ethereum.forks.bpo3.state_trackerethereum.forks.bpo4.state_tracker

State Tracking for Block Execution.

Track state changes on top of a read-only PreState. At block end, accumulated diffs feed into PreState.compute_state_root_and_trie_changes().

.. contents:: Table of Contents :backlinks: none :local:

Introduction

Replace the mutable State class with lightweight state trackers that record diffs. BlockState accumulates committed transaction changes across a block. TransactionState tracks in-flight changes within a single transaction and supports copy-on-write rollback.

BlockState

Accumulate committed transaction-level changes across a block.

Read chain: block writes -> pre_state.

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@dataclass
class BlockState:

pre_state

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    pre_state: PreState

account_writes

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    account_writes: Dict[Address, Optional[Account]] = field(
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        default_factory=dict
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    )

storage_writes

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    storage_writes: Dict[Address, Dict[Bytes32, U256]] = field(
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        default_factory=dict
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    )

code_writes

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    code_writes: Dict[Hash32, Bytes] = field(default_factory=dict)

TransactionState

Track in-flight state changes within a single transaction.

Read chain: tx writes -> block writes -> pre_state.

57
@dataclass
class TransactionState:

parent

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    parent: BlockState

account_writes

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    account_writes: Dict[Address, Optional[Account]] = field(
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        default_factory=dict
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    )

storage_writes

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    storage_writes: Dict[Address, Dict[Bytes32, U256]] = field(
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        default_factory=dict
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    )

code_writes

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    code_writes: Dict[Hash32, Bytes] = field(default_factory=dict)

created_accounts

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    created_accounts: Set[Address] = field(default_factory=set)

transient_storage

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    transient_storage: Dict[Tuple[Address, Bytes32], U256] = field(
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        default_factory=dict
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    )

get_account_optional

Get the Account object at an address. Return None (rather than EMPTY_ACCOUNT) if there is no account at the address.

Parameters

tx_state : The transaction state. address : Address to look up.

Returns

account : Optional[Account] Account at address.

def get_account_optional(​tx_state: TransactionState, ​​address: Address​) -> Optional[Account]:
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    <snip>
99
    if address in tx_state.account_writes:
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        return tx_state.account_writes[address]
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    if address in tx_state.parent.account_writes:
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        return tx_state.parent.account_writes[address]
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    return tx_state.parent.pre_state.get_account_optional(address)

get_account

Get the Account object at an address. Return EMPTY_ACCOUNT if there is no account at the address.

Use get_account_optional() if you care about the difference between a non-existent account and EMPTY_ACCOUNT.

Parameters

tx_state : The transaction state. address : Address to look up.

Returns

account : Account Account at address.

def get_account(​tx_state: TransactionState, ​​address: Address​) -> Account:
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    <snip>
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    account = get_account_optional(tx_state, address)
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    if account is None:
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        return EMPTY_ACCOUNT
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    else:
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        return account

get_code

Get the bytecode for a given code hash.

Read chain: tx code_writes -> block code_writes -> pre_state.

Parameters

tx_state : The transaction state. code_hash : Hash of the code to look up.

Returns

code : Bytes The bytecode.

def get_code(​tx_state: TransactionState, ​​code_hash: Hash32​) -> Bytes:
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    <snip>
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    if code_hash == EMPTY_CODE_HASH:
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        return b""
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    if code_hash in tx_state.code_writes:
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        return tx_state.code_writes[code_hash]
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    if code_hash in tx_state.parent.code_writes:
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        return tx_state.parent.code_writes[code_hash]
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    return tx_state.parent.pre_state.get_code(code_hash)

get_storage

Get a value at a storage key on an account. Return U256(0) if the storage key has not been set previously.

Parameters

tx_state : The transaction state. address : Address of the account. key : Key to look up.

