safer snapshot commit revert and dispose

nimbus/vm/computation.nim

@@ -103,9 +103,12 @@ proc revert*(snapshot: var ComputationSnapshot, burnsGas: bool = false) =
   snapshot.snapshot.revert()
   snapshot.computation.error = Error(info: getCurrentExceptionMsg(), burnsGas: burnsGas)
 
-proc commit*(snapshot: var ComputationSnapshot) =
+proc commit*(snapshot: var ComputationSnapshot) {.inline.} =
   snapshot.snapshot.commit()
 
+proc dispose*(snapshot: var ComputationSnapshot) {.inline.} =
+  snapshot.snapshot.dispose()
+
 proc applyMessageAux(computation: var BaseComputation, opCode: static[Op]) =
   if computation.msg.depth > STACK_DEPTH_LIMIT:
     raise newException(StackDepthError, "Stack depth limit reached")
@@ -171,6 +174,8 @@ proc applyMessageAux(computation: var BaseComputation, opCode: static[Op]) =
 
 proc applyMessage(computation: var BaseComputation, opCode: static[Op]) =
   var snapshot = computation.snapshot()
+  defer: snapshot.dispose()
+
   try:
     computation.applyMessageAux(opCode)
   except VMError:
@@ -197,6 +202,7 @@ proc applyCreateMessage(fork: Fork, computation: var BaseComputation, opCode: st
   if contractCode.len == 0: return
 
   var snapshot = computation.snapshot()
+  defer: snapshot.dispose()
 
   if fork >= FkSpurious and contractCode.len >= EIP170_CODE_SIZE_LIMIT:
     raise newException(OutOfGas, &"Contract code size exceeds EIP170 limit of {EIP170_CODE_SIZE_LIMIT}.  Got code of size: {contractCode.len}")

nimbus/vm_state.nim

@@ -144,7 +144,7 @@ proc snapshot*(vmState: BaseVMState): Snapshot =
   result.vmState = vmState
 
 proc revert*(s: var Snapshot) =
-  s.transaction.dispose()
+  s.transaction.rollback()
   s.vmState.accountDb.rootHash = s.intermediateRoot
   s.vmState.blockHeader.stateRoot = s.intermediateRoot
 
@@ -152,6 +152,9 @@ proc commit*(s: var Snapshot) =
   s.transaction.commit()
   s.vmState.accountDb.rootHash = s.vmState.blockHeader.stateRoot
 
+proc dispose*(s: var Snapshot) {.inline.} =
+  s.transaction.dispose()
+
 proc getTracingResult*(vmState: BaseVMState): JsonNode =
   assert(vmState.tracingEnabled)
   vmState.tracer.trace

nimbus/vm_state_transactions.nim

@@ -42,6 +42,7 @@ proc setupComputation*(vmState: BaseVMState, transaction: Transaction, sender: E
 
 proc execComputation*(computation: var BaseComputation): bool =
   var snapshot = computation.snapshot()
+  defer: snapshot.dispose()
 
   try:
     computation.executeOpcodes()