static ClientRequestContext current() {
        final RequestContext ctx = RequestContext.current();
        checkState(ctx instanceof ClientRequestContext,
                   "The current context is not a client-side context: %s", ctx);
        return (ClientRequestContext) ctx;
    }
Returns the client-side context of the {@link Request} that is being handled in the current thread.

@throws IllegalStateException if the context is unavailable in the current thread or
                              the current context is not a {@link ClientRequestContext}.
core/src/main/java/com/linecorp/armeria/client/ClientRequestContext.java