hostname.go

// Copyright (C) 2022 Andrew Ayer
//
// Permission is hereby granted, free of charge, to any person obtaining a
// copy of this software and associated documentation files (the "Software"),
// to deal in the Software without restriction, including without limitation
// the rights to use, copy, modify, merge, publish, distribute, sublicense,
// and/or sell copies of the Software, and to permit persons to whom the
// Software is furnished to do so, subject to the following conditions:
//
// The above copyright notice and this permission notice shall be included
// in all copies or substantial portions of the Software.
//
// THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
// IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
// FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL
// THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR
// OTHER LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE,
// ARISING FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR
// OTHER DEALINGS IN THE SOFTWARE.
//
// Except as contained in this notice, the name(s) of the above copyright
// holders shall not be used in advertising or otherwise to promote the
// sale, use or other dealings in this Software without prior written
// authorization.

package main

import (
	"errors"
	"strings"
)

func replaceFirstLabel(hostname string, replacement string) string {
	dot := strings.IndexByte(hostname, '.')
	if dot == -1 {
		return replacement
	} else {
		return replacement + hostname[dot:]
	}
}

func canonicalizeHostname(hostname string) (string, error) {
	if len(hostname) == 0 || hostname[0] == '.' || strings.IndexByte(hostname, '/') >= 0 {
		return "", errors.New("invalid hostname")
	}

	hostname = strings.ToLower(hostname)
	hostname = strings.TrimSuffix(hostname, ".")

	return hostname, nil
}

func wildcardHostname(hostname string) string {
	return replaceFirstLabel(hostname, "_")
}