headscale/hscontrol/util/dns.go

package util

import (
	"errors"
	"fmt"
	"regexp"
	"strings"
)

const (
	// value related to RFC 1123 and 952.
	LabelHostnameLength = 63
)

var invalidCharsInUserRegex = regexp.MustCompile("[^a-z0-9-.]+")

var ErrInvalidUserName = errors.New("invalid user name")

// NormalizeToFQDNRules will replace forbidden chars in user
// it can also return an error if the user doesn't respect RFC 952 and 1123.
func NormalizeToFQDNRules(name string, stripEmailDomain bool) (string, error) {
	name = strings.ToLower(name)
	name = strings.ReplaceAll(name, "'", "")
	atIdx := strings.Index(name, "@")
	if stripEmailDomain && atIdx > 0 {
		name = name[:atIdx]
	} else {
		name = strings.ReplaceAll(name, "@", ".")
	}
	name = invalidCharsInUserRegex.ReplaceAllString(name, "-")

	for _, elt := range strings.Split(name, ".") {
		if len(elt) > LabelHostnameLength {
			return "", fmt.Errorf(
				"label %v is more than 63 chars: %w",
				elt,
				ErrInvalidUserName,
			)
		}
	}

	return name, nil
}

func CheckForFQDNRules(name string) error {
	if len(name) > LabelHostnameLength {
		return fmt.Errorf(
			"DNS segment must not be over 63 chars. %v doesn't comply with this rule: %w",
			name,
			ErrInvalidUserName,
		)
	}
	if strings.ToLower(name) != name {
		return fmt.Errorf(
			"DNS segment should be lowercase. %v doesn't comply with this rule: %w",
			name,
			ErrInvalidUserName,
		)
	}
	if invalidCharsInUserRegex.MatchString(name) {
		return fmt.Errorf(
			"DNS segment should only be composed of lowercase ASCII letters numbers, hyphen and dots. %v doesn't comply with theses rules: %w",
			name,
			ErrInvalidUserName,
		)
	}

	return nil
}