Set subprotocols=None when there is no subprotocol proposed

jupyter_server_proxy/handlers.py

@@ -493,7 +493,7 @@ async def start_websocket_connection():
                 request=request,
                 on_message_callback=message_cb,
                 on_ping_callback=ping_cb,
-                subprotocols=self.subprotocols,
+                subprotocols=self.subprotocols if self.subprotocols else None,
                 resolver=resolver,
             )
             self._record_activity()

tests/resources/websocket.py

@@ -36,7 +36,6 @@ def __init__(self):
         handlers = [
             (r"/", MainHandler),
             (r"/echosocket", EchoWebSocket),
-            (r"/subprotocolsocket", SubprotocolWebSocket),
             (r"/headerssocket", HeadersWebSocket),
         ]
         settings = dict(
@@ -63,19 +62,6 @@ def on_message(self, message):
         self.write_message(json.dumps(dict(self.request.headers)))
 
 
-class SubprotocolWebSocket(tornado.websocket.WebSocketHandler):
-    def __init__(self, *args, **kwargs):
-        self._subprotocols = None
-        super().__init__(*args, **kwargs)
-
-    def select_subprotocol(self, subprotocols):
-        self._subprotocols = subprotocols
-        return None
-
-    def on_message(self, message):
-        self.write_message(json.dumps(self._subprotocols))
-
-
 def main():
     tornado.options.parse_command_line()
     app = Application()

tests/test_proxies.py

@@ -374,11 +374,13 @@ def test_server_proxy_websocket_headers(
 
 async def _websocket_subprotocols(a_server_port_and_token: Tuple[int, str]) -> None:
     PORT, TOKEN = a_server_port_and_token
-    url = f"ws://{LOCALHOST}:{PORT}/python-websocket/subprotocolsocket"
+    url = f"ws://{LOCALHOST}:{PORT}/python-websocket/headerssocket"
     conn = await websocket_connect(url, subprotocols=["protocol_1", "protocol_2"])
     await conn.write_message("Hello, world!")
     msg = await conn.read_message()
-    assert json.loads(msg) == ["protocol_1", "protocol_2"]
+    headers = json.loads(msg)
+    assert "Sec-Websocket-Protocol" in headers
+    assert headers["Sec-Websocket-Protocol"] == "protocol_1,protocol_2"
 
 
 def test_server_proxy_websocket_subprotocols(
@@ -387,6 +389,39 @@ def test_server_proxy_websocket_subprotocols(
     event_loop.run_until_complete(_websocket_subprotocols(a_server_port_and_token))
 
 
+async def _websocket_empty_subprotocols(a_server_port_and_token: Tuple[int, str]) -> None:
+    PORT, TOKEN = a_server_port_and_token
+    url = f"ws://{LOCALHOST}:{PORT}/python-websocket/headerssocket"
+    conn = await websocket_connect(url, subprotocols=[])
+    await conn.write_message("Hello, world!")
+    msg = await conn.read_message()
+    headers = json.loads(msg)
+    assert "Sec-Websocket-Protocol" in headers
+    assert headers["Sec-Websocket-Protocol"] == ""
+
+
+def test_server_proxy_websocket_empty_subprotocols(
+    event_loop, a_server_port_and_token: Tuple[int, str]
+):
+    event_loop.run_until_complete(_websocket_empty_subprotocols(a_server_port_and_token))
+
+
+async def _websocket_no_subprotocols(a_server_port_and_token: Tuple[int, str]) -> None:
+    PORT, TOKEN = a_server_port_and_token
+    url = f"ws://{LOCALHOST}:{PORT}/python-websocket/headerssocket"
+    conn = await websocket_connect(url)
+    await conn.write_message("Hello, world!")
+    msg = await conn.read_message()
+    headers = json.loads(msg)
+    assert "Sec-Websocket-Protocol" not in headers
+
+
+def test_server_proxy_websocket_no_subprotocols(
+    event_loop, a_server_port_and_token: Tuple[int, str]
+):
+    event_loop.run_until_complete(_websocket_no_subprotocols(a_server_port_and_token))
+
+
 @pytest.mark.parametrize(
     "proxy_path, status",
     [