Add abstraction method of processTxs to StateDB

- Update GHA lint.yml increasing timeout time to avoid GHA Lint errors
- Update common.BatchNum & common.Idx & common.Nonce usage in StateDB
- Add abstraction method of processTxs to StateDB
    - Which will be used by Synchronizer & BatchBuilder

.github/workflows/lint.yml

@@ -13,4 +13,4 @@ jobs:
       - name: Lint
         run: |
           curl -sSfL https://raw.githubusercontent.com/golangci/golangci-lint/master/install.sh | sh -s -- -b $(go env GOPATH)/bin v1.24.0
-          $(go env GOPATH)/bin/golangci-lint run
+          $(go env GOPATH)/bin/golangci-lint run --timeout=5m

batchbuilder/batchbuilder.go

@@ -51,25 +51,7 @@ func (bb *BatchBuilder) Reset(batchNum uint64, fromSynchronizer bool) error {
 }
 
 // BuildBatch takes the transactions and returns the common.ZKInputs of the next batch
-func (bb *BatchBuilder) BuildBatch(configBatch *ConfigBatch, l1usertxs, l1coordinatortxs []*common.L1Tx, l2txs []*common.PoolL2Tx, tokenIDs []common.TokenID) (*common.ZKInputs, error) {
-	for _, tx := range l1usertxs {
-		err := bb.localStateDB.ProcessL1Tx(tx)
-		if err != nil {
-			return nil, err
-		}
-	}
-	for _, tx := range l1coordinatortxs {
-		err := bb.localStateDB.ProcessL1Tx(tx)
-		if err != nil {
-			return nil, err
-		}
-	}
-	for _, tx := range l2txs {
-		err := bb.localStateDB.ProcessPoolL2Tx(tx)
-		if err != nil {
-			return nil, err
-		}
-	}
-
-	return nil, nil
+func (bb *BatchBuilder) BuildBatch(configBatch *ConfigBatch, l1usertxs, l1coordinatortxs []*common.L1Tx, l2txs []*common.L2Tx, tokenIDs []common.TokenID) (*common.ZKInputs, error) {
+	zkInputs, _, err := bb.localStateDB.ProcessTxs(l1usertxs, l1coordinatortxs, l2txs)
+	return zkInputs, err
 }

common/account.go

@@ -17,7 +17,7 @@ const NLEAFELEMS = 4
 // Account is a struct that gives information of the holdings of an address and a specific token. Is the data structure that generates the Value stored in the leaf of the MerkleTree
 type Account struct {
 	TokenID   TokenID
-	Nonce     uint64   // max of 40 bits used
+	Nonce     Nonce    // max of 40 bits used
 	Balance   *big.Int // max of 192 bits used
 	PublicKey *babyjub.PublicKey
 	EthAddr   ethCommon.Address
@@ -44,8 +44,10 @@ func (a *Account) Bytes() ([32 * NLEAFELEMS]byte, error) {
 		return b, fmt.Errorf("%s Balance", ErrNumOverflow)
 	}
 
-	var nonceBytes [8]byte
-	binary.LittleEndian.PutUint64(nonceBytes[:], a.Nonce)
+	nonceBytes, err := a.Nonce.Bytes()
+	if err != nil {
+		return b, err
+	}
 
 	copy(b[0:4], a.TokenID.Bytes())
 	copy(b[4:9], nonceBytes[:])
@@ -107,9 +109,9 @@ func AccountFromBigInts(e [NLEAFELEMS]*big.Int) (*Account, error) {
 // AccountFromBytes returns a Account from a byte array
 func AccountFromBytes(b [32 * NLEAFELEMS]byte) (*Account, error) {
 	tokenID := binary.LittleEndian.Uint32(b[0:4])
-	var nonceBytes [8]byte
-	copy(nonceBytes[:], b[4:9])
-	nonce := binary.LittleEndian.Uint64(nonceBytes[:])
+	var nonceBytes5 [5]byte
+	copy(nonceBytes5[:], b[4:9])
+	nonce := NonceFromBytes(nonceBytes5)
 	sign := b[10] == 1
 	balance := new(big.Int).SetBytes(SwapEndianness(b[32:56])) // b[32:56], as Balance is 192 bits (24 bytes)
 	if !bytes.Equal(b[56:64], []byte{0, 0, 0, 0, 0, 0, 0, 0}) {

