/* 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_SYS_SOCKET_H

# include <sys/socket.h>

#endif

#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 <stdlib.h>

#include <string.h>

#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;

}