Jeiwan · Aug 29, 2017 · Sep 3, 2017 · Sep 3, 2017 · Sep 3, 2017 · Sep 3, 2017
Showing with 366 additions and 56 deletions.

+4 −2 README.md

+19 −5 block.go

+150 −24 blockchain.go

+79 −19 cli.go

+1 −4 main.go

+2 −2 proofofwork.go

+111 −0 transaction.go
diff --git a/README.md b/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/)
diff --git a/block.go b/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

diff --git a/blockchain.go b/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
 	})

diff --git a/cli.go b/cli.go
@@ -9,14 +9,34 @@ import (
 )
 
 // CLI responsible for processing command line arguments
-type CLI struct {
-	bc *Blockchain
+type CLI struct{}
+
+func (cli *CLI) createBlockchain(address string) {
+	bc := CreateBlockchain(address)
+	bc.db.Close()
+	fmt.Println("Done!")
+}
+
+func (cli *CLI) getBalance(address string) {
+	bc := NewBlockchain(address)
+	defer bc.db.Close()
+
+	balance := 0
+	UTXOs := bc.FindUTXO(address)
+
+	for _, out := range UTXOs {
+		balance += out.Value
+	}
+
+	fmt.Printf("Balance of '%s': %d\n", address, balance)
 }
 
 func (cli *CLI) printUsage() {
 	fmt.Println("Usage:")
-	fmt.Println("  addblock -data BLOCK_DATA - add a block to the blockchain")
-	fmt.Println("  printchain - print all the blocks of the blockchain")
+	fmt.Println("  getbalance -address ADDRESS - Get balance of ADDRESS")
+	fmt.Println("  createblockchain -address ADDRESS - Create a blockchain and send genesis block reward to ADDRESS")
+	fmt.Println("  printchain - Print all the blocks of the blockchain")
+	fmt.Println("  send -from FROM -to TO -amount AMOUNT - Send AMOUNT of coins from FROM address to TO")
 }
 
 func (cli *CLI) validateArgs() {
@@ -26,19 +46,17 @@ func (cli *CLI) validateArgs() {
 	}
 }
 
-func (cli *CLI) addBlock(data string) {
-	cli.bc.AddBlock(data)
-	fmt.Println("Success!")
-}
-
 func (cli *CLI) printChain() {
-	bci := cli.bc.Iterator()
+	// TODO: Fix this
+	bc := NewBlockchain("")
+	defer bc.db.Close()
+
+	bci := bc.Iterator()
 
 	for {
 		block := bci.Next()
 
 		fmt.Printf("Prev. hash: %x\n", block.PrevBlockHash)
-		fmt.Printf("Data: %s\n", block.Data)
 		fmt.Printf("Hash: %x\n", block.Hash)
 		pow := NewProofOfWork(block)
 		fmt.Printf("PoW: %s\n", strconv.FormatBool(pow.Validate()))
@@ -50,18 +68,38 @@ func (cli *CLI) printChain() {
 	}
 }
 
+func (cli *CLI) send(from, to string, amount int) {
+	bc := NewBlockchain(from)
+	defer bc.db.Close()
+
+	tx := NewUTXOTransaction(from, to, amount, bc)
+	bc.MineBlock([]*Transaction{tx})
+	fmt.Println("Success!")
+}
+
 // Run parses command line arguments and processes commands
 func (cli *CLI) Run() {
 	cli.validateArgs()
 
-	addBlockCmd := flag.NewFlagSet("addblock", flag.ExitOnError)
+	getBalanceCmd := flag.NewFlagSet("getbalance", flag.ExitOnError)
+	createBlockchainCmd := flag.NewFlagSet("createblockchain", flag.ExitOnError)
+	sendCmd := flag.NewFlagSet("send", flag.ExitOnError)
 	printChainCmd := flag.NewFlagSet("printchain", flag.ExitOnError)
 
-	addBlockData := addBlockCmd.String("data", "", "Block data")
+	getBalanceAddress := getBalanceCmd.String("address", "", "The address to get balance for")
+	createBlockchainAddress := createBlockchainCmd.String("address", "", "The address to send genesis block reward to")
+	sendFrom := sendCmd.String("from", "", "Source wallet address")
+	sendTo := sendCmd.String("to", "", "Destination wallet address")
+	sendAmount := sendCmd.Int("amount", 0, "Amount to send")
 
 	switch os.Args[1] {
-	case "addblock":
-		err := addBlockCmd.Parse(os.Args[2:])
+	case "getbalance":
+		err := getBalanceCmd.Parse(os.Args[2:])
+		if err != nil {
+			log.Panic(err)
+		}
+	case "createblockchain":
+		err := createBlockchainCmd.Parse(os.Args[2:])
 		if err != nil {
 			log.Panic(err)
 		}
@@ -70,20 +108,42 @@ func (cli *CLI) Run() {
 		if err != nil {
 			log.Panic(err)
 		}
+	case "send":
+		err := sendCmd.Parse(os.Args[2:])
+		if err != nil {
+			log.Panic(err)
+		}
 	default:
 		cli.printUsage()
 		os.Exit(1)
 	}
 
