// Copyright 2009 The Go Authors. All rights reserved. // Use of this source code is governed by a BSD-style // license that can be found in the LICENSE file. // +build darwin dragonfly freebsd linux netbsd openbsd solaris // Read system DNS config from /etc/resolv.conf package net var defaultNS = []string{"127.0.0.1", "::1"} type dnsConfig struct { servers []string // servers to use search []string // suffixes to append to local name ndots int // number of dots in name to trigger absolute lookup timeout int // seconds before giving up on packet attempts int // lost packets before giving up on server rotate bool // round robin among servers unknownOpt bool // anything unknown was encountered lookup []string // OpenBSD top-level database "lookup" order err error // any error that occurs during open of resolv.conf } // See resolv.conf(5) on a Linux machine. // TODO(rsc): Supposed to call uname() and chop the beginning // of the host name to get the default search domain. func dnsReadConfig(filename string) *dnsConfig { conf := &dnsConfig{ ndots: 1, timeout: 5, attempts: 2, } file, err := open(filename) if err != nil { conf.servers = defaultNS conf.err = err return conf } defer file.close() for line, ok := file.readLine(); ok; line, ok = file.readLine() { if len(line) > 0 && (line[0] == ';' || line[0] == '#') { // comment. continue } f := getFields(line) if len(f) < 1 { continue } switch f[0] { case "nameserver": // add one name server if len(f) > 1 && len(conf.servers) < 3 { // small, but the standard limit // One more check: make sure server name is // just an IP address. Otherwise we need DNS // to look it up. if parseIPv4(f[1]) != nil { conf.servers = append(conf.servers, f[1]) } else if ip, _ := parseIPv6(f[1], true); ip != nil { conf.servers = append(conf.servers, f[1]) } } case "domain": // set search path to just this domain if len(f) > 1 { conf.search = []string{f[1]} } case "search": // set search path to given servers conf.search = make([]string, len(f)-1) for i := 0; i < len(conf.search); i++ { conf.search[i] = f[i+1] } case "options": // magic options for _, s := range f[1:] { switch { case hasPrefix(s, "ndots:"): n, _, _ := dtoi(s, 6) if n < 1 { n = 1 } conf.ndots = n case hasPrefix(s, "timeout:"): n, _, _ := dtoi(s, 8) if n < 1 { n = 1 } conf.timeout = n case hasPrefix(s, "attempts:"): n, _, _ := dtoi(s, 9) if n < 1 { n = 1 } conf.attempts = n case s == "rotate": conf.rotate = true default: conf.unknownOpt = true } } case "lookup": // OpenBSD option: // http://www.openbsd.org/cgi-bin/man.cgi/OpenBSD-current/man5/resolv.conf.5 // "the legal space-separated values are: bind, file, yp" conf.lookup = f[1:] default: conf.unknownOpt = true } } if len(conf.servers) == 0 { conf.servers = defaultNS } return conf } func hasPrefix(s, prefix string) bool { return len(s) >= len(prefix) && s[:len(prefix)] == prefix }