Passing context between chained Uni

[gnieser]

Hello,

I'm looking for a way to implicitly propagate a io.smallrye.mutiny.Context when chaining several Uni?

So far, I only succeed when I explicitly add the Context as a parameter to all the mappers, suppliers, etc.

I've read that the context is set upon subscription, otherwise the context will be empty. I can testify it is :-)

Shall I do so from the mappers called by chain method?
Could someone please hint me toward a working solution?

Here is some pseudo-code to try to illustrate what I would like to achieve.
(I'm using Quarkus 2.16.6 and migrating progressively from imperative to reactive)

public Response post(MyRequest request) {
    return Uni.createFrom().context(ctx -> {
        ctx.put("name", securityIdentity.getPrincipal().getName());
        ctx.put("request", request);
        ...

        return Uni.createFrom().item(request)
                .invoke(() -> log.info(ctx.get("name"))) // Obviously, it works
                ...
                .chain(a ->  doStep1(a)) // Hoping for the context to be passed implicitly
                ...
                .chain(b -> Uni.createFrom().item(b)
                        ...
                        .chain(c -> doStepX(c)) // Also here
                        ...
                        .eventually(() -> doNotify())) // Here too would be super
                ...
                .map(z -> {
                    return Response.entity(z).build();
                })
                .onFailure(WebApplicationException.class).recoverWithItem(w -> ((WebApplicationException) w).getResponse());
    }).await().indefinitely();
}

private Uni<SomeEntity> doStep1(A a) {
    return Uni.createFrom().context(ctx-> { // <-- Here the context is empty!
        return doCheck(a)
                .chain(m -> Uni.createFrom().item(() -> QuarkusTransaction.requiringNew().call(() -> {
                    SomeEntity entity = mapper.toEntity(m);
                    entity.setName(ctx.get("name"));
                    entity.persist();
                    return entity;
                })));
    });
}
... // And so on for other steps

Many thanks

[cescoffier]

In Quarkus, depending on what you do in the "chain", it should work OOTB using either a RequestScope bean (used as container) or VertxLocals

[jponge]

Contexts are not created at the start of the chain but by the entity that performs the initial subscription.

1st snippet: you need to pass the context at subscription time using .awaitUsing(context).

2nd snippet: you won't have a context, I don't recall Quarkus providing one for reactive methods.

[gnieser]

Thanks for you answers!

In the chain, I'm doing various operations (Panache, SSH, File,...), and I have to make sure I do not hold some database resources since the file operations takes some time to complete. So I have to take care of detached and merged JPA entities.

With awaitUsing(context) in the first snippet propagates it, even in the nested Uni of the second snippet which exactly the kind of "magic" I was looking for. Awesome :)