common/account_test.go

@@ -23,7 +23,7 @@ func TestAccount(t *testing.T) {
 
 	account := &Account{
 		TokenID:   TokenID(1),
-		Nonce:     uint64(1234),
+		Nonce:     Nonce(1234),
 		Balance:   big.NewInt(1000),
 		PublicKey: pk,
 		EthAddr:   ethCommon.HexToAddress("0xc58d29fA6e86E4FAe04DDcEd660d45BCf3Cb2370"),
@@ -66,7 +66,7 @@ func TestAccountLoop(t *testing.T) {
 
 		account := &Account{
 			TokenID:   TokenID(i),
-			Nonce:     uint64(i),
+			Nonce:     Nonce(i),
 			Balance:   big.NewInt(1000),
 			PublicKey: pk,
 			EthAddr:   address,
@@ -98,7 +98,7 @@ func TestAccountHashValue(t *testing.T) {
 
 	account := &Account{
 		TokenID:   TokenID(1),
-		Nonce:     uint64(1234),
+		Nonce:     Nonce(1234),
 		Balance:   big.NewInt(1000),
 		PublicKey: pk,
 		EthAddr:   ethCommon.HexToAddress("0xc58d29fA6e86E4FAe04DDcEd660d45BCf3Cb2370"),
@@ -142,7 +142,7 @@ func TestAccountErrNumOverflowNonce(t *testing.T) {
 	// check limit
 	account := &Account{
 		TokenID:   TokenID(1),
-		Nonce:     uint64(math.Pow(2, 40) - 1),
+		Nonce:     Nonce(math.Pow(2, 40) - 1),
 		Balance:   big.NewInt(1000),
 		PublicKey: pk,
 		EthAddr:   ethCommon.HexToAddress("0xc58d29fA6e86E4FAe04DDcEd660d45BCf3Cb2370"),
@@ -151,7 +151,7 @@ func TestAccountErrNumOverflowNonce(t *testing.T) {
 	assert.Nil(t, err)
 
 	// force value overflow
-	account.Nonce = uint64(math.Pow(2, 40))
+	account.Nonce = Nonce(math.Pow(2, 40))
 	b, err := account.Bytes()
 	assert.NotNil(t, err)
 	assert.Equal(t, fmt.Errorf("%s Nonce", ErrNumOverflow), err)
@@ -169,7 +169,7 @@ func TestAccountErrNumOverflowBalance(t *testing.T) {
 	// check limit
 	account := &Account{
 		TokenID:   TokenID(1),
-		Nonce:     uint64(math.Pow(2, 40) - 1),
+		Nonce:     Nonce(math.Pow(2, 40) - 1),
 		Balance:   new(big.Int).Sub(new(big.Int).Exp(big.NewInt(2), big.NewInt(192), nil), big.NewInt(1)),
 		PublicKey: pk,
 		EthAddr:   ethCommon.HexToAddress("0xc58d29fA6e86E4FAe04DDcEd660d45BCf3Cb2370"),

common/batch.go

@@ -1,6 +1,8 @@
 package common
 
 import (
+	"encoding/binary"
+	"fmt"
 	"math/big"
 
 	ethCommon "github.com/ethereum/go-ethereum/common"
@@ -26,3 +28,19 @@ type Batch struct {
 
