eth2.0-specs/specs/deneb/light-client/fork.md

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# Deneb Light Client -- Fork Logic
## Table of contents
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- [Introduction](#introduction)
- [Upgrading light client data](#upgrading-light-client-data)
- [Upgrading the store](#upgrading-the-store)
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## Introduction
This document describes how to upgrade existing light client objects based on the [Capella specification](../../capella/light-client/sync-protocol.md) to Deneb. This is necessary when processing pre-Deneb data with a post-Deneb `LightClientStore`. Note that the data being exchanged over the network protocols uses the original format.
## Upgrading light client data
A Deneb `LightClientStore` can still process earlier light client data. In order to do so, that pre-Deneb data needs to be locally upgraded to Deneb before processing.
```python
def upgrade_lc_header_to_deneb(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,
blob_gas_used=uint64(0), # [New in Deneb:EIP4844]
excess_blob_gas=uint64(0), # [New in Deneb:EIP4844]
),
execution_branch=pre.execution_branch,
)
```
```python
def upgrade_lc_bootstrap_to_deneb(pre: capella.LightClientBootstrap) -> LightClientBootstrap:
return LightClientBootstrap(
header=upgrade_lc_header_to_deneb(pre.header),
current_sync_committee=pre.current_sync_committee,
current_sync_committee_branch=pre.current_sync_committee_branch,
)
```
```python
def upgrade_lc_update_to_deneb(pre: capella.LightClientUpdate) -> LightClientUpdate:
return LightClientUpdate(
attested_header=upgrade_lc_header_to_deneb(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_deneb(pre.finalized_header),
finality_branch=pre.finality_branch,
sync_aggregate=pre.sync_aggregate,
signature_slot=pre.signature_slot,
)
```
```python
def upgrade_lc_finality_update_to_deneb(pre: capella.LightClientFinalityUpdate) -> LightClientFinalityUpdate:
return LightClientFinalityUpdate(
attested_header=upgrade_lc_header_to_deneb(pre.attested_header),
finalized_header=upgrade_lc_header_to_deneb(pre.finalized_header),
finality_branch=pre.finality_branch,
sync_aggregate=pre.sync_aggregate,
signature_slot=pre.signature_slot,
)
```
```python
def upgrade_lc_optimistic_update_to_deneb(pre: capella.LightClientOptimisticUpdate) -> LightClientOptimisticUpdate:
return LightClientOptimisticUpdate(
attested_header=upgrade_lc_header_to_deneb(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 Deneb before Deneb based light client data can be processed. The `LightClientStore` upgrade MAY be performed before `DENEB_FORK_EPOCH`.
```python
def upgrade_lc_store_to_deneb(pre: capella.LightClientStore) -> LightClientStore:
if pre.best_valid_update is None:
best_valid_update = None
else:
best_valid_update = upgrade_lc_update_to_deneb(pre.best_valid_update)
return LightClientStore(
finalized_header=upgrade_lc_header_to_deneb(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_deneb(pre.optimistic_header),
previous_max_active_participants=pre.previous_max_active_participants,
current_max_active_participants=pre.current_max_active_participants,
)
```