validator/baked_in.go

package validator

import (
	"bytes"
	"context"
	"crypto/sha256"
	"fmt"
	"net"
	"net/url"
	"os"
	"reflect"
	"strconv"
	"strings"
	"sync"
	"time"
	"unicode/utf8"

	urn "github.com/leodido/go-urn"
)

// Func accepts a FieldLevel interface for all validation needs. The return
// value should be true when validation succeeds.
type Func func(fl FieldLevel) bool

// FuncCtx accepts a context.Context and FieldLevel interface for all
// validation needs. The return value should be true when validation succeeds.
type FuncCtx func(ctx context.Context, fl FieldLevel) bool

// wrapFunc wraps noramal Func makes it compatible with FuncCtx
func wrapFunc(fn Func) FuncCtx {
	if fn == nil {
		return nil // be sure not to wrap a bad function.
	}
	return func(ctx context.Context, fl FieldLevel) bool {
		return fn(fl)
	}
}

var (
	restrictedTags = map[string]struct{}{
		diveTag:           {},
		keysTag:           {},
		endKeysTag:        {},
		structOnlyTag:     {},
		omitempty:         {},
		skipValidationTag: {},
		utf8HexComma:      {},
		utf8Pipe:          {},
		noStructLevelTag:  {},
		requiredTag:       {},
		isdefault:         {},
	}

	// BakedInAliasValidators is a default mapping of a single validation tag that
	// defines a common or complex set of validation(s) to simplify
	// adding validation to structs.
	bakedInAliases = map[string]string{
		"iscolor": "hexcolor|rgb|rgba|hsl|hsla",
	}

	// BakedInValidators is the default map of ValidationFunc
	// you can add, remove or even replace items to suite your needs,
	// or even disregard and use your own map if so desired.
	bakedInValidators = map[string]Func{
		"required":         hasValue,
		"isdefault":        isDefault,
		"len":              hasLengthOf,
		"min":              hasMinOf,
		"max":              hasMaxOf,
		"eq":               isEq,
		"ne":               isNe,
		"lt":               isLt,
		"lte":              isLte,
		"gt":               isGt,
		"gte":              isGte,
		"eqfield":          isEqField,
		"eqcsfield":        isEqCrossStructField,
		"necsfield":        isNeCrossStructField,
		"gtcsfield":        isGtCrossStructField,
		"gtecsfield":       isGteCrossStructField,
		"ltcsfield":        isLtCrossStructField,
		"ltecsfield":       isLteCrossStructField,
		"nefield":          isNeField,
		"gtefield":         isGteField,
		"gtfield":          isGtField,
		"ltefield":         isLteField,
		"ltfield":          isLtField,
		"fieldcontains":    fieldContains,
		"fieldexcludes":    fieldExcludes,
		"alpha":            isAlpha,
		"alphanum":         isAlphanum,
		"alphaunicode":     isAlphaUnicode,
		"alphanumunicode":  isAlphanumUnicode,
		"numeric":          isNumeric,
		"number":           isNumber,
		"hexadecimal":      isHexadecimal,
		"hexcolor":         isHEXColor,
		"rgb":              isRGB,
		"rgba":             isRGBA,
		"hsl":              isHSL,
		"hsla":             isHSLA,
		"email":            isEmail,
		"url":              isURL,
		"uri":              isURI,
		"urn_rfc2141":      isUrnRFC2141, // RFC 2141
		"file":             isFile,
		"base64":           isBase64,
		"base64url":        isBase64URL,
		"contains":         contains,
		"containsany":      containsAny,
		"containsrune":     containsRune,
		"excludes":         excludes,
		"excludesall":      excludesAll,
		"excludesrune":     excludesRune,
		"isbn":             isISBN,
		"isbn10":           isISBN10,
		"isbn13":           isISBN13,
		"eth_addr":         isEthereumAddress,
		"btc_addr":         isBitcoinAddress,
		"btc_addr_bech32":  isBitcoinBech32Address,
		"uuid":             isUUID,
		"uuid3":            isUUID3,
		"uuid4":            isUUID4,
		"uuid5":            isUUID5,
		"uuid_rfc4122":     isUUIDRFC4122,
		"uuid3_rfc4122":    isUUID3RFC4122,
		"uuid4_rfc4122":    isUUID4RFC4122,
		"uuid5_rfc4122":    isUUID5RFC4122,
		"ascii":            isASCII,
		"printascii":       isPrintableASCII,
		"multibyte":        hasMultiByteCharacter,
		"datauri":          isDataURI,
		"latitude":         isLatitude,
		"longitude":        isLongitude,
		"ssn":              isSSN,
		"ipv4":             isIPv4,
		"ipv6":             isIPv6,
		"ip":               isIP,
		"cidrv4":           isCIDRv4,
		"cidrv6":           isCIDRv6,
		"cidr":             isCIDR,
		"tcp4_addr":        isTCP4AddrResolvable,
		"tcp6_addr":        isTCP6AddrResolvable,
		"tcp_addr":         isTCPAddrResolvable,
		"udp4_addr":        isUDP4AddrResolvable,
		"udp6_addr":        isUDP6AddrResolvable,
		"udp_addr":         isUDPAddrResolvable,
		"ip4_addr":         isIP4AddrResolvable,
		"ip6_addr":         isIP6AddrResolvable,
		"ip_addr":          isIPAddrResolvable,
		"unix_addr":        isUnixAddrResolvable,
		"mac":              isMAC,
		"hostname":         isHostnameRFC952,  // RFC 952
		"hostname_rfc1123": isHostnameRFC1123, // RFC 1123
		"fqdn":             isFQDN,
		"unique":           isUnique,
		"oneof":            isOneOf,
		"html":             isHTML,
		"html_encoded":     isHTMLEncoded,
		"url_encoded":      isURLEncoded,
	}
)

var oneofValsCache = map[string][]string{}
var oneofValsCacheRWLock = sync.RWMutex{}

func parseOneOfParam2(s string) []string {
	oneofValsCacheRWLock.RLock()
	vals, ok := oneofValsCache[s]
	oneofValsCacheRWLock.RUnlock()
	if !ok {
		oneofValsCacheRWLock.Lock()
		vals = strings.Fields(s)
		oneofValsCache[s] = vals
		oneofValsCacheRWLock.Unlock()
	}
	return vals
}

func isURLEncoded(fl FieldLevel) bool {
	return uRLEncodedRegex.MatchString(fl.Field().String())
}

func isHTMLEncoded(fl FieldLevel) bool {
	return hTMLEncodedRegex.MatchString(fl.Field().String())
}

func isHTML(fl FieldLevel) bool {
	return hTMLRegex.MatchString(fl.Field().String())
}

func isOneOf(fl FieldLevel) bool {
	vals := parseOneOfParam2(fl.Param())

	field := fl.Field()

	var v string
	switch field.Kind() {
	case reflect.String:
		v = field.String()
	case reflect.Int, reflect.Int8, reflect.Int16, reflect.Int32, reflect.Int64:
		v = strconv.FormatInt(field.Int(), 10)
	case reflect.Uint, reflect.Uint8, reflect.Uint16, reflect.Uint32, reflect.Uint64:
		v = strconv.FormatUint(field.Uint(), 10)
	default:
		panic(fmt.Sprintf("Bad field type %T", field.Interface()))
	}
	for i := 0; i < len(vals); i++ {
		if vals[i] == v {
			return true
		}
	}
	return false
}

