@@ -52,10 +52,10 @@ }
 
 // BuildBatch takes the transactions and returns the common.ZKInputs of the next batch
 func (bb *BatchBuilder) BuildBatch(coordIdxs []common.Idx, configBatch *ConfigBatch, l1usertxs, l1coordinatortxs []common.L1Tx, pooll2txs []common.PoolL2Tx, tokenIDs []common.TokenID) (*common.ZKInputs, error) {
-	zkInputs, _, _, err := bb.localStateDB.ProcessTxs(coordIdxs, l1usertxs, l1coordinatortxs, pooll2txs)
+	ptOut, err := bb.localStateDB.ProcessTxs(coordIdxs, l1usertxs, l1coordinatortxs, pooll2txs)
 	if err != nil {
 		return nil, err
 	}
 	err = bb.localStateDB.MakeCheckpoint()
-	return zkInputs, err
+	return ptOut.ZKInputs, err
 }

@@ -21,7 +21,7 @@ )
 
 func (s *StateDB) resetZKInputs() {
 	s.zki = nil
-	s.i = 0
+	s.i = 0 // initialize current transaction index in the ZKInputs generation
 }
 
 type processedExit struct {
@@ -31,6 +31,14 @@ idx     common.Idx
 	acc     common.Account
 }
 
+// ProcessTxOutput contains the output of the ProcessTxs method
+type ProcessTxOutput struct {
+	ZKInputs           *common.ZKInputs
+	ExitInfos          []common.ExitInfo
+	CreatedAccounts    []common.Account
+	CoordinatorIdxsMap map[common.TokenID]common.Idx
+}
+
 // ProcessTxs process the given L1Txs & L2Txs applying the needed updates to
 // the StateDB depending on the transaction Type.  If StateDB
 // type==TypeBatchBuilder, returns the common.ZKInputs to generate the
@@ -40,27 +48,32 @@ // returns common.ExitTreeLeaf that is later used by the Synchronizer to update
 // the HistoryDB, and adds Nonce & TokenID to the L2Txs.
 // And if TypeSynchronizer returns an array of common.Account with all the
 // created accounts.
-func (s *StateDB) ProcessTxs(coordIdxs []common.Idx, l1usertxs, l1coordinatortxs []common.L1Tx, l2txs []common.PoolL2Tx) (*common.ZKInputs, []common.ExitInfo, []common.Account, error) {
+func (s *StateDB) ProcessTxs(coordIdxs []common.Idx, l1usertxs, l1coordinatortxs []common.L1Tx, l2txs []common.PoolL2Tx) (*ProcessTxOutput, error) {
 	var err error
 	var exitTree *merkletree.MerkleTree
 	var createdAccounts []common.Account
 
 	if s.zki != nil {
-		return nil, nil, nil, errors.New("Expected StateDB.zki==nil, something went wrong and it's not empty")
+		return nil, errors.New("Expected StateDB.zki==nil, something went wrong and it's not empty")
 	}
 	defer s.resetZKInputs()
 
 	nTx := len(l1usertxs) + len(l1coordinatortxs) + len(l2txs)
 	if nTx == 0 {
 		// TODO return ZKInputs of batch without txs
-		return nil, nil, nil, nil
+		return &ProcessTxOutput{
+			ZKInputs:           nil,
+			ExitInfos:          nil,
+			CreatedAccounts:    nil,
+			CoordinatorIdxsMap: nil,
+		}, nil
 	}
 	exits := make([]processedExit, nTx)
 
 	// get TokenIDs of coordIdxs
 	coordIdxsMap, err := s.getTokenIDsFromIdxs(coordIdxs)
 	if err != nil {
-		return nil, nil, nil, err
+		return nil, err
 	}
 
 	if s.typ == TypeBatchBuilder {
@@ -74,7 +87,7 @@ // only needed in memory
 	if s.typ == TypeSynchronizer || s.typ == TypeBatchBuilder {
 		tmpDir, err := ioutil.TempDir("", "hermez-statedb-exittree")
 		if err != nil {
-			return nil, nil, nil, err
+			return nil, err
 		}
 		defer func() {
 			if err := os.RemoveAll(tmpDir); err != nil {
@@ -83,11 +96,11 @@ }
 		}()
 		sto, err := pebble.NewPebbleStorage(tmpDir, false)
 		if err != nil {
-			return nil, nil, nil, err
+			return nil, err
 		}
 		exitTree, err = merkletree.NewMerkleTree(sto, s.mt.MaxLevels())
 		if err != nil {
-			return nil, nil, nil, err
+			return nil, err
 		}
 	}
 
