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dns: change parseAnswers function to return error
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nadoo
parent
e91d4bcb6e
commit
ff632f23a6
136
dns.go
136
dns.go
@ -44,11 +44,11 @@ const DNSQTypeAAAA = 28
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// | Authority | RRs pointing toward an authority
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// +---------------------+
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// | Additional | RRs holding additional information
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type DNSMsg struct {
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DNSHeader
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Questions []*DNSQuestion
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Answers []*DNSRR
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}
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// type DNSMsg struct {
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// DNSHeader
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// Questions []DNSQuestion
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// Answers []DNSRR
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// }
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// DNSHeader format
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// https://tools.ietf.org/html/rfc1035#section-4.1.1
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@ -70,9 +70,9 @@ type DNSMsg struct {
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// | ARCOUNT |
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// +--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+
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//
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type DNSHeader struct {
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ID uint16
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}
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// type DNSHeader struct {
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// ID uint16
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// }
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// DNSQuestion format
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// https://tools.ietf.org/html/rfc1035#section-4.1.2
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@ -134,8 +134,8 @@ type DNSRR struct {
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IP string
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}
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// DNSAnswerHandler .
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type DNSAnswerHandler func(domain, ip string) error
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// DNSAnswerHandler function handles the dns TypeA or TypeAAAA answer
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type DNSAnswerHandler func(Domain, ip string) error
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// DNS .
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type DNS struct {
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@ -191,22 +191,26 @@ func (s *DNS) ListenAndServeUDP() {
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}
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reqLen := uint16(n)
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if reqLen <= DNSHeaderLen {
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// TODO: check here
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if reqLen <= DNSHeaderLen+2 {
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logf("proxy-dns not enough data")
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continue
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}
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reqMsg := b[:n]
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go func() {
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_, respMsg := s.Exchange(reqLen, reqMsg)
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_, respMsg, err := s.Exchange(reqLen, reqMsg, clientAddr.String())
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if err != nil {
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logf("proxy-dns error in exchange: %s", err)
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return
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}
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_, err = c.WriteTo(respMsg, clientAddr)
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if err != nil {
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logf("proxy-dns error in local write: %s", err)
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return
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}
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// logf("proxy-dns %s <-> %s, type: %d, %s: %s", clientAddr.String(), dnsServer, query.QueryType, domain, ip)
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}()
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}
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}
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@ -241,11 +245,12 @@ func (s *DNS) ServeTCP(c net.Conn) {
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var reqLen uint16
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if err := binary.Read(c, binary.BigEndian, &reqLen); err != nil {
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logf("proxy-dns-tcp failed to read request length: %v", err)
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logf("proxy-dns-tcp failed to get request length: %v", err)
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return
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}
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if reqLen <= DNSHeaderLen {
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// TODO: check here
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if reqLen <= DNSHeaderLen+2 {
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logf("proxy-dns-tcp not enough data")
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return
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}
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@ -257,29 +262,34 @@ func (s *DNS) ServeTCP(c net.Conn) {
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return
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}
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respLen, respMsg := s.Exchange(reqLen, reqMsg)
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if err := binary.Write(c, binary.BigEndian, respLen); err != nil {
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logf("proxy-dns-tcp error in local write respLen: %s\n", err)
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}
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if err := binary.Write(c, binary.BigEndian, respMsg); err != nil {
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logf("proxy-dns-tcp error in local write respMsg: %s\n", err)
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}
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// logf("proxy-dns-tcp %s <-> %s, type: %d, %s: %s", c.RemoteAddr(), dnsServer, query.QueryType, domain, ip)
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}
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// Exchange handles request msg and return response msg
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func (s *DNS) Exchange(reqLen uint16, reqMsg []byte) (respLen uint16, respMsg []byte) {
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// fmt.Printf("\ndns req len %d:\n%s\n", reqLen, hex.Dump(reqMsg[:]))
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query, err := parseQuestion(reqMsg)
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respLen, respMsg, err := s.Exchange(reqLen, reqMsg, c.RemoteAddr().String())
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if err != nil {
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logf("proxy-dns error in parseQuestion reqMsg %s", err)
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logf("proxy-dns-tcp error in exchange: %s", err)
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return
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}
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dnsServer := s.GetServer(query.QNAME)
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if s.Tunnel {
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dnsServer = s.DNSServer
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if err := binary.Write(c, binary.BigEndian, respLen); err != nil {
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logf("proxy-dns-tcp error in local write respLen: %s", err)
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return
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}
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if err := binary.Write(c, binary.BigEndian, respMsg); err != nil {
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logf("proxy-dns-tcp error in local write respMsg: %s", err)
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return
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}
