Fork choice compiles (but untested)

This commit is contained in:
mratsim 2019-01-08 18:28:21 +01:00 committed by zah
parent f0e3de6b19
commit 423f632606
4 changed files with 81 additions and 28 deletions

View File

@ -1,11 +1,12 @@
import
os, json,
os, json, tables,
chronicles, json_serialization, eth_common/eth_types_json_serialization,
spec/[datatypes, digest, crypto]
type
BeaconChainDB* = ref object
dataRoot: string
blocks*: Table[Eth2Digest, BeaconBlock]
BeaconStateRef* = ref BeaconState

View File

@ -3,7 +3,8 @@ import
asyncdispatch2, chronicles, confutils, eth_p2p, eth_keys,
spec/[datatypes, digest, crypto, beaconstate, helpers], conf, time,
state_transition, fork_choice, ssz, beacon_chain_db, validator_pool, extras,
mainchain_monitor, sync_protocol, gossipsub_protocol, trusted_state_snapshots
mainchain_monitor, sync_protocol, gossipsub_protocol, trusted_state_snapshots,
tables
type
BeaconNode* = ref object
@ -18,6 +19,7 @@ type
lastScheduledEpoch: uint64
headBlock: BeaconBlock
headBlockRoot: Eth2Digest
blocksChildren: Table[Eth2Digest, seq[Eth2Digest]]
const
version = "v0.1" # TODO: read this from the nimble file

View File

@ -1,8 +1,8 @@
import
deques, options,
deques, options, tables,
milagro_crypto,
./spec/[datatypes, crypto, digest, helpers, validator], extras,
tables, hashes
./beacon_chain_db
type
AttestationCandidate* = object
@ -170,6 +170,18 @@ func getAttestationCandidate*(attestation: Attestation): AttestationCandidate =
# - We use a simple fork choice rule without finalized and justified head
# - We don't implement "get_latest_attestation(store, validator) -> Attestation"
# nor get_latest_attestation_target
# - We use block hashes (Eth2Digest) instead of raw blocks where possible
func get_parent(db: BeaconChainDB, blck: Eth2Digest): Eth2Digest =
db.blocks[blck].parent_root
func get_ancestor(store: BeaconChainDB, blck: Eth2Digest, slot: uint64): Eth2Digest =
## Find the ancestor with a specific slot number
if store.blocks[blck].slot == slot:
return blck
else:
return store.get_ancestor(store.get_parent(blck), slot)
# TODO: what if the slot was never observed/verified?
func getVoteCount(participation_bitfield: openarray[byte]): int =
## Get the number of votes
@ -179,8 +191,9 @@ func getVoteCount(participation_bitfield: openarray[byte]): int =
for validatorIdx in 0 ..< participation_bitfield.len * 8:
result += int participation_bitfield.bitIsSet(validatorIdx)
func getAttestationVoteCount(pool: AttestationPool, state: BeaconState): CountTable[BlockHash] =
## Returns all blocks that were attested and their vote count for a specific slot.
func getAttestationVoteCount(pool: AttestationPool, current_slot: int): CountTable[Eth2Digest] =
## Returns all blocks more recent that the current slot
## that were attested and their vote count
# This replaces:
# - get_latest_attestation,
# - get_latest_attestation_targets
@ -191,29 +204,55 @@ func getAttestationVoteCount(pool: AttestationPool, state: BeaconState): CountTa
# ```
# Note that attestation_targets in the Eth2 specs can have duplicates
# while the following implementation will count such blockhash multiple times instead.
result = initCountTable[BlockHash]()
for attestation in pool.attestations[state.slot.int - pool.startingSlot]:
if attestation.isSome:
# Increase the block attestation counts by the number of validators aggregated
let voteCount = attestation.get.participation_bitfield.getVoteCount()
result.inc(attestation.get.data.beacon_block_root, voteCount)
result = initCountTable[Eth2Digest]()
func getParent(db: BeaconChainDB, blck: BeaconBlock): BeaconBlock =
db.blocks[blck.parent_root]
for slot in current_slot - pool.startingSlot ..< pool.attestations.len:
for attestation in pool.attestations[slot]:
if attestation.isSome:
# Increase the block attestation counts by the number of validators aggregated
let voteCount = attestation.get.participation_bitfield.getVoteCount()
result.inc(attestation.get.data.beacon_block_root, voteCount)
func get_ancestor(store: BeaconChainDB, blck: BeaconBlock, slot: uint64): BeaconBlock =
## Find the ancestor with a specific slot number
if blck.slot == slot:
return blck
else:
return store.get_ancestor(store.get_parent(blck), slot)
# TODO: what if the slot was never observed/verified?
func lmdGhost*(store: BeaconChainDB, pool: AttestationPool, state: BeaconState): BeaconBlock =
func lmdGhost*(
store: BeaconChainDB,
pool: AttestationPool,
state: BeaconState,
blocksChildren: Table[Eth2Digest, seq[Eth2Digest]]): BeaconBlock =
# Recompute the new head of the beacon chain according to
# LMD GHOST (Latest Message Driven - Greediest Heaviest Observed SubTree)
let validators = state.validator_registry
var active_validators: seq[ValidatorRecord]
for i in validators.get_active_validator_indices:
active_validators.add validators[i]
# Raw vote count from all attestations
let rawVoteCount = pool.getAttestationVoteCount(state.slot.int)
# The real vote count for a block also takes into account votes for its children
# TODO: a Fenwick Tree datastructure to keep track of cumulated votes
# in O(log N) complexity
# https://en.wikipedia.org/wiki/Fenwick_tree
# Nim implementation for cumulative frequencies at
# https://github.com/numforge/laser/blob/990e59fffe50779cdef33aa0b8f22da19e1eb328/benchmarks/random_sampling/fenwicktree.nim
proc childBlockVoteCount(child: Eth2Digest): int =
for target, votes in rawVoteCount.pairs:
if store.get_ancestor(target, store.blocks[child].slot) == child:
result += votes
var head = state.latest_block_roots[state.slot mod LATEST_BLOCK_ROOTS_LENGTH]
var childVotes = initCountTable[Eth2Digest]()
while true: # TODO use a O(log N) implementation instead of O(N^2)
let children = blocksChildren[head]
if children.len == 0:
return store.blocks[head]
# For now we assume that all children are direct descendant of the current head
let next_slot = store.blocks[head].slot + 1
for child in children:
doAssert store.blocks[child].slot == next_slot
childVotes.clear()
for target, votes in rawVoteCount.pairs:
if store.blocks[target].slot >= next_slot:
childVotes.inc(store.get_ancestor(target, next_slot), votes)
head = childVotes.largest().key

View File

@ -21,7 +21,8 @@
# `eth2hash`, and it outputs a `Eth2Digest`. Easy to sed :)
import
nimcrypto/[blake2, hash], eth_common/eth_types_json_serialization
nimcrypto/[blake2, hash], eth_common/eth_types_json_serialization,
hashes
export
eth_types_json_serialization, hash.`$`
@ -45,3 +46,13 @@ template withEth2Hash*(body: untyped): Eth2Digest =
var tmp = h.finish()
copyMem(res.data.addr, tmp.data.addr, sizeof(res))
res
func hash*(x: Eth2Digest): Hash =
## Hash for Keccak digests for Nim hash tables
# Stub for BeaconChainDB
# We just slice the first 4 or 8 bytes of the block hash
# depending of if we are on a 32 or 64-bit platform
const size = x.sizeof
const num_hashes = size div sizeof(int)
result = cast[array[num_hashes, Hash]](x)[0]