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