Fix eth_estimateGas and simulated txs (#142)

rpc/eth_api.go

@@ -374,7 +374,10 @@ type account struct {
 // DoCall performs a simulated call operation through the evm
 func (e *PublicEthAPI) doCall(args CallArgs, blockNr rpc.BlockNumber, globalGasCap *big.Int) (sdk.Result, error) {
 	// Set height for historical queries
-	ctx := e.cliCtx.WithHeight(blockNr.Int64())
+	ctx := e.cliCtx
+	if blockNr.Int64() != 0 {
+		ctx = e.cliCtx.WithHeight(blockNr.Int64())
+	}
 
 	// Set sender address or use a default if none specified
 	var addr common.Address
@@ -452,13 +455,14 @@ func (e *PublicEthAPI) doCall(args CallArgs, blockNr rpc.BlockNumber, globalGasC
 }
 
 // EstimateGas estimates gas usage for the given smart contract call.
-func (e *PublicEthAPI) EstimateGas(args CallArgs, blockNr rpc.BlockNumber) (hexutil.Uint64, error) {
-	result, err := e.doCall(args, blockNr, big.NewInt(emint.DefaultRPCGasLimit))
+func (e *PublicEthAPI) EstimateGas(args CallArgs) (hexutil.Uint64, error) {
+	result, err := e.doCall(args, 0, big.NewInt(emint.DefaultRPCGasLimit))
 	if err != nil {
 		return 0, err
 	}
 
-	return hexutil.Uint64(result.GasUsed), nil
+	// TODO: change 1000 buffer for more accurate buffer (must be at least 1 to not run OOG)
+	return hexutil.Uint64(result.GasUsed + 1000), nil
 }
 
 // GetBlockByHash returns the block identified by hash.
@@ -916,7 +920,7 @@ func (e *PublicEthAPI) GenerateFromArgs(args params.SendTxArgs) (msg *types.Ethe
 			Value:    args.Value,
 			Data:     args.Data,
 		}
-		g, _ := e.EstimateGas(callArgs, rpc.BlockNumber(e.cliCtx.Height))
+		g, _ := e.EstimateGas(callArgs)
 		gasLimit = uint64(g)
 	} else {
 		gasLimit = (uint64)(*args.Gas)

x/evm/types/state_transition.go

@@ -44,13 +44,19 @@ func (st StateTransition) TransitionCSDB(ctx sdk.Context) (*big.Int, sdk.Result)
 	// This gas limit the the transaction gas limit with intrinsic gas subtracted
 	gasLimit := st.GasLimit - ctx.GasMeter().GasConsumed()
 
-	var snapshot int
+	csdb := st.Csdb
 	if st.Simulate {
 		// gasLimit is set here because stdTxs incur gaskv charges in the ante handler, but for eth_call
 		// the cost needs to be the same as an Ethereum transaction sent through the web3 API
+		consumedGas := ctx.GasMeter().GasConsumed()
 		gasLimit = st.GasLimit - cost
+		if consumedGas < cost {
+			// If Cosmos standard tx ante handler cost is less than EVM intrinsic cost
+			// gas must be consumed to match to accurately simulate an Ethereum transaction
+			ctx.GasMeter().ConsumeGas(cost-consumedGas, "Intrinsic gas match")
+		}
 
-		snapshot = st.Csdb.Snapshot()
+		csdb = st.Csdb.Copy()
 	}
 
 	// Create context for evm
@@ -70,7 +76,7 @@ func (st StateTransition) TransitionCSDB(ctx sdk.Context) (*big.Int, sdk.Result)
 	evmGasMeter := sdk.NewInfiniteGasMeter()
 
 	vmenv := vm.NewEVM(
-		context, st.Csdb.WithContext(ctx.WithGasMeter(evmGasMeter)),
+		context, csdb.WithContext(ctx.WithGasMeter(evmGasMeter)),
 		GenerateChainConfig(st.ChainID), vm.Config{},
 	)
 
@@ -86,15 +92,15 @@ func (st StateTransition) TransitionCSDB(ctx sdk.Context) (*big.Int, sdk.Result)
 		ret, addr, leftOverGas, vmerr = vmenv.Create(senderRef, st.Payload, gasLimit, st.Amount)
 	} else {
 		// Increment the nonce for the next transaction
-		st.Csdb.SetNonce(st.Sender, st.Csdb.GetNonce(st.Sender)+1)
+		csdb.SetNonce(st.Sender, csdb.GetNonce(st.Sender)+1)
 		ret, leftOverGas, vmerr = vmenv.Call(senderRef, *st.Recipient, st.Payload, gasLimit, st.Amount)
 	}
 
 	// Generate bloom filter to be saved in tx receipt data
 	bloomInt := big.NewInt(0)
 	var bloomFilter ethtypes.Bloom
-	if st.THash != nil {
-		logs := st.Csdb.GetLogs(*st.THash)
+	if st.THash != nil && !st.Simulate {
+		logs := csdb.GetLogs(*st.THash)
 		bloomInt = ethtypes.LogsBloom(logs)
 		bloomFilter = ethtypes.BytesToBloom(bloomInt.Bytes())
 	}
@@ -114,13 +120,11 @@ func (st StateTransition) TransitionCSDB(ctx sdk.Context) (*big.Int, sdk.Result)
 		return nil, res
 	}
 
-	if st.Simulate {
-		st.Csdb.RevertToSnapshot(snapshot)
-	}
-
 	// TODO: Refund unused gas here, if intended in future
-
-	st.Csdb.Finalise(true) // Change to depend on config
+	if !st.Simulate {
+		// Finalise state if not a simulated transaction
+		st.Csdb.Finalise(true) // Change to depend on config
+	}
 
 	// Consume gas from evm execution
 	// Out of gas check does not need to be done here since it is done within the EVM execution

x/evm/types/statedb.go

@@ -571,7 +571,7 @@ func (csdb *CommitStateDB) CreateAccount(addr ethcmn.Address) {
 // Copy creates a deep, independent copy of the state.
 //
 // NOTE: Snapshots of the copied state cannot be applied to the copy.
-func (csdb *CommitStateDB) Copy() ethvm.StateDB {
+func (csdb *CommitStateDB) Copy() *CommitStateDB {
 	csdb.lock.Lock()
 	defer csdb.lock.Unlock()