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dns: add some comment
This commit is contained in:
nadoo
parent
8a1111d3b5
commit
ed30f295d7
252
dns.go
252
dns.go
@ -10,11 +10,8 @@ import (
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"strings"
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)
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// DNSUDPHeaderLen is the length of UDP dns msg header
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const DNSUDPHeaderLen = 12
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// DNSTCPHeaderLen is the length of TCP dns msg header
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const DNSTCPHeaderLen = 2 + DNSUDPHeaderLen
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// DNSHeaderLen is the length of dns msg header
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const DNSHeaderLen = 12
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// DNSUDPMaxLen is the max size of udp dns request.
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// https://tools.ietf.org/html/rfc1035#section-4.2.1
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@ -25,26 +22,114 @@ const DNSTCPHeaderLen = 2 + DNSUDPHeaderLen
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// so we should also serve tcp requests.
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const DNSUDPMaxLen = 512
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// DNSQueryTypeA ipv4
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const DNSQueryTypeA = 1
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// DNSQTypeA ipv4
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const DNSQTypeA = 1
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// DNSQueryTypeAAAA ipv6
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const DNSQueryTypeAAAA = 28
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// DNSQTypeAAAA ipv6
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const DNSQTypeAAAA = 28
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// DNSMsg format
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// https://tools.ietf.org/html/rfc1035#section-4.1
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// All communications inside of the domain protocol are carried in a single
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// format called a message. The top level format of message is divided
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// into 5 sections (some of which are empty in certain cases) shown below:
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//
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// +---------------------+
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// | Header |
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// +---------------------+
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// | Question | the question for the name server
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// +---------------------+
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// | Answer | RRs answering the question
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// +---------------------+
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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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// DNSHeader format
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// https://tools.ietf.org/html/rfc1035#section-4.1.1
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// The header contains the following fields:
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//
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// 1 1 1 1 1 1
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// 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5
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// +--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+
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// | ID |
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// +--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+
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// |QR| Opcode |AA|TC|RD|RA| Z | RCODE |
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// +--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+
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// | QDCOUNT |
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// +--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+
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// | ANCOUNT |
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// +--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+
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// | NSCOUNT |
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// +--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+
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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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// DNSQuestion format
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// https://tools.ietf.org/html/rfc1035#section-4.1.2
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// The question section is used to carry the "question" in most queries,
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// i.e., the parameters that define what is being asked. The section
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// contains QDCOUNT (usually 1) entries, each of the following format:
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//
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// 1 1 1 1 1 1
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// 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5
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// +--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+
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// | |
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// / QNAME /
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// / /
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// +--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+
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// | QTYPE |
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// +--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+
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// | QCLASS |
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// +--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+
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type DNSQuestion struct {
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QNAME string
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QTYPE uint16
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QCLASS uint16
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type dnsQuery struct {
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DomainName string
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QueryType uint16
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QueryClass uint16
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Offset int
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}
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type dnsAnswer struct {
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// DomainName string
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QueryType uint16
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QueryClass uint16
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// DNSRR format
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// https://tools.ietf.org/html/rfc1035#section-3.2.1
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// All RRs have the same top level format shown below:
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//
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// 1 1 1 1 1 1
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// 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5
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// +--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+
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// | |
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// / /
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// / NAME /
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// | |
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// +--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+
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// | TYPE |
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// +--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+
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// | CLASS |
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// +--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+
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// | TTL |
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// | |
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// +--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+
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// | RDLENGTH |
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// +--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--|
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// / RDATA /
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// / /
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// +--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+
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type DNSRR struct {
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// NAME string
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TYPE uint16
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CLASS uint16
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TTL uint32
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DataLength uint16
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Data []byte
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RDLENGTH uint16
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RDATA []byte
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IP string
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}
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@ -57,12 +142,12 @@ type DNS struct {
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*Forwarder // as proxy client
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sDialer Dialer // dialer for server
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tunnel bool
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Tunnel bool
