dns.c

00001 /**
00002  * @file
00003  * DNS - host name to IP address resolver.
00004  *
00005  */
00006 
00007 /**
00008 
00009  * This file implements a DNS host name to IP address resolver.
00010 
00011  * Port to lwIP from uIP
00012  * by Jim Pettinato April 2007
00013 
00014  * uIP version Copyright (c) 2002-2003, Adam Dunkels.
00015  * All rights reserved.
00016  *
00017  * Redistribution and use in source and binary forms, with or without
00018  * modification, are permitted provided that the following conditions
00019  * are met:
00020  * 1. Redistributions of source code must retain the above copyright
00021  *    notice, this list of conditions and the following disclaimer.
00022  * 2. Redistributions in binary form must reproduce the above copyright
00023  *    notice, this list of conditions and the following disclaimer in the
00024  *    documentation and/or other materials provided with the distribution.
00025  * 3. The name of the author may not be used to endorse or promote
00026  *    products derived from this software without specific prior
00027  *    written permission.
00028  *
00029  * THIS SOFTWARE IS PROVIDED BY THE AUTHOR ``AS IS'' AND ANY EXPRESS
00030  * OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED
00031  * WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
00032  * ARE DISCLAIMED.  IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR ANY
00033  * DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
00034  * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE
00035  * GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS
00036  * INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY,
00037  * WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING
00038  * NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF THIS
00039  * SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
00040  *
00041  *
00042  * DNS.C
00043  *
00044  * The lwIP DNS resolver functions are used to lookup a host name and
00045  * map it to a numerical IP address. It maintains a list of resolved
00046  * hostnames that can be queried with the dns_lookup() function.
00047  * New hostnames can be resolved using the dns_query() function.
00048  *
00049  * The lwIP version of the resolver also adds a non-blocking version of
00050  * gethostbyname() that will work with a raw API application. This function
00051  * checks for an IP address string first and converts it if it is valid.
00052  * gethostbyname() then does a dns_lookup() to see if the name is 
00053  * already in the table. If so, the IP is returned. If not, a query is 
00054  * issued and the function returns with a ERR_INPROGRESS status. The app
00055  * using the dns client must then go into a waiting state.
00056  *
00057  * Once a hostname has been resolved (or found to be non-existent),
00058  * the resolver code calls a specified callback function (which 
00059  * must be implemented by the module that uses the resolver).
00060  */
00061 
00062 /*-----------------------------------------------------------------------------
00063  * RFC 1035 - Domain names - implementation and specification
00064  * RFC 2181 - Clarifications to the DNS Specification
00065  *----------------------------------------------------------------------------*/
00066 
00067 /** @todo: define good default values (rfc compliance) */
00068 /** @todo: improve answer parsing, more checkings... */
00069 /** @todo: check RFC1035 - 7.3. Processing responses */
00070 
00071 /*-----------------------------------------------------------------------------
00072  * Includes
00073  *----------------------------------------------------------------------------*/
00074 
00075 #include "lwip/opt.h"
00076 
00077 #if LWIP_DNS /* don't build if not configured for use in lwipopts.h */
00078 
00079 #include "lwip/udp.h"
00080 #include "lwip/mem.h"
00081 #include "lwip/dns.h"
00082 
00083 #include <string.h>
00084 
00085 /** DNS server IP address */
00086 #ifndef DNS_SERVER_ADDRESS
00087 #define DNS_SERVER_ADDRESS        inet_addr("208.67.222.222") /* resolver1.opendns.com */
00088 #endif
00089 
