refactor computation logic to reduce needless code duplication

suggested changes from PR #2018

Author: fselmo

eth/vm/forks/london/computation.py

@@ -1,15 +1,10 @@
-from eth_utils import encode_hex, keccak
-
-from eth import constants
-from eth.abc import ComputationAPI, MessageAPI, StateAPI, TransactionContextAPI
-from eth.exceptions import OutOfGas, ReservedBytesInCode
+from eth.exceptions import ReservedBytesInCode
 from eth.vm.forks.berlin.computation import (
     BerlinComputation,
 )
 
 from .opcodes import LONDON_OPCODES
 from ..london.constants import EIP3541_RESERVED_STARTING_BYTE
-from ..spurious_dragon.constants import EIP170_CODE_SIZE_LIMIT
 
 
 class LondonComputation(BerlinComputation):
@@ -20,60 +15,8 @@ class LondonComputation(BerlinComputation):
     opcodes = LONDON_OPCODES
 
     @classmethod
-    def apply_create_message(
-        cls,
-        state: StateAPI,
-        message: MessageAPI,
-        transaction_context: TransactionContextAPI
-    ) -> ComputationAPI:
-
-        snapshot = state.snapshot()
-
-        # EIP161 nonce incrementation
-        state.increment_nonce(message.storage_address)
-
-        computation = cls.apply_message(state, message, transaction_context)
-
-        if computation.is_error:
-            state.revert(snapshot)
-            return computation
-        else:
-            contract_code = computation.output
-
-            if contract_code and len(contract_code) >= EIP170_CODE_SIZE_LIMIT:
-                computation.error = OutOfGas(
-                    f"Contract code size exceeds EIP170 limit of {EIP170_CODE_SIZE_LIMIT}."
-                    f" Got code of size: {len(contract_code)}"
-                )
-                state.revert(snapshot)
-            elif contract_code:
-                contract_code_gas_cost = len(contract_code) * constants.GAS_CODEDEPOSIT
-                try:
-                    computation.consume_gas(
-                        contract_code_gas_cost,
-                        reason="Write contract code for CREATE / CREATE2",
-                    )
-                except OutOfGas as err:
-                    computation.error = err
-                    state.revert(snapshot)
-                else:
-                    if contract_code[:1] == EIP3541_RESERVED_STARTING_BYTE:
-                        # As per EIP-3541, gas is still consumed on a revert of this nature
-                        state.revert(snapshot)
-                        raise ReservedBytesInCode(
-                            "Contract code begins with EIP3541 reserved byte '0xEF'."
-                        )
-                    else:
-                        if cls.logger:
-                            cls.logger.debug2(
-                                "SETTING CODE: %s -> length: %s | hash: %s",
-                                encode_hex(message.storage_address),
-                                len(contract_code),
-                                encode_hex(keccak(contract_code))
-                            )
-
-                        state.set_code(message.storage_address, contract_code)
-                        state.commit(snapshot)
-            else:
-                state.commit(snapshot)
-            return computation
+    def validate_new_contract_code(cls, contract_code: bytes) -> None:
+        if contract_code[:1] == EIP3541_RESERVED_STARTING_BYTE:
+            raise ReservedBytesInCode(
+                "Contract code begins with EIP3541 reserved byte '0xEF'."
+            )

eth/vm/forks/spurious_dragon/computation.py

@@ -1,4 +1,5 @@
 from eth_hash.auto import keccak
+
 from eth_utils import (
     encode_hex,
 )
@@ -12,12 +13,13 @@
 )
 from eth.exceptions import (
     OutOfGas,
+    VMError,
 )
 from eth.vm.forks.homestead.computation import (
     HomesteadComputation,
 )
 
-from .constants import EIP170_CODE_SIZE_LIMIT
+from ..spurious_dragon.constants import EIP170_CODE_SIZE_LIMIT
 from .opcodes import SPURIOUS_DRAGON_OPCODES
 
 
@@ -68,6 +70,12 @@ def apply_create_message(
                     computation.error = err
                     state.revert(snapshot)
                 else:
+                    try:
+                        cls.validate_new_contract_code(contract_code)
+                    except VMError as err:
+                        state.revert(snapshot)
+                        raise err
+
                     if cls.logger:
                         cls.logger.debug2(
                             "SETTING CODE: %s -> length: %s | hash: %s",
@@ -81,3 +89,8 @@ def apply_create_message(
             else:
                 state.commit(snapshot)
             return computation
+
+    @classmethod
+    def validate_new_contract_code(cls, contract_code: bytes) -> None:
+        # helps facilitate EIP-3541 validation in LondonComputation
+        pass