2021-12-02 17:52:56 +00:00
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# Capella -- The Beacon Chain
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2021-12-01 18:37:30 +00:00
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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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- [Constants](#constants)
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- [Domain types](#domain-types)
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- [Preset](#preset)
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- [Max operations per block](#max-operations-per-block)
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- [Execution](#execution)
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- [Containers](#containers)
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- [New containers](#new-containers)
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- [`Withdrawal`](#withdrawal)
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- [`BLSToExecutionChange`](#blstoexecutionchange)
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- [`SignedBLSToExecutionChange`](#signedblstoexecutionchange)
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- [Extended Containers](#extended-containers)
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- [`ExecutionPayload`](#executionpayload)
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- [`ExecutionPayloadHeader`](#executionpayloadheader)
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- [`BeaconBlockBody`](#beaconblockbody)
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- [`BeaconState`](#beaconstate)
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- [Helpers](#helpers)
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- [Predicates](#predicates)
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- [`has_eth1_withdrawal_credential`](#has_eth1_withdrawal_credential)
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- [`is_fully_withdrawable_validator`](#is_fully_withdrawable_validator)
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2022-06-08 19:16:12 +00:00
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- [`is_partially_withdrawable_validator`](#is_partially_withdrawable_validator)
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- [Beacon chain state transition function](#beacon-chain-state-transition-function)
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- [Block processing](#block-processing)
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- [New `get_expected_withdrawals`](#new-get_expected_withdrawals)
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- [New `process_withdrawals`](#new-process_withdrawals)
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- [Modified `process_execution_payload`](#modified-process_execution_payload)
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- [Modified `process_operations`](#modified-process_operations)
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- [New `process_bls_to_execution_change`](#new-process_bls_to_execution_change)
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- [Testing](#testing)
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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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2022-02-24 19:43:57 +00:00
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Capella is a consensus-layer upgrade containing a number of features related
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to validator withdrawals. Including:
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* Automatic withdrawals of `withdrawable` validators.
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* Partial withdrawals sweep for validators with 0x01 withdrawal
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credentials and balances in excess of `MAX_EFFECTIVE_BALANCE`.
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* Operation to change from `BLS_WITHDRAWAL_PREFIX` to
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`ETH1_ADDRESS_WITHDRAWAL_PREFIX` versioned withdrawal credentials to enable withdrawals for a validator.
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2022-10-31 18:32:16 +00:00
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## Custom types
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We define the following Python custom types for type hinting and readability:
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| Name | SSZ equivalent | Description |
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| - | - | - |
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| `WithdrawalIndex` | `uint64` | an index of a `Withdrawal` |
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## Constants
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### Domain types
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| Name | Value |
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| - | - |
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| `DOMAIN_BLS_TO_EXECUTION_CHANGE` | `DomainType('0x0A000000')` |
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## Preset
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### Max operations per block
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| Name | Value |
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| - | - |
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| `MAX_BLS_TO_EXECUTION_CHANGES` | `2**4` (= 16) |
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2022-02-23 22:05:55 +00:00
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### Execution
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| Name | Value | Description |
