/* 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 #endif #ifdef HAVE_ARPA_NAMESER_H # include #else # include "nameser.h" #endif #ifdef HAVE_ARPA_NAMESER_COMPAT_H # include #endif #include "ares.h" #include "ares_dns.h" #include "ares_private.h" #ifndef T_OPT # define T_OPT 41 /* EDNS0 option (meta-RR) */ #endif /* 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_create_query(const char *name, int dnsclass, int type, unsigned short id, int rd, unsigned char **buf, int *buflen, int max_udp_size) { 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 + (max_udp_size ? EDNSFIXEDSZ : 0); *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); 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 == '.') 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); if (max_udp_size) { q += QFIXEDSZ; memset(q, 0, EDNSFIXEDSZ); q++; DNS_RR_SET_TYPE(q, T_OPT); DNS_RR_SET_CLASS(q, max_udp_size); } return ARES_SUCCESS; }