Golang之错误处理

1、错误只在逻辑的最外层处理一次，底层只返回错误。
2、底层除了返回错误外，要对原始错误进行包装，增加错误信息、调用栈等这些有利于排查的上下文信息。

1、errors包：

//只附加新的信息
func WithMessage(err error, message string) error
如：
if err != nil {
  errors.WithMessage(err, "could not read config")
}


//只附加调用堆栈信息
func WithStack(err error) error


//同时附加堆栈和信息
func Wrap(err error, message string) error
如：
if err != nil {
  return errors.Wrap(err, "open failed")
}


// 返回包装错误对应的最原始错误
errors.Cause(err)
如：
fmt.Printf("original error: %T %v\n", errors.Cause(err), errors.Cause(err))

2、Err集中判断：

初始：
// 开车去商店 
shopper, err := shopper.Drive(FuelNeededToGetToStore)
if nil != err {
    log.Fatalf("could not complete shopping: %s", err)
}
// 买鸡蛋 
shopper, err = shopper.BuyEggs(EggsRequired)
if nil != err {
    log.Fatalf("could not complete shopping: %s", err)
}
// 买完鸡蛋开车回家 
shopper, err = shopper.Drive(FuelNeededToGetHome)
if nil != err {
    log.Fatalf("could not complete shopping: %s", err)
}


只打印不返回的err集中判断
func main(){
    shopper, err := shopper.Drive(FuelNeededToGetToStore)
    FatalIfErrNotNil(err)
    shopper, err = shopper.BuyEggs(EggsRequired)
    FatalIfErrNotNil(err)
    shopper, err = shopper.Drive(FuelNeededToGetHome)
    FatalIfErrNotNil(err)
}  

func FatalIfErrNotNil(err error) {
    if nil != err {
        log.Fatalf("could not complete shopping: %s", err)
    }
}

3、责任链迭代变换

func main(){
    driveToStore := Flavorize(Drive, FuelNeededToGetToStore)
    buyEggs := Flavorize(BuyEggs, EggsRequired)
    driveHome := Flavorize(Drive, FuelNeededToGetHome)
  
    shopper, err := ProcessSteps(shopper,
        driveToStore,
        buyEggs,
        driveHome,
    )
    if nil != err {
        log.Fatalf("could not complete shopping: %s", err)
    }
}

func ProcessSteps(s Shopper, steps ...func(Shopper) (Shopper, error)) (Shopper, error) {
    for _, step := range steps {
        var err error 
        s, err = step(s)
        if nil != err {
            return s, err
        }
    }
    return s, nil
}

func Flavorize(f func(Shopper, int) (Shopper, error), arg int) func(Shopper) (Shopper, error) {
 return func(s Shopper) (Shopper, error) {
  return f(s, arg)
 }
}

4、使用defer消除冗余

func writeConfig(data interface{}) (err error) {
  defer func() {
    if err != nil {
      err = errors.WithMessage(err, "writing configuration")
    }
  }()
  b, err := json.Marshal(data)
  if err != nil {
    return err
  }
  if err = ioutil.WriteFile("config.json", b, 0644); err != nil {
    return err
  }
  return
}

5、