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// 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 freebsd linux netbsd openbsd
// Read system DNS config from /etc/resolv.conf
package net
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 error
type DNSConfigError struct {
Err error
}
func (e *DNSConfigError) Error() string {
return "error reading DNS config: " + e.Err.Error()
}
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, 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
}
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