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Ethereum 2.0 The Merge
Warning: This document is currently based on Phase 0 but will be rebased to Altair once the latter is shipped.
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 Phase 0 -- Validator. All behaviors and definitions defined in the Phase 0 doc 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) -> 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
get_pow_chain_head
Let get_pow_chain_head() -> PowBlock be the function that returns the head of the PoW chain. The body of the function is implementation specific.
produce_execution_payload
Let produce_execution_payload(parent_hash: Hash32, timestamp: uint64) -> ExecutionPayload be the function that produces new instance of execution payload.
The ExecutionEngine protocol is used for the implementation specific part of execution payload proposals.
- Set
block.body.execution_payload = get_execution_payload(state)where:
def get_execution_payload(state: BeaconState, execution_engine: ExecutionEngine) -> ExecutionPayload:
if not is_transition_completed(state):
pow_block = get_pow_chain_head()
if not is_valid_transition_block(pow_block):
# Pre-merge, empty payload
return ExecutionPayload()
else:
# Signify merge via producing on top of the last PoW block
timestamp = compute_time_at_slot(state, state.slot)
return execution_engine.assemble_block(pow_block.block_hash, timestamp)
# Post-merge, normal payload
execution_parent_hash = state.latest_execution_payload_header.block_hash
timestamp = compute_time_at_slot(state, state.slot)
return execution_engine.assemble_block(execution_parent_hash, timestamp)