136 lines
3.3 KiB
Go
136 lines
3.3 KiB
Go
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 = cloneSlice(f[1:])
|
|
|
|
case "options": // magic options
|
|
for _, s := range f[1:] {
|
|
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
|
|
}
|