116 lines
4.8 KiB
Markdown
116 lines
4.8 KiB
Markdown
# Ethereum 2.0 The Merge
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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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- [Helpers](#helpers)
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- [`PowBlock`](#powblock)
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- [`get_pow_block`](#get_pow_block)
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- [`is_valid_transition_block`](#is_valid_transition_block)
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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 executable beacon chain proposal.
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*Note*: It introduces the process of transition from the last PoW block to the first PoS block.
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### Helpers
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#### `PowBlock`
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```python
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class PowBlock(Container):
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block_hash: Hash32
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is_processed: boolean
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is_valid: boolean
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total_difficulty: uint256
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```
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#### `get_pow_block`
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Let `get_pow_block(block_hash: Hash32) -> PowBlock` be the function that given the hash of the PoW block returns its data.
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*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.
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#### `is_valid_transition_block`
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Used by fork-choice handler, `on_block`.
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```python
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def is_valid_transition_block(block: PowBlock) -> bool:
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is_total_difficulty_reached = block.total_difficulty >= TRANSITION_TOTAL_DIFFICULTY
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return block.is_valid and is_total_difficulty_reached
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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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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 the 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 Merge]
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if is_transition_block(pre_state, block):
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# Delay consideration of block until PoW block is processed by the PoW node
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pow_block = get_pow_block(block.body.execution_payload.parent_hash)
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assert pow_block.is_processed
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assert is_valid_transition_block(pow_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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state_transition(state, signed_block, True)
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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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# 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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# Potentially update justified if different from store
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if store.justified_checkpoint != state.current_justified_checkpoint:
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# Update justified if new justified is later than store justified
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if state.current_justified_checkpoint.epoch > store.justified_checkpoint.epoch:
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store.justified_checkpoint = state.current_justified_checkpoint
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return
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# Update justified if store justified is not in chain with finalized checkpoint
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finalized_slot = compute_start_slot_at_epoch(store.finalized_checkpoint.epoch)
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ancestor_at_finalized_slot = get_ancestor(store, store.justified_checkpoint.root, finalized_slot)
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if ancestor_at_finalized_slot != store.finalized_checkpoint.root:
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store.justified_checkpoint = state.current_justified_checkpoint
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```
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