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| - | - | - |
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| `MAX_WITHDRAWALS_PER_PAYLOAD` | `uint64(2**4)` (= 16) | Maximum amount of withdrawals allowed in each payload |
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## Containers
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### New containers
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#### `Withdrawal`
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```python
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class Withdrawal(Container):
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index: WithdrawalIndex
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validator_index: ValidatorIndex
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address: ExecutionAddress
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amount: Gwei
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```
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2022-03-22 14:19:31 +00:00
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#### `BLSToExecutionChange`
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```python
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class BLSToExecutionChange(Container):
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validator_index: ValidatorIndex
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from_bls_pubkey: BLSPubkey
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to_execution_address: ExecutionAddress
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```
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#### `SignedBLSToExecutionChange`
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```python
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class SignedBLSToExecutionChange(Container):
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message: BLSToExecutionChange
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signature: BLSSignature
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```
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### Extended Containers
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#### `ExecutionPayload`
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```python
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class ExecutionPayload(Container):
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# Execution block header fields
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parent_hash: Hash32
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fee_recipient: ExecutionAddress # 'beneficiary' in the yellow paper
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state_root: Bytes32
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receipts_root: Bytes32
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logs_bloom: ByteVector[BYTES_PER_LOGS_BLOOM]
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prev_randao: Bytes32 # 'difficulty' in the yellow paper
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block_number: uint64 # 'number' in the yellow paper
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gas_limit: uint64
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gas_used: uint64
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timestamp: uint64
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extra_data: ByteList[MAX_EXTRA_DATA_BYTES]
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base_fee_per_gas: uint256
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# Extra payload fields
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block_hash: Hash32 # Hash of execution block
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transactions: List[Transaction, MAX_TRANSACTIONS_PER_PAYLOAD]
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withdrawals: List[Withdrawal, MAX_WITHDRAWALS_PER_PAYLOAD] # [New in Capella]
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```
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#### `ExecutionPayloadHeader`
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```python
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class ExecutionPayloadHeader(Container):
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# Execution block header fields
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parent_hash: Hash32
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fee_recipient: ExecutionAddress
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state_root: Bytes32
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receipts_root: Bytes32
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logs_bloom: ByteVector[BYTES_PER_LOGS_BLOOM]
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prev_randao: Bytes32
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block_number: uint64
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gas_limit: uint64
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gas_used: uint64
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timestamp: uint64
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extra_data: ByteList[MAX_EXTRA_DATA_BYTES]
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base_fee_per_gas: uint256
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# Extra payload fields
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block_hash: Hash32 # Hash of execution block
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transactions_root: Root
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withdrawals_root: Root # [New in Capella]
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```
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#### `BeaconBlockBody`
