req, _ := http.NewRequest("POST", "localhost", strings.NewReader("hello"))

func main() {  go func() {    http.HandleFunc("/", http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {      time.Sleep(time.Millisecond * 20)      body, _ := ioutil.ReadAll(r.Body)        fmt.Printf("received body with length %v containing: %v\n", len(body), string(body))      w.WriteHeader(http.StatusOK)    }))    http.ListenAndServe(":8090", nil)  }()  fmt.Print("Try with bare strings.Reader\n")   retryDo(req)}
func retryDo() {  originalBody := []byte("abcdefghigklmnopqrst")  reader := strings.NewReader(string(originalBody))  req, _ := http.NewRequest("POST", "http://localhost:8090/", reader)  client := http.Client{    Timeout: time.Millisecond * 10,  }
  for {    _, err := client.Do(req)    if err != nil {      fmt.Printf("error sending the first time: %v\n", err)    }     time.Sleep(1000)  }}
// output:error sending the first time: Post "http://localhost:8090/": context deadline exceeded (Client.Timeout exceeded while awaiting headers)error sending the first time: Post "http://localhost:8090/": http: ContentLength=20 with Body length 0error sending the first time: Post "http://localhost:8090/": http: ContentLength=20 with Body length 0received body with length 20 containing: abcdefghigklmnopqrsterror sending the first time: Post "http://localhost:8090/": http: ContentLength=20 with Body length 0....

func resetBody(request *http.Request, originalBody []byte) {  request.Body = io.NopCloser(bytes.NewBuffer(originalBody))  request.GetBody = func() (io.ReadCloser, error) {    return io.NopCloser(bytes.NewBuffer(originalBody)), nil  }}

func retryDo(req *http.Request, maxRetries int, timeout time.Duration,  backoffStrategy BackoffStrategy) (*http.Response, error) {  var (    originalBody []byte    err          error  )  if req != nil && req.Body != nil {    originalBody, err = copyBody(req.Body)    resetBody(req, originalBody)  }  if err != nil {    return nil, err  }  AttemptLimit := maxRetries  if AttemptLimit <= 0 {    AttemptLimit = 1  }
  client := http.Client{    Timeout: timeout,  }  var resp *http.Response  //重試次數(shù)  for i := 1; i <= AttemptLimit; i++ {    resp, err = client.Do(req)    if err != nil {      fmt.Printf("error sending the first time: %v\n", err)    }     // 重試 500 以上的錯(cuò)誤碼    if err == nil && resp.StatusCode < 500 {      return resp, err    }    // 如果正在重試，那么釋放fd    if resp != nil {      resp.Body.Close()    }    // 重置body    if req.Body != nil {      resetBody(req, originalBody)    }    time.Sleep(backoffStrategy(i) + 1*time.Microsecond)  }  // 到這里，說(shuō)明重試也沒(méi)用  return resp, req.Context().Err()}
func copyBody(src io.ReadCloser) ([]byte, error) {  b, err := ioutil.ReadAll(src)  if err != nil {    return nil, ErrReadingRequestBody  }  src.Close()  return b, nil}
func resetBody(request *http.Request, originalBody []byte) {  request.Body = io.NopCloser(bytes.NewBuffer(originalBody))  request.GetBody = func() (io.ReadCloser, error) {    return io.NopCloser(bytes.NewBuffer(originalBody)), nil  }}

func main() {  totalSentRequests := &sync.WaitGroup{}  allRequestsBackCh := make(chan struct{})  multiplexCh := make(chan struct {    result string    retry  int  })  go func() {    //所有請(qǐng)求完成之后會(huì)close掉allRequestsBackCh    totalSentRequests.Wait()    close(allRequestsBackCh)  }()  for i := 1; i <= 10; i++ {    totalSentRequests.Add(1)    go func() {      // 標(biāo)記已經(jīng)執(zhí)行完      defer totalSentRequests.Done()      // 模擬耗時(shí)操作      time.Sleep(500 * time.Microsecond)      // 模擬處理成功      if random.Intn(500)%2 == 0 {        multiplexCh <- struct {          result string          retry  int        }{"finsh success", i}      }      // 處理失敗不關(guān)心，當(dāng)然，也可以加入一個(gè)錯(cuò)誤的channel中進(jìn)一步處理    }()  }  select {  case <-multiplexCh:    fmt.Println("finish success")  case <-allRequestsBackCh:    // 到這里，說(shuō)明全部的 goroutine 都執(zhí)行完畢，但是都請(qǐng)求失敗了    fmt.Println("all req finish，but all fail")  }}

func main() {  req, _ := http.NewRequest("POST", "localhost", strings.NewReader("hello"))  req2 := req.Clone(req.Context())  contents, _ := io.ReadAll(req.Body)  contents2, _ := io.ReadAll(req2.Body)  fmt.Printf("First read: %v\n", string(contents))  fmt.Printf("Second read: %v\n", string(contents2))}
//output:First read: helloSecond read:

func retryHedged(req *http.Request, maxRetries int, timeout time.Duration,  backoffStrategy BackoffStrategy) (*http.Response, error) {  var (    originalBody []byte    err          error  )  if req != nil && req.Body != nil {    originalBody, err = copyBody(req.Body)  }  if err != nil {    return nil, err  }
  AttemptLimit := maxRetries  if AttemptLimit <= 0 {    AttemptLimit = 1  }
  client := http.Client{    Timeout: timeout,  }
  // 每次請(qǐng)求copy新的request  copyRequest := func() (request *http.Request) {    request = req.Clone(req.Context())    if request.Body != nil {      resetBody(request, originalBody)    }    return  }
  multiplexCh := make(chan struct {    resp  *http.Response    err   error    retry int  })
  totalSentRequests := &sync.WaitGroup{}  allRequestsBackCh := make(chan struct{})  go func() {    totalSentRequests.Wait()    close(allRequestsBackCh)  }()  var resp *http.Response  for i := 1; i <= AttemptLimit; i++ {    totalSentRequests.Add(1)    go func() {      // 標(biāo)記已經(jīng)執(zhí)行完      defer totalSentRequests.Done()      req = copyRequest()      resp, err = client.Do(req)      if err != nil {        fmt.Printf("error sending the first time: %v\n", err)      }      // 重試 500 以上的錯(cuò)誤碼      if err == nil && resp.StatusCode < 500 {        multiplexCh <- struct {          resp  *http.Response          err   error          retry int        }{resp: resp, err: err, retry: i}        return      }      // 如果正在重試，那么釋放fd      if resp != nil {        resp.Body.Close()      }      // 重置body      if req.Body != nil {        resetBody(req, originalBody)      }      time.Sleep(backoffStrategy(i) + 1*time.Microsecond)    }()  }
  select {  case res := <-multiplexCh:    return res.resp, res.err  case <-allRequestsBackCh:    // 到這里，說(shuō)明全部的 goroutine 都執(zhí)行完畢，但是都請(qǐng)求失敗了    return nil, errors.New("all req finish，but all fail")  }}

hystrix.ConfigureCommand("my_service", hystrix.CommandConfig{         ErrorPercentThreshold:  30,    })    _ = hystrix.Do("my_service", func() error {         req, _ := http.NewRequest("POST", "http://localhost:8090/", strings.NewReader("test"))        _, err := retryDo(req, 5, 20*time.Millisecond, ExponentialBackoff)        if err != nil {            fmt.Println("get error:%v",err)            return err        }        return nil    }, func(err error) error {        fmt.Printf("handle  error:%v\n", err)        return nil    })