core: fix nspcc-dev#2845 system fee refund attribute

pkg/core/blockchain.go

@@ -1418,6 +1418,7 @@ func (bc *Blockchain) storeBlock(block *block.Block, txpool *mempool.Pool) error
 		cache          = bc.dao.GetPrivate()
 		aerCache       = bc.dao.GetPrivate()
 		appExecResults = make([]*state.AppExecResult, 0, 2+len(block.Transactions))
+		txesConsumed   = make(map[util.Uint256]int64, len(block.Transactions))
 		aerchan        = make(chan *state.AppExecResult, len(block.Transactions)/8) // Tested 8 and 4 with no practical difference, but feel free to test more and tune.
 		aerdone        = make(chan error)
 	)
@@ -1500,7 +1501,7 @@ func (bc *Blockchain) storeBlock(block *block.Block, txpool *mempool.Pool) error
 		close(aerdone)
 	}()
 	_ = cache.GetItemCtx() // Prime serialization context cache (it'll be reused by upper layer DAOs).
-	aer, v, err := bc.runPersist(bc.contracts.GetPersistScript(), block, cache, trigger.OnPersist, nil)
+	aer, v, err := bc.runPersist(bc.contracts.GetPersistScript(), block, cache, trigger.OnPersist, nil, nil)
 	if err != nil {
 		// Release goroutines, don't care about errors, we already have one.
 		close(aerchan)
@@ -1533,6 +1534,7 @@ func (bc *Blockchain) storeBlock(block *block.Block, txpool *mempool.Pool) error
 				zap.Error(err))
 			faultException = err.Error()
 		}
+		txesConsumed[tx.Hash()] = v.GasConsumed()
 		aer := &state.AppExecResult{
 			Container: tx.Hash(),
 			Execution: state.Execution{
@@ -1548,7 +1550,7 @@ func (bc *Blockchain) storeBlock(block *block.Block, txpool *mempool.Pool) error
 		aerchan <- aer
 	}
 
-	aer, _, err = bc.runPersist(bc.contracts.GetPostPersistScript(), block, cache, trigger.PostPersist, v)
+	aer, _, err = bc.runPersist(bc.contracts.GetPostPersistScript(), block, cache, trigger.PostPersist, v, txesConsumed)
 	if err != nil {
 		// Release goroutines, don't care about errors, we already have one.
 		close(aerchan)
@@ -1683,13 +1685,14 @@ func (bc *Blockchain) IsExtensibleAllowed(u util.Uint160) bool {
 	return n < len(us)
 }
 
-func (bc *Blockchain) runPersist(script []byte, block *block.Block, cache *dao.Simple, trig trigger.Type, v *vm.VM) (*state.AppExecResult, *vm.VM, error) {
+func (bc *Blockchain) runPersist(script []byte, block *block.Block, cache *dao.Simple, trig trigger.Type, v *vm.VM, txesConsumed map[util.Uint256]int64) (*state.AppExecResult, *vm.VM, error) {
 	systemInterop := bc.newInteropContext(trig, cache, block, nil)
 	if v == nil {
 		v = systemInterop.SpawnVM()
 	} else {
 		systemInterop.ReuseVM(v)
 	}
+	systemInterop.TxesConsumed = txesConsumed
 	v.LoadScriptWithFlags(script, callflag.All)
 	if err := systemInterop.Exec(); err != nil {
 		return nil, v, fmt.Errorf("VM has failed: %w", err)
@@ -2248,6 +2251,11 @@ func (bc *Blockchain) FeePerByte() int64 {
 	return bc.contracts.Policy.GetFeePerByteInternal(bc.dao)
 }
 
