dns.h

/* dns.c
 * By Ron Bowes
 * Created December, 2009
 *
 * (See LICENSE.txt)
 *
 * This module implements a reasonably functional DNS library that can build or parse DNS packets
 * in a platform-agnostic way. It implements a number of record types (A, NS, CNAME, MX, TXT, and
 * AAAA), and can add and parse questions or answers.
 *
 * On Windows, due to IPv6 parsing being unavailable on older systems, I disable AAAA records
 * entirely.
 *
 * In the future I may opt to add more record types and stronger parsing, but for now this was
 * enough.
 */

#ifndef __DNS_H__
#define __DNS_H__

#include "types.h"

/* Define a list of dns types. Windows defines these automatically,
 * so we need to wrap this in an #ifdef block. */
#ifndef DNS_TYPE_A
typedef enum
{
	/* RFC 1034/1035 */
	DNS_TYPE_A          = 0x0001,
	DNS_TYPE_NS         = 0x0002,
	DNS_TYPE_MD         = 0x0003,
	DNS_TYPE_MF         = 0x0004,
	DNS_TYPE_CNAME      = 0x0005,
	DNS_TYPE_SOA        = 0x0006,
	DNS_TYPE_MB         = 0x0007,
	DNS_TYPE_MG         = 0x0008,
	DNS_TYPE_MR         = 0x0009,
	DNS_TYPE_NULL       = 0x000a,
	DNS_TYPE_WKS        = 0x000b,
	DNS_TYPE_PTR        = 0x000c,
	DNS_TYPE_HINFO      = 0x000d,
	DNS_TYPE_MINFO      = 0x000e,
	DNS_TYPE_MX         = 0x000f,
	DNS_TYPE_TEXT       = 0x0010,

	/*  RFC 1183 */
	DNS_TYPE_RP         = 0x0011,
	DNS_TYPE_AFSDB      = 0x0012,
	DNS_TYPE_X25        = 0x0013,
	DNS_TYPE_ISDN       = 0x0014,
	DNS_TYPE_RT         = 0x0015,

	/*  RFC 1348 */
	DNS_TYPE_NSAP       = 0x0016,
	DNS_TYPE_NSAPPTR    = 0x0017,

	/*  RFC 2065 (DNS security) */
	DNS_TYPE_SIG        = 0x0018,
	DNS_TYPE_KEY        = 0x0019,

	/*  RFC 1664 (X.400 mail) */
	DNS_TYPE_PX         = 0x001a,

	/*  RFC 1712 (Geographic position) */
	DNS_TYPE_GPOS       = 0x001b,

	/*  RFC 1886 (IPv6 Address) */
	DNS_TYPE_AAAA       = 0x001c,

	/*  RFC 1876 (Geographic location) */
	DNS_TYPE_LOC        = 0x001d,

	/*  RFC 2065 (Secure negative response) */
	DNS_TYPE_NXT        = 0x001e,

	/*  Patton (Endpoint Identifier) */
	DNS_TYPE_EID        = 0x001f,

	/*  Patton (Nimrod Locator) */
/*	DNS_TYPE_NIMLOC     = 0x0020,*/
	/*  RFC 2052 (Service location) */
/*	DNS_TYPE_SRV        = 0x0021,*/

	/* NetBIOS. */
	DNS_TYPE_NB         = 0x0020,

	/* Adapter status. */
	DNS_TYPE_NBSTAT     = 0x0021,

	/*  ATM Address */
	DNS_TYPE_ATMA       = 0x0022,

	/*  RFC 2168 (Naming Authority Pointer) */
	DNS_TYPE_NAPTR      = 0x0023,

	/*  RFC 2230 (Key Exchanger) */
	DNS_TYPE_KX         = 0x0024,

	/*  RFC 2538 (CERT) */
	DNS_TYPE_CERT       = 0x0025,

	/*  A6 Draft (A6) */
	DNS_TYPE_A6         = 0x0026,

	/*  DNAME Draft (DNAME) */
	DNS_TYPE_DNAME      = 0x0027,

	/*  Eastlake (Kitchen Sink) */
	DNS_TYPE_SINK       = 0x0028,

	/*  RFC 2671 (EDNS OPT) */
	DNS_TYPE_OPT        = 0x0029,

	/*  IANA Reserved */

	DNS_TYPE_UINFO      = 0x0064,
	DNS_TYPE_UID        = 0x0065,
	DNS_TYPE_GID        = 0x0066,
	DNS_TYPE_UNSPEC     = 0x0067,

