112 lines
4.0 KiB
Markdown
112 lines
4.0 KiB
Markdown
# Ethereum 2.0 Phase 1 -- Beacon Chain 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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- [Updated data structures](#updated-data-structures)
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- [Extended `Store`](#extended-store)
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- [New data structures](#new-data-structures)
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- [`ShardLatestMessage`](#shardlatestmessage)
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- [`ShardStore`](#shardstore)
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- [Updated helpers](#updated-helpers)
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- [Updated `get_forkchoice_store`](#updated-get_forkchoice_store)
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- [Updated `update_latest_messages`](#updated-update_latest_messages)
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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 document is the beacon chain fork choice spec for part of Ethereum 2.0 Phase 1.
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### Updated data structures
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#### Extended `Store`
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```python
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@dataclass
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class Store(object):
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time: uint64
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genesis_time: uint64
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justified_checkpoint: Checkpoint
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finalized_checkpoint: Checkpoint
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best_justified_checkpoint: Checkpoint
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blocks: Dict[Root, BeaconBlock] = field(default_factory=dict)
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block_states: Dict[Root, BeaconState] = field(default_factory=dict)
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checkpoint_states: Dict[Checkpoint, BeaconState] = field(default_factory=dict)
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latest_messages: Dict[ValidatorIndex, LatestMessage] = field(default_factory=dict)
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shard_stores: Dict[Shard, ShardStore] = field(default_factory=dict)
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```
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### New data structures
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#### `ShardLatestMessage`
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```python
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@dataclass(eq=True, frozen=True)
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class ShardLatestMessage(object):
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epoch: Epoch
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root: Root
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```
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#### `ShardStore`
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```python
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@dataclass
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class ShardStore:
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shard: Shard
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signed_blocks: Dict[Root, SignedShardBlock] = field(default_factory=dict)
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block_states: Dict[Root, ShardState] = field(default_factory=dict)
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latest_messages: Dict[ValidatorIndex, ShardLatestMessage] = field(default_factory=dict)
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```
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### Updated helpers
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#### Updated `get_forkchoice_store`
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```python
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def get_forkchoice_store(anchor_state: BeaconState) -> Store:
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anchor_block_header = anchor_state.latest_block_header.copy()
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if anchor_block_header.state_root == Bytes32():
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anchor_block_header.state_root = hash_tree_root(anchor_state)
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anchor_root = hash_tree_root(anchor_block_header)
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anchor_epoch = get_current_epoch(anchor_state)
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justified_checkpoint = Checkpoint(epoch=anchor_epoch, root=anchor_root)
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finalized_checkpoint = Checkpoint(epoch=anchor_epoch, root=anchor_root)
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return Store(
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time=anchor_state.genesis_time + SECONDS_PER_SLOT * anchor_state.slot,
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genesis_time=anchor_state.genesis_time,
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justified_checkpoint=justified_checkpoint,
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finalized_checkpoint=finalized_checkpoint,
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best_justified_checkpoint=justified_checkpoint,
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blocks={anchor_root: anchor_block_header},
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block_states={anchor_root: anchor_state.copy()},
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checkpoint_states={justified_checkpoint: anchor_state.copy()},
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shard_stores={
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Shard(shard): get_forkchoice_shard_store(anchor_state, Shard(shard))
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for shard in range(get_active_shard_count(anchor_state))
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}
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)
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```
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#### Updated `update_latest_messages`
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```python
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def update_latest_messages(store: Store, attesting_indices: Sequence[ValidatorIndex], attestation: Attestation) -> None:
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target = attestation.data.target
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beacon_block_root = attestation.data.beacon_block_root
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# TODO: separate shard chain vote
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shard = attestation.data.shard
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for i in attesting_indices:
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if i not in store.latest_messages or target.epoch > store.latest_messages[i].epoch:
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store.latest_messages[i] = LatestMessage(epoch=target.epoch, root=beacon_block_root)
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shard_latest_message = ShardLatestMessage(epoch=target.epoch, root=attestation.data.shard_head_root)
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store.shard_stores[shard].latest_messages[i] = shard_latest_message
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```
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