3 持久化和命令行

引言

数据库选型

BoltDB

• 足够简洁
• 基于Go实现
• 不需要服务端

• Bolt是基于纯Go语言开发的KV存储，灵感来自于Howard Chu的LMDB项目。该项目目标是开发一个简单、快速、可靠的无服务端的数据库。API非常小巧和简洁，仅仅关注如何获取或设置数据，这就是全部。

• 注: 关于BoltDB与levelDB的对比, 请查看 http://www.opscoder.info/boltdb_intro.html
• 安装BoltDB: `go get github.com/boltdb/bolt`

数据库结构

• blocks存储用于描述所有block的元数据信息。
• chainstate用于存储blockchain的状态，包括所有交易元数据和部分元数据。

• 'b' + 32-byte block hash -> block index record
• 'f' + 4-byte file number -> file information record
• 'l' -> 4-byte file number: the last block file number used
• 'R' -> 1-byte boolean: whether we're in the process of reindexing
• 'F' + 1-byte flag name length + flag name string -> 1 byte boolean: various flags that can be on or off
• 't' + 32-byte transaction hash -> transaction index record

• 'c' + 32-byte transaction hash -> unspent transaction output record for that transaction. These records are only present for transactions that have at least one unspent output left. Each record stores:
  • The version of the transaction.
  • Whether the transaction was a coinbase or not.
  • Which height block contains the transaction.
  • Which outputs of that transaction are unspent.
  • The scriptPubKey and amount for those unspent outputs.
• 'B' -> 32-byte block hash: the block hash up to which the database represents the unspent transaction outputs

• 32-byte block-hash -> Block structure (serialized)
• 'l' -> the hash of the last block in a chain 最近一个block的hash

序列化

func (b *Block) Serialize() []byte {
    var result bytes.Buffer
    encoder := gob.NewEncoder(&result)


    err := encoder.Encode(b)


    return result.Bytes()
}

func DeserializeBlock(d []byte) *Block {
    var block Block


    decoder := gob.NewDecoder(bytes.NewReader(d))
    err := decoder.Decode(&block)


    return &block
}

持久化

• 打开数据库文件
• 检查是否有blockchain
• 如果有blockchain
  • 创建一个blockchain实例
  • 将blockchain的tip指向最新的block
• 如果没有blockchain
  • 创建genesis block
  • 存储在数据库中
  • 将genesis block的hash值保存为最新的block hash值
  • 创建一个新的blockchain实例，同时tip指向最新的block

func NewBlockchain() *Blockchain {
    var tip []byte
    db, err := bolt.Open(dbFile, 0600, nil)


    err = db.Update(func(tx *bolt.Tx) error {
        b := tx.Bucket([]byte(blocksBucket))


        if b == nil {
            genesis := NewGenesisBlock()
            b, err := tx.CreateBucket([]byte(blocksBucket))
            err = b.Put(genesis.Hash, genesis.Serialize())
            err = b.Put([]byte("l"), genesis.Hash)
            tip = genesis.Hash
        } else {
            tip = b.Get([]byte("l"))
        }


        return nil
    })


    bc := Blockchain{tip, db}


    return &bc
}

db, err := bolt.Open(dbFile, 0600, nil)

err = db.Update(func(tx *bolt.Tx) error {
...
})

b := tx.Bucket([]byte(blocksBucket))
if b == nil {
    genesis := NewGenesisBlock()
    b, err := tx.CreateBucket([]byte(blocksBucket))
    err = b.Put(genesis.Hash, genesis.Serialize())
    err = b.Put([]byte("l"), genesis.Hash)
    tip = genesis.Hash
} else {
    tip = b.Get([]byte("l"))
}

bc := Blockchain{tip, db}

type Blockchain struct {
    tip []byte
    db  *bolt.DB
}

func (bc *Blockchain) AddBlock(data string) {
    var lastHash []byte


    err := bc.db.View(func(tx *bolt.Tx) error {
        b := tx.Bucket([]byte(blocksBucket))
        lastHash = b.Get([]byte("l"))


        return nil
    })


    newBlock := NewBlock(data, lastHash)


    err = bc.db.Update(func(tx *bolt.Tx) error {
        b := tx.Bucket([]byte(blocksBucket))
        err := b.Put(newBlock.Hash, newBlock.Serialize())
        err = b.Put([]byte("l"), newBlock.Hash)
        bc.tip = newBlock.Hash


        return nil
    })
}

err := bc.db.View(func(tx *bolt.Tx) error {
    b := tx.Bucket([]byte(blocksBucket))
    lastHash = b.Get([]byte("l"))


    return nil
})

newBlock := NewBlock(data, lastHash)
b := tx.Bucket([]byte(blocksBucket))
err := b.Put(newBlock.Hash, newBlock.Serialize())
err = b.Put([]byte("l"), newBlock.Hash)
bc.tip = newBlock.Hash