+// GasRefundFee returns extra fee for system fee refundable transaction
+func (bc *Blockchain) SystemFeeRefundCost() int64 {
+	return bc.contracts.Policy.GetSystemFeeRefundCostInternal(bc.dao)
+}
+
 // GetMemPool returns the memory pool of the blockchain.
 func (bc *Blockchain) GetMemPool() *mempool.Pool {
 	return bc.memPool
@@ -2367,6 +2375,9 @@ func (bc *Blockchain) verifyAndPoolTx(t *transaction.Transaction, pool *mempool.
 			needNetworkFee += (int64(na.NKeys) + 1) * bc.contracts.Notary.GetNotaryServiceFeePerKey(bc.dao)
 		}
 	}
+	if len(t.GetAttributes(transaction.RefundableSystemFeeT)) > 0 {
+		needNetworkFee += bc.SystemFeeRefundCost()
+	}
 	netFee := t.NetworkFee - needNetworkFee
 	if netFee < 0 {
 		return fmt.Errorf("%w: net fee is %v, need %v", ErrTxSmallNetworkFee, t.NetworkFee, needNetworkFee)
@@ -2480,6 +2491,11 @@ func (bc *Blockchain) verifyTxAttributes(d *dao.Simple, tx *transaction.Transact
 			if !tx.HasSigner(bc.contracts.Notary.Hash) {
 				return fmt.Errorf("%w: NotaryAssisted attribute was found, but transaction is not signed by the Notary native contract", ErrInvalidAttribute)
 			}
+		case transaction.RefundableSystemFeeT:
+			state := bc.GetContractState(tx.Sender())
+			if state != nil {
+				return fmt.Errorf("%w: RefundableSystemFee attribute was found, but transaction sender is contract", ErrInvalidAttribute)
+			}
 		default:
 			if !bc.config.ReservedAttributes && attrType >= transaction.ReservedLowerBound && attrType <= transaction.ReservedUpperBound {
 				return fmt.Errorf("%w: attribute of reserved type was found, but ReservedAttributes are disabled", ErrInvalidAttribute)

pkg/core/interop/context.go

@@ -45,21 +45,23 @@ type Ledger interface {
 
 // Context represents context in which interops are executed.
 type Context struct {
-	Chain            Ledger
-	Container        hash.Hashable
-	Network          uint32
-	Hardforks        map[string]uint32
-	Natives          []Contract
-	Trigger          trigger.Type
-	Block            *block.Block
-	NonceData        [16]byte
-	Tx               *transaction.Transaction
-	DAO              *dao.Simple
-	Notifications    []state.NotificationEvent
-	Log              *zap.Logger
-	VM               *vm.VM
-	Functions        []Function
-	Invocations      map[util.Uint160]int
+	Chain         Ledger
+	Container     hash.Hashable
+	Network       uint32
+	Hardforks     map[string]uint32
+	Natives       []Contract
+	Trigger       trigger.Type
+	Block         *block.Block
+	NonceData     [16]byte
+	Tx            *transaction.Transaction
+	DAO           *dao.Simple
+	Notifications []state.NotificationEvent
+	Log           *zap.Logger
+	VM            *vm.VM
+	Functions     []Function
+	Invocations   map[util.Uint160]int
+	TxesConsumed  map[util.Uint256]int64
+
 	cancelFuncs      []context.CancelFunc
 	getContract      func(*dao.Simple, util.Uint160) (*state.Contract, error)
 	baseExecFee      int64

pkg/core/native/native_gas.go

@@ -129,6 +129,15 @@ func (g *GAS) OnPersist(ic *interop.Context) error {
 
 // PostPersist implements the Contract interface.
 func (g *GAS) PostPersist(ic *interop.Context) error {
+	for _, tx := range ic.Block.Transactions {
+		attrs := tx.GetAttributes(transaction.RefundableSystemFeeT)
+		if len(attrs) != 0 {
+			consumed := ic.TxesConsumed[tx.Hash()]
+			if consumed < tx.SystemFee {
+				g.mint(ic, tx.Sender(), big.NewInt(tx.SystemFee-consumed), false)
+			}
+		}
+	}
 	return nil
 }
 

pkg/core/native/policy.go

@@ -21,9 +21,10 @@ import (
 const (
 	policyContractID = -7
 
-	defaultExecFeeFactor      = interop.DefaultBaseExecFee
-	defaultFeePerByte         = 1000
-	defaultMaxVerificationGas = 1_50000000
+	defaultExecFeeFactor       = interop.DefaultBaseExecFee
+	defaultFeePerByte          = 1000
+	defaultMaxVerificationGas  = 1_50000000
+	defaultSystemFeeRefundCost = 0_10000000
 	// DefaultStoragePrice is the price to pay for 1 byte of storage.
 	DefaultStoragePrice = 100000
 
