MagiTrickle/pkg/dns-proxy/dns-proxy.go
2024-09-04 09:15:03 +03:00

120 lines
2.4 KiB
Go

package dnsProxy
import (
"context"
"errors"
"fmt"
"net"
"os"
"time"
"github.com/rs/zerolog/log"
)
const (
DNSMaxUDPPackageSize = 4096
)
type DNSProxy struct {
udpConn *net.UDPConn
listenPort uint16
targetDNSServerAddress string
MsgHandler func(*Message)
}
func (p DNSProxy) Listen(ctx context.Context) error {
var err error
udpAddr, err := net.ResolveUDPAddr("udp", fmt.Sprintf(":%d", p.listenPort))
if err != nil {
return fmt.Errorf("failed to resolve UDP address: %v", err)
}
p.udpConn, err = net.ListenUDP("udp", udpAddr)
if err != nil {
return fmt.Errorf("failed to listen UDP address: %v", err)
}
defer func() {
if p.udpConn != nil {
err := p.udpConn.Close()
if err != nil {
log.Error().Err(err).Msg("failed to close UDP connection")
}
}
}()
for {
select {
case <-ctx.Done():
return nil
default:
buffer := make([]byte, DNSMaxUDPPackageSize)
n, clientAddr, err := p.udpConn.ReadFromUDP(buffer)
if err != nil {
log.Error().Err(err).Msg("failed to read UDP packet")
continue
}
go p.handleDNSRequest(clientAddr, buffer[:n])
}
}
}
func (p DNSProxy) handleDNSRequest(clientAddr *net.UDPAddr, buffer []byte) {
conn, err := net.Dial("udp", p.targetDNSServerAddress)
if err != nil {
log.Error().Err(err).Msg("failed to dial target DNS")
return
}
defer conn.Close()
_, err = conn.Write(buffer)
if err != nil {
log.Error().Err(err).Msg("failed to send request to target DNS")
return
}
err = conn.SetReadDeadline(time.Now().Add(5 * time.Second))
if err != nil {
log.Error().Err(err).Msg("failed to set read deadline")
return
}
response := make([]byte, DNSMaxUDPPackageSize)
n, err := conn.Read(response)
if err != nil {
if errors.Is(err, os.ErrDeadlineExceeded) {
// Just skip it
return
}
log.Error().Err(err).Msg("failed to read response from target DNS")
return
}
msg, err := ParseResponse(response[:n])
if err == nil {
if p.MsgHandler != nil {
p.MsgHandler(msg)
}
} else {
log.Warn().Err(err).Msg("error while parsing DNS message")
}
_, err = p.udpConn.WriteToUDP(response[:n], clientAddr)
if err != nil {
log.Error().Err(err).Msg("failed to send DNS message")
return
}
}
func New(listenPort uint16, targetDNSServerAddress string) *DNSProxy {
return &DNSProxy{
listenPort: listenPort,
targetDNSServerAddress: targetDNSServerAddress,
}
}