Implementation of Batch fetch via feature toggle.

[to11mtm]

(Will edit title if this is acceptable to see through to completion and I switch from draft)

Proposal for resolving #95

Basically, via options toggle, we can let users opt-in to batch fetch requests. This can be especially helpful for use cases where lots of secrets are involved and refreshes are enabled to minimize API calls and improve overall load times.

I will note some of this implementation is naive/paranoid, AWS Batch fetches can sometimes have vexing behavior so I coded this POC defensively based on experiences with other services batch calls.

There's also opportunity for some code consolidation, but in my head this makes for easier diff.

[ransagy]

By default, SecretFilter is set to always return true, So assuming it is meant to be a positive filter, The ! operator here prevents those secrets from passing. I.e. on a default setup, this drops all secrets and return an empty list.

[to11mtm]

I derped hard on this one, my bad. Fixing.

[ransagy]

Don't we all. No worries :]

[Kralizek]

I think later versions of .net include a chunk method but not sure if it's compatible with the targeted frameworks.

[ransagy]

Yeah, NET 6.0 and up - https://learn.microsoft.com/en-us/dotnet/api/system.linq.enumerable.chunk?view=net-9.0

[to11mtm]

Per this not being part of netstandard2.0 decided to leave as-is. Doubly so since currently lib is only published that way for now.

In future if desired, folks can do a #if NET6_0_OR_GREATER dance for the more optimized call in separate PR.

Similar for multitargeting; I -thought- about it for a moment but decided better to keep changes small. (That said I may do it in separate PR if someone doesn't beat me to it)

[justinstenning]

Ignoring the multi-targeting changes required, here it is with #if NET6_0_OR_GREATER:

        private static IEnumerable<SecretListEntry[]> ChunkList(IReadOnlyList<SecretListEntry> source,
            Func<SecretListEntry, bool> optionsSecretFilter, int chunkSize)
        {
#if NET6_0_OR_GREATER
            return source.Where(optionsSecretFilter).Chunk(20);
#else
            // This is for sake of cleanliness vs getting 'fancy' with things.
            // We can always optimize later.
            return source
                .Where(optionsSecretFilter)
                .Select(static (item, index) => (item, index))
                .GroupBy(x => x.index / chunkSize)
                .Select(static group => group.Select(static x => x.item).ToArray())
                .ToList();
#endif
        }

[to11mtm]

Addressed feedback, also while cleaning up I observed that the way I was looping on nexttoken wasn't checking for errors in all cases. I've switched it to a do pattern similar to FetchAllSecretsAsync for uniformity (and TBH it looks cleaner now.)

[Kralizek]

Thanks for the nice work. I'll check everything sometimes this week. I hope this is not blocking you.

[to11mtm]

Thanks for the nice work. I'll check everything sometimes this week. I hope this is not blocking you.

Appreciate the consideration.

This is not blocking me so I'm not in a rush on this (but can't speak for @ransagy ).

[ransagy]

I'm going to use a NuGet package made from @to11mtm 's branch in our local private feed for now, until this lands in a release. So not technically blocked either, but would be nice to see it coming officially.