Use maybe_future from notebook or tornado

Author: rmorshea

jupyter_server_proxy/websocket.py

@@ -14,6 +14,13 @@
 from notebook.utils import url_path_join
 from notebook.base.handlers import IPythonHandler, utcnow
 
+try:
+    # Tornado 6.0 deprecated its `maybe_future` function so `notebook` made their own.
+    # See: https://github.com/jupyter/notebook/pull/4453
+    from notebook.utils import maybe_future
+except ImportError:
+    # We can't find it in `notebook` then we should be able to find it in Tornado
+    from tornado.gen import maybe_future
 
 
 class PingableWSClientConnection(websocket.WebSocketClientConnection):
@@ -86,10 +93,7 @@ async def get(self, *args, **kwargs):
         if self.request.headers.get("Upgrade", "").lower() != 'websocket':
             return await self.http_get(*args, **kwargs)
         else:
-            result = super().get(*args, **kwargs)
-            if inspect.isawaitable(result):
-                await result
-
+            awwait maybe_future(super().get(*args, **kwargs))
 
 
 def setup_handlers(web_app):