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dns_unix.go
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dns_unix.go
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//go:build !windows
package dns
import (
"bufio"
"fmt"
"github.com/alibaba/kt-connect/pkg/kt/util"
"github.com/rs/zerolog/log"
"os"
"regexp"
"strings"
)
// listen address of systemd-resolved
const resolvedAddr = "127.0.0.53"
const resolvedConf = "/run/systemd/resolve/resolv.conf"
// GetLocalDomains get domain search postfixes
func GetLocalDomains() string {
f, err := os.Open(util.ResolvConf)
if err != nil {
return ""
}
defer f.Close()
var localDomains []string
scanner := bufio.NewScanner(f)
for scanner.Scan() {
line := scanner.Text()
if strings.HasPrefix(line, util.FieldDomain) {
localDomains = append(localDomains, strings.TrimSpace(strings.TrimPrefix(line, util.FieldDomain)))
} else if strings.HasPrefix(line, util.FieldSearch) {
for _, s := range strings.Split(strings.TrimPrefix(line, util.FieldSearch), " ") {
if s != "" {
localDomains = append(localDomains, s)
}
}
}
}
return strings.Join(localDomains, ",")
}
// GetNameServer get primary dns server
func GetNameServer() string {
ns := fetchNameServerInConf(util.ResolvConf)
if util.IsLinux() && ns == resolvedAddr {
log.Debug().Msgf("Using systemd-resolved")
return fetchNameServerInConf(resolvedConf)
}
return ns
}
func fetchNameServerInConf(resolvConf string) string {
f, err := os.Open(resolvConf)
if err != nil {
return ""
}
defer f.Close()
scanner := bufio.NewScanner(f)
pattern, _ := regexp.Compile(fmt.Sprintf("^%s[ \t]+" + util.IpAddrPattern, util.FieldNameserver))
for scanner.Scan() {
line := scanner.Text()
if pattern.MatchString(line) {
return strings.TrimSpace(strings.TrimPrefix(line, util.FieldNameserver))
}
}
return ""
}