make routing less DHT specific

[Stebalien]

Motivation: According to the documentation/signature, it looks like GetValues
exists to return a bunch of different values from the ValueStore. However:

1. In practice, we use it to tell the DHT how many peers it should contact (not
   because we actually want multiple values).
2. It exposes non-valuestore related information (the peers from which we got
   the values).
3. It doesn't correct peers that have the wrong values (it doesn't validate
   anything).
4. Callers end up duplicating a lot of the GetValue code to select the best value.

This interface change removes GetValues and modifies GetValue to give us
everything we need. I've also left in a commented-out SearchValue method that
I'd like to eventually implement as a "progressive" GetValue (that keeps
returning better and better records).

[Stebalien]

I originally started working on this to try to make using pubsub as a ValueStore reasonable. Unfortunately, I couldn't quite get all of the abstractions in line. However, IMO, this change is still a step in the right direction.

[vyzo]

It exposes non-valuestore related information (the peers from which we got the values).

Agreed on the sentiment that this leaks as an abstraction, but on the same time it can also be useful for users of the DHT.
Is there a substitute?

[Stebalien]

Which information, the peers from which we got the values? At the moment, you can use the routing notification system.

[vyzo]

So coming back to the premise, are we sure we won't have any use case that is interested in multiple different values?

[Stebalien]

So coming back to the premise, are we sure we won't have any use case that is interested in multiple different values?

There probably are but the semantics will likely be a bit different:

1. The selector may look different (currently, we can always pick a single best value).
2. We'll probably want to return at most k values instead of requiring k values.
3. We'll probably want to use a channel to return them as we find them.

Basically, we may need a method with this name however, I'd hold off on that until we actually know what the semantics of that method will be.

[whyrusleeping]

any particular reason this isnt just:

func Expired(opts *Options) error {
// ....
}

[whyrusleeping]

This feels a little weird, and I do like the idea of being able to get multiple values out, but otherwise, this is probably a good step forward

[Stebalien]

This feels a little weird, and I do like the idea of being able to get multiple values out, but otherwise, this is probably a good step forward

That's the idea behind the commented out search method. Basically, we'll want something more powerful than "give me K (possibly identical) values from N peers".