// isUnique is the validation function for validating if each array|slice|map value is unique
func isUnique(fl FieldLevel) bool {

	field := fl.Field()
	v := reflect.ValueOf(struct{}{})

	switch field.Kind() {
	case reflect.Slice, reflect.Array:
		m := reflect.MakeMap(reflect.MapOf(field.Type().Elem(), v.Type()))

		for i := 0; i < field.Len(); i++ {
			m.SetMapIndex(field.Index(i), v)
		}
		return field.Len() == m.Len()
	case reflect.Map:
		m := reflect.MakeMap(reflect.MapOf(field.Type().Elem(), v.Type()))

		for _, k := range field.MapKeys() {
			m.SetMapIndex(field.MapIndex(k), v)
		}
		return field.Len() == m.Len()
	default:
		panic(fmt.Sprintf("Bad field type %T", field.Interface()))
	}
}

// IsMAC is the validation function for validating if the field's value is a valid MAC address.
func isMAC(fl FieldLevel) bool {

	_, err := net.ParseMAC(fl.Field().String())

	return err == nil
}

// IsCIDRv4 is the validation function for validating if the field's value is a valid v4 CIDR address.
func isCIDRv4(fl FieldLevel) bool {

	ip, _, err := net.ParseCIDR(fl.Field().String())

	return err == nil && ip.To4() != nil
}

// IsCIDRv6 is the validation function for validating if the field's value is a valid v6 CIDR address.
func isCIDRv6(fl FieldLevel) bool {

	ip, _, err := net.ParseCIDR(fl.Field().String())

	return err == nil && ip.To4() == nil
}

// IsCIDR is the validation function for validating if the field's value is a valid v4 or v6 CIDR address.
func isCIDR(fl FieldLevel) bool {

	_, _, err := net.ParseCIDR(fl.Field().String())

	return err == nil
}

// IsIPv4 is the validation function for validating if a value is a valid v4 IP address.
func isIPv4(fl FieldLevel) bool {

	ip := net.ParseIP(fl.Field().String())

	return ip != nil && ip.To4() != nil
}

// IsIPv6 is the validation function for validating if the field's value is a valid v6 IP address.
func isIPv6(fl FieldLevel) bool {

	ip := net.ParseIP(fl.Field().String())

	return ip != nil && ip.To4() == nil
}

// IsIP is the validation function for validating if the field's value is a valid v4 or v6 IP address.
func isIP(fl FieldLevel) bool {

	ip := net.ParseIP(fl.Field().String())

	return ip != nil
}

// IsSSN is the validation function for validating if the field's value is a valid SSN.
func isSSN(fl FieldLevel) bool {

	field := fl.Field()

	if field.Len() != 11 {
		return false
	}

	return sSNRegex.MatchString(field.String())
}

// IsLongitude is the validation function for validating if the field's value is a valid longitude coordinate.
func isLongitude(fl FieldLevel) bool {
	return longitudeRegex.MatchString(fl.Field().String())
}

// IsLatitude is the validation function for validating if the field's value is a valid latitude coordinate.
func isLatitude(fl FieldLevel) bool {
	return latitudeRegex.MatchString(fl.Field().String())
}

// IsDataURI is the validation function for validating if the field's value is a valid data URI.
func isDataURI(fl FieldLevel) bool {

	uri := strings.SplitN(fl.Field().String(), ",", 2)

	if len(uri) != 2 {
		return false
	}

	if !dataURIRegex.MatchString(uri[0]) {
		return false
	}

	return base64Regex.MatchString(uri[1])
}

// HasMultiByteCharacter is the validation function for validating if the field's value has a multi byte character.
func hasMultiByteCharacter(fl FieldLevel) bool {

	field := fl.Field()

	if field.Len() == 0 {
		return true
	}

	return multibyteRegex.MatchString(field.String())
}

// IsPrintableASCII is the validation function for validating if the field's value is a valid printable ASCII character.
func isPrintableASCII(fl FieldLevel) bool {
	return printableASCIIRegex.MatchString(fl.Field().String())
}

// IsASCII is the validation function for validating if the field's value is a valid ASCII character.
func isASCII(fl FieldLevel) bool {
	return aSCIIRegex.MatchString(fl.Field().String())
}

// IsUUID5 is the validation function for validating if the field's value is a valid v5 UUID.
func isUUID5(fl FieldLevel) bool {
	return uUID5Regex.MatchString(fl.Field().String())
}

// IsUUID4 is the validation function for validating if the field's value is a valid v4 UUID.
func isUUID4(fl FieldLevel) bool {
	return uUID4Regex.MatchString(fl.Field().String())
}

// IsUUID3 is the validation function for validating if the field's value is a valid v3 UUID.
func isUUID3(fl FieldLevel) bool {
	return uUID3Regex.MatchString(fl.Field().String())
}

// IsUUID is the validation function for validating if the field's value is a valid UUID of any version.
func isUUID(fl FieldLevel) bool {
	return uUIDRegex.MatchString(fl.Field().String())
}

// IsUUID5RFC4122 is the validation function for validating if the field's value is a valid RFC4122 v5 UUID.
func isUUID5RFC4122(fl FieldLevel) bool {
	return uUID5RFC4122Regex.MatchString(fl.Field().String())
}

// IsUUID4RFC4122 is the validation function for validating if the field's value is a valid RFC4122 v4 UUID.
func isUUID4RFC4122(fl FieldLevel) bool {
	return uUID4RFC4122Regex.MatchString(fl.Field().String())
}

// IsUUID3RFC4122 is the validation function for validating if the field's value is a valid RFC4122 v3 UUID.
func isUUID3RFC4122(fl FieldLevel) bool {
	return uUID3RFC4122Regex.MatchString(fl.Field().String())
}

// IsUUIDRFC4122 is the validation function for validating if the field's value is a valid RFC4122 UUID of any version.
func isUUIDRFC4122(fl FieldLevel) bool {
	return uUIDRFC4122Regex.MatchString(fl.Field().String())
}

