4.3 KiB
4.3 KiB
Capella -- Fork Choice
Notice: This document is a work-in-progress for researchers and implementers.
Table of contents
Introduction
This is the modification of the fork choice according to the Capella upgrade.
Unless stated explicitly, all prior functionality from Bellatrix is inherited.
Custom types
Protocols
ExecutionEngine
Note: The notify_forkchoice_updated function is modified in the ExecutionEngine protocol at the Capella upgrade.
notify_forkchoice_updated
The only change made is to the PayloadAttributes container through the addition of withdrawals.
Otherwise, notify_forkchoice_updated inherits all prior functionality.
def notify_forkchoice_updated(self: ExecutionEngine,
head_block_hash: Hash32,
safe_block_hash: Hash32,
finalized_block_hash: Hash32,
payload_attributes: Optional[PayloadAttributes]) -> Optional[PayloadId]:
...
Helpers
Extended PayloadAttributes
PayloadAttributes is extended with the withdrawals field.
@dataclass
class PayloadAttributes(object):
timestamp: uint64
prev_randao: Bytes32
suggested_fee_recipient: ExecutionAddress
withdrawals: Sequence[Withdrawal] # [New in Capella]
Updated fork-choice handlers
on_block
Note: The only modification is the deletion of the verification of merge transition block conditions.
def on_block(store: Store, signed_block: SignedBeaconBlock) -> None:
"""
Run ``on_block`` upon receiving a new block.
"""
block = signed_block.message
# Parent block must be known
assert block.parent_root in store.block_states
# Make a copy of the state to avoid mutability issues
pre_state = copy(store.block_states[block.parent_root])
# Blocks cannot be in the future. If they are, their consideration must be delayed until they are in the past.
assert get_current_slot(store) >= block.slot
# Check that block is later than the finalized epoch slot (optimization to reduce calls to get_ancestor)
finalized_slot = compute_start_slot_at_epoch(store.finalized_checkpoint.epoch)
assert block.slot > finalized_slot
# Check block is a descendant of the finalized block at the checkpoint finalized slot
finalized_checkpoint_block = get_checkpoint_block(
store,
block.parent_root,
store.finalized_checkpoint.epoch,
)
assert store.finalized_checkpoint.root == finalized_checkpoint_block
# Check the block is valid and compute the post-state
state = pre_state.copy()
block_root = hash_tree_root(block)
state_transition(state, signed_block, True)
# Add new block to the store
store.blocks[block_root] = block
# Add new state for this block to the store
store.block_states[block_root] = state
# Add block timeliness to the store
time_into_slot = (store.time - store.genesis_time) % SECONDS_PER_SLOT
is_before_attesting_interval = time_into_slot < SECONDS_PER_SLOT // INTERVALS_PER_SLOT
is_timely = get_current_slot(store) == block.slot and is_before_attesting_interval
store.block_timeliness[hash_tree_root(block)] = is_timely
# Add proposer score boost if the block is timely and not conflicting with an existing block
is_first_block = store.proposer_boost_root == Root()
if is_timely and is_first_block:
store.proposer_boost_root = hash_tree_root(block)
# Update checkpoints in store if necessary
update_checkpoints(store, state.current_justified_checkpoint, state.finalized_checkpoint)
# Eagerly compute unrealized justification and finality.
compute_pulled_up_tip(store, block_root)