aboutsummaryrefslogtreecommitdiff
path: root/libgo/go/net/dnsclient.go
blob: 93c04f6b590c32be4997634aff7d1ac974941bf1 (plain)
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
159
160
161
162
163
164
165
166
167
168
169
170
171
172
173
174
175
176
177
178
179
180
181
182
183
184
185
186
187
188
189
190
191
192
193
194
195
196
197
198
199
200
201
202
203
204
205
206
207
208
209
210
211
212
213
214
215
216
217
218
219
220
221
222
223
224
225
226
227
228
229
230
231
232
233
234
235
236
237
238
239
240
241
242
243
244
245
246
247
// Copyright 2009 The Go Authors. All rights reserved.
// Use of this source code is governed by a BSD-style
// license that can be found in the LICENSE file.

package net

import (
	"bytes"
	"fmt"
	"os"
	"rand"
	"sort"
)

// DNSError represents a DNS lookup error.
type DNSError struct {
	Error     string // description of the error
	Name      string // name looked for
	Server    string // server used
	IsTimeout bool
}

func (e *DNSError) String() string {
	if e == nil {
		return "<nil>"
	}
	s := "lookup " + e.Name
	if e.Server != "" {
		s += " on " + e.Server
	}
	s += ": " + e.Error
	return s
}

func (e *DNSError) Timeout() bool   { return e.IsTimeout }
func (e *DNSError) Temporary() bool { return e.IsTimeout }

const noSuchHost = "no such host"

// reverseaddr returns the in-addr.arpa. or ip6.arpa. hostname of the IP
// address addr suitable for rDNS (PTR) record lookup or an error if it fails
// to parse the IP address.
func reverseaddr(addr string) (arpa string, err os.Error) {
	ip := ParseIP(addr)
	if ip == nil {
		return "", &DNSError{Error: "unrecognized address", Name: addr}
	}
	if ip.To4() != nil {
		return fmt.Sprintf("%d.%d.%d.%d.in-addr.arpa.", ip[15], ip[14], ip[13], ip[12]), nil
	}
	// Must be IPv6
	var buf bytes.Buffer
	// Add it, in reverse, to the buffer
	for i := len(ip) - 1; i >= 0; i-- {
		s := fmt.Sprintf("%02x", ip[i])
		buf.WriteByte(s[1])
		buf.WriteByte('.')
		buf.WriteByte(s[0])
		buf.WriteByte('.')
	}
	// Append "ip6.arpa." and return (buf already has the final .)
	return buf.String() + "ip6.arpa.", nil
}

// Find answer for name in dns message.
// On return, if err == nil, addrs != nil.
func answer(name, server string, dns *dnsMsg, qtype uint16) (cname string, addrs []dnsRR, err os.Error) {
	addrs = make([]dnsRR, 0, len(dns.answer))

	if dns.rcode == dnsRcodeNameError && dns.recursion_available {
		return "", nil, &DNSError{Error: noSuchHost, Name: name}
	}
	if dns.rcode != dnsRcodeSuccess {
		// None of the error codes make sense
		// for the query we sent.  If we didn't get
		// a name error and we didn't get success,
		// the server is behaving incorrectly.
		return "", nil, &DNSError{Error: "server misbehaving", Name: name, Server: server}
	}

	// Look for the name.
	// Presotto says it's okay to assume that servers listed in
	// /etc/resolv.conf are recursive resolvers.
	// We asked for recursion, so it should have included
	// all the answers we need in this one packet.
Cname:
	for cnameloop := 0; cnameloop < 10; cnameloop++ {
		addrs = addrs[0:0]
		for _, rr := range dns.answer {
			if _, justHeader := rr.(*dnsRR_Header); justHeader {
				// Corrupt record: we only have a
				// header. That header might say it's
				// of type qtype, but we don't
				// actually have it. Skip.
				continue
			}
			h := rr.Header()
			if h.Class == dnsClassINET && h.Name == name {
				switch h.Rrtype {
				case qtype:
					addrs = append(addrs, rr)
				case dnsTypeCNAME:
					// redirect to cname
					name = rr.(*dnsRR_CNAME).Cname
					continue Cname
				}
			}
		}
		if len(addrs) == 0 {
			return "", nil, &DNSError{Error: noSuchHost, Name: name, Server: server}
		}
		return name, addrs, nil
	}

