go语言编写小型的区块链示例

本文介绍了：
如何创建自己的区块链
理解hash函数是如何保证区块链的完整性的
如何创建并添加新的块
多个节点如何竞争生成块
关于区块链的基本知识

但是，对于比如工作量证明算法（PoW）以及权益证明算法（PoS）这类的共识算法文章中将不会涉及。同时为了让你更清楚得查看区块链以及块的添加，我们将网络交互的过程简化了。

package main

import (
    "crypto/sha256"
    "encoding/hex"
    "encoding/json"
    "github.com/davecgh/go-spew/spew"
    "github.com/gorilla/mux"
    "github.com/joho/godotenv"
    "io"
    "log"
    "net/http"
    "os"
    "time"
)

//区块链块的结构体
type Block struct {
    //Index 是这个块在整个链中的位置
    Index int
    //Timestamp 块生成时的时间戳
    Timestamp string
    //每分钟心跳数，也就是心率
    BPM int
    //通过 SHA256 算法生成的散列值
    Hash string
    //代表前一个块的 SHA256 散列值
    PrevHash string
}

//表示整个链
var Blockchain []Block

//计算数据的sha256散列值
func calculateHash(block Block) string {
    record := string(block.Index) + block.Timestamp + string(block.BPM) + block.PrevHash
    h := sha256.New()
    h.Write([]byte(record))
    hashed := h.Sum(nil)
    return hex.EncodeToString(hashed)
}

//生成块
func generateBlock(oldBlock Block, BPM int) (Block, error) {
    var newBlock Block

    t := time.Now()
    newBlock.Index = oldBlock.Index + 1
    newBlock.Timestamp = t.String()
    newBlock.BPM = BPM
    newBlock.PrevHash = oldBlock.Hash
    newBlock.Hash = calculateHash(newBlock)

    return newBlock, nil
}

//校验块
func isBlockValid(newBlock, oldBlock Block) bool {
    if oldBlock.Index+1 != newBlock.Index {
        return false
    }

    if oldBlock.Hash != newBlock.PrevHash {
        return false
    }

    if calculateHash(newBlock) != newBlock.Hash {
        return false
    }
    return true
}

//将过期的链更新为最新的链
func replaceChain(newBlocks []Block) {
    if len(newBlocks) > len(Blockchain) {
        Blockchain = newBlocks
    }
}

//初始化web服务
func run() error {
    mux := makeMuxRouter()
    httpAddr := os.Getenv("ADDR")
    log.Println("Listening on", os.Getenv("ADDR"))
    s := &http.Server{
        Addr:           ":" + httpAddr,
        Handler:        mux,
        ReadTimeout:    10 * time.Second,
        WriteTimeout:   10 * time.Second,
        MaxHeaderBytes: 1 << 20,
    }

    if err := s.ListenAndServe(); err != nil {
        return err
    }

    return nil
}

func makeMuxRouter() http.Handler {
    muxRouter := mux.NewRouter()
    muxRouter.HandleFunc("/", handleGetBlockchain).Methods("GET")
    muxRouter.HandleFunc("/", handleWriteBlock).Methods("POST")
    return muxRouter
}

//get请求的handler
func handleGetBlockchain(w http.ResponseWriter, r *http.Request) {
    bytes, err := json.MarshalIndent(Blockchain, "", " ")
    if err != nil {
        http.Error(w, err.Error(), http.StatusInternalServerError)
        return
    }
    io.WriteString(w, string(bytes))
}

//post请求的payload
type Message struct {
    BPM int
}

//post请求的handler
func handleWriteBlock(w http.ResponseWriter, r *http.Request) {
    var m Message

    decoder := json.NewDecoder(r.Body)
    if err := decoder.Decode(&m); err != nil {
        respondWidthJSON(w, r, http.StatusBadRequest, r.Body)
        return
    }
    defer r.Body.Close()

    newBlock, err := generateBlock(Blockchain[len(Blockchain)-1], m.BPM)
    if err != nil {
        respondWidthJSON(w, r, http.StatusCreated, newBlock)
    }

    //spew.Dump(isBlockValid(newBlock, Blockchain[len(Blockchain)-1]))
    //respondWidthJSON(w, r, http.StatusCreated, isBlockValid(newBlock, Blockchain[len(Blockchain)-1]))


    if isBlockValid(newBlock, Blockchain[len(Blockchain)-1]) {
        newBlockchain := append(Blockchain, newBlock)
        replaceChain(newBlockchain)
        spew.Dump(Blockchain)
    }

    respondWidthJSON(w, r, http.StatusCreated, newBlock)
}

//返回客户端响应
func respondWidthJSON(w http.ResponseWriter, r *http.Request, code int, payload interface{}) {
    response, err := json.MarshalIndent(payload, "", "  ")
    if err != nil {
        w.WriteHeader(http.StatusInternalServerError)
        w.Write([]byte("HTTP 500: Internal Server Error"))
    }
    w.WriteHeader(code)
    w.Write(response)
}

func main() {
    err := godotenv.Load()
    if err != nil {
        log.Fatal(err)
    }

    //初始化区块链
    go func() {
        t := time.Now()
        genesisBlock := Block{0, t.String(), 0, "", ""}
        spew.Dump(genesisBlock)
        Blockchain = append(Blockchain, genesisBlock)
    }()
    log.Fatal(run())
}