dns.c

SEP3203_DTU

/**
 * @file
 * DNS - host name to IP address resolver.
 *
 */

/**

 * This file implements a DNS host name to IP address resolver.

 * Port to lwIP from uIP
 * by Jim Pettinato April 2007

 * uIP version Copyright (c) 2002-2003, Adam Dunkels.
 * All rights reserved.
 *
 * Redistribution and use in source and binary forms, with or without
 * modification, are permitted provided that the following conditions
 * are met:
 * 1. Redistributions of source code must retain the above copyright
 *    notice, this list of conditions and the following disclaimer.
 * 2. Redistributions in binary form must reproduce the above copyright
 *    notice, this list of conditions and the following disclaimer in the
 *    documentation and/or other materials provided with the distribution.
 * 3. The name of the author may not be used to endorse or promote
 *    products derived from this software without specific prior
 *    written permission.
 *
 * THIS SOFTWARE IS PROVIDED BY THE AUTHOR ``AS IS'' AND ANY EXPRESS
 * OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED
 * WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
 * ARE DISCLAIMED.  IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR ANY
 * DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
 * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE
 * GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS
 * INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY,
 * WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING
 * NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF THIS
 * SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
 *
 *
 * DNS.C
 *
 * The lwIP DNS resolver functions are used to lookup a host name and
 * map it to a numerical IP address. It maintains a list of resolved
 * hostnames that can be queried with the dns_lookup() function.
 * New hostnames can be resolved using the dns_query() function.
 *
 * The lwIP version of the resolver also adds a non-blocking version of
 * gethostbyname() that will work with a raw API application. This function
 * checks for an IP address string first and converts it if it is valid.
 * gethostbyname() then does a dns_lookup() to see if the name is 
 * already in the table. If so, the IP is returned. If not, a query is 
 * issued and the function returns with a QUERY_QUEUED status. The app
 * using the resolver must then go into a waiting state.
 *
 * Once a hostname has been resolved (or found to be non-existent),
 * the resolver code calls a specified callback function (which 
 * must be implemented by the module that uses the resolver).
 */

/** @todo: define good default values (rfc compliance) */
/** @todo: secondary server support */
/** @todo: compressed answer support */
/** @todo: improve answer parsing, more checkings... */

#include "lwip/opt.h"

#if LWIP_DNS /* don't build if not configured for use in lwipopts.h */

#include "lwip/udp.h"
#include "dns.h"

#include <string.h>

/**
 * DNS_DEBUG: Enable debugging for DNS.
 */
#ifndef DNS_DEBUG
#define DNS_DEBUG                 LWIP_DBG_ON
#endif

/** DNS server port address */
#ifndef DNS_SERVER_PORT
#define DNS_SERVER_PORT           53
#endif

/* The maximum number of table entries to maintain locally */
#ifndef DNS_TABLE_SIZE
#define DNS_TABLE_SIZE            4
#endif

/* The maximum length of a host name supported in the name table. */
#ifndef DNS_MAX_NAME_LENGTH
#define DNS_MAX_NAME_LENGTH       256
#endif

/* The maximum number of retries when asking for a name. */
#ifndef DNS_MAX_RETRIES
#define DNS_MAX_RETRIES           8
#endif 

/* DNS entry time to live */
#ifndef DNS_TTL_ENTRY
#define DNS_TTL_ENTRY             60
#endif

/* DNS protocol flags */
#define DNS_FLAG1_RESPONSE        0x80
#define DNS_FLAG1_OPCODE_STATUS   0x10
#define DNS_FLAG1_OPCODE_INVERSE  0x08
#define DNS_FLAG1_OPCODE_STANDARD 0x00
#define DNS_FLAG1_AUTHORATIVE     0x04
#define DNS_FLAG1_TRUNC           0x02
#define DNS_FLAG1_RD              0x01
#define DNS_FLAG2_RA              0x80
#define DNS_FLAG2_ERR_MASK        0x0f
#define DNS_FLAG2_ERR_NONE        0x00
#define DNS_FLAG2_ERR_NAME        0x03

/* DNS protocol states */
#define DNS_STATE_UNUSED          0
#define DNS_STATE_NEW             1
#define DNS_STATE_ASKING          2
#define DNS_STATE_DONE            3

/* DNS field TYPE used for "Resource Records" */
#define DNS_RRTYPE_A              1     /* a host address */
#define DNS_RRTYPE_NS             2     /* an authoritative name server */
#define DNS_RRTYPE_MD             3     /* a mail destination (Obsolete - use MX) */
#define DNS_RRTYPE_MF             4     /* a mail forwarder (Obsolete - use MX) */
#define DNS_RRTYPE_CNAME          5     /* the canonical name for an alias */
#define DNS_RRTYPE_SOA            6     /* marks the start of a zone of authority */
#define DNS_RRTYPE_MB             7     /* a mailbox domain name (EXPERIMENTAL) */
#define DNS_RRTYPE_MG             8     /* a mail group member (EXPERIMENTAL) */
#define DNS_RRTYPE_MR             9     /* a mail rename domain name (EXPERIMENTAL) */
#define DNS_RRTYPE_NULL           10    /* a null RR (EXPERIMENTAL) */
#define DNS_RRTYPE_WKS            11    /* a well known service description */
#define DNS_RRTYPE_PTR            12    /* a domain name pointer */
#define DNS_RRTYPE_HINFO          13    /* host information */
#define DNS_RRTYPE_MINFO          14    /* mailbox or mail list information */
#define DNS_RRTYPE_MX             15    /* mail exchange */
#define DNS_RRTYPE_TXT            16    /* text strings */