// IsISBN is the validation function for validating if the field's value is a valid v10 or v13 ISBN.
func isISBN(fl FieldLevel) bool {
	return isISBN10(fl) || isISBN13(fl)
}

// IsISBN13 is the validation function for validating if the field's value is a valid v13 ISBN.
func isISBN13(fl FieldLevel) bool {

	s := strings.Replace(strings.Replace(fl.Field().String(), "-", "", 4), " ", "", 4)

	if !iSBN13Regex.MatchString(s) {
		return false
	}

	var checksum int32
	var i int32

	factor := []int32{1, 3}

	for i = 0; i < 12; i++ {
		checksum += factor[i%2] * int32(s[i]-'0')
	}

	return (int32(s[12]-'0'))-((10-(checksum%10))%10) == 0
}

// IsISBN10 is the validation function for validating if the field's value is a valid v10 ISBN.
func isISBN10(fl FieldLevel) bool {

	s := strings.Replace(strings.Replace(fl.Field().String(), "-", "", 3), " ", "", 3)

	if !iSBN10Regex.MatchString(s) {
		return false
	}

	var checksum int32
	var i int32

	for i = 0; i < 9; i++ {
		checksum += (i + 1) * int32(s[i]-'0')
	}

	if s[9] == 'X' {
		checksum += 10 * 10
	} else {
		checksum += 10 * int32(s[9]-'0')
	}

	return checksum%11 == 0
}

// IsEthereumAddress is the validation function for validating if the field's value is a valid ethereum address based currently only on the format
func isEthereumAddress(fl FieldLevel) bool {
	address := fl.Field().String()

	if !ethAddressRegex.MatchString(address) {
		return false
	}

	if ethaddressRegexUpper.MatchString(address) || ethAddressRegexLower.MatchString(address) {
		return true
	}

	// checksum validation is blocked by https://github.com/golang/crypto/pull/28

	return true
}

// IsBitcoinAddress is the validation function for validating if the field's value is a valid btc address
func isBitcoinAddress(fl FieldLevel) bool {
	address := fl.Field().String()

	if !btcAddressRegex.MatchString(address) {
		return false
	}

	alphabet := []byte("123456789ABCDEFGHJKLMNPQRSTUVWXYZabcdefghijkmnopqrstuvwxyz")

	decode := [25]byte{}

	for _, n := range []byte(address) {
		d := bytes.IndexByte(alphabet, n)

		for i := 24; i >= 0; i-- {
			d += 58 * int(decode[i])
			decode[i] = byte(d % 256)
			d /= 256
		}
	}

	h := sha256.New()
	_, _ = h.Write(decode[:21])
	d := h.Sum([]byte{})
	h = sha256.New()
	_, _ = h.Write(d)

	validchecksum := [4]byte{}
	computedchecksum := [4]byte{}

	copy(computedchecksum[:], h.Sum(d[:0]))
	copy(validchecksum[:], decode[21:])

	return validchecksum == computedchecksum
}

// IsBitcoinBech32Address is the validation function for validating if the field's value is a valid bech32 btc address
func isBitcoinBech32Address(fl FieldLevel) bool {
	address := fl.Field().String()

	if !btcLowerAddressRegexBech32.MatchString(address) && !btcUpperAddressRegexBech32.MatchString(address) {
		return false
	}

	am := len(address) % 8

	if am == 0 || am == 3 || am == 5 {
		return false
	}

	address = strings.ToLower(address)

	alphabet := "qpzry9x8gf2tvdw0s3jn54khce6mua7l"

	hr := []int{3, 3, 0, 2, 3} // the human readable part will always be bc
	addr := address[3:]
	dp := make([]int, 0, len(addr))

	for _, c := range addr {
		dp = append(dp, strings.IndexRune(alphabet, c))
	}

	ver := dp[0]

	if ver < 0 || ver > 16 {
		return false
	}

	if ver == 0 {
		if len(address) != 42 && len(address) != 62 {
			return false
		}
	}

	values := append(hr, dp...)

	GEN := []int{0x3b6a57b2, 0x26508e6d, 0x1ea119fa, 0x3d4233dd, 0x2a1462b3}

	p := 1

	for _, v := range values {
		b := p >> 25
		p = (p&0x1ffffff)<<5 ^ v

		for i := 0; i < 5; i++ {
			if (b>>uint(i))&1 == 1 {
				p ^= GEN[i]
			}
		}
	}

	if p != 1 {
		return false
	}

	b := uint(0)
	acc := 0
	mv := (1 << 5) - 1
	var sw []int

	for _, v := range dp[1 : len(dp)-6] {
		acc = (acc << 5) | v
		b += 5
		for b >= 8 {
			b -= 8
			sw = append(sw, (acc>>b)&mv)
		}
	}

	if len(sw) < 2 || len(sw) > 40 {
		return false
	}

	return true
}

// ExcludesRune is the validation function for validating that the field's value does not contain the rune specified within the param.
func excludesRune(fl FieldLevel) bool {
	return !containsRune(fl)
}

// ExcludesAll is the validation function for validating that the field's value does not contain any of the characters specified within the param.
func excludesAll(fl FieldLevel) bool {
	return !containsAny(fl)
}

// Excludes is the validation function for validating that the field's value does not contain the text specified within the param.
func excludes(fl FieldLevel) bool {
	return !contains(fl)
}

// ContainsRune is the validation function for validating that the field's value contains the rune specified within the param.
func containsRune(fl FieldLevel) bool {

	r, _ := utf8.DecodeRuneInString(fl.Param())

	return strings.ContainsRune(fl.Field().String(), r)
}

// ContainsAny is the validation function for validating that the field's value contains any of the characters specified within the param.
func containsAny(fl FieldLevel) bool {
	return strings.ContainsAny(fl.Field().String(), fl.Param())
}

// Contains is the validation function for validating that the field's value contains the text specified within the param.
func contains(fl FieldLevel) bool {
	return strings.Contains(fl.Field().String(), fl.Param())
}