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```python
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class BeaconBlockBody(Container):
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randao_reveal: BLSSignature
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eth1_data: Eth1Data # Eth1 data vote
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graffiti: Bytes32 # Arbitrary data
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# Operations
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proposer_slashings: List[ProposerSlashing, MAX_PROPOSER_SLASHINGS]
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attester_slashings: List[AttesterSlashing, MAX_ATTESTER_SLASHINGS]
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attestations: List[Attestation, MAX_ATTESTATIONS]
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deposits: List[Deposit, MAX_DEPOSITS]
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voluntary_exits: List[SignedVoluntaryExit, MAX_VOLUNTARY_EXITS]
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sync_aggregate: SyncAggregate
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# Execution
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execution_payload: ExecutionPayload
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# Capella operations
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bls_to_execution_changes: List[SignedBLSToExecutionChange, MAX_BLS_TO_EXECUTION_CHANGES] # [New in Capella]
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```
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#### `BeaconState`
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```python
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class BeaconState(Container):
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# Versioning
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genesis_time: uint64
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genesis_validators_root: Root
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slot: Slot
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fork: Fork
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# History
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latest_block_header: BeaconBlockHeader
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block_roots: Vector[Root, SLOTS_PER_HISTORICAL_ROOT]
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state_roots: Vector[Root, SLOTS_PER_HISTORICAL_ROOT]
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historical_roots: List[Root, HISTORICAL_ROOTS_LIMIT]
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# Eth1
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eth1_data: Eth1Data
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eth1_data_votes: List[Eth1Data, EPOCHS_PER_ETH1_VOTING_PERIOD * SLOTS_PER_EPOCH]
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eth1_deposit_index: uint64
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# Registry
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validators: List[Validator, VALIDATOR_REGISTRY_LIMIT]
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balances: List[Gwei, VALIDATOR_REGISTRY_LIMIT]
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# Randomness
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randao_mixes: Vector[Bytes32, EPOCHS_PER_HISTORICAL_VECTOR]
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# Slashings
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slashings: Vector[Gwei, EPOCHS_PER_SLASHINGS_VECTOR] # Per-epoch sums of slashed effective balances
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# Participation
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previous_epoch_participation: List[ParticipationFlags, VALIDATOR_REGISTRY_LIMIT]
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current_epoch_participation: List[ParticipationFlags, VALIDATOR_REGISTRY_LIMIT]
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# Finality
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justification_bits: Bitvector[JUSTIFICATION_BITS_LENGTH] # Bit set for every recent justified epoch
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previous_justified_checkpoint: Checkpoint
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current_justified_checkpoint: Checkpoint
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finalized_checkpoint: Checkpoint
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# Inactivity
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inactivity_scores: List[uint64, VALIDATOR_REGISTRY_LIMIT]
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# Sync
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current_sync_committee: SyncCommittee
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next_sync_committee: SyncCommittee
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# Execution
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latest_execution_payload_header: ExecutionPayloadHeader
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# Withdrawals
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next_withdrawal_index: WithdrawalIndex # [New in Capella]
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last_withdrawal_validator_index: ValidatorIndex # [New in Capella]
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```
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## Helpers
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### Predicates
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2022-06-08 19:16:12 +00:00
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#### `has_eth1_withdrawal_credential`
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```python