/* DNS field CLASS used for "Resource Records" */
#define DNS_RRCLASS_IN            1     /* the Internet */
#define DNS_RRCLASS_CS            2     /* the CSNET class (Obsolete - used only for examples in some obsolete RFCs) */
#define DNS_RRCLASS_CH            3     /* the CHAOS class */
#define DNS_RRCLASS_HS            4     /* Hesiod [Dyer 87] */
#define DNS_RRCLASS_FLUSH         0x800 /* Flush bit */

#ifdef PACK_STRUCT_USE_INCLUDES
#  include "arch/bpstruct.h"
#endif
PACK_STRUCT_BEGIN
/** DNS message header */
struct dns_hdr {
  u16_t id;
  u8_t flags1;
  u8_t flags2;
  u16_t numquestions;
  u16_t numanswers;
  u16_t numauthrr;
  u16_t numextrarr;
} PACK_STRUCT_STRUCT;
PACK_STRUCT_END
#ifdef PACK_STRUCT_USE_INCLUDES
#  include "arch/epstruct.h"
#endif

#ifdef PACK_STRUCT_USE_INCLUDES
#  include "arch/bpstruct.h"
#endif
PACK_STRUCT_BEGIN
/** DNS answer message structure */
struct dns_answer {
  /* DNS answer record starts with either a domain name or a pointer
     to a name already present somewhere in the packet. */
  u16_t type;
  u16_t class;
  u16_t ttl[2];
  u16_t len;
  struct ip_addr ipaddr;
} PACK_STRUCT_STRUCT;
PACK_STRUCT_END
#ifdef PACK_STRUCT_USE_INCLUDES
#  include "arch/epstruct.h"
#endif

#ifdef PACK_STRUCT_USE_INCLUDES
#  include "arch/bpstruct.h"
#endif
PACK_STRUCT_BEGIN
/** DNS table entry */
struct dns_table_entry {
  u8_t state;
  u8_t tmr;
  u8_t retries;
  u8_t ttl;
  u8_t seqno;
  u8_t err;
  char name[DNS_MAX_NAME_LENGTH];
  struct ip_addr ipaddr;
  void (* found)(char *name, struct ip_addr *ipaddr, void *arg); /* pointer to callback on DNS query done */
  void *arg;
} PACK_STRUCT_STRUCT;
PACK_STRUCT_END
#ifdef PACK_STRUCT_USE_INCLUDES
#  include "arch/epstruct.h"
#endif

/* DNS variables */
static struct udp_pcb        *dns_pcb;
static struct dns_table_entry dns_table[DNS_TABLE_SIZE];
static u8_t                   dns_seqno;

/* DNS request termination sequence: zero(1)+type(2)+class(2) */
static unsigned char dns_endquery[] = {0,0,1,0,1};

/* forward declarations */
static void dns_recv(void *s, struct udp_pcb *pcb, struct pbuf *p, struct ip_addr *addr, u16_t port);
static void dns_check_entries(void);


/**
 * Initialize the resolver and configure which DNS server to use for queries.
 *
 * param dnsserver A pointer to a 4-byte representation of the IP
 * address of the DNS server to be configured.
 */
err_t
dns_init(struct ip_addr *dnsserver)
{
  u8_t i;

  LWIP_DEBUGF(DNS_DEBUG, ("dns_init: initializing\n"));

  if (dns_pcb == NULL) {
    dns_pcb = udp_new();

    if ((dns_pcb != NULL) && (dnsserver->addr != 0)) {
      /* initialize DNS table */
      for (i=0; i<DNS_TABLE_SIZE; ++i) {
        dns_table[i].state = DNS_STATE_UNUSED;
        dns_table[i].found = NULL;
      }

      /* initialize DNS client */
      udp_bind   ( dns_pcb, IP_ADDR_ANY, 0);
      udp_connect( dns_pcb, dnsserver, DNS_SERVER_PORT);
      udp_recv   ( dns_pcb, dns_recv, NULL);
    }
  }
  return ERR_OK;
}

/**
 * Obtain the currently configured DNS server.
 * return unsigned long encoding of the IP address of
 * the currently configured DNS server or NULL if no DNS server has
 * been configured.
 */
u32_t
dns_getserver(void)
{
  return ((dns_pcb != NULL)?dns_pcb->remote_ip.addr:0);
}

/**
 * The DNS resolver client timer - handle retries and timeouts
 */
void
dns_tmr(void)
{
  if (dns_pcb != NULL) {
    LWIP_DEBUGF(DNS_DEBUG, ("dns_tmr: dns_check_entries\n"));
    dns_check_entries();
  }
}

/**
 * Look up a hostname in the array of known hostnames.
 *
 * \note This function only looks in the internal array of known
 * hostnames, it does not send out a query for the hostname if none
 * was found. The function dns_query() can be used to send a query
 * for a hostname.
 *
 * return A pointer to a 4-byte representation of the hostname's IP
 * address, or NULL if the hostname was not found in the array of
 * hostnames.
 */
u32_t
dns_lookup(char *name)
{
  u8_t i;

  /* Walk through name list, return entry if found. If not, return NULL. */
  for (i=0; i<DNS_TABLE_SIZE; ++i) {
    if ( (dns_table[i].state==DNS_STATE_DONE) && (strcmp(name, dns_table[i].name)==0) ) {
      LWIP_DEBUGF(DNS_DEBUG, ("dns_lookup: \"%s\": found = ", name));
      ip_addr_debug_print(DNS_DEBUG, (&(dns_table[i].ipaddr)));
      LWIP_DEBUGF(DNS_DEBUG, ("\n"));
      return dns_table[i].ipaddr.addr;
    }