def is_aggregator(
state: BeaconState,
slot: Slot,
index: CommitteeIndex,
signature: BLSSignature,
config: Eth2Config,
) -> bool:
"""
Check if the validator is one of the aggregators of the given ``slot``.
.. note::
- Probabilistically, with enought validators, the aggregator count should
approach ``TARGET_AGGREGATORS_PER_COMMITTEE``.
- With ``len(committee)`` is 128 and ``TARGET_AGGREGATORS_PER_COMMITTEE`` is 16,
the expected length of selected validators is 16.
- It's possible that this algorithm selects *no one* as the aggregator, but with the
above parameters, the chance of having no aggregator has a probability of 3.78E-08.
- Chart analysis: https://docs.google.com/spreadsheets/d/1C7pBqEWJgzk3_jesLkqJoDTnjZOODnGTOJUrxUMdxMA # noqa: E501
"""
committee = get_beacon_committee(state, slot, index, config)
modulo = max(1, len(committee) // TARGET_AGGREGATORS_PER_COMMITTEE)
return int.from_bytes(hash_eth2(signature)[0:8],
byteorder="little") % modulo == 0
def test_get_attesting_indices(genesis_state, config):
state = genesis_state.set(
"slot", compute_start_slot_at_epoch(3, config.SLOTS_PER_EPOCH))
target_epoch = state.current_epoch(config.SLOTS_PER_EPOCH)
target_slot = compute_start_slot_at_epoch(target_epoch,
config.SLOTS_PER_EPOCH)
committee_index = 0
some_committee = get_beacon_committee(state, target_slot, committee_index,
config)
data = AttestationData.create(
slot=target_slot,
index=committee_index,
target=Checkpoint.create(epoch=target_epoch),
)
some_subset_count = random.randrange(1, len(some_committee) // 2)
some_subset = random.sample(some_committee, some_subset_count)
bitfield = get_empty_bitfield(len(some_committee))
for i, index in enumerate(some_committee):
if index in some_subset:
bitfield = set_voted(bitfield, i)
indices = get_attesting_indices(state, data, bitfield, config)
assert set(indices) == set(some_subset)
assert len(indices) == len(some_subset)
def _validate_aggregation_bits(state: BeaconState, attestation: Attestation,
config: Eth2Config) -> None:
data = attestation.data
committee = get_beacon_committee(state, data.slot, data.index, config)
if not (len(attestation.aggregation_bits) == len(committee)):
raise ValidationError(
f"The attestation bit lengths not match:"
f"\tlen(attestation.aggregation_bits)={len(attestation.aggregation_bits)}\n"
f"\tlen(committee)={len(committee)}")
def get_attesting_indices(
state: BeaconState,
attestation_data: AttestationData,
bitfield: Bitfield,
config: CommitteeConfig,
) -> Set[ValidatorIndex]:
"""
Return the attesting indices corresponding to ``attestation_data`` and ``bitfield``.
"""
committee = get_beacon_committee(state, attestation_data.slot,
attestation_data.index, config)
return set(index for i, index in enumerate(committee)
if has_voted(bitfield, i))
def test_get_beacon_committee(genesis_state, config):
state = genesis_state
indices = tuple()
epoch_start_slot = state.slot
for slot in range(epoch_start_slot,
epoch_start_slot + config.SLOTS_PER_EPOCH):
committees_at_slot = get_committee_count_at_slot(
state,
slot,
config.MAX_COMMITTEES_PER_SLOT,
config.SLOTS_PER_EPOCH,
config.TARGET_COMMITTEE_SIZE,
)
for committee_index in range(committees_at_slot):
some_committee = get_beacon_committee(state, slot, committee_index,
config)
indices += tuple(some_committee)
assert set(indices) == set(range(len(genesis_state.validators)))
assert len(indices) == len(genesis_state.validators)
def test_get_unslashed_attesting_indices(genesis_state, config):
state = genesis_state.set(
"slot", compute_start_slot_at_epoch(3, config.SLOTS_PER_EPOCH)
)
target_epoch = state.current_epoch(config.SLOTS_PER_EPOCH)
target_slot = compute_start_slot_at_epoch(target_epoch, config.SLOTS_PER_EPOCH)
committee_index = 0
some_committee = get_beacon_committee(
state, target_slot, committee_index, CommitteeConfig(config)
)
data = AttestationData.create(
slot=state.slot,
index=committee_index,
target=Checkpoint.create(epoch=target_epoch),
)
some_subset_count = random.randrange(1, len(some_committee) // 2)
some_subset = random.sample(some_committee, some_subset_count)
bitfield = get_empty_bitfield(len(some_committee))
for i, index in enumerate(some_committee):
if index in some_subset:
if random.choice([True, False]):
state = state.transform(["validators", index, "slashed"], True)
bitfield = set_voted(bitfield, i)
some_subset = tuple(
filter(lambda index: not state.validators[index].slashed, some_subset)
)
indices = get_unslashed_attesting_indices(
state,
(PendingAttestation.create(data=data, aggregation_bits=bitfield),),
CommitteeConfig(config),
)
assert set(indices) == set(some_subset)
assert len(indices) == len(some_subset)