@@ -95,7 +108,7 @@ // assumption: l1usertx are sorted by L1Tx.Position
 	for i := 0; i < len(l1usertxs); i++ {
 		exitIdx, exitAccount, newExit, createdAccount, err := s.processL1Tx(exitTree, &l1usertxs[i])
 		if err != nil {
-			return nil, nil, nil, err
+			return nil, err
 		}
 		if s.typ == TypeSynchronizer || s.typ == TypeBatchBuilder {
 			if exitIdx != nil && exitTree != nil {
@@ -115,7 +128,7 @@ }
 	for i := 0; i < len(l1coordinatortxs); i++ {
 		exitIdx, _, _, createdAccount, err := s.processL1Tx(exitTree, &l1coordinatortxs[i])
 		if err != nil {
-			return nil, nil, nil, err
+			return nil, err
 		}
 		if exitIdx != nil {
 			log.Error("Unexpected Exit in L1CoordinatorTx")
@@ -127,7 +140,7 @@ }
 	for i := 0; i < len(l2txs); i++ {
 		exitIdx, exitAccount, newExit, err := s.processL2Tx(coordIdxsMap, exitTree, &l2txs[i])
 		if err != nil {
-			return nil, nil, nil, err
+			return nil, err
 		}
 		if s.typ == TypeSynchronizer || s.typ == TypeBatchBuilder {
 			if exitIdx != nil && exitTree != nil {
@@ -143,12 +156,13 @@ }
 	}
 
 	if s.typ == TypeTxSelector {
-		return nil, nil, nil, nil
+		return nil, nil
 	}
 
 	// once all txs processed (exitTree root frozen), for each Exit,
 	// generate common.ExitInfo data
 	var exitInfos []common.ExitInfo
+	// exitInfos := []common.ExitInfo{}
 	for i := 0; i < nTx; i++ {
 		if !exits[i].exit {
 			continue
@@ -159,7 +173,7 @@
 		// 0. generate MerkleProof
 		p, err := exitTree.GenerateCircomVerifierProof(exitIdx.BigInt(), nil)
 		if err != nil {
-			return nil, nil, nil, err
+			return nil, err
 		}
 		// 1. generate common.ExitInfo
 		ei := common.ExitInfo{
@@ -190,9 +204,14 @@ s.zki.OldValue2[i] = p.OldValue.BigInt()
 		}
 	}
 	if s.typ == TypeSynchronizer {
-		// return exitInfos and createdAccounts, so Synchronizer will be able
-		// to store it into HistoryDB for the concrete BatchNum
-		return nil, exitInfos, createdAccounts, nil
+		// return exitInfos and createdAccounts, so Synchronizer will
+		// be able to store it into HistoryDB for the concrete BatchNum
+		return &ProcessTxOutput{
+			ZKInputs:           nil,
+			ExitInfos:          exitInfos,
+			CreatedAccounts:    createdAccounts,
+			CoordinatorIdxsMap: coordIdxsMap,
+		}, nil
 	}
 
 	// compute last ZKInputs parameters
@@ -200,7 +219,7 @@ s.zki.GlobalChainID = big.NewInt(0) // TODO, 0: ethereum, this will be get from config file
 	// zki.FeeIdxs = ? // TODO, this will be get from the config file
 	tokenIDs, err := s.getTokenIDsBigInt(l1usertxs, l1coordinatortxs, l2txs)
 	if err != nil {
-		return nil, nil, nil, err
+		return nil, err
 	}
 	s.zki.FeePlanTokens = tokenIDs
 
