Opening a websocket connection to WebLogic 12.2.1.4.0 fails because the server includes a "Transfer-encoding: chunked" header in the 101 response. This is invalid according to RFC 7230: "A server MUST NOT send a Transfer-Encoding header field in any response with a status code of 1xx (Informational) or 204 (No Content).". However there seems no way to prevent the header being generated. Other clients (such as node.js ws module) ignore the header.