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The Merge -- Honest Validator
Notice: This document is a work-in-progress for researchers and implementers.
Table of contents
Introduction
This document represents the changes to be made in the code of an "honest validator" to implement executable beacon chain proposal.
Prerequisites
This document is an extension of the Altair -- Honest Validator guide. All behaviors and definitions defined in this document, and documents it extends, carry over unless explicitly noted or overridden.
All terminology, constants, functions, and protocol mechanics defined in the updated Beacon Chain doc of The Merge are requisite for this document and used throughout. Please see related Beacon Chain doc before continuing and use them as a reference throughout.
Protocols
ExecutionEngine
The following methods are added to the ExecutionEngine protocol for use as a validator:
assemble_block
Produces a new instance of an execution payload, with the specified timestamp,
on top of the execution payload chain tip identified by block_hash.
The body of this function is implementation dependent. The Consensus API may be used to implement this with an external execution engine.
def assemble_block(self: ExecutionEngine, block_hash: Hash32, timestamp: uint64, random: Bytes32) -> ExecutionPayload:
...
Beacon chain responsibilities
All validator responsibilities remain unchanged other than those noted below. Namely, the transition block handling and the addition of ExecutionPayload.
Block proposal
Constructing the BeaconBlockBody
Execution Payload
- Set
block.body.execution_payload = get_execution_payload(state, execution_engine, pow_chain)where:
def get_pow_block_at_total_difficulty(total_difficulty: uint256, pow_chain: Sequence[PowBlock]) -> Optional[PowBlock]:
# `pow_chain` abstractly represents all blocks in the PoW chain
for block in pow_chain:
parent = get_pow_block(block.parent_hash)
if block.total_difficulty >= total_difficulty and parent.total_difficulty < total_difficulty:
return block
return None
def produce_execution_payload(state: BeaconState,
parent_hash: Hash32,
execution_engine: ExecutionEngine) -> ExecutionPayload:
timestamp = compute_timestamp_at_slot(state, state.slot)
randao_mix = get_randao_mix(state, get_current_epoch(state))
return execution_engine.assemble_block(parent_hash, timestamp, randao_mix)
def get_execution_payload(state: BeaconState,
execution_engine: ExecutionEngine,
pow_chain: Sequence[PowBlock]) -> ExecutionPayload:
if not is_merge_complete(state):
terminal_pow_block = get_pow_block_at_total_difficulty(TERMINAL_TOTAL_DIFFICULTY, pow_chain)
if terminal_pow_block is None:
# Pre-merge, empty payload
return ExecutionPayload()
else:
# Signify merge via producing on top of the last PoW block
return produce_execution_payload(state, terminal_pow_block.block_hash, execution_engine)
# Post-merge, normal payload
parent_hash = state.latest_execution_payload_header.block_hash
return produce_execution_payload(state, parent_hash, execution_engine)