apps/resolv/resolv.c

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00001 /**
00002  * \addtogroup apps
00003  * @{
00004  */
00005 
00006 /**
00007  * \defgroup resolv DNS resolver
00008  * @{
00009  *
00010  * The uIP DNS resolver functions are used to lookup a hostname and
00011  * map it to a numerical IP address. It maintains a list of resolved
00012  * hostnames that can be queried with the resolv_lookup()
00013  * function. New hostnames can be resolved using the resolv_query()
00014  * function.
00015  *
00016  * When a hostname has been resolved (or found to be non-existant),
00017  * the resolver code calls a callback function called resolv_found()
00018  * that must be implemented by the module that uses the resolver.
00019  */
00020 
00021 /**
00022  * \file
00023  * DNS host name to IP address resolver.
00024  * \author Adam Dunkels <adam@dunkels.com>
00025  *
00026  * This file implements a DNS host name to IP address resolver.
00027  */
00028 
00029 /*
00030  * Copyright (c) 2002-2003, Adam Dunkels.
00031  * All rights reserved.
00032  *
00033  * Redistribution and use in source and binary forms, with or without
00034  * modification, are permitted provided that the following conditions
00035  * are met:
00036  * 1. Redistributions of source code must retain the above copyright
00037  *    notice, this list of conditions and the following disclaimer.
00038  * 2. Redistributions in binary form must reproduce the above copyright
00039  *    notice, this list of conditions and the following disclaimer in the
00040  *    documentation and/or other materials provided with the distribution.
00041  * 3. The name of the author may not be used to endorse or promote
00042  *    products derived from this software without specific prior
00043  *    written permission.
00044  *
00045  * THIS SOFTWARE IS PROVIDED BY THE AUTHOR ``AS IS'' AND ANY EXPRESS
00046  * OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED
00047  * WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
00048  * ARE DISCLAIMED.  IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR ANY
00049  * DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
00050  * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE
00051  * GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS
00052  * INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY,
00053  * WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING
00054  * NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF THIS
00055  * SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
00056  *
00057  * This file is part of the uIP TCP/IP stack.
00058  *
00059  * $Id: resolv.c,v 1.5 2006/06/11 21:46:37 adam Exp $
00060  *
00061  */
00062 
00063 #include "resolv.h"
00064 #include "uip.h"
00065 
00066 #include <string.h>
00067 
00068 #ifndef NULL
00069 #define NULL (void *)0
00070 #endif /* NULL */
00071 
00072 /** \internal The maximum number of retries when asking for a name. */
00073 #define MAX_RETRIES 8
00074 
00075 /** \internal The DNS message header. */
00076 struct dns_hdr {
00077   u16_t id;
00078   u8_t flags1, flags2;
00079 #define DNS_FLAG1_RESPONSE        0x80
00080 #define DNS_FLAG1_OPCODE_STATUS   0x10
00081 #define DNS_FLAG1_OPCODE_INVERSE  0x08
00082 #define DNS_FLAG1_OPCODE_STANDARD 0x00
00083 #define DNS_FLAG1_AUTHORATIVE     0x04
00084 #define DNS_FLAG1_TRUNC           0x02
00085 #define DNS_FLAG1_RD              0x01
00086 #define DNS_FLAG2_RA              0x80
00087 #define DNS_FLAG2_ERR_MASK        0x0f
00088 #define DNS_FLAG2_ERR_NONE        0x00
00089 #define DNS_FLAG2_ERR_NAME        0x03
00090   u16_t numquestions;
00091   u16_t numanswers;
00092   u16_t numauthrr;
00093   u16_t numextrarr;
00094 };
00095 
00096 /** \internal The DNS answer message structure. */
00097 struct dns_answer {
00098   /* DNS answer record starts with either a domain name or a pointer
00099      to a name already present somewhere in the packet. */
00100   u16_t type;
00101   u16_t class;
00102   u16_t ttl[2];
00103   u16_t len;
00104   uip_ipaddr_t ipaddr;
00105 };
00106 
00107 struct namemap {
00108 #define STATE_UNUSED 0
00109 #define STATE_NEW    1
00110 #define STATE_ASKING 2
00111 #define STATE_DONE   3
00112 #define STATE_ERROR  4
00113   u8_t state;
00114   u8_t tmr;
00115   u8_t retries;
00116   u8_t seqno;
00117   u8_t err;
00118   char name[32];
00119   uip_ipaddr_t ipaddr;
00120 };
00121 
00122 #ifndef UIP_CONF_RESOLV_ENTRIES
00123 #define RESOLV_ENTRIES 4
00124 #else /* UIP_CONF_RESOLV_ENTRIES */
00125 #define RESOLV_ENTRIES UIP_CONF_RESOLV_ENTRIES
00126 #endif /* UIP_CONF_RESOLV_ENTRIES */
00127 
00128 
00129 static struct namemap names[RESOLV_ENTRIES];
00130 
00131 static u8_t seqno;
00132 
00133 static struct uip_udp_conn *resolv_conn = NULL;
00134 
00135 
00136 /*---------------------------------------------------------------------------*/
00137 /** \internal
00138  * Walk through a compact encoded DNS name and return the end of it.
