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dns.go
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package main
import (
"github.com/miekg/dns"
log "github.com/sirupsen/logrus"
"net"
)
type DNSForwarder struct {
server *dns.Server
}
type DNSRewriteForwardHandler struct {
upstreamServer string
redirectTo string
}
func (D DNSRewriteForwardHandler) ServeDNS(w dns.ResponseWriter, r *dns.Msg) {
client := dns.Client{
Net: "udp",
}
response, _, err := client.Exchange(r, D.upstreamServer+":53")
if err != nil {
log.Errorln("Error connecting to upstream: ", err)
return
}
for _, rr := range response.Answer {
switch rr.Header().Rrtype {
case dns.TypeA:
if t, ok := rr.(*dns.A); ok {
if t.A.Equal(net.IPv4(127, 0, 0, 1)) {
log.Debugln("Redirecting answer for ", t.Header().Name, "to ", D.redirectTo)
t.A = net.ParseIP(D.redirectTo)
}
}
}
}
err = w.WriteMsg(response)
if err != nil {
log.Errorln("Error writing response: ", err)
}
}
func NewDnsForwarder(upstreamServer string) (*DNSForwarder, error) {
forwarder := &DNSForwarder{
server: &dns.Server{
Net: "udp",
Handler: DNSRewriteForwardHandler{
upstreamServer: upstreamServer,
redirectTo: upstreamServer,
},
},
}
return forwarder, nil
}
func (c *DNSForwarder) Start() {
go func() {
err := c.server.ListenAndServe()
if err != nil {
log.Errorln("Error starting DNS server: ", err)
}
}()
}
func (c *DNSForwarder) Shutdown() {
err := c.server.Shutdown()
if err != nil {
log.Errorln("Error shutting down DNS server: ", err)
}
}