// FieldContains is the validation function for validating if the current field's value contains the field specified by the param's value.
func fieldContains(fl FieldLevel) bool {
	field := fl.Field()

	currentField, _, ok := fl.GetStructFieldOK()

	if !ok {
		return false
	}

	return strings.Contains(field.String(), currentField.String())
}

// FieldExcludes is the validation function for validating if the current field's value excludes the field specified by the param's value.
func fieldExcludes(fl FieldLevel) bool {
	field := fl.Field()

	currentField, _, ok := fl.GetStructFieldOK()
	if !ok {
		return true
	}

	return !strings.Contains(field.String(), currentField.String())
}

// IsNeField is the validation function for validating if the current field's value is not equal to the field specified by the param's value.
func isNeField(fl FieldLevel) bool {

	field := fl.Field()
	kind := field.Kind()

	currentField, currentKind, ok := fl.GetStructFieldOK()

	if !ok || currentKind != kind {
		return true
	}

	switch kind {

	case reflect.Int, reflect.Int8, reflect.Int16, reflect.Int32, reflect.Int64:
		return field.Int() != currentField.Int()

	case reflect.Uint, reflect.Uint8, reflect.Uint16, reflect.Uint32, reflect.Uint64, reflect.Uintptr:
		return field.Uint() != currentField.Uint()

	case reflect.Float32, reflect.Float64:
		return field.Float() != currentField.Float()

	case reflect.Slice, reflect.Map, reflect.Array:
		return int64(field.Len()) != int64(currentField.Len())

	case reflect.Struct:

		fieldType := field.Type()

		// Not Same underlying type i.e. struct and time
		if fieldType != currentField.Type() {
			return true
		}

		if fieldType == timeType {

			t := currentField.Interface().(time.Time)
			fieldTime := field.Interface().(time.Time)

			return !fieldTime.Equal(t)
		}

	}

	// default reflect.String:
	return field.String() != currentField.String()
}

// IsNe is the validation function for validating that the field's value does not equal the provided param value.
func isNe(fl FieldLevel) bool {
	return !isEq(fl)
}

// IsLteCrossStructField is the validation function for validating if the current field's value is less than or equal to the field, within a separate struct, specified by the param's value.
func isLteCrossStructField(fl FieldLevel) bool {

	field := fl.Field()
	kind := field.Kind()

	topField, topKind, ok := fl.GetStructFieldOK()
	if !ok || topKind != kind {
		return false
	}

	switch kind {

	case reflect.Int, reflect.Int8, reflect.Int16, reflect.Int32, reflect.Int64:
		return field.Int() <= topField.Int()

	case reflect.Uint, reflect.Uint8, reflect.Uint16, reflect.Uint32, reflect.Uint64, reflect.Uintptr:
		return field.Uint() <= topField.Uint()

	case reflect.Float32, reflect.Float64:
		return field.Float() <= topField.Float()

	case reflect.Slice, reflect.Map, reflect.Array:
		return int64(field.Len()) <= int64(topField.Len())

	case reflect.Struct:

		fieldType := field.Type()

		// Not Same underlying type i.e. struct and time
		if fieldType != topField.Type() {
			return false
		}

		if fieldType == timeType {

			fieldTime := field.Interface().(time.Time)
			topTime := topField.Interface().(time.Time)

			return fieldTime.Before(topTime) || fieldTime.Equal(topTime)
		}
	}

	// default reflect.String:
	return field.String() <= topField.String()
}

// IsLtCrossStructField is the validation function for validating if the current field's value is less than the field, within a separate struct, specified by the param's value.
// NOTE: This is exposed for use within your own custom functions and not intended to be called directly.
func isLtCrossStructField(fl FieldLevel) bool {

	field := fl.Field()
	kind := field.Kind()

	topField, topKind, ok := fl.GetStructFieldOK()
	if !ok || topKind != kind {
		return false
	}

	switch kind {

	case reflect.Int, reflect.Int8, reflect.Int16, reflect.Int32, reflect.Int64:
		return field.Int() < topField.Int()

	case reflect.Uint, reflect.Uint8, reflect.Uint16, reflect.Uint32, reflect.Uint64, reflect.Uintptr:
		return field.Uint() < topField.Uint()

	case reflect.Float32, reflect.Float64:
		return field.Float() < topField.Float()

	case reflect.Slice, reflect.Map, reflect.Array:
		return int64(field.Len()) < int64(topField.Len())

	case reflect.Struct:

		fieldType := field.Type()

		// Not Same underlying type i.e. struct and time
		if fieldType != topField.Type() {
			return false
		}

		if fieldType == timeType {

			fieldTime := field.Interface().(time.Time)
			topTime := topField.Interface().(time.Time)

			return fieldTime.Before(topTime)
		}
	}

	// default reflect.String:
	return field.String() < topField.String()
}

// IsGteCrossStructField is the validation function for validating if the current field's value is greater than or equal to the field, within a separate struct, specified by the param's value.
func isGteCrossStructField(fl FieldLevel) bool {

	field := fl.Field()
	kind := field.Kind()

	topField, topKind, ok := fl.GetStructFieldOK()
	if !ok || topKind != kind {
		return false
	}

	switch kind {

	case reflect.Int, reflect.Int8, reflect.Int16, reflect.Int32, reflect.Int64:
		return field.Int() >= topField.Int()

	case reflect.Uint, reflect.Uint8, reflect.Uint16, reflect.Uint32, reflect.Uint64, reflect.Uintptr:
		return field.Uint() >= topField.Uint()

	case reflect.Float32, reflect.Float64:
		return field.Float() >= topField.Float()

	case reflect.Slice, reflect.Map, reflect.Array:
		return int64(field.Len()) >= int64(topField.Len())

	case reflect.Struct:

		fieldType := field.Type()

		// Not Same underlying type i.e. struct and time
		if fieldType != topField.Type() {
			return false
		}

		if fieldType == timeType {

			fieldTime := field.Interface().(time.Time)
			topTime := topField.Interface().(time.Time)

			return fieldTime.After(topTime) || fieldTime.Equal(topTime)
		}
	}

	// default reflect.String:
	return field.String() >= topField.String()
}

// IsGtCrossStructField is the validation function for validating if the current field's value is greater than the field, within a separate struct, specified by the param's value.
func isGtCrossStructField(fl FieldLevel) bool {

	field := fl.Field()
	kind := field.Kind()

	topField, topKind, ok := fl.GetStructFieldOK()
	if !ok || topKind != kind {
		return false
	}

	switch kind {

	case reflect.Int, reflect.Int8, reflect.Int16, reflect.Int32, reflect.Int64:
		return field.Int() > topField.Int()

	case reflect.Uint, reflect.Uint8, reflect.Uint16, reflect.Uint32, reflect.Uint64, reflect.Uintptr:
		return field.Uint() > topField.Uint()

	case reflect.Float32, reflect.Float64:
		return field.Float() > topField.Float()

	case reflect.Slice, reflect.Map, reflect.Array:
		return int64(field.Len()) > int64(topField.Len())

	case reflect.Struct:

		fieldType := field.Type()

