pow介绍

工作量证明（PoW，Proof of Work）。
通过计算一个数值（nonce ），使得拼揍上交易数据后内容的 Hash 值满足规定的上限。在节点成功找到满足的Hash值之后，会马上对全网进行广播打包区块，网络的节点收到广播打包区块，会立刻对其进行验证。

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。
参考黎跃春的翻译

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

代码出处

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      intTimestamp  stringBPM        intHash       stringPrevHash   stringDifficulty intNonce      string
}var Blockchain []Blocktype Message struct {BPM int
}var mutex = &sync.Mutex{}func generateBlock(oldBlock Block, BPM int) Block {var newBlock Blockt := time.Now()newBlock.Index = oldBlock.Index + 1newBlock.Timestamp = t.String()newBlock.BPM = BPMnewBlock.PrevHash = oldBlock.HashnewBlock.Difficulty = difficultyfor i := 0; ; i++ {hex := fmt.Sprintf("%x", i)newBlock.Nonce = hexif !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 00prefix := strings.Repeat("0", difficulty)// HasPrefix判断字符串 hash 是否包含前缀 prefixreturn strings.HasPrefix(hash, prefix)
}func calculateHash(block Block) string {record := strconv.Itoa(block.Index) + block.Timestamp + strconv.Itoa(block.BPM) + block.PrevHash + block.Nonceh := 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 Messagedecoder := 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 blockmutex.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())}