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nimbus-eth2/beacon_chain/spec/state_transition.nim

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# beacon_chain
# Copyright (c) 2018-2022 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.
# State transition, as described in
# https://github.com/ethereum/consensus-specs/blob/v1.3.0-alpha.1/specs/phase0/beacon-chain.md#beacon-chain-state-transition-function
#
# The entry point is `state_transition` which is at the bottom of the file!
#
# General notes about the code:
# * Weird styling - the sections taken from the spec use python styling while
# the others use NEP-1 - helps grepping identifiers in spec
# * When updating the code, add TODO sections to mark where there are clear
# improvements to be made - other than that, keep things similar to spec unless
# motivated by security or performance considerations
#
# Performance notes:
# * The state transition is used in two contexts: to verify that incoming blocks
# are correct and to replay existing blocks from database. Incoming blocks
# are processed one-by-one while replay happens multiple blocks at a time.
# * Although signature verification is the slowest operation in the state
# state transition, we skip it during replay - this is also when we repeatedly
# call the state transition, making the non-signature part of the code
# important from a performance point of view.
# * It's important to start with a prefilled cache - generating the shuffled
# list of active validators is generally very slow.
# * Throughout, the code is affected by inefficient for loop codegen, meaning
# that we have to iterate over indices and pick out the value manually:
# https://github.com/nim-lang/Nim/issues/14421
# * Throughout, we're affected by inefficient `let` borrowing, meaning we
# often have to take the address of a sequence item due to the above - look
# for `let ... = unsafeAddr sequence[idx]`
# * Throughout, we're affected by the overloading rules that prefer a `var`
# overload to a non-var overload - look for `asSeq()` - when the `var`
# overload is used, the hash tree cache is cleared, which, aside from being
# slow itself, causes additional processing to recalculate the merkle tree.
when (NimMajor, NimMinor) < (1, 4):
{.push raises: [Defect].}
else:
{.push raises: [].}
import
chronicles,
stew/results,
../extras,
./datatypes/[phase0, altair, bellatrix],
"."/[
beaconstate, eth2_merkleization, forks, helpers, signatures,
state_transition_block, state_transition_epoch, validator]
export results, extras, phase0, altair, bellatrix
# https://github.com/ethereum/consensus-specs/blob/v1.3.0-alpha.1/specs/phase0/beacon-chain.md#beacon-chain-state-transition-function
proc verify_block_signature(
state: ForkyBeaconState, signed_block: SomeForkySignedBeaconBlock):
Result[void, cstring] =
let
proposer_index = signed_block.message.proposer_index
if proposer_index >= state.validators.lenu64:
return err("block: invalid proposer index")
if not verify_block_signature(
state.fork, state.genesis_validators_root, signed_block.message.slot,
signed_block.root, state.validators[proposer_index].pubkey,
signed_block.signature):
return err("block: signature verification failed")
ok()
# https://github.com/ethereum/consensus-specs/blob/v1.3.0-alpha.1/specs/phase0/beacon-chain.md#beacon-chain-state-transition-function
func verifyStateRoot(
state: ForkyBeaconState, blck: ForkyBeaconBlock | ForkySigVerifiedBeaconBlock):
Result[void, cstring] =
# This is inlined in state_transition(...) in spec.
let state_root = hash_tree_root(state)
if state_root != blck.state_root:
err("block: state root verification failed")
else:
ok()
func verifyStateRoot(
state: ForkyBeaconState, blck: ForkyTrustedBeaconBlock):
Result[void, cstring] =
# This is inlined in state_transition(...) in spec.
ok()
type
RollbackProc* = proc() {.gcsafe, noSideEffect, raises: [Defect].}
RollbackHashedProc*[T] =
proc(state: var T) {.gcsafe, noSideEffect, raises: [Defect].}
RollbackForkedHashedProc* = RollbackHashedProc[ForkedHashedBeaconState]
func noRollback*() =
trace "Skipping rollback of broken state"
# Hashed-state transition functions
# ---------------------------------------------------------------
# https://github.com/ethereum/consensus-specs/blob/v1.3.0-alpha.1/specs/phase0/beacon-chain.md#beacon-chain-state-transition-function
