1 /* Copyright 1998 by the Massachusetts Institute of Technology.
2  *
3  * Permission to use, copy, modify, and distribute this
4  * software and its documentation for any purpose and without
5  * fee is hereby granted, provided that the above copyright
6  * notice appear in all copies and that both that copyright
7  * notice and this permission notice appear in supporting
8  * documentation, and that the name of M.I.T. not be used in
9  * advertising or publicity pertaining to distribution of the
10  * software without specific, written prior permission.
11  * M.I.T. makes no representations about the suitability of
12  * this software for any purpose.  It is provided "as is"
13  * without express or implied warranty.
14  */
15 
16 static const char rcsid[] = "$Id: ares_mkquery.c,v 1.3 2000/09/21 19:15:51 ghudson Exp $";
17 
18 #include <sys/types.h>
19 #include <netinet/in.h>
20 #include <arpa/nameser.h>
21 #include <stdlib.h>
22 #include <string.h>
23 #include "ares.h"
24 #include "ares_dns.h"
25 
26 /* Header format, from RFC 1035:
27  *                                  1  1  1  1  1  1
28  *    0  1  2  3  4  5  6  7  8  9  0  1  2  3  4  5
29  *  +--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+
30  *  |                      ID                       |
31  *  +--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+
32  *  |QR|   Opcode  |AA|TC|RD|RA|   Z    |   RCODE   |
33  *  +--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+
34  *  |                    QDCOUNT                    |
35  *  +--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+
36  *  |                    ANCOUNT                    |
37  *  +--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+
38  *  |                    NSCOUNT                    |
39  *  +--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+
40  *  |                    ARCOUNT                    |
41  *  +--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+
42  *
43  * AA, TC, RA, and RCODE are only set in responses.  Brief description
44  * of the remaining fields:
45  *	ID	Identifier to match responses with queries
46  *	QR	Query (0) or response (1)
47  *	Opcode	For our purposes, always QUERY
48  * 	RD	Recursion desired
49  *	Z	Reserved (zero)
50  *	QDCOUNT	Number of queries
51  *	ANCOUNT	Number of answers
52  *	NSCOUNT	Number of name server records
53  *	ARCOUNT	Number of additional records
54  *
55  * Question format, from RFC 1035:
56  *                                  1  1  1  1  1  1
57  *    0  1  2  3  4  5  6  7  8  9  0  1  2  3  4  5
58  *  +--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+
59  *  |                                               |
60  *  /                     QNAME                     /
61  *  /                                               /
62  *  +--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+
63  *  |                     QTYPE                     |
64  *  +--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+
65  *  |                     QCLASS                    |
66  *  +--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+
67  *
68  * The query name is encoded as a series of labels, each represented
69  * as a one-byte length (maximum 63) followed by the text of the
70  * label.  The list is terminated by a label of length zero (which can
71  * be thought of as the root domain).
72  */
73 
ares_mkquery(const char * name,int dnsclass,int type,unsigned short id,int rd,unsigned char ** buf,int * buflen)74 int ares_mkquery(const char *name, int dnsclass, int type, unsigned short id,
75 		 int rd, unsigned char **buf, int *buflen)
76 {
77   int len;
78   unsigned char *q;
79   const char *p;
80 
81   /* Compute the length of the encoded name so we can check buflen.
82    * Start counting at 1 for the zero-length label at the end. */
83   len = 1;
84   for (p = name; *p; p++)
85     {
86       if (*p == '\\' && *(p + 1) != 0)
87 	p++;
88       len++;
89     }
90   /* If there are n periods in the name, there are n + 1 labels, and
91    * thus n + 1 length fields, unless the name is empty or ends with a
92    * period.  So add 1 unless name is empty or ends with a period.
93    */
94   if (*name && *(p - 1) != '.')
95     len++;
96 
97   *buflen = len + HFIXEDSZ + QFIXEDSZ;
98   *buf = malloc(*buflen);
99   if (!*buf)
100       return ARES_ENOMEM;
101 
102   /* Set up the header. */
103   q = *buf;
104   memset(q, 0, HFIXEDSZ);
105   DNS_HEADER_SET_QID(q, id);
106   DNS_HEADER_SET_OPCODE(q, QUERY);
107   DNS_HEADER_SET_RD(q, (rd) ? 1 : 0);
108   DNS_HEADER_SET_QDCOUNT(q, 1);
109 
110   /* A name of "." is a screw case for the loop below, so adjust it. */
111   if (strcmp(name, ".") == 0)
112     name++;
113 
114   /* Start writing out the name after the header. */
115   q += HFIXEDSZ;
116   while (*name)
117     {
118       if (*name == '.')
119 	return ARES_EBADNAME;
120 
121       /* Count the number of bytes in this label. */
122       len = 0;
123       for (p = name; *p && *p != '.'; p++)
124 	{
125 	  if (*p == '\\' && *(p + 1) != 0)
126 	    p++;
127 	  len++;
128 	}
129       if (len > MAXLABEL)
130 	return ARES_EBADNAME;
131 
132       /* Encode the length and copy the data. */
133       *q++ = len;
134       for (p = name; *p && *p != '.'; p++)
135 	{
136 	  if (*p == '\\' && *(p + 1) != 0)
137 	    p++;
138 	  *q++ = *p;
139 	}
140 
141       /* Go to the next label and repeat, unless we hit the end. */
142       if (!*p)
143 	break;
144       name = p + 1;
145     }
146 
147   /* Add the zero-length label at the end. */
148   *q++ = 0;
149 
150   /* Finish off the question with the type and class. */
151   DNS_QUESTION_SET_TYPE(q, type);
152   DNS_QUESTION_SET_CLASS(q, dnsclass);
153 
154   return ARES_SUCCESS;
155 }
156