eth2.0-specs/specs/capella/light-client/full-node.md

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# Capella Light Client -- Full Node
**Notice**: This document is a work-in-progress for researchers and implementers.
## Table of contents
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- [Introduction](#introduction)
- [Helper functions](#helper-functions)
- [Modified `block_to_light_client_header`](#modified-block_to_light_client_header)
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## Introduction
This upgrade adds information about the execution payload to light client data as part of the Capella upgrade.
## Helper functions
### Modified `block_to_light_client_header`
```python
def block_to_light_client_header(block: SignedBeaconBlock) -> LightClientHeader:
epoch = compute_epoch_at_slot(block.message.slot)
if epoch >= CAPELLA_FORK_EPOCH:
payload = block.message.body.execution_payload
execution_header = ExecutionPayloadHeader(
parent_hash=payload.parent_hash,
fee_recipient=payload.fee_recipient,
state_root=payload.state_root,
receipts_root=payload.receipts_root,
logs_bloom=payload.logs_bloom,
prev_randao=payload.prev_randao,
block_number=payload.block_number,
gas_limit=payload.gas_limit,
gas_used=payload.gas_used,
timestamp=payload.timestamp,
extra_data=payload.extra_data,
base_fee_per_gas=payload.base_fee_per_gas,
block_hash=payload.block_hash,
transactions_root=hash_tree_root(payload.transactions),
withdrawals_root=hash_tree_root(payload.withdrawals),
)
execution_branch = ExecutionBranch(
compute_merkle_proof(block.message.body, EXECUTION_PAYLOAD_GINDEX))
else:
# Note that during fork transitions, `finalized_header` may still point to earlier forks.
# While Bellatrix blocks also contain an `ExecutionPayload` (minus `withdrawals_root`),
# it was not included in the corresponding light client data. To ensure compatibility
# with legacy data going through `upgrade_lc_header_to_capella`, leave out execution data.
execution_header = ExecutionPayloadHeader()
execution_branch = ExecutionBranch()
return LightClientHeader(
beacon=BeaconBlockHeader(
slot=block.message.slot,
proposer_index=block.message.proposer_index,
parent_root=block.message.parent_root,
state_root=block.message.state_root,
body_root=hash_tree_root(block.message.body),
),
execution=execution_header,
execution_branch=execution_branch,
)
```