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}
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// Exchange handles request msg and returns response msg
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func (s *DNS) Exchange(reqLen uint16, reqMsg []byte, addr string) (respLen uint16, respMsg []byte, err error) {
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// fmt.Printf("\ndns req len %d:\n%s\n", reqLen, hex.Dump(reqMsg[:]))
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query, err := parseQuestion(reqMsg)
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if err != nil {
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logf("proxy-dns error in parseQuestion reqMsg: %s", err)
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return
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}
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dnsServer := s.DNSServer
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if !s.Tunnel {
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dnsServer = s.GetServer(query.QNAME)
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}
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rc, err := s.sDialer.NextDialer(query.QNAME+":53").Dial("tcp", dnsServer)
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@ -289,16 +299,16 @@ func (s *DNS) Exchange(reqLen uint16, reqMsg []byte) (respLen uint16, respMsg []
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}
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defer rc.Close()
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if err := binary.Write(rc, binary.BigEndian, reqLen); err != nil {
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if err = binary.Write(rc, binary.BigEndian, reqLen); err != nil {
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logf("proxy-dns failed to write req length: %v", err)
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return
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}
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if err := binary.Write(rc, binary.BigEndian, reqMsg); err != nil {
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if err = binary.Write(rc, binary.BigEndian, reqMsg); err != nil {
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logf("proxy-dns failed to write req message: %v", err)
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return
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}
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if err := binary.Read(rc, binary.BigEndian, &respLen); err != nil {
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if err = binary.Read(rc, binary.BigEndian, &respLen); err != nil {
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logf("proxy-dns failed to read response length: %v", err)
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return
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}
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@ -313,30 +323,35 @@ func (s *DNS) Exchange(reqLen uint16, reqMsg []byte) (respLen uint16, respMsg []
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// fmt.Printf("\ndns resp len %d:\n%s\n", respLen, hex.Dump(respMsg[:]))
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var ip string
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if respLen > 0 {
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query, err := parseQuestion(respMsg)
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respReq, err := parseQuestion(respMsg)
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if err != nil {
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logf("proxy-dns error in parseQuestion respMsg: %s", err)
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return
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}
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if (respReq.QTYPE == DNSQTypeA || respReq.QTYPE == DNSQTypeAAAA) &&
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len(respMsg) > respReq.Offset {
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var answers []*DNSRR
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answers, err = parseAnswers(respMsg[respReq.Offset:])
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if err != nil {
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logf("proxy-dns error in parseQuestion respMsg %s", err)
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logf("proxy-dns error in parseAnswers: %s", err)
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return
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}
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if (query.QTYPE == DNSQTypeA || query.QTYPE == DNSQTypeAAAA) &&
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len(respMsg) > query.Offset {
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for _, answer := range answers {
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for _, h := range s.AnswerHandlers {
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h(respReq.QNAME, answer.IP)
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}
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answers := parseAnswers(respMsg[query.Offset:])
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for _, answer := range answers {
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if answer.IP != "" {
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ip += answer.IP + ","
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}
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for _, h := range s.AnswerHandlers {
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h(query.QNAME, answer.IP)
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}
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if answer.IP != "" {
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ip += answer.IP + ","
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}
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}
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}
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logf("proxy-dns %s <-> %s, type: %d, %s: %s", addr, dnsServer, query.QTYPE, query.QNAME, ip)
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return
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}
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@ -389,9 +404,13 @@ func parseQuestion(p []byte) (*DNSQuestion, error) {
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i = i + l + 1
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}
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if len(domain) == 0 {
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return nil, errors.New("no QNAME")
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}
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q.QNAME = string(domain[:len(domain)-1])
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if len(p) < i+4 {
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if lenP < i+4 {
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return nil, errors.New("not enough data")
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}
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@ -402,10 +421,11 @@ func parseQuestion(p []byte) (*DNSQuestion, error) {
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return q, nil
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}
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func parseAnswers(p []byte) []*DNSRR {
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func parseAnswers(p []byte) ([]*DNSRR, error) {
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var answers []*DNSRR
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lenP := len(p)
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for i := 0; i < len(p); {
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for i := 0; i < lenP; {
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// https://tools.ietf.org/html/rfc1035#section-4.1.4
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// "Message compression",
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@ -420,6 +440,10 @@ func parseAnswers(p []byte) []*DNSRR {
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break
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}
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if lenP <= i+10 {
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return nil, errors.New("not enough data")
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}
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answer := &DNSRR{}
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answer.TYPE = binary.BigEndian.Uint16(p[i:])
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@ -439,5 +463,5 @@ func parseAnswers(p []byte) []*DNSRR {
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i = i + 10 + int(answer.RDLENGTH)
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}
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return answers
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return answers, nil
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}
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