scratch/dns-server/packet.go (view raw)
| 1 | package main |
| 2 | |
| 3 | import ( |
| 4 | "bytes" |
| 5 | "net" |
| 6 | "strings" |
| 7 | ) |
| 8 | |
| 9 | type Packet struct { |
| 10 | Header Header |
| 11 | Questions []Question |
| 12 | Answers []Record |
| 13 | Authorities []Record |
| 14 | Resources []Record |
| 15 | } |
| 16 | |
| 17 | func ParsePacket(packet []byte) (Packet, error) { |
| 18 | r := bytes.NewReader(packet) |
| 19 | |
| 20 | var err error |
| 21 | var p Packet |
| 22 | |
| 23 | p.Header, err = ReadHeader(r) |
| 24 | if err != nil { |
| 25 | return Packet{}, err |
| 26 | } |
| 27 | |
| 28 | for i := 0; i < int(p.Header.Questions); i++ { |
| 29 | q, err := ReadQuestion(r, packet) |
| 30 | if err != nil { |
| 31 | return Packet{}, err |
| 32 | } |
| 33 | p.Questions = append(p.Questions, q) |
| 34 | } |
| 35 | |
| 36 | for i := 0; i < int(p.Header.Answers); i++ { |
| 37 | a, err := ReadRecord(r, packet) |
| 38 | if err != nil { |
| 39 | return Packet{}, err |
| 40 | } |
| 41 | p.Answers = append(p.Answers, a) |
| 42 | } |
| 43 | |
| 44 | for i := 0; i < int(p.Header.AuthoritativeEntries); i++ { |
| 45 | ae, err := ReadRecord(r, packet) |
| 46 | if err != nil { |
| 47 | return Packet{}, err |
| 48 | } |
| 49 | p.Authorities = append(p.Authorities, ae) |
| 50 | } |
| 51 | |
| 52 | for i := 0; i < int(p.Header.ResourceEntries); i++ { |
| 53 | re, err := ReadRecord(r, packet) |
| 54 | if err != nil { |
| 55 | return Packet{}, err |
| 56 | } |
| 57 | p.Resources = append(p.Resources, re) |
| 58 | } |
| 59 | |
| 60 | return p, nil |
| 61 | } |
| 62 | |
| 63 | func (p *Packet) Write(b *bytes.Buffer) error { |
| 64 | p.Header.Questions = uint16(len(p.Questions)) |
| 65 | p.Header.Answers = uint16(len(p.Answers)) |
| 66 | p.Header.AuthoritativeEntries = uint16(len(p.Authorities)) |
| 67 | p.Header.ResourceEntries = uint16(len(p.Resources)) |
| 68 | _ = p.Header.Write(b) |
| 69 | |
| 70 | for i := range p.Questions { |
| 71 | _ = p.Questions[i].Write(b) |
| 72 | } |
| 73 | |
| 74 | for i := range p.Answers { |
| 75 | _, _ = p.Answers[i].Write(b) |
| 76 | } |
| 77 | |
| 78 | for i := range p.Authorities { |
| 79 | _, _ = p.Authorities[i].Write(b) |
| 80 | } |
| 81 | |
| 82 | for i := range p.Resources { |
| 83 | _, _ = p.Resources[i].Write(b) |
| 84 | } |
| 85 | |
| 86 | return nil |
| 87 | } |
| 88 | |
| 89 | func (p Packet) GetRandomA() (net.IP, bool) { |
| 90 | for _, r := range p.Answers { |
| 91 | if r.Type == AType { |
| 92 | return net.ParseIP(r.Data), true |
| 93 | } |
| 94 | } |
| 95 | return nil, false |
| 96 | } |
| 97 | |
| 98 | func (p Packet) GetResolvedNS(qname string) (net.IP, bool) { |
| 99 | for _, ns := range p.getNS(qname) { |
| 100 | host := ns[1] |
| 101 | for _, r := range p.Resources { |
| 102 | if r.Type == AType && r.Name == host { |
| 103 | return net.ParseIP(r.Data), true |
| 104 | } |
| 105 | } |
| 106 | } |
| 107 | return nil, false |
| 108 | } |
| 109 | |
| 110 | func (p Packet) GetUnresolvedNS(qname string) (string, bool) { |
| 111 | ns := p.getNS(qname) |
| 112 | if len(ns) == 0 { |
| 113 | return "", false |
| 114 | } |
| 115 | return ns[0][1], true |
| 116 | } |
| 117 | |
| 118 | func (p Packet) getNS(qname string) [][2]string { |
| 119 | var res [][2]string |
| 120 | for _, r := range p.Authorities { |
| 121 | if r.Type == NSType && strings.HasPrefix(qname, r.Name) { |
| 122 | res = append(res, [2]string{r.Name, r.Data}) |
| 123 | } |
| 124 | } |
| 125 | return res |
| 126 | } |