resolv.c

/**
 * \addtogroup apps
 * @{
 */

/**
 * \defgroup resolv DNS resolver
 * @{
 *
 * The uIP DNS resolver functions are used to lookup a hostname and
 * map it to a numerical IP address. It maintains a list of resolved
 * hostnames that can be queried with the resolv_lookup()
 * function. New hostnames can be resolved using the resolv_query()
 * function.
 *
 * When a hostname has been resolved (or found to be non-existant),
 * the resolver code calls a callback function called resolv_found()
 * that must be implemented by the module that uses the resolver.
 */

/**
 * \file
 * DNS host name to IP address resolver.
 * \author Adam Dunkels <adam@dunkels.com>
 *
 * This file implements a DNS host name to IP address resolver.
 */

/*
 * 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.
 *
 * This file is part of the uIP TCP/IP stack.
 *
 * $Id: resolv.c,v 1.5 2006/06/11 21:46:37 adam Exp $
 *
 */

#include "resolv.h"
#include "uip.h"

#include <string.h>

#ifndef NULL
#define NULL (void *)0
#endif /* NULL */

/** \internal The maximum number of retries when asking for a name. */
#define MAX_RETRIES 8

/** \internal The DNS message header. */
struct dns_hdr {
  u16_t id;
  u8_t flags1, flags2;
#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
  u16_t numquestions;
  u16_t numanswers;
  u16_t numauthrr;
  u16_t numextrarr;
};

/** \internal The 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;
  uip_ipaddr_t ipaddr;
};

struct namemap {
#define STATE_UNUSED 0
#define STATE_NEW    1
#define STATE_ASKING 2
#define STATE_DONE   3
#define STATE_ERROR  4
  u8_t state;
  u8_t tmr;
  u8_t retries;
  u8_t seqno;
  u8_t err;
  char name[32];
  uip_ipaddr_t ipaddr;
};

#ifndef UIP_CONF_RESOLV_ENTRIES
#define RESOLV_ENTRIES 4
#else /* UIP_CONF_RESOLV_ENTRIES */
#define RESOLV_ENTRIES UIP_CONF_RESOLV_ENTRIES
#endif /* UIP_CONF_RESOLV_ENTRIES */


static struct namemap names[RESOLV_ENTRIES];

static u8_t seqno;

static struct uip_udp_conn *resolv_conn = NULL;


/*---------------------------------------------------------------------------*/
/** \internal
 * Walk through a compact encoded DNS name and return the end of it.
 *
 * \return The end of the name.
 */
/*---------------------------------------------------------------------------*/
static unsigned char *
parse_name(unsigned char *query)
{
  unsigned char n;

  do {
    n = *query++;
    
    while(n > 0) {
      /*      printf("%c", *query);*/
      ++query;
      --n;
    };
    /*    printf(".");*/
  } while(*query != 0);
  /*  printf("\n");*/
  return query + 1;
}
/*---------------------------------------------------------------------------*/
/** \internal
 * Runs through the list of names to see if there are any that have
 * not yet been queried and, if so, sends out a query.
 */
/*---------------------------------------------------------------------------*/
static void
check_entries(void)
{
  register struct dns_hdr *hdr;
  char *query, *nptr, *nameptr;
  static u8_t i;
  static u8_t n;
  register struct namemap *namemapptr;
  
