Source file src/pkg/net/dnsconfig.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 // +build darwin freebsd linux netbsd openbsd 6 7 // Read system DNS config from /etc/resolv.conf 8 9 package net 10 11 type dnsConfig struct { 12 servers []string // servers to use 13 search []string // suffixes to append to local name 14 ndots int // number of dots in name to trigger absolute lookup 15 timeout int // seconds before giving up on packet 16 attempts int // lost packets before giving up on server 17 rotate bool // round robin among servers 18 } 19 20 // See resolv.conf(5) on a Linux machine. 21 // TODO(rsc): Supposed to call uname() and chop the beginning 22 // of the host name to get the default search domain. 23 // We assume it's in resolv.conf anyway. 24 func dnsReadConfig() (*dnsConfig, error) { 25 file, err := open("/etc/resolv.conf") 26 if err != nil { 27 return nil, &DNSConfigError{err} 28 } 29 conf := new(dnsConfig) 30 conf.servers = make([]string, 3)[0:0] // small, but the standard limit 31 conf.search = make([]string, 0) 32 conf.ndots = 1 33 conf.timeout = 5 34 conf.attempts = 2 35 conf.rotate = false 36 for line, ok := file.readLine(); ok; line, ok = file.readLine() { 37 f := getFields(line) 38 if len(f) < 1 { 39 continue 40 } 41 switch f[0] { 42 case "nameserver": // add one name server 43 a := conf.servers 44 n := len(a) 45 if len(f) > 1 && n < cap(a) { 46 // One more check: make sure server name is 47 // just an IP address. Otherwise we need DNS 48 // to look it up. 49 name := f[1] 50 switch len(ParseIP(name)) { 51 case 16: 52 name = "[" + name + "]" 53 fallthrough 54 case 4: 55 a = a[0 : n+1] 56 a[n] = name 57 conf.servers = a 58 } 59 } 60 61 case "domain": // set search path to just this domain 62 if len(f) > 1 { 63 conf.search = make([]string, 1) 64 conf.search[0] = f[1] 65 } else { 66 conf.search = make([]string, 0) 67 } 68 69 case "search": // set search path to given servers 70 conf.search = make([]string, len(f)-1) 71 for i := 0; i < len(conf.search); i++ { 72 conf.search[i] = f[i+1] 73 } 74 75 case "options": // magic options 76 for i := 1; i < len(f); i++ { 77 s := f[i] 78 switch { 79 case len(s) >= 6 && s[0:6] == "ndots:": 80 n, _, _ := dtoi(s, 6) 81 if n < 1 { 82 n = 1 83 } 84 conf.ndots = n 85 case len(s) >= 8 && s[0:8] == "timeout:": 86 n, _, _ := dtoi(s, 8) 87 if n < 1 { 88 n = 1 89 } 90 conf.timeout = n 91 case len(s) >= 8 && s[0:9] == "attempts:": 92 n, _, _ := dtoi(s, 9) 93 if n < 1 { 94 n = 1 95 } 96 conf.attempts = n 97 case s == "rotate": 98 conf.rotate = true 99 } 100 } 101 } 102 } 103 file.close() 104 105 return conf, nil 106 }