fix: leader appeal uses stored contract snapshot (#983)

Author: kstroobants

backend/consensus/base.py

@@ -11,6 +11,7 @@
 from abc import ABC, abstractmethod
 import threading
 import random
+from copy import deepcopy
 
 from sqlalchemy.orm import Session
 from backend.consensus.vrf import get_validators_for_transaction
@@ -1034,6 +1035,12 @@ async def process_leader_appeal(
             )
             transaction.appeal_undetermined = True
 
+            context.contract_snapshot_supplier = (
+                lambda: context.contract_snapshot_factory(
+                    context.transaction.to_address
+                )
+            )
+
             # Begin state transitions starting from PendingState
             state = PendingState()
             while True:
@@ -1597,16 +1604,21 @@ async def handle(self, context):
         if context.transaction.leader_only:
             context.remaining_validators = []
 
-        # Create a contract snapshot for the transaction
-        contract_snapshot_supplier = lambda: context.contract_snapshot_factory(
-            context.transaction.to_address
-        )
+        # Create a contract snapshot for the transaction if not exists
+        if context.transaction.contract_snapshot:
+            contract_snapshot = deepcopy(context.transaction.contract_snapshot)
+        else:
+            contract_snapshot_supplier = lambda: context.contract_snapshot_factory(
+                context.transaction.to_address
+            )
+            context.contract_snapshot_supplier = contract_snapshot_supplier
+            contract_snapshot = contract_snapshot_supplier()
 
         # Create a leader node for executing the transaction
         leader_node = context.node_factory(
             leader,
             ExecutionMode.LEADER,
-            contract_snapshot_supplier(),
+            contract_snapshot,
             None,
             context.msg_handler,
             context.contract_snapshot_factory,
@@ -1626,7 +1638,6 @@ async def handle(self, context):
 
         # Set the validators and other context attributes
         context.num_validators = len(context.remaining_validators) + 1
-        context.contract_snapshot_supplier = contract_snapshot_supplier
         context.votes = votes
 
         # Transition to the CommittingState
@@ -1991,9 +2002,10 @@ async def handle(self, context):
             leaders_contract_snapshot = context.contract_snapshot_supplier()
 
             # Set the contract snapshot for the transaction for a future rollback
-            context.transactions_processor.set_transaction_contract_snapshot(
-                context.transaction.hash, leaders_contract_snapshot.to_dict()
-            )
+            if not context.transaction.contract_snapshot:
+                context.transactions_processor.set_transaction_contract_snapshot(
+                    context.transaction.hash, leaders_contract_snapshot.to_dict()
+                )
 
             # Do not deploy or update the contract if the execution failed
             if leader_receipt.execution_result == ExecutionResultStatus.SUCCESS:
@@ -2093,6 +2105,12 @@ async def handle(self, context):
         else:
             consensus_round = "Undetermined"
 
+        # Save the contract snapshot for potential future appeals
+        if not context.transaction.contract_snapshot:
+            context.transactions_processor.set_transaction_contract_snapshot(
+                context.transaction.hash, context.contract_snapshot_supplier().to_dict()
+            )
+
         # Set the transaction result with the current consensus data
         context.transactions_processor.set_transaction_result(
             context.transaction.hash,