blockchain sandbox: UTXO chain, p2p mining, attacker node

chain/transaction.go

@@ -0,0 +1,123 @@
+package chain
+
+import (
+	"crypto/ed25519"
+	"crypto/sha256"
+	"encoding/hex"
+	"fmt"
+	"strconv"
+	"strings"
+)
+
+// CoinSpend references a coin being spent, with proof of ownership.
+type CoinSpend struct {
+	CoinID    CoinID
+	Owner     ed25519.PublicKey
+	Signature []byte
+}
+
+type Transaction struct {
+	Spends []CoinSpend
+	Coins  []Coin
+
+	cachedID string
+}
+
+func (tx *Transaction) IsCoinbase() bool {
+	return len(tx.Spends) == 0
+}
+
+func (tx *Transaction) TxID() string {
+	if tx.cachedID != "" {
+		return tx.cachedID
+	}
+
+	var b strings.Builder
+	for _, s := range tx.Spends {
+		b.WriteString(s.CoinID.TxHash)
+		b.WriteString(strconv.Itoa(s.CoinID.Index))
+	}
+	for _, c := range tx.Coins {
+		b.Write(c.Owner)
+		b.WriteString(strconv.Itoa(c.Amount))
+	}
+	h := sha256.Sum256([]byte(b.String()))
+	tx.cachedID = hex.EncodeToString(h[:])
+	return tx.cachedID
+}
+
+func (tx *Transaction) Verify() bool {
+	if tx.IsCoinbase() {
+		return true
+	}
+
+	hash := []byte(tx.TxID())
+	for _, s := range tx.Spends {
+		if s.Owner == nil {
+			return false
+		}
+		if !ed25519.Verify(s.Owner, hash, s.Signature) {
+			return false
+		}
+	}
+
+	return true
+}
+
+func (tx *Transaction) String() string {
+	if tx.IsCoinbase() {
+		return fmt.Sprintf("COINBASE -> %s: %d", tx.Coins[0].OwnerHex()[:7], tx.Coins[0].Amount)
+	}
+
+	from := hex.EncodeToString(tx.Spends[0].Owner)[:7]
+	to := tx.Coins[0].OwnerHex()[:7]
+
+	return fmt.Sprintf("%s -> %s: %d", from, to, tx.Coins[0].Amount)
+}
+
+func NewCoinbaseTransaction(to ed25519.PublicKey, amount int) *Transaction {
+	return &Transaction{
+		Coins: []Coin{{Amount: amount, Owner: to}},
+	}
+}
+
+func NewTransaction(wallet *Wallet, to ed25519.PublicKey, amount int, unspent []UnspentCoin) *Transaction {
+	var selected []UnspentCoin
+	var total int
+
+	for _, u := range unspent {
+		selected = append(selected, u)
+		total += u.Amount
+		if total >= amount {
+			break
+		}
+	}
+
+	if total < amount {
+		return nil
+	}
+
+	coins := []Coin{{Amount: amount, Owner: to}}
+
+	change := total - amount
+
+	if change > 0 {
+		coins = append(coins, Coin{Amount: change, Owner: wallet.PublicKey})
+	}
+
+	spends := make([]CoinSpend, len(selected))
+	for i, u := range selected {
+		spends[i] = CoinSpend{
+			CoinID: u.CoinID,
+			Owner:  wallet.PublicKey,
+		}
+	}
+
+	tx := &Transaction{Spends: spends, Coins: coins}
+	hash := []byte(tx.TxID())
+	for i := range tx.Spends {
+		tx.Spends[i].Signature = ed25519.Sign(wallet.PrivateKey, hash)
+	}
+
+	return tx
+}