Part 4

README.md

@@ -2,5 +2,7 @@
 
 A blockchain implementation in Go, as described in these articles:
 
-1. [Basic Prototype](https://jeiwan.cc/posts/building-blockchain-in-go-part-1/)
-2. [Proof-of-Work](https://jeiwan.cc/posts/building-blockchain-in-go-part-2/)
+1. [Basic Prototype](https://jeiwan.net/posts/building-blockchain-in-go-part-1/)
+2. [Proof-of-Work](https://jeiwan.net/posts/building-blockchain-in-go-part-2/)
+2. [Persistence and CLI](https://jeiwan.net/posts/building-blockchain-in-go-part-3/)
+3. [Transactions 1](https://jeiwan.net/posts/building-blockchain-in-go-part-4/)

block.go

@@ -2,6 +2,7 @@ package main
 
 import (
 	"bytes"
+	"crypto/sha256"
 	"encoding/gob"
 	"log"
 	"time"
@@ -10,7 +11,7 @@ import (
 // Block keeps block headers
 type Block struct {
 	Timestamp     int64
-	Data          []byte
+	Transactions  []*Transaction
 	PrevBlockHash []byte
 	Hash          []byte
 	Nonce         int
@@ -29,9 +30,22 @@ func (b *Block) Serialize() []byte {
 	return result.Bytes()
 }
 
+// HashTransactions returns a hash of the transactions in the block
+func (b *Block) HashTransactions() []byte {
+	var txHashes [][]byte
+	var txHash [32]byte
+
+	for _, tx := range b.Transactions {
+		txHashes = append(txHashes, tx.ID)
+	}
+	txHash = sha256.Sum256(bytes.Join(txHashes, []byte{}))
+
+	return txHash[:]
+}
+
 // NewBlock creates and returns Block
-func NewBlock(data string, prevBlockHash []byte) *Block {
-	block := &Block{time.Now().Unix(), []byte(data), prevBlockHash, []byte{}, 0}
+func NewBlock(transactions []*Transaction, prevBlockHash []byte) *Block {
+	block := &Block{time.Now().Unix(), transactions, prevBlockHash, []byte{}, 0}
 	pow := NewProofOfWork(block)
 	nonce, hash := pow.Run()
 
@@ -42,8 +56,8 @@ func NewBlock(data string, prevBlockHash []byte) *Block {
 }
 
 // NewGenesisBlock creates and returns genesis Block
-func NewGenesisBlock() *Block {
-	return NewBlock("Genesis Block", []byte{})
+func NewGenesisBlock(coinbase *Transaction) *Block {
+	return NewBlock([]*Transaction{coinbase}, []byte{})
 }
 
 // DeserializeBlock deserializes a block

blockchain.go

@@ -1,16 +1,19 @@
 package main
 
 import (
+	"encoding/hex"
 	"fmt"
 	"log"
+	"os"
 
 	"github.com/boltdb/bolt"
 )
 
 const dbFile = "blockchain.db"
 const blocksBucket = "blocks"
+const genesisCoinbaseData = "The Times 03/Jan/2009 Chancellor on brink of second bailout for banks"
 
-// Blockchain keeps a sequence of Blocks
+// Blockchain implements interactions with a DB
 type Blockchain struct {
 	tip []byte
 	db  *bolt.DB
@@ -22,8 +25,8 @@ type BlockchainIterator struct {
 	db          *bolt.DB
 }
 
-// AddBlock saves provided data as a block in the blockchain
-func (bc *Blockchain) AddBlock(data string) {
+// MineBlock mines a new block with the provided transactions
+func (bc *Blockchain) MineBlock(transactions []*Transaction) {
 	var lastHash []byte
 
 	err := bc.db.View(func(tx *bolt.Tx) error {
@@ -37,7 +40,7 @@ func (bc *Blockchain) AddBlock(data string) {
 		log.Panic(err)
 	}
 
-	newBlock := NewBlock(data, lastHash)
+	newBlock := NewBlock(transactions, lastHash)
 
 	err = bc.db.Update(func(tx *bolt.Tx) error {
 		b := tx.Bucket([]byte(blocksBucket))
@@ -57,7 +60,94 @@ func (bc *Blockchain) AddBlock(data string) {
 	})
 }
 
