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
|
// Copyright 2012 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 (
"internal/singleflight"
"time"
)
// protocols contains minimal mappings between internet protocol
// names and numbers for platforms that don't have a complete list of
// protocol numbers.
//
// See http://www.iana.org/assignments/protocol-numbers
var protocols = map[string]int{
"icmp": 1, "ICMP": 1,
"igmp": 2, "IGMP": 2,
"tcp": 6, "TCP": 6,
"udp": 17, "UDP": 17,
"ipv6-icmp": 58, "IPV6-ICMP": 58, "IPv6-ICMP": 58,
}
// LookupHost looks up the given host using the local resolver.
// It returns an array of that host's addresses.
func LookupHost(host string) (addrs []string, err error) {
// Make sure that no matter what we do later, host=="" is rejected.
// ParseIP, for example, does accept empty strings.
if host == "" {
return nil, &DNSError{Err: errNoSuchHost.Error(), Name: host}
}
if ip := ParseIP(host); ip != nil {
return []string{host}, nil
}
return lookupHost(host)
}
// LookupIP looks up host using the local resolver.
// It returns an array of that host's IPv4 and IPv6 addresses.
func LookupIP(host string) (ips []IP, err error) {
// Make sure that no matter what we do later, host=="" is rejected.
// ParseIP, for example, does accept empty strings.
if host == "" {
return nil, &DNSError{Err: errNoSuchHost.Error(), Name: host}
}
if ip := ParseIP(host); ip != nil {
return []IP{ip}, nil
}
addrs, err := lookupIPMerge(host)
if err != nil {
return
}
ips = make([]IP, len(addrs))
for i, addr := range addrs {
ips[i] = addr.IP
}
return
}
var lookupGroup singleflight.Group
// lookupIPMerge wraps lookupIP, but makes sure that for any given
// host, only one lookup is in-flight at a time. The returned memory
// is always owned by the caller.
func lookupIPMerge(host string) (addrs []IPAddr, err error) {
addrsi, err, shared := lookupGroup.Do(host, func() (interface{}, error) {
return testHookLookupIP(lookupIP, host)
})
return lookupIPReturn(addrsi, err, shared)
}
// lookupIPReturn turns the return values from singleflight.Do into
// the return values from LookupIP.
func lookupIPReturn(addrsi interface{}, err error, shared bool) ([]IPAddr, error) {
if err != nil {
return nil, err
}
addrs := addrsi.([]IPAddr)
if shared {
clone := make([]IPAddr, len(addrs))
copy(clone, addrs)
addrs = clone
}
return addrs, nil
}
// lookupIPDeadline looks up a hostname with a deadline.
func lookupIPDeadline(host string, deadline time.Time) (addrs []IPAddr, err error) {
if deadline.IsZero() {
return lookupIPMerge(host)
}
// We could push the deadline down into the name resolution
// functions. However, the most commonly used implementation
// calls getaddrinfo, which has no timeout.
timeout := deadline.Sub(time.Now())
if timeout <= 0 {
return nil, errTimeout
}
t := time.NewTimer(timeout)
defer t.Stop()
ch := lookupGroup.DoChan(host, func() (interface{}, error) {
return testHookLookupIP(lookupIP, host)
})
select {
case <-t.C:
// The DNS lookup timed out for some reason. Force
// future requests to start the DNS lookup again
// rather than waiting for the current lookup to
// complete. See issue 8602.
lookupGroup.Forget(host)
return nil, errTimeout
case r := <-ch:
return lookupIPReturn(r.Val, r.Err, r.Shared)
}
}
// LookupPort looks up the port for the given network and service.
func LookupPort(network, service string) (port int, err error) {
if service == "" {
// Lock in the legacy behavior that an empty string
// means port 0. See Issue 13610.
return 0, nil
}
port, _, ok := dtoi(service, 0)
if !ok && port != big && port != -big {
port, err = lookupPort(network, service)
if err != nil {
return 0, err
}
}
if 0 > port || port > 65535 {
return 0, &AddrError{Err: "invalid port", Addr: service}
}
return port, nil
}
// LookupCNAME returns the canonical DNS host for the given name.
// Callers that do not care about the canonical name can call
// LookupHost or LookupIP directly; both take care of resolving
// the canonical name as part of the lookup.
func LookupCNAME(name string) (cname string, err error) {
return lookupCNAME(name)
}
// LookupSRV tries to resolve an SRV query of the given service,
// protocol, and domain name. The proto is "tcp" or "udp".
// The returned records are sorted by priority and randomized
// by weight within a priority.
//
// LookupSRV constructs the DNS name to look up following RFC 2782.
// That is, it looks up _service._proto.name. To accommodate services
// publishing SRV records under non-standard names, if both service
// and proto are empty strings, LookupSRV looks up name directly.
func LookupSRV(service, proto, name string) (cname string, addrs []*SRV, err error) {
return lookupSRV(service, proto, name)
}
// LookupMX returns the DNS MX records for the given domain name sorted by preference.
func LookupMX(name string) (mxs []*MX, err error) {
return lookupMX(name)
}
// LookupNS returns the DNS NS records for the given domain name.
func LookupNS(name string) (nss []*NS, err error) {
return lookupNS(name)
}
// LookupTXT returns the DNS TXT records for the given domain name.
func LookupTXT(name string) (txts []string, err error) {
return lookupTXT(name)
}
// LookupAddr performs a reverse lookup for the given address, returning a list
// of names mapping to that address.
func LookupAddr(addr string) (names []string, err error) {
return lookupAddr(addr)
}
|