		// Not Same underlying type i.e. struct and time
		if fieldType != topField.Type() {
			return false
		}

		if fieldType == timeType {

			fieldTime := field.Interface().(time.Time)
			topTime := topField.Interface().(time.Time)

			return fieldTime.After(topTime)
		}
	}

	// default reflect.String:
	return field.String() > topField.String()
}

// IsNeCrossStructField is the validation function for validating that the current field's value is not equal to the field, within a separate struct, specified by the param's value.
func isNeCrossStructField(fl FieldLevel) bool {

	field := fl.Field()
	kind := field.Kind()

	topField, currentKind, ok := fl.GetStructFieldOK()
	if !ok || currentKind != kind {
		return true
	}

	switch kind {

	case reflect.Int, reflect.Int8, reflect.Int16, reflect.Int32, reflect.Int64:
		return topField.Int() != field.Int()

	case reflect.Uint, reflect.Uint8, reflect.Uint16, reflect.Uint32, reflect.Uint64, reflect.Uintptr:
		return topField.Uint() != field.Uint()

	case reflect.Float32, reflect.Float64:
		return topField.Float() != field.Float()

	case reflect.Slice, reflect.Map, reflect.Array:
		return int64(topField.Len()) != int64(field.Len())

	case reflect.Struct:

		fieldType := field.Type()

		// Not Same underlying type i.e. struct and time
		if fieldType != topField.Type() {
			return true
		}

		if fieldType == timeType {

			t := field.Interface().(time.Time)
			fieldTime := topField.Interface().(time.Time)

			return !fieldTime.Equal(t)
		}
	}

	// default reflect.String:
	return topField.String() != field.String()
}

// IsEqCrossStructField is the validation function for validating that the current field's value is equal to the field, within a separate struct, specified by the param's value.
func isEqCrossStructField(fl FieldLevel) bool {

	field := fl.Field()
	kind := field.Kind()

	topField, topKind, ok := fl.GetStructFieldOK()
	if !ok || topKind != kind {
		return false
	}

	switch kind {

	case reflect.Int, reflect.Int8, reflect.Int16, reflect.Int32, reflect.Int64:
		return topField.Int() == field.Int()

	case reflect.Uint, reflect.Uint8, reflect.Uint16, reflect.Uint32, reflect.Uint64, reflect.Uintptr:
		return topField.Uint() == field.Uint()

	case reflect.Float32, reflect.Float64:
		return topField.Float() == field.Float()

	case reflect.Slice, reflect.Map, reflect.Array:
		return int64(topField.Len()) == int64(field.Len())

	case reflect.Struct:

		fieldType := field.Type()

		// Not Same underlying type i.e. struct and time
		if fieldType != topField.Type() {
			return false
		}

		if fieldType == timeType {

			t := field.Interface().(time.Time)
			fieldTime := topField.Interface().(time.Time)

			return fieldTime.Equal(t)
		}
	}

	// default reflect.String:
	return topField.String() == field.String()
}

// IsEqField is the validation function for validating if the current field's value is equal to the field specified by the param's value.
func isEqField(fl FieldLevel) bool {

	field := fl.Field()
	kind := field.Kind()

	currentField, currentKind, ok := fl.GetStructFieldOK()
	if !ok || currentKind != kind {
		return false
	}

	switch kind {

	case reflect.Int, reflect.Int8, reflect.Int16, reflect.Int32, reflect.Int64:
		return field.Int() == currentField.Int()

	case reflect.Uint, reflect.Uint8, reflect.Uint16, reflect.Uint32, reflect.Uint64, reflect.Uintptr:
		return field.Uint() == currentField.Uint()

	case reflect.Float32, reflect.Float64:
		return field.Float() == currentField.Float()

	case reflect.Slice, reflect.Map, reflect.Array:
		return int64(field.Len()) == int64(currentField.Len())

	case reflect.Struct:

		fieldType := field.Type()

		// Not Same underlying type i.e. struct and time
		if fieldType != currentField.Type() {
			return false
		}

		if fieldType == timeType {

			t := currentField.Interface().(time.Time)
			fieldTime := field.Interface().(time.Time)

			return fieldTime.Equal(t)
		}

	}

	// default reflect.String:
	return field.String() == currentField.String()
}

// IsEq is the validation function for validating if the current field's value is equal to the param's value.
func isEq(fl FieldLevel) bool {

	field := fl.Field()
	param := fl.Param()

	switch field.Kind() {

	case reflect.String:
		return field.String() == param

	case reflect.Slice, reflect.Map, reflect.Array:
		p := asInt(param)

		return int64(field.Len()) == p

	case reflect.Int, reflect.Int8, reflect.Int16, reflect.Int32, reflect.Int64:
		p := asInt(param)

		return field.Int() == p

	case reflect.Uint, reflect.Uint8, reflect.Uint16, reflect.Uint32, reflect.Uint64, reflect.Uintptr:
		p := asUint(param)

		return field.Uint() == p

	case reflect.Float32, reflect.Float64:
		p := asFloat(param)

		return field.Float() == p
	}

	panic(fmt.Sprintf("Bad field type %T", field.Interface()))
}

// IsBase64 is the validation function for validating if the current field's value is a valid base 64.
func isBase64(fl FieldLevel) bool {
	return base64Regex.MatchString(fl.Field().String())
}

// IsBase64URL is the validation function for validating if the current field's value is a valid base64 URL safe string.
func isBase64URL(fl FieldLevel) bool {
	return base64URLRegex.MatchString(fl.Field().String())
}

// IsURI is the validation function for validating if the current field's value is a valid URI.
func isURI(fl FieldLevel) bool {

	field := fl.Field()

	switch field.Kind() {

	case reflect.String:

		s := field.String()

		// checks needed as of Go 1.6 because of change https://github.com/golang/go/commit/617c93ce740c3c3cc28cdd1a0d712be183d0b328#diff-6c2d018290e298803c0c9419d8739885L195
		// emulate browser and strip the '#' suffix prior to validation. see issue-#237
		if i := strings.Index(s, "#"); i > -1 {
			s = s[:i]
		}

		if len(s) == 0 {
			return false
		}

		_, err := url.ParseRequestURI(s)

		return err == nil
	}

	panic(fmt.Sprintf("Bad field type %T", field.Interface()))
}

// IsURL is the validation function for validating if the current field's value is a valid URL.
func isURL(fl FieldLevel) bool {

	field := fl.Field()

	switch field.Kind() {

	case reflect.String:

		var i int
		s := field.String()

