplementedError("Override in subclass. Must be a Tornado gen.coroutine.")
     
     @gen.coroutine
@@ -456,9 +473,7 @@ class LocalProcessSpawner(Spawner):
     @gen.coroutine
     def start(self):
         """Start the process"""
-        if self.ip:
-            self.user.server.ip = self.ip
-        self.user.server.port = random_port()
+        self.port = random_port()
         cmd = []
         env = self.get_env()
 
@@ -480,6 +495,7 @@ class LocalProcessSpawner(Spawner):
             raise
 
         self.pid = self.proc.pid
+        return (self.ip or '127.0.0.1', self.port)
 
     @gen.coroutine
     def poll(self):

jupyterhub/tests/mocking.py

@@ -62,8 +62,9 @@ class SlowSpawner(MockSpawner):
     
     @gen.coroutine
     def start(self):
-        yield super().start()
+        (ip, port) = yield super().start()
         yield gen.sleep(2)
+        return ip, port
     
     @gen.coroutine
     def stop(self):

jupyterhub/tests/test_spawner.py

@@ -50,8 +50,14 @@ def new_spawner(db, **kwargs):
 
 def test_spawner(db, io_loop):
     spawner = new_spawner(db)
-    io_loop.run_sync(spawner.start)
-    assert spawner.user.server.ip == '127.0.0.1'
+    ip, port = io_loop.run_sync(spawner.start)
+    assert ip == '127.0.0.1'
+    assert isinstance(port, int)
+    assert port > 0
+    spawner.user.server.ip = ip
+    spawner.user.server.port = port
+    db.commit()
+    
 
     # wait for the process to get to the while True: loop
     time.sleep(1)
@@ -65,8 +71,13 @@ def test_spawner(db, io_loop):
 def test_single_user_spawner(db, io_loop):
     spawner = new_spawner(db, cmd=['jupyterhub-singleuser'])
     spawner.api_token = 'secret'
-    io_loop.run_sync(spawner.start)
-    assert spawner.user.server.ip == '127.0.0.1'
+    ip, port = io_loop.run_sync(spawner.start)
+    assert ip == '127.0.0.1'
+    assert isinstance(port, int)
+    assert port > 0
+    spawner.user.server.ip = ip
+    spawner.user.server.port = port
+    db.commit()
     # wait for http server to come up,
     # checking for early termination every 1s
     def wait():

jupyterhub/user.py

@@ -225,7 +225,14 @@ class User(HasTraits):
             f = spawner.start()
             # commit any changes in spawner.start (always commit db changes before yield)
             db.commit()
-            yield gen.with_timeout(timedelta(seconds=spawner.start_timeout), f)
+            ip_port = yield gen.with_timeout(timedelta(seconds=spawner.start_timeout), f)
+            if ip_port:
+                # get ip, port info from return value of start()
+                self.server.ip, self.server.port = ip_port
+            else:
+                # prior to 0.7, spawners had to store this info in user.server themselves.
+                # Handle < 0.7 behavior with a warning, assuming info was stored in db by the Spawner.
+                self.log.warning("DEPRECATION: Spawner.start should return (ip, port) in JupyterHub >= 0.7")
         except Exception as e:
             if isinstance(e, gen.TimeoutError):
                 self.log.warning("{user}'s server failed to start in {s} seconds, giving up".format(