Mismatch between Finalized Block And Epoch

[nisdas]

🐞 Bug Report

Description

Currently there is a mismatch between finalized epochs and their related blocks. The finalized
epoch does not exactly match the one provided by the slot in the block.

Has this worked before in a previous version?

Before #5811

🔬 Minimal Reproduction

Run the node and look at the handshake errors from it from other peers.

🔥 Error

[2020-05-12 20:19:13]  WARN sync: Failed to handle p2p RPC error=invalid epoch peer=16Uiu2HAmDstiv2UPX3pRgnTWuVgfoDZvkaUp7jbfoVi43nGsPt6P topic=/eth2/beacon_chain/req/status/1/ssz_snappy

What version of Prysm are you running? (Which release)

baf9ec6

[terencechain]

This worries me. I wonder how it could happen

[nisdas]

Yeah it is off in a few places,
Ex:

	if helpers.SlotToEpoch(blk.Block.Slot) != msg.FinalizedEpoch {
		return errInvalidEpoch
	}

is there anything wrong with doing this ? @terencechain . I feel like I might be missing something, I was looking at our code for indexing finalized blocks in the db, and it seems like there are quite a few gotchas on determining which block is finalized and for what epoch it is finalized.

[terencechain]

@nisdas that won't work if there's skip slot. You have to account for skip slot scenario similar to this:

fBlkSlot := helpers.SlotToEpoch(blk.Block.Slot)
fEpochStartSlot := helpers.StartSlot(msg.FinalizedEpoch)
if fEpochStartSlot > fBlkSlot {
  filter := filters.NewFilter().SetStartSlot(fBlkSlot).SetEndSlot(fEpochStartSlot)
  blks, err := s.beaconDB.Blocks(ctx, filter)
  if len(blks) != empty {
     // Should be empty if skipped.
     return errInvalidEpoch
  }
}
...

Probably best to write a test for this

[rauljordan]

Is this still an issue @terencechain and @nisdas ?

[rauljordan]

Bump @terencechain @nisdas have we observed this since?

[nisdas]

Still an issue @rauljordan , we still need to verify it.

[protolambda]

This is actually quite important, can someone take a look at this please?

[nisdas]

@protolambda been on my todo list for too long, will take a look at it today. Thanks for the reminder.