 // BatchNum identifies a batch
 type BatchNum uint32
+
+// Bytes returns a byte array of length 4 representing the BatchNum
+func (bn BatchNum) Bytes() []byte {
+	var batchNumBytes [4]byte
+	binary.LittleEndian.PutUint32(batchNumBytes[:], uint32(bn))
+	return batchNumBytes[:]
+}
+
+// BatchNumFromBytes returns BatchNum from a []byte
+func BatchNumFromBytes(b []byte) (BatchNum, error) {
+	if len(b) != 4 {
+		return 0, fmt.Errorf("can not parse BatchNumFromBytes, bytes len %d, expected 4", len(b))
+	}
+	batchNum := binary.LittleEndian.Uint32(b[:4])
+	return BatchNum(batchNum), nil
+}

common/l1tx.go

@@ -31,7 +31,6 @@ func (tx *L1Tx) Tx() *Tx {
 		TxID:    tx.TxID,
 		FromIdx: tx.FromIdx,
 		ToIdx:   tx.ToIdx,
-		TokenID: tx.TokenID,
 		Amount:  tx.Amount,
 		Nonce:   0,
 		Fee:     0,

common/l2tx.go

@@ -18,3 +18,15 @@ type L2Tx struct {
 	// Extra metadata, may be uninitialized
 	Type TxType `meddler:"-"` // optional, descrives which kind of tx it's
 }
+
+func (tx *L2Tx) Tx() *Tx {
+	return &Tx{
+		TxID:    tx.TxID,
+		FromIdx: tx.FromIdx,
+		ToIdx:   tx.ToIdx,
+		Amount:  tx.Amount,
+		Nonce:   tx.Nonce,
+		Fee:     tx.Fee,
+		Type:    tx.Type,
+	}
+}

common/pooll2tx.go

@@ -27,11 +27,12 @@ func (n Nonce) Bytes() ([5]byte, error) {
 	return b, nil
 }
 
-func NonceFromBytes(b [5]byte) (Nonce, error) {
+// NonceFromBytes returns Nonce from a [5]byte
+func NonceFromBytes(b [5]byte) Nonce {
 	var nonceBytes [8]byte
 	copy(nonceBytes[:], b[:5])
 	nonce := binary.LittleEndian.Uint64(nonceBytes[:])
-	return Nonce(nonce), nil
+	return Nonce(nonce)
 }
 
 // PoolL2Tx is a struct that represents a L2Tx sent by an account to the coordinator hat is waiting to be forged
@@ -171,12 +172,24 @@ func (tx *PoolL2Tx) VerifySignature(pk *babyjub.PublicKey) bool {
 	return pk.VerifyPoseidon(h, tx.Signature)
 }
 
+func (tx *PoolL2Tx) L2Tx() *L2Tx {
+	return &L2Tx{
+		TxID:     tx.TxID,
+		BatchNum: tx.BatchNum,
+		FromIdx:  tx.FromIdx,
+		ToIdx:    tx.ToIdx,
+		Amount:   tx.Amount,
+		Fee:      tx.Fee,
+		Nonce:    tx.Nonce,
+		Type:     tx.Type,
+	}
+}
+
 func (tx *PoolL2Tx) Tx() *Tx {
 	return &Tx{
 		TxID:    tx.TxID,
 		FromIdx: tx.FromIdx,
 		ToIdx:   tx.ToIdx,
-		TokenID: tx.TokenID,
 		Amount:  tx.Amount,
 		Nonce:   tx.Nonce,
 		Fee:     tx.Fee,
@@ -184,6 +197,14 @@ func (tx *PoolL2Tx) Tx() *Tx {
 	}
 }
 
+func PoolL2TxsToL2Txs(txs []*PoolL2Tx) []*L2Tx {
+	var r []*L2Tx
+	for _, tx := range txs {
+		r = append(r, tx.L2Tx())
+	}
+	return r
+}
+
 // PoolL2TxState is a struct that represents the status of a L2 transaction
 type PoolL2TxState string
 

common/pooll2tx_test.go

@@ -16,8 +16,7 @@ func TestNonceParser(t *testing.T) {
 	assert.Nil(t, err)
 	assert.Equal(t, 5, len(nBytes))
 	assert.Equal(t, "0100000000", hex.EncodeToString(nBytes[:]))
-	n2, err := NonceFromBytes(nBytes)
-	assert.Nil(t, err)
+	n2 := NonceFromBytes(nBytes)
 	assert.Equal(t, n, n2)
 