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dnsServer string
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DNSServer string
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dnsServerMap map[string]string
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answerHandlers []DNSAnswerHandler
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DNSServerMap map[string]string
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AnswerHandlers []DNSAnswerHandler
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}
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// NewDNS returns a dns forwarder. client[dns.udp] -> glider[tcp] -> forwarder[dns.tcp] -> remote dns addr
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@ -71,10 +156,10 @@ func NewDNS(addr, raddr string, sDialer Dialer, tunnel bool) (*DNS, error) {
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Forwarder: NewForwarder(addr, nil),
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sDialer: sDialer,
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tunnel: tunnel,
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Tunnel: tunnel,
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dnsServer: raddr,
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dnsServerMap: make(map[string]string),
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DNSServer: raddr,
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DNSServerMap: make(map[string]string),
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}
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return s, nil
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@ -90,31 +175,34 @@ func (s *DNS) ListenAndServe() {
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func (s *DNS) ListenAndServeUDP() {
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c, err := net.ListenPacket("udp", s.addr)
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if err != nil {
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logf("proxy-dns failed to listen on %s: %v", s.addr, err)
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logf("proxy-dns failed to listen on %s, error: %v", s.addr, err)
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return
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}
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defer c.Close()
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logf("proxy-dns listening on udp:%s", s.addr)
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logf("proxy-dns listening UDP on %s", s.addr)
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for {
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data := make([]byte, DNSUDPMaxLen)
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n, clientAddr, err := c.ReadFrom(data)
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b := make([]byte, DNSUDPMaxLen)
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n, clientAddr, err := c.ReadFrom(b)
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if err != nil {
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logf("proxy-dns DNS local read error: %v", err)
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logf("proxy-dns local read error: %v", err)
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continue
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}
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data = data[:n]
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reqLen := uint16(n)
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if reqLen <= DNSHeaderLen {
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logf("proxy-dns not enough data")
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continue
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}
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b = b[:n]
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go func() {
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_, respMsg := s.handleReqMsg(uint16(len(data)), data)
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_, respMsg := s.handleReqMsg(reqLen, b)
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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\n", err)
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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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@ -131,7 +219,7 @@ func (s *DNS) ListenAndServeTCP() {
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return
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}
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logf("proxy-dns-tcp listening on tcp:%s", s.addr)
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logf("proxy-dns-tcp listening TCP on %s", s.addr)
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for {
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c, err := l.Accept()
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@ -157,6 +245,11 @@ func (s *DNS) ServeTCP(c net.Conn) {
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return
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}
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if reqLen <= DNSHeaderLen {
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logf("proxy-dns not enough data")
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return
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}
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reqMsg := make([]byte, reqLen)
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_, err := io.ReadFull(c, reqMsg)
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if err != nil {
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@ -165,7 +258,6 @@ func (s *DNS) ServeTCP(c net.Conn) {
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}
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respLen, respMsg := s.handleReqMsg(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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@ -178,19 +270,19 @@ func (s *DNS) ServeTCP(c net.Conn) {
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// handle request msg and return response msg
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func (s *DNS) handleReqMsg(reqLen uint16, reqMsg []byte) (respLen uint16, respMsg []byte) {
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query, err := parseQuery(reqMsg)
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// fmt.Printf("dns req len %d:\n%s\n\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-tcp error in parseQuery reqMsg %s", err)
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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.GetServer(query.DomainName)
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if s.tunnel {
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dnsServer = s.dnsServer
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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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}
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rc, err := s.sDialer.NextDialer(query.DomainName+":53").Dial("tcp", dnsServer)
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rc, err := s.sDialer.NextDialer(query.QNAME+":53").Dial("tcp", dnsServer)
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if err != nil {
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logf("proxy-dns failed to connect to server %v: %v", dnsServer, err)
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return
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@ -198,21 +290,23 @@ func (s *DNS) handleReqMsg(reqLen uint16, reqMsg []byte) (respLen uint16, respMs
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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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logf("proxy-dns failed to connect to server %v: %v", dnsServer, err)
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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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logf("proxy-dns failed to connect to server %v: %v", dnsServer, err)
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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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logf("proxy-dns-tcp failed to read response length: %v", err)
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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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respMsg = make([]byte, respLen)
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_, err = io.ReadFull(rc, respMsg)
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if err != nil {
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logf("proxy-dns-tcp error in read respMsg %s\n", err)
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logf("proxy-dns error in read respMsg %s\n", err)
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return
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}
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@ -220,24 +314,23 @@ func (s *DNS) handleReqMsg(reqLen uint16, reqMsg []byte) (respLen uint16, respMs
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var ip string
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if respLen > 0 {
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query, err := parseQuery(respMsg)
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query, err := parseQuestion(respMsg)
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if err != nil {
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logf("proxy-dns error in parseQuery respMsg %s", err)
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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 (query.QueryType == DNSQueryTypeA || query.QueryType == DNSQueryTypeAAAA) &&
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if (query.QTYPE == DNSQTypeA || query.QTYPE == DNSQTypeAAAA) &&
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len(respMsg) > query.Offset {
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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.DomainName, answer.IP)
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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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}
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}
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@ -249,36 +342,35 @@ func (s *DNS) handleReqMsg(reqLen uint16, reqMsg []byte) (respLen uint16, respMs
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// SetServer .
