baked_in.go

package validator

import (
	"bytes"
	"context"
	"crypto/sha256"
	"encoding/hex"
	"encoding/json"
	"fmt"
	"io/fs"
	"net"
	"net/url"
	"os"
	"reflect"
	"strconv"
	"strings"
	"sync"
	"syscall"
	"time"
	"unicode/utf8"

	"golang.org/x/crypto/sha3"
	"golang.org/x/text/language"

	"github.com/gabriel-vasile/mimetype"
	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 normal 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:         {},
		omitnil:           {},
		skipValidationTag: {},
		utf8HexComma:      {},
		utf8Pipe:          {},
		noStructLevelTag:  {},
		requiredTag:       {},
		isdefault:         {},
	}

	// bakedInAliases 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",
		"country_code":    "iso3166_1_alpha2|iso3166_1_alpha3|iso3166_1_alpha_numeric",
		"eu_country_code": "iso3166_1_alpha2_eu|iso3166_1_alpha3_eu|iso3166_1_alpha_numeric_eu",
	}

	// 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,
		"required_if":                   requiredIf,
		"required_unless":               requiredUnless,
		"skip_unless":                   skipUnless,
		"required_with":                 requiredWith,
		"required_with_all":             requiredWithAll,
		"required_without":              requiredWithout,
		"required_without_all":          requiredWithoutAll,
		"excluded_if":                   excludedIf,
		"excluded_unless":               excludedUnless,
		"excluded_with":                 excludedWith,
		"excluded_with_all":             excludedWithAll,
		"excluded_without":              excludedWithout,
		"excluded_without_all":          excludedWithoutAll,
		"isdefault":                     isDefault,
		"len":                           hasLengthOf,
		"min":                           hasMinOf,
		"max":                           hasMaxOf,
		"eq":                            isEq,
		"eq_ignore_case":                isEqIgnoreCase,
		"ne":                            isNe,
		"ne_ignore_case":                isNeIgnoreCase,
		"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,
		"boolean":                       isBoolean,
		"numeric":                       isNumeric,
		"number":                        isNumber,
		"hexadecimal":                   isHexadecimal,
		"hexcolor":                      isHEXColor,
		"rgb":                           isRGB,
		"rgba":                          isRGBA,
		"hsl":                           isHSL,
		"hsla":                          isHSLA,
		"e164":                          isE164,
		"email":                         isEmail,
		"url":                           isURL,
		"http_url":                      isHttpURL,
		"uri":                           isURI,
		"urn_rfc2141":                   isUrnRFC2141, // RFC 2141
		"file":                          isFile,
		"filepath":                      isFilePath,
		"base32":                        isBase32,
		"base64":                        isBase64,
		"base64url":                     isBase64URL,
		"base64rawurl":                  isBase64RawURL,
		"contains":                      contains,
		"containsany":                   containsAny,
		"containsrune":                  containsRune,
		"excludes":                      excludes,
		"excludesall":                   excludesAll,
		"excludesrune":                  excludesRune,
		"startswith":                    startsWith,
		"endswith":                      endsWith,
		"startsnotwith":                 startsNotWith,
		"endsnotwith":                   endsNotWith,
		"image":                         isImage,
		"isbn":                          isISBN,
		"isbn10":                        isISBN10,
		"isbn13":                        isISBN13,
		"issn":                          isISSN,
		"eth_addr":                      isEthereumAddress,
		"eth_addr_checksum":             isEthereumAddressChecksum,
		"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,
		"ulid":                          isULID,
		"md4":                           isMD4,
		"md5":                           isMD5,
		"sha256":                        isSHA256,
		"sha384":                        isSHA384,
		"sha512":                        isSHA512,
		"ripemd128":                     isRIPEMD128,
		"ripemd160":                     isRIPEMD160,
		"tiger128":                      isTIGER128,
		"tiger160":                      isTIGER160,
		"tiger192":                      isTIGER192,
		"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,
		"dir":                           isDir,
		"dirpath":                       isDirPath,
		"json":                          isJSON,
		"jwt":                           isJWT,
		"hostname_port":                 isHostnamePort,
		"lowercase":                     isLowercase,
		"uppercase":                     isUppercase,
		"datetime":                      isDatetime,
		"timezone":                      isTimeZone,
		"iso3166_1_alpha2":              isIso3166Alpha2,
		"iso3166_1_alpha2_eu":           isIso3166Alpha2EU,
		"iso3166_1_alpha3":              isIso3166Alpha3,
		"iso3166_1_alpha3_eu":           isIso3166Alpha3EU,
		"iso3166_1_alpha_numeric":       isIso3166AlphaNumeric,
		"iso3166_1_alpha_numeric_eu":    isIso3166AlphaNumericEU,
		"iso3166_2":                     isIso31662,
		"iso4217":                       isIso4217,
		"iso4217_numeric":               isIso4217Numeric,
		"bcp47_language_tag":            isBCP47LanguageTag,
		"postcode_iso3166_alpha2":       isPostcodeByIso3166Alpha2,
		"postcode_iso3166_alpha2_field": isPostcodeByIso3166Alpha2Field,
		"bic":                           isIsoBicFormat,
		"semver":                        isSemverFormat,
		"dns_rfc1035_label":             isDnsRFC1035LabelFormat,
		"credit_card":                   isCreditCard,
		"cve":                           isCveFormat,
		"luhn_checksum":                 hasLuhnChecksum,
		"mongodb":                       isMongoDBObjectId,
		"mongodb_connection_string":     isMongoDBConnectionString,
		"cron":                          isCron,
		"spicedb":                       isSpiceDB,
	}
)