func process_slot*(
state: var ForkyBeaconState, pre_state_root: Eth2Digest) =
# `process_slot` is the first stage of per-slot processing - it is run for
# every slot, including epoch slots - it does not however update the slot
# number! `pre_state_root` refers to the state root of the incoming
# state before any slot processing has been done.
# Cache state root
state.state_roots[state.slot mod SLOTS_PER_HISTORICAL_ROOT] = pre_state_root
# Cache latest block header state root
if state.latest_block_header.state_root == ZERO_HASH:
state.latest_block_header.state_root = pre_state_root
# Cache block root
state.block_roots[state.slot mod SLOTS_PER_HISTORICAL_ROOT] =
hash_tree_root(state.latest_block_header)
func clear_epoch_from_cache(cache: var StateCache, epoch: Epoch) =
cache.shuffled_active_validator_indices.del epoch
for slot in epoch.slots():
cache.beacon_proposer_indices.del slot
# https://github.com/ethereum/consensus-specs/blob/v1.3.0-alpha.1/specs/phase0/beacon-chain.md#beacon-chain-state-transition-function
proc advance_slot(
cfg: RuntimeConfig,
state: var ForkyBeaconState, previous_slot_state_root: Eth2Digest,
flags: UpdateFlags, cache: var StateCache, info: var ForkyEpochInfo):
Result[void, cstring] =
# Do the per-slot and potentially the per-epoch processing, then bump the
# slot number - we've now arrived at the slot state on top of which a block
# optionally can be applied.
process_slot(state, previous_slot_state_root)
info.clear()
let is_epoch_transition = (state.slot + 1).is_epoch
if is_epoch_transition:
# Note: Genesis epoch = 0, no need to test if before Genesis
? process_epoch(cfg, state, flags, cache, info)
clear_epoch_from_cache(cache, (state.slot + 1).epoch)
state.slot += 1
ok()
func noRollback*(state: var phase0.HashedBeaconState) =
trace "Skipping rollback of broken phase 0 state"
func noRollback*(state: var altair.HashedBeaconState) =
trace "Skipping rollback of broken Altair state"
func noRollback*(state: var bellatrix.HashedBeaconState) =
trace "Skipping rollback of broken Bellatrix state"
from ./datatypes/capella import
ExecutionPayload, HashedBeaconState, SignedBLSToExecutionChangeList,
asSigVerified
func noRollback*(state: var capella.HashedBeaconState) =
trace "Skipping rollback of broken Capella state"
func maybeUpgradeStateToAltair(
cfg: RuntimeConfig, state: var ForkedHashedBeaconState) =
# Both process_slots() and state_transition_block() call this, so only run it
# once by checking for existing fork.
if getStateField(state, slot).epoch == cfg.ALTAIR_FORK_EPOCH and
state.kind == BeaconStateFork.Phase0:
let newState = upgrade_to_altair(cfg, state.phase0Data.data)
state = (ref ForkedHashedBeaconState)(
kind: BeaconStateFork.Altair,
altairData: altair.HashedBeaconState(
root: hash_tree_root(newState[]), data: newState[]))[]
func maybeUpgradeStateToBellatrix(
cfg: RuntimeConfig, state: var ForkedHashedBeaconState) =
# Both process_slots() and state_transition_block() call this, so only run it
# once by checking for existing fork.
if getStateField(state, slot).epoch == cfg.BELLATRIX_FORK_EPOCH and
state.kind == BeaconStateFork.Altair:
let newState = upgrade_to_bellatrix(cfg, state.altairData.data)
state = (ref ForkedHashedBeaconState)(
kind: BeaconStateFork.Bellatrix,
bellatrixData: bellatrix.HashedBeaconState(
root: hash_tree_root(newState[]), data: newState[]))[]
