/*
 * Licensed to the Apache Software Foundation (ASF) under one or more
 * contributor license agreements.  See the NOTICE file distributed with
 * this work for additional information regarding copyright ownership.
 * The ASF licenses this file to You 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 (
	"fmt"
	"strings"
)

// DualUseCommonName extracts a valid CommonName from a comma-delimited host string
// for dual-use certificates.
func DualUseCommonName(host string) (string, error) {
	// cn uses one hostname, drop the rest
	first := strings.SplitN(host, ",", 2)[0]

	// cn max length is 64 (ub-common-name @ https://tools.ietf.org/html/rfc5280)
	if l := len(first); l > 64 {
		return "", fmt.Errorf("certificate CN upper bound exceeded (%v>64): %s", l, first)
	}

	return first, nil
}
