Refactor consensus handling to be more flexible and sound

eth/abc.py

@@ -43,6 +43,7 @@
     JournalDBCheckpoint,
     AccountState,
     HeaderParams,
+    VMConfiguration,
 )
 
 
@@ -1638,9 +1639,8 @@ def validate_receipt(self, receipt: ReceiptAPI) -> None:
     def validate_block(self, block: BlockAPI) -> None:
         ...
 
-    @classmethod
     @abstractmethod
-    def validate_header(cls,
+    def validate_header(self,
                         header: BlockHeaderAPI,
                         parent_header: BlockHeaderAPI,
                         check_seal: bool = True
@@ -1661,9 +1661,8 @@ def validate_transaction_against_header(self,
         """
         ...
 
-    @classmethod
     @abstractmethod
-    def validate_seal(cls, header: BlockHeaderAPI) -> None:
+    def validate_seal(self, header: BlockHeaderAPI) -> None:
         ...
 
     @classmethod
@@ -1688,6 +1687,34 @@ def state_in_temp_block(self) -> ContextManager[StateAPI]:
         ...
 
 
+class VirtualMachineModifierAPI(ABC):
+    """
+    Amend a set of VMs for a chain. This allows modifying a chain for different consensus schemes.
+    """
+
+    @abstractmethod
+    def __init__(self, base_db: AtomicDatabaseAPI) -> None:
+        ...
+
+    @classmethod
+    @abstractmethod
+    def amend_vm_configuration_for_chain_class(cls, vm_config: VMConfiguration) -> None:
+        """
+        Make amendments to the ``vm_config`` that are independent of any instance state. These
+        changes are applied across all instances of the chain where this
+        ``VirtualMachineModifierAPI`` is applied on.
+        """
+        ...
+
+    @abstractmethod
+    def amend_vm_for_chain_instance(self, vm: VirtualMachineAPI) -> None:
+        """
+        Make amendments to ``vm`` that are only valid for a specific chain instance. This
+        includes any modifications that depend on stateful data.
+        """
+        ...
+
+
 class HeaderChainAPI(ABC):
     header: BlockHeaderAPI
     chain_id: int
@@ -1748,6 +1775,8 @@ class ChainAPI(ConfigurableAPI):
     vm_configuration: Tuple[Tuple[BlockNumber, Type[VirtualMachineAPI]], ...]
     chain_id: int
     chaindb: ChainDatabaseAPI
+    consensus_engine_class: Type[VirtualMachineModifierAPI]
+    consensus_engine: VirtualMachineModifierAPI
 
     #
     # Helpers
@@ -1923,10 +1952,9 @@ def validate_gaslimit(self, header: BlockHeaderAPI) -> None:
     def validate_uncles(self, block: BlockAPI) -> None:
         ...
 
-    @classmethod
     @abstractmethod
     def validate_chain(
-            cls,
+            self,
             root: BlockHeaderAPI,
             descendants: Tuple[BlockHeaderAPI, ...],
             seal_check_random_sample_rate: int = 1) -> None:

eth/chains/base.py

@@ -45,12 +45,16 @@
     ChainAPI,
     ChainDatabaseAPI,
     VirtualMachineAPI,
+    VirtualMachineModifierAPI,
     ReceiptAPI,
     ComputationAPI,
     StateAPI,
     SignedTransactionAPI,
     UnsignedTransactionAPI,
 )
+from eth.consensus.pow import (
+    PowConsensus,
+)
 from eth.constants import (
     EMPTY_UNCLE_HASH,
     MAX_UNCLE_DEPTH,
@@ -113,6 +117,8 @@ class BaseChain(Configurable, ChainAPI):
     chaindb_class: Type[ChainDatabaseAPI] = None
     vm_configuration: Tuple[Tuple[BlockNumber, Type[VirtualMachineAPI]], ...] = None
     chain_id: int = None
+    consensus_engine: VirtualMachineModifierAPI = None
+    consensus_engine_class: Type[VirtualMachineModifierAPI] = PowConsensus
 
     @classmethod
     def get_vm_class_for_block_number(cls, block_number: BlockNumber) -> Type[VirtualMachineAPI]:
@@ -136,9 +142,8 @@ def get_vm_class(cls, header: BlockHeaderAPI) -> Type[VirtualMachineAPI]:
     #
     # Validation API
     #
-    @classmethod
     def validate_chain(
-            cls,
+            self,
             root: BlockHeaderAPI,
             descendants: Tuple[BlockHeaderAPI, ...],
             seal_check_random_sample_rate: int = 1) -> None:
@@ -168,9 +173,9 @@ def validate_chain(
                     f" but expected {encode_hex(parent.hash)}"
                 )
             should_check_seal = index in indices_to_check_seal
-            vm_class = cls.get_vm_class_for_block_number(child.block_number)
+            vm = self.get_vm(child)
             try:
-                vm_class.validate_header(child, parent, check_seal=should_check_seal)
+                vm.validate_header(child, parent, check_seal=should_check_seal)
             except ValidationError as exc:
                 raise ValidationError(
                     f"{child} is not a valid child of {parent}: {exc}"
@@ -197,11 +202,23 @@ def __init__(self, base_db: AtomicDatabaseAPI) -> None:
         else:
             validate_vm_configuration(self.vm_configuration)
 
