private void ensureInitiated() throws Exception {
        if (!connectionInitiated) {
            // ConnectionAck not sent yet. Must be closed with 4401 Unauthorized.
            throw new GraphqlWebSocketCloseException(4401, "Unauthorized");
        }
    }
Receives an event and returns a response if one should be sent.
graphql/src/main/java/com/linecorp/armeria/server/graphql/GraphqlWSSubProtocol.java