Temporary solution to use regex

[rafaelgustavolv]

I created a function called regex62 that uses Base62 to avoid special characters and prevent the validate tag errors.

Example of use:

type Test struct {
	alias string `validate:"required, regex62=byfTeMLWFJRIi2Me, min=3, max=25"` // base62 of regex ^[a-z0-9_]+$
}

Custom validator:

v.RegisterValidation("regex62", func(fl validator.FieldLevel) bool {
	// Expect a base62-encoded regex in the parameter
	param := fl.Param()
	if param == "" {
		return false
	}

	var err error

	vbig := big.NewInt(0)
	for i := 0; i < len(param); i++ {
		b := param[i]
		var idx int

		switch {
		case b >= '0' && b <= '9':
			idx = int(b - '0')
		case b >= 'A' && b <= 'Z':
			idx = int(10 + (b - 'A'))
		case b >= 'a' && b <= 'z':
			idx = int(36 + (b - 'a'))
		default:
			idx = -1
		}

		if idx < 0 {
			return false
		}

		vbig.Mul(vbig, big.NewInt(62))
		vbig.Add(vbig, big.NewInt(int64(idx)))
	}

	decoded := vbig.Bytes()

	re, err := regexp.Compile(string(decoded))
	if err != nil {
		return false
	}

	// Support string and *string fields
	fv := fl.Field()

	var s string
	switch fv.Kind() {
	case reflect.String:
		s = fv.String()
	case reflect.Ptr:
		if fv.IsNil() {
			return false
		}
		if fv.Elem().Kind() != reflect.String {
			return false
		}
		s = fv.Elem().String()
	default:
		return false
	}

	if s == "" {
		return false
	}

	return re.MatchString(s)
})

[deankarn]

Please see comment here

This seems like multiple laters of indirection with little upside.

I recommend registering your own validation that can be backed by a regex.

[rafaelgustavolv]

I agree it’s not ideal 😅 the idea isn’t to add this to the library, just to offer an option for anyone who wants to use the regex tag in some way.