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def has_eth1_withdrawal_credential(validator: Validator) -> bool:
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"""
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Check if ``validator`` has an 0x01 prefixed "eth1" withdrawal credential.
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"""
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return validator.withdrawal_credentials[:1] == ETH1_ADDRESS_WITHDRAWAL_PREFIX
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```
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2022-02-24 22:06:31 +00:00
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#### `is_fully_withdrawable_validator`
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```python
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def is_fully_withdrawable_validator(validator: Validator, balance: Gwei, epoch: Epoch) -> bool:
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"""
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Check if ``validator`` is fully withdrawable.
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"""
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return (
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has_eth1_withdrawal_credential(validator)
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and validator.withdrawable_epoch <= epoch
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and balance > 0
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)
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```
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#### `is_partially_withdrawable_validator`
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```python
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def is_partially_withdrawable_validator(validator: Validator, balance: Gwei) -> bool:
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"""
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Check if ``validator`` is partially withdrawable.
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"""
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has_max_effective_balance = validator.effective_balance == MAX_EFFECTIVE_BALANCE
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has_excess_balance = balance > MAX_EFFECTIVE_BALANCE
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return has_eth1_withdrawal_credential(validator) and has_max_effective_balance and has_excess_balance
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```
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## Beacon chain state transition function
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2022-02-23 22:05:55 +00:00
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### Block processing
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```python
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def process_block(state: BeaconState, block: BeaconBlock) -> None:
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process_block_header(state, block)
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if is_execution_enabled(state, block.body):
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process_withdrawals(state, block.body.execution_payload) # [New in Capella]
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process_execution_payload(state, block.body.execution_payload, EXECUTION_ENGINE) # [Modified in Capella]
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process_randao(state, block.body)
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process_eth1_data(state, block.body)
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process_operations(state, block.body)
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process_sync_aggregate(state, block.body.sync_aggregate)
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```
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#### New `get_expected_withdrawals`
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```python
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def get_expected_withdrawals(state: BeaconState) -> Sequence[Withdrawal]:
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epoch = get_current_epoch(state)
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withdrawal_index = state.next_withdrawal_index
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index = ValidatorIndex((state.last_withdrawal_validator_index + 1) % len(state.validators))
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ret: List[Withdrawal] = []
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for probed in range(len(state.validators)):
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val = state.validators[index]
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balance = state.balances[index]
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if is_fully_withdrawable_validator(val, balance, epoch):
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withdrawal = Withdrawal(
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index=withdrawal_index,
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validator_index=index,
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address=ExecutionAddress(val.withdrawal_credentials[12:]),
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amount=balance,
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)
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ret.append(withdrawal)
|
|
|
|
withdrawal_index = WithdrawalIndex(withdrawal_index + 1)
|
2022-10-31 19:52:07 +00:00
|
|
|
elif is_partially_withdrawable_validator(val, balance):
|
2022-10-31 18:32:16 +00:00
|
|
|
withdrawal = Withdrawal(
|
|
|