	return "", nil, &DNSError{Error: "too many redirects", Name: name, Server: server}
}

func isDomainName(s string) bool {
	// See RFC 1035, RFC 3696.
	if len(s) == 0 {
		return false
	}
	if len(s) > 255 {
		return false
	}
	if s[len(s)-1] != '.' { // simplify checking loop: make name end in dot
		s += "."
	}

	last := byte('.')
	ok := false // ok once we've seen a letter
	partlen := 0
	for i := 0; i < len(s); i++ {
		c := s[i]
		switch {
		default:
			return false
		case 'a' <= c && c <= 'z' || 'A' <= c && c <= 'Z' || c == '_':
			ok = true
			partlen++
		case '0' <= c && c <= '9':
			// fine
			partlen++
		case c == '-':
			// byte before dash cannot be dot
			if last == '.' {
				return false
			}
			partlen++
		case c == '.':
			// byte before dot cannot be dot, dash
			if last == '.' || last == '-' {
				return false
			}
			if partlen > 63 || partlen == 0 {
				return false
			}
			partlen = 0
		}
		last = c
	}

	return ok
}

// An SRV represents a single DNS SRV record.
type SRV struct {
	Target   string
	Port     uint16
	Priority uint16
	Weight   uint16
}

// byPriorityWeight sorts SRV records by ascending priority and weight.
type byPriorityWeight []*SRV

func (s byPriorityWeight) Len() int { return len(s) }

func (s byPriorityWeight) Swap(i, j int) { s[i], s[j] = s[j], s[i] }

func (s byPriorityWeight) Less(i, j int) bool {
	return s[i].Priority < s[j].Priority ||
		(s[i].Priority == s[j].Priority && s[i].Weight < s[j].Weight)
}

// shuffleByWeight shuffles SRV records by weight using the algorithm
// described in RFC 2782.  
func (addrs byPriorityWeight) shuffleByWeight() {
	sum := 0
	for _, addr := range addrs {
		sum += int(addr.Weight)
	}
	for sum > 0 && len(addrs) > 1 {
		s := 0
		n := rand.Intn(sum + 1)
		for i := range addrs {
			s += int(addrs[i].Weight)
			if s >= n {
				if i > 0 {
					t := addrs[i]
					copy(addrs[1:i+1], addrs[0:i])
					addrs[0] = t
				}
				break
			}
		}
		sum -= int(addrs[0].Weight)
		addrs = addrs[1:]
	}
}

// sort reorders SRV records as specified in RFC 2782.
func (addrs byPriorityWeight) sort() {
	sort.Sort(addrs)
	i := 0
	for j := 1; j < len(addrs); j++ {
		if addrs[i].Priority != addrs[j].Priority {
			addrs[i:j].shuffleByWeight()
			i = j
		}
	}
	addrs[i:].shuffleByWeight()
}

// An MX represents a single DNS MX record.
type MX struct {
	Host string
	Pref uint16
}

// byPref implements sort.Interface to sort MX records by preference
type byPref []*MX

func (s byPref) Len() int { return len(s) }

func (s byPref) Less(i, j int) bool { return s[i].Pref < s[j].Pref }

func (s byPref) Swap(i, j int) { s[i], s[j] = s[j], s[i] }

// sort reorders MX records as specified in RFC 5321.
func (s byPref) sort() {
	for i := range s {
		j := rand.Intn(i + 1)
		s[i], s[j] = s[j], s[i]
	}
	sort.Sort(s)
}