pow介绍

工作量证明（PoW，Proof of Work）。

如果验证通过，则表明已经有节点成功解迷，自己就不再竞争当前区块打包，而是选择接受这个区块，记录到自己的账本中，然后进行下一个区块的竞争猜谜。 网络中只有最快解谜的区块，才会添加的账本中，其他的节点进行复制，这样就保证了整个账本的唯一性。

假如节点有任何的作弊行为，都会导致网络的节点验证不通过，直接丢弃其打包的区块，这个区块就无法记录到总账本中，作弊的节点耗费的成本就白费了，因此在巨大的挖矿成本下，也使得矿工自觉自愿的遵守比特币系统的共识协议，也就确保了整个系统的安全。

pow优缺点

• 优点：完全去中心化，节点自由进出；
• 缺点：目前bitcoin已经吸引全球大部分的算力，其它再用Pow共识机制的区块链应用很难获得相同的算力来保障自身的安全；挖矿造成大量的资源浪费；共识达成的周期较长，不适合商业应用

go实现pow共识算法

依赖软件

• spew 在控制台中格式化输出相应的结果。
  $ go get github.com/davecgh/go-spew/spew
• gorilla/mux 是编写web处理程序的流行软件包。
  $ go get github.com/gorilla/mux
• godotenv 可以从我们项目的根目录的 .env 文件中读取数据。
  $ go get github.com/joho/godotenv

.env

ADDR=8080

main.go

package mainimport (        "crypto/sha256"        "encoding/hex"        "encoding/json"        "fmt"        "io"        "log"        "net/http"        "os"        "strconv"        "strings"        "sync"        "time"        "github.com/davecgh/go-spew/spew"        "github.com/gorilla/mux"        "github.com/joho/godotenv")const difficulty = 1type Block struct {        Index      int        Timestamp  string        BPM        int        Hash       string        PrevHash   string        Difficulty int        Nonce      string}var Blockchain []Blocktype Message struct {        BPM int}var mutex = &sync.Mutex{}func generateBlock(oldBlock Block, BPM int) Block {    var newBlock Block    t := time.Now()    newBlock.Index = oldBlock.Index + 1    newBlock.Timestamp = t.String()    newBlock.BPM = BPM    newBlock.PrevHash = oldBlock.Hash    newBlock.Difficulty = difficulty    for i := 0; ; i++ {            hex := fmt.Sprintf("%x", i)            newBlock.Nonce = hex            if !isHashValid(calculateHash(newBlock), newBlock.Difficulty) {                    fmt.Println(calculateHash(newBlock), " do more work!")                    time.Sleep(time.Second)                    continue            } else {                    fmt.Println(calculateHash(newBlock), " work done!")                    newBlock.Hash = calculateHash(newBlock)                    break            }    }    return newBlock}func isHashValid(hash string, difficulty int) bool {    //复制 difficulty 个0，并返回新字符串，当 difficulty 为2 ，则 prefix 为 00    prefix := strings.Repeat("0", difficulty)    // HasPrefix判断字符串 hash 是否包含前缀 prefix    return strings.HasPrefix(hash, prefix)}func calculateHash(block Block) string {    record := strconv.Itoa(block.Index) + block.Timestamp + strconv.Itoa(block.BPM) + block.PrevHash + block.Nonce    h := sha256.New()    h.Write([]byte(record))    hashed := h.Sum(nil)    return hex.EncodeToString(hashed)}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}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}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))}func handleWriteBlock(w http.ResponseWriter, r *http.Request) {    w.Header().Set("Content-Type", "application/json")    var m Message    decoder := json.NewDecoder(r.Body)    if err := decoder.Decode(&m); err != nil {            respondWithJSON(w, r, http.StatusBadRequest, r.Body)            return    }       defer r.Body.Close()    //ensure atomicity when creating new block    mutex.Lock()    newBlock := generateBlock(Blockchain[len(Blockchain)-1], m.BPM)    mutex.Unlock()    if isBlockValid(newBlock, Blockchain[len(Blockchain)-1]) {            Blockchain = append(Blockchain, newBlock)            spew.Dump(Blockchain)    }       respondWithJSON(w, r, http.StatusCreated, newBlock)}func respondWithJSON(w http.ResponseWriter, r *http.Request, code int, payload interface{}) {    w.Header().Set("Content-Type", "application/json")    response, err := json.MarshalIndent(payload, "", "  ")    if err != nil {            w.WriteHeader(http.StatusInternalServerError)            w.Write([]byte("HTTP 500: Internal Server Error"))            return    }    w.WriteHeader(code)    w.Write(response)}func main() {    err := godotenv.Load()    if err != nil {            log.Fatal(err)    }       go func() {            t := time.Now()            genesisBlock := Block{}            genesisBlock = Block{0, t.String(), 0, calculateHash(genesisBlock), "", difficulty, ""}             spew.Dump(genesisBlock)            mutex.Lock()            Blockchain = append(Blockchain, genesisBlock)            mutex.Unlock()    }()     log.Fatal(run())}