modified withdrawals for push

specs/capella/beacon-chain.md

@@ -20,10 +20,6 @@ to validator withdrawals. Including:
 
 ## Custom types
 
-| Name | SSZ equivalent | Description |
-| - | - | - |
-| `WithdrawalReceiptIndex` | `uint64` | a withdrawal receipt index |
-
 ## Constants
 
 ## Preset
@@ -32,7 +28,14 @@ to validator withdrawals. Including:
 
 | Name | Value | Unit | Duration |
 | - | - | :-: | :-: |
-| `WITHDRAWAL_RECEIPT_LIMIT` | `uint64(2**40)` (= 1,099,511,627,776) | withdrawal receipts|
+| `WITHDRAWAL_TRANSACTION_LIMIT` | `uint64(2**40)` (= 1,099,511,627,776) | withdrawal transactions enqueued in state|
+
+### Execution
+
+| Name | Value | Description |
+| - | - | - |
+| `WITHDRAWAL_TX_TYPE` | `Bytes1(0x05)` | EIP-2718 TX Type |
+| `MAX_WITHDRAWAL_TRANSACTIONS_PER_PAYLOAD` | `uint64(2**4)` (= 16) | Maximum amount of withdrawal transactions allowed in each payload |
 
 ## Configuration
 
@@ -56,7 +59,6 @@ class Validator(Container):
     withdrawn_epoch: Epoch  # [New in Capella]
 ```
 
-
 #### `BeaconState`
 
 ```python
@@ -98,18 +100,66 @@ class BeaconState(Container):
     # Execution
     latest_execution_payload_header: ExecutionPayloadHeader
     # Withdrawals
-    withdrawal_receipts: List[WithdrawalReceipt, WITHDRAWAL_RECEIPT_LIMIT]  # [New in Capella]
+    withdrawal_receipts: List[WithdrawalTransaction, WITHDRAWAL_TRANSACTION_LIMIT]  # [New in Capella]
+```
+
+#### `ExecutionPayload`
+
+```python
+class ExecutionPayload(Container):
+    # Execution block header fields
+    parent_hash: Hash32
+    fee_recipient: ExecutionAddress  # 'beneficiary' in the yellow paper
+    state_root: Bytes32
+    receipt_root: Bytes32  # 'receipts root' in the yellow paper
+    logs_bloom: ByteVector[BYTES_PER_LOGS_BLOOM]
+    random: Bytes32  # 'difficulty' in the yellow paper
+    block_number: uint64  # 'number' in the yellow paper
+    gas_limit: uint64
+    gas_used: uint64
+    timestamp: uint64
+    extra_data: ByteList[MAX_EXTRA_DATA_BYTES]
+    base_fee_per_gas: uint256
+    # Extra payload fields
+    block_hash: Hash32  # Hash of execution block
+    transactions: List[Transaction, MAX_TRANSACTIONS_PER_PAYLOAD]
+    withdrawal_transactions: List[WithdrawalTransaction, MAX_WITHDRAWAL_TRANSACTIONS_PER_PAYLOAD]  # [New in Capella]
+```
+
+#### `ExecutionPayloadHeader`
+
+```python
+class ExecutionPayloadHeader(Container):
+    # Execution block header fields
+    parent_hash: Hash32
+    fee_recipient: ExecutionAddress
+    state_root: Bytes32
+    receipt_root: Bytes32
+    logs_bloom: ByteVector[BYTES_PER_LOGS_BLOOM]
+    random: Bytes32
+    block_number: uint64
+    gas_limit: uint64
+    gas_used: uint64
+    timestamp: uint64
+    extra_data: ByteList[MAX_EXTRA_DATA_BYTES]
+    base_fee_per_gas: uint256
+    # Extra payload fields
+    block_hash: Hash32  # Hash of execution block
+    transactions_root: Root
+    withdrawal_transactions_root: Root  # [New in Capella]
 ```
 
 ### New containers
 
-#### `WithdrawalReceipt`
+#### `WithdrawalTransaction`
+
+New EIP-2718 transaction type, with the format being the single byte `WITHDRAWAL_TX_TYPE`
+followed by an SSZ encoding of the `WithdrawalTransaction` container comprising the transaction contents.
 
