Notice: This document is a work-in-progress for researchers and implementers.
This document is the beacon chain fork choice spec for Ethereum 2.0 Data Availability Sampling. The only change that we add from phase 0 is that we add a concept of "data dependencies";
a block is only eligible for consideration in the fork choice after a data availability test has been successfully completed for all dependencies.
The "root" of a shard block for data dependency purposes is considered to be a DataCommitment
object, which is a pair of a Kate commitment and a length.
def get_new_dependencies(state: BeaconState) -> Set[DataCommitment]:
return set(
# Already confirmed during this epoch
[c.commitment for c in state.current_epoch_pending_headers if c.confirmed] +
# Already confirmed during previous epoch
[c.commitment for c in state.previous_epoch_pending_headers if c.confirmed] +
# Confirmed in the epoch before the previous
[c for c in shard for shard in state.grandparent_epoch_confirmed_commitments if c != DataCommitment()]
)
def get_all_dependencies(store: Store, block: BeaconBlock) -> Set[DataCommitment]:
if compute_epoch_at_slot(block.slot) < SHARDING_FORK_EPOCH:
return set()
else:
latest = get_new_dependencies(store.block_states[hash_tree_root(block)])
older = get_all_dependencies(store, store.blocks[block.parent_root])
return latest.union(older)