目前为止，程序还没有提供任何交互接口，仅仅在main函数中调用NewBlockchain, bc.AddBlock等函数。现在让我们实现以下命令：

blockchain_go addblock "Pay 0.031337 for a coffee"
blockchain_go printchain

所有命令行命令通过CLI结构处理：

type CLI struct {
    bc *Blockchain
}

CLI的入口是Run函数：

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()
    }
}

我们使用flag标准库处理命令行参数：

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

首先，创建两个子命令：addblock、printchain，addblock具有一个命令参数-data，printchain没有任何命令参数。

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)
}

接下来，我们检查用户输入的命令以及与之相关的命令参数：

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

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

对于解析成功的应命令执行对应的函数。

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
        }
    }
}

整个过程与之前非常相似，唯一区别在于现在使用BlockchainIterator遍历blockchain。

最后，修改一下main函数：

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

    cli := CLI{bc}
    cli.Run()
}

需要注意的是无论是否有命令行参数，程序一运行就会创建一个blockchain。

一切OK，尝试运行下吧：

$ 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