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 #define SIZEOF_DNS_HDR 12
00147 
00148 #ifdef PACK_STRUCT_USE_INCLUDES
00149 #  include "arch/bpstruct.h"
00150 #endif
00151 PACK_STRUCT_BEGIN
00152 /** DNS query message structure */
00153 struct dns_query {
00154   /* DNS query record starts with either a domain name or a pointer
00155      to a name already present somewhere in the packet. */
00156   u16_t type;
00157   u16_t class;
00158 } PACK_STRUCT_STRUCT;
00159 PACK_STRUCT_END
00160 #ifdef PACK_STRUCT_USE_INCLUDES
00161 #  include "arch/epstruct.h"
00162 #endif
00163 #define SIZEOF_DNS_QUERY 4
00164 
00165 #ifdef PACK_STRUCT_USE_INCLUDES
00166 #  include "arch/bpstruct.h"
00167 #endif
00168 PACK_STRUCT_BEGIN
00169 /** DNS answer message structure */
00170 struct dns_answer {
00171   /* DNS answer record starts with either a domain name or a pointer
00172      to a name already present somewhere in the packet. */
00173   u16_t type;
00174   u16_t class;
00175   u32_t ttl;
00176   u16_t len;
00177 } PACK_STRUCT_STRUCT;
00178 PACK_STRUCT_END
00179 #ifdef PACK_STRUCT_USE_INCLUDES
00180 #  include "arch/epstruct.h"
00181 #endif
00182 #define SIZEOF_DNS_ANSWER 10
00183 
00184 /** DNS table entry */
00185 struct dns_table_entry {
00186   u8_t  state;
00187   u8_t  numdns;
00188   u8_t  tmr;
00189   u8_t  retries;
00190   u8_t  seqno;
00191   u8_t  err;
00192   u32_t ttl;
00193   char name[DNS_MAX_NAME_LENGTH];
00194   struct ip_addr ipaddr;
00195   /* pointer to callback on DNS query done */
00196   dns_found_callback found;
00197   void *arg;
00198 };
00199 
00200 #if DNS_LOCAL_HOSTLIST
00201 /** struct used for local host-list */
00202 struct local_hostlist_entry {
00203   /** static hostname */
00204   const char *name;
00205   /** static host address in network byteorder */
00206   u32_t addr;
00207   struct local_hostlist_entry *next;
00208 };
00209 
00210 #if !DNS_LOCAL_HOSTLIST_IS_DYNAMIC
00211 static struct local_hostlist_entry local_hostlist_static[] = DNS_LOCAL_HOSTLIST_INIT MEM_POSITION;
00212 #endif /* DNS_LOCAL_HOSTLIST_IS_DYNAMIC */
00213 
00214 /** Local host-list. For hostnames in this list, no
00215  *  external name resolution is performed */
00216 static struct local_hostlist_entry *local_hostlist;
00217 
00218 static void dns_init_local();
00219 #endif /* DNS_LOCAL_HOSTLIST */
00220 
00221 
00222 /* forward declarations */
00223 static void dns_recv(void *s, struct udp_pcb *pcb, struct pbuf *p, struct ip_addr *addr, u16_t port);
00224 static void dns_check_entries(void);
00225 
00226 /*-----------------------------------------------------------------------------
00227  * Globales
00228  *----------------------------------------------------------------------------*/
00229 
00230 /* DNS variables */
00231 static struct udp_pcb        *dns_pcb;
00232 static u8_t                   dns_seqno;
00233 static struct dns_table_entry dns_table[DNS_TABLE_SIZE] MEM_POSITION;
00234 static struct ip_addr         dns_servers[DNS_MAX_SERVERS] MEM_POSITION;
00235 
00236 #if (DNS_USES_STATIC_BUF == 1)
00237 static u8_t                   dns_payload[DNS_MSG_SIZE] MEM_POSITION;
00238 #endif /* (DNS_USES_STATIC_BUF == 1) */
00239 
00240 /**
00241  * Initialize the resolver: set up the UDP pcb and configure the default server
00242  * (DNS_SERVER_ADDRESS).
00243  */
00244 void
00245 dns_init()
00246 {
00247   struct ip_addr dnsserver;
00248   
00249   /* initialize default DNS server address */
00250   dnsserver.addr = DNS_SERVER_ADDRESS;
00251 
00252   LWIP_DEBUGF(DNS_DEBUG, ("dns_init: initializing\n"));
00253 
00254   /* if dns client not yet initialized... */
00255   if (dns_pcb == NULL) {
00256     dns_pcb = udp_new();
00257 
00258     if (dns_pcb != NULL) {
00259       /* initialize DNS table not needed (initialized to zero since it is a
00260        * global variable) */
00261       LWIP_ASSERT("For implicit initialization to work, DNS_STATE_UNUSED needs to be 0",
00262         DNS_STATE_UNUSED == 0);
00263 
00264       /* initialize DNS client */
00265       udp_bind(dns_pcb, IP_ADDR_ANY, 0);
00266       udp_recv(dns_pcb, dns_recv, NULL);
00267 
00268       /* initialize default DNS primary server */
00269       dns_setserver(0, &dnsserver);
00270     }
00271   }
00272 #if DNS_LOCAL_HOSTLIST
00273   dns_init_local();
00274 #endif
00275 }
00276 
00277 /**
00278  * Initialize one of the DNS servers.
