Websocket subprotocol (#1887)

* Added fix to include subprotocols from scope

* Added unit test to validate fix

* Changes by black

* Made changes to WebsocketConnection protocol

* Linter changes

* Added unit tests

* Fixing bugs in linting due to isort import checks

* Reverting compat import changes

* Fixing linter errors in compat.py

Co-authored-by: Adam Hopkins <admhpkns@gmail.com>

sanic/asgi.py

@@ -98,7 +98,9 @@ class MockTransport:
     def create_websocket_connection(
         self, send: ASGISend, receive: ASGIReceive
     ) -> WebSocketConnection:
-        self._websocket_connection = WebSocketConnection(send, receive)
+        self._websocket_connection = WebSocketConnection(
+            send, receive, self.scope.get("subprotocols", [])
+        )
         return self._websocket_connection
 
     def add_task(self) -> None:

sanic/websocket.py

@@ -3,6 +3,7 @@ from typing import (
     Awaitable,
     Callable,
     Dict,
+    List,
     MutableMapping,
     Optional,
     Union,
@@ -137,9 +138,11 @@ class WebSocketConnection:
         self,
         send: Callable[[ASIMessage], Awaitable[None]],
         receive: Callable[[], Awaitable[ASIMessage]],
+        subprotocols: Optional[List[str]] = None,
     ) -> None:
         self._send = send
         self._receive = receive
+        self.subprotocols = subprotocols or []
 
     async def send(self, data: Union[str, bytes], *args, **kwargs) -> None:
         message: Dict[str, Union[str, bytes]] = {"type": "websocket.send"}
@@ -164,7 +167,14 @@ class WebSocketConnection:
     receive = recv
 
     async def accept(self) -> None:
-        await self._send({"type": "websocket.accept", "subprotocol": ""})
+        await self._send(
+            {
+                "type": "websocket.accept",
+                "subprotocol": ",".join(
+                    [subprotocol for subprotocol in self.subprotocols]
+                ),
+            }
+        )
 
     async def close(self) -> None:
         pass