github.com/m10x/go/src@v0.0.0-20220112094212-ba61592315da/net/hosts.go (about) 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 "internal/bytealg" 9 "sync" 10 "time" 11 ) 12 13 const cacheMaxAge = 5 * time.Second 14 15 func parseLiteralIP(addr string) string { 16 var ip IP 17 var zone string 18 ip = parseIPv4(addr) 19 if ip == nil { 20 ip, zone = parseIPv6Zone(addr) 21 } 22 if ip == nil { 23 return "" 24 } 25 if zone == "" { 26 return ip.String() 27 } 28 return ip.String() + "%" + zone 29 } 30 31 // hosts contains known host entries. 32 var hosts struct { 33 sync.Mutex 34 35 // Key for the list of literal IP addresses must be a host 36 // name. It would be part of DNS labels, a FQDN or an absolute 37 // FQDN. 38 // For now the key is converted to lower case for convenience. 39 byName map[string][]string 40 41 // Key for the list of host names must be a literal IP address 42 // including IPv6 address with zone identifier. 43 // We don't support old-classful IP address notation. 44 byAddr map[string][]string 45 46 expire time.Time 47 path string 48 mtime time.Time 49 size int64 50 } 51 52 func readHosts() { 53 now := time.Now() 54 hp := testHookHostsPath 55 56 if now.Before(hosts.expire) && hosts.path == hp && len(hosts.byName) > 0 { 57 return 58 } 59 mtime, size, err := stat(hp) 60 if err == nil && hosts.path == hp && hosts.mtime.Equal(mtime) && hosts.size == size { 61 hosts.expire = now.Add(cacheMaxAge) 62 return 63 } 64 65 hs := make(map[string][]string) 66 is := make(map[string][]string) 67 var file *file 68 if file, _ = open(hp); file == nil { 69 return 70 } 71 for line, ok := file.readLine(); ok; line, ok = file.readLine() { 72 if i := bytealg.IndexByteString(line, '#'); i >= 0 { 73 // Discard comments. 74 line = line[0:i] 75 } 76 f := getFields(line) 77 if len(f) < 2 { 78 continue 79 } 80 addr := parseLiteralIP(f[0]) 81 if addr == "" { 82 continue 83 } 84 for i := 1; i < len(f); i++ { 85 name := absDomainName(f[i]) 86 h := []byte(f[i]) 87 lowerASCIIBytes(h) 88 key := absDomainName(string(h)) 89 hs[key] = append(hs[key], addr) 90 is[addr] = append(is[addr], name) 91 } 92 } 93 // Update the data cache. 94 hosts.expire = now.Add(cacheMaxAge) 95 hosts.path = hp 96 hosts.byName = hs 97 hosts.byAddr = is 98 hosts.mtime = mtime 99 hosts.size = size 100 file.close() 101 } 102 103 // lookupStaticHost looks up the addresses for the given host from /etc/hosts. 104 func lookupStaticHost(host string) []string { 105 hosts.Lock() 106 defer hosts.Unlock() 107 readHosts() 108 if len(hosts.byName) != 0 { 109 if hasUpperCase(host) { 110 lowerHost := []byte(host) 111 lowerASCIIBytes(lowerHost) 112 host = string(lowerHost) 113 } 114 if ips, ok := hosts.byName[absDomainName(host)]; ok { 115 ipsCp := make([]string, len(ips)) 116 copy(ipsCp, ips) 117 return ipsCp 118 } 119 } 120 return nil 121 } 122 123 // lookupStaticAddr looks up the hosts for the given address from /etc/hosts. 124 func lookupStaticAddr(addr string) []string { 125 hosts.Lock() 126 defer hosts.Unlock() 127 readHosts() 128 addr = parseLiteralIP(addr) 129 if addr == "" { 130 return nil 131 } 132 if len(hosts.byAddr) != 0 { 133 if hosts, ok := hosts.byAddr[addr]; ok { 134 hostsCp := make([]string, len(hosts)) 135 copy(hostsCp, hosts) 136 return hostsCp 137 } 138 } 139 return nil 140 }