Send a 400 if data is received before the websocket is accepted

This is necessary as the data is not known to be either websocket or
http data as the server must accept or reject the connection and hence
it is a bad request.

In practice this is rare as the upgrade request is a GET request which
rarely has body data and most websocket clients wait for acceptance.

src/hypercorn/protocol/ws_stream.py

@@ -56,6 +56,7 @@ class FrameTooLargeError(Exception):
 
 class Handshake:
     def __init__(self, headers: List[Tuple[bytes, bytes]], http_version: str) -> None:
+        self.accepted = False
         self.http_version = http_version
         self.connection_tokens: Optional[List[str]] = None
         self.extensions: Optional[List[str]] = None
@@ -129,6 +130,7 @@ def accept(
 
             headers.append((name, value))
 
+        self.accepted = True
         return status_code, headers, Connection(ConnectionType.SERVER, extensions)
 
 
@@ -232,6 +234,9 @@ async def handle(self, event: Event) -> None:
                     self.app, self.config, self.scope, self.app_send
                 )
                 await self.app_put({"type": "websocket.connect"})
+        elif isinstance(event, (Body, Data)) and not self.handshake.accepted:
+            await self._send_error_response(400)
+            self.closed = True
         elif isinstance(event, (Body, Data)):
             self.connection.receive_data(event.data)
             await self._handle_events()

tests/protocol/test_ws_stream.py

@@ -203,6 +203,35 @@ async def test_handle_request(stream: WSStream) -> None:
     }
 
 
+@pytest.mark.asyncio
+async def test_handle_data_before_acceptance(stream: WSStream) -> None:
+    await stream.handle(
+        Request(
+            stream_id=1,
+            http_version="2",
+            headers=[(b"sec-websocket-version", b"13")],
+            raw_path=b"/?a=b",
+            method="GET",
+        )
+    )
+    await stream.handle(
+        Data(
+            stream_id=1,
+            data=b"X",
+        )
+    )
+    assert stream.send.call_args_list == [  # type: ignore
+        call(
+            Response(
+                stream_id=1,
+                headers=[(b"content-length", b"0"), (b"connection", b"close")],
+                status_code=400,
+            )
+        ),
+        call(EndBody(stream_id=1)),
+    ]
+
+
 @pytest.mark.asyncio
 async def test_handle_connection(stream: WSStream) -> None:
     await stream.handle(