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EIP4844 Light Client -- Fork Logic

Table of contents

Introduction

This document describes how to upgrade existing light client objects based on the Capella specification to EIP4844. This is necessary when processing pre-EIP4844 data with a post-EIP4844 LightClientStore. Note that the data being exchanged over the network protocols uses the original format.

Upgrading light client data

A EIP4844 LightClientStore can still process earlier light client data. In order to do so, that pre-EIP4844 data needs to be locally upgraded to EIP4844 before processing.

def upgrade_lc_header_to_eip4844(pre: capella.LightClientHeader) -> LightClientHeader:
    return LightClientHeader(
        beacon=pre.beacon,
        execution=ExecutionPayloadHeader(
            parent_hash=pre.execution.parent_hash,
            fee_recipient=pre.execution.fee_recipient,
            state_root=pre.execution.state_root,
            receipts_root=pre.execution.receipts_root,
            logs_bloom=pre.execution.logs_bloom,
            prev_randao=pre.execution.prev_randao,
            block_number=pre.execution.block_number,
            gas_limit=pre.execution.gas_limit,
            gas_used=pre.execution.gas_used,
            timestamp=pre.execution.timestamp,
            extra_data=pre.execution.extra_data,
            base_fee_per_gas=pre.execution.base_fee_per_gas,
            block_hash=pre.execution.block_hash,
            transactions_root=pre.execution.transactions_root,
            withdrawals_root=pre.execution.withdrawals_root,
        ),
        execution_branch=pre.execution_branch,
    )
def upgrade_lc_bootstrap_to_eip4844(pre: capella.LightClientBootstrap) -> LightClientBootstrap:
    return LightClientBootstrap(
        header=upgrade_lc_header_to_eip4844(pre.header),
        current_sync_committee=pre.current_sync_committee,
        current_sync_committee_branch=pre.current_sync_committee_branch,
    )
def upgrade_lc_update_to_eip4844(pre: capella.LightClientUpdate) -> LightClientUpdate:
    return LightClientUpdate(
        attested_header=upgrade_lc_header_to_eip4844(pre.attested_header),
        next_sync_committee=pre.next_sync_committee,
        next_sync_committee_branch=pre.next_sync_committee_branch,
        finalized_header=upgrade_lc_header_to_eip4844(pre.finalized_header),
        finality_branch=pre.finality_branch,
        sync_aggregate=pre.sync_aggregate,
        signature_slot=pre.signature_slot,
    )
def upgrade_lc_finality_update_to_eip4844(pre: capella.LightClientFinalityUpdate) -> LightClientFinalityUpdate:
    return LightClientFinalityUpdate(
        attested_header=upgrade_lc_header_to_eip4844(pre.attested_header),
        finalized_header=upgrade_lc_header_to_eip4844(pre.finalized_header),
        finality_branch=pre.finality_branch,
        sync_aggregate=pre.sync_aggregate,
        signature_slot=pre.signature_slot,
    )
def upgrade_lc_optimistic_update_to_eip4844(pre: capella.LightClientOptimisticUpdate) -> LightClientOptimisticUpdate:
    return LightClientOptimisticUpdate(
        attested_header=upgrade_lc_header_to_eip4844(pre.attested_header),
        sync_aggregate=pre.sync_aggregate,
        signature_slot=pre.signature_slot,
    )

Upgrading the store

Existing LightClientStore objects based on Capella MUST be upgraded to EIP4844 before EIP4844 based light client data can be processed. The LightClientStore upgrade MAY be performed before EIP4844_FORK_EPOCH.

def upgrade_lc_store_to_eip4844(pre: capella.LightClientStore) -> LightClientStore:
    if pre.best_valid_update is None:
        best_valid_update = None
    else:
        best_valid_update = upgrade_lc_update_to_eip4844(pre.best_valid_update)
    return LightClientStore(
        finalized_header=upgrade_lc_header_to_eip4844(pre.finalized_header),
        current_sync_committee=pre.current_sync_committee,
        next_sync_committee=pre.next_sync_committee,
        best_valid_update=best_valid_update,
        optimistic_header=upgrade_lc_header_to_eip4844(pre.optimistic_header),
        previous_max_active_participants=pre.previous_max_active_participants,
        current_max_active_participants=pre.current_max_active_participants,
    )