查看区块链内容

type BlockchainIterator struct {
    currentHash []byte
    db          *bolt.DB
}

func (bc *Blockchain) Iterator() *BlockchainIterator {
    bci := &BlockchainIterator{bc.tip, bc.db}


    return bci
}

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
    })


    i.currentHash = block.PrevBlockHash


    return block
}

命令行接口

blockchain_go addblock "Pay 0.031337 for a coffee"
blockchain_go printchain

type CLI struct {
    bc *Blockchain
}

func (cli *CLI) Run() {
    cli.validateArgs()


    addBlockCmd := flag.NewFlagSet("addblock", flag.ExitOnError)
    printChainCmd := flag.NewFlagSet("printchain", flag.ExitOnError)


    addBlockData := addBlockCmd.String("data", "", "Block data")


    switch os.Args[1] {
    case "addblock":
        err := addBlockCmd.Parse(os.Args[2:])
    case "printchain":
        err := printChainCmd.Parse(os.Args[2:])
    default:
        cli.printUsage()
        os.Exit(1)
    }


    if addBlockCmd.Parsed() {
        if *addBlockData == "" {
            addBlockCmd.Usage()
            os.Exit(1)
        }
        cli.addBlock(*addBlockData)
    }


    if printChainCmd.Parsed() {
        cli.printChain()
    }
}

addBlockCmd := flag.NewFlagSet("addblock", flag.ExitOnError)
printChainCmd := flag.NewFlagSet("printchain", flag.ExitOnError)
addBlockData := addBlockCmd.String("data", "", "Block data")

switch os.Args[1] {case "addblock":
    err := addBlockCmd.Parse(os.Args[2:])case "printchain":
    err := printChainCmd.Parse(os.Args[2:])default:
    cli.printUsage()
    os.Exit(1)
}

f addBlockCmd.Parsed() {
    if *addBlockData == "" {
        addBlockCmd.Usage()
        os.Exit(1)
    }
    cli.addBlock(*addBlockData)
}
if printChainCmd.Parsed() {
    cli.printChain()
}

func (cli *CLI) addBlock(data string) {
    cli.bc.AddBlock(data)
    fmt.Println("Success!")
}
func (cli *CLI) printChain() {
    bci := cli.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()))
        fmt.Println()


        if len(block.PrevBlockHash) == 0 {
            break
        }
    }
}

func main() {
    bc := NewBlockchain()
    defer bc.db.Close()


    cli := CLI{bc}
    cli.Run()
}

$ blockchain_go printchain
No existing blockchain found. Creating a new one...
Mining the block containing "Genesis Block"
000000edc4a82659cebf087adee1ea353bd57fcd59927662cd5ff1c4f618109b


Prev. hash:
Data: Genesis Block
Hash: 000000edc4a82659cebf087adee1ea353bd57fcd59927662cd5ff1c4f618109b
PoW: true


$ blockchain_go addblock -data "Send 1 BTC to Ivan"
Mining the block containing "Send 1 BTC to Ivan"
000000d7b0c76e1001cdc1fc866b95a481d23f3027d86901eaeb77ae6d002b13


Success!


$ blockchain_go addblock -data "Pay 0.31337 BTC for a coffee"
Mining the block containing "Pay 0.31337 BTC for a coffee"
000000aa0748da7367dec6b9de5027f4fae0963df89ff39d8f20fd7299307148


Success!


$ blockchain_go printchain
Prev. hash: 000000d7b0c76e1001cdc1fc866b95a481d23f3027d86901eaeb77ae6d002b13
Data: Pay 0.31337 BTC for a coffee
Hash: 000000aa0748da7367dec6b9de5027f4fae0963df89ff39d8f20fd7299307148
PoW: true


Prev. hash: 000000edc4a82659cebf087adee1ea353bd57fcd59927662cd5ff1c4f618109b
Data: Send 1 BTC to Ivan
Hash: 000000d7b0c76e1001cdc1fc866b95a481d23f3027d86901eaeb77ae6d002b13
PoW: true


Prev. hash:
Data: Genesis Block
Hash: 000000edc4a82659cebf087adee1ea353bd57fcd59927662cd5ff1c4f618109b
PoW: true

总结