include websocket protocol in response

Chrome doesn't accept websocket connections if protocol is requested but not provided

jupyter_server/base/websocket.py

@@ -1,4 +1,7 @@
 """Base websocket classes."""
+
+from __future__ import annotations
+
 import re
 import warnings
 from typing import Optional, no_type_check
@@ -164,3 +167,10 @@ def send_ping(self):
     def on_pong(self, data):
         """Handle a pong message."""
         self.last_pong = ioloop.IOLoop.current().time()
+
+    def select_subprotocol(self, subprotocols: list[str]) -> str | None:
+        # default subprotocol
+        # some clients (Chrome)
+        # require selected subprotocol to match one of the requested subprotocols
+        # otherwise connection is rejected
+        return "v1.token.websocket.jupyter.org"

jupyter_server/services/events/handlers.py

@@ -14,13 +14,15 @@
 
 from jupyter_server.auth.decorator import authorized, ws_authenticated
 from jupyter_server.base.handlers import JupyterHandler
+from jupyter_server.base.websocket import WebSocketMixin
 
 from ...base.handlers import APIHandler
 
 AUTH_RESOURCE = "events"
 
 
 class SubscribeWebsocket(
+    WebSocketMixin,
     JupyterHandler,
     websocket.WebSocketHandler,
 ):

jupyter_server/services/kernels/websocket.py

@@ -90,6 +90,12 @@ def select_subprotocol(self, subprotocols):
             preferred_protocol = "v1.kernel.websocket.jupyter.org"
         elif preferred_protocol == "":
             preferred_protocol = None
-        selected_subprotocol = preferred_protocol if preferred_protocol in subprotocols else None
+
+        # super() subprotocol enables token authentication via subprotocol
+        selected_subprotocol = (
+            preferred_protocol
+            if preferred_protocol in subprotocols
+            else super().select_subprotocol(subprotocols)
+        )
         # None is the default, "legacy" protocol
         return selected_subprotocol

tests/base/test_websocket.py

@@ -149,10 +149,11 @@ async def test_websocket_token_subprotocol_auth(jp_serverapp, jp_ws_fetch):
         "ws",
         headers={
             "Authorization": "",
-            "Sec-WebSocket-Protocol": "v1.kernel.websocket.jupyter.org, v1.token.websocket.jupyter.org."
+            "Sec-WebSocket-Protocol": "v1.kernel.websocket.jupyter.org, v1.token.websocket.jupyter.org, v1.token.websocket.jupyter.org."
             + token,
         },
     )
+    assert ws.protocol.selected_subprotocol == "v1.token.websocket.jupyter.org"
     ws.close()