+        if not self.consensus_engine_class:
+            raise ValueError(
+                "The Chain class cannot be instantiated without a `consensus_engine_class`"
+            )
+        else:
+            self.consensus_engine = self.consensus_engine_class(base_db)
+            self.apply_consensus_engine_to_vms(self.consensus_engine)
+
         self.chaindb = self.get_chaindb_class()(base_db)
         self.headerdb = HeaderDB(base_db)
         if self.gas_estimator is None:
             self.gas_estimator = get_gas_estimator()
 
+    @classmethod
+    def apply_consensus_engine_to_vms(cls, consensus_engine: VirtualMachineModifierAPI) -> None:
+        consensus_engine.amend_vm_configuration_for_chain_class(cls.vm_configuration)
+
     #
     # Helpers
     #
@@ -272,7 +289,9 @@ def get_vm(self, at_header: BlockHeaderAPI = None) -> VirtualMachineAPI:
         header = self.ensure_header(at_header)
         vm_class = self.get_vm_class_for_block_number(header.block_number)
         chain_context = ChainContext(self.chain_id)
-        return vm_class(header=header, chaindb=self.chaindb, chain_context=chain_context)
+        vm = vm_class(header=header, chaindb=self.chaindb, chain_context=chain_context)
+        self.consensus_engine.amend_vm_for_chain_instance(vm)
+        return vm
 
     #
     # Header API
@@ -578,18 +597,18 @@ def validate_block(self, block: BlockAPI) -> None:
         """
         if block.is_genesis:
             raise ValidationError("Cannot validate genesis block this way")
-        VM_class = self.get_vm_class_for_block_number(BlockNumber(block.number))
+        vm = self.get_vm(block.header)
         parent_header = self.get_block_header_by_hash(block.header.parent_hash)
-        VM_class.validate_header(block.header, parent_header, check_seal=True)
+        vm.validate_header(block.header, parent_header, check_seal=True)
         self.validate_uncles(block)
         self.validate_gaslimit(block.header)
 
     def validate_seal(self, header: BlockHeaderAPI) -> None:
         """
         Validate the seal on the given header.
         """
-        VM_class = self.get_vm_class_for_block_number(BlockNumber(header.block_number))
-        VM_class.validate_seal(header)
+        vm = self.get_vm(header)
+        vm.validate_seal(header)
 
     def validate_gaslimit(self, header: BlockHeaderAPI) -> None:
         """

eth/chains/mainnet/__init__.py

@@ -45,26 +45,25 @@
 class MainnetDAOValidatorVM(HomesteadVM):
     """Only on mainnet, TheDAO fork is accompanied by special extra data. Validate those headers"""
 
-    @classmethod
-    def validate_header(cls,
+    def validate_header(self,
                         header: BlockHeaderAPI,
                         previous_header: BlockHeaderAPI,
                         check_seal: bool=True) -> None:
 
         super().validate_header(header, previous_header, check_seal)
 
         # The special extra_data is set on the ten headers starting at the fork
-        dao_fork_at = cls.get_dao_fork_block_number()
+        dao_fork_at = self.get_dao_fork_block_number()
         extra_data_block_nums = range(dao_fork_at, dao_fork_at + 10)
 
         if header.block_number in extra_data_block_nums:
-            if cls.support_dao_fork and header.extra_data != DAO_FORK_MAINNET_EXTRA_DATA:
+            if self.support_dao_fork and header.extra_data != DAO_FORK_MAINNET_EXTRA_DATA:
                 raise ValidationError(
                     f"Block {header!r} must have extra data "
                     f"{encode_hex(DAO_FORK_MAINNET_EXTRA_DATA)} not "
                     f"{encode_hex(header.extra_data)} when supporting DAO fork"
                 )
-            elif not cls.support_dao_fork and header.extra_data == DAO_FORK_MAINNET_EXTRA_DATA:
+            elif not self.support_dao_fork and header.extra_data == DAO_FORK_MAINNET_EXTRA_DATA:
                 raise ValidationError(
                     f"Block {header!r} must not have extra data "
                     f"{encode_hex(DAO_FORK_MAINNET_EXTRA_DATA)} when declining the DAO fork"