 	// value before overflow
@@ -26,8 +25,7 @@ func TestNonceParser(t *testing.T) {
 	assert.Nil(t, err)
 	assert.Equal(t, 5, len(nBytes))
 	assert.Equal(t, "ffffffffff", hex.EncodeToString(nBytes[:]))
-	n2, err = NonceFromBytes(nBytes)
-	assert.Nil(t, err)
+	n2 = NonceFromBytes(nBytes)
 	assert.Equal(t, n, n2)
 
 	// expect value overflow
@@ -35,8 +33,6 @@ func TestNonceParser(t *testing.T) {
 	nBytes, err = n.Bytes()
 	assert.NotNil(t, err)
 	assert.Equal(t, ErrNonceOverflow, err)
-	_, err = NonceFromBytes(nBytes)
-	assert.Nil(t, err)
 }
 
 func TestTxCompressedData(t *testing.T) {

common/tx.go

@@ -2,6 +2,7 @@ package common
 
 import (
 	"encoding/binary"
+	"fmt"
 	"math/big"
 )
 
@@ -20,6 +21,15 @@ func (idx Idx) BigInt() *big.Int {
 	return big.NewInt(int64(idx))
 }
 
+// IdxFromBytes returns Idx from a byte array
+func IdxFromBytes(b []byte) (Idx, error) {
+	if len(b) != 4 {
+		return 0, fmt.Errorf("can not parse Idx, bytes len %d, expected 4", len(b))
+	}
+	idx := binary.LittleEndian.Uint32(b[:4])
+	return Idx(idx), nil
+}
+
 // IdxFromBigInt converts a *big.Int to Idx type
 func IdxFromBigInt(b *big.Int) (Idx, error) {
 	if b.Int64() > 0xffffffff { // 2**32-1
@@ -64,7 +74,6 @@ type Tx struct {
 	TxID     TxID
 	FromIdx  Idx // FromIdx is used by L1Tx/Deposit to indicate the Idx receiver of the L1Tx.LoadAmount (deposit)
 	ToIdx    Idx // ToIdx is ignored in L1Tx/Deposit, but used in the L1Tx/DepositTransfer
-	TokenID  TokenID
 	Amount   *big.Int
 	Nonce    Nonce // effective 40 bits used
 	Fee      FeeSelector

common/zk.go

@@ -58,3 +58,7 @@ type ZKInputs struct {
 type CallDataForge struct {
 	// TBD
 }
+
+type ExitTreeLeaf struct {
+	// TBD
+}

coordinator/coordinator.go

@@ -98,21 +98,21 @@ func (c *Coordinator) forgeSequence() error {
 	c.batchNum = c.batchNum + 1
 	batchInfo := NewBatchInfo(c.batchNum, serverProofInfo) // to accumulate metadata of the batch
 
-	var l2Txs []*common.PoolL2Tx
+	var poolL2Txs []*common.PoolL2Tx
 	// var feesInfo
 	var l1UserTxsExtra, l1OperatorTxs []*common.L1Tx
 	// 1. Decide if we forge L2Tx or L1+L2Tx
 	if c.shouldL1L2Batch() {
 		// 2a: L1+L2 txs
 		// l1UserTxs, toForgeL1TxsNumber := c.synchronizer.GetNextL1UserTxs() // TODO once synchronizer is ready, uncomment
-		var l1UserTxs []*common.L1Tx = nil                                                            // tmp, depends on synchronizer
-		l1UserTxsExtra, l1OperatorTxs, l2Txs, err = c.txsel.GetL1L2TxSelection(c.batchNum, l1UserTxs) // TODO once feesInfo is added to method return, add the var
+		var l1UserTxs []*common.L1Tx = nil                                                                // tmp, depends on synchronizer
+		l1UserTxsExtra, l1OperatorTxs, poolL2Txs, err = c.txsel.GetL1L2TxSelection(c.batchNum, l1UserTxs) // TODO once feesInfo is added to method return, add the var
 		if err != nil {
 			return err
 		}
 	} else {
 		// 2b: only L2 txs
-		l2Txs, err = c.txsel.GetL2TxSelection(c.batchNum) // TODO once feesInfo is added to method return, add the var
+		poolL2Txs, err = c.txsel.GetL2TxSelection(c.batchNum) // TODO once feesInfo is added to method return, add the var
 		if err != nil {
 			return err
 		}
@@ -121,21 +121,22 @@ func (c *Coordinator) forgeSequence() error {
 	}
 
