171 lines
6.6 KiB
Markdown
171 lines
6.6 KiB
Markdown
# Ethereum 2.0 The Merge
|
|
|
|
**Notice**: This document is a work-in-progress for researchers and implementers.
|
|
|
|
## 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 -->
|
|
|
|
- [Introduction](#introduction)
|
|
- [Protocols](#protocols)
|
|
- [`ExecutionEngine`](#executionengine)
|
|
- [`set_head`](#set_head)
|
|
- [`finalize_block`](#finalize_block)
|
|
- [Helpers](#helpers)
|
|
- [`TransitionStore`](#transitionstore)
|
|
- [`PowBlock`](#powblock)
|
|
- [`get_pow_block`](#get_pow_block)
|
|
- [`is_valid_terminal_pow_block`](#is_valid_terminal_pow_block)
|
|
- [Updated fork-choice handlers](#updated-fork-choice-handlers)
|
|
- [`on_block`](#on_block)
|
|
|
|
<!-- END doctoc generated TOC please keep comment here to allow auto update -->
|
|
<!-- /TOC -->
|
|
|
|
## Introduction
|
|
|
|
This is the modification of the fork choice according to the executable beacon chain proposal.
|
|
|
|
*Note*: It introduces the process of transition from the last PoW block to the first PoS block.
|
|
|
|
## Protocols
|
|
|
|
### `ExecutionEngine`
|
|
|
|
The following methods are added to the `ExecutionEngine` protocol for use in the fork choice:
|
|
|
|
#### `set_head`
|
|
|
|
Re-organizes the execution payload chain and corresponding state to make `block_hash` the head.
|
|
|
|
The body of this function is implementation dependent.
|
|
The Consensus API may be used to implement this with an external execution engine.
|
|
|
|
```python
|
|
def set_head(self: ExecutionEngine, block_hash: Hash32) -> bool:
|
|
"""
|
|
Returns True if the ``block_hash`` was successfully set as head of the execution payload chain.
|
|
"""
|
|
...
|
|
```
|
|
|
|
#### `finalize_block`
|
|
|
|
Applies finality to the execution state: it irreversibly persists the chain of all execution payloads
|
|
and corresponding state, up to and including `block_hash`.
|
|
|
|
The body of this function is implementation dependent.
|
|
The Consensus API may be used to implement this with an external execution engine.
|
|
|
|
```python
|
|
def finalize_block(self: ExecutionEngine, block_hash: Hash32) -> bool:
|
|
"""
|
|
Returns True if the data up to and including ``block_hash`` was successfully finalized.
|
|
"""
|
|
...
|
|
```
|
|
|
|
## Helpers
|
|
|
|
### `TransitionStore`
|
|
|
|
```python
|
|
@dataclass
|
|
class TransitionStore(object):
|
|
transition_total_difficulty: uint256
|
|
```
|
|
|
|
### `PowBlock`
|
|
|
|
```python
|
|
@dataclass
|
|
class PowBlock(object):
|
|
block_hash: Hash32
|
|
parent_hash: Hash32
|
|
is_processed: boolean
|
|
is_valid: boolean
|
|
total_difficulty: uint256
|
|
difficulty: uint256
|
|
```
|
|
|
|
### `get_pow_block`
|
|
|
|
Let `get_pow_block(block_hash: Hash32) -> PowBlock` be the function that given the hash of the PoW block returns its data.
|
|
|
|
*Note*: The `eth_getBlockByHash` JSON-RPC method does not distinguish invalid blocks from blocks that haven't been processed yet. Either extending this existing method or implementing a new one is required.
|
|
|
|
### `is_valid_terminal_pow_block`
|
|
|
|
Used by fork-choice handler, `on_block`.
|
|
|
|
```python
|
|
def is_valid_terminal_pow_block(transition_store: TransitionStore, block: PowBlock, parent: PowBlock) -> bool:
|
|
is_total_difficulty_reached = block.total_difficulty >= transition_store.transition_total_difficulty
|
|
is_parent_total_difficulty_valid = parent.total_difficulty < transition_store.transition_total_difficulty
|
|
return block.is_valid and is_total_difficulty_reached and is_parent_total_difficulty_valid
|
|
```
|
|
|
|
## Updated fork-choice handlers
|
|
|
|
### `on_block`
|
|
|
|
*Note*: The only modification is the addition of the verification of transition block conditions.
|
|
|
|
```python
|
|
def on_block(store: Store, signed_block: SignedBeaconBlock, transition_store: TransitionStore=None) -> None:
|
|
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 the are in the past.
|
|
assert get_current_slot(store) >= block.slot
|
|
|
|
# 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
|
|
|
|
# [New in Merge]
|
|
if (transition_store is not None) and is_merge_block(pre_state, block):
|
|
# Delay consideration of block until PoW block is processed by the PoW node
|
|
pow_block = get_pow_block(block.body.execution_payload.parent_hash)
|
|
pow_parent = get_pow_block(pow_block.parent_hash)
|
|
assert pow_block.is_processed
|
|
assert is_valid_terminal_pow_block(transition_store, pow_block, pow_parent)
|
|
|
|
# Check the block is valid and compute the post-state
|
|
state = pre_state.copy()
|
|
state_transition(state, signed_block, True)
|
|
# 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
|
|
|
|
# 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
|
|
|
|
# Update finalized checkpoint
|
|
if state.finalized_checkpoint.epoch > store.finalized_checkpoint.epoch:
|
|
store.finalized_checkpoint = state.finalized_checkpoint
|
|
|
|
# Potentially update justified if different from store
|
|
if store.justified_checkpoint != state.current_justified_checkpoint:
|
|
# Update justified if new justified is later than store justified
|
|
if state.current_justified_checkpoint.epoch > store.justified_checkpoint.epoch:
|
|
store.justified_checkpoint = state.current_justified_checkpoint
|
|
return
|
|
|
|
# Update justified if store justified is not in chain with finalized checkpoint
|
|
finalized_slot = compute_start_slot_at_epoch(store.finalized_checkpoint.epoch)
|
|
ancestor_at_finalized_slot = get_ancestor(store, store.justified_checkpoint.root, finalized_slot)
|
|
if ancestor_at_finalized_slot != store.finalized_checkpoint.root:
|
|
store.justified_checkpoint = state.current_justified_checkpoint
|
|
```
|