00279  *
00280  * @param numdns the index of the DNS server to set must be < DNS_MAX_SERVERS
00281  * @param dnsserver IP address of the DNS server to set
00282  */
00283 void
00284 dns_setserver(u8_t numdns, struct ip_addr *dnsserver)
00285 {
00286   if ((numdns < DNS_MAX_SERVERS) && (dns_pcb != NULL) &&
00287       (dnsserver != NULL) && (dnsserver->addr !=0 )) {
00288     dns_servers[numdns] = (*dnsserver);
00289   }
00290 }
00291 
00292 /**
00293  * Obtain one of the currently configured DNS server.
00294  *
00295  * @param numdns the index of the DNS server
00296  * @return IP address of the indexed DNS server or "ip_addr_any" if the DNS
00297  *         server has not been configured.
00298  */
00299 struct ip_addr
00300 dns_getserver(u8_t numdns)
00301 {
00302   if (numdns < DNS_MAX_SERVERS) {
00303     return dns_servers[numdns];
00304   } else {
00305     return *IP_ADDR_ANY;
00306   }
00307 }
00308 
00309 /**
00310  * The DNS resolver client timer - handle retries and timeouts and should
00311  * be called every DNS_TMR_INTERVAL milliseconds (every second by default).
00312  */
00313 void
00314 dns_tmr(void)
00315 {
00316   if (dns_pcb != NULL) {
00317     LWIP_DEBUGF(DNS_DEBUG, ("dns_tmr: dns_check_entries\n"));
00318     dns_check_entries();
00319   }
00320 }
00321 
00322 #if DNS_LOCAL_HOSTLIST
00323 static void
00324 dns_init_local()
00325 {
00326 #ifdef DNS_LOCAL_HOSTLIST_INIT
00327   int i;
00328   struct local_hostlist_entry *entry;
00329 #if DNS_LOCAL_HOSTLIST_IS_DYNAMIC
00330   /* Dynamic: copy entries from DNS_LOCAL_HOSTLIST_INIT to list */
00331   struct local_hostlist_entry local_hostlist_init[] = DNS_LOCAL_HOSTLIST_INIT;
00332   for (i = 0; i < sizeof(local_hostlist_init) / sizeof(struct local_hostlist_entry); i++) {
00333     entry = mem_malloc(sizeof(struct local_hostlist_entry));
00334     LWIP_ASSERT("mem-error in dns_init_local", entry != NULL);
00335     if (entry != NULL) {
00336       struct local_hostlist_entry *init_entry = &local_hostlist_init[i];
00337       entry->name = init_entry->name;
00338       entry->addr = init_entry->addr;
00339       entry->next = local_hostlist;
00340       local_hostlist = entry;
00341     }
00342   }
00343 #else /* DNS_LOCAL_HOSTLIST_IS_DYNAMIC */
00344   /* Static: only adjust the 'next' pointers */
00345   entry = NULL;
00346   local_hostlist = local_hostlist_static;
00347   for (i = sizeof(local_hostlist_static) / sizeof(struct local_hostlist_entry) - 1; i >= 0; i--) {
00348     local_hostlist_static[i].next = entry;
00349     entry = &local_hostlist_static[i];
00350   }
00351 #endif /* DNS_LOCAL_HOSTLIST_IS_DYNAMIC */
00352 #endif /* DNS_LOCAL_HOSTLIST_INIT */
00353 }
00354 
00355 static u32_t
00356 dns_lookup_static(const char *name)
00357 {
00358   struct local_hostlist_entry *entry = local_hostlist;
00359   while(entry != NULL) {
00360     if(strcmp(entry->name, name) == 0) {
00361       return htons(entry->addr);
00362     }
00363     entry = entry->next;
00364   }
00365   return INADDR_NONE;
00366 }
00367 
00368 #if DNS_LOCAL_HOSTLIST_IS_DYNAMIC
00369 /** Remove all entries from the local host-list for a specific hostname
00370  *
00371  * @param hostname hostname for which entries shall be removed from the local
00372  *                 host-list
00373  * @return the number of removed entries
00374  */
00375 int
00376 dns_local_removehostname(const char *hostname)
00377 {
00378   int removed = 0;
00379   struct local_hostlist_entry *entry = local_hostlist;
00380   struct local_hostlist_entry *last_entry = NULL;
00381   while (entry != NULL) {
00382     if (!strcmp(entry->name, hostname)) {
00383       if (last_entry != NULL) {
00384         last_entry->next = entry->next;
00385       } else {
00386         local_hostlist = entry->next;
00387       }
00388       mem_free(entry);
00389       removed++;
00390     }
00391     last_entry = entry;
00392     entry = entry->next;
00393   }
00394   return removed;
00395 }
00396 
00397 /** Remove all entries from the local host-list for a specific address
00398  *
00399  * @param addr address for which entries shall be removed from the local
00400  *                 host-list
00401  * @return the number of removed entries
00402  */
00403 int
00404 dns_local_removehostaddr(const struct ip_addr *addr)
