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:

  1. 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
  2. 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
  3. 当余额不足时,提示余额不足信息
  4. 当余额充足时,新建一条交易,即一个UTXO
  5. 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。
  6. 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:
从Go语言编码角度解释实现简易区块链——实现交易-LMLPHP
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。

在下一节,将实现区块链的地址机制,逐步完善整个区块链。

10-31 00:54