libgo/go/net/hosts.go

   1 // Copyright 2009 The Go Authors. All rights reserved.
   2 // Use of this source code is governed by a BSD-style
   3 // license that can be found in the LICENSE file.
   4
   5 // Read static host/IP entries from /etc/hosts.
   6
   7 package net
   8
   9 import (
  10         "os"
  11         "sync"
  12 )
  13
  14 const cacheMaxAge = int64(300) // 5 minutes.
  15
  16 // hostsPath points to the file with static IP/address entries.
  17 var hostsPath = "/etc/hosts"
  18
  19 // Simple cache.
  20 var hosts struct {
  21         sync.Mutex
  22         data map[string][]string
  23         time int64
  24         path string
  25 }
  26
  27 func readHosts() {
  28         now, _, _ := os.Time()
  29         hp := hostsPath
  30         if len(hosts.data) == 0 || hosts.time+cacheMaxAge <= now || hosts.path != hp {
  31                 hs := make(map[string][]string)
  32                 var file *file
  33                 if file, _ = open(hp); file == nil {
  34                         return
  35                 }
  36                 for line, ok := file.readLine(); ok; line, ok = file.readLine() {
  37                         if i := byteIndex(line, '#'); i >= 0 {
  38                                 // Discard comments.
  39                                 line = line[0:i]
  40                         }
  41                         f := getFields(line)
  42                         if len(f) < 2 || ParseIP(f[0]) == nil {
  43                                 continue
  44                         }
  45                         for i := 1; i < len(f); i++ {
  46                                 h := f[i]
  47                                 hs[h] = append(hs[h], f[0])
  48                         }
  49                 }
  50                 // Update the data cache.
  51                 hosts.time, _, _ = os.Time()
  52                 hosts.path = hp
  53                 hosts.data = hs
  54                 file.close()
  55         }
  56 }
  57
  58 // lookupStaticHosts looks up the addresses for the given host from /etc/hosts.
  59 func lookupStaticHost(host string) []string {
  60         hosts.Lock()
  61         defer hosts.Unlock()
  62         readHosts()
  63         if len(hosts.data) != 0 {
  64                 if ips, ok := hosts.data[host]; ok {
  65                         return ips
  66                 }
  67         }
  68         return nil
  69 }