00090 /** DNS server port address */
00091 #ifndef DNS_SERVER_PORT
00092 #define DNS_SERVER_PORT           53
00093 #endif
00094 
00095 /** DNS maximum number of retries when asking for a name, before "timeout". */
00096 #ifndef DNS_MAX_RETRIES
00097 #define DNS_MAX_RETRIES           4
00098 #endif
00099 
00100 /** DNS resource record max. TTL (one week as default) */
00101 #ifndef DNS_MAX_TTL
00102 #define DNS_MAX_TTL               604800
00103 #endif
00104 
00105 /* DNS protocol flags */
00106 #define DNS_FLAG1_RESPONSE        0x80
00107 #define DNS_FLAG1_OPCODE_STATUS   0x10
00108 #define DNS_FLAG1_OPCODE_INVERSE  0x08
00109 #define DNS_FLAG1_OPCODE_STANDARD 0x00
00110 #define DNS_FLAG1_AUTHORATIVE     0x04
00111 #define DNS_FLAG1_TRUNC           0x02
00112 #define DNS_FLAG1_RD              0x01
00113 #define DNS_FLAG2_RA              0x80
00114 #define DNS_FLAG2_ERR_MASK        0x0f
00115 #define DNS_FLAG2_ERR_NONE        0x00
00116 #define DNS_FLAG2_ERR_NAME        0x03
00117 
00118 /* DNS protocol states */
00119 #define DNS_STATE_UNUSED          0
00120 #define DNS_STATE_NEW             1
00121 #define DNS_STATE_ASKING          2
00122 #define DNS_STATE_DONE            3
00123 
00124 
00125 // XXX: For C++ compatibility
00126 #define class mclass
00127 
00128 #ifdef PACK_STRUCT_USE_INCLUDES
00129 #  include "arch/bpstruct.h"
00130 #endif
00131 PACK_STRUCT_BEGIN
00132 /** DNS message header */
00133 struct dns_hdr {
00134   u16_t id;
00135   u8_t flags1;
00136   u8_t flags2;
00137   u16_t numquestions;
00138   u16_t numanswers;
00139   u16_t numauthrr;
00140   u16_t numextrarr;
00141 } PACK_STRUCT_STRUCT;
00142 PACK_STRUCT_END
00143 #ifdef PACK_STRUCT_USE_INCLUDES
00144 #  include "arch/epstruct.h"
00145 #endif
00146 
00147 #ifdef PACK_STRUCT_USE_INCLUDES
00148 #  include "arch/bpstruct.h"
00149 #endif
00150 PACK_STRUCT_BEGIN
00151 /** DNS query message structure */
00152 struct dns_query {
00153   /* DNS query record starts with either a domain name or a pointer
00154      to a name already present somewhere in the packet. */
00155   u16_t type;
00156   u16_t class;
00157 } PACK_STRUCT_STRUCT;
00158 PACK_STRUCT_END
00159 #ifdef PACK_STRUCT_USE_INCLUDES
00160 #  include "arch/epstruct.h"
00161 #endif
00162 
00163 #ifdef PACK_STRUCT_USE_INCLUDES
00164 #  include "arch/bpstruct.h"
00165 #endif
00166 PACK_STRUCT_BEGIN
00167 /** DNS answer message structure */
00168 struct dns_answer {
00169   /* DNS answer record starts with either a domain name or a pointer
00170      to a name already present somewhere in the packet. */
00171   u16_t type;
00172   u16_t class;
00173   u32_t ttl;
00174   u16_t len;
00175 } PACK_STRUCT_STRUCT;
00176 PACK_STRUCT_END
00177 #ifdef PACK_STRUCT_USE_INCLUDES
00178 #  include "arch/epstruct.h"
00179 #endif
00180 
00181 /** DNS table entry */
00182 struct dns_table_entry {
00183   u8_t  state;
00184   u8_t  numdns;
00185   u8_t  tmr;
00186   u8_t  retries;
00187   u8_t  seqno;
00188   u8_t  err;
00189   u32_t ttl;
00190   char name[DNS_MAX_NAME_LENGTH];
00191   struct ip_addr ipaddr;
00192   /* pointer to callback on DNS query done */
00193   dns_found_callback found;
00194   void *arg;
00195 };
00196 
00197 
00198 /* forward declarations */
00199 static void dns_recv(void *s, struct udp_pcb *pcb, struct pbuf *p, struct ip_addr *addr, u16_t port);
00200 static void dns_check_entries(void);
00201 
00202 /*-----------------------------------------------------------------------------
00203  * Globales
00204  *----------------------------------------------------------------------------*/
00205 
00206 /* DNS variables */
00207 static struct udp_pcb        *dns_pcb;
00208 static u8_t                   dns_seqno;
00209 static struct dns_table_entry dns_table[DNS_TABLE_SIZE];
00210 static struct ip_addr         dns_servers[DNS_MAX_SERVERS];
00211 
00212 #if (DNS_USES_STATIC_BUF == 1)
00213 static u8_t                   dns_payload[DNS_MSG_SIZE];
00214 #endif /* (DNS_USES_STATIC_BUF == 1) */
00215 
00216 /**
00217  * Initialize the resolver: set up the UDP pcb and configure the default server
00218  * (DNS_SERVER_ADDRESS).