 ```python
-class WithdrawalReceipt(Container):
-    index: WithdrawalReceiptIndex
+class WithdrawalTransaction(Container):
     address: ExecutionAddress
-    amount: Gwei
+    value: Gwei
 ```
 
 ## Helpers
@@ -123,8 +173,7 @@ def withdraw(state: BeaconState, index: ValidatorIndex, amount: Gwei) -> None:
     # Decrease the validator's balance
     decrease_balance(state, index, amount)
     # Create a corresponding withdrawal receipt
-    receipt = WithdrawalReceipt(
-        index=WithdrawalReceiptIndex(len(state.withdrawal_receipts)),
+    receipt = WithdrawalTransaction(
         address=state.validators[index].withdrawal_credentials[12:],
         amount=amount,
     )
@@ -162,19 +211,86 @@ def process_epoch(state: BeaconState) -> None:
     process_historical_roots_update(state)
     process_participation_flag_updates(state)
     process_sync_committee_updates(state)
-    process_withdrawals(state)  # [New in Capella]
+    process_full_withdrawals(state)  # [New in Capella]
 ```
 
 #### Withdrawals
 
-*Note*: The function `process_withdrawals` is new.
+*Note*: The function `process_full_withdrawals` is new.
 
 ```python
-def process_withdrawals(state: BeaconState) -> None:
+def process_full_withdrawals(state: BeaconState) -> None:
     current_epoch = get_current_epoch(state)
     for index, validator in enumerate(state.validators):
         if is_withdrawable_validator(validator, current_epoch):
             # TODO, consider the zero-balance case
             withdraw(state, ValidatorIndex(index), state.balances[index])
             validator.withdrawn_epoch = current_epoch
 ```
+
+### Block processing
+
+```python
+def process_block(state: BeaconState, block: BeaconBlock) -> None:
+    process_block_header(state, block)
+    process_withdrawal_transactions(state, block.body.execution_payload)  # [New in Capella]
+    process_execution_payload(state, block.body.execution_payload, EXECUTION_ENGINE)  # [Modified in Capella]
+    process_randao(state, block.body)
+    process_eth1_data(state, block.body)
+    process_operations(state, block.body)
+    process_sync_aggregate(state, block.body.sync_aggregate)
+```
+
+#### New `process_withdrawal_transactions`
+
+```python
+def process_withdrawal_transactions(state: BeaconState, payload: ExecutionPayload) -> None:
+    num_withdrawal_transactions = min(MAX_WITHDRAWAL_TRANSACTIONS_PER_PAYLOAD, len(state.withdrawal_receipts))
+    dequeued_withdrawal_receipts = state.withdrawal_receipts[:num_withdrawal_transactions]
+
+    assert len(dequeued_withdrawal_receipts) == len(payload.withdrawal_transactions)
+    for dequeued_receipt, withdrawal_transaction in zip(dequeued_withdrawal_receipts, payload.withdrawal_transactions):
+        assert dequeued_receipt == withdrawal_transaction
+
+    # Ensure no withdrawal type transactions in the normal payload transactions
+    # assert no_withdrawal_type_transactions_in(payload.transactions)
+
+    # Remove dequeued receipts from state
+    state.withdrawal_receipts = state.withdrawal_receipts[num_withdrawal_transactions:]
+```
+
+#### 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
+    # Verify random
+    assert payload.random == get_randao_mix(state, get_current_epoch(state))
+    # Verify timestamp
+    assert payload.timestamp == compute_timestamp_at_slot(state, state.slot)
+    # Verify the execution payload is valid
+    assert execution_engine.execute_payload(payload)
+    # 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,
+        receipt_root=payload.receipt_root,
+        logs_bloom=payload.logs_bloom,
+        random=payload.random,
+        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),
+        withdrawal_transactions=hash_tree_root(payload.withdrawal_transactions),
+    )
+```
+