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
|
.\"
.\" Copyright 1998 by the Massachusetts Institute of Technology.
.\"
.\" Permission to use, copy, modify, and distribute this
.\" software and its documentation for any purpose and without
.\" fee is hereby granted, provided that the above copyright
.\" notice appear in all copies and that both that copyright
.\" notice and this permission notice appear in supporting
.\" documentation, and that the name of M.I.T. not be used in
.\" advertising or publicity pertaining to distribution of the
.\" software without specific, written prior permission.
.\" M.I.T. makes no representations about the suitability of
.\" this software for any purpose. It is provided "as is"
.\" without express or implied warranty.
.\"
.TH ARES_GETADDRINFO 3 "4 November 2018"
.SH NAME
ares_getaddrinfo \- Initiate a host query by name and service
.SH SYNOPSIS
.nf
.B #include <ares.h>
.PP
.B typedef void (*ares_addrinfo_callback)(void *\fIarg\fP, int \fIstatus\fP,
.B int \fItimeouts\fP, struct ares_addrinfo *\fIresult\fP)
.PP
.B void ares_getaddrinfo(ares_channel \fIchannel\fP, const char *\fIname\fP,
.B const char* \fIservice\fP, const struct ares_addrinfo_hints *\fIhints\fP,
.B ares_addrinfo_callback \fIcallback\fP, void *\fIarg\fP)
.fi
.SH DESCRIPTION
The
.B ares_getaddrinfo
function initiates a host query by name on the name service channel
identified by
.IR channel .
The
.I name
and
.I service
parameters give the hostname and service as NULL-terminated C strings.
The
.I hints
parameter is an
.BR ares_addrinfo_hints
structure:
.PP
.RS
.EX
struct ares_addrinfo_hints {
int ai_flags;
int ai_family;
int ai_socktype;
int ai_protocol;
};
.EE
.RE
.TP
.I ai_family
Specifies desired address family. AF_UNSPEC means return both AF_INET and AF_INET6.
.TP
.I ai_socktype
Specifies desired socket type, for example SOCK_STREAM or SOCK_DGRAM.
Setting this to 0 means any type.
.TP
.I ai_protocol
Setting this to 0 means any protocol.
.TP
.I ai_flags
Specifies additional options, see below.
.PP
.TP 19
.B ARES_AI_NUMERICSERV
If this option is set
.I service
field will be treated as a numeric value.
.TP 19
.B ARES_AI_CANONNAME
The ares_addrinfo structure will return a canonical names list.
.TP 19
.B ARES_AI_NOSORT
Result addresses will not be sorted and no connections to resolved addresses will be attempted.
.TP 19
.B ARES_AI_ENVHOSTS
Read hosts file path from the environment variable
.I CARES_HOSTS .
.PP
When the query is complete or has failed, the ares library will invoke \fIcallback\fP.
Completion or failure of the query may happen immediately, or may happen
during a later call to \fIares_process(3)\fP, \fIares_destroy(3)\fP or
\fIares_cancel(3)\fP.
.PP
The callback argument
.I arg
is copied from the
.B ares_getaddrinfo
argument
.IR arg .
The callback argument
.I status
indicates whether the query succeeded and, if not, how it failed. It
may have any of the following values:
.TP 19
.B ARES_SUCCESS
The host lookup completed successfully.
.TP 19
.B ARES_ENOTIMP
The ares library does not know how to find addresses of type
.IR family .
.TP 19
.B ARES_ENOTFOUND
The
.I name
was not found.
.TP 19
.B ARES_ENOMEM
Memory was exhausted.
.TP 19
.B ARES_ECANCELLED
The query was cancelled.
.TP 19
.B ARES_EDESTRUCTION
The name service channel
.I channel
is being destroyed; the query will not be completed.
.PP
On successful completion of the query, the callback argument
.I result
points to a
.B struct ares_addrinfo
which contains two linked lists, one with resolved addresses and another with canonical names.
.PP
.RS
.EX
struct ares_addrinfo {
struct ares_addrinfo_cname *cnames;
struct ares_addrinfo_node *nodes;
};
.EE
.RE
.PP
.I ares_addrinfo_node
structure is similar to RFC3493 addrinfo, but without canonname and with extra ttl field.
.RS
.PP
.EX
struct ares_addrinfo_node {
int ai_ttl;
int ai_flags;
int ai_family;
int ai_socktype;
int ai_protocol;
ares_socklen_t ai_addrlen;
struct sockaddr *ai_addr;
struct ares_addrinfo_node *ai_next;
};
.EE
.RE
.PP
.I ares_addrinfo_cname
structure is a linked list of CNAME records where
.I ttl
is a time to live
.I alias
is a label of the resource record and
.I name
is a value (canonical name) of the resource record.
See RFC2181 10.1.1. CNAME terminology.
.RS
.PP
.EX
struct ares_addrinfo_cname {
int ttl;
char *alias;
char *name;
struct ares_addrinfo_cname *next;
};
.EE
.RE
.PP
The reserved memory has to be deleted by
.B ares_freeaddrinfo.
The result is sorted according to RFC6724 except:
- Rule 3 (Avoid deprecated addresses)
- Rule 4 (Prefer home addresses)
- Rule 7 (Prefer native transport)
Please note that the function will attempt a connection
on each of the resolved addresses as per RFC6724.
.SH SEE ALSO
.BR ares_freeaddrinfo (3)
.SH AUTHOR
Christian Ammer
.br
Andrew Selivanov <andrew.selivanov@gmail.com>
|