00219  */
00220 void
00221 dns_init()
00222 {
00223   struct ip_addr dnsserver;
00224   
00225   /* initialize default DNS server address */
00226   dnsserver.addr = DNS_SERVER_ADDRESS;
00227 
00228   LWIP_DEBUGF(DNS_DEBUG, ("dns_init: initializing\n"));
00229 
00230   /* if dns client not yet initialized... */
00231   if (dns_pcb == NULL) {
00232     dns_pcb = udp_new();
00233 
00234     if (dns_pcb != NULL) {
00235       /* initialize DNS table not needed (initialized to zero since it is a
00236        * global variable) */
00237       LWIP_ASSERT("For implicit initialization to work, DNS_STATE_UNUSED needs to be 0",
00238         DNS_STATE_UNUSED == 0);
00239 
00240       /* initialize DNS client */
00241       udp_bind(dns_pcb, IP_ADDR_ANY, 0);
00242       udp_recv(dns_pcb, dns_recv, NULL);
00243 
00244       /* initialize default DNS primary server */
00245       dns_setserver(0, &dnsserver);
00246     }
00247   }
00248 }
00249 
00250 /**
00251  * Initialize one of the DNS servers.
00252  *
00253  * @param numdns the index of the DNS server to set must be < DNS_MAX_SERVERS
00254  * @param dnsserver IP address of the DNS server to set
00255  */
00256 void
00257 dns_setserver(u8_t numdns, struct ip_addr *dnsserver)
00258 {
00259   if ((numdns < DNS_MAX_SERVERS) && (dns_pcb != NULL) &&
00260       (dnsserver != NULL) && (dnsserver->addr !=0 )) {
00261     dns_servers[numdns] = (*dnsserver);
00262   }
00263 }
00264 
00265 /**
00266  * Obtain one of the currently configured DNS server.
00267  *
00268  * @param numdns the index of the DNS server
00269  * @return IP address of the indexed DNS server or "ip_addr_any" if the DNS
00270  *         server has not been configured.
00271  */
00272 struct ip_addr
00273 dns_getserver(u8_t numdns)
00274 {
00275   if (numdns < DNS_MAX_SERVERS) {
00276     return dns_servers[numdns];
00277   } else {
00278     return *IP_ADDR_ANY;
00279   }
00280 }
00281 
00282 /**
00283  * The DNS resolver client timer - handle retries and timeouts and should
00284  * be called every DNS_TMR_INTERVAL milliseconds (every second by default).
00285  */
00286 void
00287 dns_tmr(void)
00288 {
00289   if (dns_pcb != NULL) {
00290     LWIP_DEBUGF(DNS_DEBUG, ("dns_tmr: dns_check_entries\n"));
00291     dns_check_entries();
00292   }
00293 }
00294 
00295 /**
00296  * Look up a hostname in the array of known hostnames.
00297  *
00298  * @note This function only looks in the internal array of known
00299  * hostnames, it does not send out a query for the hostname if none
00300  * was found. The function dns_enqueue() can be used to send a query
00301  * for a hostname.
00302  *
00303  * @param name the hostname to look up
00304  * @return the hostname's IP address, as u32_t (instead of struct ip_addr to
00305  *         better check for failure: != 0) or 0 if the hostname was not found
00306  *         in the cached dns_table.
