@Override
    public String toString() {
        return MoreObjects.toStringHelper(this)
                          .add("ctx", ctx)
                          .add("responseHeaders", responseHeaders)
                          .add("subprotocol", subprotocol)
                          .add("inbound", inbound)
                          .add("outboundFuture", outboundFuture)
                          .add("encoder", encoder)
                          .toString();
    }
Sets the {@link WebSocket} that is used to send WebSocket frames to the server.

@throws IllegalStateException if this method or {@link #outbound()} has been called already.
core/src/main/java/com/linecorp/armeria/client/websocket/WebSocketSession.java