297 lines
13 KiB
Nim
297 lines
13 KiB
Nim
# beacon_chain
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# Copyright (c) 2018-2020 Status Research & Development GmbH
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# Licensed and distributed under either of
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# * MIT license (license terms in the root directory or at https://opensource.org/licenses/MIT).
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# * Apache v2 license (license terms in the root directory or at https://www.apache.org/licenses/LICENSE-2.0).
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# at your option. This file may not be copied, modified, or distributed except according to those terms.
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# State transition, as described in
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# https://github.com/ethereum/eth2.0-specs/blob/master/specs/core/0_beacon-chain.md#beacon-chain-state-transition-function
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#
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# The purpose of this code right is primarily educational, to help piece
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# together the mechanics of the beacon state and to discover potential problem
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# areas. The entry point is `state_transition` which is at the bottom of the file!
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#
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# General notes about the code (TODO):
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# * Weird styling - the sections taken from the spec use python styling while
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# the others use NEP-1 - helps grepping identifiers in spec
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# * We mix procedural and functional styles for no good reason, except that the
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# spec does so also.
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# * For indices, we get a mix of uint64, ValidatorIndex and int - this is currently
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# swept under the rug with casts
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# * Sane error handling is missing in most cases (yay, we'll get the chance to
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# debate exceptions again!)
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# When updating the code, add TODO sections to mark where there are clear
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# improvements to be made - other than that, keep things similar to spec for
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# now.
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{.push raises: [Defect].}
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import
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tables,
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chronicles,
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stew/results,
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../extras, ../ssz/merkleization, metrics,
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datatypes, crypto, digest, helpers, signatures, validator,
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state_transition_block, state_transition_epoch,
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../../nbench/bench_lab
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# https://github.com/ethereum/eth2.0-metrics/blob/master/metrics.md#additional-metrics
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declareGauge beacon_current_validators, """Number of status="pending|active|exited|withdrawable" validators in current epoch""" # On epoch transition
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declareGauge beacon_previous_validators, """Number of status="pending|active|exited|withdrawable" validators in previous epoch""" # On epoch transition
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func get_epoch_validator_count(state: BeaconState): int64 {.nbench.} =
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# https://github.com/ethereum/eth2.0-metrics/blob/master/metrics.md#additional-metrics
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#
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# This O(n) loop doesn't add to the algorithmic complexity of the epoch
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# transition -- registry update already does this. It is not great, but
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# isn't new, either. If profiling shows issues some of this can be loop
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# fusion'ed.
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for index, validator in state.validators:
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# These work primarily for the `beacon_current_validators` metric defined
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# as 'Number of status="pending|active|exited|withdrawable" validators in
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# current epoch'. This is, in principle, equivalent to checking whether a
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# validator's either at less than MAX_EFFECTIVE_BALANCE, or has withdrawn
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# already because withdrawable_epoch has passed, which more precisely has
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# intuitive meaning of all-the-current-relevant-validators. So, check for
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# not-(either (not-even-pending) or withdrawn). That is validators change
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# from not-even-pending to pending to active to exited to withdrawable to
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# withdrawn, and this avoids bugs on potential edge cases and off-by-1's.
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if (validator.activation_epoch != FAR_FUTURE_EPOCH or
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validator.effective_balance > MAX_EFFECTIVE_BALANCE) and
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validator.withdrawable_epoch > get_current_epoch(state):
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result += 1
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# https://github.com/ethereum/eth2.0-specs/blob/v0.12.2/specs/phase0/beacon-chain.md#beacon-chain-state-transition-function
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proc verify_block_signature*(
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state: BeaconState, signed_block: SomeSignedBeaconBlock): bool {.nbench.} =
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let
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proposer_index = signed_block.message.proposer_index
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if proposer_index >= state.validators.lenu64:
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notice "Invalid proposer index in block",
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blck = shortLog(signed_block.message)
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return false
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if not verify_block_signature(
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state.fork, state.genesis_validators_root, signed_block.message.slot,
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signed_block.message, state.validators[proposer_index].pubkey,
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signed_block.signature):
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notice "Block: signature verification failed",
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blck = shortLog(signedBlock)
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return false
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true
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# https://github.com/ethereum/eth2.0-specs/blob/v0.12.2/specs/phase0/beacon-chain.md#beacon-chain-state-transition-function
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proc verifyStateRoot(state: BeaconState, blck: BeaconBlock): bool =
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# This is inlined in state_transition(...) in spec.
