如何在Golang中实现Web应用错误处理_统一返回错误信息

type ErrorResponse struct {
    Code    int    `json:"code"`    // 业务错误码，如 1001
    Message string `json:"message"` // 用户可见提示
    TraceID string `json:"trace_id,omitempty` // 用于日志追踪（可选）
}

func ErrorHandler(next http.Handler) http.Handler {
    return http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
        defer func() {
            if err := recover(); err != nil {
                http.Error(w, "Internal Server Error", http.StatusInternalServerError)
                log.Printf("PANIC: %v, trace: %s", err, debug.Stack())
            }
        }()

        // 包装 ResponseWriter，捕获 WriteHeader 调用（可选：用于日志或重写状态码）
        rw := &responseWriter{ResponseWriter: w, statusCode: http.StatusOK}
        next.ServeHTTP(rw, r)

        // 如果 handler 显式返回了 error（需配合自定义 context 或返回值约定），此处可扩展处理
        // 更推荐：handler 返回 (interface{}, error)，由中间件判断并渲染
    })
}

type Result struct {
    Data  interface{} `json:"data,omitempty"`
    Error *ErrorResponse `json:"error,omitempty"`
}

func UserHandler(w http.ResponseWriter, r *http.Request) (interface{}, error) {
    id := chi.URLParam(r, "id")
    if id == "" {
        return nil, &AppError{Code: 1001, Message: "用户 ID 不能为空"}
    }
    user, err := db.GetUser(id)
    if err != nil {
        return nil, &AppError{Code: 1002, Message: "用户不存在"}
    }
    return user, nil
}

// 中间件解析 result 并写入响应
func ResultHandler(handler func(http.ResponseWriter, *http.Request) (interface{}, error)) http.Handler {
    return http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
        data, err := handler(w, r)
        if err != nil {
            // 假设 AppError 实现了 error 接口，并携带 Code/Message
            appErr, ok := err.(*AppError)
            if !ok {
                appErr = &AppError{Code: 5000, Message: "未知错误"}
            }
            w.Header().Set("Content-Type", "application/json; charset=utf-8")
            w.WriteHeader(appErr.HTTPStatus()) // 如 400 → 400，500 → 500
            json.NewEncoder(w).Encode(Result{Error: &ErrorResponse{
                Code:    appErr.Code,
                Message: appErr.Message,
                TraceID: getTraceID(r),
            }})
            return
        }
        w.Header().Set("Content-Type", "application/json; charset=utf-8")
        w.WriteHeader(http.StatusOK)
        json.NewEncoder(w).Encode(Result{Data: data})
    })
}

type AppError struct {
    Code    int
    Message string
    status  int // 对应 HTTP 状态码
}

func (e *AppError) HTTPStatus() int {
    switch e.Code {
    case 1001, 1002:
        return http.StatusBadRequest
    case 1003:
        return http.StatusForbidden
    case 1004:
        return http.StatusNotFound
    default:
        return http.StatusInternalServerError
    }
}