| // 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. |
| |
| // Read system DNS config from /etc/resolv.conf |
| |
| package net |
| |
| import "os" |
| |
| 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 |
| } |
| |
| var dnsconfigError os.Error |
| |
| type DNSConfigError struct { |
| Error os.Error |
| } |
| |
| func (e *DNSConfigError) String() string { |
| return "error reading DNS config: " + e.Error.String() |
| } |
| |
| func (e *DNSConfigError) Timeout() bool { return false } |
| func (e *DNSConfigError) Temporary() bool { return false } |
| |
| |
| // 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. |
| // We assume it's in resolv.conf anyway. |
| func dnsReadConfig() (*dnsConfig, os.Error) { |
| file, err := open("/etc/resolv.conf") |
| if err != nil { |
| return nil, &DNSConfigError{err} |
| } |
| conf := new(dnsConfig) |
| conf.servers = make([]string, 3)[0:0] // small, but the standard limit |
| conf.search = make([]string, 0) |
| conf.ndots = 1 |
| conf.timeout = 5 |
| conf.attempts = 2 |
| conf.rotate = false |
| for line, ok := file.readLine(); ok; line, ok = file.readLine() { |
| f := getFields(line) |
| if len(f) < 1 { |
| continue |
| } |
| switch f[0] { |
| case "nameserver": // add one name server |
| a := conf.servers |
| n := len(a) |
| if len(f) > 1 && n < cap(a) { |
| // One more check: make sure server name is |
| // just an IP address. Otherwise we need DNS |
| // to look it up. |
| name := f[1] |
| switch len(ParseIP(name)) { |
| case 16: |
| name = "[" + name + "]" |
| fallthrough |
| case 4: |
| a = a[0 : n+1] |
| a[n] = name |
| conf.servers = a |
| } |
| } |
| |
| case "domain": // set search path to just this domain |
| if len(f) > 1 { |
| conf.search = make([]string, 1) |
| conf.search[0] = f[1] |
| } else { |
| conf.search = make([]string, 0) |
| } |
| |
| 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 i := 1; i < len(f); i++ { |
| s := f[i] |
| switch { |
| case len(s) >= 6 && s[0:6] == "ndots:": |
| n, _, _ := dtoi(s, 6) |
| if n < 1 { |
| n = 1 |
| } |
| conf.ndots = n |
| case len(s) >= 8 && s[0:8] == "timeout:": |
| n, _, _ := dtoi(s, 8) |
| if n < 1 { |
| n = 1 |
| } |
| conf.timeout = n |
| case len(s) >= 8 && s[0:9] == "attempts:": |
| n, _, _ := dtoi(s, 9) |
| if n < 1 { |
| n = 1 |
| } |
| conf.attempts = n |
| case s == "rotate": |
| conf.rotate = true |
| } |
| } |
| } |
| } |
| file.close() |
| |
| return conf, nil |
| } |