Implement Blockchain.FindUTXOs

blockchain.go

@@ -58,6 +58,57 @@ func (bc *Blockchain) AddBlock(transactions []*Transaction) {
 	})
 }
 
+// FindUTXOs finds and returns unspend transaction outputs for the address
+func (bc *Blockchain) FindUTXOs(address string, amount int) (int, map[string][]int) {
+	var spentTXs map[string][]int
+	var unspentTXs map[string][]int
+	accumulated := 0
+	bci := bc.Iterator()
+
+	for {
+		block := bci.Next()
+
+	Work:
+		for _, tx := range block.Transactions {
+			txid := string(tx.GetHash())
+
+			for outid, out := range tx.Vout {
+				// Was the output spent?
+				if spentTXs[txid] != nil {
+					for _, spentOut := range spentTXs[txid] {
+						if spentOut == outid {
+							continue
+						}
+					}
+				}
+
+				if out.Unlock(address) && accumulated < amount {
+					accumulated += out.Value
+					unspentTXs[txid] = append(unspentTXs[txid], outid)
+
+					if accumulated >= amount {
+						break Work
+					}
+				}
+			}
+
+			if tx.IsCoinbase() == false {
+				for _, in := range tx.Vin {
+					if in.LockedBy(address) {
+						spentTXs[string(in.Txid)] = append(spentTXs[string(in.Txid)], in.Vout)
+					}
+				}
+			}
+		}
+
+		if len(block.PrevBlockHash) == 0 {
+			break
+		}
+	}
+
+	return accumulated, unspentTXs
+}
+
 // Iterator ...
 func (bc *Blockchain) Iterator() *BlockchainIterator {
 	bci := &BlockchainIterator{bc.tip, bc.db}

transaction.go

@@ -4,6 +4,7 @@ import (
 	"bytes"
 	"crypto/sha256"
 	"encoding/gob"
+	"encoding/hex"
 	"log"
 )
 
@@ -17,7 +18,7 @@ type Transaction struct {
 
 // IsCoinbase checks whether the transaction is coinbase
 func (tx Transaction) IsCoinbase() bool {
-	return len(tx.Vin) == 1 && tx.Vin[0].Txid == -1 && tx.Vin[0].Vout == -1
+	return len(tx.Vin) == 1 && len(tx.Vin[0].Txid) == 0 && tx.Vin[0].Vout == -1
 }
 
 // GetHash hashes the transaction and returns the hash
@@ -37,7 +38,7 @@ func (tx Transaction) GetHash() []byte {
 
 // TXInput represents a transaction input
 type TXInput struct {
-	Txid      int
+	Txid      []byte
 	Vout      int
 	ScriptSig string
 }
@@ -48,6 +49,11 @@ type TXOutput struct {
 	ScriptPubKey string
 }
 
+// LockedBy checks whether the address initiated the transaction
+func (in *TXInput) LockedBy(address string) bool {
+	return in.ScriptSig == address
+}
+
 // Unlock checks if the output can be unlocked with the provided data
 func (out *TXOutput) Unlock(unlockingData string) bool {
 	return out.ScriptPubKey == unlockingData
@@ -59,7 +65,7 @@ func NewCoinbaseTX(to, data string) *Transaction {
 		data = "Coinbase"
 	}
 
-	txin := TXInput{-1, -1, data}
+	txin := TXInput{[]byte{}, -1, data}
 	txout := TXOutput{subsidy, to}
 	tx := Transaction{[]TXInput{txin}, []TXOutput{txout}}
 
@@ -67,11 +73,11 @@ func NewCoinbaseTX(to, data string) *Transaction {
 }
 
 // NewUTXOTransaction creates a new transaction
-func NewUTXOTransaction(from, to string, value int) *Transaction {
+func NewUTXOTransaction(from, to string, value int, bc *Blockchain) *Transaction {
 	var inputs []TXInput
 	var outputs []TXOutput
 
-	acc, validOutputs := s.findUnspentOutputs(from, value)
+	acc, validOutputs := bc.FindUTXOs(from, value)
 
 	if acc < value {
 		log.Panic("ERROR: Not enough funds")
@@ -80,7 +86,12 @@ func NewUTXOTransaction(from, to string, value int) *Transaction {
 	// Build a list of inputs
 	for txid, outs := range validOutputs {
 		for _, out := range outs {
-			input := TXInput{txid, out, from}
+			txidbytes, err := hex.DecodeString(txid)
+			if err != nil {
+				log.Panic(err)
+			}
+
+			input := TXInput{txidbytes, out, from}
 			inputs = append(inputs, input)
 		}
 	}