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let state_root = hash_tree_root(state)
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if state_root != blck.state_root:
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notice "Block: root verification failed",
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block_state_root = shortLog(blck.state_root), state_root = shortLog(state_root)
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false
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else:
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true
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proc verifyStateRoot(state: BeaconState, blck: TrustedBeaconBlock): bool =
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# This is inlined in state_transition(...) in spec.
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true
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type
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RollbackProc* = proc(v: var BeaconState) {.gcsafe, raises: [Defect].}
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proc noRollback*(state: var BeaconState) =
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trace "Skipping rollback of broken state"
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type
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RollbackHashedProc* = proc(state: var HashedBeaconState) {.gcsafe.}
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# Hashed-state transition functions
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# ---------------------------------------------------------------
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# https://github.com/ethereum/eth2.0-specs/blob/v0.12.2/specs/phase0/beacon-chain.md#beacon-chain-state-transition-function
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func process_slot*(state: var HashedBeaconState) {.nbench.} =
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# Cache state root
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let previous_slot_state_root = state.root
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state.data.state_roots[state.data.slot mod SLOTS_PER_HISTORICAL_ROOT] =
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previous_slot_state_root
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# Cache latest block header state root
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if state.data.latest_block_header.state_root == ZERO_HASH:
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state.data.latest_block_header.state_root = previous_slot_state_root
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# Cache block root
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state.data.block_roots[state.data.slot mod SLOTS_PER_HISTORICAL_ROOT] =
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hash_tree_root(state.data.latest_block_header)
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func clear_epoch_from_cache(cache: var StateCache, epoch: Epoch) =
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cache.shuffled_active_validator_indices.del epoch
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let
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start_slot = epoch.compute_start_slot_at_epoch
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end_slot = (epoch + 1).compute_start_slot_at_epoch
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for i in start_slot ..< end_slot:
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cache.beacon_proposer_indices.del i
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# https://github.com/ethereum/eth2.0-specs/blob/v0.12.2/specs/phase0/beacon-chain.md#beacon-chain-state-transition-function
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proc advance_slot*(
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state: var HashedBeaconState, updateFlags: UpdateFlags,
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epochCache: var StateCache) {.nbench.} =
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# Special case version of process_slots that moves one slot at a time - can
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# run faster if the state root is known already (for example when replaying
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# existing slots)
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process_slot(state)
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let is_epoch_transition = (state.data.slot + 1).isEpoch
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if is_epoch_transition:
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# Note: Genesis epoch = 0, no need to test if before Genesis
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beacon_previous_validators.set(get_epoch_validator_count(state.data))
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process_epoch(state.data, updateFlags, epochCache)
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clear_epoch_from_cache(
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epochCache, (state.data.slot + 1).compute_epoch_at_slot)
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state.data.slot += 1
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if is_epoch_transition:
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beacon_current_validators.set(get_epoch_validator_count(state.data))
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state.root = hash_tree_root(state.data)
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# https://github.com/ethereum/eth2.0-specs/blob/v0.12.2/specs/phase0/beacon-chain.md#beacon-chain-state-transition-function
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proc process_slots*(state: var HashedBeaconState, slot: Slot,
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cache: var StateCache, updateFlags: UpdateFlags = {}): bool {.nbench.} =
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# TODO this function is not _really_ necessary: when replaying states, we
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# advance slots one by one before calling `state_transition` - this way,
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# we avoid the state root calculation - as such, instead of advancing
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# slots "automatically" in `state_transition`, perhaps it would be better
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# to keep a pre-condition that state must be at the right slot already?
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if not (state.data.slot < slot):
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if slotProcessed notin updateFlags or state.data.slot != slot:
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notice(
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"Unusual request for a slot in the past",
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state_root = shortLog(state.root),
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current_slot = state.data.slot,
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target_slot = slot
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)
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return false
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# Catch up to the target slot
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while state.data.slot < slot:
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advance_slot(state, updateFlags, cache)
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true
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proc noRollback*(state: var HashedBeaconState) =
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trace "Skipping rollback of broken state"
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proc state_transition*(
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preset: RuntimePreset,
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state: var HashedBeaconState, signedBlock: SomeSignedBeaconBlock,
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# TODO this is ... okay, but not perfect; align with EpochRef
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stateCache: var StateCache,
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flags: UpdateFlags, rollback: RollbackHashedProc): bool {.nbench.} =
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## Time in the beacon chain moves by slots. Every time (haha.) that happens,
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## we will update the beacon state. Normally, the state updates will be driven
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## by the contents of a new block, but it may happen that the block goes
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## missing - the state updates happen regardless.
