knative.dev/pkg@v0.0.0-20260602142205-ac97e43f6622/network/domain.go (about)

     1  /*
     2  Copyright 2019 The Knative Authors
     3  
     4  Licensed under the Apache License, Version 2.0 (the "License");
     5  you may not use this file except in compliance with the License.
     6  You may obtain a copy of the License at
     7  
     8      http://www.apache.org/licenses/LICENSE-2.0
     9  
    10  Unless required by applicable law or agreed to in writing, software
    11  distributed under the License is distributed on an "AS IS" BASIS,
    12  WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
    13  See the License for the specific language governing permissions and
    14  limitations under the License.
    15  */
    16  
    17  package network
    18  
    19  import (
    20  	"bufio"
    21  	"fmt"
    22  	"io"
    23  	"os"
    24  	"strings"
    25  	"sync"
    26  )
    27  
    28  const (
    29  	resolverFileName    = "/etc/resolv.conf"
    30  	clusterDomainEnvKey = "CLUSTER_DOMAIN"
    31  	defaultDomainName   = "cluster.local"
    32  )
    33  
    34  var (
    35  	domainName = defaultDomainName
    36  	once       sync.Once
    37  )
    38  
    39  // GetServiceHostname returns the fully qualified service hostname
    40  func GetServiceHostname(name, namespace string) string {
    41  	return fmt.Sprintf("%s.%s.svc.%s", name, namespace, GetClusterDomainName())
    42  }
    43  
    44  // GetClusterDomainName returns cluster's domain name or an error
    45  // Closes issue: https://github.com/knative/eventing/issues/714
    46  func GetClusterDomainName() string {
    47  	once.Do(func() {
    48  		f, err := os.Open(resolverFileName)
    49  		if err != nil {
    50  			return
    51  		}
    52  		defer f.Close()
    53  		domainName = getClusterDomainName(f)
    54  	})
    55  	return domainName
    56  }
    57  
    58  func getClusterDomainName(r io.Reader) string {
    59  	// First check the ENV variable (allows override).
    60  	if domain := os.Getenv(clusterDomainEnvKey); len(domain) > 0 {
    61  		return domain
    62  	}
    63  
    64  	// Then look in the conf file.
    65  	for scanner := bufio.NewScanner(r); scanner.Scan(); {
    66  		elements := strings.Split(scanner.Text(), " ")
    67  		if elements[0] != "search" {
    68  			continue
    69  		}
    70  		for _, e := range elements[1:] {
    71  			if strings.HasPrefix(e, "svc.") {
    72  				return strings.TrimSuffix(e[4:], ".")
    73  			}
    74  		}
    75  	}
    76  
    77  	// For all abnormal cases return default domain name.
    78  	return defaultDomainName
    79  }