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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 dragonfly freebsd linux netbsd openbsd solaris
// 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
}
// 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, error) {
file, err := open(filename)
if err != nil {
return nil, &DNSConfigError{err}
}
defer file.close()
conf := &dnsConfig{
ndots: 1,
timeout: 5,
attempts: 2,
}
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
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 i := 1; i < len(f); i++ {
s := f[i]
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
}
}
}
}
return conf, nil
}
func hasPrefix(s, prefix string) bool {
return len(s) >= len(prefix) && s[:len(prefix)] == prefix
}
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