@@ -33,7 +34,8 @@ const (
 	maxFeePerByte = 100_000_000
 	// maxStoragePrice is the maximum allowed price for a byte of storage.
 	maxStoragePrice = 10000000
-
+	// maxSystemFeeRefundCost is the maximun allowed extra fee for gas refundable transaction
+	maxSystemFeeRefundCost = 1_00000000
 	// blockedAccountPrefix is a prefix used to store blocked account.
 	blockedAccountPrefix = 15
 )
@@ -46,6 +48,8 @@ var (
 	feePerByteKey = []byte{10}
 	// storagePriceKey is a key used to store storage price.
 	storagePriceKey = []byte{19}
+	// systemFeeRefundCostKey is a key usesd to store gas refund fee
+	systemFeeRefundCostKey = []byte{20}
 )
 
 // Policy represents Policy native contract.
@@ -59,6 +63,7 @@ type PolicyCache struct {
 	feePerByte         int64
 	maxVerificationGas int64
 	storagePrice       uint32
+	systemFeeRefundCost       int64
 	blockedAccounts    []util.Uint160
 }
 
@@ -127,6 +132,11 @@ func newPolicy() *Policy {
 	md = newMethodAndPrice(p.unblockAccount, 1<<15, callflag.States)
 	p.AddMethod(md, desc)
 
+	desc = newDescriptor("setSystemFeeRefundCost", smartcontract.VoidType,
+		manifest.NewParameter("value", smartcontract.IntegerType))
+	md = newMethodAndPrice(p.setSystemFeeRefundCost, 1<<15, callflag.States)
+	p.AddMethod(md, desc)
+
 	return p
 }
 
@@ -140,12 +150,14 @@ func (p *Policy) Initialize(ic *interop.Context) error {
 	setIntWithKey(p.ID, ic.DAO, feePerByteKey, defaultFeePerByte)
 	setIntWithKey(p.ID, ic.DAO, execFeeFactorKey, defaultExecFeeFactor)
 	setIntWithKey(p.ID, ic.DAO, storagePriceKey, DefaultStoragePrice)
+	setIntWithKey(p.ID, ic.DAO, systemFeeRefundCostKey, defaultSystemFeeRefundCost)
 
 	cache := &PolicyCache{
 		execFeeFactor:      defaultExecFeeFactor,
 		feePerByte:         defaultFeePerByte,
 		maxVerificationGas: defaultMaxVerificationGas,
 		storagePrice:       DefaultStoragePrice,
+		systemFeeRefundCost:       defaultSystemFeeRefundCost,
 		blockedAccounts:    make([]util.Uint160, 0),
 	}
 	ic.DAO.SetCache(p.ID, cache)
@@ -168,6 +180,7 @@ func (p *Policy) fillCacheFromDAO(cache *PolicyCache, d *dao.Simple) error {
 	cache.feePerByte = getIntWithKey(p.ID, d, feePerByteKey)
 	cache.maxVerificationGas = defaultMaxVerificationGas
 	cache.storagePrice = uint32(getIntWithKey(p.ID, d, storagePriceKey))
+	cache.systemFeeRefundCost = getIntWithKey(p.ID, d, systemFeeRefundCostKey)
 
 	cache.blockedAccounts = make([]util.Uint160, 0)
 	var fErr error
@@ -354,6 +367,26 @@ func (p *Policy) unblockAccount(ic *interop.Context, args []stackitem.Item) stac
 	return stackitem.NewBool(true)
 }
 
+func (p *Policy) GetSystemFeeRefundCostInternal(d *dao.Simple) int64 {
+	cache := d.GetROCache(p.ID).(*PolicyCache)
+	return cache.systemFeeRefundCost
+}
+
+// setSystemFeeRefundCost is a Policy contract method that set extra network fee for gas refundable transaction.
+func (p *Policy) setSystemFeeRefundCost(ic *interop.Context, args []stackitem.Item) stackitem.Item {
+	value := toBigInt(args[0]).Int64()
+	if value < 0 || value > maxSystemFeeRefundCost {
+		panic(fmt.Errorf("SystemFeeRefundCost shouldn't be negative or greater than %d", maxSystemFeeRefundCost))
+	}
+	if !p.NEO.checkCommittee(ic) {
+		panic("invalid committee signature")
+	}
+	setIntWithKey(p.ID, ic.DAO, systemFeeRefundCostKey, value)
+	cache := ic.DAO.GetRWCache(p.ID).(*PolicyCache)
+	cache.systemFeeRefundCost = value
+	return stackitem.Null{}
+}
+
 // CheckPolicy checks whether a transaction conforms to the current policy restrictions,
 // like not being signed by a blocked account or not exceeding the block-level system
 // fee limit.