@@ -210,7 +229,12 @@ // TODO once the Node Config sets the Accounts where to send the Fees
 	// compute fees & update ZKInputs
 
 	// return ZKInputs as the BatchBuilder will return it to forge the Batch
-	return s.zki, nil, nil, nil
+	return &ProcessTxOutput{
+		ZKInputs:           s.zki,
+		ExitInfos:          nil,
+		CreatedAccounts:    nil,
+		CoordinatorIdxsMap: coordIdxsMap,
+	}, nil
 }
 
 // getTokenIDsBigInt returns the list of TokenIDs in *big.Int format

@@ -45,50 +45,50 @@ // Idx of user 'A'
 	idxA1 := tc.Users["A"].Accounts[common.TokenID(1)].Idx
 
 	log.Debug("1st batch, 1st block, only L1CoordinatorTxs")
-	_, _, createdAccounts, err := sdb.ProcessTxs(nil, nil, blocks[0].Batches[0].L1CoordinatorTxs, nil)
+	ptOut, err := sdb.ProcessTxs(nil, nil, blocks[0].Batches[0].L1CoordinatorTxs, nil)
 	require.Nil(t, err)
-	assert.Equal(t, 4, len(createdAccounts))
+	assert.Equal(t, 4, len(ptOut.CreatedAccounts))
 
 	log.Debug("2nd batch, 1st block")
 	l2Txs := common.L2TxsToPoolL2Txs(blocks[0].Batches[1].L2Txs)
-	_, exitInfos, createdAccounts, err := sdb.ProcessTxs(coordIdxs, blocks[0].L1UserTxs, blocks[0].Batches[1].L1CoordinatorTxs, l2Txs)
+	ptOut, err = sdb.ProcessTxs(coordIdxs, blocks[0].L1UserTxs, blocks[0].Batches[1].L1CoordinatorTxs, l2Txs)
 	require.Nil(t, err)
-	assert.Equal(t, 0, len(exitInfos))
-	assert.Equal(t, 31, len(createdAccounts))
+	assert.Equal(t, 0, len(ptOut.ExitInfos))
+	assert.Equal(t, 31, len(ptOut.CreatedAccounts))
 	acc, err := sdb.GetAccount(idxA1)
 	require.Nil(t, err)
 	assert.Equal(t, "50", acc.Balance.String())
 
 	log.Debug("3rd batch, 1st block")
 	l2Txs = common.L2TxsToPoolL2Txs(blocks[0].Batches[2].L2Txs)
-	_, exitInfos, createdAccounts, err = sdb.ProcessTxs(coordIdxs, nil, blocks[0].Batches[2].L1CoordinatorTxs, l2Txs)
+	ptOut, err = sdb.ProcessTxs(coordIdxs, nil, blocks[0].Batches[2].L1CoordinatorTxs, l2Txs)
 	require.Nil(t, err)
 	// TODO once TTGL is updated, add a check that a input poolL2Tx with
 	// Nonce & TokenID =0, after ProcessTxs call has the expected value
 
-	assert.Equal(t, 0, len(exitInfos))
-	assert.Equal(t, 0, len(createdAccounts))
+	assert.Equal(t, 0, len(ptOut.ExitInfos))
+	assert.Equal(t, 0, len(ptOut.CreatedAccounts))
 	acc, err = sdb.GetAccount(idxA1)
 	require.Nil(t, err)
 	assert.Equal(t, "28", acc.Balance.String())
 
 	log.Debug("1st batch, 2nd block")
 	l2Txs = common.L2TxsToPoolL2Txs(blocks[1].Batches[0].L2Txs)
-	_, exitInfos, createdAccounts, err = sdb.ProcessTxs(coordIdxs, nil, blocks[1].Batches[0].L1CoordinatorTxs, l2Txs)
+	ptOut, err = sdb.ProcessTxs(coordIdxs, nil, blocks[1].Batches[0].L1CoordinatorTxs, l2Txs)
 	require.Nil(t, err)
-	assert.Equal(t, 4, len(exitInfos)) // the 'ForceExit(1)' is not computed yet, as the batch is without L1UserTxs
-	assert.Equal(t, 1, len(createdAccounts))
+	assert.Equal(t, 4, len(ptOut.ExitInfos)) // the 'ForceExit(1)' is not computed yet, as the batch is without L1UserTxs
+	assert.Equal(t, 1, len(ptOut.CreatedAccounts))
 	acc, err = sdb.GetAccount(idxA1)
 	require.Nil(t, err)
 	assert.Equal(t, "53", acc.Balance.String())
 