00139  *
00140  * \return The end of the name.
00141  */
00142 /*---------------------------------------------------------------------------*/
00143 static unsigned char *
00144 parse_name(unsigned char *query)
00145 {
00146   unsigned char n;
00147 
00148   do {
00149     n = *query++;
00150     
00151     while(n > 0) {
00152       /*      printf("%c", *query);*/
00153       ++query;
00154       --n;
00155     };
00156     /*    printf(".");*/
00157   } while(*query != 0);
00158   /*  printf("\n");*/
00159   return query + 1;
00160 }
00161 /*---------------------------------------------------------------------------*/
00162 /** \internal
00163  * Runs through the list of names to see if there are any that have
00164  * not yet been queried and, if so, sends out a query.
00165  */
00166 /*---------------------------------------------------------------------------*/
00167 static void
00168 check_entries(void)
00169 {
00170   register struct dns_hdr *hdr;
00171   char *query, *nptr, *nameptr;
00172   static u8_t i;
00173   static u8_t n;
00174   register struct namemap *namemapptr;
00175   
00176   for(i = 0; i < RESOLV_ENTRIES; ++i) {
00177     namemapptr = &names[i];
00178     if(namemapptr->state == STATE_NEW ||
00179        namemapptr->state == STATE_ASKING) {
00180       if(namemapptr->state == STATE_ASKING) {
00181         if(--namemapptr->tmr == 0) {
00182           if(++namemapptr->retries == MAX_RETRIES) {
00183             namemapptr->state = STATE_ERROR;
00184             resolv_found(namemapptr->name, NULL);
00185             continue;
00186           }
00187           namemapptr->tmr = namemapptr->retries;
00188         } else {
00189           /*      printf("Timer %d\n", namemapptr->tmr);*/
00190           /* Its timer has not run out, so we move on to next
00191              entry. */
00192           continue;
00193         }
00194       } else {
00195         namemapptr->state = STATE_ASKING;
00196         namemapptr->tmr = 1;
00197         namemapptr->retries = 0;
00198       }
00199       hdr = (struct dns_hdr *)uip_appdata;
00200       memset(hdr, 0, sizeof(struct dns_hdr));
00201       hdr->id = htons(i);
00202       hdr->flags1 = DNS_FLAG1_RD;
00203       hdr->numquestions = HTONS(1);
00204       query = (char *)uip_appdata + 12;
00205       nameptr = namemapptr->name;
00206       --nameptr;
00207       /* Convert hostname into suitable query format. */
00208       do {
00209         ++nameptr;
00210         nptr = query;
00211         ++query;
00212         for(n = 0; *nameptr != '.' && *nameptr != 0; ++nameptr) {
00213           *query = *nameptr;
00214           ++query;
00215           ++n;
00216         }
00217         *nptr = n;
00218       } while(*nameptr != 0);
00219       {
00220         static unsigned char endquery[] =
00221           {0,0,1,0,1};
00222         memcpy(query, endquery, 5);
00223       }
00224       uip_udp_send((unsigned char)(query + 5 - (char *)uip_appdata));
00225       break;
00226     }
00227   }
00228 }
00229 /*---------------------------------------------------------------------------*/
00230 /** \internal
00231  * Called when new UDP data arrives.
