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/*
* ZLint Copyright 2024 Regents of the University of Michigan
*
* Licensed under the Apache License, Version 2.0 (the "License"); you may not
* use this file except in compliance with the License. You may obtain a copy
* of the License at http://www.apache.org/licenses/LICENSE-2.0
*
* Unless required by applicable law or agreed to in writing, software
* distributed under the License is distributed on an "AS IS" BASIS,
* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or
* implied. See the License for the specific language governing
* permissions and limitations under the License.
*/
package util
import (
"regexp"
"golang.org/x/net/idna"
)
var reservedLabelPrefix = regexp.MustCompile(`^..--`)
var xnLabelPrefix = regexp.MustCompile(`(?i)^xn--`)
// HasReservedLabelPrefix checks whether the given string (presumably
// a domain label) has hyphens ("-") as the third and fourth characters. Domain
// labels with hyphens in these positions are considered to be "Reserved Labels"
// per RFC 5890, section 2.3.1.
// (https://datatracker.ietf.org/doc/html/rfc5890#section-2.3.1)
func HasReservedLabelPrefix(s string) bool {
return reservedLabelPrefix.MatchString(s)
}
// HasXNLabelPrefix checks whether the given string (presumably a
// domain label) is prefixed with the case-insensitive string "xn--" (the
// IDNA ACE prefix).
//
// This check is useful given the bug following bug report for IDNA wherein
// the ACE prefix incorrectly taken to be case-sensitive.
//
// https://github.com/golang/go/issues/48778
func HasXNLabelPrefix(s string) bool {
return xnLabelPrefix.MatchString(s)
}
// IdnaToUnicode is a wrapper around idna.ToUnicode.
//
// If the provided string starts with the IDNA ACE prefix ("xn--", case
// insensitive), then that ACE prefix is coerced to a lowercase "xn--" before
// processing by the idna package.
//
// This is only necessary due to the bug at https://github.com/golang/go/issues/48778
func IdnaToUnicode(s string) (string, error) {
if HasXNLabelPrefix(s) {
s = "xn--" + s[4:]
}
return idna.ToUnicode(s)
}
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