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

func parseOneOfParam2(s string) []string {
	oneofValsCacheRWLock.RLock()
	vals, ok := oneofValsCache[s]
	oneofValsCacheRWLock.RUnlock()
	if !ok {
		oneofValsCacheRWLock.Lock()
		vals = splitParamsRegex().FindAllString(s, -1)
		for i := 0; i < len(vals); i++ {
			vals[i] = strings.Replace(vals[i], "'", "", -1)
		}
		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()
	param := fl.Param()
	v := reflect.ValueOf(struct{}{})

	switch field.Kind() {
	case reflect.Slice, reflect.Array:
		elem := field.Type().Elem()
		if elem.Kind() == reflect.Ptr {
			elem = elem.Elem()
		}

		if param == "" {
			m := reflect.MakeMap(reflect.MapOf(elem, v.Type()))

			for i := 0; i < field.Len(); i++ {
				m.SetMapIndex(reflect.Indirect(field.Index(i)), v)
			}
			return field.Len() == m.Len()
		}

		sf, ok := elem.FieldByName(param)
		if !ok {
			panic(fmt.Sprintf("Bad field name %s", param))
		}

		sfTyp := sf.Type
		if sfTyp.Kind() == reflect.Ptr {
			sfTyp = sfTyp.Elem()
		}

		m := reflect.MakeMap(reflect.MapOf(sfTyp, v.Type()))
		var fieldlen int
		for i := 0; i < field.Len(); i++ {
			key := reflect.Indirect(reflect.Indirect(field.Index(i)).FieldByName(param))
			if key.IsValid() {
				fieldlen++
				m.SetMapIndex(key, v)
			}
		}
		return fieldlen == m.Len()
	case reflect.Map:
		var m reflect.Value
		if field.Type().Elem().Kind() == reflect.Ptr {
			m = reflect.MakeMap(reflect.MapOf(field.Type().Elem().Elem(), v.Type()))
		} else {
			m = reflect.MakeMap(reflect.MapOf(field.Type().Elem(), v.Type()))
		}

		for _, k := range field.MapKeys() {
			m.SetMapIndex(reflect.Indirect(field.MapIndex(k)), v)
		}

		return field.Len() == m.Len()
	default:
		if parent := fl.Parent(); parent.Kind() == reflect.Struct {
			uniqueField := parent.FieldByName(param)
			if uniqueField == reflect.ValueOf(nil) {
				panic(fmt.Sprintf("Bad field name provided %s", param))
			}

			if uniqueField.Kind() != field.Kind() {
				panic(fmt.Sprintf("Bad field type %T:%T", field.Interface(), uniqueField.Interface()))
			}

			return field.Interface() != uniqueField.Interface()
		}

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

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

// 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 {
	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)
	case reflect.Float32:
		v = strconv.FormatFloat(field.Float(), 'f', -1, 32)
	case reflect.Float64:
		v = strconv.FormatFloat(field.Float(), 'f', -1, 64)
	default:
		panic(fmt.Sprintf("Bad field type %T", field.Interface()))
	}

	return longitudeRegex().MatchString(v)
}

// isLatitude is the validation function for validating if the field's value is a valid latitude coordinate.
func isLatitude(fl FieldLevel) bool {
	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)
	case reflect.Float32:
		v = strconv.FormatFloat(field.Float(), 'f', -1, 32)
	case reflect.Float64:
		v = strconv.FormatFloat(field.Float(), 'f', -1, 64)
	default:
		panic(fmt.Sprintf("Bad field type %T", field.Interface()))
	}

	return latitudeRegex().MatchString(v)
}

// 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 fieldMatchesRegexByStringerValOrString(uUID5Regex, fl)
}

