nimbus-eth2/beacon_chain/spec/validator.nim

345 lines
14 KiB
Nim

# Copyright (c) 2018-2020 Status Research & Development GmbH
# Licensed and distributed under either of
# * MIT license (license terms in the root directory or at https://opensource.org/licenses/MIT).
# * Apache v2 license (license terms in the root directory or at https://www.apache.org/licenses/LICENSE-2.0).
# at your option. This file may not be copied, modified, or distributed except according to those terms.
# Helpers and functions pertaining to managing the validator set
{.push raises: [Defect].}
import
algorithm, options, sequtils, math, tables,
./datatypes, ./digest, ./helpers
# https://github.com/ethereum/eth2.0-specs/blob/v0.12.2/specs/phase0/beacon-chain.md#compute_shuffled_index
# https://github.com/ethereum/eth2.0-specs/blob/v0.12.2/specs/phase0/beacon-chain.md#compute_committee
func get_shuffled_seq*(seed: Eth2Digest,
list_size: uint64,
): seq[ValidatorIndex] =
## Via https://github.com/protolambda/eth2-shuffle/blob/master/shuffle.go
## Shuffles ``validators`` into beacon committees, seeded by ``seed`` and
## ``slot``.
## Returns a list of ``SLOTS_PER_EPOCH * committees_per_slot`` committees
## where each committee is itself a list of validator indices.
##
## Invert the inner/outer loops from the spec, essentially. Most useful
## hash result re-use occurs within a round.
# Empty size -> empty list.
if list_size == 0:
return
var
# Share these buffers.
# TODO: Redo to follow spec.
# We can have an "Impl" private version that takes buffer as parameters
# so that we avoid alloc on repeated calls from compute_committee
pivot_buffer: array[(32+1), byte]
source_buffer: array[(32+1+4), byte]
shuffled_active_validator_indices = mapIt(
0 ..< list_size.int, it.ValidatorIndex)
sources = repeat(Eth2Digest(), (list_size div 256) + 1)
## The pivot's a function of seed and round only.
## This doesn't change across rounds.
pivot_buffer[0..31] = seed.data
source_buffer[0..31] = seed.data
static: doAssert SHUFFLE_ROUND_COUNT < uint8.high
for round in 0'u8 ..< SHUFFLE_ROUND_COUNT.uint8:
pivot_buffer[32] = round
source_buffer[32] = round
# Only one pivot per round.
let pivot =
bytes_to_uint64(eth2digest(pivot_buffer).data.toOpenArray(0, 7)) mod
list_size
## Only need to run, per round, position div 256 hashes, so precalculate
## them. This consumes memory, but for low-memory devices, it's possible
## to mitigate by some light LRU caching and similar.
for reduced_position in 0 ..< sources.len:
source_buffer[33..36] = uint_to_bytes4(reduced_position.uint64)
sources[reduced_position] = eth2digest(source_buffer)
## Iterate over all the indices. This was in get_permuted_index, but large
## efficiency gains exist in caching and re-using data.
for index in 0 ..< list_size.int:
let
cur_idx_permuted = shuffled_active_validator_indices[index]
flip = ((list_size + pivot) - cur_idx_permuted.uint64) mod list_size
position = max(cur_idx_permuted.int, flip.int)
let
source = sources[position div 256].data
byte_value = source[(position mod 256) div 8]
bit = (byte_value shr (position mod 8)) mod 2
if bit != 0:
shuffled_active_validator_indices[index] = flip.ValidatorIndex
shuffled_active_validator_indices
func get_shuffled_active_validator_indices*(state: BeaconState, epoch: Epoch):
seq[ValidatorIndex] =
# Non-spec function, to cache a data structure from which one can cheaply
# compute both get_active_validator_indexes() and get_beacon_committee().
let active_validator_indices = get_active_validator_indices(state, epoch)
mapIt(
get_shuffled_seq(
get_seed(state, epoch, DOMAIN_BEACON_ATTESTER),
active_validator_indices.lenu64),
active_validator_indices[it])
func get_shuffled_active_validator_indices*(
cache: var StateCache, state: BeaconState, epoch: Epoch):
var seq[ValidatorIndex] =
# `cache` comes first because of nim's borrowing rules for the `var` return -
# the `var` returns avoids copying the validator set.
cache.shuffled_active_validator_indices.withValue(epoch, validator_indices) do:
return validator_indices[]
do:
let indices = get_shuffled_active_validator_indices(state, epoch)
return cache.shuffled_active_validator_indices.mgetOrPut(epoch, indices)
# https://github.com/ethereum/eth2.0-specs/blob/v0.12.2/specs/phase0/beacon-chain.md#get_active_validator_indices
func count_active_validators*(state: BeaconState,
epoch: Epoch,
cache: var StateCache): uint64 =
cache.get_shuffled_active_validator_indices(state, epoch).lenu64
# https://github.com/ethereum/eth2.0-specs/blob/v0.12.2/specs/phase0/beacon-chain.md#get_committee_count_per_slot
func get_committee_count_per_slot*(num_active_validators: uint64): uint64 =
clamp(
num_active_validators div SLOTS_PER_EPOCH div TARGET_COMMITTEE_SIZE,
1'u64, MAX_COMMITTEES_PER_SLOT)
