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;
}
/* Handle an answer from a server. */
static void process_answer(ares_channel channel, unsigned char *abuf,
int alen, int whichserver, int tcp,
struct timeval *now)
{
int tc, rcode, packetsz;
unsigned short id;
struct query *query;
struct list_node* list_head;
struct list_node* list_node;
/* If there's no room in the answer for a header, we can't do much
* with it. */
if (alen < HFIXEDSZ)
return;
/* Grab the query ID, truncate bit, and response code from the packet. */
id = DNS_HEADER_QID(abuf);
tc = DNS_HEADER_TC(abuf);
rcode = DNS_HEADER_RCODE(abuf);
/* Find the query corresponding to this packet. The queries are
* hashed/bucketed by query id, so this lookup should be quick. Note that
* both the query id and the questions must be the same; when the query id
* wraps around we can have multiple outstanding queries with the same query
* id, so we need to check both the id and question.
*/
query = NULL;
list_head = &(channel->queries_by_qid[id % ARES_QID_TABLE_SIZE]);
for (list_node = list_head->next; list_node != list_head;
list_node = list_node->next)
{
struct query *q = list_node->data;
if ((q->qid == id) && same_questions(q->qbuf, q->qlen, abuf, alen))
{
query = q;
break;
}
}
if (!query)
return;
packetsz = PACKETSZ;
/* If we use EDNS and server answers with one of these RCODES, the protocol
* extension is not understood by the responder. We must retry the query
* without EDNS enabled.
*/
if (channel->flags & ARES_FLAG_EDNS)
{
packetsz = channel->ednspsz;
if (rcode == NOTIMP || rcode == FORMERR || rcode == SERVFAIL)
{
int qlen = alen - EDNSFIXEDSZ;
channel->flags ^= ARES_FLAG_EDNS;
query->tcplen -= EDNSFIXEDSZ;
query->qlen -= EDNSFIXEDSZ;
query->tcpbuf[0] = (unsigned char)((qlen >> 8) & 0xff);
query->tcpbuf[1] = (unsigned char)(qlen & 0xff);
DNS_HEADER_SET_ARCOUNT(query->tcpbuf + 2, 0);
query->tcpbuf = realloc(query->tcpbuf, query->tcplen);
ares__send_query(channel, query, now);
return;
}
