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Diffstat (limited to 'src/c-ares/ares_create_query.c')
| -rw-r--r-- | src/c-ares/ares_create_query.c | 202 |
1 files changed, 202 insertions, 0 deletions
diff --git a/src/c-ares/ares_create_query.c b/src/c-ares/ares_create_query.c new file mode 100644 index 000000000..7f4c52d41 --- /dev/null +++ b/src/c-ares/ares_create_query.c @@ -0,0 +1,202 @@ + +/* 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 +#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 "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 **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; + + /* 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, 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 == '.') { + 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) { + 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 > (MAXCDNAME + HFIXEDSZ + QFIXEDSZ + + (max_udp_size ? EDNSFIXEDSZ : 0))) { + free (buf); + return ARES_EBADNAME; + } + + /* we know this fits in an int at this point */ + *buflenp = (int) buflen; + *bufp = buf; + + return ARES_SUCCESS; +} |