	/*  Query only types (1035, 1995) */
	DNS_TYPE_ADDRS      = 0x00f8,
	DNS_TYPE_TKEY       = 0x00f9,
	DNS_TYPE_TSIG       = 0x00fa,
	DNS_TYPE_IXFR       = 0x00fb,
	DNS_TYPE_AXFR       = 0x00fc,
	DNS_TYPE_MAILB      = 0x00fd,
	DNS_TYPE_MAILA      = 0x00fe,
	DNS_TYPE_ALL        = 0x00ff,
	DNS_TYPE_ANY        = 0x00ff,
} dns_types_t;
#else
/* Do a typedif so we can still use the name. */
typedef int dns_types_t;

/* Declare our two custom types. */
#ifndef DNS_TYPE_NB
#define DNS_TYPE_NB         0x0020
#endif
#ifndef DNS_TYPE_NBSTAT
#define DNS_TYPE_NBSTAT     0x0021
#endif

#endif

/* A DNS question. Questions are simple, they just have a name, type, and class. */
typedef struct
{
	char *name;
	uint16_t type;
	uint16_t class;
} question_t;

/* An answer for an A packet. */
typedef struct
{
	char *address;
} A_answer_t;

/* Only define AAAA on Linux. */
#ifndef WIN32
typedef A_answer_t AAAA_answer_t;
#endif

/* Nameserver and CNAME (alias) records simply have a name. */
typedef struct
{
	char *name;
} NS_answer_t, CNAME_answer_t;

/* Mail server requests (MX) have a name and a preference number. */
typedef struct
{
	uint16_t preference;
	char *name;
} MX_answer_t;

/* A text record (TXT) has the text data and a length. Unlike MX, NS, and CNAME, text
 * records aren't encoded as a dns name. */
typedef struct
{
	uint8_t *text;
	uint8_t  length;
} TEXT_answer_t;

/* A NetBIOS answer (NB) is used by Windows on port 137. */
typedef struct
{
	uint16_t  flags;
	char     *address;
} NB_answer_t;

/* One element returned by a NBSTAT query (NBSTAT answers typically contain multiple names). */
typedef struct
{
	char    *name;
	uint8_t  name_type;
	uint16_t name_flags;
} NBSTAT_name_t;

/* A NetBIOS Status answer (NBSTAT or NBTSTAT) is used by Windows to get more information over 137. */
typedef struct
{
	uint8_t        name_count;
	NBSTAT_name_t *names;
	uint8_t        stats[64];
} NBSTAT_answer_t;

/* Let us refer to any kind of answer type together. */
typedef union
{
	A_answer_t      A;
	NS_answer_t     NS;
	CNAME_answer_t  CNAME;
	MX_answer_t     MX;
	TEXT_answer_t   TEXT;
#ifndef WIN32
	AAAA_answer_t   AAAA;
#endif
	NB_answer_t     NB;
	NBSTAT_answer_t NBSTAT;
} answer_types_t;

/* And finally, define a DNS answer. */
typedef struct
{
	char           *question;
	dns_types_t     type;
	uint16_t        class;
	uint32_t        ttl;
	answer_types_t *answer;
} answer_t;

/* We don't implement authority records. */
typedef struct
{
	/* TODO */
	int dummy;
} authority_t;

/* An additional for an A packet. */
typedef struct
{
	char *address;
} A_additional_t;

/* Only define AAAA on Linux. */
#ifndef WIN32
typedef A_additional_t AAAA_additional_t;
#endif

/* Nameserver and CNAME (alias) records simply have a name. */
typedef struct
{
	char *name;
} NS_additional_t, CNAME_additional_t;

/* Mail server requests (MX) have a name and a preference number. */
typedef struct
{
	uint16_t preference;
	char *name;
} MX_additional_t;

/* A text record (TXT) has the text data and a length. Unlike MX, NS, and CNAME, text
 * records aren't encoded as a dns name. */
typedef struct
{
	uint8_t *text;
	uint8_t  length;
} TEXT_additional_t;

/* A NetBIOS additional (NB) is used by Windows on port 137. */
typedef struct
{
	uint16_t  flags;
	char     *address;
} NB_additional_t;

/* A NetBIOS Status additional (NBSTAT or NBTSTAT) is used by Windows to get more information over 137. */
typedef struct
{
	uint8_t        name_count;
	NBSTAT_name_t *names;
	uint8_t        stats[64];
} NBSTAT_additional_t;