		// checks needed as of Go 1.6 because of change https://github.com/golang/go/commit/617c93ce740c3c3cc28cdd1a0d712be183d0b328#diff-6c2d018290e298803c0c9419d8739885L195
		// emulate browser and strip the '#' suffix prior to validation. see issue-#237
		if i = strings.Index(s, "#"); i > -1 {
			s = s[:i]
		}

		if len(s) == 0 {
			return false
		}

		url, err := url.ParseRequestURI(s)

		if err != nil || url.Scheme == "" {
			return false
		}

		return err == nil
	}

	panic(fmt.Sprintf("Bad field type %T", field.Interface()))
}

// isUrnRFC2141 is the validation function for validating if the current field's value is a valid URN as per RFC 2141.
func isUrnRFC2141(fl FieldLevel) bool {
	field := fl.Field()

	switch field.Kind() {

	case reflect.String:

		str := field.String()

		_, match := urn.Parse([]byte(str))

		return match
	}

	panic(fmt.Sprintf("Bad field type %T", field.Interface()))
}

// IsFile is the validation function for validating if the current field's value is a valid file path.
func isFile(fl FieldLevel) bool {
	field := fl.Field()

	switch field.Kind() {
	case reflect.String:
		fileInfo, err := os.Stat(field.String())
		if err != nil {
			return false
		}

		return !fileInfo.IsDir()
	}

	panic(fmt.Sprintf("Bad field type %T", field.Interface()))
}

// IsEmail is the validation function for validating if the current field's value is a valid email address.
func isEmail(fl FieldLevel) bool {
	return emailRegex.MatchString(fl.Field().String())
}

// IsHSLA is the validation function for validating if the current field's value is a valid HSLA color.
func isHSLA(fl FieldLevel) bool {
	return hslaRegex.MatchString(fl.Field().String())
}

// IsHSL is the validation function for validating if the current field's value is a valid HSL color.
func isHSL(fl FieldLevel) bool {
	return hslRegex.MatchString(fl.Field().String())
}

// IsRGBA is the validation function for validating if the current field's value is a valid RGBA color.
func isRGBA(fl FieldLevel) bool {
	return rgbaRegex.MatchString(fl.Field().String())
}

// IsRGB is the validation function for validating if the current field's value is a valid RGB color.
func isRGB(fl FieldLevel) bool {
	return rgbRegex.MatchString(fl.Field().String())
}

// IsHEXColor is the validation function for validating if the current field's value is a valid HEX color.
func isHEXColor(fl FieldLevel) bool {
	return hexcolorRegex.MatchString(fl.Field().String())
}

// IsHexadecimal is the validation function for validating if the current field's value is a valid hexadecimal.
func isHexadecimal(fl FieldLevel) bool {
	return hexadecimalRegex.MatchString(fl.Field().String())
}

// IsNumber is the validation function for validating if the current field's value is a valid number.
func isNumber(fl FieldLevel) bool {
	switch fl.Field().Kind() {
	case reflect.Int, reflect.Int8, reflect.Int16, reflect.Int32, reflect.Int64, reflect.Uint, reflect.Uint8, reflect.Uint16, reflect.Uint32, reflect.Uint64, reflect.Uintptr, reflect.Float32, reflect.Float64:
		return true
	default:
		return numberRegex.MatchString(fl.Field().String())
	}
}

// IsNumeric is the validation function for validating if the current field's value is a valid numeric value.
func isNumeric(fl FieldLevel) bool {
	switch fl.Field().Kind() {
	case reflect.Int, reflect.Int8, reflect.Int16, reflect.Int32, reflect.Int64, reflect.Uint, reflect.Uint8, reflect.Uint16, reflect.Uint32, reflect.Uint64, reflect.Uintptr, reflect.Float32, reflect.Float64:
		return true
	default:
		return numericRegex.MatchString(fl.Field().String())
	}
}

// IsAlphanum is the validation function for validating if the current field's value is a valid alphanumeric value.
func isAlphanum(fl FieldLevel) bool {
	return alphaNumericRegex.MatchString(fl.Field().String())
}

// IsAlpha is the validation function for validating if the current field's value is a valid alpha value.
func isAlpha(fl FieldLevel) bool {
	return alphaRegex.MatchString(fl.Field().String())
}

// IsAlphanumUnicode is the validation function for validating if the current field's value is a valid alphanumeric unicode value.
func isAlphanumUnicode(fl FieldLevel) bool {
	return alphaUnicodeNumericRegex.MatchString(fl.Field().String())
}

// IsAlphaUnicode is the validation function for validating if the current field's value is a valid alpha unicode value.
func isAlphaUnicode(fl FieldLevel) bool {
	return alphaUnicodeRegex.MatchString(fl.Field().String())
}

// isDefault is the opposite of required aka hasValue
func isDefault(fl FieldLevel) bool {
	return !hasValue(fl)
}

// HasValue is the validation function for validating if the current field's value is not the default static value.
func hasValue(fl FieldLevel) bool {

	field := fl.Field()

	switch field.Kind() {
	case reflect.Slice, reflect.Map, reflect.Ptr, reflect.Interface, reflect.Chan, reflect.Func:
		return !field.IsNil()
	default:

		if fl.(*validate).fldIsPointer && field.Interface() != nil {
			return true
		}

		return field.IsValid() && field.Interface() != reflect.Zero(field.Type()).Interface()
	}
}

// IsGteField is the validation function for validating if the current field's value is greater than or equal to the field specified by the param's value.
func isGteField(fl FieldLevel) bool {

	field := fl.Field()
	kind := field.Kind()

	currentField, currentKind, ok := fl.GetStructFieldOK()
	if !ok || currentKind != kind {
		return false
	}

	switch kind {

	case reflect.Int, reflect.Int8, reflect.Int16, reflect.Int32, reflect.Int64:

		return field.Int() >= currentField.Int()

	case reflect.Uint, reflect.Uint8, reflect.Uint16, reflect.Uint32, reflect.Uint64, reflect.Uintptr:

		return field.Uint() >= currentField.Uint()

	case reflect.Float32, reflect.Float64:

		return field.Float() >= currentField.Float()

	case reflect.Struct:

		fieldType := field.Type()

		// Not Same underlying type i.e. struct and time
		if fieldType != currentField.Type() {
			return false
		}

		if fieldType == timeType {

			t := currentField.Interface().(time.Time)
			fieldTime := field.Interface().(time.Time)

			return fieldTime.After(t) || fieldTime.Equal(t)
		}
	}

	// default reflect.String
	return len(field.String()) >= len(currentField.String())
}

// IsGtField is the validation function for validating if the current field's value is greater than the field specified by the param's value.
func isGtField(fl FieldLevel) bool {

	field := fl.Field()
	kind := field.Kind()

	currentField, currentKind, ok := fl.GetStructFieldOK()
	if !ok || currentKind != kind {
		return false
	}

	switch kind {

	case reflect.Int, reflect.Int8, reflect.Int16, reflect.Int32, reflect.Int64:

		return field.Int() > currentField.Int()

	case reflect.Uint, reflect.Uint8, reflect.Uint16, reflect.Uint32, reflect.Uint64, reflect.Uintptr:

		return field.Uint() > currentField.Uint()

	case reflect.Float32, reflect.Float64:

		return field.Float() > currentField.Float()

	case reflect.Struct:

		fieldType := field.Type()

