proxy: Provide clear reason for websocket connection error

Also, the error code seems to have changed from 503 -> 599
Not too sure why, but modifying tests appropriately

Author: AbdealiLoKo

configurable_http_proxy/handlers.py

@@ -400,10 +400,12 @@ def write(msg):
                 self.proxy.timeout, websocket_connect(req, on_message_callback=write)
             )
         except HTTPClientError as err:
-            self.set_status(err.code)
+            self.closed = True
+            self.set_status(err.code, reason=err.message)
             self.write(err.message)
             self.finish()
         except Exception as err:
+            self.closed = True
             await self.handle_proxy_error(503, err)
             raise
 

configurable_http_proxy_test/test_proxy.py

@@ -325,7 +325,7 @@ def test_last_activity_not_updated_on_errors_websocket(self):
         self.proxy._routes.update("/missing", {"last_activity": now})
 
         # fail a websocket activity
-        with pytest.raises(HTTPClientError, match="HTTP 503: Service Unavailable"):
+        with pytest.raises(HTTPClientError, match="HTTP 599: Timeout while connecting"):
             yield websocket_connect(self.get_url("/missing/ws").replace("http:", "ws:"))
 
         # expect an error, since there is no websocket handler - check last_activity was not updated