|
index=withdrawal_index,
|
|
|
|
validator_index=index,
|
|
|
|
address=ExecutionAddress(val.withdrawal_credentials[12:]),
|
2022-10-31 19:52:07 +00:00
|
|
|
amount=balance - MAX_EFFECTIVE_BALANCE,
|
2022-10-31 18:32:16 +00:00
|
|
|
)
|
|
|
|
ret.append(withdrawal)
|
|
|
|
withdrawal_index = WithdrawalIndex(withdrawal_index + 1)
|
2022-11-01 20:06:35 +00:00
|
|
|
if len(ret) == MAX_WITHDRAWALS_PER_PAYLOAD:
|
|
|
|
break
|
2022-10-31 18:32:16 +00:00
|
|
|
probed += 1
|
|
|
|
index = ValidatorIndex((index + probed) % len(state.validators))
|
|
|
|
return ret
|
|
|
|
```
|
|
|
|
|
|
|
|
#### New `process_withdrawals`
|
|
|
|
|
|
|
|
```python
|
|
|
|
def process_withdrawals(state: BeaconState, payload: ExecutionPayload) -> None:
|
|
|
|
expected_withdrawals = get_expected_withdrawals(state)
|
|
|
|
assert len(payload.withdrawals) == len(expected_withdrawals)
|
|
|
|
|
|
|
|
for expected_withdrawal, withdrawal in zip(get_expected_withdrawals(state), payload.withdrawals):
|
|
|
|
assert withdrawal == expected_withdrawal
|
|
|
|
decrease_balance(state, withdrawal.validator_index, withdrawal.amount)
|
|
|
|
|
|
|
|
state.next_withdrawal_index = WithdrawalIndex(withdrawal.index + 1)
|
|
|
|
state.last_withdrawal_validator_index = withdrawal.validator_index
|
2022-02-23 22:05:55 +00:00
|
|
|
```
|
|
|
|
|
|
|
|
#### Modified `process_execution_payload`
|
|
|
|
|
|
|
|
*Note*: The function `process_execution_payload` is modified to use the new `ExecutionPayloadHeader` type.
|
|
|
|
|
|
|
|
```python
|
|
|
|
def process_execution_payload(state: BeaconState, payload: ExecutionPayload, execution_engine: ExecutionEngine) -> None:
|
|
|
|
# Verify consistency of the parent hash with respect to the previous execution payload header
|
|
|
|
if is_merge_transition_complete(state):
|
|
|
|
assert payload.parent_hash == state.latest_execution_payload_header.block_hash
|
2022-02-24 21:26:15 +00:00
|
|
|
# Verify prev_randao
|
|
|
|
assert payload.prev_randao == get_randao_mix(state, get_current_epoch(state))
|
2022-02-23 22:05:55 +00:00
|
|
|
# Verify timestamp
|
|
|
|
assert payload.timestamp == compute_timestamp_at_slot(state, state.slot)
|
|
|
|
# Verify the execution payload is valid
|
2022-02-24 21:26:15 +00:00
|
|
|
assert execution_engine.notify_new_payload(payload)
|
2022-02-23 22:05:55 +00:00
|
|
|
# Cache execution payload header
|
|
|
|
state.latest_execution_payload_header = ExecutionPayloadHeader(
|
|
|
|
parent_hash=payload.parent_hash,
|
|
|
|
fee_recipient=payload.fee_recipient,
|
|
|
|
state_root=payload.state_root,
|
2022-02-24 21:26:15 +00:00
|
|
|
receipts_root=payload.receipts_root,
|
2022-02-23 22:05:55 +00:00
|
|
|
logs_bloom=payload.logs_bloom,
|
2022-02-24 21:26:15 +00:00
|
|
|
prev_randao=payload.prev_randao,
|
2022-02-23 22:05:55 +00:00
|
|
|
block_number=payload.block_number,
|
|
|
|
gas_limit=payload.gas_limit,
|
|
|
|
gas_used=payload.gas_used,
|
|
|
|
timestamp=payload.timestamp,
|
|
|
|
extra_data=payload.extra_data,
|
|
|
|
base_fee_per_gas=payload.base_fee_per_gas,
|
|
|
|
block_hash=payload.block_hash,
|
|
|
|
transactions_root=hash_tree_root(payload.transactions),
|
2022-03-22 14:00:53 +00:00
|
|
|
withdrawals_root=hash_tree_root(payload.withdrawals), # [New in Capella]
|
2022-02-23 22:05:55 +00:00
|
|
|
)
|
|
|
|
```
|
2022-03-16 21:41:37 +00:00
|
|
|
|
|
|
|
#### Modified `process_operations`
|
|
|
|
|
|
|
|
*Note*: The function `process_operations` is modified to process `BLSToExecutionChange` operations included in the block.
|
|
|
|
|
|
|
|
```python
|
|
|
|
def process_operations(state: BeaconState, body: BeaconBlockBody) -> None:
|
|
|
|
# Verify that outstanding deposits are processed up to the maximum number of deposits
|
|
|
|
assert len(body.deposits) == min(MAX_DEPOSITS, state.eth1_data.deposit_count - state.eth1_deposit_index)
|
|
|
|
|
|
|
|
def for_ops(operations: Sequence[Any], fn: Callable[[BeaconState, Any], None]) -> None:
|
|
|
|
for operation in operations:
|
|
|
|
fn(state, operation)
|
|
|
|
|
|
|
|
for_ops(body.proposer_slashings, process_proposer_slashing)
|
|
|
|
for_ops(body.attester_slashings, process_attester_slashing)
|
|
|
|
for_ops(body.attestations, process_attestation)
|
|
|
|
for_ops(body.deposits, process_deposit)
|
|
|
|
for_ops(body.voluntary_exits, process_voluntary_exit)
|
2022-03-23 16:54:40 +00:00
|
|
|
for_ops(body.bls_to_execution_changes, process_bls_to_execution_change) # [New in Capella]
|
2022-03-16 21:41:37 +00:00
|
|
|
```
|
|
|
|
|
|
|
|
#### New `process_bls_to_execution_change`
|
|
|
|
|
|
|
|
```python
|
|
|
|
def process_bls_to_execution_change(state: BeaconState,
|
|
|
|
signed_address_change: SignedBLSToExecutionChange) -> None:
|
|
|
|
address_change = signed_address_change.message
|
|
|
|
|
|
|
|
assert address_change.validator_index < len(state.validators)
|
|
|
|
|
|
|
|
validator = state.validators[address_change.validator_index]
|
|
|
|
|
|
|
|
assert validator.withdrawal_credentials[:1] == BLS_WITHDRAWAL_PREFIX
|
|
|
|
assert validator.withdrawal_credentials[1:] == hash(address_change.from_bls_pubkey)[1:]
|
|
|
|
|
|
|
|
domain = get_domain(state, DOMAIN_BLS_TO_EXECUTION_CHANGE)
|
|
|
|
signing_root = compute_signing_root(address_change, domain)
|
|
|
|
assert bls.Verify(address_change.from_bls_pubkey, signing_root, signed_address_change.signature)
|
|
|
|
|
|
|
|
validator.withdrawal_credentials = (
|
|
|
|
ETH1_ADDRESS_WITHDRAWAL_PREFIX
|
2022-05-10 15:37:01 +00:00
|
|
|
+ b'\x00' * 11
|
2022-03-16 21:41:37 +00:00
|
|
|
+ address_change.to_execution_address
|
|
|
|
)
|
|
|
|
```
|
2022-07-15 14:18:33 +00:00
|
|
|
|
|
|
|
## Testing
|
|
|
|
|
|
|
|
*Note*: The function `initialize_beacon_state_from_eth1` is modified for pure Capella testing only.
