Re: [Sidrops] trying to limit RP processing variability

[Robert Kisteleki <[e-mail]>]

Hi,

> Missing: an object named in a Manifest, but not available for download
> from a PP, is termed *missing*. An RP has no obvious way to acquire
> missing objects, but operators SHOULD be warned about which objects are
> missing.

IMO an "RP has no obvious way to acquire missing objects" is not
entirely true.

If, at the previous run, the RP fetched the relevant (now missing)
object, then I see no reason to not use it again. Think of the previous
run as an object a cache if you will: if you're looking for an object
mentioned in the manifest, and you have it already (hash / name / etc.
matches) then you can reuse it.

Of course it can be useful to check if it still exists in the PP, but it
seems to me the only benefit is to detect that it is missing from there
and perhaps warn the PP operator. Otherwise the RP has a hard time
arguing "no idea what this is since it's not there!".

For bonus points: an implementation that fetched a PP's manifest,
detected that it's exactly the same as before, and therefore reused the
validation outcome from the previous run would not even have to fetch
*any* other objects from the same PP. The downside is that this process
will not be able to point out the omission. The upside is saves a lot of
resources (bandwidth, CPU and all). A further upside is that as a
side-effect this protects against a malicious attacker (selectively)
hiding objects.

Where this comes back to the current discussion is: would this behaviour
be mandated, recommended, or considered a big no-no?

Robert