Returns

value : U256 Value at the key.

def get_storage(​tx_state: TransactionState, ​​address: Address, ​​key: Bytes32​) -> U256:
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    <snip>
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    if address in tx_state.storage_writes:
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        if key in tx_state.storage_writes[address]:
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            return tx_state.storage_writes[address][key]
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    if address in tx_state.parent.storage_writes:
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        if key in tx_state.parent.storage_writes[address]:
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            return tx_state.parent.storage_writes[address][key]
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    return tx_state.parent.pre_state.get_storage(address, key)

get_storage_original

Get the original value in a storage slot i.e. the value before the current transaction began. Read from block-level writes, then pre_state. Return U256(0) for accounts created in the current transaction.

Parameters

tx_state : The transaction state. address : Address of the account to read the value from. key : Key of the storage slot.

def get_storage_original(​tx_state: TransactionState, ​​address: Address, ​​key: Bytes32​) -> U256:
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    <snip>
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    if address in tx_state.created_accounts:
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        return U256(0)
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    if address in tx_state.parent.storage_writes:
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        if key in tx_state.parent.storage_writes[address]:
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            return tx_state.parent.storage_writes[address][key]
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    return tx_state.parent.pre_state.get_storage(address, key)

get_transient_storage

Get a value at a storage key on an account from transient storage. Return U256(0) if the storage key has not been set previously.

Parameters

tx_state : The transaction state. address : Address of the account. key : Key to look up.

Returns

value : U256 Value at the key.

def get_transient_storage(​tx_state: TransactionState, ​​address: Address, ​​key: Bytes32​) -> U256:
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    <snip>
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    return tx_state.transient_storage.get((address, key), U256(0))

account_exists

Check if an account exists in the state trie.

Parameters

tx_state : The transaction state. address : Address of the account that needs to be checked.

Returns

account_exists : bool True if account exists in the state trie, False otherwise.

def account_exists(​tx_state: TransactionState, ​​address: Address​) -> bool:
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    <snip>
262
    return get_account_optional(tx_state, address) is not None

account_has_code_or_nonce

Check if an account has non-zero nonce or non-empty code.

Parameters

tx_state : The transaction state. address : Address of the account that needs to be checked.

Returns

has_code_or_nonce : bool True if the account has non-zero nonce or non-empty code, False otherwise.

def account_has_code_or_nonce(​tx_state: TransactionState, ​​address: Address​) -> bool:
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    <snip>
285
    account = get_account(tx_state, address)
286
    return account.nonce != Uint(0) or account.code_hash != EMPTY_CODE_HASH

account_has_storage

Check if an account has storage.

Parameters

tx_state : The transaction state. address : Address of the account that needs to be checked.

Returns

has_storage : bool True if the account has storage, False otherwise.

def account_has_storage(​tx_state: TransactionState, ​​address: Address​) -> bool:
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    <snip>
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    if tx_state.storage_writes.get(address):
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        return True
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    if tx_state.parent.storage_writes.get(address):
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        return True
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    return tx_state.parent.pre_state.account_has_storage(address)

account_exists_and_is_empty

Check if an account exists and has zero nonce, empty code and zero balance.

Parameters

tx_state : The transaction state. address : Address of the account that needs to be checked.

Returns

exists_and_is_empty : bool True if an account exists and has zero nonce, empty code and zero balance, False otherwise.

def account_exists_and_is_empty(​tx_state: TransactionState, ​​address: Address​) -> bool:
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    <snip>
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    account = get_account_optional(tx_state, address)
335
    return (
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        account is not None
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        and account.nonce == Uint(0)
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        and account.code_hash == EMPTY_CODE_HASH
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        and account.balance == 0
340
    )

is_account_alive

Check whether an account is both in the state and non-empty.

Parameters

tx_state : The transaction state. address : Address of the account that needs to be checked.

Returns

is_alive : bool True if the account is alive.

def is_account_alive(​tx_state: TransactionState, ​​address: Address​) -> bool:
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    <snip>
360
    account = get_account_optional(tx_state, address)
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    return account is not None and account != EMPTY_ACCOUNT

set_account

Set the Account object at an address. Setting to None deletes the account (but not its storage, see destroy_account()).

Parameters

tx_state : The transaction state. address : Address to set. account : Account to set at address.

def set_account(​tx_state: TransactionState, ​​address: Address, ​​account: Optional[Account]​) -> None:
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    <snip>
384
    tx_state.account_writes[address] = account

set_storage

Set a value at a storage key on an account.

