core: Add version to DepositTx (ethereum#19)

This adds a second byte after the EIP-2718 Type byte to deposit
transactions that versions the deposit. It is placed prior to the start
of the RLP to make it easier to extend the transaction in the future. We
choose to version inside the EIP-2718 envelope to limit the number of
EIP-2718 prefixes we take for deposit transactions.

Author: trianglesphere

core/types/deposit_tx.go

@@ -22,6 +22,10 @@ import (
 	"github.com/ethereum/go-ethereum/common"
 )
 
+const (
+	DepositTxVersionZeroType = iota
+)
+
 const DepositTxType = 0x7E
 
 type DepositTx struct {

core/types/transaction.go

@@ -38,6 +38,10 @@ var (
 	ErrTxTypeNotSupported   = errors.New("transaction type not supported")
 	ErrGasFeeCapTooLow      = errors.New("fee cap less than base fee")
 	errShortTypedTx         = errors.New("typed transaction too short")
+
+	// Custom Errors for deposits
+	ErrDepositTxTypeNotSupported = errors.New("deposit transaction type not supported")
+	errUnversionedDeposit        = errors.New("deposit transaction does not have version byte")
 )
 
 // Transaction types.
@@ -105,6 +109,10 @@ func (tx *Transaction) EncodeRLP(w io.Writer) error {
 // encodeTyped writes the canonical encoding of a typed transaction to w.
 func (tx *Transaction) encodeTyped(w *bytes.Buffer) error {
 	w.WriteByte(tx.Type())
+	// Only support v0 right now.
+	if tx.Type() == DepositTxType {
+		w.WriteByte(DepositTxVersionZeroType)
+	}
 	return rlp.Encode(w, tx.inner)
 }
 
@@ -186,7 +194,13 @@ func (tx *Transaction) decodeTyped(b []byte) (TxData, error) {
 		return &inner, err
 	case DepositTxType:
 		var inner DepositTx
-		err := rlp.DecodeBytes(b[1:], &inner)
+		if len(b) < 2 {
+			return nil, errUnversionedDeposit
+		}
+		if b[1] != DepositTxVersionZeroType {
+			return nil, ErrDepositTxTypeNotSupported
+		}
+		err := rlp.DecodeBytes(b[2:], &inner)
 		return &inner, err
 	default:
 		return nil, ErrTxTypeNotSupported