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main.go
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main.go
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package main
import (
"bufio"
"fmt"
"log"
"net"
"os"
"regexp"
"strings"
"time"
"github.com/miekg/dns"
)
const (
ColorRed = "\033[31m"
ColorGreen = "\033[32m"
ColorYellow = "\033[33m"
ColorBlue = "\x1b[34m"
ColorReset = "\033[0m"
)
type DNSConfig struct {
HostsFilePath string
Laddr string
ListRaddr []string
UseWildCard bool // *.google.com
Timeout uint8
}
var config = &DNSConfig{
HostsFilePath: "/etc/hosts",
Laddr: ":5053",
ListRaddr: []string{"8.8.8.8:53", "8.8.4.4:53", "1.1.1.1:53", "9.9.9.9:53"},
UseWildCard: true,
Timeout: 15,
}
func main() {
server := &dns.Server{Addr: config.Laddr, Net: "udp"}
dns.HandleFunc(".", handleDNSRequest)
log.Printf("\n%sDNS Server listen on %s%s\n", ColorBlue, config.Laddr, ColorReset)
log.Fatal(server.ListenAndServe())
}
func handleDNSRequest(w dns.ResponseWriter, r *dns.Msg) {
for _, question := range r.Question {
ip := checkHostsFile(question.Name)
var rr dns.RR
var rrtype uint16
switch question.Qtype {
case dns.TypeA:
rrtype = dns.TypeA
case dns.TypeAAAA:
rrtype = dns.TypeAAAA
default:
m := new(dns.Msg)
m.SetReply(r)
m.SetRcode(r, dns.RcodeNameError)
w.WriteMsg(m)
continue
}
if ip != "" {
if rrtype == dns.TypeA {
rr = &dns.A{
Hdr: dns.RR_Header{Name: question.Name, Rrtype: rrtype, Class: dns.ClassINET, Ttl: 0},
A: net.ParseIP(ip),
}
} else {
rr = &dns.AAAA{
Hdr: dns.RR_Header{Name: question.Name, Rrtype: rrtype, Class: dns.ClassINET, Ttl: 0},
AAAA: net.ParseIP(ip),
}
}
} else {
queryRemote(w, r)
}
m := new(dns.Msg)
m.SetReply(r)
m.Answer = append(m.Answer, rr)
w.WriteMsg(m)
}
}
func checkHostsFile(host string) string {
host = strings.TrimSuffix(host, ".")
wildcardPattern := regexp.MustCompile(`^\s*\*\s*\.(.+)$`)
file, err := os.Open(config.HostsFilePath)
if err != nil {
log.Fatal(err)
}
defer file.Close()
scanner := bufio.NewScanner(file)
for scanner.Scan() {
fields := strings.Fields(scanner.Text())
if len(fields) >= 2 && net.ParseIP(fields[0]) != nil {
ip := fields[0]
hosts_domain := fields[1]
if config.UseWildCard && wildcardPattern.MatchString(hosts_domain) {
domain := wildcardPattern.FindStringSubmatch(hosts_domain)[1]
if strings.HasSuffix(host, "."+domain) {
fmt.Printf("%s[%s] Resolve From Hosts File: %s (%s) %s\n", ColorBlue, hosts_domain, host, ip, ColorReset)
return ip
}
} else if host == hosts_domain {
fmt.Printf("%s[hosts file] %s (%s) %s\n", ColorBlue, host, ip, ColorReset)
return ip
}
}
}
if err := scanner.Err(); err != nil {
log.Fatal(err)
}
return ""
}
func queryRemote(w dns.ResponseWriter, r *dns.Msg) {
c := new(dns.Client)
c.Timeout = time.Second * time.Duration(config.Timeout)
for _, dnsServer := range config.ListRaddr {
in, _, err := c.Exchange(r, dnsServer)
if err == nil {
fmt.Printf("\n> %s[%s] %s (%s)%s", ColorYellow, dnsServer, string(r.Question[0].Name), in.Answer[0], ColorReset)
w.WriteMsg(in)
return
}
if netErr, ok := err.(net.Error); ok && netErr.Timeout() {
log.Printf("> UDP read timeout: %s", err)
log.Printf("%sRetrying query %s %s", ColorRed, dnsServer, ColorReset)
continue
}
log.Println(err)
}
}