-	if addBlockCmd.Parsed() {
-		if *addBlockData == "" {
-			addBlockCmd.Usage()
+	if getBalanceCmd.Parsed() {
+		if *getBalanceAddress == "" {
+			getBalanceCmd.Usage()
 			os.Exit(1)
 		}
-		cli.addBlock(*addBlockData)
+		cli.getBalance(*getBalanceAddress)
+	}
+
+	if createBlockchainCmd.Parsed() {
+		if *createBlockchainAddress == "" {
+			createBlockchainCmd.Usage()
+			os.Exit(1)
+		}
+		cli.createBlockchain(*createBlockchainAddress)
 	}
 
 	if printChainCmd.Parsed() {
 		cli.printChain()
 	}
+
+	if sendCmd.Parsed() {
+		if *sendFrom == "" || *sendTo == "" || *sendAmount <= 0 {
+			sendCmd.Usage()
+			os.Exit(1)
+		}
+
+		cli.send(*sendFrom, *sendTo, *sendAmount)
+	}
 }
diff --git a/main.go b/main.go
@@ -1,9 +1,6 @@
 package main
 
 func main() {
-	bc := NewBlockchain()
-	defer bc.db.Close()
-
-	cli := CLI{bc}
+	cli := CLI{}
 	cli.Run()
 }
diff --git a/proofofwork.go b/proofofwork.go
@@ -34,7 +34,7 @@ func (pow *ProofOfWork) prepareData(nonce int) []byte {
 	data := bytes.Join(
 		[][]byte{
 			pow.block.PrevBlockHash,
-			pow.block.Data,
+			pow.block.HashTransactions(),
 			IntToHex(pow.block.Timestamp),
 			IntToHex(int64(targetBits)),
 			IntToHex(int64(nonce)),
@@ -51,7 +51,7 @@ func (pow *ProofOfWork) Run() (int, []byte) {
 	var hash [32]byte
 	nonce := 0
 
-	fmt.Printf("Mining the block containing \"%s\"\n", pow.block.Data)
+	fmt.Printf("Mining a new block")
 	for nonce < maxNonce {
 		data := pow.prepareData(nonce)
 

diff --git a/transaction.go b/transaction.go
@@ -0,0 +1,111 @@
+package main
+
+import (
+	"bytes"
+	"crypto/sha256"
+	"encoding/gob"
+	"encoding/hex"
+	"fmt"
+	"log"
+)
+
+const subsidy = 10
+
+// Transaction represents a Bitcoin transaction
+type Transaction struct {
+	ID   []byte
+	Vin  []TXInput
+	Vout []TXOutput
+}
+
+// IsCoinbase checks whether the transaction is coinbase
+func (tx Transaction) IsCoinbase() bool {
+	return len(tx.Vin) == 1 && len(tx.Vin[0].Txid) == 0 && tx.Vin[0].Vout == -1
+}
+
+// SetID sets ID of a transaction
+func (tx *Transaction) SetID() {
+	var encoded bytes.Buffer
+	var hash [32]byte
+
+	enc := gob.NewEncoder(&encoded)
+	err := enc.Encode(tx)
+	if err != nil {
+		log.Panic(err)
+	}
+	hash = sha256.Sum256(encoded.Bytes())
+	tx.ID = hash[:]
+}
+
+// TXInput represents a transaction input
+type TXInput struct {
+	Txid      []byte
+	Vout      int
+	ScriptSig string
+}
+
+// TXOutput represents a transaction output
+type TXOutput struct {
+	Value        int
+	ScriptPubKey string
+}
+
+// CanUnlockOutputWith checks whether the address initiated the transaction
+func (in *TXInput) CanUnlockOutputWith(unlockingData string) bool {
+	return in.ScriptSig == unlockingData
+}
+
+// CanBeUnlockedWith checks if the output can be unlocked with the provided data
+func (out *TXOutput) CanBeUnlockedWith(unlockingData string) bool {
+	return out.ScriptPubKey == unlockingData
+}
+
+// NewCoinbaseTX creates a new coinbase transaction
+func NewCoinbaseTX(to, data string) *Transaction {
+	if data == "" {
+		data = fmt.Sprintf("Reward to '%s'", to)
+	}
+
+	txin := TXInput{[]byte{}, -1, data}
+	txout := TXOutput{subsidy, to}
+	tx := Transaction{nil, []TXInput{txin}, []TXOutput{txout}}
+	tx.SetID()
+
+	return &tx
+}
+
+// NewUTXOTransaction creates a new transaction
+func NewUTXOTransaction(from, to string, amount int, bc *Blockchain) *Transaction {
+	var inputs []TXInput
+	var outputs []TXOutput
+
+	acc, validOutputs := bc.FindSpendableOutputs(from, amount)
+
+	if acc < amount {
+		log.Panic("ERROR: Not enough funds")
+	}
+
+	// Build a list of inputs
+	for txid, outs := range validOutputs {
+		txID, err := hex.DecodeString(txid)
+		if err != nil {
+			log.Panic(err)
+		}
+
+		for _, out := range outs {
+			input := TXInput{txID, out, from}
+			inputs = append(inputs, input)
+		}
+	}
+
+	// Build a list of outputs
+	outputs = append(outputs, TXOutput{amount, to})
+	if acc > amount {
+		outputs = append(outputs, TXOutput{acc - amount, from}) // a change
+	}
+
+	tx := Transaction{nil, inputs, outputs}
+	tx.SetID()
+
+	return &tx
+}