diff --git a/specs/core/0_fork-choice.md b/specs/core/0_fork-choice.md index d62b04169..3cdbcbc5a 100644 --- a/specs/core/0_fork-choice.md +++ b/specs/core/0_fork-choice.md @@ -155,22 +155,22 @@ def filter_block_tree(store: Store, block_root: Root, blocks: Dict[Root, BeaconB return False # If leaf block, check finalized/justified checkpoints as matching latest. - # If matching, add to viable block-tree and signal viability to parent. head_state = store.block_states[block_root] - # Handle base case where justified hasn't updated yet - if head_state.current_justified_checkpoint.epoch == GENESIS_EPOCH: - is_viable_branch = True - else: - is_viable_branch = ( - head_state.finalized_checkpoint == store.finalized_checkpoint - and head_state.current_justified_checkpoint == store.justified_checkpoint - ) - if is_viable_branch: + correct_justified = ( + store.justified_checkpoint.epoch == GENESIS_EPOCH + or head_state.current_justified_checkpoint == store.justified_checkpoint + ) + correct_finalized = ( + store.finalized_checkpoint.epoch == GENESIS_EPOCH + or head_state.finalized_checkpoint == store.finalized_checkpoint + ) + # If expected finalized/justified, add to viable block-tree and signal viability to parent. + if correct_justified and correct_finalized: blocks[block_root] = block return True - # Otherwise, not viable + # Otherwise, branch not viable return False ``` @@ -178,9 +178,13 @@ def filter_block_tree(store: Store, block_root: Root, blocks: Dict[Root, BeaconB ```python def get_filtered_block_tree(store: Store) -> Dict[Root, BeaconBlock]: - head = store.justified_checkpoint.root + """ + Retrieve a filtered block true from ``store``, only returning branches + whose leaf state's justified/finalized info agrees with that in ``store``. + """ + base = store.justified_checkpoint.root blocks: Dict[Root, BeaconBlock] = {} - filter_block_tree(store, head, blocks) + filter_block_tree(store, base, blocks) return blocks ``` @@ -188,10 +192,8 @@ def get_filtered_block_tree(store: Store) -> Dict[Root, BeaconBlock]: ```python def get_head(store: Store) -> Root: - # Get filtered block tree that includes viable branches + # Get filtered block tree that only includes viable branches blocks = get_filtered_block_tree(store) - print(len(blocks)) - print(len(store.blocks)) # Execute the LMD-GHOST fork choice head = store.justified_checkpoint.root justified_slot = compute_start_slot_at_epoch(store.justified_checkpoint.epoch) @@ -224,8 +226,8 @@ def should_update_justified_checkpoint(store: Store, new_justified_checkpoint: C if new_justified_block.slot <= compute_start_slot_at_epoch(store.justified_checkpoint.epoch): return False if not ( - get_ancestor(store, new_justified_checkpoint.root, store.blocks[store.justified_checkpoint.root].slot) == - store.justified_checkpoint.root + get_ancestor(store, new_justified_checkpoint.root, store.blocks[store.justified_checkpoint.root].slot) + == store.justified_checkpoint.root ): return False diff --git a/test_libs/pyspec/eth2spec/test/fork_choice/test_get_head.py b/test_libs/pyspec/eth2spec/test/fork_choice/test_get_head.py index ff5a822fb..f0098bb98 100644 --- a/test_libs/pyspec/eth2spec/test/fork_choice/test_get_head.py +++ b/test_libs/pyspec/eth2spec/test/fork_choice/test_get_head.py @@ -1,7 +1,12 @@ from eth2spec.test.context import with_all_phases, spec_state_test from eth2spec.test.helpers.attestations import get_valid_attestation from eth2spec.test.helpers.block import build_empty_block_for_next_slot -from eth2spec.test.helpers.state import state_transition_and_sign_block +from eth2spec.test.helpers.state import ( + next_epoch, + next_epoch_with_attestations, + state_transition_and_sign_block, +) +from eth2spec.utils.ssz.ssz_impl import signing_root def add_block_to_store(spec, store, block): @@ -112,3 +117,76 @@ def test_shorter_chain_but_heavier_weight(spec, state): add_attestation_to_store(spec, store, short_attestation) assert spec.get_head(store) == spec.signing_root(short_block) + + +@with_all_phases +@spec_state_test +def test_filtered_block_tree(spec, state): + genesis_state = state.copy() + + # transition state past initial couple of epochs + next_epoch(spec, state) + next_epoch(spec, state) + + # Initialization + store = spec.get_genesis_store(genesis_state) + genesis_block = spec.BeaconBlock(state_root=genesis_state.hash_tree_root()) + assert spec.get_head(store) == spec.signing_root(genesis_block) + + # fill in attestations for entire epoch, justifying the recent epoch + prev_state, blocks, state = next_epoch_with_attestations(spec, state, True, False) + attestations = [attestation for block in blocks for attestation in block.body.attestations] + assert state.current_justified_checkpoint.epoch > prev_state.current_justified_checkpoint.epoch + + # tick time forward and add blocks and attestations to store + current_time = state.slot * spec.SECONDS_PER_SLOT + store.genesis_time + spec.on_tick(store, current_time) + for block in blocks: + spec.on_block(store, block) + for attestation in attestations: + spec.on_attestation(store, attestation) + + assert store.justified_checkpoint == state.current_justified_checkpoint + + # the last block in the branch should be the head + expected_head_root = signing_root(blocks[-1]) + assert spec.get_head(store) == expected_head_root + + # + # create branch containing the justified block but not containing enough on + # chain votes to justify that block + # + + # build a chain without attestations off of previous justified block + non_viable_state = store.block_states[store.justified_checkpoint.root].copy() + + # ensure that next wave of votes are for future epoch + next_epoch(spec, non_viable_state) + next_epoch(spec, non_viable_state) + next_epoch(spec, non_viable_state) + assert spec.get_current_epoch(non_viable_state) > store.justified_checkpoint.epoch + + # create rogue block that will be attested to in this non-viable branch + rogue_block = build_empty_block_for_next_slot(spec, non_viable_state, True) + state_transition_and_sign_block(spec, non_viable_state, rogue_block) + + # create an epoch's worth of attestations for the rogue block + next_epoch(spec, non_viable_state) + attestations = [] + for i in range(spec.SLOTS_PER_EPOCH): + slot = rogue_block.slot + i + for index in range(spec.get_committee_count_at_slot(non_viable_state, slot)): + attestation = get_valid_attestation(spec, non_viable_state, rogue_block.slot + i, index) + attestations.append(attestation) + + # tick time forward to be able to include up to the latest attestation + current_time = (attestations[-1].data.slot + 1) * spec.SECONDS_PER_SLOT + store.genesis_time + spec.on_tick(store, current_time) + + # include rogue block and associated attestations in the store + spec.on_block(store, rogue_block) + for attestation in attestations: + spec.on_attestation(store, attestation) + + # ensure that get_head still returns the head from the previous branch + assert spec.get_head(store) == expected_head_root