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Merge pull request #3185 from ethereum/fc-is_data_available
Move `is_data_available` check to fork-choice `on_block`
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| Original file line number | Diff line number | Diff line change |
|---|---|---|
| @@ -0,0 +1,137 @@ | ||
| # EIP-4844 -- Fork Choice | ||
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| ## Table of contents | ||
| <!-- TOC --> | ||
| <!-- START doctoc generated TOC please keep comment here to allow auto update --> | ||
| <!-- DON'T EDIT THIS SECTION, INSTEAD RE-RUN doctoc TO UPDATE --> | ||
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| - [Introduction](#introduction) | ||
| - [Containers](#containers) | ||
| - [`BlobsSidecar`](#blobssidecar) | ||
| - [Helpers](#helpers) | ||
| - [`validate_blobs_sidecar`](#validate_blobs_sidecar) | ||
| - [`is_data_available`](#is_data_available) | ||
| - [Updated fork-choice handlers](#updated-fork-choice-handlers) | ||
| - [`on_block`](#on_block) | ||
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| <!-- END doctoc generated TOC please keep comment here to allow auto update --> | ||
| <!-- /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 | ||
| class BlobsSidecar(Container): | ||
| beacon_block_root: Root | ||
| beacon_block_slot: Slot | ||
| blobs: List[Blob, MAX_BLOBS_PER_BLOCK] | ||
| kzg_aggregated_proof: KZGProof | ||
| ``` | ||
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| ## Helpers | ||
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| #### `validate_blobs_sidecar` | ||
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| ```python | ||
| def validate_blobs_sidecar(slot: Slot, | ||
| beacon_block_root: Root, | ||
| expected_kzg_commitments: Sequence[KZGCommitment], | ||
| blobs_sidecar: BlobsSidecar) -> None: | ||
| assert slot == blobs_sidecar.beacon_block_slot | ||
| assert beacon_block_root == blobs_sidecar.beacon_block_root | ||
| blobs = blobs_sidecar.blobs | ||
| kzg_aggregated_proof = blobs_sidecar.kzg_aggregated_proof | ||
| 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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| #### `is_data_available` | ||
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| The implementation of `is_data_available` will become more sophisticated during later scaling upgrades. | ||
| Initially, verification requires every verifying actor to retrieve the matching `BlobsSidecar`, | ||
| 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 | ||
| def is_data_available(slot: Slot, beacon_block_root: Root, blob_kzg_commitments: Sequence[KZGCommitment]) -> bool: | ||
| # `retrieve_blobs_sidecar` is implementation and context dependent, raises an exception if not available. | ||
| # Note: the p2p network does not guarantee sidecar retrieval outside of `MIN_EPOCHS_FOR_BLOBS_SIDECARS_REQUESTS` | ||
| sidecar = retrieve_blobs_sidecar(slot, beacon_block_root) | ||
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| # For testing, `retrieve_blobs_sidecar` returns "TEST". | ||
| # TODO: Remove it once we have a way to inject `BlobsSidecar` into tests. | ||
| if isinstance(sidecar, str): | ||
| return True | ||
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| validate_blobs_sidecar(slot, beacon_block_root, blob_kzg_commitments, sidecar) | ||
| return True | ||
| ``` | ||
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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 | ||
| 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 | ||
| pre_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 | ||
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| # 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 | ||
| assert get_ancestor(store, block.parent_root, finalized_slot) == store.finalized_checkpoint.root | ||
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| # [New in EIP-4844] | ||
| # Check if blob data is available | ||
| # If not, this block MAY be queued and subsequently considered when blob data becomes available | ||
| 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 | ||
| state = pre_state.copy() | ||
| state_transition(state, signed_block, True) | ||
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| # Check the merge transition | ||
| if is_merge_transition_block(pre_state, block.body): | ||
| validate_merge_block(block) | ||
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| # Add new block to the store | ||
| store.blocks[hash_tree_root(block)] = block | ||
| # Add new state for this block to the store | ||
| store.block_states[hash_tree_root(block)] = state | ||
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| # Add proposer score boost if the block is timely | ||
| time_into_slot = (store.time - store.genesis_time) % SECONDS_PER_SLOT | ||
| is_before_attesting_interval = time_into_slot < SECONDS_PER_SLOT // INTERVALS_PER_SLOT | ||
| if get_current_slot(store) == block.slot and is_before_attesting_interval: | ||
| store.proposer_boost_root = hash_tree_root(block) | ||
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| # Update justified checkpoint | ||
| if state.current_justified_checkpoint.epoch > store.justified_checkpoint.epoch: | ||
| if state.current_justified_checkpoint.epoch > store.best_justified_checkpoint.epoch: | ||
| store.best_justified_checkpoint = state.current_justified_checkpoint | ||
| if should_update_justified_checkpoint(store, state.current_justified_checkpoint): | ||
| store.justified_checkpoint = state.current_justified_checkpoint | ||
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| # Update finalized checkpoint | ||
| if state.finalized_checkpoint.epoch > store.finalized_checkpoint.epoch: | ||
| store.finalized_checkpoint = state.finalized_checkpoint | ||
| store.justified_checkpoint = state.current_justified_checkpoint | ||
| ``` |
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