ouroboros-consensus
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IntersectMBO
Implement getBlockHash in LedgerPeersConsensusInterface
I'd appreciate if someone could lend me a hand with implementing a small facility for the upcoming node 10.7 release.
We want to verify that a particular block hash matches the one recorded in the big ledger peer snapshot file when syncing in GenesisMode. The function has the signature forall r. SlotNo -> (forall a. STM m (Block SlotNo (Hash Blake2b_256 a)) -> r) -> r. The first parameter is the slot number to be examined and the second is a continuation which accepts an STM action, which is expected to block until the slot becomes part of the immutable chain, and which provides the corresponding Block value for the given input slot when it is available. A dummy implementation is defined in Ouroboros.Consensus.Node on mw/integrate-o-n-0.23 in commit wip.
@crocodile-dentist the commit 7cde5cc82586444c5ad98b7be5eb16c3b32217b4 referenced in the s-r-p on ouroboros-network does not exist. Which branch should I track? Would it be OK to try integrating with the current main, or is there a dedicated release branch?
I've updated the srp in the branch. The wip commit just shows the location where we need this, but conceptually this work sits on top of the network branch mw/ledgerpeersnapshot-hash which is under review. I gave the branch mw/integrate-o-n-0.23 instead because at least the main consensus libraries build with it as there are other unrelated breaking changes which we're still integrating.
@crocodile-dentist I have a couple of questions that came into my head when I started working on this:
Questions 1
is is possible that there's no block at the requested slot? What would you like to get at as result if that's the case? Some sort of Left Error?
As I understand, the precondition is that the requested slot has a block, since the slot comes from the big ledger peer snapshot?
Question 2
Would it be OK to return a Point instead of a (Block SlotNo (Hash Blake2b_256 a)? I think it alights a little better with the API that is available in Consensus.
is is possible that there's no block at the requested slot? What would you like to get at as result if that's the case? Some sort of Left Error?
If we change the signature to return a boolean, then simply False will be sufficient for me.
As I understand, the precondition is that the requested slot has a block, since the slot comes from the big ledger peer snapshot?
True.
@crocodile-dentist I've pushed https://github.com/IntersectMBO/ouroboros-consensus/commit/b5f25fd95 to the mw/integrate-o-n-0.23 branch.
I ended up needing to change the signature of getBlockHash again, but now it is much closer to your original request:
getBlockHash :: forall r. SlotNo -> (forall a. STM m (Point a) -> r) -> r
i.e. given a slot, the implementation will wait for the immutable tip to appear at that slot, and return the Point. I unfortunately cannot give you Block SlotNo (Hash Blake2b_256 a) as the immutable DB only allows me to extract the more abstract Point. Is this sufficient?