func maybeUpgradeStateToCapella(
cfg: RuntimeConfig, state: var ForkedHashedBeaconState) =
# Both process_slots() and state_transition_block() call this, so only run it
# once by checking for existing fork.
if getStateField(state, slot).epoch == cfg.CAPELLA_FORK_EPOCH and
state.kind == BeaconStateFork.Bellatrix:
let newState = upgrade_to_capella(cfg, state.bellatrixData.data)
state = (ref ForkedHashedBeaconState)(
kind: BeaconStateFork.Capella,
capellaData: capella.HashedBeaconState(
root: hash_tree_root(newState[]), data: newState[]))[]
func maybeUpgradeState*(
cfg: RuntimeConfig, state: var ForkedHashedBeaconState) =
cfg.maybeUpgradeStateToAltair(state)
cfg.maybeUpgradeStateToBellatrix(state)
cfg.maybeUpgradeStateToCapella(state)
proc process_slots*(
cfg: RuntimeConfig, state: var ForkedHashedBeaconState, slot: Slot,
cache: var StateCache, info: var ForkedEpochInfo, flags: UpdateFlags):
Result[void, cstring] =
if not (getStateField(state, slot) < slot):
if slotProcessed notin flags or getStateField(state, slot) != slot:
return err("process_slots: cannot rewind state to past slot")
# Update the state so its slot matches that of the block
while getStateField(state, slot) < slot:
withState(state):
withEpochInfo(forkyState.data, info):
? advance_slot(
cfg, forkyState.data, forkyState.root, flags, cache, info)
if skipLastStateRootCalculation notin flags or
forkyState.data.slot < slot:
# Don't update state root for the slot of the block if going to process
# block after
forkyState.root = hash_tree_root(forkyState.data)
maybeUpgradeState(cfg, state)
ok()
proc state_transition_block_aux(
cfg: RuntimeConfig,
state: var ForkyHashedBeaconState,
signedBlock: SomeForkySignedBeaconBlock,
cache: var StateCache, flags: UpdateFlags): Result[void, cstring] =
# Block updates - these happen when there's a new block being suggested
# by the block proposer. Every actor in the network will update its state
# according to the contents of this block - but first they will validate
# that the block is sane.
if skipBlsValidation notin flags:
? verify_block_signature(state.data, signedBlock)
trace "state_transition: processing block, signature passed",
signature = shortLog(signedBlock.signature),
blockRoot = shortLog(signedBlock.root)
? process_block(cfg, state.data, signedBlock.message, flags, cache)
if skipStateRootValidation notin flags:
? verifyStateRoot(state.data, signedBlock.message)
# only blocks currently being produced have an empty state root - we use a
# separate function for those
doAssert not signedBlock.message.state_root.isZero,
"see makeBeaconBlock for block production"
state.root = signedBlock.message.state_root
ok()
func noRollback*(state: var ForkedHashedBeaconState) =
trace "Skipping rollback of broken state"
proc state_transition_block*(
cfg: RuntimeConfig,
state: var ForkedHashedBeaconState,
signedBlock: SomeForkySignedBeaconBlock,
cache: var StateCache, flags: UpdateFlags,
rollback: RollbackForkedHashedProc): Result[void, cstring] =
## `rollback` is called if the transition fails and the given state has been
## partially changed. If a temporary state was given to `state_transition`,
## it is safe to use `noRollback` and leave it broken, else the state
## object should be rolled back to a consistent state. If the transition fails
## before the state has been updated, `rollback` will not be called.
doAssert not rollback.isNil, "use noRollback if it's ok to mess up state"
let res = withState(state):
when stateFork.toBeaconBlockFork() == type(signedBlock).toFork:
state_transition_block_aux(cfg, forkyState, signedBlock, cache, flags)
else:
err("State/block fork mismatch")
if res.isErr():
rollback(state)
