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 package net 6 7 import ( 8 "sync" 9 "time" 10 ) 11 12 const cacheMaxAge = 5 * time.Second 13 14 func parseLiteralIP(addr string) string { 15 var ip IP 16 var zone string 17 ip = parseIPv4(addr) 18 if ip == nil { 19 ip, zone = parseIPv6(addr, true) 20 } 21 if ip == nil { 22 return "" 23 } 24 if zone == "" { 25 return ip.String() 26 } 27 return ip.String() + "%" + zone 28 } 29 30 // hosts contains known host entries. 31 var hosts struct { 32 sync.Mutex 33 34 // Key for the list of literal IP addresses must be a host 35 // name. It would be part of DNS labels, a FQDN or an absolute 36 // FQDN. 37 // For now the key is converted to lower case for convenience. 38 byName map[string][]string 39 40 // Key for the list of host names must be a literal IP address 41 // including IPv6 address with zone identifier. 42 // We don't support old-classful IP address notation. 43 byAddr map[string][]string 44 45 expire time.Time 46 path string 47 mtime time.Time 48 size int64 49 } 50 51 func readHosts() { 52 now := time.Now() 53 hp := testHookHostsPath 54 55 if now.Before(hosts.expire) && hosts.path == hp && len(hosts.byName) > 0 { 56 return 57 } 58 mtime, size, err := stat(hp) 59 if err == nil && hosts.path == hp && hosts.mtime.Equal(mtime) && hosts.size == size { 60 hosts.expire = now.Add(cacheMaxAge) 61 return 62 } 63 64 hs := make(map[string][]string) 65 is := make(map[string][]string) 66 var file *file 67 if file, _ = open(hp); file == nil { 68 return 69 } 70 for line, ok := file.readLine(); ok; line, ok = file.readLine() { 71 if i := byteIndex(line, '#'); i >= 0 { 72 // Discard comments. 73 line = line[0:i] 74 } 75 f := getFields(line) 76 if len(f) < 2 { 77 continue 78 } 79 addr := parseLiteralIP(f[0]) 80 if addr == "" { 81 continue 82 } 83 for i := 1; i < len(f); i++ { 84 name := absDomainName([]byte(f[i])) 85 h := []byte(f[i]) 86 lowerASCIIBytes(h) 87 key := absDomainName(h) 88 hs[key] = append(hs[key], addr) 89 is[addr] = append(is[addr], name) 90 } 91 } 92 // Update the data cache. 93 hosts.expire = now.Add(cacheMaxAge) 94 hosts.path = hp 95 hosts.byName = hs 96 hosts.byAddr = is 97 hosts.mtime = mtime 98 hosts.size = size 99 file.close() 100 } 101 102 // lookupStaticHost looks up the addresses for the given host from /etc/hosts. 103 func lookupStaticHost(host string) []string { 104 hosts.Lock() 105 defer hosts.Unlock() 106 readHosts() 107 if len(hosts.byName) != 0 { 108 // TODO(jbd,bradfitz): avoid this alloc if host is already all lowercase? 109 // or linear scan the byName map if it's small enough? 110 lowerHost := []byte(host) 111 lowerASCIIBytes(lowerHost) 112 if ips, ok := hosts.byName[absDomainName(lowerHost)]; ok { 113 ipsCp := make([]string, len(ips)) 114 copy(ipsCp, ips) 115 return ipsCp 116 } 117 } 118 return nil 119 } 120 121 // lookupStaticAddr looks up the hosts for the given address from /etc/hosts. 122 func lookupStaticAddr(addr string) []string { 123 hosts.Lock() 124 defer hosts.Unlock() 125 readHosts() 126 addr = parseLiteralIP(addr) 127 if addr == "" { 128 return nil 129 } 130 if len(hosts.byAddr) != 0 { 131 if hosts, ok := hosts.byAddr[addr]; ok { 132 hostsCp := make([]string, len(hosts)) 133 copy(hostsCp, hosts) 134 return hostsCp 135 } 136 } 137 return nil 138 } 139
