Package validator

Package validator implements value validations for structs and individual fields based on tags.

It has the following unique features:

• Cross Field and Cross Struct validations by using validation tags or custom validators.
• Slice, Array and Map diving, which allows any or all levels of a multidimensional field to be validated.
• Handles type interface by determining it's underlying type prior to validation.
• Handles custom field types such as sql driver Valuer see Valuer
• Alias validation tags, which allows for mapping of several validations to a single tag for easier defining of validations on structs
• Extraction of custom defined Field Name e.g. can specify to extract the JSON name while validating and have it available in the resulting FieldError

Installation

Use go get.

go get gopkg.in/go-playground/validator.v8

or to update

go get -u gopkg.in/go-playground/validator.v8

Then import the validator package into your own code.

import "gopkg.in/go-playground/validator.v8"

Error Return Value

Validation functions return type error

They return type error to avoid the issue discussed in the following, where err is always != nil:

• http://stackoverflow.com/a/29138676/3158232
• https://github.com/go-playground/validator/issues/134

validator only returns nil or ValidationErrors as type error; so in you code all you need to do is check if the error returned is not nil, and if it's not type cast it to type ValidationErrors like so:

err := validate.Struct(mystruct)
validationErrors := err.(validator.ValidationErrors)

Usage and documentation

Please see http://godoc.org/gopkg.in/go-playground/validator.v8 for detailed usage docs.

Examples:

Struct & Field validation

package main

import (
	"fmt"

	"gopkg.in/go-playground/validator.v8"
)

// User contains user information
type User struct {
	FirstName      string     `validate:"required"`
	LastName       string     `validate:"required"`
	Age            uint8      `validate:"gte=0,lte=130"`
	Email          string     `validate:"required,email"`
	FavouriteColor string     `validate:"hexcolor|rgb|rgba"`
	Addresses      []*Address `validate:"required,dive,required"` // a person can have a home and cottage...
}

// Address houses a users address information
type Address struct {
	Street string `validate:"required"`
	City   string `validate:"required"`
	Planet string `validate:"required"`
	Phone  string `validate:"required"`
}

var validate *validator.Validate

func main() {

	config := &validator.Config{TagName: "validate"}

	validate = validator.New(config)

	validateStruct()
	validateField()
}

func validateStruct() {

	address := &Address{
		Street: "Eavesdown Docks",
		Planet: "Persphone",
		Phone:  "none",
	}

	user := &User{
		FirstName:      "Badger",
		LastName:       "Smith",
		Age:            135,
		Email:          "Badger.Smith@gmail.com",
		FavouriteColor: "#000",
		Addresses:      []*Address{address},
	}

	// returns nil or ValidationErrors ( map[string]*FieldError )
	errs := validate.Struct(user)

	if errs != nil {

		fmt.Println(errs) // output: Key: "User.Age" Error:Field validation for "Age" failed on the "lte" tag
		//	                         Key: "User.Addresses[0].City" Error:Field validation for "City" failed on the "required" tag
		err := errs.(validator.ValidationErrors)["User.Addresses[0].City"]
		fmt.Println(err.Field) // output: City
		fmt.Println(err.Tag)   // output: required
		fmt.Println(err.Kind)  // output: string
		fmt.Println(err.Type)  // output: string
		fmt.Println(err.Param) // output:
		fmt.Println(err.Value) // output:

		// from here you can create your own error messages in whatever language you wish
		return
	}

	// save user to database
}

func validateField() {
	myEmail := "joeybloggs.gmail.com"

	errs := validate.Field(myEmail, "required,email")

	if errs != nil {
		fmt.Println(errs) // output: Key: "" Error:Field validation for "" failed on the "email" tag
		return
	}

	// email ok, move on
}

Custom Field Type

package main

import (
	"database/sql"
	"database/sql/driver"
	"fmt"
	"reflect"

	"gopkg.in/go-playground/validator.v8"
)

// DbBackedUser User struct
type DbBackedUser struct {
	Name sql.NullString `validate:"required"`
	Age  sql.NullInt64  `validate:"required"`
}

func main() {

	config := &validator.Config{TagName: "validate"}

	validate := validator.New(config)

