123 lines
4.3 KiB
Markdown
123 lines
4.3 KiB
Markdown
# Capella -- Fork Choice
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**Notice**: This document is a work-in-progress for researchers and implementers.
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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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- [Custom types](#custom-types)
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- [Protocols](#protocols)
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- [`ExecutionEngine`](#executionengine)
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- [`notify_forkchoice_updated`](#notify_forkchoice_updated)
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- [Helpers](#helpers)
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- [Extended `PayloadAttributes`](#extended-payloadattributes)
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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 according to the Capella upgrade.
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Unless stated explicitly, all prior functionality from [Bellatrix](../bellatrix/fork-choice.md) is inherited.
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## Custom types
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## Protocols
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### `ExecutionEngine`
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*Note*: The `notify_forkchoice_updated` function is modified in the `ExecutionEngine` protocol at the Capella upgrade.
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#### `notify_forkchoice_updated`
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The only change made is to the `PayloadAttributes` container through the addition of `withdrawals`.
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Otherwise, `notify_forkchoice_updated` inherits all prior functionality.
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```python
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def notify_forkchoice_updated(self: ExecutionEngine,
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head_block_hash: Hash32,
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safe_block_hash: Hash32,
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finalized_block_hash: Hash32,
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payload_attributes: Optional[PayloadAttributes]) -> Optional[PayloadId]:
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...
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```
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## Helpers
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### Extended `PayloadAttributes`
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`PayloadAttributes` is extended with the `withdrawals` field.
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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] # [New in Capella]
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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 deletion of the verification of merge 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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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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# 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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