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

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

// 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 fieldMatchesRegexByStringerValOrString(uUIDRegex, fl)
}

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

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

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

// 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 fieldMatchesRegexByStringerValOrString(uUIDRFC4122Regex, fl)
}

// isULID is the validation function for validating if the field's value is a valid ULID.
func isULID(fl FieldLevel) bool {
	return fieldMatchesRegexByStringerValOrString(uLIDRegex, fl)
}

// isMD4 is the validation function for validating if the field's value is a valid MD4.
func isMD4(fl FieldLevel) bool {
	return md4Regex().MatchString(fl.Field().String())
}

// isMD5 is the validation function for validating if the field's value is a valid MD5.
func isMD5(fl FieldLevel) bool {
	return md5Regex().MatchString(fl.Field().String())
}

// isSHA256 is the validation function for validating if the field's value is a valid SHA256.
func isSHA256(fl FieldLevel) bool {
	return sha256Regex().MatchString(fl.Field().String())
}

// isSHA384 is the validation function for validating if the field's value is a valid SHA384.
func isSHA384(fl FieldLevel) bool {
	return sha384Regex().MatchString(fl.Field().String())
}

// isSHA512 is the validation function for validating if the field's value is a valid SHA512.
func isSHA512(fl FieldLevel) bool {
	return sha512Regex().MatchString(fl.Field().String())
}

// isRIPEMD128 is the validation function for validating if the field's value is a valid PIPEMD128.
func isRIPEMD128(fl FieldLevel) bool {
	return ripemd128Regex().MatchString(fl.Field().String())
}

// isRIPEMD160 is the validation function for validating if the field's value is a valid PIPEMD160.
func isRIPEMD160(fl FieldLevel) bool {
	return ripemd160Regex().MatchString(fl.Field().String())
}

// isTIGER128 is the validation function for validating if the field's value is a valid TIGER128.
func isTIGER128(fl FieldLevel) bool {
	return tiger128Regex().MatchString(fl.Field().String())
}

// isTIGER160 is the validation function for validating if the field's value is a valid TIGER160.
func isTIGER160(fl FieldLevel) bool {
	return tiger160Regex().MatchString(fl.Field().String())
}

// isTIGER192 is the validation function for validating if the field's value is a valid isTIGER192.
func isTIGER192(fl FieldLevel) bool {
	return tiger192Regex().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
}

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

	if !iSSNRegex().MatchString(s) {
		return false
	}
	s = strings.ReplaceAll(s, "-", "")

	pos := 8
	checksum := 0

	for i := 0; i < 7; i++ {
		checksum += pos * int(s[i]-'0')
		pos--
	}

	if s[7] == 'X' {
		checksum += 10
	} else {
		checksum += int(s[7] - '0')
	}

	return checksum%11 == 0
}

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

	return ethAddressRegex().MatchString(address)
}

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

	if !ethAddressRegex().MatchString(address) {
		return false
	}
	// Checksum validation. Reference: https://github.com/ethereum/EIPs/blob/master/EIPS/eip-55.md
	address = address[2:] // Skip "0x" prefix.
	h := sha3.NewLegacyKeccak256()
	// hash.Hash's io.Writer implementation says it never returns an error. https://golang.org/pkg/hash/#Hash
	_, _ = h.Write([]byte(strings.ToLower(address)))
	hash := hex.EncodeToString(h.Sum(nil))

	for i := 0; i < len(address); i++ {
		if address[i] <= '9' { // Skip 0-9 digits: they don't have upper/lower-case.
			continue
		}
		if hash[i] > '7' && address[i] >= 'a' || hash[i] <= '7' && address[i] <= 'F' {
			return false
		}
	}

	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())
}

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

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

// startsNotWith is the validation function for validating that the field's value does not start with the text specified within the param.
func startsNotWith(fl FieldLevel) bool {
	return !startsWith(fl)
}

// endsNotWith is the validation function for validating that the field's value does not end with the text specified within the param.
func endsNotWith(fl FieldLevel) bool {
	return !endsWith(fl)
}

// 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.Bool:
		return field.Bool() != currentField.Bool()

	case reflect.Struct:

		fieldType := field.Type()

		if fieldType.ConvertibleTo(timeType) && currentField.Type().ConvertibleTo(timeType) {

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

			return !fieldTime.Equal(t)
		}

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

	// 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)
}

// isNeIgnoreCase is the validation function for validating that the field's string value does not equal the
// provided param value. The comparison is case-insensitive
func isNeIgnoreCase(fl FieldLevel) bool {
	return !isEqIgnoreCase(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: