127 lines
5.1 KiB
Markdown
127 lines
5.1 KiB
Markdown
# Deneb -- Fork Choice
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## Table of contents
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<!-- TOC -->
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<!-- START doctoc generated TOC please keep comment here to allow auto update -->
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<!-- DON'T EDIT THIS SECTION, INSTEAD RE-RUN doctoc TO UPDATE -->
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- [Introduction](#introduction)
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- [Containers](#containers)
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- [Helpers](#helpers)
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- [Extended `PayloadAttributes`](#extended-payloadattributes)
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- [`is_data_available`](#is_data_available)
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- [Updated fork-choice handlers](#updated-fork-choice-handlers)
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- [`on_block`](#on_block)
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<!-- END doctoc generated TOC please keep comment here to allow auto update -->
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<!-- /TOC -->
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## Introduction
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This is the modification of the fork choice accompanying the Deneb upgrade.
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## Containers
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## Helpers
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### Extended `PayloadAttributes`
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`PayloadAttributes` is extended with the parent beacon block root for EIP-4788.
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```python
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@dataclass
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class PayloadAttributes(object):
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timestamp: uint64
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prev_randao: Bytes32
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suggested_fee_recipient: ExecutionAddress
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withdrawals: Sequence[Withdrawal]
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parent_beacon_block_root: Root # [New in Deneb:EIP4788]
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```
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### `is_data_available`
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*[New in Deneb:EIP4844]*
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The implementation of `is_data_available` will become more sophisticated during later scaling upgrades.
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Initially, verification requires every verifying actor to retrieve all matching `Blob`s and `KZGProof`s, and validate them with `verify_blob_kzg_proof_batch`.
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The block MUST NOT be considered valid until all valid `Blob`s have been downloaded. Blocks that have been previously validated as available SHOULD be considered available even if the associated `Blob`s have subsequently been pruned.
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*Note*: Extraneous or invalid Blobs (in addition to KZG expected/referenced valid blobs) received on the p2p network MUST NOT invalidate a block that is otherwise valid and available.
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```python
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def is_data_available(beacon_block_root: Root, blob_kzg_commitments: Sequence[KZGCommitment]) -> bool:
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# `retrieve_blobs_and_proofs` is implementation and context dependent
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# It returns all the blobs for the given block root, and raises an exception if not available
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# Note: the p2p network does not guarantee sidecar retrieval outside of
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# `MIN_EPOCHS_FOR_BLOB_SIDECARS_REQUESTS`
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blobs, proofs = retrieve_blobs_and_proofs(beacon_block_root)
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return verify_blob_kzg_proof_batch(blobs, blob_kzg_commitments, proofs)
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```
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## Updated fork-choice handlers
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### `on_block`
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*Note*: The only modification is the addition of the blob data availability check.
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```python
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def on_block(store: Store, signed_block: SignedBeaconBlock) -> None:
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"""
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Run ``on_block`` upon receiving a new block.
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"""
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block = signed_block.message
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# Parent block must be known
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assert block.parent_root in store.block_states
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# Make a copy of the state to avoid mutability issues
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pre_state = copy(store.block_states[block.parent_root])
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# Blocks cannot be in the future. If they are, their consideration must be delayed until they are in the past.
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assert get_current_slot(store) >= block.slot
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# Check that block is later than the finalized epoch slot (optimization to reduce calls to get_ancestor)
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finalized_slot = compute_start_slot_at_epoch(store.finalized_checkpoint.epoch)
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assert block.slot > finalized_slot
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# Check block is a descendant of the finalized block at the checkpoint finalized slot
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finalized_checkpoint_block = get_checkpoint_block(
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store,
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block.parent_root,
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store.finalized_checkpoint.epoch,
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)
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assert store.finalized_checkpoint.root == finalized_checkpoint_block
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# [New in Deneb:EIP4844]
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# Check if blob data is available
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# If not, this block MAY be queued and subsequently considered when blob data becomes available
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# *Note*: Extraneous or invalid Blobs (in addition to the expected/referenced valid blobs)
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# received on the p2p network MUST NOT invalidate a block that is otherwise valid and available
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assert is_data_available(hash_tree_root(block), block.body.blob_kzg_commitments)
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# Check the block is valid and compute the post-state
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state = pre_state.copy()
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block_root = hash_tree_root(block)
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state_transition(state, signed_block, True)
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# Add new block to the store
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store.blocks[block_root] = block
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# Add new state for this block to the store
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store.block_states[block_root] = state
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# Add block timeliness to the store
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time_into_slot = (store.time - store.genesis_time) % SECONDS_PER_SLOT
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is_before_attesting_interval = time_into_slot < SECONDS_PER_SLOT // INTERVALS_PER_SLOT
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is_timely = get_current_slot(store) == block.slot and is_before_attesting_interval
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store.block_timeliness[hash_tree_root(block)] = is_timely
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# Add proposer score boost if the block is timely and not conflicting with an existing block
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is_first_block = store.proposer_boost_root == Root()
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if is_timely and is_first_block:
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store.proposer_boost_root = hash_tree_root(block)
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# Update checkpoints in store if necessary
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update_checkpoints(store, state.current_justified_checkpoint, state.finalized_checkpoint)
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# Eagerly compute unrealized justification and finality.
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compute_pulled_up_tip(store, block_root)
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```
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