eth/chains/tester/__init__.py

@@ -146,8 +146,8 @@ class MainnetTesterChain(BaseMainnetTesterChain):
     It exposes one additional API `configure_forks` to allow for in-flight
     configuration of fork rules.
     """
-    @classmethod
-    def validate_seal(cls, block: BlockAPI) -> None:
+
+    def validate_seal(self, block: BlockAPI) -> None:
         """
         We don't validate the proof of work seal on the tester chain.
         """

eth/consensus/__init__.py

@@ -0,0 +1,3 @@
+from .clique.clique import CliqueConsensus  # noqa: F401
+from .noproof import NoProofConsensus  # noqa: F401
+from .pow import PowConsensus  # noqa: F401

eth/consensus/clique/clique.py

@@ -1,10 +1,14 @@
 import logging
-from typing import Sequence, Iterable
+from typing import (
+    Iterable,
+    Sequence,
+)
 
 from eth.abc import (
     AtomicDatabaseAPI,
     BlockHeaderAPI,
     VirtualMachineAPI,
+    VirtualMachineModifierAPI,
 )
 from eth.db.chain import ChainDB
 
@@ -14,14 +18,12 @@
 )
 from eth_utils import (
     encode_hex,
-    to_tuple,
     ValidationError,
 )
 
 from eth.typing import (
     HeaderParams,
     VMConfiguration,
-    VMFork,
 )
 from eth.vm.chain_context import ChainContext
 from eth.vm.execution_context import (
@@ -65,7 +67,7 @@ def _construct_turn_error_message(expected_difficulty: int,
     )
 
 
-class CliqueConsensus:
+class CliqueConsensus(VirtualMachineModifierAPI):
     """
     This class is the entry point to operate a chain under the rules of Clique consensus which
     is defined in EIP-225: https://eips.ethereum.org/EIPS/eip-225
@@ -85,22 +87,23 @@ def __init__(self, base_db: AtomicDatabaseAPI, epoch_length: int = EPOCH_LENGTH)
             self._epoch_length,
         )
 
-    @to_tuple
-    def amend_vm_configuration(self, config: VMConfiguration) -> Iterable[VMFork]:
+    @classmethod
+    def amend_vm_configuration_for_chain_class(cls, config: VMConfiguration) -> None:
         """
         Amend the given ``VMConfiguration`` to operate under the rules of Clique consensus.
         """
         for pair in config:
             block_number, vm = pair
-            vm_class = vm.configure(
-                extra_data_max_bytes=65535,
-                validate_seal=staticmethod(self.validate_seal),
-                create_execution_context=staticmethod(self.create_execution_context),
-                configure_header=configure_header,
-                _assign_block_rewards=lambda _, __: None,
-            )
-
-            yield block_number, vm_class
+            setattr(vm, 'extra_data_max_bytes', 65535)
+            setattr(vm, 'create_execution_context', staticmethod(cls.create_execution_context))
+            setattr(vm, 'configure_header', configure_header)
+            setattr(vm, '_assign_block_rewards', lambda *_: None)
+
+    def amend_vm_for_chain_instance(self, vm: VirtualMachineAPI) -> None:
+        # `validate_seal` is stateful. We would not want two different instances of GoerliChain
+        # to operate on the same instance of CliqueConsensus. Therefore, this modification needs
+        # to be done for a specic chain instance, not chain class.
+        setattr(vm, 'validate_seal', self.validate_seal)
 
     @staticmethod
     def create_execution_context(header: BlockHeaderAPI,

eth/consensus/noproof.py

@@ -0,0 +1,29 @@
+from eth.abc import (
+    AtomicDatabaseAPI,
+    VirtualMachineAPI,
+    VirtualMachineModifierAPI,
+)
+from eth.typing import (
+    VMConfiguration,
+)
+
+
+class NoProofConsensus(VirtualMachineModifierAPI):
+    """
+    Modify a set of VMs to accept blocks without any validation.
+    """
+
+    def __init__(self, base_db: AtomicDatabaseAPI) -> None:
+        pass
+
+    @classmethod
+    def amend_vm_configuration_for_chain_class(cls, config: VMConfiguration) -> None:
+        """
+        Amend the given ``VMConfiguration`` to operate under the default POW rules.
+        """
+        for pair in config:
+            block_number, vm = pair
+            setattr(vm, 'validate_seal', lambda *_: None)
+
+    def amend_vm_for_chain_instance(self, vm: VirtualMachineAPI) -> None:
+        setattr(vm, 'validate_seal', lambda *_: None)