validate/length.go

package validate

import "unicode/utf8"

var (
	ErrMustBeLonger       = NewError("must contain at least %d characters")
	ErrMustBeShorter      = NewError("must contain no more than %d characters")
	ErrMustHaveMoreBytes  = NewError("must have at least %d bytes")
	ErrMustHaveFewerBytes = NewError("must have no more than %d bytes")
)

// MaxLength validates that a string is no longer than a given maximum.
// Length is counted in runes, so multi-byte characters count as one.
func MaxLength(l int) func(string) error {
	return func(value string) error {
		if utf8.RuneCountInString(value) > l {
			return ErrMustBeShorter.With(l)
		}
		return nil
	}
}

// MinLength validates that a string is at least a given minimum length.
// Length is counted in runes, so multi-byte characters count as one.
func MinLength(l int) func(string) error {
	return func(value string) error {
		if utf8.RuneCountInString(value) < l {
			return ErrMustBeLonger.With(l)
		}
		return nil
	}
}

// MaxLengthBytes validates that a string is no longer than a given maximum
// number of bytes (len). Prefer [MaxLength] for a limit on visible
// characters; use this when the budget is genuinely a byte count, such as
// a fixed-width column or a wire-format field.
func MaxLengthBytes(l int) func(string) error {
	return func(value string) error {
		if len(value) > l {
			return ErrMustHaveFewerBytes.With(l)
		}
		return nil
	}
}

// MinLengthBytes validates that a string is at least a given minimum
// number of bytes (len). See [MaxLengthBytes] on when to prefer this over
// [MinLength].
func MinLengthBytes(l int) func(string) error {
	return func(value string) error {
		if len(value) < l {
			return ErrMustHaveMoreBytes.With(l)
		}
		return nil
	}
}