golang 如何验证struct字段的数据格式 #125

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zhangyachen opened this Issue 8 days ago · 0 comments

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zhangyachen commented 8 days ago edited

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的长度在某一个范围内。
  • 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。如果对这个比较陌生的话,看看下面这个:

type User struct {
    Id        int       `json:"id"`
    Name      string    `json:"name"`
    Bio       string    `json:"about,omitempty"`
    Active    bool      `json:"active"`
    Admin     bool      `json:"-"`
    CreatedAt time.Time `json:"created_at"`
}

写过golang的基本都用过json:xxx这个用法,json:xxx其实也是一个structTag,只不过这是golang帮你实现好特定用法的structTag。而validate:"number,min=1,max=1000"是我们自定义的structTag。

实现思路

image

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StringValidatorNumberValidatorEmailValidator来实现接口Validator
这里为什么要使用接口?假设我们不使用接口代码会怎么写?

if tagIsOfNumber(){
        validator := NumberValidator{}
}else if tagIsOfString() {
        validator := StringValidator{}
}else if tagIsOfEmail() {
        validator := EmailValidator{}
}else if tagIsOfDefault() {
        validator := DefaultValidator{}
}

这样的话判断逻辑不能写在一个函数中,因为返回值validator会因为structTag的不同而不同,而且validator也不能当做函数参数做传递。而我们定义一个接口,所有的validator都去实现这个接口,上述的问题就能解决,而且逻辑更加清晰和紧凑。 关于接口的使用可以看下标准库的io Writer,Writer是个interface,只有一个方法Writer:

type Writer interface {
	Write(p []byte) (n int, err error)
}

而输出函数可以直接调用参数的Write方法即可,无需关心到底是写到文件还是写到标准输出:

func Fprintf(w io.Writer, format string, a ...interface{}) (n int, err error) {
	p := newPrinter()
	p.doPrintf(format, a)
	n, err = w.Write(p.buf)      //调用Write方法
	p.free()
	return
}

//调用
Fprintf(os.Stdout, format, a...)    //标准输出
Fprintf(os.Stderr, msg+"\n", args...)   //标准错误输出

var buf bytes.Buffer
Fprintf(&buf, "[")    //写入到Buffer的缓存中

言归正传,我们看下完整代码,代码是Custom struct field tags in Golang中给出的:

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())
    }
}

代码很好理解,结构也很清晰,不做过多解释了^_^

github上其实已经有现成的验证包了govalidator,支持内置支持的验证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)
    }
}

参考资料:

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