  for(i = 0; i < RESOLV_ENTRIES; ++i) {
    namemapptr = &names[i];
    if(namemapptr->state == STATE_NEW ||
       namemapptr->state == STATE_ASKING) {
      if(namemapptr->state == STATE_ASKING) {
        if(--namemapptr->tmr == 0) {
          if(++namemapptr->retries == MAX_RETRIES) {
            namemapptr->state = STATE_ERROR;
            resolv_found(namemapptr->name, NULL);
            continue;
          }
          namemapptr->tmr = namemapptr->retries;
        } else {
          /*      printf("Timer %d\n", namemapptr->tmr);*/
          /* Its timer has not run out, so we move on to next
             entry. */
          continue;
        }
      } else {
        namemapptr->state = STATE_ASKING;
        namemapptr->tmr = 1;
        namemapptr->retries = 0;
      }
      hdr = (struct dns_hdr *)uip_appdata;
      memset(hdr, 0, sizeof(struct dns_hdr));
      hdr->id = htons(i);
      hdr->flags1 = DNS_FLAG1_RD;
      hdr->numquestions = HTONS(1);
      query = (char *)uip_appdata + 12;
      nameptr = namemapptr->name;
      --nameptr;
      /* Convert hostname into suitable query format. */
      do {
        ++nameptr;
        nptr = query;
        ++query;
        for(n = 0; *nameptr != '.' && *nameptr != 0; ++nameptr) {
          *query = *nameptr;
          ++query;
          ++n;
        }
        *nptr = n;
      } while(*nameptr != 0);
      {
        static unsigned char endquery[] =
          {0,0,1,0,1};
        memcpy(query, endquery, 5);
      }
      uip_udp_send((unsigned char)(query + 5 - (char *)uip_appdata));
      break;
    }
  }
}
/*---------------------------------------------------------------------------*/
/** \internal
 * Called when new UDP data arrives.
 */
/*---------------------------------------------------------------------------*/
static void
newdata(void)
{
  char *nameptr;
  struct dns_answer *ans;
  struct dns_hdr *hdr;
  static u8_t nquestions, nanswers;
  static u8_t i;
  register struct namemap *namemapptr;
  
  hdr = (struct dns_hdr *)uip_appdata;
  /*  printf("ID %d\n", htons(hdr->id));
      printf("Query %d\n", hdr->flags1 & DNS_FLAG1_RESPONSE);
      printf("Error %d\n", hdr->flags2 & DNS_FLAG2_ERR_MASK);
      printf("Num questions %d, answers %d, authrr %d, extrarr %d\n",
      htons(hdr->numquestions),
      htons(hdr->numanswers),
      htons(hdr->numauthrr),
      htons(hdr->numextrarr));
  */

  /* The ID in the DNS header should be our entry into the name
     table. */
  i = htons(hdr->id);
  namemapptr = &names[i];
  if(i < RESOLV_ENTRIES &&
     namemapptr->state == STATE_ASKING) {

    /* This entry is now finished. */
    namemapptr->state = STATE_DONE;
    namemapptr->err = hdr->flags2 & DNS_FLAG2_ERR_MASK;

    /* Check for error. If so, call callback to inform. */
    if(namemapptr->err != 0) {
      namemapptr->state = STATE_ERROR;
      resolv_found(namemapptr->name, NULL);
      return;
    }

    /* We only care about the question(s) and the answers. The authrr
       and the extrarr are simply discarded. */
    nquestions = htons(hdr->numquestions);
    nanswers = htons(hdr->numanswers);

    /* Skip the name in the question. XXX: This should really be
       checked agains the name in the question, to be sure that they
       match. */
    nameptr = parse_name((char *)uip_appdata + 12) + 4;

    while(nanswers > 0) {
      /* The first byte in the answer resource record determines if it
         is a compressed record or a normal one. */
      if(*nameptr & 0xc0) {
        /* Compressed name. */
        nameptr +=2;
        /*      printf("Compressed anwser\n");*/
      } else {
        /* Not compressed name. */
        nameptr = parse_name((char *)nameptr);
      }

      ans = (struct dns_answer *)nameptr;
      /*      printf("Answer: type %x, class %x, ttl %x, length %x\n",
             htons(ans->type), htons(ans->class), (htons(ans->ttl[0])
             << 16) | htons(ans->ttl[1]), htons(ans->len));*/