00232  */
00233 /*---------------------------------------------------------------------------*/
00234 static void
00235 newdata(void)
00236 {
00237   char *nameptr;
00238   struct dns_answer *ans;
00239   struct dns_hdr *hdr;
00240   static u8_t nquestions, nanswers;
00241   static u8_t i;
00242   register struct namemap *namemapptr;
00243   
00244   hdr = (struct dns_hdr *)uip_appdata;
00245   /*  printf("ID %d\n", htons(hdr->id));
00246       printf("Query %d\n", hdr->flags1 & DNS_FLAG1_RESPONSE);
00247       printf("Error %d\n", hdr->flags2 & DNS_FLAG2_ERR_MASK);
00248       printf("Num questions %d, answers %d, authrr %d, extrarr %d\n",
00249       htons(hdr->numquestions),
00250       htons(hdr->numanswers),
00251       htons(hdr->numauthrr),
00252       htons(hdr->numextrarr));
00253   */
00254 
00255   /* The ID in the DNS header should be our entry into the name
00256      table. */
00257   i = htons(hdr->id);
00258   namemapptr = &names[i];
00259   if(i < RESOLV_ENTRIES &&
00260      namemapptr->state == STATE_ASKING) {
00261 
00262     /* This entry is now finished. */
00263     namemapptr->state = STATE_DONE;
00264     namemapptr->err = hdr->flags2 & DNS_FLAG2_ERR_MASK;
00265 
00266     /* Check for error. If so, call callback to inform. */
00267     if(namemapptr->err != 0) {
00268       namemapptr->state = STATE_ERROR;
00269       resolv_found(namemapptr->name, NULL);
00270       return;
00271     }
00272 
00273     /* We only care about the question(s) and the answers. The authrr
00274        and the extrarr are simply discarded. */
00275     nquestions = htons(hdr->numquestions);
00276     nanswers = htons(hdr->numanswers);
00277 
00278     /* Skip the name in the question. XXX: This should really be
00279        checked agains the name in the question, to be sure that they
00280        match. */
00281     nameptr = parse_name((char *)uip_appdata + 12) + 4;
00282 
00283     while(nanswers > 0) {
00284       /* The first byte in the answer resource record determines if it
00285          is a compressed record or a normal one. */
00286       if(*nameptr & 0xc0) {
00287         /* Compressed name. */
00288         nameptr +=2;
00289         /*      printf("Compressed anwser\n");*/
00290       } else {
00291         /* Not compressed name. */
00292         nameptr = parse_name((char *)nameptr);
00293       }
00294 
00295       ans = (struct dns_answer *)nameptr;
00296       /*      printf("Answer: type %x, class %x, ttl %x, length %x\n",
00297              htons(ans->type), htons(ans->class), (htons(ans->ttl[0])
00298              << 16) | htons(ans->ttl[1]), htons(ans->len));*/
00299 
00300       /* Check for IP address type and Internet class. Others are
00301          discarded. */
00302       if(ans->type == HTONS(1) &&
00303          ans->class == HTONS(1) &&
00304          ans->len == HTONS(4)) {
00305         /*      printf("IP address %d.%d.%d.%d\n",
00306                htons(ans->ipaddr[0]) >> 8,
00307                htons(ans->ipaddr[0]) & 0xff,
00308                htons(ans->ipaddr[1]) >> 8,
00309                htons(ans->ipaddr[1]) & 0xff);*/
00310         /* XXX: we should really check that this IP address is the one
00311            we want. */
00312         namemapptr->ipaddr[0] = ans->ipaddr[0];
00313         namemapptr->ipaddr[1] = ans->ipaddr[1];
00314         
00315         resolv_found(namemapptr->name, namemapptr->ipaddr);
00316         return;
00317       } else {
00318         nameptr = nameptr + 10 + htons(ans->len);
00319       }
00320       --nanswers;
00321     }
00322   }
00323 
00324 }
00325 /*---------------------------------------------------------------------------*/
00326 /** \internal
00327  * The main UDP function.