/* Let us refer to any kind of additional type together. */
typedef union
{
	A_additional_t      A;
	NS_additional_t     NS;
	CNAME_additional_t  CNAME;
	MX_additional_t     MX;
	TEXT_additional_t   TEXT;
#ifndef WIN32
	AAAA_additional_t   AAAA;
#endif
	NB_additional_t     NB;
	NBSTAT_additional_t NBSTAT;
} additional_types_t;

/* And finally, define a DNS additional. */
typedef struct
{
	char           *question;
	dns_types_t     type;
	uint16_t        class;
	uint32_t        ttl;
	additional_types_t *additional;
} additional_t;

/* Define an entire DNS packet. */
typedef struct
{
	uint16_t trn_id;
	uint16_t flags;

	uint16_t question_count;
	uint16_t answer_count;
	uint16_t authority_count;
	uint16_t additional_count;

	question_t *questions;
	answer_t *answers;
	authority_t *authorities;
	additional_t *additionals;
} dns_t;

/* Allocate memory for a blank dns structure. Should be freed with dns_free(). */
dns_t   *dns_create();

/* Take a DNS packet as a stream of bytes, and create a dns_t structure from it.
 * Should also be cleaned up with dns_destroy(). */
dns_t   *dns_create_from_packet(uint8_t *packet, uint32_t length);

/* De-allocate memory and resources from a dns object. */
void     dns_destroy(dns_t *dns);

/* Add a question to the DNS packet. A DNS packet can have any number of questions, but
 * I normally limit it to one at a time. */
void     dns_add_question(dns_t *dns, char *name, uint16_t type, uint16_t class);

/* Add a NetBIOS question to the DNS packet. This is similar to a normal question but
 * with a couple extra fields and an encoded name. */
void dns_add_netbios_question(dns_t *dns, char *name, uint8_t name_type, char *scope, uint16_t type, uint16_t class);

/* These functions add answers of the various types. */
void     dns_add_answer_A(dns_t *dns,     char *question, uint16_t class, uint32_t ttl, char *address);
void     dns_add_answer_NS(dns_t *dns,    char *question, uint16_t class, uint32_t ttl, char *name);
void     dns_add_answer_CNAME(dns_t *dns, char *question, uint16_t class, uint32_t ttl, char *name);
void     dns_add_answer_MX(dns_t *dns,    char *question, uint16_t class, uint32_t ttl, uint16_t preference, char *name);
void     dns_add_answer_TEXT(dns_t *dns,  char *question, uint16_t class, uint32_t ttl, uint8_t *text, uint8_t length);
#ifndef WIN32
void     dns_add_answer_AAAA(dns_t *dns,  char *question, uint16_t class, uint32_t ttl, char *address);
#endif
void     dns_add_answer_NB(dns_t *dns,  char *question, uint8_t question_type, char *scope, uint16_t class, uint32_t ttl, uint16_t flags, char *address);

/* These functions add additionals of the various types. */
void     dns_add_additional_A(dns_t *dns,     char *question, uint16_t class, uint32_t ttl, char *address);
void     dns_add_additional_NS(dns_t *dns,    char *question, uint16_t class, uint32_t ttl, char *name);
void     dns_add_additional_CNAME(dns_t *dns, char *question, uint16_t class, uint32_t ttl, char *name);
void     dns_add_additional_MX(dns_t *dns,    char *question, uint16_t class, uint32_t ttl, uint16_t preference, char *name);
void     dns_add_additional_TEXT(dns_t *dns,  char *question, uint16_t class, uint32_t ttl, uint8_t *text, uint8_t length);
#ifndef WIN32
void     dns_add_additional_AAAA(dns_t *dns,  char *question, uint16_t class, uint32_t ttl, char *address);
#endif
void     dns_add_additional_NB(dns_t *dns,  char *question, uint8_t question_type, char *scope, uint16_t class, uint32_t ttl, uint16_t flags, char *address);

/* Convert a DNS request into a packet that can be sent on port 53. Memory has to be freed. */
uint8_t *dns_to_packet(dns_t *dns, uint32_t *length);

/* Print the DNS request. Useful for debugging. */
void     dns_print(dns_t *dns);

/* Create a DNS error object. */
dns_t   *dns_create_error(uint16_t trn_id, question_t question);
/* Create a DNS error packet, ready to send. */
uint8_t *dns_create_error_string(uint16_t trn_id, question_t question, uint32_t *length);

/* Get the first system DNS server. Works on Windows and any system that uses /etc/resolv.conf. */
char *dns_get_system();

/* Runs dnstest and exits. Useful for --test parameters on any of the dns* programs. */
void dns_do_test(char *domain);

#endif