|
|
|
|
Modifications include:
|
2022-07-18 06:45:00 +00:00
|
|
|
1. Use `CAPELLA_FORK_VERSION` as the previous and current fork version.
|
2022-07-15 14:18:33 +00:00
|
|
|
2. Utilize the Capella `BeaconBlockBody` when constructing the initial `latest_block_header`.
|
|
|
|
|
|
|
|
```python
|
|
|
|
def initialize_beacon_state_from_eth1(eth1_block_hash: Hash32,
|
|
|
|
eth1_timestamp: uint64,
|
|
|
|
deposits: Sequence[Deposit],
|
|
|
|
execution_payload_header: ExecutionPayloadHeader=ExecutionPayloadHeader()
|
|
|
|
) -> BeaconState:
|
|
|
|
fork = Fork(
|
|
|
|
previous_version=CAPELLA_FORK_VERSION, # [Modified in Capella] for testing only
|
|
|
|
current_version=CAPELLA_FORK_VERSION, # [Modified in Capella]
|
|
|
|
epoch=GENESIS_EPOCH,
|
|
|
|
)
|
|
|
|
state = BeaconState(
|
|
|
|
genesis_time=eth1_timestamp + GENESIS_DELAY,
|
|
|
|
fork=fork,
|
|
|
|
eth1_data=Eth1Data(block_hash=eth1_block_hash, deposit_count=uint64(len(deposits))),
|
|
|
|
latest_block_header=BeaconBlockHeader(body_root=hash_tree_root(BeaconBlockBody())),
|
|
|
|
randao_mixes=[eth1_block_hash] * EPOCHS_PER_HISTORICAL_VECTOR, # Seed RANDAO with Eth1 entropy
|
|
|
|
)
|
|
|
|
|
|
|
|
# Process deposits
|
|
|
|
leaves = list(map(lambda deposit: deposit.data, deposits))
|
|
|
|
for index, deposit in enumerate(deposits):
|
|
|
|
deposit_data_list = List[DepositData, 2**DEPOSIT_CONTRACT_TREE_DEPTH](*leaves[:index + 1])
|
|
|
|
state.eth1_data.deposit_root = hash_tree_root(deposit_data_list)
|
|
|
|
process_deposit(state, deposit)
|
|
|
|
|
|
|
|
# Process activations
|
|
|
|
for index, validator in enumerate(state.validators):
|
|
|
|
balance = state.balances[index]
|
|
|
|
validator.effective_balance = min(balance - balance % EFFECTIVE_BALANCE_INCREMENT, MAX_EFFECTIVE_BALANCE)
|
|
|
|
if validator.effective_balance == MAX_EFFECTIVE_BALANCE:
|
|
|
|
validator.activation_eligibility_epoch = GENESIS_EPOCH
|
|
|
|
validator.activation_epoch = GENESIS_EPOCH
|
|
|
|
|
|
|
|
# Set genesis validators root for domain separation and chain versioning
|
|
|
|
state.genesis_validators_root = hash_tree_root(state.validators)
|
|
|
|
|
|
|
|
# Fill in sync committees
|
|
|
|
# Note: A duplicate committee is assigned for the current and next committee at genesis
|
|
|
|
state.current_sync_committee = get_next_sync_committee(state)
|
|
|
|
state.next_sync_committee = get_next_sync_committee(state)
|
|
|
|
|
|
|
|
# Initialize the execution payload header
|
|
|
|
state.latest_execution_payload_header = execution_payload_header
|
|
|
|
|
|
|
|
return state
|
|
|
|
```
|