00328  */
00329 /*---------------------------------------------------------------------------*/
00330 void
00331 resolv_appcall(void)
00332 {
00333   if(uip_udp_conn->rport == HTONS(53)) {
00334     if(uip_poll()) {
00335       check_entries();
00336     }
00337     if(uip_newdata()) {
00338       newdata();
00339     }
00340   }
00341 }
00342 /*---------------------------------------------------------------------------*/
00343 /**
00344  * Queues a name so that a question for the name will be sent out.
00345  *
00346  * \param name The hostname that is to be queried.
00347  */
00348 /*---------------------------------------------------------------------------*/
00349 void
00350 resolv_query(char *name)
00351 {
00352   static u8_t i;
00353   static u8_t lseq, lseqi;
00354   register struct namemap *nameptr;
00355       
00356   lseq = lseqi = 0;
00357   
00358   for(i = 0; i < RESOLV_ENTRIES; ++i) {
00359     nameptr = &names[i];
00360     if(nameptr->state == STATE_UNUSED) {
00361       break;
00362     }
00363     if(seqno - nameptr->seqno > lseq) {
00364       lseq = seqno - nameptr->seqno;
00365       lseqi = i;
00366     }
00367   }
00368 
00369   if(i == RESOLV_ENTRIES) {
00370     i = lseqi;
00371     nameptr = &names[i];
00372   }
00373 
00374   /*  printf("Using entry %d\n", i);*/
00375 
00376   strcpy(nameptr->name, name);
00377   nameptr->state = STATE_NEW;
00378   nameptr->seqno = seqno;
00379   ++seqno;
00380 }
00381 /*---------------------------------------------------------------------------*/
00382 /**
00383  * Look up a hostname in the array of known hostnames.
00384  *
00385  * \note This function only looks in the internal array of known
00386  * hostnames, it does not send out a query for the hostname if none
00387  * was found. The function resolv_query() can be used to send a query
00388  * for a hostname.
00389  *
00390  * \return A pointer to a 4-byte representation of the hostname's IP
00391  * address, or NULL if the hostname was not found in the array of
00392  * hostnames.
00393  */
00394 /*---------------------------------------------------------------------------*/
00395 u16_t *
00396 resolv_lookup(char *name)
00397 {
00398   static u8_t i;
00399   struct namemap *nameptr;
00400   
00401   /* Walk through the list to see if the name is in there. If it is
00402      not, we return NULL. */
00403   for(i = 0; i < RESOLV_ENTRIES; ++i) {
00404     nameptr = &names[i];
00405     if(nameptr->state == STATE_DONE &&
00406        strcmp(name, nameptr->name) == 0) {
00407       return nameptr->ipaddr;
00408     }
00409   }
00410   return NULL;
00411 }
00412 /*---------------------------------------------------------------------------*/
00413 /**
00414  * Obtain the currently configured DNS server.
00415  *
00416  * \return A pointer to a 4-byte representation of the IP address of
00417  * the currently configured DNS server or NULL if no DNS server has
00418  * been configured.
00419  */
00420 /*---------------------------------------------------------------------------*/
00421 u16_t *
00422 resolv_getserver(void)
00423 {
00424   if(resolv_conn == NULL) {
00425     return NULL;
00426   }
00427   return resolv_conn->ripaddr;
00428 }
00429 /*---------------------------------------------------------------------------*/
00430 /**
00431  * Configure which DNS server to use for queries.
00432  *
00433  * \param dnsserver A pointer to a 4-byte representation of the IP
00434  * address of the DNS server to be configured.
00435  */
00436 /*---------------------------------------------------------------------------*/
00437 void
00438 resolv_conf(u16_t *dnsserver)
00439 {
00440   if(resolv_conn != NULL) {
00441     uip_udp_remove(resolv_conn);
00442   }
00443   
00444   resolv_conn = uip_udp_new(dnsserver, HTONS(53));
00445 }
00446 /*---------------------------------------------------------------------------*/
00447 /**
00448  * Initalize the resolver.
00449  */
00450 /*---------------------------------------------------------------------------*/
00451 void
00452 resolv_init(void)
00453 {
00454   static u8_t i;
00455   
00456   for(i = 0; i < RESOLV_ENTRIES; ++i) {
00457     names[i].state = STATE_DONE;
00458   }
00459 
00460 }
00461 /*---------------------------------------------------------------------------*/
00462 
00463 /** @} */
00464 /** @} */

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