310 lines
13 KiB
Nim
310 lines
13 KiB
Nim
# beacon_chain
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# Copyright (c) 2018-2021 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 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:
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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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# * 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 unless
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# motivated by security or performance considerations
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#
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# Performance notes:
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# * The state transition is used in two contexts: to verify that incoming blocks
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# are correct and to replay existing blocks from database. Incoming blocks
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# are processed one-by-one while replay happens multiple blocks at a time.
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# * Although signature verification is the slowest operation in the state
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# state transition, we skip it during replay - this is also when we repeatedly
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# call the state transition, making the non-signature part of the code
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# important from a performance point of view.
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# * It's important to start with a prefilled cache - generating the shuffled
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# list of active validators is generally very slow.
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# * Throughout, the code is affected by inefficient for loop codegen, meaning
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# that we have to iterate over indices and pick out the value manually:
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# https://github.com/nim-lang/Nim/issues/14421
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# * Throughout, we're affected by inefficient `let` borrowing, meaning we
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# often have to take the address of a sequence item due to the above - look
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# for `let ... = unsafeAddr sequence[idx]`
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# * Throughout, we're affected by the overloading rules that prefer a `var`
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# overload to a non-var overload - look for `asSeq()` - when the `var`
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# overload is used, the hash tree cache is cleared, which, aside from being
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# slow itself, causes additional processing to recalculate the merkle tree.
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{.push raises: [Defect].}
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import
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std/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-specs/blob/v1.0.1/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/v1.0.1/specs/phase0/beacon-chain.md#beacon-chain-state-transition-function
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proc verifyStateRoot(state: BeaconState, blck: BeaconBlock or SigVerifiedBeaconBlock): 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, raises: [Defect].}
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# Hashed-state transition functions
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# ---------------------------------------------------------------
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# https://github.com/ethereum/eth2.0-specs/blob/v1.0.1/specs/phase0/beacon-chain.md#beacon-chain-state-transition-function
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func process_slot*(
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state: var BeaconState, pre_state_root: Eth2Digest) {.nbench.} =
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# `process_slot` is the first stage of per-slot processing - it is run for
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# every slot, including epoch slots - it does not however update the slot
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# number! `pre_state_root` refers to the state root of the incoming
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# state before any slot processing has been done.
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# Cache state root
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state.state_roots[state.slot mod SLOTS_PER_HISTORICAL_ROOT] = pre_state_root
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# Cache latest block header state root
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if state.latest_block_header.state_root == ZERO_HASH:
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state.latest_block_header.state_root = pre_state_root
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# Cache block root
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state.block_roots[state.slot mod SLOTS_PER_HISTORICAL_ROOT] =
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hash_tree_root(state.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/v1.0.1/specs/phase0/beacon-chain.md#beacon-chain-state-transition-function
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proc advance_slot(
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state: var BeaconState, previous_slot_state_root: Eth2Digest,
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flags: UpdateFlags, cache: var StateCache, rewards: var RewardInfo) {.nbench.} =
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# Do the per-slot and potentially the per-epoch processing, then bump the
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# slot number - we've now arrived at the slot state on top of which a block
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# optionally can be applied.
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process_slot(state, previous_slot_state_root)
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rewards.statuses.setLen(0)
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rewards.total_balances = TotalBalances()
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let is_epoch_transition = (state.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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process_epoch(state, flags, cache, rewards)
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clear_epoch_from_cache(cache, (state.slot + 1).compute_epoch_at_slot)
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state.slot += 1
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# https://github.com/ethereum/eth2.0-specs/blob/v1.0.1/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, rewards: var RewardInfo,
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flags: UpdateFlags = {}): bool {.nbench.} =
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## Process one or more slot transitions without blocks - if the slot transtion
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## passes an epoch boundary, epoch processing will run and `rewards` will be
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## updated, else it will be cleared
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if not (state.data.slot < slot):
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if slotProcessed notin flags 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.data, state.root, flags, cache, rewards)
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# The root must be updated on every slot update, or the next `process_slot`
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# will be incorrect
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state.root = hash_tree_root(state.data)
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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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cache: var StateCache, rewards: var RewardInfo, flags: UpdateFlags,
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rollback: RollbackHashedProc): bool {.nbench.} =
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## Apply a block to the state, advancing the slot counter as necessary. The
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## given state must be of a lower slot, or, in case the `slotProcessed` flag
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## is set, can be the slot state of the same slot as the block (where the
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## slot state is the state without any block applied). To create a slot state,
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## advance the state corresponding to the the parent block using
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## `process_slots`.
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##
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## To run the state transition function in preparation for block production,
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## use `makeBeaconBlock` instead.
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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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let slot = signedBlock.message.slot
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if not (state.data.slot < slot):
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if slotProcessed notin flags or state.data.slot != slot:
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notice "State must precede block",
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state_root = shortLog(state.root),
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current_slot = state.data.slot,
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blck = shortLog(signedBlock)
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return false
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# Update the state so its slot matches that of the block
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while state.data.slot < slot:
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advance_slot(state.data, state.root, flags, cache, rewards)
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if state.data.slot < slot:
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# Don't update state root for the slot of the block
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state.root = hash_tree_root(state.data)
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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 not (skipBLSValidation in flags or
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verify_block_signature(state.data, signedBlock)):
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rollback(state)
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return false
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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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let res = process_block(preset, state.data, signedBlock.message, flags, cache)
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if not res.isOk():
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debug "state_transition: process_block failed",
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blck = shortLog(signedBlock.message),
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slot = state.data.slot,
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eth1_deposit_index = state.data.eth1_deposit_index,
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deposit_root = shortLog(state.data.eth1_data.deposit_root),
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error = res.error
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rollback(state)
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return false
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if not (skipStateRootValidation in flags or
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verifyStateRoot(state.data, signedBlock.message)):
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rollback(state)
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return false
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# only blocks currently being produced have an empty state root - we use a
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# separate function for those
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doAssert signedBlock.message.state_root != Eth2Digest(),
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"see makeBeaconBlock for block production"
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state.root = signedBlock.message.state_root
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true
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# https://github.com/ethereum/eth2.0-specs/blob/v1.0.1/specs/phase0/validator.md#preparing-for-a-beaconblock
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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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proposerSlashings: seq[ProposerSlashing],
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attesterSlashings: seq[AttesterSlashing],
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voluntaryExits: seq[SignedVoluntaryExit],
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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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proposer_slashings: List[ProposerSlashing, Limit MAX_PROPOSER_SLASHINGS](
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proposerSlashings),
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attester_slashings: List[AttesterSlashing, Limit MAX_ATTESTER_SLASHINGS](
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attesterSlashings),
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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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voluntary_exits:
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List[SignedVoluntaryExit, Limit MAX_VOLUNTARY_EXITS](voluntaryExits)))
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let res = process_block(preset, state.data, blck, {skipBlsValidation}, cache)
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if res.isErr:
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warn "Unable to apply new block to state",
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blck = shortLog(blck),
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slot = state.data.slot,
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eth1_deposit_index = state.data.eth1_deposit_index,
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deposit_root = shortLog(state.data.eth1_data.deposit_root),
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error = res.error
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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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