00307  */
00308 static u32_t
00309 dns_lookup(const char *name)
00310 {
00311   u8_t i;
00312 
00313   /* Walk through name list, return entry if found. If not, return NULL. */
00314   for (i = 0; i < DNS_TABLE_SIZE; ++i) {
00315     if ((dns_table[i].state == DNS_STATE_DONE) &&
00316         (strcmp(name, dns_table[i].name) == 0)) {
00317       LWIP_DEBUGF(DNS_DEBUG, ("dns_lookup: \"%s\": found = ", name));
00318       ip_addr_debug_print(DNS_DEBUG, &(dns_table[i].ipaddr));
00319       LWIP_DEBUGF(DNS_DEBUG, ("\n"));
00320       return dns_table[i].ipaddr.addr;
00321     }
00322   }
00323 
00324   return 0;
00325 }
00326 
00327 #if DNS_DOES_NAME_CHECK
00328 /**
00329  * Compare the "dotted" name "query" with the encoded name "response"
00330  * to make sure an answer from the DNS server matches the current dns_table
00331  * entry (otherwise, answers might arrive late for hostname not on the list
00332  * any more).
00333  *
00334  * @param query hostname (not encoded) from the dns_table
00335  * @param response encoded hostname in the DNS response
00336  * @return 0: names equal; 1: names differ
00337  */
00338 static u8_t
00339 dns_compare_name(unsigned char *query, unsigned char *response)
00340 {
00341   unsigned char n;
00342 
00343   do {
00344     n = *response++;
00345     /** @see RFC 1035 - 4.1.4. Message compression */
00346     if ((n & 0xc0) == 0xc0) {
00347       /* Compressed name */
00348       break;
00349     } else {
00350       /* Not compressed name */
00351       while (n > 0) {
00352         if ((*query) != (*response)) {
00353           return 1;
00354         }
00355         ++response;
00356         ++query;
00357         --n;
00358       };
00359       ++query;
00360     }
00361   } while (*response != 0);
00362 
00363   return 0;
00364 }
00365 #endif /* DNS_DOES_NAME_CHECK */
00366 
00367 /**
00368  * Walk through a compact encoded DNS name and return the end of the name.
00369  *
00370  * @param query encoded DNS name in the DNS server response
00371  * @return end of the name
00372  */
00373 static unsigned char *
00374 dns_parse_name(unsigned char *query)
00375 {
00376   unsigned char n;
00377 
00378   do {
00379     n = *query++;
00380     /** @see RFC 1035 - 4.1.4. Message compression */
00381     if ((n & 0xc0) == 0xc0) {
00382       /* Compressed name */
00383       break;
00384     } else {
00385       /* Not compressed name */
00386       while (n > 0) {
00387         ++query;
00388         --n;
00389       };
00390     }
00391   } while (*query != 0);
00392 
00393   return query + 1;
00394 }
00395 
00396 /**
00397  * Send a DNS query packet.
00398  *
00399  * @param numdns index of the DNS server in the dns_servers table
00400  * @param name hostname to query
00401  * @param id index of the hostname in dns_table, used as transaction ID in the
00402  *        DNS query packet
00403  * @return ERR_OK if packet is sent; an err_t indicating the problem otherwise
00404  */
00405 static err_t
00406 dns_send(u8_t numdns, const char* name, u8_t id)
00407 {
00408   err_t err;
00409   struct dns_hdr *hdr;
00410   struct dns_query qry;
00411   struct pbuf *p;
00412   char *query, *nptr;
00413   const char *pHostname;
00414   u8_t n;
00415 
00416   LWIP_DEBUGF(DNS_DEBUG, ("dns_send: dns_servers[%"U16_F"] \"%s\": request\n",
00417               (u16_t)(numdns), name));
00418   LWIP_ASSERT("dns server out of array", numdns < DNS_MAX_SERVERS);
00419   LWIP_ASSERT("dns server has no IP address set", dns_servers[numdns].addr != 0);
00420 
00421   /* if here, we have either a new query or a retry on a previous query to process */
00422   p = pbuf_alloc(PBUF_TRANSPORT, sizeof(struct dns_hdr) + DNS_MAX_NAME_LENGTH +
00423                  sizeof(struct dns_query), PBUF_RAM);
00424   if (p != NULL) {
00425     LWIP_ASSERT("pbuf must be in one piece", p->next == NULL);
00426     /* fill dns header */
00427     hdr = (struct dns_hdr*)p->payload;
00428     memset(hdr, 0, sizeof(struct dns_hdr));
00429     hdr->id = htons(id);
00430     hdr->flags1 = DNS_FLAG1_RD;
00431     hdr->numquestions = htons(1);
