static RpcPreprocessor of(SessionProtocol sessionProtocol, EndpointGroup endpointGroup) {
        requireNonNull(sessionProtocol, "sessionProtocol");
        requireNonNull(endpointGroup, "endpointGroup");
        return (delegate, ctx, req) -> {
            ctx.setSessionProtocol(sessionProtocol);
            ctx.setEndpointGroup(endpointGroup);
            return delegate.execute(ctx, req);
        };
    }
A simple {@link RpcPreprocessor} which overwrites the {@link SessionProtocol},
{@link EndpointGroup}, and {@link EventLoop} for a request.
core/src/main/java/com/linecorp/armeria/client/RpcPreprocessor.java