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Fulu -- Fork Choice

Introduction

This is the modification of the fork choice accompanying Fulu.

Helpers

Modified is_data_available

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def is_data_available(beacon_block_root: Root) -> bool:
    # `retrieve_column_sidecars` is implementation and context dependent, replacing
    # `retrieve_blobs_and_proofs`. For the given block root, it returns all column
    # sidecars to sample, or raises an exception if they are not available.
    # The p2p network does not guarantee sidecar retrieval outside of
    # `MIN_EPOCHS_FOR_DATA_COLUMN_SIDECARS_REQUESTS` epochs.
    column_sidecars = retrieve_column_sidecars(beacon_block_root)
    return all(
        verify_data_column_sidecar(column_sidecar)
        and verify_data_column_sidecar_kzg_proofs(column_sidecar)
        for column_sidecar in column_sidecars
    )

Handlers

Modified on_block

Note: The only modification is that is_data_available does not take blob_kzg_commitments as input.

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def on_block(store: Store, signed_block: SignedBeaconBlock) -> None:
    """
    Run ``on_block`` upon receiving a new block.
    """
    block = signed_block.message
    # Parent block must be known
    assert block.parent_root in store.block_states
    # Make a copy of the state to avoid mutability issues
    state = copy(store.block_states[block.parent_root])
    # Blocks cannot be in the future. If they are, their consideration must be delayed until they are in the past.
    assert get_current_slot(store) >= block.slot

    # Check that block is later than the finalized epoch slot (optimization to reduce calls to get_ancestor)
    finalized_slot = compute_start_slot_at_epoch(store.finalized_checkpoint.epoch)
    assert block.slot > finalized_slot
    # Check block is a descendant of the finalized block at the checkpoint finalized slot
    finalized_checkpoint_block = get_checkpoint_block(
        store,
        block.parent_root,
        store.finalized_checkpoint.epoch,
    )
    assert store.finalized_checkpoint.root == finalized_checkpoint_block

    # [Modified in Fulu:EIP7594]
    # Check if blob data is available
    # If not, this payload MAY be queued and subsequently considered when blob data becomes available
    assert is_data_available(hash_tree_root(block))

    # Check the block is valid and compute the post-state
    block_root = hash_tree_root(block)
    state_transition(state, signed_block, True)

    # Add new block to the store
    store.blocks[block_root] = block
    # Add new state for this block to the store
    store.block_states[block_root] = state

    record_block_timeliness(store, block_root)
    update_proposer_boost_root(store, block_root)

    # Update checkpoints in store if necessary
    update_checkpoints(store, state.current_justified_checkpoint, state.finalized_checkpoint)

    # Eagerly compute unrealized justification and finality.
    compute_pulled_up_tip(store, block_root)