Parameters

tx_state : The transaction state. address : Address of the account. key : Key to set. value : Value to set at the key.

def set_storage(​tx_state: TransactionState, ​​address: Address, ​​key: Bytes32, ​​value: U256​) -> None:
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    <snip>
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    assert get_account_optional(tx_state, address) is not None
409
    if address not in tx_state.storage_writes:
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        tx_state.storage_writes[address] = {}
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    tx_state.storage_writes[address][key] = value

destroy_account

Completely remove the account at address and all of its storage.

This function is made available exclusively for the SELFDESTRUCT opcode. It is expected that SELFDESTRUCT will be disabled in a future hardfork and this function will be removed. Only supports same transaction destruction.

Parameters

tx_state : The transaction state. address : Address of account to destroy.

def destroy_account(​tx_state: TransactionState, ​​address: Address​) -> None:
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    <snip>
431
    destroy_storage(tx_state, address)
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    set_account(tx_state, address, None)

destroy_storage

Completely remove the storage at address.

Only supports same transaction destruction.

Parameters

tx_state : The transaction state. address : Address of account whose storage is to be deleted.

def destroy_storage(​tx_state: TransactionState, ​​address: Address​) -> None:
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    <snip>
449
    if address in tx_state.storage_writes:
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        del tx_state.storage_writes[address]

mark_account_created

Mark an account as having been created in the current transaction. This information is used by get_storage_original() to handle an obscure edgecase, and to respect the constraints added to SELFDESTRUCT by EIP-6780.

The marker is not removed even if the account creation reverts. Since the account cannot have had code prior to its creation and can't call get_storage_original(), this is harmless.

Parameters

tx_state : The transaction state. address : Address of the account that has been created.

def mark_account_created(​tx_state: TransactionState, ​​address: Address​) -> None:
454
    <snip>
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    tx_state.created_accounts.add(address)

set_transient_storage

Set a value at a storage key on an account in transient storage.

Parameters

tx_state : The transaction state. address : Address of the account. key : Key to set. value : Value to set at the key.

def set_transient_storage(​tx_state: TransactionState, ​​address: Address, ​​key: Bytes32, ​​value: U256​) -> None:
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    <snip>
496
    if value == U256(0):
497
        tx_state.transient_storage.pop((address, key), None)
498
    else:
499
        tx_state.transient_storage[(address, key)] = value

modify_state

Modify an Account in the state. If, after modification, the account exists and has zero nonce, empty code, and zero balance, it is destroyed.

def modify_state(​tx_state: TransactionState, ​​address: Address, ​​f: Callable[[Account], None]​) -> None:
507
    <snip>
512
    set_account(tx_state, address, modify(get_account(tx_state, address), f))
513
    if account_exists_and_is_empty(tx_state, address):
514
        destroy_account(tx_state, address)

move_ether

Move funds between accounts.

Parameters

tx_state : The transaction state. sender_address : Address of the sender. recipient_address : Address of the recipient. amount : The amount to transfer.

def move_ether(​tx_state: TransactionState, ​​sender_address: Address, ​​recipient_address: Address, ​​amount: U256​) -> None:
523
    <snip>
538
539
    def reduce_sender_balance(sender: Account) -> None:
540
        if sender.balance < amount:
541
            raise AssertionError
542
        sender.balance -= amount
543
544
    def increase_recipient_balance(recipient: Account) -> None:
545
        recipient.balance += amount
546
547
    modify_state(tx_state, sender_address, reduce_sender_balance)
548
    modify_state(tx_state, recipient_address, increase_recipient_balance)

create_ether

Add newly created ether to an account.

Parameters

tx_state : The transaction state. address : Address of the account to which ether is added. amount : The amount of ether to be added to the account of interest.

def create_ether(​tx_state: TransactionState, ​​address: Address, ​​amount: U256​) -> None:
554
    <snip>
567
568
    def increase_balance(account: Account) -> None:
569
        account.balance += amount
570
571
    modify_state(tx_state, address, increase_balance)

set_account_balance

Set the balance of an account.