 	// Run purger to invalidate transactions that become invalid beause of
-	// the l2Txs selected.  Will mark as invalid the txs that have a
+	// the poolL2Txs selected.  Will mark as invalid the txs that have a
 	// (fromIdx, nonce) which already appears in the selected txs (includes
 	// all the nonces smaller than the current one)
-	err = c.purgeInvalidDueToL2TxsSelection(l2Txs)
+	err = c.purgeInvalidDueToL2TxsSelection(poolL2Txs)
 	if err != nil {
 		return err
 	}
 
 	// 3.  Save metadata from TxSelector output for BatchNum
-	batchInfo.SetTxsInfo(l1UserTxsExtra, l1OperatorTxs, l2Txs) // TODO feesInfo
+	batchInfo.SetTxsInfo(l1UserTxsExtra, l1OperatorTxs, poolL2Txs) // TODO feesInfo
 
 	// 4. Call BatchBuilder with TxSelector output
 	configBatch := &batchbuilder.ConfigBatch{
 		ForgerAddress: c.config.ForgerAddress,
 	}
+	l2Txs := common.PoolL2TxsToL2Txs(poolL2Txs)
 	zkInputs, err := c.batchBuilder.BuildBatch(configBatch, l1UserTxsExtra, l1OperatorTxs, l2Txs, nil) // TODO []common.TokenID --> feesInfo
 	if err != nil {
 		return err

db/statedb/statedb.go

@@ -1,7 +1,6 @@
 package statedb
 
 import (
-	"encoding/binary"
 	"errors"
 	"fmt"
 	"os"
@@ -31,11 +30,11 @@ const PATHCURRENT = "/current"
 // StateDB represents the StateDB object
 type StateDB struct {
 	path         string
-	currentBatch uint64
+	currentBatch common.BatchNum
 	db           *pebble.PebbleStorage
 	mt           *merkletree.MerkleTree
 	// idx holds the current Idx that the BatchBuilder is using
-	idx uint64
+	idx common.Idx
 }
 
 // NewStateDB creates a new StateDB, allowing to use an in-memory or in-disk
@@ -77,7 +76,7 @@ func (s *StateDB) DB() *pebble.PebbleStorage {
 }
 
 // GetCurrentBatch returns the current BatchNum stored in the StateDB
-func (s *StateDB) GetCurrentBatch() (uint64, error) {
+func (s *StateDB) GetCurrentBatch() (common.BatchNum, error) {
 	cbBytes, err := s.db.Get(KEYCURRENTBATCH)
 	if err == db.ErrNotFound {
 		return 0, nil
@@ -85,8 +84,7 @@ func (s *StateDB) GetCurrentBatch() (uint64, error) {
 	if err != nil {
 		return 0, err
 	}
-	cb := binary.LittleEndian.Uint64(cbBytes[:8])
-	return cb, nil
+	return common.BatchNumFromBytes(cbBytes)
 }
 
