feat: Apply wasmtime fuel

go.mod

@@ -55,3 +55,5 @@ replace (
 	github.com/linxGnu/grocksdb => github.com/gohornet/grocksdb v1.6.38-0.20211012114404-55f425442260
 	go.dedis.ch/kyber/v3 v3.0.13 => github.com/kape1395/kyber/v3 v3.0.14-0.20210622094514-fefb81148dc3
 )
+
+replace github.com/bytecodealliance/wasmtime-go => ../wasmtime-go

packages/wasmvm/wasmhost/wasmtimevm.go

@@ -11,31 +11,55 @@ import (
 
 type WasmTimeVM struct {
 	WasmVMBase
-	engine    *wasmtime.Engine
-	instance  *wasmtime.Instance
-	interrupt *wasmtime.InterruptHandle
-	linker    *wasmtime.Linker
-	memory    *wasmtime.Memory
-	module    *wasmtime.Module
-	store     *wasmtime.Store
+	engine       *wasmtime.Engine
+	instance     *wasmtime.Instance
+	interrupt    *wasmtime.InterruptHandle
+	linker       *wasmtime.Linker
+	memory       *wasmtime.Memory
+	module       *wasmtime.Module
+	store        *wasmtime.Store
+	remainingGas uint64
 }
 
 func NewWasmTimeVM() WasmVM {
 	vm := &WasmTimeVM{}
 	config := wasmtime.NewConfig()
 	config.SetInterruptable(true)
+	config.SetConsumeFuel(true)
 	vm.engine = wasmtime.NewEngineWithConfig(config)
 	return vm
 }
 
-func (vm *WasmTimeVM) GasBudget(budget uint64) {
-	// TODO turn on gas usage for VM somewhere
-	// set gas budget to provided budget here
+// GasBudget sets gas budget. Each time GasBudget is called, we will restart counting the total burned gas
+func (vm *WasmTimeVM) GasBudget(budget uint64) error {
+	remaining, err := vm.store.ConsumeFuel(0)
+	if err != nil {
+		return err
+	}
+
+	vm.remainingGas = remaining
+
+	if budget > remaining {
+		return vm.store.AddFuel(budget - remaining)
+	}
+
+	_, err = vm.store.ConsumeFuel(remaining - budget)
+	if err != nil {
+		return err
+	}
+	return nil
 }
 
+// GasBurned will return the gas has been burned by wasmtime since the last time WasmTimeVM.GasBudget was called
 func (vm *WasmTimeVM) GasBurned() uint64 {
-	// TODO return actual amount of gas burned by VM
-	return 0
+	gasBurned, ok := vm.store.FuelConsumed()
+	if !ok {
+		return 0
+	}
+
+	// gasBurned is the gas has been burned since the vm.store instance was been created
+	// so we need to subtract the remaining gas before calling vm.GasBudget
+	return gasBurned - vm.remainingGas
 }
 
 func (vm *WasmTimeVM) Instantiate() (err error) {

packages/wasmvm/wasmhost/wasmvm.go

@@ -37,7 +37,7 @@ var (
 )
 
 type WasmVM interface {
-	GasBudget(budget uint64)
+	GasBudget(budget uint64) error
 	GasBurned() uint64
 	GasEnable(enable bool)
 	Instantiate() error
@@ -61,8 +61,9 @@ type WasmVMBase struct {
 	timeoutStarted bool
 }
 
-func (vm *WasmVMBase) GasBudget(budget uint64) {
+func (vm *WasmVMBase) GasBudget(budget uint64) error {
 	// ignore gas budget
+	return nil
 }
 
 func (vm *WasmVMBase) GasBurned() uint64 {