	// register all sql.Null* types to use the ValidateValuer CustomTypeFunc
	validate.RegisterCustomTypeFunc(ValidateValuer, sql.NullString{}, sql.NullInt64{}, sql.NullBool{}, sql.NullFloat64{})

	x := DbBackedUser{Name: sql.NullString{String: "", Valid: true}, Age: sql.NullInt64{Int64: 0, Valid: false}}
	errs := validate.Struct(x)

	if len(errs.(validator.ValidationErrors)) > 0 {
		fmt.Printf("Errs:\n%+v\n", errs)
	}
}

// ValidateValuer implements validator.CustomTypeFunc
func ValidateValuer(field reflect.Value) interface{} {
	if valuer, ok := field.Interface().(driver.Valuer); ok {
		val, err := valuer.Value()
		if err == nil {
			return val
		}
		// handle the error how you want
	}
	return nil
}

Struct Level Validation

package main

import (
	"fmt"
	"reflect"

	"gopkg.in/go-playground/validator.v8"
)

// User contains user information
type User struct {
	FirstName      string     `json:"fname"`
	LastName       string     `json:"lname"`
	Age            uint8      `validate:"gte=0,lte=130"`
	Email          string     `validate:"required,email"`
	FavouriteColor string     `validate:"hexcolor|rgb|rgba"`
	Addresses      []*Address `validate:"required,dive,required"` // a person can have a home and cottage...
}

// Address houses a users address information
type Address struct {
	Street string `validate:"required"`
	City   string `validate:"required"`
	Planet string `validate:"required"`
	Phone  string `validate:"required"`
}

var validate *validator.Validate

func main() {

	config := &validator.Config{TagName: "validate"}

	validate = validator.New(config)
	validate.RegisterStructValidation(UserStructLevelValidation, User{})

	validateStruct()
}

// UserStructLevelValidation contains custom struct level validations that don't always
// make sense at the field validation level. For Example this function validates that either
// FirstName or LastName exist; could have done that with a custom field validation but then
// would have had to add it to both fields duplicating the logic + overhead, this way it's
// only validated once.
//
// NOTE: you may ask why wouldn't I just do this outside of validator, because doing this way
// hooks right into validator and you can combine with validation tags and still have a
// common error output format.
func UserStructLevelValidation(v *validator.Validate, structLevel *validator.StructLevel) {

	user := structLevel.CurrentStruct.Interface().(User)

	if len(user.FirstName) == 0 && len(user.LastName) == 0 {
		structLevel.ReportError(reflect.ValueOf(user.FirstName), "FirstName", "fname", "fnameorlname")
		structLevel.ReportError(reflect.ValueOf(user.LastName), "LastName", "lname", "fnameorlname")
	}

	// plus can to more, even with different tag than "fnameorlname"
}

func validateStruct() {

	address := &Address{
		Street: "Eavesdown Docks",
		Planet: "Persphone",
		Phone:  "none",
		City:   "Unknown",
	}

	user := &User{
		FirstName:      "",
		LastName:       "",
		Age:            45,
		Email:          "Badger.Smith@gmail.com",
		FavouriteColor: "#000",
		Addresses:      []*Address{address},
	}

	// returns nil or ValidationErrors ( map[string]*FieldError )
	errs := validate.Struct(user)

	if errs != nil {

		fmt.Println(errs) // output: Key: 'User.LastName' Error:Field validation for 'LastName' failed on the 'fnameorlname' tag
		//	                         Key: 'User.FirstName' Error:Field validation for 'FirstName' failed on the 'fnameorlname' tag
		err := errs.(validator.ValidationErrors)["User.FirstName"]
		fmt.Println(err.Field) // output: FirstName
		fmt.Println(err.Tag)   // output: fnameorlname
		fmt.Println(err.Kind)  // output: string
		fmt.Println(err.Type)  // output: string
		fmt.Println(err.Param) // output:
		fmt.Println(err.Value) // output:

		// from here you can create your own error messages in whatever language you wish
		return
	}

