Golang如何实现错误分类管理

type ValidationError struct {
    Field string
    Msg   string
}

func (e *ValidationError) Error() string {
    return fmt.Sprintf("validation error on field %s: %s", e.Field, e.Msg)
}

type DBError struct {
    Query string
    Cause string
}

func (e *DBError) Error() string {
    return fmt.Sprintf("db error during query %s: %s", e.Query, e.Cause)
}

if err := validate(input); err != nil {
    if vErr, ok := err.(*ValidationError); ok {
        log.Printf("Invalid input: %v", vErr.Field)
        // 返回400
    }
}

var (
    ErrNotFound  = fmt.Errorf("resource not found")
    ErrTimeout   = fmt.Errorf("request timed out")
    ErrForbidden = fmt.Errorf("access forbidden")
)

if errors.Is(err, ErrNotFound) {
    // 返回404
}

var dbErr *DBError
if errors.As(err, &dbErr) {
    log.Printf("DB query failed: %s", dbErr.Query)
}

_, err := db.Query("SELECT ...")
if err != nil {
    return fmt.Errorf("failed to fetch user data: %w", ErrDBQueryFailed)
}

type AppError struct {
    Code    int
    Message string
    Err     error
}

func (e *AppError) Error() string {
    return e.Message
}

// 预定义错误
var (
    ErrUserNotFound = &AppError{Code: 1001, Message: "用户不存在"}
    ErrInvalidArgs  = &AppError{Code: 1002, Message: "参数无效"}
)

{"code": 1001, "message": "用户不存在"}