 // setCurrentBatch stores the current BatchNum in the StateDB
@@ -95,9 +93,7 @@ func (s *StateDB) setCurrentBatch() error {
 	if err != nil {
 		return err
 	}
-	var cbBytes [8]byte
-	binary.LittleEndian.PutUint64(cbBytes[:], s.currentBatch)
-	tx.Put(KEYCURRENTBATCH, cbBytes[:])
+	tx.Put(KEYCURRENTBATCH, s.currentBatch.Bytes())
 	if err := tx.Commit(); err != nil {
 		return err
 	}

db/statedb/statedb_test.go

@@ -27,7 +27,7 @@ func newAccount(t *testing.T, i int) *common.Account {
 
 	return &common.Account{
 		TokenID:   common.TokenID(i),
-		Nonce:     uint64(i),
+		Nonce:     common.Nonce(i),
 		Balance:   big.NewInt(1000),
 		PublicKey: pk,
 		EthAddr:   address,
@@ -159,7 +159,7 @@ func TestCheckpoints(t *testing.T) {
 	assert.Nil(t, err)
 	cb, err := sdb.GetCurrentBatch()
 	assert.Nil(t, err)
-	assert.Equal(t, uint64(1), cb)
+	assert.Equal(t, common.BatchNum(1), cb)
 
 	for i := 1; i < 10; i++ {
 		err = sdb.MakeCheckpoint()
@@ -167,7 +167,7 @@ func TestCheckpoints(t *testing.T) {
 
 		cb, err = sdb.GetCurrentBatch()
 		assert.Nil(t, err)
-		assert.Equal(t, uint64(i+1), cb)
+		assert.Equal(t, common.BatchNum(i+1), cb)
 	}
 
 	// printCheckpoints(t, sdb.path)
@@ -184,14 +184,14 @@ func TestCheckpoints(t *testing.T) {
 	// check that currentBatch is as expected after Reset
 	cb, err = sdb.GetCurrentBatch()
 	assert.Nil(t, err)
-	assert.Equal(t, uint64(3), cb)
+	assert.Equal(t, common.BatchNum(3), cb)
 
 	// advance one checkpoint and check that currentBatch is fine
 	err = sdb.MakeCheckpoint()
 	assert.Nil(t, err)
 	cb, err = sdb.GetCurrentBatch()
 	assert.Nil(t, err)
-	assert.Equal(t, uint64(4), cb)
+	assert.Equal(t, common.BatchNum(4), cb)
 
 	err = sdb.DeleteCheckpoint(uint64(9))
 	assert.Nil(t, err)
@@ -214,13 +214,13 @@ func TestCheckpoints(t *testing.T) {
 	// check that currentBatch is 4 after the Reset
 	cb, err = ldb.GetCurrentBatch()
 	assert.Nil(t, err)
-	assert.Equal(t, uint64(4), cb)
+	assert.Equal(t, common.BatchNum(4), cb)
 	// advance one checkpoint in ldb
 	err = ldb.MakeCheckpoint()
 	assert.Nil(t, err)
 	cb, err = ldb.GetCurrentBatch()
 	assert.Nil(t, err)
-	assert.Equal(t, uint64(5), cb)
+	assert.Equal(t, common.BatchNum(5), cb)
 
 	// Create a 2nd LocalStateDB from the initial StateDB
 	dirLocal2, err := ioutil.TempDir("", "ldb2")
@@ -234,13 +234,13 @@ func TestCheckpoints(t *testing.T) {
 	// check that currentBatch is 4 after the Reset
 	cb, err = ldb2.GetCurrentBatch()
 	assert.Nil(t, err)
-	assert.Equal(t, uint64(4), cb)
+	assert.Equal(t, common.BatchNum(4), cb)
 	// advance one checkpoint in ldb2
 	err = ldb2.MakeCheckpoint()
 	assert.Nil(t, err)
 	cb, err = ldb2.GetCurrentBatch()
 	assert.Nil(t, err)
-	assert.Equal(t, uint64(5), cb)
+	assert.Equal(t, common.BatchNum(5), cb)
 
 	debug := false
 	if debug {

db/statedb/txprocessors.go

@@ -1,19 +1,46 @@
 package statedb
 
 import (
-	"encoding/binary"
 	"math/big"
 