-// Iterator ...
+// FindUnspentTransactions returns a list of transactions containing unspent outputs
+func (bc *Blockchain) FindUnspentTransactions(address string) []Transaction {
+	var unspentTXs []Transaction
+	spentTXOs := make(map[string][]int)
+	bci := bc.Iterator()
+
+	for {
+		block := bci.Next()
+
+		for _, tx := range block.Transactions {
+			txID := hex.EncodeToString(tx.ID)
+
+		Outputs:
+			for outIdx, out := range tx.Vout {
+				// Was the output spent?
+				if spentTXOs[txID] != nil {
+					for _, spentOut := range spentTXOs[txID] {
+						if spentOut == outIdx {
+							continue Outputs
+						}
+					}
+				}
+
+				if out.CanBeUnlockedWith(address) {
+					unspentTXs = append(unspentTXs, *tx)
+				}
+			}
+
+			if tx.IsCoinbase() == false {
+				for _, in := range tx.Vin {
+					if in.CanUnlockOutputWith(address) {
+						inTxID := hex.EncodeToString(in.Txid)
+						spentTXOs[inTxID] = append(spentTXOs[inTxID], in.Vout)
+					}
+				}
+			}
+		}
+
+		if len(block.PrevBlockHash) == 0 {
+			break
+		}
+	}
+
+	return unspentTXs
+}
+
+// FindUTXO finds and returns all unspent transaction outputs
+func (bc *Blockchain) FindUTXO(address string) []TXOutput {
+	var UTXOs []TXOutput
+	unspentTransactions := bc.FindUnspentTransactions(address)
+
+	for _, tx := range unspentTransactions {
+		for _, out := range tx.Vout {
+			if out.CanBeUnlockedWith(address) {
+				UTXOs = append(UTXOs, out)
+			}
+		}
+	}
+
+	return UTXOs
+}
+
+// FindSpendableOutputs finds and returns unspent outputs to reference in inputs
+func (bc *Blockchain) FindSpendableOutputs(address string, amount int) (int, map[string][]int) {
+	unspentOutputs := make(map[string][]int)
+	unspentTXs := bc.FindUnspentTransactions(address)
+	accumulated := 0
+
+Work:
+	for _, tx := range unspentTXs {
+		txID := hex.EncodeToString(tx.ID)
+
+		for outIdx, out := range tx.Vout {
+			if out.CanBeUnlockedWith(address) && accumulated < amount {
+				accumulated += out.Value
+				unspentOutputs[txID] = append(unspentOutputs[txID], outIdx)
+
+				if accumulated >= amount {
+					break Work
+				}
+			}
+		}
+	}
+
+	return accumulated, unspentOutputs
+}
+
+// Iterator returns a BlockchainIterat
 func (bc *Blockchain) Iterator() *BlockchainIterator {
 	bci := &BlockchainIterator{bc.tip, bc.db}
 
@@ -85,8 +175,21 @@ func (i *BlockchainIterator) Next() *Block {
 	return block
 }
 
+func dbExists() bool {
+	if _, err := os.Stat(dbFile); os.IsNotExist(err) {
+		return false
+	}
+
+	return true
+}
+
 // NewBlockchain creates a new Blockchain with genesis Block
-func NewBlockchain() *Blockchain {
+func NewBlockchain(address string) *Blockchain {
+	if dbExists() == false {
+		fmt.Println("No existing blockchain found. Create one first.")
+		os.Exit(1)
+	}
+
 	var tip []byte
 	db, err := bolt.Open(dbFile, 0600, nil)
 	if err != nil {
@@ -95,29 +198,52 @@ func NewBlockchain() *Blockchain {
 
 	err = db.Update(func(tx *bolt.Tx) error {
 		b := tx.Bucket([]byte(blocksBucket))
+		tip = b.Get([]byte("l"))
 
-		if b == nil {
-			fmt.Println("No existing blockchain found. Creating a new one...")
-			genesis := NewGenesisBlock()
+		return nil
+	})
 
-			b, err := tx.CreateBucket([]byte(blocksBucket))
-			if err != nil {
-				log.Panic(err)
-			}
+	if err != nil {
+		log.Panic(err)
+	}
 
-			err = b.Put(genesis.Hash, genesis.Serialize())
-			if err != nil {
-				log.Panic(err)
-			}
+	bc := Blockchain{tip, db}
 
-			err = b.Put([]byte("l"), genesis.Hash)
-			if err != nil {
-				log.Panic(err)
-			}
-			tip = genesis.Hash
-		} else {
-			tip = b.Get([]byte("l"))
+	return &bc
+}
+
+// CreateBlockchain creates a new blockchain DB
+func CreateBlockchain(address string) *Blockchain {
+	if dbExists() {
+		fmt.Println("Blockchain already exists.")
+		os.Exit(1)
+	}
+
+	var tip []byte
+	db, err := bolt.Open(dbFile, 0600, nil)
+	if err != nil {
+		log.Panic(err)
+	}
+
+	err = db.Update(func(tx *bolt.Tx) error {
+		cbtx := NewCoinbaseTX(address, genesisCoinbaseData)
+		genesis := NewGenesisBlock(cbtx)
+
+		b, err := tx.CreateBucket([]byte(blocksBucket))
+		if err != nil {
+			log.Panic(err)
+		}
+
+		err = b.Put(genesis.Hash, genesis.Serialize())
+		if err != nil {
+			log.Panic(err)
+		}
+
+		err = b.Put([]byte("l"), genesis.Hash)
+		if err != nil {
+			log.Panic(err)
 		}
+		tip = genesis.Hash
 
 		return nil
 	})