121 lines
2.6 KiB
Go
121 lines
2.6 KiB
Go
package dnsProxy
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import (
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"encoding/hex"
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"fmt"
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"log"
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"net"
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"time"
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)
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const (
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DNSMaxUDPPackageSize = 4096
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DNSMaxTCPPackageSize = 65536
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)
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type DNSProxy struct {
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listenAddr string
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upstreamAddr string
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udpConn *net.UDPConn
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MsgHandler func(*Message)
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}
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func (p DNSProxy) Close() error {
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return p.udpConn.Close()
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}
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func (p DNSProxy) sendToUpstream(isTCP bool, request []byte) ([]byte, error) {
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protocol := "udp"
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if isTCP {
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protocol = "tcp"
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}
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conn, err := net.Dial(protocol, p.upstreamAddr)
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if err != nil {
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return nil, fmt.Errorf("failed to dial upstream DNS: %w", err)
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}
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defer conn.Close()
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_, err = conn.Write(request)
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if err != nil {
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return nil, fmt.Errorf("failed to send request to upstream DNS: %w", err)
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}
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err = conn.SetReadDeadline(time.Now().Add(5 * time.Second))
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if err != nil {
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return nil, fmt.Errorf("failed to set timeout: %w", err)
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}
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var response []byte
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if !isTCP {
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response = make([]byte, DNSMaxUDPPackageSize)
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} else {
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response = make([]byte, DNSMaxTCPPackageSize)
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}
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n, err := conn.Read(response)
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if err != nil {
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return nil, fmt.Errorf("failed to read response from upstream DNS: %w", err)
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}
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return response[:n], nil
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}
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func (p DNSProxy) handleDNSRequest(clientAddr *net.UDPAddr, buffer []byte) {
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upstreamResponse, err := p.sendToUpstream(false, buffer)
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if err != nil {
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log.Printf("Failed to get response from upstream DNS: %v", err)
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return
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}
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log.Printf("Response: %s", hex.EncodeToString(upstreamResponse))
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msg, err := ParseResponse(upstreamResponse)
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if err == nil {
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if p.MsgHandler != nil {
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p.MsgHandler(msg)
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}
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} else {
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log.Printf("error while parsing response: %v", err)
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}
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_, err = p.udpConn.WriteToUDP(upstreamResponse, clientAddr)
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if err != nil {
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log.Printf("Failed to send DNS response: %v", err)
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}
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}
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func (p DNSProxy) Listen() error {
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var err error
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udpAddr, err := net.ResolveUDPAddr("udp", p.listenAddr)
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if err != nil {
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return fmt.Errorf("failed to resolve UDP address: %v", err)
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}
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p.udpConn, err = net.ListenUDP("udp", udpAddr)
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if err != nil {
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return fmt.Errorf("failed to listen on UDP: %v", err)
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}
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for {
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buffer := make([]byte, DNSMaxUDPPackageSize)
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n, clientAddr, err := p.udpConn.ReadFromUDP(buffer)
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if err != nil {
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log.Printf("Failed to read from UDP: %v", err)
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continue
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}
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go p.handleDNSRequest(clientAddr, buffer[:n])
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}
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}
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func New(listenAddr string, listenPort uint16, upstreamAddr string, upstreamPort uint16) *DNSProxy {
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return &DNSProxy{
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listenAddr: fmt.Sprintf("%s:%d", listenAddr, listenPort),
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upstreamAddr: fmt.Sprintf("%s:%d", upstreamAddr, upstreamPort),
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}
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}
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