context_binding_validator.go

// Copyright 2017 Manu Martinez-Almeida. All rights reserved.
// see: https://github.com/gin-gonic/gin/blob/master/binding/default_validator.go
package chain

import (
	"fmt"
	"reflect"
	"strings"
	"sync"

	"github.com/go-playground/validator/v10"
)

// StructValidator is the minimal interface which needs to be implemented in
// order for it to be used as the validator engine for ensuring the correctness
// of the request. Gin provides a default implementation for this using
// https://github.com/go-playground/validator/tree/v10.6.1.
type StructValidator interface {
	// ValidateStruct can receive any kind of type and it should never panic, even if the configuration is not right.
	// If the received type is a slice|array, the validation should be performed travel on every element.
	// If the received type is not a struct or slice|array, any validation should be skipped and nil must be returned.
	// If the received type is a struct or pointer to a struct, the validation should be performed.
	// If the struct is not valid or the validation itself fails, a descriptive error should be returned.
	// Otherwise nil must be returned.
	ValidateStruct(any) error

	// Engine returns the underlying validator engine which powers the
	// StructValidator implementation.
	Engine() any
}

// Validator is the default validator which implements the StructValidator
// interface. It uses https://github.com/go-playground/validator/tree/v10.6.1
// under the hood.
var Validator StructValidator = &defaultValidator{}

func validate(obj any) error {
	if Validator == nil {
		return nil
	}
	return Validator.ValidateStruct(obj)
}

type defaultValidator struct {
	once     sync.Once
	validate *validator.Validate
}

type SliceValidationError []error

// Error concatenates all error elements in SliceValidationError into a single string separated by \n.
func (err SliceValidationError) Error() string {
	n := len(err)
	switch n {
	case 0:
		return ""
	default:
		var b strings.Builder
		if err[0] != nil {
			fmt.Fprintf(&b, "[%d]: %s", 0, err[0].Error())
		}
		if n > 1 {
			for i := 1; i < n; i++ {
				if err[i] != nil {
					b.WriteString("\n")
					fmt.Fprintf(&b, "[%d]: %s", i, err[i].Error())
				}
			}
		}
		return b.String()
	}
}

var _ StructValidator = (*defaultValidator)(nil)

// ValidateStruct receives any kind of type, but only performed struct or pointer to struct type.
func (v *defaultValidator) ValidateStruct(obj any) error {
	if obj == nil {
		return nil
	}

	value := reflect.ValueOf(obj)
	switch value.Kind() {
	case reflect.Ptr:
		if value.Elem().Kind() != reflect.Struct {
			return v.ValidateStruct(value.Elem().Interface())
		}
		return v.validateStruct(obj)
	case reflect.Struct:
		return v.validateStruct(obj)
	case reflect.Slice, reflect.Array:
		count := value.Len()
		validateRet := make(SliceValidationError, 0)
		for i := 0; i < count; i++ {
			if err := v.ValidateStruct(value.Index(i).Interface()); err != nil {
				validateRet = append(validateRet, err)
			}
		}
		if len(validateRet) == 0 {
			return nil
		}
		return validateRet
	default:
		return nil
	}
}

// validateStruct receives struct type
func (v *defaultValidator) validateStruct(obj any) error {
	v.lazyinit()
	return v.validate.Struct(obj)
}

// Engine returns the underlying validator engine which powers the default
// Validator instance. This is useful if you want to register custom validations
// or struct level validations. See validator GoDoc for more info -
// https://pkg.go.dev/github.com/go-playground/validator/v10
func (v *defaultValidator) Engine() any {
	v.lazyinit()
	return v.validate
}

func (v *defaultValidator) lazyinit() {
	v.once.Do(func() {
		v.validate = validator.New()
		v.validate.SetTagName("binding")
	})
}