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func (s *DNS) SetServer(domain, server string) {
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s.dnsServerMap[domain] = server
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s.DNSServerMap[domain] = server
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}
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// GetServer .
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func (s *DNS) GetServer(domain string) string {
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domainParts := strings.Split(domain, ".")
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length := len(domainParts)
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for i := length - 2; i >= 0; i-- {
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domain := strings.Join(domainParts[i:length], ".")
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if server, ok := s.dnsServerMap[domain]; ok {
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if server, ok := s.DNSServerMap[domain]; ok {
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return server
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}
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}
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return s.dnsServer
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return s.DNSServer
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}
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// AddAnswerHandler .
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func (s *DNS) AddAnswerHandler(h DNSAnswerHandler) {
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s.answerHandlers = append(s.answerHandlers, h)
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s.AnswerHandlers = append(s.AnswerHandlers, h)
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}
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func parseQuery(p []byte) (*dnsQuery, error) {
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q := &dnsQuery{}
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func parseQuestion(p []byte) (*DNSQuestion, error) {
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q := &DNSQuestion{}
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var i int
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var domain []byte
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for i = DNSUDPHeaderLen; i < len(p); {
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for i = DNSHeaderLen; i < len(p); {
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l := int(p[i])
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if l == 0 {
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@ -292,21 +384,21 @@ func parseQuery(p []byte) (*dnsQuery, error) {
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i = i + l + 1
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}
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q.DomainName = string(domain[:len(domain)-1])
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q.QNAME = string(domain[:len(domain)-1])
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if len(p) < i+4 {
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return nil, errors.New("parseQuery error, not enough data")
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return nil, errors.New("parseQuestion error, not enough data")
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}
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q.QueryType = binary.BigEndian.Uint16(p[i:])
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q.QueryClass = binary.BigEndian.Uint16(p[i+2:])
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q.QTYPE = binary.BigEndian.Uint16(p[i:])
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q.QCLASS = binary.BigEndian.Uint16(p[i+2:])
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q.Offset = i + 4
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return q, nil
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}
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func parseAnswers(p []byte) []*dnsAnswer {
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var answers []*dnsAnswer
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func parseAnswers(p []byte) []*DNSRR {
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var answers []*DNSRR
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for i := 0; i < len(p); {
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@ -323,23 +415,23 @@ func parseAnswers(p []byte) []*dnsAnswer {
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break
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}
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answer := &dnsAnswer{}
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answer := &DNSRR{}
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answer.QueryType = binary.BigEndian.Uint16(p[i:])
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answer.QueryClass = binary.BigEndian.Uint16(p[i+2:])
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answer.TYPE = binary.BigEndian.Uint16(p[i:])
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answer.CLASS = binary.BigEndian.Uint16(p[i+2:])
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answer.TTL = binary.BigEndian.Uint32(p[i+4:])
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answer.DataLength = binary.BigEndian.Uint16(p[i+8:])
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answer.Data = p[i+10 : i+10+int(answer.DataLength)]
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answer.RDLENGTH = binary.BigEndian.Uint16(p[i+8:])
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answer.RDATA = p[i+10 : i+10+int(answer.RDLENGTH)]
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if answer.QueryType == DNSQueryTypeA {
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answer.IP = net.IP(answer.Data[:net.IPv4len]).String()
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} else if answer.QueryType == DNSQueryTypeAAAA {
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answer.IP = net.IP(answer.Data[:net.IPv6len]).String()
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if answer.TYPE == DNSQTypeA {
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answer.IP = net.IP(answer.RDATA[:net.IPv4len]).String()
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} else if answer.TYPE == DNSQTypeAAAA {
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answer.IP = net.IP(answer.RDATA[:net.IPv6len]).String()
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}
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answers = append(answers, answer)
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i = i + 10 + int(answer.DataLength)
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i = i + 10 + int(answer.RDLENGTH)
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}
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return answers
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