17.统一异常处理，设置自己的Error对象

package utils

type MyError struct {
    Code    int
    Message string
}


func NewMyError(code int, msg string) error {
    return &MyError{Code: code, Message: msg}
}

func (this *MyError) Error() string {
    return this.Message
}

func MyErrorEncoder(ctx context.Context, err error, w http.ResponseWriter) {
    contentType, body := "text/plain; charset=utf-8", []byte(err.Error())
    w.Header().Set("Content-type", contentType) //设置请求头
    if myerr, ok := err.(*utils.MyError); ok { //通过类型断言判断当前error的类型，走相应的处理
        w.WriteHeader(myerr.Code)
        w.Write(body)
    } else {
        w.WriteHeader(500)
        w.Write(body)
    }

}

func RateLimit(limit *rate.Limiter) endpoint.Middleware { //Middleware type Middleware func(Endpoint) Endpoint
    return func(next endpoint.Endpoint) endpoint.Endpoint { //Endpoint type Endpoint func(ctx context.Context, request interface{}) (response interface{}, err error)
        return func(ctx context.Context, request interface{}) (response interface{}, err error) {
            if !limit.Allow() {
                return nil, utils.NewMyError(429, "toot many request") //使用我们自定的错误结构体
            }
            return next(ctx, request)
        }
    }
}