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/* Copyright 1998 by the Massachusetts Institute of Technology.
*
* Permission to use, copy, modify, and distribute this
* software and its documentation for any purpose and without
* fee is hereby granted, provided that the above copyright
* notice appear in all copies and that both that copyright
* notice and this permission notice appear in supporting
* documentation, and that the name of M.I.T. not be used in
* advertising or publicity pertaining to distribution of the
* software without specific, written prior permission.
* M.I.T. makes no representations about the suitability of
* this software for any purpose. It is provided "as is"
* without express or implied warranty.
*/
#include "ares_setup.h"
#ifdef HAVE_NETINET_IN_H
# include <netinet/in.h>
#endif
#include "ares_nameser.h"
#include "ares.h"
#include "ares_dns.h"
#include "ares_private.h"
/* Header format, from RFC 1035:
* 1 1 1 1 1 1
* 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5
* +--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+
* | ID |
* +--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+
* |QR| Opcode |AA|TC|RD|RA| Z | RCODE |
* +--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+
* | QDCOUNT |
* +--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+
* | ANCOUNT |
* +--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+
* | NSCOUNT |
* +--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+
* | ARCOUNT |
* +--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+
*
* AA, TC, RA, and RCODE are only set in responses. Brief description
* of the remaining fields:
* ID Identifier to match responses with queries
* QR Query (0) or response (1)
* Opcode For our purposes, always O_QUERY
* RD Recursion desired
* Z Reserved (zero)
* QDCOUNT Number of queries
* ANCOUNT Number of answers
* NSCOUNT Number of name server records
* ARCOUNT Number of additional records
*
* Question format, from RFC 1035:
* 1 1 1 1 1 1
* 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5
* +--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+
* | |
* / QNAME /
* / /
* +--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+
* | QTYPE |
* +--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+
* | QCLASS |
* +--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+
*
* The query name is encoded as a series of labels, each represented
* as a one-byte length (maximum 63) followed by the text of the
* label. The list is terminated by a label of length zero (which can
* be thought of as the root domain).
*/
int ares_create_query(const char *name, int dnsclass, int type,
unsigned short id, int rd, unsigned char **bufp,
int *buflenp, int max_udp_size)
{
size_t len;
unsigned char *q;
const char *p;
size_t buflen;
unsigned char *buf;
/* Set our results early, in case we bail out early with an error. */
*buflenp = 0;
*bufp = NULL;
/* Per RFC 7686, reject queries for ".onion" domain names with NXDOMAIN. */
if (ares__is_onion_domain(name))
return ARES_ENOTFOUND;
/* Allocate a memory area for the maximum size this packet might need. +2
* is for the length byte and zero termination if no dots or ecscaping is
* used.
*/
len = strlen(name) + 2 + HFIXEDSZ + QFIXEDSZ +
(max_udp_size ? EDNSFIXEDSZ : 0);
buf = ares_malloc(len);
if (!buf)
return ARES_ENOMEM;
/* Set up the header. */
q = buf;
memset(q, 0, HFIXEDSZ);
DNS_HEADER_SET_QID(q, id);
DNS_HEADER_SET_OPCODE(q, O_QUERY);
if (rd) {
DNS_HEADER_SET_RD(q, 1);
}
else {
DNS_HEADER_SET_RD(q, 0);
}
DNS_HEADER_SET_QDCOUNT(q, 1);
if (max_udp_size) {
DNS_HEADER_SET_ARCOUNT(q, 1);
}
/* A name of "." is a screw case for the loop below, so adjust it. */
if (strcmp(name, ".") == 0)
name++;
/* Start writing out the name after the header. */
q += HFIXEDSZ;
while (*name)
{
if (*name == '.') {
ares_free (buf);
return ARES_EBADNAME;
}
/* Count the number of bytes in this label. */
len = 0;
for (p = name; *p && *p != '.'; p++)
{
if (*p == '\\' && *(p + 1) != 0)
p++;
len++;
}
if (len > MAXLABEL) {
ares_free (buf);
return ARES_EBADNAME;
}
/* Encode the length and copy the data. */
*q++ = (unsigned char)len;
for (p = name; *p && *p != '.'; p++)
{
if (*p == '\\' && *(p + 1) != 0)
p++;
*q++ = *p;
}
/* Go to the next label and repeat, unless we hit the end. */
if (!*p)
break;
name = p + 1;
}
/* Add the zero-length label at the end. */
*q++ = 0;
/* Finish off the question with the type and class. */
DNS_QUESTION_SET_TYPE(q, type);
DNS_QUESTION_SET_CLASS(q, dnsclass);
q += QFIXEDSZ;
if (max_udp_size)
{
memset(q, 0, EDNSFIXEDSZ);
q++;
DNS_RR_SET_TYPE(q, T_OPT);
DNS_RR_SET_CLASS(q, max_udp_size);
q += (EDNSFIXEDSZ-1);
}
buflen = (q - buf);
/* Reject names that are longer than the maximum of 255 bytes that's
* specified in RFC 1035 ("To simplify implementations, the total length of
* a domain name (i.e., label octets and label length octets) is restricted
* to 255 octets or less."). */
if (buflen > (size_t)(MAXCDNAME + HFIXEDSZ + QFIXEDSZ +
(max_udp_size ? EDNSFIXEDSZ : 0))) {
ares_free (buf);
return ARES_EBADNAME;
}
/* we know this fits in an int at this point */
*buflenp = (int) buflen;
*bufp = buf;
return ARES_SUCCESS;
}
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