00432     query = (char*)hdr + sizeof(struct dns_hdr);
00433     pHostname = name;
00434     --pHostname;
00435 
00436     /* convert hostname into suitable query format. */
00437     do {
00438       ++pHostname;
00439       nptr = query;
00440       ++query;
00441       for(n = 0; *pHostname != '.' && *pHostname != 0; ++pHostname) {
00442         *query = *pHostname;
00443         ++query;
00444         ++n;
00445       }
00446       *nptr = n;
00447     } while(*pHostname != 0);
00448     *query++='\0';
00449 
00450     /* fill dns query */
00451     qry.type  = htons(DNS_RRTYPE_A);
00452     qry.class = htons(DNS_RRCLASS_IN);
00453     MEMCPY( query, &qry, sizeof(struct dns_query));
00454 
00455     /* resize pbuf to the exact dns query */
00456     pbuf_realloc(p, (query + sizeof(struct dns_query)) - ((char*)(p->payload)));
00457 
00458     /* connect to the server for faster receiving */
00459     udp_connect(dns_pcb, &dns_servers[numdns], DNS_SERVER_PORT);
00460     /* send dns packet */
00461     err = udp_sendto(dns_pcb, p, &dns_servers[numdns], DNS_SERVER_PORT);
00462 
00463     /* free pbuf */
00464     pbuf_free(p);
00465   } else {
00466     err = ERR_MEM;
00467   }
00468 
00469   return err;
00470 }
00471 
00472 /**
00473  * dns_check_entry() - see if pEntry has not yet been queried and, if so, sends out a query.
00474  * Check an entry in the dns_table:
00475  * - send out query for new entries
00476  * - retry old pending entries on timeout (also with different servers)
00477  * - remove completed entries from the table if their TTL has expired
00478  *
00479  * @param i index of the dns_table entry to check
00480  */
00481 static void
00482 dns_check_entry(u8_t i)
00483 {
00484   struct dns_table_entry *pEntry = &dns_table[i];
00485 
00486   LWIP_ASSERT("array index out of bounds", i < DNS_TABLE_SIZE);
00487 
00488   switch(pEntry->state) {
00489 
00490     case DNS_STATE_NEW: {
00491       /* initialize new entry */
00492       pEntry->state   = DNS_STATE_ASKING;
00493       pEntry->numdns  = 0;
00494       pEntry->tmr     = 1;
00495       pEntry->retries = 0;
00496       
00497       /* send DNS packet for this entry */
00498       dns_send(pEntry->numdns, pEntry->name, i);
00499       break;
00500     }
00501 
00502     case DNS_STATE_ASKING: {
00503       if (--pEntry->tmr == 0) {
00504         if (++pEntry->retries == DNS_MAX_RETRIES) {
00505           if ((pEntry->numdns+1<DNS_MAX_SERVERS) && (dns_servers[pEntry->numdns+1].addr!=0)) {
00506             /* change of server */
00507             pEntry->numdns++;
00508             pEntry->tmr     = 1;
00509             pEntry->retries = 0;
00510             break;
00511           } else {
00512             LWIP_DEBUGF(DNS_DEBUG, ("dns_check_entry: \"%s\": timeout\n", pEntry->name));
00513             /* call specified callback function if provided */
00514             if (pEntry->found)
00515               (*pEntry->found)(pEntry->name, NULL, pEntry->arg);
00516             /* flush this entry */
00517             pEntry->state   = DNS_STATE_UNUSED;
00518             pEntry->found   = NULL;
00519             break;
00520           }
00521         }
00522 
00523         /* wait longer for the next retry */
00524         pEntry->tmr = pEntry->retries;
00525 
00526         /* send DNS packet for this entry */
00527         dns_send(pEntry->numdns, pEntry->name, i);
00528       }
00529       break;
00530     }
00531 
00532     case DNS_STATE_DONE: {
00533       /* if the time to live is nul */
00534       if (--pEntry->ttl == 0) {
00535         LWIP_DEBUGF(DNS_DEBUG, ("dns_check_entry: \"%s\": flush\n", pEntry->name));
00536         /* flush this entry */
00537         pEntry->state = DNS_STATE_UNUSED;
00538         pEntry->found = NULL;
00539       }
00540       break;
00541     }
00542     case DNS_STATE_UNUSED:
00543       /* nothing to do */
00544       break;
00545     default:
00546       LWIP_ASSERT("unknown dns_table entry state:", 0);
00547       break;
00548   }
00549 }
00550 
00551 /**
00552  * Call dns_check_entry for each entry in dns_table - check all entries.
