Golang如何实现简单的表单验证功能

func loginHandler(w http.ResponseWriter, r *http.Request) {
    if r.Method == "GET" {
        // 返回登录页面
        fmt.Fprintf(w, `
            <form method="post">
                用户名: <input type="text" name="username"><br>
                密码: <input type="password" name="password"><br>
                <button type="submit">登录</button>
            </form>
        `)
        return
    }

    if r.Method == "POST" {
        r.ParseForm()
        username := r.Form.Get("username")
        password := r.Form.Get("password")

        // 开始验证
        var errors []string
        if username == "" {
            errors = append(errors, "用户名不能为空")
        }
        if password == "" {
            errors = append(errors, "密码不能为空")
        }

        if len(errors) > 0 {
            // 返回错误信息
            w.WriteHeader(http.StatusBadRequest)
            for _, e := range errors {
                fmt.Fprintf(w, "<p style='color:red;'>%s</p>", e)
            }
            fmt.Fprintf(w, "<a href=''>返回</a>")
        } else {
            fmt.Fprintf(w, "登录成功，欢迎 %s！", username)
        }
    }
}

type Validator struct {
    Errors []string
}

func (v *Validator) Required(field, value string) {
    if value == "" {
        v.Errors = append(v.Errors, field+"不能为空")
    }
}

func (v *Validator) MinLength(field, value string, n int) {
    if len(value) < n {
        v.Errors = append(v.Errors, field+"至少需要%d个字符", n)
    }
}

v := &Validator{}
v.Required("用户名", username)
v.Required("密码", password)
v.MinLength("密码", password, 6)

if len(v.Errors) > 0 {
    for _, e := range v.Errors {
        fmt.Fprintf(w, "<p style='color:red;'>%s</p>", e)
    }
    return
}

import "regexp"

func isValidEmail(email string) bool {
    pattern := `^[a-zA-Z0-9._%+-]+@[a-zA-Z0-9.-]+\.[a-zA-Z]{2,}$`
    return regexp.MustCompile(pattern).MatchString(email)
}

if !isValidEmail(email) {
    errors = append(errors, "邮箱格式不正确")
}