From 7256efd1ed2b82029d983fd55001676e5a147f83 Mon Sep 17 00:00:00 2001
From: Evgenii Stratonikov <evgeniy@nspcc.ru>
Date: Tue, 9 Jun 2020 12:23:14 +0300
Subject: [PATCH] vm: implement (*VM).AddGas

Calculating interop prices can be tricky. It is more convenitent to burn
gas inside interops where necessary parameters are popped.
---
 pkg/core/gas_price.go   | 3 +++
 pkg/core/interop_neo.go | 4 ++++
 pkg/vm/vm.go            | 6 ++++++
 pkg/vm/vm_test.go       | 8 ++++++++
 4 files changed, 21 insertions(+)

diff --git a/pkg/core/gas_price.go b/pkg/core/gas_price.go
index e7318b52e..b9130b0e1 100644
--- a/pkg/core/gas_price.go
+++ b/pkg/core/gas_price.go
@@ -11,6 +11,9 @@ import (
 // of 0.001 GAS = Fixed8(10^5).
 const interopGasRatio = 100000
 
+// StoragePrice is a price for storing 1 byte of storage.
+const StoragePrice = 100000
+
 // getPrice returns a price for executing op with the provided parameter.
 // Some SYSCALLs have variable price depending on their arguments.
 func getPrice(v *vm.VM, op opcode.Opcode, parameter []byte) util.Fixed8 {
diff --git a/pkg/core/interop_neo.go b/pkg/core/interop_neo.go
index 08f07de56..b80031e28 100644
--- a/pkg/core/interop_neo.go
+++ b/pkg/core/interop_neo.go
@@ -11,6 +11,7 @@ import (
 	"github.com/nspcc-dev/neo-go/pkg/io"
 	"github.com/nspcc-dev/neo-go/pkg/smartcontract/manifest"
 	"github.com/nspcc-dev/neo-go/pkg/smartcontract/trigger"
+	"github.com/nspcc-dev/neo-go/pkg/util"
 	"github.com/nspcc-dev/neo-go/pkg/vm"
 	"github.com/nspcc-dev/neo-go/pkg/vm/stackitem"
 )
@@ -73,6 +74,9 @@ func createContractStateFromVM(ic *interop.Context, v *vm.VM) (*state.Contract,
 	if len(manifestBytes) > manifest.MaxManifestSize {
 		return nil, errors.New("manifest is too big")
 	}
+	if !v.AddGas(util.Fixed8(StoragePrice * (len(script) + len(manifestBytes)))) {
+		return nil, errors.New("gas limit exceeded")
+	}
 	var m manifest.Manifest
 	r := io.NewBinReaderFromBuf(manifestBytes)
 	m.DecodeBinary(r)
diff --git a/pkg/vm/vm.go b/pkg/vm/vm.go
index 6d0c36f29..3f933595f 100644
--- a/pkg/vm/vm.go
+++ b/pkg/vm/vm.go
@@ -136,6 +136,12 @@ func (v *VM) SetGasLimit(max util.Fixed8) {
 	v.gasLimit = max
 }
 
+// AddGas consumes specified amount of gas. It returns true iff gas limit wasn't exceeded.
+func (v *VM) AddGas(gas util.Fixed8) bool {
+	v.gasConsumed += gas
+	return v.gasLimit == 0 || v.gasConsumed <= v.gasLimit
+}
+
 // Estack returns the evaluation stack so interop hooks can utilize this.
 func (v *VM) Estack() *Stack {
 	return v.estack
diff --git a/pkg/vm/vm_test.go b/pkg/vm/vm_test.go
index 746df0494..ae9a06fd0 100644
--- a/pkg/vm/vm_test.go
+++ b/pkg/vm/vm_test.go
@@ -98,6 +98,14 @@ func TestVM_SetPriceGetter(t *testing.T) {
 	})
 }
 
+func TestAddGas(t *testing.T) {
+	v := New()
+	v.SetGasLimit(10)
+	require.True(t, v.AddGas(5))
+	require.True(t, v.AddGas(5))
+	require.False(t, v.AddGas(5))
+}
+
 func TestBytesToPublicKey(t *testing.T) {
 	v := New()
 	cache := v.GetPublicKeys()