197 lines
6.3 KiB
C
197 lines
6.3 KiB
C
/* $Id$ */
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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 "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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/* 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_mkquery(const char *name, int dnsclass, int type, unsigned short id,
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int rd, unsigned char **buf, int *buflen)
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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;
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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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/* 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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return ARES_SUCCESS;
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}
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