Allow to specify subprotocols in the websockets transport

Author: leszekhanusz

docs/transports/websockets.rst

@@ -8,7 +8,14 @@ The websockets transport supports both:
  - the `Apollo websockets transport protocol`_.
  - the `GraphQL-ws websockets transport protocol`_
 
-It will detect the backend supported protocol from the response http headers returned.
+It will propose both subprotocols to the backend and detect the supported protocol
+from the response http headers returned by the backend.
+
+.. note::
+    For some backends (graphql-ws without backwards compatibility), it may be necessary to specify
+    only one subprotocol to the backend. It can be done by using
+    :code:`subprotocols=[WebsocketsTransport.GRAPHQLWS_SUBPROTOCOL]`
+    or :code:`subprotocols=[WebsocketsTransport.APOLLO_SUBPROTOCOL]` in the transport arguments.
 
 This transport allows to do multiple queries, mutations and subscriptions on the same websocket connection.
 

gql/transport/websockets.py

@@ -3,7 +3,7 @@
 import logging
 from contextlib import suppress
 from ssl import SSLContext
-from typing import Any, Dict, Optional, Tuple, Union, cast
+from typing import Any, Dict, List, Optional, Tuple, Union, cast
 
 from graphql import DocumentNode, ExecutionResult, print_ast
 from websockets.datastructures import HeadersLike
@@ -46,6 +46,7 @@ def __init__(
         pong_timeout: Optional[Union[int, float]] = None,
         answer_pings: bool = True,
         connect_args: Dict[str, Any] = {},
+        subprotocols: Optional[List[Subprotocol]] = None,
     ) -> None:
         """Initialize the transport with the given parameters.
 
@@ -71,6 +72,9 @@ def __init__(
             (for the graphql-ws protocol).
             By default: True
         :param connect_args: Other parameters forwarded to websockets.connect
+        :param subprotocols: list of subprotocols sent to the
+            backend in the 'subprotocols' http header.
+            By default: both apollo and graphql-ws subprotocols.
         """
 
         super().__init__(
@@ -105,10 +109,13 @@ def __init__(
         """pong_received is an asyncio Event which will fire  each time
         a pong is received with the graphql-ws protocol"""
 
-        self.supported_subprotocols = [
-            self.APOLLO_SUBPROTOCOL,
-            self.GRAPHQLWS_SUBPROTOCOL,
-        ]
+        if subprotocols is None:
+            self.supported_subprotocols = [
+                self.APOLLO_SUBPROTOCOL,
+                self.GRAPHQLWS_SUBPROTOCOL,
+            ]
+        else:
+            self.supported_subprotocols = subprotocols
 
     async def _wait_ack(self) -> None:
         """Wait for the connection_ack message. Keep alive messages are ignored"""

tests/conftest.py

@@ -465,7 +465,9 @@ async def client_and_graphqlws_server(graphqlws_server):
     # Generate transport to connect to the server fixture
     path = "/graphql"
     url = f"ws://{graphqlws_server.hostname}:{graphqlws_server.port}{path}"
-    sample_transport = WebsocketsTransport(url=url)
+    sample_transport = WebsocketsTransport(
+        url=url, subprotocols=[WebsocketsTransport.GRAPHQLWS_SUBPROTOCOL],
+    )
 
     async with Client(transport=sample_transport) as session: