在公链基础上实现区块链交易
区块链的目的,是能够安全可靠的存储交易,比如我们常见的比特币的交易,这里我们会以比特币为例实现区块链上的通用交易。上一节用简单的数据结构完成了区块链的公链,本节在此基础上对区块链的交易部分进行实现。实现公链
交易机制
在区块链中,交易一旦被创建,就没有任何人能够再去修改或是删除它,本节将实现一个交易的基本框架,具体交易细节将会在之后给出。
以比特币为例,不同于一般概念的账户模型,其交易采用的是UTXO模型。我们所需要的信息,都间接的包含在了每一笔交易中,包括用户的余额信息。
对于每一笔交易,你可以想象成一个通道,通道的左端有若干个输入信息,通道的右端会有若干输出信息。输入信息代表的意义是,该交易所用的币是从何而来,一条交易可以有0到多个币源(0是特殊情况,即被挖出的矿,因为没有用户来源,所以没有输入信息)。输出信息代表的意义是,进行该交易后,数字货币变动到哪里去了。因此,一条交易信息中货币的输入数量与输出数量应该是等价的,数字货币的来源总和,等于数字货币的输出总和。不难想象,与传统的账户模型相比,在UTXO模型中用户的账户余额是记录在交易的输出部分。
举个最简单的例子,假设A需要给B支付了一个比特币,将执行以下流程:
- 查看当前已有的交易信息,找到交易输出指向自己的交易并将余额计入总和
- 判断当前交易信息输出中是否有足够的数字货币属于自己
- 当余额不足时,提示余额不足信息
- 当余额充足时,新建一条交易,即一个UTXO
- 该UTXO的输入信息是消费用户的部分余额(不需要消费用户的所有余额,只要满足够用就行),而用户的余额是记录在之前已有的UTXO的输出中,所以新交易的输入,便是之前某些交易的输出。
- 当用户找到的余额数量与本次交易所需的数量不相等时,用户可以将剩下的货币再向自己输出,即找零,以保证交易的输入与输出相等
这样我们就实现了一个简单的交易,在这场交易中有货币的来源,货币有明确的去向,同时携带了我们正在进行的交易信息。
之后我们将结合代码,让这种逻辑变得更加清晰,下面这张图是对UTXO模型的简单描述:
Coinbase交易是特殊的一种交易,它表示矿工挖出了新的矿,作用是将新挖出的矿加入公链中并将输出指向挖矿的矿工。
该例子表示,张三挖矿得到12.5个比特币,然后支付了2.5个给李四,自己剩余10比特币,之后张三李四各支付2.5个比特币给王五,最终张三还剩7.5个比特币,李四余额用尽,王五剩余5个比特币,总和12.5等于张三挖出的总矿币。
编码实现
与之前已经完成的实现公链的代码相比,区块链的交易需要新建一个transaction.go文件,用来实现交易逻辑。其余文件中的代码,会跟随交易机制的加入进行微小的调整。
transaction.go
以下为transaction.go的代码:
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
}
代码主要包含以下内容:
- Transaction 结构体,包含当前交易的ID(交易需要ID)、输入数组以及输出数组
- IsCoinbase函数,用来判断当前交易是否是Coinbase交易(挖矿交易)
- SetID函数给交易设置id
- TXInput 结构体,包含输入的某条交易的id,该交易某个输出的金额与地址
- TXOutput 结构体,包含当前交易的某个输出的金额与地址
- CanUnlockOutputWith函数判断提供的地址能否匹配某条交易记录的输入地址
- CanBeUnlockedWith函数判断提供的地址能否匹配某条交易记录的输出地址
- NewCoinbaseTX函数创建一条挖矿交易
- NewUTXOTransaction函数创建一条新的交易
关于TXInput与TXOutput中地址的问题,因为目前还没有实现区块链中的地址,所以本节涉及的地址直接用字符串代替,验证地址也只是进行了字符串对比。地址是必要的,它标注了当前的余额属于谁,这里因为刚实现交易机制,还没有引入真正的地址机制,所以是存在漏洞的,用户只要知道有哪些用户就可以直接往自己地址转钱,在下一节会实现地址机制进行完善。
block.go
在transaction.go中实现了交易的结构体,如何创建一条新的交易,以及简单的交易对象判断。在其余文件中,block.go文件做了一些改动,主要是将原本的data字符串换成了Transaction交易。同样的,下一节中我们会将本节的地址字符串换成相应机制的地址,以下是改动后的block.go文件:
package main
import (
"bytes"
"crypto/sha256"
"encoding/gob"
"log"
"time"
)
// Block keeps block headers
type Block struct {
Timestamp int64
Transactions []*Transaction
PrevBlockHash []byte
Hash []byte
Nonce int
}
// Serialize serializes the block
func (b *Block) Serialize() []byte {
var result bytes.Buffer
encoder := gob.NewEncoder(&result)
err := encoder.Encode(b)
if err != nil {
log.Panic(err)
}
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(transactions []*Transaction, prevBlockHash []byte) *Block {
block := &Block{time.Now().Unix(), transactions, prevBlockHash, []byte{}, 0}
pow := NewProofOfWork(block)
nonce, hash := pow.Run()
block.Hash = hash[:]
block.Nonce = nonce
return block
}
// NewGenesisBlock creates and returns genesis Block
func NewGenesisBlock(coinbase *Transaction) *Block {
return NewBlock([]*Transaction{coinbase}, []byte{})
}
// DeserializeBlock deserializes a block
func DeserializeBlock(d []byte) *Block {
var block Block
decoder := gob.NewDecoder(bytes.NewReader(d))
err := decoder.Decode(&block)
if err != nil {
log.Panic(err)
}
return &block
}
添加了HashTransactions函数,用来将交易转换成哈希值,其余函数随结构体中Data->Transactions的变动相应调整。
blockchain.go
在blockchain.go中,涉及到寻找用户余额(未花费交易输出)操作,需要多做一些调整:
package main
import (
"encoding/hex"
"fmt"
"log"
"os"
"bolt-master"
)
const dbFile = "blockchain.db"
const blocksBucket = "blocks"
const genesisCoinbaseData = "The Times 03/Jan/2009 Chancellor on brink of second bailout for banks"
// Blockchain implements interactions with a DB
type Blockchain struct {
tip []byte
db *bolt.DB
}
// BlockchainIterator is used to iterate over blockchain blocks
type BlockchainIterator struct {
currentHash []byte
db *bolt.DB
}
// 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 {
b := tx.Bucket([]byte(blocksBucket))
lastHash = b.Get([]byte("l"))
return nil
})
if err != nil {
log.Panic(err)
}
newBlock := NewBlock(transactions, lastHash)
err = bc.db.Update(func(tx *bolt.Tx) error {
b := tx.Bucket([]byte(blocksBucket))
err := b.Put(newBlock.Hash, newBlock.Serialize())
if err != nil {
log.Panic(err)
}
err = b.Put([]byte("l"), newBlock.Hash)
if err != nil {
log.Panic(err)
}
bc.tip = newBlock.Hash
return nil
})
}
// 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}
return bci
}
// Next returns next block starting from the tip
func (i *BlockchainIterator) Next() *Block {
var block *Block
err := i.db.View(func(tx *bolt.Tx) error {
b := tx.Bucket([]byte(blocksBucket))
encodedBlock := b.Get(i.currentHash)
block = DeserializeBlock(encodedBlock)
return nil
})
if err != nil {
log.Panic(err)
}
i.currentHash = block.PrevBlockHash
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(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 {
log.Panic(err)
}
err = db.Update(func(tx *bolt.Tx) error {
b := tx.Bucket([]byte(blocksBucket))
tip = b.Get([]byte("l"))
return nil
})
if err != nil {
log.Panic(err)
}
bc := Blockchain{tip, db}
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
})
if err != nil {
log.Panic(err)
}
bc := Blockchain{tip, db}
return &bc
}
代码的主要变动是新增了三个关于交易的函数:
- FindUnspendTransactions遍历公链,寻找交易信息中没有被使用过输出的交易,即未被花费过的余额。当一条交易中的余额被其他交易用做过输入,该余额也就不在具有余额的属性,不能再次被交易
- FindUTXO在内部调用了FindUnspendTransactions函数,与FindUnspendTransactions不同的是它用于查询用户的余额信息,即所有有效未花费余额的总和
- FindSpendableOutputs在内部调用了FindUnspendTransactions函数,用于找出哪些余额是可用的
其次,原本的Addblock被改成了更具体的Mineblock挖矿函数,新增了Createblockchain函数和dbExists函数,用来判断数据库是否存在,只有当数据库中没有公链时才能创建新的区块链。
proofofwork.go
在proofofwork文件中,仅在prepareData时将Data换成了HashTransactions,在挖矿时不再打印Data部分,proofofwork.go完整代码如下:
package main
import (
"bytes"
"crypto/sha256"
"fmt"
"math"
"math/big"
)
var (
maxNonce = math.MaxInt64
)
const targetBits = 24
// ProofOfWork represents a proof-of-work
type ProofOfWork struct {
block *Block
target *big.Int
}
// NewProofOfWork builds and returns a ProofOfWork
func NewProofOfWork(b *Block) *ProofOfWork {
target := big.NewInt(1)
target.Lsh(target, uint(256-targetBits))
pow := &ProofOfWork{b, target}
return pow
}
func (pow *ProofOfWork) prepareData(nonce int) []byte {
data := bytes.Join(
[][]byte{
pow.block.PrevBlockHash,
pow.block.HashTransactions(),
IntToHex(pow.block.Timestamp),
IntToHex(int64(targetBits)),
IntToHex(int64(nonce)),
},
[]byte{},
)
return data
}
// Run performs a proof-of-work
func (pow *ProofOfWork) Run() (int, []byte) {
var hashInt big.Int
var hash [32]byte
nonce := 0
fmt.Printf("Mining a new block")
for nonce < maxNonce {
data := pow.prepareData(nonce)
hash = sha256.Sum256(data)
// fmt.Printf("\r%x", hash)
hashInt.SetBytes(hash[:])
if hashInt.Cmp(pow.target) == -1 {
break
} else {
nonce++
}
}
// fmt.Print("\n\n")
return nonce, hash[:]
}
// Validate validates block's PoW
func (pow *ProofOfWork) Validate() bool {
var hashInt big.Int
data := pow.prepareData(pow.block.Nonce)
hash := sha256.Sum256(data)
hashInt.SetBytes(hash[:])
isValid := hashInt.Cmp(pow.target) == -1
return isValid
}
cli.go
cli.go文件随底层的一些变动,做出相应的业务逻辑改变,变动主要用于实现命令行操作,不涉及区块链的逻辑:
package main
import (
"flag"
"fmt"
"log"
"os"
"strconv"
)
// CLI responsible for processing command line arguments
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(" 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() {
if len(os.Args) < 2 {
cli.printUsage()
os.Exit(1)
}
}
func (cli *CLI) printChain() {
// 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("Hash: %x\n", block.Hash)
pow := NewProofOfWork(block)
fmt.Printf("PoW: %s\n", strconv.FormatBool(pow.Validate()))
fmt.Println()
if len(block.PrevBlockHash) == 0 {
break
}
}
}
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()
getBalanceCmd := flag.NewFlagSet("getbalance", flag.ExitOnError)
createBlockchainCmd := flag.NewFlagSet("createblockchain", flag.ExitOnError)
sendCmd := flag.NewFlagSet("send", flag.ExitOnError)
printChainCmd := flag.NewFlagSet("printchain", flag.ExitOnError)
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 "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)
}
case "printchain":
err := printChainCmd.Parse(os.Args[2:])
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 getBalanceCmd.Parsed() {
if *getBalanceAddress == "" {
getBalanceCmd.Usage()
os.Exit(1)
}
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)
}
}
main.go
在main.go中,我们将所有的操作有交给cli对象进行,原本旧main.go中的新建创世块操作,也放到了cli.go的逻辑中,所以只需要以下代码:
package main
func main() {
bc := NewBlockchain()
defer bc.db.Close()
cli := CLI{bc}
cli.Run()
}
utils.go
没有新的工具函数引入,utils.go文件不变。