pkg/core/transaction/attribute.go

@@ -41,6 +41,8 @@ func (attr *Attribute) DecodeBinary(br *io.BinReader) {
 		attr.Value = new(Conflicts)
 	case NotaryAssistedT:
 		attr.Value = new(NotaryAssisted)
+	case RefundableSystemFeeT:
+		attr.Value = new(RefundableSystemFee)
 	default:
 		if t >= ReservedLowerBound && t <= ReservedUpperBound {
 			attr.Value = new(Reserved)
@@ -57,7 +59,7 @@ func (attr *Attribute) EncodeBinary(bw *io.BinWriter) {
 	bw.WriteB(byte(attr.Type))
 	switch t := attr.Type; t {
 	case HighPriority:
-	case OracleResponseT, NotValidBeforeT, ConflictsT, NotaryAssistedT:
+	case OracleResponseT, NotValidBeforeT, ConflictsT, NotaryAssistedT, RefundableSystemFeeT:
 		attr.Value.EncodeBinary(bw)
 	default:
 		if t >= ReservedLowerBound && t <= ReservedUpperBound {
@@ -102,6 +104,9 @@ func (attr *Attribute) UnmarshalJSON(data []byte) error {
 	case NotaryAssistedT.String():
 		attr.Type = NotaryAssistedT
 		attr.Value = new(NotaryAssisted)
+	case RefundableSystemFeeT.String():
+		attr.Type = RefundableSystemFeeT
+		attr.Value = new(RefundableSystemFee)
 	default:
 		return errors.New("wrong Type")
 	}

pkg/core/transaction/attrtype.go

@@ -14,11 +14,12 @@ const (
 
 // List of valid attribute types.
 const (
-	HighPriority    AttrType = 1
-	OracleResponseT AttrType = 0x11 // OracleResponse
-	NotValidBeforeT AttrType = 0x20 // NotValidBefore
-	ConflictsT      AttrType = 0x21 // Conflicts
-	NotaryAssistedT AttrType = 0x22 // NotaryAssisted
+	HighPriority         AttrType = 1
+	OracleResponseT      AttrType = 0x11 // OracleResponse
+	NotValidBeforeT      AttrType = 0x20 // NotValidBefore
+	ConflictsT           AttrType = 0x21 // Conflicts
+	NotaryAssistedT      AttrType = 0x22 // NotaryAssisted
+	RefundableSystemFeeT AttrType = 0x30 // RefundableSystemFee
 )
 
 func (a AttrType) allowMultiple() bool {

pkg/core/transaction/refundablesystemfee.go

@@ -0,0 +1,20 @@
+package transaction
+
+import (
+	"github.com/nspcc-dev/neo-go/pkg/io"
+)
+
+// Conflicts represents attribute for refund gas transaction.
+type RefundableSystemFee struct {
+}
+
+// DecodeBinary implements the io.Serializable interface.
+func (c *RefundableSystemFee) DecodeBinary(br *io.BinReader) {
+}
+
+// EncodeBinary implements the io.Serializable interface.
+func (c *RefundableSystemFee) EncodeBinary(w *io.BinWriter) {
+}
+
+func (c *RefundableSystemFee) toJSONMap(m map[string]interface{}) {
+}

pkg/services/rpcsrv/server.go

@@ -67,6 +67,7 @@ type (
 		CalculateClaimable(h util.Uint160, endHeight uint32) (*big.Int, error)
 		CurrentBlockHash() util.Uint256
 		FeePerByte() int64
+		SystemFeeRefundCost() int64
 		ForEachNEP11Transfer(acc util.Uint160, newestTimestamp uint64, f func(*state.NEP11Transfer) (bool, error)) error
 		ForEachNEP17Transfer(acc util.Uint160, newestTimestamp uint64, f func(*state.NEP17Transfer) (bool, error)) error
 		GetAppExecResults(util.Uint256, trigger.Type) ([]state.AppExecResult, error)
@@ -847,6 +848,9 @@ func (s *Server) calculateNetworkFee(reqParams params.Params) (interface{}, *neo
 			netFee += (int64(na.NKeys) + 1) * s.chain.GetNotaryServiceFeePerKey()
 		}
 	}
+	if len(tx.GetAttributes(transaction.RefundableSystemFeeT)) > 0 {
+		netFee += s.chain.SystemFeeRefundCost()
+	}
 	fee := s.chain.FeePerByte()
 	netFee += int64(size) * fee
 	return result.NetworkFee{Value: netFee}, nil