func get_committee_count_per_slot*(state: BeaconState,
epoch: Epoch,
cache: var StateCache): uint64 =
# Return the number of committees at ``slot``.
# TODO this is mostly used in for loops which have indexes which then need to
# be converted to CommitteeIndex types for get_beacon_committee(...); replace
# with better and more type-safe use pattern, probably beginning with using a
# CommitteeIndex return type here.
let
active_validator_count = count_active_validators(state, epoch, cache)
result = get_committee_count_per_slot(active_validator_count)
# Otherwise, get_beacon_committee(...) cannot access some committees.
doAssert (SLOTS_PER_EPOCH * MAX_COMMITTEES_PER_SLOT) >= uint64(result)
func get_committee_count_per_slot*(state: BeaconState,
slot: Slot,
cache: var StateCache): uint64 =
get_committee_count_per_slot(state, slot.compute_epoch_at_slot, cache)
# https://github.com/ethereum/eth2.0-specs/blob/v0.12.2/specs/phase0/beacon-chain.md#get_previous_epoch
func get_previous_epoch*(current_epoch: Epoch): Epoch =
# Return the previous epoch (unless the current epoch is ``GENESIS_EPOCH``).
if current_epoch == GENESIS_EPOCH:
current_epoch
else:
current_epoch - 1
func get_previous_epoch*(state: BeaconState): Epoch =
# Return the previous epoch (unless the current epoch is ``GENESIS_EPOCH``).
get_previous_epoch(get_current_epoch(state))
# https://github.com/ethereum/eth2.0-specs/blob/v0.12.2/specs/phase0/beacon-chain.md#compute_committee
func compute_committee(shuffled_indices: seq[ValidatorIndex],
index: uint64, count: uint64): seq[ValidatorIndex] =
## Return the committee corresponding to ``indices``, ``seed``, ``index``,
## and committee ``count``.
## In this version, we pass in the shuffled indices meaning we no longer need
## the seed.
let
active_validators = shuffled_indices.len.uint64
start = (active_validators * index) div count
endIdx = (active_validators * (index + 1)) div count
# These assertions from compute_shuffled_index(...)
doAssert endIdx <= active_validators
doAssert active_validators <= 2'u64^40
# In spec, this calls get_shuffled_index() every time, but that's wasteful
# Here, get_beacon_committee() gets the shuffled version.
try:
shuffled_indices[start.int .. (endIdx.int-1)]
except KeyError:
raiseAssert("Cached entries are added before use")
func compute_committee_len(active_validators: uint64,
index: uint64, count: uint64): uint64 =
## Return the committee corresponding to ``indices``, ``seed``, ``index``,
## and committee ``count``.
# indices only used here for its length, or for the shuffled version,
# so unlike spec, pass the shuffled version in directly.
let
start = (active_validators * index) div count
endIdx = (active_validators * (index + 1)) div count
# These assertions from compute_shuffled_index(...)
doAssert endIdx <= active_validators
doAssert active_validators <= 2'u64^40
# In spec, this calls get_shuffled_index() every time, but that's wasteful
# Here, get_beacon_committee() gets the shuffled version.
endIdx - start
# https://github.com/ethereum/eth2.0-specs/blob/v0.12.2/specs/phase0/beacon-chain.md#get_beacon_committee
func get_beacon_committee*(
state: BeaconState, slot: Slot, index: CommitteeIndex,
cache: var StateCache): seq[ValidatorIndex] =
# Return the beacon committee at ``slot`` for ``index``.
let
epoch = compute_epoch_at_slot(slot)
committees_per_slot = get_committee_count_per_slot(state, epoch, cache)
compute_committee(
cache.get_shuffled_active_validator_indices(state, epoch),
(slot mod SLOTS_PER_EPOCH) * committees_per_slot +
index.uint64,
committees_per_slot * SLOTS_PER_EPOCH
)
func get_beacon_committee_len*(
state: BeaconState, slot: Slot, index: CommitteeIndex,
cache: var StateCache): uint64 =
# Return the number of members in the beacon committee at ``slot`` for ``index``.
let
epoch = compute_epoch_at_slot(slot)
committees_per_slot = get_committee_count_per_slot(state, epoch, cache)
compute_committee_len(
count_active_validators(state, epoch, cache),
(slot mod SLOTS_PER_EPOCH) * committees_per_slot +
index.uint64,
committees_per_slot * SLOTS_PER_EPOCH
)
