dns.h

#ifndef DNS_H
#define DNS_H

/* Contains the definitions of some common data structures used in DNS packets. */
#include <stdint.h>

#define DNS_QR_RESPONSE		0x8000
#define DNS_AUTH_ANS		0x0400
#define DNS_TRUNCATED		0x0200
#define DNS_USE_RECURSION	0x0100
#define DNS_RECURSION_AVAIL	0x0080
#define DNS_FORMAT_ERROR	0x0001
#define DNS_SERVER_FAILURE	0x0002
#define DNS_NAME_ERROR		0x0003
#define DNS_NOT_IMPLEMENTED	0x0004
#define DNS_REFUSED		0x0005
#define DNS_ERROR_MASK          0x000f
#define DNS_INET_ADDR		0x0001

#define DNS_A_RECORD		0x0001
#define DNS_NS_RECORD		0x0002
#define DNS_CNAME_RECORD	0x0005
#define DNS_MX_RECORD		0x000f

/* Specified in the RFC for DNS. */
#define MAX_DOMAIN_LENGTH	255
#define MAX_SUBDOMAIN_LENGTH    63
#define ERROR_BUFFER 100

struct dns_header {
  uint16_t id;
  uint16_t flags;
  uint16_t qd_count;
  uint16_t an_count;
  uint16_t ns_count;
  uint16_t ar_count;
};

struct dns_question_trailer {
  uint16_t q_type;
  uint16_t q_class;
};

/* Stores information from the response packet sent from the DNS server. 
   Only some of the fields will contain valid data, depending on the type
   of response from the response_type field. */
struct dns_response {
  uint16_t response_type; /* Either A, CNAME, MX, or NS. */
  uint16_t preference; /* MX only. */
  uint32_t cache_time; /* All. */
  uint32_t ip_address; /* A only. */
  char name[MAX_DOMAIN_LENGTH + 1]; /* CNAME, MX, and NS only. */
  uint8_t authoritative; /* All. 0 false, 1 true. */
};

#endif /* DNS_H */