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main.go
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main.go
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package main
import (
"context"
"errors"
"log"
"net"
"strings"
"github.com/docker/docker/api/types"
"github.com/docker/docker/client"
"github.com/miekg/dns"
)
type handler struct{}
func GetContainerIp(container string) (*string, error) {
cli, err := client.NewClientWithOpts(client.FromEnv)
if err != nil {
return nil, err
}
containers, err := cli.ContainerList(context.Background(), types.ContainerListOptions{})
if err != nil {
return nil, err
}
for _, c := range containers {
if container == strings.TrimLeft(c.Names[0], "/")+".docker." {
data, err := cli.ContainerInspect(context.Background(), c.ID)
if err != nil {
return nil, err
}
for _, net := range data.NetworkSettings.Networks {
if net.IPAddress != "" {
return &net.IPAddress, nil
}
}
return nil, nil
}
}
return nil, errors.New("container not found")
}
func (this *handler) ServeDNS(w dns.ResponseWriter, r *dns.Msg) {
msg := &dns.Msg{}
msg.SetReply(r)
log.Println("Recieved query for " + r.Question[0].String())
if strings.HasSuffix(strings.TrimRight(r.Question[0].Name, "."), ".docker") && r.Question[0].Qtype == dns.TypeA {
msg.Authoritative = true
domain := msg.Question[0].Name
ip, err := GetContainerIp(domain)
if err != nil {
} else {
msg.Answer = append(msg.Answer, &dns.A{
Hdr: dns.RR_Header{Name: domain, Rrtype: dns.TypeA, Class: dns.ClassINET, Ttl: 60},
A: net.ParseIP(*ip),
})
}
} else {
msg, _ = dns.Exchange(r, "1.1.1.1:53")
}
w.WriteMsg(msg)
}
func main() {
addr := "127.0.0.53:53"
srv := &dns.Server{Addr: addr, Net: "udp"}
srv.Handler = &handler{}
log.Println("Starting DNS server on " + addr)
if err := srv.ListenAndServe(); err != nil {
log.Fatalf("Failed to set udp listener %s\n", err.Error())
}
}