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|
package dns
import (
"bufio"
"io"
"os"
"strconv"
"strings"
)
// ClientConfig wraps the contents of the /etc/resolv.conf file.
type ClientConfig struct {
Servers []string // servers to use
Search []string // suffixes to append to local name
Port string // what port to use
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, not used in the package dns
}
// ClientConfigFromFile parses a resolv.conf(5) like file and returns
// a *ClientConfig.
func ClientConfigFromFile(resolvconf string) (*ClientConfig, error) {
file, err := os.Open(resolvconf)
if err != nil {
return nil, err
}
defer file.Close()
return ClientConfigFromReader(file)
}
// ClientConfigFromReader works like ClientConfigFromFile but takes an io.Reader as argument
func ClientConfigFromReader(resolvconf io.Reader) (*ClientConfig, error) {
c := new(ClientConfig)
scanner := bufio.NewScanner(resolvconf)
c.Servers = make([]string, 0)
c.Search = make([]string, 0)
c.Port = "53"
c.Ndots = 1
c.Timeout = 5
c.Attempts = 2
for scanner.Scan() {
if err := scanner.Err(); err != nil {
return nil, err
}
line := scanner.Text()
f := strings.Fields(line)
if len(f) < 1 {
continue
}
switch f[0] {
case "nameserver": // add one name server
if len(f) > 1 {
// One more check: make sure server name is
// just an IP address. Otherwise we need DNS
// to look it up.
name := f[1]
c.Servers = append(c.Servers, name)
}
case "domain": // set search path to just this domain
if len(f) > 1 {
c.Search = make([]string, 1)
c.Search[0] = f[1]
} else {
c.Search = make([]string, 0)
}
case "search": // set search path to given servers
c.Search = make([]string, len(f)-1)
for i := 0; i < len(c.Search); i++ {
c.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[:6] == "ndots:":
n, _ := strconv.Atoi(s[6:])
if n < 0 {
n = 0
} else if n > 15 {
n = 15
}
c.Ndots = n
case len(s) >= 8 && s[:8] == "timeout:":
n, _ := strconv.Atoi(s[8:])
if n < 1 {
n = 1
}
c.Timeout = n
case len(s) >= 9 && s[:9] == "attempts:":
n, _ := strconv.Atoi(s[9:])
if n < 1 {
n = 1
}
c.Attempts = n
case s == "rotate":
/* not imp */
}
}
}
}
return c, nil
}
// NameList returns all of the names that should be queried based on the
// config. It is based off of go's net/dns name building, but it does not
// check the length of the resulting names.
func (c *ClientConfig) NameList(name string) []string {
// if this domain is already fully qualified, no append needed.
if IsFqdn(name) {
return []string{name}
}
// Check to see if the name has more labels than Ndots. Do this before making
// the domain fully qualified.
hasNdots := CountLabel(name) > c.Ndots
// Make the domain fully qualified.
name = Fqdn(name)
// Make a list of names based off search.
names := []string{}
// If name has enough dots, try that first.
if hasNdots {
names = append(names, name)
}
for _, s := range c.Search {
names = append(names, Fqdn(name+s))
}
// If we didn't have enough dots, try after suffixes.
if !hasNdots {
names = append(names, name)
}
return names
}
|
