// Copyright 2018 Istio Authors
//
// 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 (
	"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
}