	// save user to database
}

Benchmarks

Run on MacBook Pro (Retina, 15-inch, Late 2013) 2.6 GHz Intel Core i7 16 GB 1600 MHz DDR3 using Go version go1.5.2 darwin/amd64

go test -cpu=4 -bench=. -benchmem=true
PASS
BenchmarkFieldSuccess-4                            	10000000	       176 ns/op	       0 B/op	       0 allocs/op
BenchmarkFieldFailure-4                            	 2000000	       727 ns/op	     432 B/op	       4 allocs/op
BenchmarkFieldDiveSuccess-4                        	  500000	      3220 ns/op	     480 B/op	      27 allocs/op
BenchmarkFieldDiveFailure-4                        	  500000	      3823 ns/op	     912 B/op	      31 allocs/op
BenchmarkFieldCustomTypeSuccess-4                  	 5000000	       368 ns/op	      32 B/op	       2 allocs/op
BenchmarkFieldCustomTypeFailure-4                  	 2000000	       699 ns/op	     432 B/op	       4 allocs/op
BenchmarkFieldOrTagSuccess-4                       	 1000000	      1265 ns/op	      16 B/op	       1 allocs/op
BenchmarkFieldOrTagFailure-4                       	 1000000	      1182 ns/op	     464 B/op	       6 allocs/op
BenchmarkStructLevelValidationSuccess-4            	 2000000	       739 ns/op	     176 B/op	       6 allocs/op
BenchmarkStructLevelValidationFailure-4            	 1000000	      1368 ns/op	     640 B/op	      11 allocs/op
BenchmarkStructSimpleCustomTypeSuccess-4           	 2000000	       965 ns/op	      80 B/op	       5 allocs/op
BenchmarkStructSimpleCustomTypeFailure-4           	 1000000	      1561 ns/op	     688 B/op	      11 allocs/op
BenchmarkStructPartialSuccess-4                    	 1000000	      1285 ns/op	     384 B/op	      10 allocs/op
BenchmarkStructPartialFailure-4                    	 1000000	      1879 ns/op	     832 B/op	      15 allocs/op
BenchmarkStructExceptSuccess-4                     	 2000000	      1038 ns/op	     336 B/op	       7 allocs/op
BenchmarkStructExceptFailure-4                     	 1000000	      1330 ns/op	     384 B/op	      10 allocs/op
BenchmarkStructSimpleCrossFieldSuccess-4           	 1000000	      1081 ns/op	     128 B/op	       6 allocs/op
BenchmarkStructSimpleCrossFieldFailure-4           	 1000000	      1737 ns/op	     592 B/op	      11 allocs/op
BenchmarkStructSimpleCrossStructCrossFieldSuccess-4	 1000000	      1790 ns/op	     192 B/op	      10 allocs/op
BenchmarkStructSimpleCrossStructCrossFieldFailure-4	  500000	      2431 ns/op	     656 B/op	      15 allocs/op
BenchmarkStructSimpleSuccess-4                     	 2000000	       950 ns/op	      48 B/op	       3 allocs/op
BenchmarkStructSimpleFailure-4                     	 1000000	      1672 ns/op	     688 B/op	      11 allocs/op
BenchmarkStructSimpleSuccessParallel-4             	 5000000	       271 ns/op	      48 B/op	       3 allocs/op
BenchmarkStructSimpleFailureParallel-4             	 2000000	       670 ns/op	     688 B/op	      11 allocs/op
BenchmarkStructComplexSuccess-4                    	  300000	      5828 ns/op	     544 B/op	      32 allocs/op
BenchmarkStructComplexFailure-4                    	  200000	     11382 ns/op	    3912 B/op	      77 allocs/op
BenchmarkStructComplexSuccessParallel-4            	 1000000	      1739 ns/op	     544 B/op	      32 allocs/op
BenchmarkStructComplexFailureParallel-4            	  300000	      4682 ns/op	    3912 B/op	      77 allocs/op

How to Contribute

There will always be a development branch for each version i.e. v1-development. In order to contribute, please make your pull requests against those branches.

If the changes being proposed or requested are breaking changes, please create an issue, for discussion or create a pull request against the highest development branch for example this package has a v1 and v1-development branch however, there will also be a v2-development branch even though v2 doesn't exist yet.

I strongly encourage everyone whom creates a custom validation function to contribute them and help make this package even better.

License

Distributed under MIT License, please see license file in code for more details.