00553  */
00554 static void
00555 dns_check_entries(void)
00556 {
00557   u8_t i;
00558 
00559   for (i = 0; i < DNS_TABLE_SIZE; ++i) {
00560     dns_check_entry(i);
00561   }
00562 }
00563 
00564 /**
00565  * Receive input function for DNS response packets arriving for the dns UDP pcb.
00566  *
00567  * @params see udp.h
00568  */
00569 static void
00570 dns_recv(void *arg, struct udp_pcb *pcb, struct pbuf *p, struct ip_addr *addr, u16_t port)
00571 {
00572   u8_t i;
00573   char *pHostname;
00574   struct dns_hdr *hdr;
00575   struct dns_answer ans;
00576   struct dns_table_entry *pEntry;
00577   u8_t nquestions, nanswers;
00578 #if (DNS_USES_STATIC_BUF == 0)
00579   u8_t dns_payload[DNS_MSG_SIZE];
00580 #endif /* (DNS_USES_STATIC_BUF == 0) */
00581 #if (DNS_USES_STATIC_BUF == 2)
00582   u8_t* dns_payload;
00583 #endif /* (DNS_USES_STATIC_BUF == 2) */
00584 
00585   LWIP_UNUSED_ARG(arg);
00586   LWIP_UNUSED_ARG(pcb);
00587   LWIP_UNUSED_ARG(addr);
00588   LWIP_UNUSED_ARG(port);
00589 
00590   /* is the dns message too big ? */
00591   if (p->tot_len > DNS_MSG_SIZE) {
00592     LWIP_DEBUGF(DNS_DEBUG, ("dns_recv: pbuf too big\n"));
00593     /* free pbuf and return */
00594     goto memerr1;
00595   }
00596 
00597   /* is the dns message big enough ? */
00598   if (p->tot_len < (sizeof(struct dns_hdr) + sizeof(struct dns_query) + sizeof(struct dns_answer))) {
00599     LWIP_DEBUGF(DNS_DEBUG, ("dns_recv: pbuf too small\n"));
00600     /* free pbuf and return */
00601     goto memerr1;
00602   }
00603 
00604 #if (DNS_USES_STATIC_BUF == 2)
00605   dns_payload = mem_malloc(p->tot_len);
00606   if (dns_payload == NULL) {
00607     LWIP_DEBUGF(DNS_DEBUG, ("dns_recv: mem_malloc error\n"));
00608     /* free pbuf and return */
00609     goto memerr1;
00610   }
00611 #endif /* (DNS_USES_STATIC_BUF == 2) */
00612 
00613   /* copy dns payload inside static buffer for processing */ 
00614   if (pbuf_copy_partial(p, dns_payload, p->tot_len, 0) == p->tot_len) {
00615     /* The ID in the DNS header should be our entry into the name table. */
00616     hdr = (struct dns_hdr*)dns_payload;
00617     i = htons(hdr->id);
00618     if (i < DNS_TABLE_SIZE) {
00619       pEntry = &dns_table[i];
00620       if(pEntry->state == DNS_STATE_ASKING) {
00621         /* This entry is now completed. */
00622         pEntry->state = DNS_STATE_DONE;
00623         pEntry->err   = hdr->flags2 & DNS_FLAG2_ERR_MASK;
00624 
00625         /* We only care about the question(s) and the answers. The authrr
00626            and the extrarr are simply discarded. */
00627         nquestions = htons(hdr->numquestions);
00628         nanswers   = htons(hdr->numanswers);
00629 
00630         /* Check for error. If so, call callback to inform. */
00631         if (((hdr->flags1 & DNS_FLAG1_RESPONSE) == 0) || (pEntry->err != 0) || (nquestions != 1)) {
00632           LWIP_DEBUGF(DNS_DEBUG, ("dns_recv: \"%s\": error in flags\n", pEntry->name));
00633           /* call callback to indicate error, clean up memory and return */
00634           goto responseerr;
00635         }
00636 
00637 #if DNS_DOES_NAME_CHECK
00638         /* Check if the name in the "question" part match with the name in the entry. */
00639         if (dns_compare_name((unsigned char *)(pEntry->name), (unsigned char *)dns_payload + sizeof(struct dns_hdr)) != 0) {