 	log.Debug("2nd batch, 2nd block")
 	l2Txs = common.L2TxsToPoolL2Txs(blocks[1].Batches[1].L2Txs)
-	_, exitInfos, createdAccounts, err = sdb.ProcessTxs(coordIdxs, blocks[1].L1UserTxs, blocks[1].Batches[1].L1CoordinatorTxs, l2Txs)
+	ptOut, err = sdb.ProcessTxs(coordIdxs, blocks[1].L1UserTxs, blocks[1].Batches[1].L1CoordinatorTxs, l2Txs)
 	require.Nil(t, err)
 
-	assert.Equal(t, 2, len(exitInfos)) // 2, as previous batch was without L1UserTxs, and has pending the 'ForceExit(1) A: 5'
-	assert.Equal(t, 1, len(createdAccounts))
+	assert.Equal(t, 2, len(ptOut.ExitInfos)) // 2, as previous batch was without L1UserTxs, and has pending the 'ForceExit(1) A: 5'
+	assert.Equal(t, 1, len(ptOut.CreatedAccounts))
 	acc, err = sdb.GetAccount(idxA1)
 	assert.Nil(t, err)
 	assert.Equal(t, "78", acc.Balance.String())

@@ -405,7 +405,7 @@ // TODO: Get createdAccounts from ProcessTxs()
 		// TODO: Get CollectedFees from ProcessTxs()
 		// TODO: Pass forgeBatchArgs.FeeIdxCoordinator to ProcessTxs()
 		// ProcessTxs updates poolL2Txs adding: Nonce, TokenID
-		_, exitInfo, _, err := s.stateDB.ProcessTxs([]common.Idx{}, l1UserTxs, batchData.L1CoordinatorTxs, poolL2Txs)
+		ptOut, err := s.stateDB.ProcessTxs([]common.Idx{}, l1UserTxs, batchData.L1CoordinatorTxs, poolL2Txs)
 		if err != nil {
 			return nil, err
 		}
@@ -429,7 +429,7 @@ batchData.L2Txs = append(batchData.L2Txs, *l2Tx)
 			position++
 		}
 
-		batchData.ExitTree = exitInfo
+		batchData.ExitTree = ptOut.ExitInfos
 
 		slotNum := int64(0)
 		if ethBlock.EthBlockNum >= s.auctionConstants.GenesisBlockNum {

@@ -89,7 +89,7 @@ // get most profitable L2-tx
 	txs := txsel.getL2Profitable(validTxs, txsel.MaxTxs)
 
 	// process the txs in the local AccountsDB
-	_, _, _, err = txsel.localAccountsDB.ProcessTxs(coordIdxs, nil, nil, txs)
+	_, err = txsel.localAccountsDB.ProcessTxs(coordIdxs, nil, nil, txs)
 	if err != nil {
 		return nil, err
 	}
@@ -238,7 +238,7 @@ maxL2Txs := txsel.MaxTxs - uint64(len(l1CoordinatorTxs)) // - len(l1UserTxs)
 	l2Txs := txsel.getL2Profitable(validTxs, maxL2Txs)
 
 	// process the txs in the local AccountsDB
-	_, _, _, err = txsel.localAccountsDB.ProcessTxs(coordIdxs, l1Txs, l1CoordinatorTxs, l2Txs)
+	_, err = txsel.localAccountsDB.ProcessTxs(coordIdxs, l1Txs, l1CoordinatorTxs, l2Txs)
 	if err != nil {
 		return nil, nil, nil, err
 	}