res
proc state_transition*(
cfg: RuntimeConfig,
state: var ForkedHashedBeaconState,
signedBlock: SomeForkySignedBeaconBlock,
cache: var StateCache, info: var ForkedEpochInfo, flags: UpdateFlags,
rollback: RollbackForkedHashedProc): Result[void, cstring] =
## Apply a block to the state, advancing the slot counter as necessary. The
## given state must be of a lower slot, or, in case the `slotProcessed` flag
## is set, can be the slot state of the same slot as the block (where the
## slot state is the state without any block applied). To create a slot state,
## advance the state corresponding to the the parent block using
## `process_slots`.
##
## To run the state transition function in preparation for block production,
## use `makeBeaconBlock` instead.
##
## `rollback` is called if the transition fails and the given state has been
## partially changed. If a temporary state was given to `state_transition`,
## it is safe to use `noRollback` and leave it broken, else the state
## object should be rolled back to a consistent state. If the transition fails
## before the state has been updated, `rollback` will not be called.
? process_slots(
cfg, state, signedBlock.message.slot, cache, info,
flags + {skipLastStateRootCalculation})
state_transition_block(
cfg, state, signedBlock, cache, flags, rollback)
# https://github.com/ethereum/consensus-specs/blob/v1.3.0-alpha.1/specs/phase0/validator.md#preparing-for-a-beaconblock
template partialBeaconBlock*(
cfg: RuntimeConfig,
state: var phase0.HashedBeaconState,
proposer_index: ValidatorIndex,
randao_reveal: ValidatorSig,
eth1_data: Eth1Data,
graffiti: GraffitiBytes,
attestations: seq[Attestation],
deposits: seq[Deposit],
exits: BeaconBlockExits,
sync_aggregate: SyncAggregate,
execution_payload: bellatrix.ExecutionPayload): phase0.BeaconBlock =
phase0.BeaconBlock(
slot: state.data.slot,
proposer_index: proposer_index.uint64,
parent_root: state.latest_block_root,
body: phase0.BeaconBlockBody(
randao_reveal: randao_reveal,
eth1_data: eth1data,
graffiti: graffiti,
proposer_slashings: exits.proposer_slashings,
attester_slashings: exits.attester_slashings,
attestations: List[Attestation, Limit MAX_ATTESTATIONS](attestations),
deposits: List[Deposit, Limit MAX_DEPOSITS](deposits),
voluntary_exits: exits.voluntary_exits))
# https://github.com/ethereum/consensus-specs/blob/v1.2.0/specs/altair/validator.md#preparing-a-beaconblock
template partialBeaconBlock*(
cfg: RuntimeConfig,
state: var altair.HashedBeaconState,
proposer_index: ValidatorIndex,
randao_reveal: ValidatorSig,
eth1_data: Eth1Data,
graffiti: GraffitiBytes,
attestations: seq[Attestation],
deposits: seq[Deposit],
exits: BeaconBlockExits,
sync_aggregate: SyncAggregate,
execution_payload: bellatrix.ExecutionPayload): altair.BeaconBlock =
altair.BeaconBlock(
slot: state.data.slot,
proposer_index: proposer_index.uint64,
parent_root: state.latest_block_root,
body: altair.BeaconBlockBody(
randao_reveal: randao_reveal,
eth1_data: eth1data,
graffiti: graffiti,
proposer_slashings: exits.proposer_slashings,
attester_slashings: exits.attester_slashings,
attestations: List[Attestation, Limit MAX_ATTESTATIONS](attestations),
deposits: List[Deposit, Limit MAX_DEPOSITS](deposits),
voluntary_exits: exits.voluntary_exits,
sync_aggregate: sync_aggregate))
# https://github.com/ethereum/consensus-specs/blob/v1.1.3/specs/merge/validator.md#block-proposal
template partialBeaconBlock*(
cfg: RuntimeConfig,
state: var bellatrix.HashedBeaconState,
proposer_index: ValidatorIndex,
randao_reveal: ValidatorSig,
eth1_data: Eth1Data,
graffiti: GraffitiBytes,
attestations: seq[Attestation],
deposits: seq[Deposit],
exits: BeaconBlockExits,
sync_aggregate: SyncAggregate,
execution_payload: bellatrix.ExecutionPayload): bellatrix.BeaconBlock =
bellatrix.BeaconBlock(
slot: state.data.slot,
proposer_index: proposer_index.uint64,
parent_root: state.latest_block_root,
body: bellatrix.BeaconBlockBody(
randao_reveal: randao_reveal,
eth1_data: eth1data,
graffiti: graffiti,
proposer_slashings: exits.proposer_slashings,
attester_slashings: exits.attester_slashings,
attestations: List[Attestation, Limit MAX_ATTESTATIONS](attestations),
deposits: List[Deposit, Limit MAX_DEPOSITS](deposits),