00640           LWIP_DEBUGF(DNS_DEBUG, ("dns_recv: \"%s\": response not match to query\n", pEntry->name));
00641           /* call callback to indicate error, clean up memory and return */
00642           goto responseerr;
00643         }
00644 #endif /* DNS_DOES_NAME_CHECK */
00645 
00646         /* Skip the name in the "question" part */
00647         pHostname = (char *) dns_parse_name((unsigned char *)dns_payload + sizeof(struct dns_hdr)) + sizeof(struct dns_query);
00648 
00649         while(nanswers > 0) {
00650           /* skip answer resource record's host name */
00651           pHostname = (char *) dns_parse_name((unsigned char *)pHostname);
00652 
00653           /* Check for IP address type and Internet class. Others are discarded. */
00654           MEMCPY(&ans, pHostname, sizeof(struct dns_answer));
00655           if((ntohs(ans.type) == DNS_RRTYPE_A) && (ntohs(ans.class) == DNS_RRCLASS_IN) && (ntohs(ans.len) == sizeof(struct ip_addr)) ) {
00656             /* read the answer resource record's TTL, and maximize it if needed */
00657             pEntry->ttl = ntohl(ans.ttl);
00658             if (pEntry->ttl > DNS_MAX_TTL) {
00659               pEntry->ttl = DNS_MAX_TTL;
00660             }
00661             /* read the IP address after answer resource record's header */
00662             MEMCPY( &(pEntry->ipaddr), (pHostname+sizeof(struct dns_answer)), sizeof(struct ip_addr));
00663             LWIP_DEBUGF(DNS_DEBUG, ("dns_recv: \"%s\": response = ", pEntry->name));
00664             ip_addr_debug_print(DNS_DEBUG, (&(pEntry->ipaddr)));
00665             LWIP_DEBUGF(DNS_DEBUG, ("\n"));
00666             /* call specified callback function if provided */
00667             if (pEntry->found) {
00668               (*pEntry->found)(pEntry->name, &pEntry->ipaddr, pEntry->arg);
00669             }
00670             /* deallocate memory and return */
00671             goto memerr2;
00672           } else {
00673             pHostname = pHostname + sizeof(struct dns_answer) + htons(ans.len);
00674           }
00675           --nanswers;
00676         }
00677         LWIP_DEBUGF(DNS_DEBUG, ("dns_recv: \"%s\": error in response\n", pEntry->name));
00678         /* call callback to indicate error, clean up memory and return */
00679         goto responseerr;
00680       }
00681     }
00682   }
00683 
00684   /* deallocate memory and return */
00685   goto memerr2;
00686 
00687 responseerr:
00688   /* ERROR: call specified callback function with NULL as name to indicate an error */
00689   if (pEntry->found) {
00690     (*pEntry->found)(pEntry->name, NULL, pEntry->arg);
00691   }
00692   /* flush this entry */
00693   pEntry->state = DNS_STATE_UNUSED;
00694   pEntry->found = NULL;
00695 
00696 memerr2:
00697 #if (DNS_USES_STATIC_BUF == 2)
00698   /* free dns buffer */
00699   mem_free(dns_payload);
00700 #endif /* (DNS_USES_STATIC_BUF == 2) */
00701 
00702 memerr1:
00703   /* free pbuf */
00704   pbuf_free(p);
00705   return;
00706 }
00707 
00708 /**
00709  * Queues a new hostname to resolve and sends out a DNS query for that hostname
00710  *
00711  * @param name the hostname that is to be queried
00712  * @param found a callback founction to be called on success, failure or timeout
00713  * @param callback_arg argument to pass to the callback function
00714  * @return @return a err_t return code.