		// Not Same underlying type i.e. struct and time
		if fieldType != currentField.Type() {
			return false
		}

		if fieldType == timeType {

			t := currentField.Interface().(time.Time)
			fieldTime := field.Interface().(time.Time)

			return fieldTime.After(t)
		}
	}

	// default reflect.String
	return len(field.String()) > len(currentField.String())
}

// IsGte is the validation function for validating if the current field's value is greater than or equal to the param's value.
func isGte(fl FieldLevel) bool {

	field := fl.Field()
	param := fl.Param()

	switch field.Kind() {

	case reflect.String:
		p := asInt(param)

		return int64(utf8.RuneCountInString(field.String())) >= p

	case reflect.Slice, reflect.Map, reflect.Array:
		p := asInt(param)

		return int64(field.Len()) >= p

	case reflect.Int, reflect.Int8, reflect.Int16, reflect.Int32, reflect.Int64:
		p := asInt(param)

		return field.Int() >= p

	case reflect.Uint, reflect.Uint8, reflect.Uint16, reflect.Uint32, reflect.Uint64, reflect.Uintptr:
		p := asUint(param)

		return field.Uint() >= p

	case reflect.Float32, reflect.Float64:
		p := asFloat(param)

		return field.Float() >= p

	case reflect.Struct:

		if field.Type() == timeType {

			now := time.Now().UTC()
			t := field.Interface().(time.Time)

			return t.After(now) || t.Equal(now)
		}
	}

	panic(fmt.Sprintf("Bad field type %T", field.Interface()))
}

// IsGt is the validation function for validating if the current field's value is greater than the param's value.
func isGt(fl FieldLevel) bool {

	field := fl.Field()
	param := fl.Param()

	switch field.Kind() {

	case reflect.String:
		p := asInt(param)

		return int64(utf8.RuneCountInString(field.String())) > p

	case reflect.Slice, reflect.Map, reflect.Array:
		p := asInt(param)

		return int64(field.Len()) > p

	case reflect.Int, reflect.Int8, reflect.Int16, reflect.Int32, reflect.Int64:
		p := asInt(param)

		return field.Int() > p

	case reflect.Uint, reflect.Uint8, reflect.Uint16, reflect.Uint32, reflect.Uint64, reflect.Uintptr:
		p := asUint(param)

		return field.Uint() > p

	case reflect.Float32, reflect.Float64:
		p := asFloat(param)

		return field.Float() > p
	case reflect.Struct:

		if field.Type() == timeType {

			return field.Interface().(time.Time).After(time.Now().UTC())
		}
	}

	panic(fmt.Sprintf("Bad field type %T", field.Interface()))
}

// HasLengthOf is the validation function for validating if the current field's value is equal to the param's value.
func hasLengthOf(fl FieldLevel) bool {

	field := fl.Field()
	param := fl.Param()

	switch field.Kind() {

	case reflect.String:
		p := asInt(param)

		return int64(utf8.RuneCountInString(field.String())) == p

	case reflect.Slice, reflect.Map, reflect.Array:
		p := asInt(param)

		return int64(field.Len()) == p

	case reflect.Int, reflect.Int8, reflect.Int16, reflect.Int32, reflect.Int64:
		p := asInt(param)

		return field.Int() == p

	case reflect.Uint, reflect.Uint8, reflect.Uint16, reflect.Uint32, reflect.Uint64, reflect.Uintptr:
		p := asUint(param)

		return field.Uint() == p

	case reflect.Float32, reflect.Float64:
		p := asFloat(param)

		return field.Float() == p
	}

	panic(fmt.Sprintf("Bad field type %T", field.Interface()))
}

// HasMinOf is the validation function for validating if the current field's value is greater than or equal to the param's value.
func hasMinOf(fl FieldLevel) bool {
	return isGte(fl)
}

// IsLteField is the validation function for validating if the current field's value is less than or equal to the field specified by the param's value.
func isLteField(fl FieldLevel) bool {

	field := fl.Field()
	kind := field.Kind()

	currentField, currentKind, ok := fl.GetStructFieldOK()
	if !ok || currentKind != kind {
		return false
	}

	switch kind {

	case reflect.Int, reflect.Int8, reflect.Int16, reflect.Int32, reflect.Int64:

		return field.Int() <= currentField.Int()

	case reflect.Uint, reflect.Uint8, reflect.Uint16, reflect.Uint32, reflect.Uint64, reflect.Uintptr:

		return field.Uint() <= currentField.Uint()

	case reflect.Float32, reflect.Float64:

		return field.Float() <= currentField.Float()

	case reflect.Struct:

		fieldType := field.Type()

		// Not Same underlying type i.e. struct and time
		if fieldType != currentField.Type() {
			return false
		}

		if fieldType == timeType {

			t := currentField.Interface().(time.Time)
			fieldTime := field.Interface().(time.Time)

			return fieldTime.Before(t) || fieldTime.Equal(t)
		}
	}

	// default reflect.String
	return len(field.String()) <= len(currentField.String())
}

// IsLtField is the validation function for validating if the current field's value is less than the field specified by the param's value.
func isLtField(fl FieldLevel) bool {

	field := fl.Field()
	kind := field.Kind()

	currentField, currentKind, ok := fl.GetStructFieldOK()
	if !ok || currentKind != kind {
		return false
	}

	switch kind {

	case reflect.Int, reflect.Int8, reflect.Int16, reflect.Int32, reflect.Int64:

		return field.Int() < currentField.Int()

	case reflect.Uint, reflect.Uint8, reflect.Uint16, reflect.Uint32, reflect.Uint64, reflect.Uintptr:

		return field.Uint() < currentField.Uint()

	case reflect.Float32, reflect.Float64:

		return field.Float() < currentField.Float()

	case reflect.Struct:

		fieldType := field.Type()

		// Not Same underlying type i.e. struct and time
		if fieldType != currentField.Type() {
			return false
		}

		if fieldType == timeType {

			t := currentField.Interface().(time.Time)
			fieldTime := field.Interface().(time.Time)

			return fieldTime.Before(t)
		}
	}

	// default reflect.String
	return len(field.String()) < len(currentField.String())
}

