golang 验证struct字段的数据格式

假设我们有如下结构体：

type User struct {
    Id    int    
    Name  string 
    Bio   string 
    Email string 
}

我们需要对结构体内的字段进行验证合法性：

• Id的值在某一个范围内。

• Name的长度在莫一个范围内。

• Email格式正确。

我们可能会这么写：

user := User{
        Id:    0,
        Name:  "superlongstring",
        Bio:   "",
        Email: "foobar",
}
if user.Id < 1 && user.Id > 1000 {
    return false
}
if len(user.Name) < 2 && len(user.Name) > 10 {
    return false
}
if !validateEmail(user.Email) {
    return false
}

这样的话代码比较冗余，而且如果结构体新加字段，还需要再修改验证函数再加一段if判断。这样代码比较冗余。我们可以借助golang的structTag来解决上述的问题：

type User struct {
    Id    int    `validate:"number,min=1,max=1000"`
    Name  string `validate:"string,min=2,max=10"`
    Bio   string `validate:"string"`
    Email string `validate:"email"`
}

validate:”number,min=1,max=1000”就是structTag。

实现思路

我们定义一个接口Validator，定义一个方法Validate。再定义有具体意义的验证器例如StringValidator、NumberValidator、EmailValidator来实现接口Validator。

完整实例

package main
import (
    "fmt"
    "reflect"
    "regexp"
    "strings"
)
const tagName = "validate"
//邮箱验证正则
var mailRe = regexp.MustCompile(`\A[\w+\-.]+@[a-z\d\-]+(\.[a-z]+)*\.[a-z]+\z`)
//验证接口
type Validator interface {
    Validate(interface{}) (bool, error)
}
type DefaultValidator struct {
}
func (v DefaultValidator) Validate(val interface{}) (bool, error) {
    return true, nil
}
type StringValidator struct {
    Min int
    Max int
}
func (v StringValidator) Validate(val interface{}) (bool, error) {
    l := len(val.(string))
    if l == 0 {
        return false, fmt.Errorf("cannot be blank")
    }
    if l < v.Min {
        return false, fmt.Errorf("should be at least %v chars long", v.Min)
    }
    if v.Max >= v.Min && l > v.Max {
        return false, fmt.Errorf("should be less than %v chars long", v.Max)
    }
    return true, nil
}
type NumberValidator struct {
    Min int
    Max int
}
func (v NumberValidator) Validate(val interface{}) (bool, error) {
    num := val.(int)
    if num < v.Min {
        return false, fmt.Errorf("should be greater than %v", v.Min)
    }
    if v.Max >= v.Min && num > v.Max {
        return false, fmt.Errorf("should be less than %v", v.Max)
    }
    return true, nil
}
type EmailValidator struct {
}
func (v EmailValidator) Validate(val interface{}) (bool, error) {
    if !mailRe.MatchString(val.(string)) {
        return false, fmt.Errorf("is not a valid email address")
    }
    return true, nil
}
func getValidatorFromTag(tag string) Validator {
    args := strings.Split(tag, ",")
    switch args[0] {
    case "number":
        validator := NumberValidator{}
        //将structTag中的min和max解析到结构体中
        fmt.Sscanf(strings.Join(args[1:], ","), "min=%d,max=%d", &validator.Min, &validator.Max)
        return validator
    case "string":
        validator := StringValidator{}
        fmt.Sscanf(strings.Join(args[1:], ","), "min=%d,max=%d", &validator.Min, &validator.Max)
        return validator
    case "email":
        return EmailValidator{}
    }
    return DefaultValidator{}
}
func validateStruct(s interface{}) []error {
    errs := []error{}
    v := reflect.ValueOf(s)
    for i := 0; i < v.NumField(); i++ {
        //利用反射获取structTag
        tag := v.Type().Field(i).Tag.Get(tagName)
        if tag == "" || tag == "-" {
            continue
        }
        validator := getValidatorFromTag(tag)
        valid, err := validator.Validate(v.Field(i).Interface())
        if !valid && err != nil {
            errs = append(errs, fmt.Errorf("%s %s", v.Type().Field(i).Name, err.Error()))
        }
    }
    return errs
}
type User struct {
    Id    int    `validate:"number,min=1,max=1000"`
    Name  string `validate:"string,min=2,max=10"`
    Bio   string `validate:"string"`
    Email string `validate:"email"`
}
func main() {
    user := User{
        Id:    0,
        Name:  "superlongstring",
        Bio:   "",
        Email: "foobar",
    }
    fmt.Println("Errors:")
    for i, err := range validateStruct(user) {
        fmt.Printf("\t%d. %s\n", i+1, err.Error())
    }
}

其实github上已经有现成的验证包了govalidator，支持内置的验证tag和自定义验证tag：

package main
import (
    "github.com/asaskevich/govalidator"
    "fmt"
    "strings"
)
type Server struct {
    ID         string `valid:"uuid,required"`
    Name       string `valid:"machine_id"`
    HostIP     string `valid:"ip"`
    MacAddress string `valid:"mac,required"`
    WebAddress string `valid:"url"`
    AdminEmail string `valid:"email"`
}
func main() {
    server := &Server{
        ID:         "123e4567-e89b-12d3-a456-426655440000",
        Name:       "IX01",
        HostIP:     "127.0.0.1",
        MacAddress: "01:23:45:67:89:ab",
        WebAddress: "www.example.com",
        AdminEmail: "admin@exmaple.com",
    }
    //自定义tag验证函数
    govalidator.TagMap["machine_id"] = govalidator.Validator(func(str string) bool {
        return strings.HasPrefix(str, "IX")
    })
    if ok, err := govalidator.ValidateStruct(server); err != nil {
        panic(err)
    } else {
        fmt.Printf("OK: %v\n", ok)
    }
}