00715  */
00716 static err_t
00717 dns_enqueue(const char *name, dns_found_callback found, void *callback_arg)
00718 {
00719   u8_t i;
00720   u8_t lseq, lseqi;
00721   struct dns_table_entry *pEntry = NULL;
00722 
00723   /* search an unused entry, or the oldest one */
00724   lseq = lseqi = 0;
00725   for (i = 0; i < DNS_TABLE_SIZE; ++i) {
00726     pEntry = &dns_table[i];
00727     /* is it an unused entry ? */
00728     if (pEntry->state == DNS_STATE_UNUSED)
00729       break;
00730 
00731     /* check if this is the oldest completed entry */
00732     if (pEntry->state == DNS_STATE_DONE) {
00733       if ((dns_seqno - pEntry->seqno) > lseq) {
00734         lseq = dns_seqno - pEntry->seqno;
00735         lseqi = i;
00736       }
00737     }
00738   }
00739 
00740   /* if we don't have found an unused entry, use the oldest completed one */
00741   if (i == DNS_TABLE_SIZE) {
00742     if ((lseqi >= DNS_TABLE_SIZE) || (dns_table[lseqi].state != DNS_STATE_DONE)) {
00743       /* no entry can't be used now, table is full */
00744       LWIP_DEBUGF(DNS_DEBUG, ("dns_enqueue: \"%s\": DNS entries table is full\n", name));
00745       return ERR_MEM;
00746     } else {
00747       /* use the oldest completed one */
00748       i = lseqi;
00749       pEntry = &dns_table[i];
00750     }
00751   }
00752 
00753   /* use this entry */
00754   LWIP_DEBUGF(DNS_DEBUG, ("dns_enqueue: \"%s\": use DNS entry %"U16_F"\n", name, (u16_t)(i)));
00755 
00756   /* fill the entry */
00757   pEntry->state = DNS_STATE_NEW;
00758   pEntry->seqno = dns_seqno++;
00759   pEntry->found = found;
00760   pEntry->arg   = callback_arg;
00761   strcpy(pEntry->name, name);
00762 
00763   /* force to send query without waiting timer */
00764   dns_check_entry(i);
00765 
00766   /* dns query is enqueued */
00767   return ERR_INPROGRESS;
00768 }
00769 
00770 /**
00771  * Resolve a hostname (string) into an IP address.
00772  * NON-BLOCKING callback version for use with raw API!!!
00773  *
00774  * Returns immediately with one of err_t return codes:
00775  * - ERR_OK if hostname is a valid IP address string or the host
00776  *   name is already in the local names table.
00777  * - ERR_INPROGRESS enqueue a request to be sent to the DNS server
00778  *   for resolution if no errors are present.
00779  *
00780  * @param hostname the hostname that is to be queried
00781  * @param addr pointer to a struct ip_addr where to store the address if it is already
00782  *             cached in the dns_table (only valid if ERR_OK is returned!)
00783  * @param found a callback function to be called on success, failure or timeout (only if
00784  *              ERR_INPROGRESS is returned!)
00785  * @param callback_arg argument to pass to the callback function
00786  * @return a err_t return code.
00787  */
00788 err_t
00789 dns_gethostbyname(const char *hostname, struct ip_addr *addr, dns_found_callback found,
00790                   void *callback_arg)
00791 {
00792   /* not initialized or no valid server yet, or invalid addr pointer
00793    * or invalid hostname or invalid hostname length */
00794   if ((dns_pcb == NULL) || (addr == NULL) ||
00795       (!hostname) || (!hostname[0]) ||
00796       (strlen(hostname) >= DNS_MAX_NAME_LENGTH)) {
00797     return ERR_VAL;
00798   }
00799 
00800 #if LWIP_HAVE_LOOPIF
00801   if (strcmp(hostname,"localhost")==0) {
00802     addr->addr = INADDR_LOOPBACK;
00803     return ERR_OK;
00804   }
00805 #endif /* LWIP_HAVE_LOOPIF */
00806 
00807   /* host name already in octet notation? set ip addr and return ERR_OK
00808    * already have this address cached? */
00809   if (((addr->addr = inet_addr(hostname)) != INADDR_NONE) ||
00810       ((addr->addr = dns_lookup(hostname)) != 0)) {
00811     return ERR_OK;
00812   }
00813 
00814   /* queue query with specified callback */
00815   return dns_enqueue(hostname, found, callback_arg);
00816 }
00817 
00818 #endif /* LWIP_DNS */