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1 .\"
2 .\" Copyright 1998 by the Massachusetts Institute of Technology.
3 .\" SPDX-License-Identifier: MIT
4 .\"
5 .TH ARES_SEARCH 3 "24 July 1998"
6 .SH NAME
7 ares_search \- Initiate a DNS query with domain search
8 .SH SYNOPSIS
9 .nf
10 #include <ares.h>
11
12 typedef void (*ares_callback_dnsrec)(void *\fIarg\fP,
13 ares_status_t \fIstatus\fP,
14 size_t \fItimeouts\fP,
15 const ares_dns_record_t *\fIdnsrec\fP);
16
17 void ares_search_dnsrec(ares_channel_t *\fIchannel\fP,
18 const ares_dns_record_t *\fIdnsrec\fP,
19 ares_callback_dnsrec \fIcallback\fP, void *\fIarg\fP);
20
21 typedef void (*ares_callback)(void *\fIarg\fP, int \fIstatus\fP,
22 int \fItimeouts\fP, unsigned char *\fIabuf\fP,
23 int \fIalen\fP);
24
25 void ares_search(ares_channel_t *\fIchannel\fP, const char *\fIname\fP,
26 int \fIdnsclass\fP, int \fItype\fP,
27 ares_callback \fIcallback\fP, void *\fIarg\fP);
28
29 .fi
30 .SH DESCRIPTION
31 The
32 .B ares_search
33 function initiates a series of single-question DNS queries on the name
34 service channel identified by
35 .IR channel ,
36 using the channel's search domains as well as a host alias file given
37 by the HOSTALIAS environment variable. The parameter
38 .I name
39 gives the alias name or the base of the query name as a NUL-terminated
40 C string of period-separated labels; if it ends with a period, the
41 channel's search domains will not be used. Periods and backslashes
42 within a label must be escaped with a backslash. The parameters
43 .I dnsclass
44 and
45 .I type
46 give the class and type of the query using the values defined in
47 .BR <arpa/nameser.h> .
48 When the query sequence is complete or has failed, the ares library
49 will invoke
50 .IR callback .
51 Completion or failure of the query sequence may happen immediately, or
52 may happen during a later call to
53 .BR ares_process (3)
54 or
55 .BR ares_destroy (3).
56 .PP
57 If this is called from a thread other than which the main program event loop is
58 running, care needs to be taken to ensure any file descriptor lists are updated
59 immediately within the eventloop. When the associated callback is called,
60 it is called with a channel lock so care must be taken to ensure any processing
61 is minimal to prevent DNS channel stalls.
62 .PP
63 The callback argument
64 .I arg
65 is copied from the
66 .B ares_search
67 argument
68 .IR arg .
69 The callback argument
70 .I status
71 indicates whether the query sequence ended with a successful query
72 and, if not, how the query sequence failed. It may have any of the
73 following values:
74 .TP 19
75 .B ARES_SUCCESS
76 A query completed successfully.
77 .TP 19
78 .B ARES_ENODATA
79 No query completed successfully; when the query was tried without a
80 search domain appended, a response was returned with no answers.
81 .TP 19
82 .B ARES_EFORMERR
83 A query completed but the server claimed that the query was
84 malformatted.
85 .TP 19
86 .B ARES_ESERVFAIL
87 No query completed successfully; when the query was tried without a
88 search domain appended, the server claimed to have experienced a
89 failure. (This code can only occur if the
90 .B ARES_FLAG_NOCHECKRESP
91 flag was specified at channel initialization time; otherwise, such
92 responses are ignored at the
93 .BR ares_send (3)
94 level.)
95 .TP 19
96 .B ARES_ENOTFOUND
97 No query completed successfully; when the query was tried without a
98 search domain appended, the server reported that the queried-for
99 domain name was not found.
100 .TP 19
101 .B ARES_ENOTIMP
102 A query completed but the server does not implement the operation
103 requested by the query. (This code can 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
107 .BR ares_send (3)
108 level.)
109 .TP 19
110 .B ARES_EREFUSED
111 A query completed but the server refused the query. (This code can
112 only occur returned if the
113 .B ARES_FLAG_NOCHECKRESP
114 flag was specified at channel initialization time; otherwise, such
115 responses are ignored at the
116 .BR ares_send (3)
117 level.)
118 .TP 19
119 .B ARES_TIMEOUT
120 No name servers responded to a query within the timeout period.
121 .TP 19
122 .B ARES_ECONNREFUSED
123 No name servers could be contacted.
124 .TP 19
125 .B ARES_ENOMEM
126 Memory was exhausted.
127 .TP 19
128 .B ARES_ECANCELLED
129 The query was cancelled.
130 .TP 19
131 .B ARES_EDESTRUCTION
132 The name service channel
133 .I channel
134 is being destroyed; the query will not be completed.
135 .TP 19
136 .B ARES_ENOSERVER
137 No query completed successfully; no DNS servers were configured on the channel.
138 .PP
139 The callback argument
140 .I timeouts
141 reports how many times a query timed out during the execution of the
142 given request.
143 .PP
144 If a query completed successfully, the callback argument
145 .I abuf
146 points to a result buffer of length
147 .IR alen .
148 If the query did not complete successfully,
149 .I abuf
150 will usually be NULL and
151 .I alen
152 will usually be 0, but in some cases an unsuccessful query result may
153 be placed in
154 .IR abuf .
155
156 The \fIares_search_dnsrec(3)\fP function behaves identically to
157 \fIares_search(3)\fP, but takes an initialized and filled DNS record object to
158 use for queries as the second argument
159 .I dnsrec
160 instead of a name, class and type. This object is used as the base for the
161 queries and must itself represent a valid query for a single name. Note that
162 the search domains will only be appended to the name in the question section;
163 RRs on the DNS record object will not be affected. Moreover, the
164 .I callback
165 argument is of type \fIares_callback_dnsrec\fP. This callback behaves
166 identically to \fIares_callback\fP, but is invoked with a parsed DNS record
167 object
168 .I dnsrec
169 rather than a raw buffer with length. Note that this object is read-only.
170
171 The \fIares_search_dnsrec(3)\fP function returns an \fIares_status_t\fP response
172 code. This may be useful to know that the query was enqueued properly. The
173 response code does not reflect the result of the query, just the result of the
174 enqueuing of the query.
175
176 .SH AVAILABILITY
177 \fBares_search_dnsrec(3)\fP was introduced in c-ares 1.28.0.
178
179 .SH SEE ALSO
180 .BR ares_process (3),
181 .BR ares_dns_record (3)