      /* Check for IP address type and Internet class. Others are
         discarded. */
      if(ans->type == HTONS(1) &&
         ans->class == HTONS(1) &&
         ans->len == HTONS(4)) {
        /*      printf("IP address %d.%d.%d.%d\n",
               htons(ans->ipaddr[0]) >> 8,
               htons(ans->ipaddr[0]) & 0xff,
               htons(ans->ipaddr[1]) >> 8,
               htons(ans->ipaddr[1]) & 0xff);*/
        /* XXX: we should really check that this IP address is the one
           we want. */
        namemapptr->ipaddr[0] = ans->ipaddr[0];
        namemapptr->ipaddr[1] = ans->ipaddr[1];
        
        resolv_found(namemapptr->name, namemapptr->ipaddr);
        return;
      } else {
        nameptr = nameptr + 10 + htons(ans->len);
      }
      --nanswers;
    }
  }

}
/*---------------------------------------------------------------------------*/
/** \internal
 * The main UDP function.
 */
/*---------------------------------------------------------------------------*/
void
resolv_appcall(void)
{
  if(uip_udp_conn->rport == HTONS(53)) {
    if(uip_poll()) {
      check_entries();
    }
    if(uip_newdata()) {
      newdata();
    }
  }
}
/*---------------------------------------------------------------------------*/
/**
 * Queues a name so that a question for the name will be sent out.
 *
 * \param name The hostname that is to be queried.
 */
/*---------------------------------------------------------------------------*/
void
resolv_query(char *name)
{
  static u8_t i;
  static u8_t lseq, lseqi;
  register struct namemap *nameptr;
      
  lseq = lseqi = 0;
  
  for(i = 0; i < RESOLV_ENTRIES; ++i) {
    nameptr = &names[i];
    if(nameptr->state == STATE_UNUSED) {
      break;
    }
    if(seqno - nameptr->seqno > lseq) {
      lseq = seqno - nameptr->seqno;
      lseqi = i;
    }
  }

  if(i == RESOLV_ENTRIES) {
    i = lseqi;
    nameptr = &names[i];
  }

  /*  printf("Using entry %d\n", i);*/

  strcpy(nameptr->name, name);
  nameptr->state = STATE_NEW;
  nameptr->seqno = seqno;
  ++seqno;
}
/*---------------------------------------------------------------------------*/
/**
 * 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 resolv_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.
 */
/*---------------------------------------------------------------------------*/
u16_t *
resolv_lookup(char *name)
{
  static u8_t i;
  struct namemap *nameptr;
  
  /* Walk through the list to see if the name is in there. If it is
     not, we return NULL. */
  for(i = 0; i < RESOLV_ENTRIES; ++i) {
    nameptr = &names[i];
    if(nameptr->state == STATE_DONE &&
       strcmp(name, nameptr->name) == 0) {
      return nameptr->ipaddr;
    }
  }
  return NULL;
}
/*---------------------------------------------------------------------------*/
/**
 * Obtain the currently configured DNS server.
 *
 * \return A pointer to a 4-byte representation of the IP address of
 * the currently configured DNS server or NULL if no DNS server has
 * been configured.
 */
/*---------------------------------------------------------------------------*/
u16_t *
resolv_getserver(void)
{
  if(resolv_conn == NULL) {
    return NULL;
  }
  return resolv_conn->ripaddr;
}
/*---------------------------------------------------------------------------*/
/**
 * 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.
 */
/*---------------------------------------------------------------------------*/
void
resolv_conf(u16_t *dnsserver)
{
  if(resolv_conn != NULL) {
    uip_udp_remove(resolv_conn);
  }
  
  resolv_conn = uip_udp_new(dnsserver, HTONS(53));
}
/*---------------------------------------------------------------------------*/
/**
 * Initalize the resolver.
 */
/*---------------------------------------------------------------------------*/
void
resolv_init(void)
{
  static u8_t i;
  
  for(i = 0; i < RESOLV_ENTRIES; ++i) {
    names[i].state = STATE_DONE;
  }

}
/*---------------------------------------------------------------------------*/

/** @} */
/** @} */

---