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1 .\"
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2 .\" Copyright 1998 by the Massachusetts Institute of Technology.
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3 .\" SPDX-License-Identifier: MIT
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4 .\"
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5 .TH ARES_SEND 3 "25 July 1998"
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6 .SH NAME
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7 ares_send \- Initiate a DNS query
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8 .SH SYNOPSIS
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9 .nf
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10 #include <ares.h>
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11
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12 typedef void (*ares_callback_dnsrec)(void *arg, ares_status_t status,
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13 size_t timeouts,
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14 const ares_dns_record_t *dnsrec);
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15
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16 ares_status_t ares_send_dnsrec(ares_channel_t *channel,
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17 const ares_dns_record_t *dnsrec,
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18 ares_callback_dnsrec callback,
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19 void *arg, unsigned short *qid);
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20
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21 typedef void (*ares_callback)(void *arg, int status,
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22 int timeouts, unsigned char *abuf,
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23 int alen);
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24
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25 void ares_send(ares_channel_t *channel, const unsigned char *qbuf,
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26 int qlen, ares_callback callback, void *arg);
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27
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28 .fi
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29 .SH DESCRIPTION
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30 The \fIares_send_dnsrec(3)\fP function initiates a DNS query formatted using the
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31 \fIares_dns_record_t *\fP data structure created via
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32 \fIares_dns_record_create(3)\fP in the
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33 .IR dnsrec
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34 parameter. The supplied callback in the
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35 .IR callback
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36 parameter also returns the response using a
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37 \fIares_dns_record_t *\fP data structure.
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38
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39 The \fIares_send(3)\fP function similarly initiates a DNS query, but instead uses
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40 raw binary buffers with fully formatted DNS messages passed in the request via the
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41 .IR qbuf
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42 and
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43 .IR qlen
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44 parameters. The supplied callback in the
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45 .IR callback
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46 parameter also returns the raw binary DNS response in the
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47 .IR abuf
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48 and
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49 .IR alen
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50 parameters. This method should be considered deprecated in favor of
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51 \fIares_send_dnsrec(3)\fP.
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52
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53 Both functions take an initialized ares channel identified by
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54 .IR channel .
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55
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56 The \fIares_send_dnsrec(3)\fP also can be supplied an optional output parameter of
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57 .IR qid
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58 to populate the query id as it was placed on the wire.
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59
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60 The \fIares_send_dnsrec(3)\fP function returns an \fIares_status_t\fP response
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61 code. This may be useful to know that the query was enqueued properly. The
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62 response code does not reflect the result of the query, just the result of the
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63 enqueuing of the query.
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64
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65 Completion or failure of the query may happen immediately (even before the
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66 function returning), or may happen later as network events are processed.
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67
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68 When the associated callback is called, it is called with a channel lock so care
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69 must be taken to ensure any processing is minimal to prevent DNS channel stalls.
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70
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71 The callback may be triggered from a different thread than the one which
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72 called \fIares_send_dnsrec(3)\fP or \fIares_send(3)\fP.
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73
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74 For integrators running their own event loops and not using \fBARES_OPT_EVENT_THREAD\fP,
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75 care needs to be taken to ensure any file descriptor lists are updated immediately
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76 within the eventloop when notified.
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77
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78 The callback argument
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79 .IR arg
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80 is copied from the \fIares_send_dnsrec(3)\fP or \fIares_send(3)\fP
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81 .IR arg
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82 parameter.
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83
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84 The callback argument
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85 .I status
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86 indicates whether the query succeeded and, if not, how it failed. It
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87 may have any of the following values:
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88 .TP 19
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89 .B ARES_SUCCESS
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90 The query completed.
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91 .TP 19
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92 .B ARES_EBADQUERY
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93 The query buffer was poorly formed (was not long enough for a DNS
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94 header or was too long for TCP transmission).
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95 .TP 19
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96 .B ARES_ETIMEOUT
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97 No name servers responded within the timeout period.
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98 .TP 19
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99 .B ARES_ECONNREFUSED
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100 No name servers could be contacted.
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101 .TP 19
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102 .B ARES_ENOMEM
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103 Memory was exhausted.
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104 .TP 19
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105 .B ARES_ECANCELLED
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106 The query was cancelled.
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107 .TP 19
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108 .B ARES_EDESTRUCTION
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109 The name service channel
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110 .I channel
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111 is being destroyed; the query will not be completed.
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112 .TP 19
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113 .B ARES_ENOSERVER
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114 The query will not be completed because no DNS servers were configured on the
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115 channel.
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116 .TP 19
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117 .B ARES_EBADQUERY
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118 Misformatted DNS query.
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119 .PP
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120
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121 The callback argument
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122 .I timeouts
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123 reports how many times a query timed out during the execution of the
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124 given request.
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125
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126 If the query completed, the callback argument
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127 .IR dnsrec
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128 for \fIares_send_dnsrec(3)\fP or
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129 .IR abuf
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130 and
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131 .IR alen
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132 for \fIares_send(3)\fP will be non-NULL.
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133
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134 Unless the flag
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135 .B ARES_FLAG_NOCHECKRESP
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136 was set at channel initialization time, \fIares_send_dnsrec(3)\fP and
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137 \fIares_send(3)\fP will normally ignore responses whose questions do not match
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138 the supplied questions, as well as responses with reply codes of
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139 .BR SERVFAIL ,
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140 .BR NOTIMP ,
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141 and
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142 .BR REFUSED .
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143 Unlike other query functions in the ares library, however,
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144 \fIares_send_dnsrec(3)\fP and \fIares_send(3)\fP do not inspect the header of
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145 the reply packet to determine the error status, so a callback status of
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146 .B ARES_SUCCESS
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147 does not reflect as much about the response as for other query functions.
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148
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149 .SH AVAILABILITY
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150 \fBares_send_dnsrec(3)\fP was introduced in c-ares 1.28.0.
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151
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152 .SH SEE ALSO
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153 .BR ares_dns_record_create (3),
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154 .BR ares_process (3),
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155 .BR ares_search (3),
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156 .BR ares_dns_record (3)
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