Parameters

tx_state : The transaction state. address : Address of the account whose balance needs to be set. amount : The amount that needs to be set in the balance.

def set_account_balance(​tx_state: TransactionState, ​​address: Address, ​​amount: U256​) -> None:
577
    <snip>
590
591
    def set_balance(account: Account) -> None:
592
        account.balance = amount
593
594
    modify_state(tx_state, address, set_balance)

increment_nonce

Increment the nonce of an account.

Parameters

tx_state : The transaction state. address : Address of the account whose nonce needs to be incremented.

def increment_nonce(​tx_state: TransactionState, ​​address: Address​) -> None:
598
    <snip>
609
610
    def increase_nonce(sender: Account) -> None:
611
        sender.nonce += Uint(1)
612
613
    modify_state(tx_state, address, increase_nonce)

set_code

Set Account code.

Parameters

tx_state : The transaction state. address : Address of the account whose code needs to be updated. code : The bytecode that needs to be set.

def set_code(​tx_state: TransactionState, ​​address: Address, ​​code: Bytes​) -> None:
619
    <snip>
632
    code_hash = keccak256(code)
633
    if code_hash != EMPTY_CODE_HASH:
634
        tx_state.code_writes[code_hash] = code
635
636
    def write_code_hash(sender: Account) -> None:
637
        sender.code_hash = code_hash
638
639
    modify_state(tx_state, address, write_code_hash)

copy_tx_state

Create a snapshot of the transaction state for rollback.

Deep-copy writes and transient storage. The parent reference and created_accounts are shared (not rolled back).

Parameters

tx_state : The transaction state to snapshot.

Returns

snapshot : TransactionState A copy of the transaction state.

def copy_tx_state(​tx_state: TransactionState​) -> TransactionState:
646
    <snip>
663
    return TransactionState(
664
        parent=tx_state.parent,
665
        account_writes=dict(tx_state.account_writes),
666
        storage_writes={
667
            addr: dict(slots)
668
            for addr, slots in tx_state.storage_writes.items()
669
        },
670
        code_writes=dict(tx_state.code_writes),
671
        created_accounts=tx_state.created_accounts,
672
        transient_storage=dict(tx_state.transient_storage),
673
    )

restore_tx_state

Restore transaction state from a snapshot (rollback on failure).

Parameters

tx_state : The transaction state to restore. snapshot : The snapshot to restore from.

def restore_tx_state(​tx_state: TransactionState, ​​snapshot: TransactionState​) -> None:
679
    <snip>
690
    tx_state.account_writes = snapshot.account_writes
691
    tx_state.storage_writes = snapshot.storage_writes
692
    tx_state.code_writes = snapshot.code_writes
693
    tx_state.transient_storage = snapshot.transient_storage

incorporate_tx_into_block

Merge transaction writes into the block state and clear for reuse.

Parameters

tx_state : The transaction state to commit.

def incorporate_tx_into_block(​tx_state: TransactionState​) -> None:
700
    <snip>
709
    block = tx_state.parent
710
711
    for address, account in tx_state.account_writes.items():
712
        block.account_writes[address] = account
713
714
    for address, slots in tx_state.storage_writes.items():
715
        if address not in block.storage_writes:
716
            block.storage_writes[address] = {}
717
        block.storage_writes[address].update(slots)
718
719
    block.code_writes.update(tx_state.code_writes)
720
721
    tx_state.account_writes.clear()
722
    tx_state.storage_writes.clear()
723
    tx_state.code_writes.clear()
724
    tx_state.created_accounts.clear()
725
    tx_state.transient_storage.clear()

extract_block_diff

Extract account, storage, and code diff from the block state.

Parameters

block_state : The block state.

Returns

diff : BlockDiff Account, storage, and code changes accumulated during block execution.

def extract_block_diff(​block_state: BlockState​) -> BlockDiff:
729
    <snip>
743
    return BlockDiff(
744
        account_changes=block_state.account_writes,
745
        storage_changes=block_state.storage_writes,
746
        code_changes=block_state.code_writes,
747
    )