voluntary_exits: exits.voluntary_exits,
sync_aggregate: sync_aggregate,
execution_payload: execution_payload))
# https://github.com/ethereum/consensus-specs/blob/v1.1.3/specs/merge/validator.md#block-proposal
template partialBeaconBlock*(
cfg: RuntimeConfig,
state: var capella.HashedBeaconState,
proposer_index: ValidatorIndex,
randao_reveal: ValidatorSig,
eth1_data: Eth1Data,
graffiti: GraffitiBytes,
attestations: seq[Attestation],
deposits: seq[Deposit],
exits: BeaconBlockExits,
sync_aggregate: SyncAggregate,
execution_payload: capella.ExecutionPayload,
bls_to_execution_changes: SignedBLSToExecutionChangeList
):
capella.BeaconBlock =
capella.BeaconBlock(
slot: state.data.slot,
proposer_index: proposer_index.uint64,
parent_root: state.latest_block_root,
body: capella.BeaconBlockBody(
randao_reveal: randao_reveal,
eth1_data: eth1data,
graffiti: graffiti,
proposer_slashings: exits.proposer_slashings,
attester_slashings: exits.attester_slashings,
attestations: List[Attestation, Limit MAX_ATTESTATIONS](attestations),
deposits: List[Deposit, Limit MAX_DEPOSITS](deposits),
voluntary_exits: exits.voluntary_exits,
sync_aggregate: sync_aggregate,
execution_payload: execution_payload,
bls_to_execution_changes: bls_to_execution_changes
))
proc makeBeaconBlock*(
cfg: RuntimeConfig,
state: var ForkedHashedBeaconState,
proposer_index: ValidatorIndex,
randao_reveal: ValidatorSig,
eth1_data: Eth1Data,
graffiti: GraffitiBytes,
attestations: seq[Attestation],
deposits: seq[Deposit],
exits: BeaconBlockExits,
sync_aggregate: SyncAggregate,
executionPayload: bellatrix.ExecutionPayload,
rollback: RollbackForkedHashedProc,
cache: var StateCache,
# TODO:
# `verificationFlags` is needed only in tests and can be
# removed if we don't use invalid signatures there
verificationFlags: UpdateFlags = {},
transactions_root: Opt[Eth2Digest] = Opt.none Eth2Digest,
execution_payload_root: Opt[Eth2Digest] = Opt.none Eth2Digest):
Result[ForkedBeaconBlock, cstring] =
## Create a block for the given state. The latest block applied to it will
## be used for the parent_root value, and the slot will be take from
## state.slot meaning process_slots must be called up to the slot for which
## the block is to be created.
template makeBeaconBlock(kind: untyped): Result[ForkedBeaconBlock, cstring] =
# To create a block, we'll first apply a partial block to the state, skipping
# some validations.
var blck =
ForkedBeaconBlock.init(
partialBeaconBlock(
cfg, state.`kind Data`, proposer_index, randao_reveal, eth1_data,
graffiti, attestations, deposits, exits, sync_aggregate,
executionPayload))
let res = process_block(
cfg, state.`kind Data`.data, blck.`kind Data`.asSigVerified(),
verificationFlags, cache)
if res.isErr:
rollback(state)
return err(res.error())
# Override for MEV
if transactions_root.isSome and execution_payload_root.isSome:
withState(state):
when stateFork >= BeaconStateFork.Bellatrix:
forkyState.data.latest_execution_payload_header.transactions_root =
transactions_root.get
# https://github.com/ethereum/consensus-specs/blob/v1.3.0-alpha.1/specs/bellatrix/beacon-chain.md#beaconblockbody
# Effectively hash_tree_root(ExecutionPayload) with the beacon block
# body, with the execution payload replaced by the execution payload
# header. htr(payload) == htr(payload header), so substitute.
forkyState.data.latest_block_header.body_root = hash_tree_root(
[hash_tree_root(randao_reveal),
hash_tree_root(eth1_data),
hash_tree_root(graffiti),
hash_tree_root(exits.proposer_slashings),
hash_tree_root(exits.attester_slashings),
hash_tree_root(List[Attestation, Limit MAX_ATTESTATIONS](attestations)),
hash_tree_root(List[Deposit, Limit MAX_DEPOSITS](deposits)),
hash_tree_root(exits.voluntary_exits),
hash_tree_root(sync_aggregate),
execution_payload_root.get])
state.`kind Data`.root = hash_tree_root(state.`kind Data`.data)
blck.`kind Data`.state_root = state.`kind Data`.root
ok(blck)
case state.kind
of BeaconStateFork.Phase0: makeBeaconBlock(phase0)
of BeaconStateFork.Altair: makeBeaconBlock(altair)
of BeaconStateFork.Bellatrix: makeBeaconBlock(bellatrix)
of BeaconStateFork.Capella:
raiseAssert $capellaImplementationMissing
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