eth2.0-specs/specs/merge/validator.md

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
• Prerequisites
• Beacon chain responsibilities
  • Block proposal
    • Constructing the BeaconBlockBody
      • Application Payload
        • get_pow_chain_head
        • produce_application_payload

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.

Beacon chain responsibilities

All validator responsibilities remain unchanged other than those noted below. Namely, the transition block handling and the addition of ApplicationPayload.

Block proposal

Constructing the BeaconBlockBody

Application 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_application_payload

Let produce_application_payload(parent_hash: Bytes32) -> ApplicationPayload be the function that produces new instance of application payload. The body of this function is implementation dependent.

• Set block.body.application_payload = get_application_payload(state) where:

def get_application_payload(state: BeaconState) -> ApplicationPayload:
    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 ApplicationPayload()
        else:
            # Signify merge via producing on top of the last PoW block
            return produce_application_payload(pow_block.block_hash)

    # Post-merge, normal payload
    application_parent_hash = state.latest_application_block_header.block_hash
    return produce_application_payload(application_parent_hash)