// IsLte is the validation function for validating if the current field's value is less than or equal to the param's value.
func isLte(fl FieldLevel) bool {

	field := fl.Field()
	param := fl.Param()

	switch field.Kind() {

	case reflect.String:
		p := asInt(param)

		return int64(utf8.RuneCountInString(field.String())) <= p

	case reflect.Slice, reflect.Map, reflect.Array:
		p := asInt(param)

		return int64(field.Len()) <= p

	case reflect.Int, reflect.Int8, reflect.Int16, reflect.Int32, reflect.Int64:
		p := asInt(param)

		return field.Int() <= p

	case reflect.Uint, reflect.Uint8, reflect.Uint16, reflect.Uint32, reflect.Uint64, reflect.Uintptr:
		p := asUint(param)

		return field.Uint() <= p

	case reflect.Float32, reflect.Float64:
		p := asFloat(param)

		return field.Float() <= p

	case reflect.Struct:

		if field.Type() == timeType {

			now := time.Now().UTC()
			t := field.Interface().(time.Time)

			return t.Before(now) || t.Equal(now)
		}
	}

	panic(fmt.Sprintf("Bad field type %T", field.Interface()))
}

// IsLt is the validation function for validating if the current field's value is less than the param's value.
func isLt(fl FieldLevel) bool {

	field := fl.Field()
	param := fl.Param()

	switch field.Kind() {

	case reflect.String:
		p := asInt(param)

		return int64(utf8.RuneCountInString(field.String())) < p

	case reflect.Slice, reflect.Map, reflect.Array:
		p := asInt(param)

		return int64(field.Len()) < p

	case reflect.Int, reflect.Int8, reflect.Int16, reflect.Int32, reflect.Int64:
		p := asInt(param)

		return field.Int() < p

	case reflect.Uint, reflect.Uint8, reflect.Uint16, reflect.Uint32, reflect.Uint64, reflect.Uintptr:
		p := asUint(param)

		return field.Uint() < p

	case reflect.Float32, reflect.Float64:
		p := asFloat(param)

		return field.Float() < p

	case reflect.Struct:

		if field.Type() == timeType {

			return field.Interface().(time.Time).Before(time.Now().UTC())
		}
	}

	panic(fmt.Sprintf("Bad field type %T", field.Interface()))
}

// HasMaxOf is the validation function for validating if the current field's value is less than or equal to the param's value.
func hasMaxOf(fl FieldLevel) bool {
	return isLte(fl)
}

// IsTCP4AddrResolvable is the validation function for validating if the field's value is a resolvable tcp4 address.
func isTCP4AddrResolvable(fl FieldLevel) bool {

	if !isIP4Addr(fl) {
		return false
	}

	_, err := net.ResolveTCPAddr("tcp4", fl.Field().String())
	return err == nil
}

// IsTCP6AddrResolvable is the validation function for validating if the field's value is a resolvable tcp6 address.
func isTCP6AddrResolvable(fl FieldLevel) bool {

	if !isIP6Addr(fl) {
		return false
	}

	_, err := net.ResolveTCPAddr("tcp6", fl.Field().String())

	return err == nil
}

// IsTCPAddrResolvable is the validation function for validating if the field's value is a resolvable tcp address.
func isTCPAddrResolvable(fl FieldLevel) bool {

	if !isIP4Addr(fl) && !isIP6Addr(fl) {
		return false
	}

	_, err := net.ResolveTCPAddr("tcp", fl.Field().String())

	return err == nil
}

// IsUDP4AddrResolvable is the validation function for validating if the field's value is a resolvable udp4 address.
func isUDP4AddrResolvable(fl FieldLevel) bool {

	if !isIP4Addr(fl) {
		return false
	}

	_, err := net.ResolveUDPAddr("udp4", fl.Field().String())

	return err == nil
}

// IsUDP6AddrResolvable is the validation function for validating if the field's value is a resolvable udp6 address.
func isUDP6AddrResolvable(fl FieldLevel) bool {

	if !isIP6Addr(fl) {
		return false
	}

	_, err := net.ResolveUDPAddr("udp6", fl.Field().String())

	return err == nil
}

// IsUDPAddrResolvable is the validation function for validating if the field's value is a resolvable udp address.
func isUDPAddrResolvable(fl FieldLevel) bool {

	if !isIP4Addr(fl) && !isIP6Addr(fl) {
		return false
	}

	_, err := net.ResolveUDPAddr("udp", fl.Field().String())

	return err == nil
}

// IsIP4AddrResolvable is the validation function for validating if the field's value is a resolvable ip4 address.
func isIP4AddrResolvable(fl FieldLevel) bool {

	if !isIPv4(fl) {
		return false
	}

	_, err := net.ResolveIPAddr("ip4", fl.Field().String())

	return err == nil
}

// IsIP6AddrResolvable is the validation function for validating if the field's value is a resolvable ip6 address.
func isIP6AddrResolvable(fl FieldLevel) bool {

	if !isIPv6(fl) {
		return false
	}

	_, err := net.ResolveIPAddr("ip6", fl.Field().String())

	return err == nil
}

// IsIPAddrResolvable is the validation function for validating if the field's value is a resolvable ip address.
func isIPAddrResolvable(fl FieldLevel) bool {

	if !isIP(fl) {
		return false
	}

	_, err := net.ResolveIPAddr("ip", fl.Field().String())

	return err == nil
}

// IsUnixAddrResolvable is the validation function for validating if the field's value is a resolvable unix address.
func isUnixAddrResolvable(fl FieldLevel) bool {

	_, err := net.ResolveUnixAddr("unix", fl.Field().String())

	return err == nil
}

func isIP4Addr(fl FieldLevel) bool {

	val := fl.Field().String()

	if idx := strings.LastIndex(val, ":"); idx != -1 {
		val = val[0:idx]
	}

	ip := net.ParseIP(val)

	return ip != nil && ip.To4() != nil
}

func isIP6Addr(fl FieldLevel) bool {

	val := fl.Field().String()

	if idx := strings.LastIndex(val, ":"); idx != -1 {
		if idx != 0 && val[idx-1:idx] == "]" {
			val = val[1 : idx-1]
		}
	}

	ip := net.ParseIP(val)

	return ip != nil && ip.To4() == nil
}

func isHostnameRFC952(fl FieldLevel) bool {
	return hostnameRegexRFC952.MatchString(fl.Field().String())
}

func isHostnameRFC1123(fl FieldLevel) bool {
	return hostnameRegexRFC1123.MatchString(fl.Field().String())
}

func isFQDN(fl FieldLevel) bool {
	val := fl.Field().String()

	if val == "" {
		return false
	}

	if val[len(val)-1] == '.' {
		val = val[0 : len(val)-1]
	}

	return strings.ContainsAny(val, ".") &&
		hostnameRegexRFC952.MatchString(val)
}