ares_query.3 (5013B)
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)