/c-ares

Permalink
Switch branches/tags
Nothing to show
Find file
c-ares/ares_mkquery.c
Fetching contributors…
Cannot retrieve contributors at this time
Raw Blame History
196 lines (176 sloc) 6.33 KB
/* 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_SYS_SOCKET_H
# include <sys/socket.h>
#endif
#ifdef HAVE_NETINET_IN_H
# include <netinet/in.h>
#endif
#ifdef HAVE_ARPA_NAMESER_H
# include <arpa/nameser.h>
#else
# include "nameser.h"
#endif
#ifdef HAVE_ARPA_NAMESER_COMPAT_H
# include <arpa/nameser_compat.h>
#endif
#include <stdlib.h>
#include <string.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 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_mkquery(const char *name, int dnsclass, int type, unsigned short id,
int rd, unsigned char **buf, int *buflen)
{
int len;
unsigned char *q;
const char *p;
/* Set our results early, in case we bail out early with an error. */
*buflen = 0;
*buf = NULL;
/* Compute the length of the encoded name so we can check buflen.
* Start counting at 1 for the zero-length label at the end. */
len = 1;
for (p = name; *p; p++)
{
if (*p == '\\' && *(p + 1) != 0)
p++;
len++;
}
/* If there are n periods in the name, there are n + 1 labels, and
* thus n + 1 length fields, unless the name is empty or ends with a
* period. So add 1 unless name is empty or ends with a period.
*/
if (*name && *(p - 1) != '.')
len++;
/* Immediately 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."). We aren't
* doing this just to be a stickler about RFCs. For names that are
* too long, 'dnscache' closes its TCP connection to us immediately
* (when using TCP) and ignores the request when using UDP, and
* BIND's named returns ServFail (TCP or UDP). Sending a request
* that we know will cause 'dnscache' to close the TCP connection is
* painful, since that makes any other outstanding requests on that
* connection fail. And sending a UDP request that we know
* 'dnscache' will ignore is bad because resources will be tied up
* until we time-out the request.
*/
if (len > MAXCDNAME)
return ARES_EBADNAME;
*buflen = len + HFIXEDSZ + QFIXEDSZ;
*buf = malloc(*buflen);
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, QUERY);
if (rd) {
DNS_HEADER_SET_RD(q, 1);
}
else {
DNS_HEADER_SET_RD(q, 0);
}
DNS_HEADER_SET_QDCOUNT(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 == '.')
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)
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);
return ARES_SUCCESS;
}