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##
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## The flags are used to specify that certain validations should be skipped
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## for the new block. This is done during block proposal, to create a state
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## whose hash can be included in the new block.
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##
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## `rollback` is called if the transition fails and the given state has been
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## partially changed. If a temporary state was given to `state_transition`,
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## it is safe to use `noRollback` and leave it broken, else the state
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## object should be rolled back to a consistent state. If the transition fails
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## before the state has been updated, `rollback` will not be called.
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doAssert not rollback.isNil, "use noRollback if it's ok to mess up state"
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# This only fails if it hasn't changed stateCache, so it can't create a false
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# not-followed future history in stateCache.
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if not process_slots(state, signedBlock.message.slot, stateCache, flags):
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rollback(state)
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return false
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# Block updates - these happen when there's a new block being suggested
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# by the block proposer. Every actor in the network will update its state
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# according to the contents of this block - but first they will validate
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# that the block is sane.
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if skipBLSValidation in flags or
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verify_block_signature(state.data, signedBlock):
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# TODO after checking scaffolding, remove this
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trace "state_transition: processing block, signature passed",
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signature = shortLog(signedBlock.signature),
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blockRoot = shortLog(signedBlock.root)
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if process_block(preset, state.data, signedBlock.message, flags, stateCache):
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if skipStateRootValidation in flags or verifyStateRoot(state.data, signedBlock.message):
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# State root is what it should be - we're done!
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# TODO when creating a new block, state_root is not yet set.. comparing
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# with zero hash here is a bit fragile however, but this whole thing
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# should go away with proper hash caching
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# TODO shouldn't ever have to recalculate; verifyStateRoot() does it
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state.root =
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if signedBlock.message.state_root == Eth2Digest(): hash_tree_root(state.data)
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else: signedBlock.message.state_root
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return true
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# Block processing failed, roll back changes
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rollback(state)
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false
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proc state_transition*(
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preset: RuntimePreset,
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state: var HashedBeaconState, signedBlock: SomeSignedBeaconBlock,
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flags: UpdateFlags, rollback: RollbackHashedProc): bool {.nbench.} =
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# TODO consider moving this to testutils or similar, since non-testing
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# and fuzzing code should always be coming from block pool which should
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# always be providing cache or equivalent
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var cache = StateCache()
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state_transition(preset, state, signedBlock, cache, flags, rollback)
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# https://github.com/ethereum/eth2.0-specs/blob/v0.12.2/specs/phase0/validator.md#preparing-for-a-beaconblock
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# TODO There's more to do here - the spec has helpers that deal set up some of
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# the fields in here!
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proc makeBeaconBlock*(
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preset: RuntimePreset,
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state: var HashedBeaconState,
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proposer_index: ValidatorIndex,
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parent_root: Eth2Digest,
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randao_reveal: ValidatorSig,
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eth1_data: Eth1Data,
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graffiti: GraffitiBytes,
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attestations: seq[Attestation],
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deposits: seq[Deposit],
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rollback: RollbackHashedProc,
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cache: var StateCache): Option[BeaconBlock] =
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## Create a block for the given state. The last block applied to it must be
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## the one identified by parent_root and process_slots must be called up to
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## the slot for which a block is to be created.
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# To create a block, we'll first apply a partial block to the state, skipping
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# some validations.
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var blck = BeaconBlock(
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slot: state.data.slot,
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proposer_index: proposer_index.uint64,
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parent_root: parent_root,
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body: BeaconBlockBody(
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randao_reveal: randao_reveal,
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eth1_data: eth1data,
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graffiti: graffiti,
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attestations: List[Attestation, Limit MAX_ATTESTATIONS](attestations),
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deposits: List[Deposit, Limit MAX_DEPOSITS](deposits)))
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let ok = process_block(preset, state.data, blck, {skipBlsValidation}, cache)
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if not ok:
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warn "Unable to apply new block to state", blck = shortLog(blck)
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rollback(state)
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return
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state.root = hash_tree_root(state.data)
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blck.state_root = state.root
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some(blck)
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