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213 lines
6.7 KiB
213 lines
6.7 KiB
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/* Copyright 1998 by the Massachusetts Institute of Technology. |
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* |
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* Permission to use, copy, modify, and distribute this |
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* software and its documentation for any purpose and without |
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* fee is hereby granted, provided that the above copyright |
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* notice appear in all copies and that both that copyright |
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* notice and this permission notice appear in supporting |
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* documentation, and that the name of M.I.T. not be used in |
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* advertising or publicity pertaining to distribution of the |
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* software without specific, written prior permission. |
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* M.I.T. makes no representations about the suitability of |
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* this software for any purpose. It is provided "as is" |
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* without express or implied warranty. |
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*/ |
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#include "ares_setup.h" |
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#ifdef HAVE_SYS_SOCKET_H |
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# include <sys/socket.h> |
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#endif |
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#ifdef HAVE_NETINET_IN_H |
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# include <netinet/in.h> |
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#endif |
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#ifdef HAVE_ARPA_NAMESER_H |
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# include <arpa/nameser.h> |
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#else |
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# include "nameser.h" |
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#endif |
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#ifdef HAVE_ARPA_NAMESER_COMPAT_H |
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# include <arpa/nameser_compat.h> |
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#endif |
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#include <stdlib.h> |
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#include <string.h> |
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#include "ares.h" |
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#include "ares_dns.h" |
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#include "ares_private.h" |
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#ifndef T_OPT |
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# define T_OPT 41 /* EDNS0 option (meta-RR) */ |
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#endif |
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/* Header format, from RFC 1035: |
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* 1 1 1 1 1 1 |
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* 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 |
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* +--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+ |
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* | ID | |
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* +--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+ |
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* |QR| Opcode |AA|TC|RD|RA| Z | RCODE | |
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* +--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+ |
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* | QDCOUNT | |
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* +--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+ |
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* | ANCOUNT | |
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* +--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+ |
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* | NSCOUNT | |
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* +--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+ |
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* | ARCOUNT | |
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* +--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+ |
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* |
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* AA, TC, RA, and RCODE are only set in responses. Brief description |
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* of the remaining fields: |
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* ID Identifier to match responses with queries |
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* QR Query (0) or response (1) |
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* Opcode For our purposes, always QUERY |
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* RD Recursion desired |
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* Z Reserved (zero) |
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* QDCOUNT Number of queries |
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* ANCOUNT Number of answers |
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* NSCOUNT Number of name server records |
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* ARCOUNT Number of additional records |
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* |
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* Question format, from RFC 1035: |
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* 1 1 1 1 1 1 |
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* 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 |
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* +--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+ |
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* | | |
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* / QNAME / |
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* / / |
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* +--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+ |
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* | QTYPE | |
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* +--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+ |
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* | QCLASS | |
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* +--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+ |
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* |
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* The query name is encoded as a series of labels, each represented |
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* as a one-byte length (maximum 63) followed by the text of the |
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* label. The list is terminated by a label of length zero (which can |
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* be thought of as the root domain). |
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*/ |
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int ares_create_query(const char *name, int dnsclass, int type, |
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unsigned short id, int rd, unsigned char **buf, |
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int *buflen, int max_udp_size) |
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{ |
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int len; |
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unsigned char *q; |
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const char *p; |
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/* Set our results early, in case we bail out early with an error. */ |
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*buflen = 0; |
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*buf = NULL; |
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/* Compute the length of the encoded name so we can check buflen. |
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* Start counting at 1 for the zero-length label at the end. */ |
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len = 1; |
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for (p = name; *p; p++) |
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{ |
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if (*p == '\\' && *(p + 1) != 0) |
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p++; |
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len++; |
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} |
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/* If there are n periods in the name, there are n + 1 labels, and |
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* thus n + 1 length fields, unless the name is empty or ends with a |
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* period. So add 1 unless name is empty or ends with a period. |
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*/ |
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if (*name && *(p - 1) != '.') |
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len++; |
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/* Immediately reject names that are longer than the maximum of 255 |
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* bytes that's specified in RFC 1035 ("To simplify implementations, |
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* the total length of a domain name (i.e., label octets and label |
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* length octets) is restricted to 255 octets or less."). We aren't |
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* doing this just to be a stickler about RFCs. For names that are |
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* too long, 'dnscache' closes its TCP connection to us immediately |
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* (when using TCP) and ignores the request when using UDP, and |
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* BIND's named returns ServFail (TCP or UDP). Sending a request |
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* that we know will cause 'dnscache' to close the TCP connection is |
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* painful, since that makes any other outstanding requests on that |
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* connection fail. And sending a UDP request that we know |
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* 'dnscache' will ignore is bad because resources will be tied up |
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* until we time-out the request. |
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*/ |
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if (len > MAXCDNAME) |
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return ARES_EBADNAME; |
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*buflen = len + HFIXEDSZ + QFIXEDSZ + (max_udp_size ? EDNSFIXEDSZ : 0); |
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*buf = malloc(*buflen); |
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if (!*buf) |
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return ARES_ENOMEM; |
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/* Set up the header. */ |
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q = *buf; |
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memset(q, 0, HFIXEDSZ); |
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DNS_HEADER_SET_QID(q, id); |
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DNS_HEADER_SET_OPCODE(q, QUERY); |
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if (rd) { |
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DNS_HEADER_SET_RD(q, 1); |
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} |
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else { |
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DNS_HEADER_SET_RD(q, 0); |
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} |
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DNS_HEADER_SET_QDCOUNT(q, 1); |
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if (max_udp_size) { |
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DNS_HEADER_SET_ARCOUNT(q, 1); |
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} |
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/* A name of "." is a screw case for the loop below, so adjust it. */ |
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if (strcmp(name, ".") == 0) |
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name++; |
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/* Start writing out the name after the header. */ |
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q += HFIXEDSZ; |
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while (*name) |
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{ |
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if (*name == '.') |
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return ARES_EBADNAME; |
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/* Count the number of bytes in this label. */ |
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len = 0; |
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for (p = name; *p && *p != '.'; p++) |
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{ |
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if (*p == '\\' && *(p + 1) != 0) |
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p++; |
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len++; |
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} |
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if (len > MAXLABEL) |
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return ARES_EBADNAME; |
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/* Encode the length and copy the data. */ |
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*q++ = (unsigned char)len; |
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for (p = name; *p && *p != '.'; p++) |
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{ |
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if (*p == '\\' && *(p + 1) != 0) |
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p++; |
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*q++ = *p; |
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} |
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/* Go to the next label and repeat, unless we hit the end. */ |
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if (!*p) |
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break; |
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name = p + 1; |
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} |
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/* Add the zero-length label at the end. */ |
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*q++ = 0; |
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/* Finish off the question with the type and class. */ |
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DNS_QUESTION_SET_TYPE(q, type); |
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DNS_QUESTION_SET_CLASS(q, dnsclass); |
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if (max_udp_size) |
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{ |
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q += QFIXEDSZ; |
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memset(q, 0, EDNSFIXEDSZ); |
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q++; |
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DNS_RR_SET_TYPE(q, T_OPT); |
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DNS_RR_SET_CLASS(q, max_udp_size); |
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} |
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return ARES_SUCCESS; |
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}
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