 	"github.com/hermeznetwork/hermez-node/common"
 	"github.com/iden3/go-merkletree/db"
 )
 
-// KEYIDX is used as key in the db to store the current Idx
-var KEYIDX = []byte("idx")
+// keyidx is used as key in the db to store the current Idx
+var keyidx = []byte("idx")
+
+// ProcessTxs process the given L1Txs & L2Txs applying the needed updates
+// to the StateDB depending on the transaction Type. Returns the
+// common.ZKInputs to generate the SnarkProof later used by the BatchBuilder,
+// and returns common.ExitTreeLeaf that is later used by the Synchronizer to
+// update the HistoryDB.
+func (s *StateDB) ProcessTxs(l1usertxs, l1coordinatortxs []*common.L1Tx, l2txs []*common.L2Tx) (*common.ZKInputs, []*common.ExitTreeLeaf, error) {
+	for _, tx := range l1usertxs {
+		err := s.processL1Tx(tx)
+		if err != nil {
+			return nil, nil, err
+		}
+	}
+	for _, tx := range l1coordinatortxs {
+		err := s.processL1Tx(tx)
+		if err != nil {
+			return nil, nil, err
+		}
+	}
+	for _, tx := range l2txs {
+		err := s.processL2Tx(tx)
+		if err != nil {
+			return nil, nil, err
+		}
+	}
+
+	return nil, nil, nil
+}
 
-// ProcessPoolL2Tx process the given PoolL2Tx applying the needed updates to
+// processL2Tx process the given L2Tx applying the needed updates to
 // the StateDB depending on the transaction Type.
-func (s *StateDB) ProcessPoolL2Tx(tx *common.PoolL2Tx) error {
+func (s *StateDB) processL2Tx(tx *common.L2Tx) error {
 	switch tx.Type {
 	case common.TxTypeTransfer:
 		// go to the MT account of sender and receiver, and update
@@ -29,9 +56,9 @@ func (s *StateDB) ProcessPoolL2Tx(tx *common.PoolL2Tx) error {
 	return nil
 }
 
-// ProcessL1Tx process the given L1Tx applying the needed updates to the
+// processL1Tx process the given L1Tx applying the needed updates to the
 // StateDB depending on the transaction Type.
-func (s *StateDB) ProcessL1Tx(tx *common.L1Tx) error {
+func (s *StateDB) processL1Tx(tx *common.L1Tx) error {
 	switch tx.Type {
 	case common.TxTypeForceTransfer, common.TxTypeTransfer:
 		// go to the MT account of sender and receiver, and update balance
@@ -170,27 +197,24 @@ func (s *StateDB) applyTransfer(tx *common.Tx) error {
 
 // getIdx returns the stored Idx from the localStateDB, which is the last Idx
 // used for an Account in the localStateDB.
-func (s *StateDB) getIdx() (uint64, error) {
-	idxBytes, err := s.DB().Get(KEYIDX)
+func (s *StateDB) getIdx() (common.Idx, error) {
+	idxBytes, err := s.DB().Get(keyidx)
 	if err == db.ErrNotFound {
 		return 0, nil
 	}
 	if err != nil {
 		return 0, err
 	}
-	idx := binary.LittleEndian.Uint64(idxBytes[:8])
-	return idx, nil
+	return common.IdxFromBytes(idxBytes[:4])
 }
 
 // setIdx stores Idx in the localStateDB
-func (s *StateDB) setIdx(idx uint64) error {
+func (s *StateDB) setIdx(idx common.Idx) error {
 	tx, err := s.DB().NewTx()
 	if err != nil {
 		return err
 	}
-	var idxBytes [8]byte
-	binary.LittleEndian.PutUint64(idxBytes[:], idx)
-	tx.Put(KEYIDX, idxBytes[:])
+	tx.Put(keyidx, idx.Bytes())
 	if err := tx.Commit(); err != nil {
 		return err
 	}