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1 .\"
2 .\" Copyright 1998 by the Massachusetts Institute of Technology.
3 .\" SPDX-License-Identifier: MIT
4 .\"
5 .TH ARES_QUERY 3 "24 July 1998"
6 .SH NAME
7 ares_query \- Initiate a single-question DNS query
8 .SH SYNOPSIS
9 .nf
10 #include <ares.h>
11
12 typedef void (*ares_callback_dnsrec)(void *arg, ares_status_t status,
13 size_t timeouts,
14 const ares_dns_record_t *dnsrec);
15
16 ares_status_t ares_query_dnsrec(ares_channel_t *channel,
17 const char *name,
18 ares_dns_class_t dnsclass,
19 ares_dns_rec_type_t type,
20 ares_callback_dnsrec callback,
21 void *arg,
22 unsigned short *qid);
23
24 typedef void (*ares_callback)(void *arg, int status,
25 int timeouts, unsigned char *abuf,
26 int alen);
27
28 void ares_query(ares_channel_t *channel, const char *name,
29 int dnsclass, int type,
30 ares_callback callback, void *arg);
31
32 .fi
33
34 .SH DESCRIPTION
35
36 The \fBares_query_dnsrec(3)\fP and \fBares_query(3)\fP functions initiate a
37 single-question DNS query on the name service channel identified by
38 .IR channel .
39 The parameter
40 .I name
41 gives the query name as a NUL-terminated C string of period-separated
42 labels optionally ending with a period; periods and backslashes within
43 a label must be escaped with a backslash. The parameters
44 .I dnsclass
45 and
46 .I type
47 give the class and type of the query.
48
49 \fBares_query_dnsrec(3)\fP uses the ares \fBares_dns_class_t\fP and
50 \fBares_dns_rec_type_t\fP defined types. However, \fBares_query(3)\fP uses
51 the values defined in \fB<arpa/nameser.h>\fP.
52
53 When the query is complete or has failed, the ares library will invoke
54 .IR callback .
55 Completion or failure of the query may happen immediately (even before the
56 return of the function call), or may happen during a later call to
57 \fBares_process(3)\fP or \fBares_destroy(3)\fP.
58
59 If this is called from a thread other than which the main program event loop is
60 running, care needs to be taken to ensure any file descriptor lists are updated
61 immediately within the eventloop. When the associated callback is called,
62 it is called with a channel lock so care must be taken to ensure any processing
63 is minimal to prevent DNS channel stalls.
64
65 The callback argument
66 .I arg
67 is copied from the \fBares_query_dnsrec(3)\fP or \fBares_query(3)\fP argument
68 .IR arg .
69 The callback argument
70 .I status
71 indicates whether the query succeeded and, if not, how it failed. It
72 may have any of the following values:
73 .TP 19
74 .B ARES_SUCCESS
75 The query completed successfully.
76 .TP 19
77 .B ARES_ENODATA
78 The query completed but contains no answers.
79 .TP 19
80 .B ARES_EFORMERR
81 The query completed but the server claims that the query was
82 malformatted.
83 .TP 19
84 .B ARES_ESERVFAIL
85 The query completed but the server claims to have experienced a
86 failure. (This code can only occur if the
87 .B ARES_FLAG_NOCHECKRESP
88 flag was specified at channel initialization time; otherwise, such
89 responses are ignored at the \fBares_send_dnsrec(3)\fP level.)
90 .TP 19
91 .B ARES_ENOTFOUND
92 The query completed but the queried-for domain name was not found.
93 .TP 19
94 .B ARES_ENOTIMP
95 The query completed but the server does not implement the operation
96 requested by the query. (This code can only occur if the
97 .B ARES_FLAG_NOCHECKRESP
98 flag was specified at channel initialization time; otherwise, such
99 responses are ignored at the \fBares_send_dnsrec(3)\fP level.)
100 .TP 19
101 .B ARES_EREFUSED
102 The query completed but the server refused the query. (This code can
103 only occur if the
104 .B ARES_FLAG_NOCHECKRESP
105 flag was specified at channel initialization time; otherwise, such
106 responses are ignored at the \fBares_send_dnsrec(3)\fP level.)
107 .TP 19
108 .B ARES_EBADNAME
109 The query name
110 .I name
111 could not be encoded as a domain name, either because it contained a
112 zero-length label or because it contained a label of more than 63
113 characters.
114 .TP 19
115 .B ARES_ETIMEOUT
116 No name servers responded within the timeout period.
117 .TP 19
118 .B ARES_ECONNREFUSED
119 No name servers could be contacted.
120 .TP 19
121 .B ARES_ENOMEM
122 Memory was exhausted.
123 .TP 19
124 .B ARES_ECANCELLED
125 The query was cancelled.
126 .TP 19
127 .B ARES_EDESTRUCTION
128 The name service channel
129 .I channel
130 is being destroyed; the query will not be completed.
131 .TP 19
132 .B ARES_ENOSERVER
133 The query will not be completed because no DNS servers were configured on the
134 channel.
135 .PP
136
137 The callback argument
138 .I timeouts
139 reports how many times a query timed out during the execution of the
140 given request.
141
142 If the query completed (even if there was something wrong with it, as
143 indicated by some of the above error codes), the callback argument
144 .I dnsrec
145 or
146 .I abuf
147 will be non-NULL, otherwise they will be NULL.
148
149 .SH AVAILABILITY
150 \fBares_query_dnsrec(3)\fP was introduced in c-ares 1.28.0.
151
152 .SH SEE ALSO
153 .BR ares_process (3),
154 .BR ares_dns_record (3)