text: /**
   * \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 1.2 2008/08/13 20:12:50 andrewlxia Exp $
   *
   */
  
  #include <uip/resolv.h>
  #include <uip/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;
  
  
  int appcall(void){ //for UIP_APPCALL, referred in uip-conf.h
  
     	return 0;
  }
  
  void uip_log(char *msg)  //you should replace this by your own log function
  {
      //PrintDebug("\nuIP log:");
      //PrintDebug(msg);
  }
  
  
  /**
   * Callback function which is called when a hostname is found.
   *
   * This function must be implemented by the module that uses the DNS
   * resolver. It is called when a hostname is found, or when a hostname
   * was not found.
   *
   * \param name A pointer to the name that was looked up.  \param
   * ipaddr A pointer to a 4-byte array containing the IP address of the
   * hostname, or NULL if the hostname could not be found.
   */
  void resolv_found(char *name, u16_t *ipaddr){
  
  }
  
  /*---------------------------------------------------------------------------*/
  /** \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((uip_ipaddr_t *)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;
    }
  
  }
  /*---------------------------------------------------------------------------*/
  
  /** @} */
  /** @} */
  