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Allow `LightClientUpdate` with genesis finality 

When `state.finalized_checkpoint` references the genesis slot, it points
to an empty `root`, instead of the actual genesis block hash. This patch
updates the `LightClientUpdate` logic to allow including finality proofs
for genesis `finalized_checkpoint.root`, better supporting non-mainnet.
When including such a finality proof, the proof is for the empty `root`,
but `finalized_header` is kept zeroed out to signify this edge case.
This commit is contained in:
Etan Kissling 2022-05-09 14:37:54 +02:00
parent a40a64440c
commit c10daf1709
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1 changed files with 8 additions and 3 deletions
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11
specs/altair/sync-protocol.md
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@ -100,7 +100,7 @@ class LightClientStore(object):
```python
def is_finality_update(update: LightClientUpdate) -> bool:
return update.finalized_header != BeaconBlockHeader()
return update.finality_branch != [Bytes32() for _ in range(floorlog2(FINALIZED_ROOT_INDEX))]
```
### `get_subtree_index`
@ -173,10 +173,15 @@ def validate_light_client_update(store: LightClientStore,
# Verify that the `finalized_header`, if present, actually is the finalized header saved in the
# state of the `attested_header`
if not is_finality_update(update):
assert update.finality_branch == [Bytes32() for _ in range(floorlog2(FINALIZED_ROOT_INDEX))]
assert update.finalized_header == BeaconBlockHeader()
else:
if update.finalized_header.slot != GENESIS_SLOT:
finalized_root = hash_tree_root(update.finalized_header)
else:
finalized_root = Bytes32()
assert update.finalized_header == BeaconBlockHeader()
assert is_valid_merkle_branch(
leaf=hash_tree_root(update.finalized_header),
leaf=finalized_root,
branch=update.finality_branch,
depth=floorlog2(FINALIZED_ROOT_INDEX),
index=get_subtree_index(FINALIZED_ROOT_INDEX),