GitHub - pengux/check: Package for data validation in Go

Design goals

Composite pattern
Multiple constraints on the same value by applying multiple validators
Easy to create custom validators
Easy to customize error messages

Usage

go get github.com/pengux/check

To run tests:

cd $GOPATH/src/github.com/pengux/check && go test

To validate your data, create a new Struct and add validators to it:

type User struct {
	Username string
}

func main() {
	u := &User{
		Username: "invalid*",
	}

	s := check.Struct{
		"Username": check.Composite{
			check.NonEmpty{},
			check.Regex{`^[a-zA-Z0-9]+$`},
			check.MinChar{10},
		},
	}

	e := s.Validate(u)

	if e.HasErrors() {
		err, ok := e.GetErrorsByKey("Username")
		if !ok {
			panic("key 'Username' does not exists")
		}
		fmt.Println(err)
	}
}

To use your own custom validator, just implement the Validator interface:

type CustomStringContainValidator struct {
	Constraint string
}

func (validator CustomStringContainValidator) Validate(v interface{}) check.Error {
	if !strings.Contains(v.(string), validator.Constraint) {
		return check.NewValidationError("customStringContainValidator", v, validator.Constraint)
	}

	return nil
}

func main() {
	username := "invalid*"
	validator := CustomStringContainValidator{"admin"}
	e := validator.Validate(username)
	fmt.Println(check.ErrorMessages[e.Error()])
}

To use custom error messages, either overwrite the package variable ErrorMessages or create your own map[string]string:

check.ErrorMessages["minChar"] := "the string must be minimum %v characters long"
errMessages := errs.ToMessages()
fmt.Println(errMessages)

For more example code check the file e2e_test.go.