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         "sync"
  11         "time"
  12 )
  13
  14 const cacheMaxAge = 5 * time.Minute
  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         byName map[string][]string
  23         byAddr map[string][]string
  24         expire time.Time
  25         path   string
  26 }
  27
  28 func readHosts() {
  29         now := time.Now()
  30         hp := hostsPath
  31         if len(hosts.byName) == 0 || now.After(hosts.expire) || hosts.path != hp {
  32                 hs := make(map[string][]string)
  33                 is := make(map[string][]string)
  34                 var file *file
  35                 if file, _ = open(hp); file == nil {
  36                         return
  37                 }
  38                 for line, ok := file.readLine(); ok; line, ok = file.readLine() {
  39                         if i := byteIndex(line, '#'); i >= 0 {
  40                                 // Discard comments.
  41                                 line = line[0:i]
  42                         }
  43                         f := getFields(line)
  44                         if len(f) < 2 || ParseIP(f[0]) == nil {
  45                                 continue
  46                         }
  47                         for i := 1; i < len(f); i++ {
  48                                 h := f[i]
  49                                 hs[h] = append(hs[h], f[0])
  50                                 is[f[0]] = append(is[f[0]], h)
  51                         }
  52                 }
  53                 // Update the data cache.
  54                 hosts.expire = time.Now().Add(cacheMaxAge)
  55                 hosts.path = hp
  56                 hosts.byName = hs
  57                 hosts.byAddr = is
  58                 file.close()
  59         }
  60 }
  61
  62 // lookupStaticHost looks up the addresses for the given host from /etc/hosts.
  63 func lookupStaticHost(host string) []string {
  64         hosts.Lock()
  65         defer hosts.Unlock()
  66         readHosts()
  67         if len(hosts.byName) != 0 {
  68                 if ips, ok := hosts.byName[host]; ok {
  69                         return ips
  70                 }
  71         }
  72         return nil
  73 }
  74
  75 // lookupStaticAddr looks up the hosts for the given address from /etc/hosts.
  76 func lookupStaticAddr(addr string) []string {
  77         hosts.Lock()
  78         defer hosts.Unlock()
  79         readHosts()
  80         if len(hosts.byAddr) != 0 {
  81                 if hosts, ok := hosts.byAddr[addr]; ok {
  82                         return hosts
  83                 }
  84         }
  85         return nil
  86 }