Update txs constructors and helpers

For each tx, move the logic of setting the Type and TxID to separate functions,
so that they can be called when necessary.

In synchronizer, set all the required fields using the `SetID` and `SetType`
for l2txs when needed.  This is necessary because the `ProcessTxs()` works with
`common.PoolL2Tx`, which misses some fields from `common.L2Tx`, and because
`ProcessTxs()` needs the Type to be set, but at the same time `ProcessTxs()`
sets the Nonce, which is required for the `TxID`.

common/l2tx.go

@@ -24,38 +24,57 @@ type L2Tx struct {
 
 // NewL2Tx returns the given L2Tx with the TxId & Type parameters calculated
 // from the L2Tx values
-func NewL2Tx(l2Tx *L2Tx) (*L2Tx, error) {
-	// calculate TxType
-	var txType TxType
-	if l2Tx.ToIdx == Idx(1) {
-		txType = TxTypeExit
-	} else if l2Tx.ToIdx >= IdxUserThreshold {
-		txType = TxTypeTransfer
+func NewL2Tx(tx *L2Tx) (*L2Tx, error) {
+	txTypeOld := tx.Type
+	if err := tx.SetType(); err != nil {
+		return nil, err
+	}
+	// If original Type doesn't match the correct one, return error
+	if txTypeOld != "" && txTypeOld != tx.Type {
+		return nil, tracerr.Wrap(fmt.Errorf("L2Tx.Type: %s, should be: %s",
+			tx.Type, txTypeOld))
+	}
+
+	txIDOld := tx.TxID
+	if err := tx.SetID(); err != nil {
+		return nil, err
+	}
+	// If original TxID doesn't match the correct one, return error
+	if txIDOld != (TxID{}) && txIDOld != tx.TxID {
+		return tx, tracerr.Wrap(fmt.Errorf("L2Tx.TxID: %s, should be: %s",
+			tx.TxID.String(), txIDOld.String()))
+	}
+
+	return tx, nil
+}
+
+// SetType sets the type of the transaction.  Uses (FromIdx, Nonce).
+func (tx *L2Tx) SetType() error {
+	if tx.ToIdx == Idx(1) {
+		tx.Type = TxTypeExit
+	} else if tx.ToIdx >= IdxUserThreshold {
+		tx.Type = TxTypeTransfer
 	} else {
-		return l2Tx, tracerr.Wrap(fmt.Errorf("Can not determine type of L2Tx, invalid ToIdx value: %d", l2Tx.ToIdx))
+		return tracerr.Wrap(fmt.Errorf(
+			"cannot determine type of L2Tx, invalid ToIdx value: %d", tx.ToIdx))
 	}
+	return nil
+}
 
-	// if TxType!=l2Tx.TxType return error
-	if l2Tx.Type != "" && l2Tx.Type != txType {
-		return l2Tx, tracerr.Wrap(fmt.Errorf("L2Tx.Type: %s, should be: %s", l2Tx.Type, txType))
-	}
-	l2Tx.Type = txType
-
-	var txid [TxIDLen]byte
-	txid[0] = TxIDPrefixL2Tx
-	fromIdxBytes, err := l2Tx.FromIdx.Bytes()
+// SetID sets the ID of the transaction
+func (tx *L2Tx) SetID() error {
+	tx.TxID[0] = TxIDPrefixL2Tx
+	fromIdxBytes, err := tx.FromIdx.Bytes()
 	if err != nil {
-		return l2Tx, tracerr.Wrap(err)
+		return tracerr.Wrap(err)
 	}
-	copy(txid[1:7], fromIdxBytes[:])
-	nonceBytes, err := l2Tx.Nonce.Bytes()
+	copy(tx.TxID[1:7], fromIdxBytes[:])
+	nonceBytes, err := tx.Nonce.Bytes()
 	if err != nil {
-		return l2Tx, tracerr.Wrap(err)
+		return tracerr.Wrap(err)
 	}
-	copy(txid[7:12], nonceBytes[:])
-	l2Tx.TxID = TxID(txid)
-
-	return l2Tx, nil
+	copy(tx.TxID[7:12], nonceBytes[:])
+	return nil
 }
 
 // Tx returns a *Tx from the L2Tx