acl: add ACL hostcalls

[dgryski]

No description provided.

[dgryski]

Note we can't merge this or run any tests until we have a viceroy release including fastly/Viceroy#438

[awilliams-fastly]

In the context of Handle.Lookup, I wonder if something like ErrNoMatch would be more easily understood?

[dgryski]

So replace ErrNoContent with a new error ErrNoMatch which improves the semenatic match but pulls it farther away from the underlying response code (and Rust SDK I guess).

[awilliams-fastly]

Yes, agree that it pulls it further from the underlying response code. The Rust SDK uses Option<Response> with None when there's no match.

I think ErrNoContent is fine, but wanted to ask in case we could think of anything better.

[dgryski]

The other way to represent "not found" would be to return a pointer to the entry, or a nil pointer (and no error) if it's not found. That puts the onus on the user, but they're already checking for error (and in fact maybe this is "nicer" since it doesn't conflate an error and a success-not-found case.)

[awilliams-fastly]

Yes, I think using a pointer/nil could work and agree that it's not conflating errors with not-found cases. One final alternative would be to return something like:
(r Result, ok bool, err error)
where ok is false in the not-found case.

[dgryski]

Rethinking this; I think I'm going to stick with returning an error. For example, Go's database/sql package returns ErrNoRows for query returning no rows. This is the same. And I want to stick with the error name in the wit file for consistency (and also in case things change in the future we won't end up in a situation where our SDK code drifts more from the underlying host calls.)