raise on misdirected websocket handshake

responding "HTTP/1.1 101 Switching Protocols" to a HEAD request is unlikely intended.

Author: pajod

aiohttp/web_ws.py

@@ -36,7 +36,7 @@
 from .log import ws_logger
 from .streams import EofStream
 from .typedefs import JSONDecoder, JSONEncoder
-from .web_exceptions import HTTPBadRequest, HTTPException
+from .web_exceptions import HTTPBadRequest, HTTPException, HTTPMethodNotAllowed
 from .web_request import BaseRequest
 from .web_response import StreamResponse
 
@@ -226,6 +226,9 @@ def _handshake(
         self, request: BaseRequest
     ) -> Tuple["CIMultiDict[str]", Optional[str], int, bool]:
         headers = request.headers
+        if request.method != hdrs.METH_GET:
+            raise HTTPMethodNotAllowed(request.method, {hdrs.METH_GET})
+
         if "websocket" != headers.get(hdrs.UPGRADE, "").lower().strip():
             raise HTTPBadRequest(
                 text=(