# https://github.com/ethereum/eth2.0-specs/blob/v0.12.2/specs/phase0/beacon-chain.md#compute_shuffled_index
func compute_shuffled_index(
index: uint64, index_count: uint64, seed: Eth2Digest): uint64 =
# Return the shuffled index corresponding to ``seed`` (and ``index_count``).
doAssert index < index_count
var
pivot_buffer: array[(32+1), byte]
source_buffer: array[(32+1+4), byte]
cur_idx_permuted = index
pivot_buffer[0..31] = seed.data
source_buffer[0..31] = seed.data
# Swap or not (https://link.springer.com/content/pdf/10.1007%2F978-3-642-32009-5_1.pdf)
# See the 'generalized domain' algorithm on page 3
for current_round in 0'u8 ..< SHUFFLE_ROUND_COUNT.uint8:
pivot_buffer[32] = current_round
source_buffer[32] = current_round
let
# If using multiple indices, can amortize this
pivot =
bytes_to_uint64(eth2digest(pivot_buffer).data.toOpenArray(0, 7)) mod
index_count
flip = ((index_count + pivot) - cur_idx_permuted) mod index_count
position = max(cur_idx_permuted.int, flip.int)
source_buffer[33..36] = uint_to_bytes4((position div 256).uint64)
let
source = eth2digest(source_buffer).data
byte_value = source[(position mod 256) div 8]
bit = (byte_value shr (position mod 8)) mod 2
cur_idx_permuted = if bit != 0: flip else: cur_idx_permuted
cur_idx_permuted
# https://github.com/ethereum/eth2.0-specs/blob/v0.12.2/specs/phase0/beacon-chain.md#compute_proposer_index
func compute_proposer_index(state: BeaconState, indices: seq[ValidatorIndex],
seed: Eth2Digest): Option[ValidatorIndex] =
# Return from ``indices`` a random index sampled by effective balance.
const MAX_RANDOM_BYTE = 255
if len(indices) == 0:
return none(ValidatorIndex)
let seq_len = indices.lenu64
var
i = 0'u64
buffer: array[32+8, byte]
buffer[0..31] = seed.data
while true:
buffer[32..39] = uint_to_bytes8(i div 32)
let
candidate_index =
indices[compute_shuffled_index(i mod seq_len, seq_len, seed)]
random_byte = (eth2digest(buffer).data)[i mod 32]
effective_balance = state.validators[candidate_index].effective_balance
if effective_balance * MAX_RANDOM_BYTE >=
MAX_EFFECTIVE_BALANCE * random_byte:
return some(candidate_index)
i += 1
# https://github.com/ethereum/eth2.0-specs/blob/v0.12.2/specs/phase0/beacon-chain.md#get_beacon_proposer_index
func get_beacon_proposer_index*(state: BeaconState, cache: var StateCache, slot: Slot):
Option[ValidatorIndex] =
cache.beacon_proposer_indices.withValue(slot, proposer) do:
return proposer[]
do:
# Return the beacon proposer index at the current slot.
let epoch = get_current_epoch(state)
var buffer: array[32 + 8, byte]
buffer[0..31] = get_seed(state, epoch, DOMAIN_BEACON_PROPOSER).data
buffer[32..39] = uint_to_bytes8(slot.uint64)
# There's exactly one beacon proposer per slot.
let
seed = eth2digest(buffer)
indices =
sorted(cache.get_shuffled_active_validator_indices(state, epoch), system.cmp)
return cache.beacon_proposer_indices.mgetOrPut(
slot, compute_proposer_index(state, indices, seed))
# https://github.com/ethereum/eth2.0-specs/blob/v0.12.2/specs/phase0/beacon-chain.md#get_beacon_proposer_index
func get_beacon_proposer_index*(state: BeaconState, cache: var StateCache):
Option[ValidatorIndex] =
get_beacon_proposer_index(state, cache, state.slot)
# https://github.com/ethereum/eth2.0-specs/blob/v0.12.1/specs/phase0/validator.md#validator-assignments
func get_committee_assignment*(
state: BeaconState, epoch: Epoch,
validator_index: ValidatorIndex):
Option[tuple[a: seq[ValidatorIndex], b: CommitteeIndex, c: Slot]] =
# Return the committee assignment in the ``epoch`` for ``validator_index``.
# ``assignment`` returned is a tuple of the following form:
# * ``assignment[0]`` is the list of validators in the committee
# * ``assignment[1]`` is the index to which the committee is assigned
# * ``assignment[2]`` is the slot at which the committee is assigned
# Return None if no assignment.
let next_epoch = get_current_epoch(state) + 1
doAssert epoch <= next_epoch
var cache = StateCache()
let
start_slot = compute_start_slot_at_epoch(epoch)
committee_count_per_slot =
get_committee_count_per_slot(state, epoch, cache)
for slot in start_slot ..< start_slot + SLOTS_PER_EPOCH:
for index in 0'u64 ..< committee_count_per_slot:
let idx = index.CommitteeIndex
let committee = get_beacon_committee(state, slot, idx, cache)
if validator_index in committee:
return some((committee, idx, slot))
none(tuple[a: seq[ValidatorIndex], b: CommitteeIndex, c: Slot])