138 lines
5.6 KiB
Markdown
138 lines
5.6 KiB
Markdown
# EIP-4844 -- 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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- [`BlobsSidecar`](#blobssidecar)
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- [Helpers](#helpers)
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- [`validate_blobs_sidecar`](#validate_blobs_sidecar)
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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 EIP-4844 upgrade.
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## Containers
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### `BlobsSidecar`
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```python
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class BlobsSidecar(Container):
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beacon_block_root: Root
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beacon_block_slot: Slot
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blobs: List[Blob, MAX_BLOBS_PER_BLOCK]
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kzg_aggregated_proof: KZGProof
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```
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## Helpers
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#### `validate_blobs_sidecar`
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```python
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def validate_blobs_sidecar(slot: Slot,
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beacon_block_root: Root,
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expected_kzg_commitments: Sequence[KZGCommitment],
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blobs_sidecar: BlobsSidecar) -> None:
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assert slot == blobs_sidecar.beacon_block_slot
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assert beacon_block_root == blobs_sidecar.beacon_block_root
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blobs = blobs_sidecar.blobs
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kzg_aggregated_proof = blobs_sidecar.kzg_aggregated_proof
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assert len(expected_kzg_commitments) == len(blobs)
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assert verify_aggregate_kzg_proof(blobs, expected_kzg_commitments, kzg_aggregated_proof)
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```
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#### `is_data_available`
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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 the matching `BlobsSidecar`,
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and validate the sidecar with `validate_blobs_sidecar`.
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The block MUST NOT be considered valid until a valid `BlobsSidecar` has been downloaded. Blocks that have been previously validated as available SHOULD be considered available even if the associated `BlobsSidecar` has subsequently been pruned.
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```python
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def is_data_available(slot: Slot, beacon_block_root: Root, blob_kzg_commitments: Sequence[KZGCommitment]) -> bool:
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# `retrieve_blobs_sidecar` is implementation and context dependent, raises an exception if not available.
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# Note: the p2p network does not guarantee sidecar retrieval outside of `MIN_EPOCHS_FOR_BLOBS_SIDECARS_REQUESTS`
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sidecar = retrieve_blobs_sidecar(slot, beacon_block_root)
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# For testing, `retrieve_blobs_sidecar` returns "TEST".
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# TODO: Remove it once we have a way to inject `BlobsSidecar` into tests.
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if isinstance(sidecar, str):
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return True
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validate_blobs_sidecar(slot, beacon_block_root, blob_kzg_commitments, sidecar)
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return True
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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 verification of transition block conditions.
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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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assert get_ancestor(store, block.parent_root, finalized_slot) == store.finalized_checkpoint.root
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# [New in EIP-4844]
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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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assert is_data_available(block.slot, 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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state_transition(state, signed_block, True)
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# Check the merge transition
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if is_merge_transition_block(pre_state, block.body):
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validate_merge_block(block)
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# Add new block to the store
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store.blocks[hash_tree_root(block)] = block
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# Add new state for this block to the store
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store.block_states[hash_tree_root(block)] = state
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# Add proposer score boost if the block is timely
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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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if get_current_slot(store) == block.slot and is_before_attesting_interval:
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store.proposer_boost_root = hash_tree_root(block)
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# Update justified checkpoint
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if state.current_justified_checkpoint.epoch > store.justified_checkpoint.epoch:
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if state.current_justified_checkpoint.epoch > store.best_justified_checkpoint.epoch:
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store.best_justified_checkpoint = state.current_justified_checkpoint
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if should_update_justified_checkpoint(store, state.current_justified_checkpoint):
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store.justified_checkpoint = state.current_justified_checkpoint
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# Update finalized checkpoint
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if state.finalized_checkpoint.epoch > store.finalized_checkpoint.epoch:
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store.finalized_checkpoint = state.finalized_checkpoint
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store.justified_checkpoint = state.current_justified_checkpoint
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```
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