00405 {
00406   int removed = 0;
00407   struct local_hostlist_entry *entry = local_hostlist;
00408   struct local_hostlist_entry *last_entry = NULL;
00409   while (entry != NULL) {
00410     if (entry->addr == addr->addr) {
00411       struct local_hostlist_entry *removed_entry = entry;
00412       if (last_entry != NULL) {
00413         last_entry->next = entry->next;
00414       } else {
00415         local_hostlist = entry->next;
00416       }
00417       entry = entry->next;
00418       mem_free(removed_entry);
00419       removed++;
00420     } else {
00421       last_entry = entry;
00422       entry = entry->next;
00423     }
00424   }
00425   return removed;
00426 }
00427 
00428 err_t
00429 dns_local_addhost(const char *hostname, const struct ip_addr *addr)
00430 {
00431   struct local_hostlist_entry *entry;
00432   entry = mem_malloc(sizeof(struct local_hostlist_entry));
00433   if (entry == NULL) {
00434     return ERR_MEM;
00435   }
00436   entry->name = hostname;
00437   entry->addr = addr->addr;
00438   entry->next = local_hostlist;
00439   local_hostlist = entry;
00440   return ERR_OK;
00441 }
00442 #endif /* DNS_LOCAL_HOSTLIST_IS_DYNAMIC*/
00443 #endif /* DNS_LOCAL_HOSTLIST */
00444 
00445 /**
00446  * Look up a hostname in the array of known hostnames.
00447  *
00448  * @note This function only looks in the internal array of known
00449  * hostnames, it does not send out a query for the hostname if none
00450  * was found. The function dns_enqueue() can be used to send a query
00451  * for a hostname.
00452  *
00453  * @param name the hostname to look up
00454  * @return the hostname's IP address, as u32_t (instead of struct ip_addr to
00455  *         better check for failure: != INADDR_NONE) or INADDR_NONE if the hostname
00456  *         was not found in the cached dns_table.
00457  */
00458 static u32_t
00459 dns_lookup(const char *name)
00460 {
00461   u8_t i;
00462 #if DNS_LOCAL_HOSTLIST
00463   u32_t addr;
00464 
00465   if ((addr = dns_lookup_static(name)) != INADDR_NONE) {
00466     return addr;
00467   }
00468 #endif /* DNS_LOCAL_HOSTLIST */
00469 
00470   /* Walk through name list, return entry if found. If not, return NULL. */
00471   for (i = 0; i < DNS_TABLE_SIZE; ++i) {
00472     if ((dns_table[i].state == DNS_STATE_DONE) &&
00473         (strcmp(name, dns_table[i].name) == 0)) {
00474       LWIP_DEBUGF(DNS_DEBUG, ("dns_lookup: \"%s\": found = ", name));
00475       ip_addr_debug_print(DNS_DEBUG, &(dns_table[i].ipaddr));
00476       LWIP_DEBUGF(DNS_DEBUG, ("\n"));
00477       return dns_table[i].ipaddr.addr;
00478     }
00479   }
00480 
00481   return INADDR_NONE;
00482 }
00483 
00484 #if DNS_DOES_NAME_CHECK
00485 /**
00486  * Compare the "dotted" name "query" with the encoded name "response"
00487  * to make sure an answer from the DNS server matches the current dns_table
00488  * entry (otherwise, answers might arrive late for hostname not on the list
00489  * any more).
00490  *
00491  * @param query hostname (not encoded) from the dns_table
00492  * @param response encoded hostname in the DNS response
00493  * @return 0: names equal; 1: names differ
00494  */
00495 static u8_t
00496 dns_compare_name(unsigned char *query, unsigned char *response)
00497 {
00498   unsigned char n;
00499 
00500   do {
00501     n = *response++;
00502     /** @see RFC 1035 - 4.1.4. Message compression */
00503     if ((n & 0xc0) == 0xc0) {
00504       /* Compressed name */
00505       break;
00506     } else {
00507       /* Not compressed name */
00508       while (n > 0) {
00509         if ((*query) != (*response)) {
00510           return 1;
00511         }
00512         ++response;
00513         ++query;
00514         --n;
00515       };
00516       ++query;
00517     }
00518   } while (*response != 0);
00519 
00520   return 0;
00521 }
00522 #endif /* DNS_DOES_NAME_CHECK */
00523 
00524 /**
00525  * Walk through a compact encoded DNS name and return the end of the name.
00526  *
00527  * @param query encoded DNS name in the DNS server response
00528  * @return end of the name
00529  */
00530 static unsigned char *
00531 dns_parse_name(unsigned char *query)
00532 {
00533   unsigned char n;
00534 
00535   do {
00536     n = *query++;
00537     /** @see RFC 1035 - 4.1.4. Message compression */
00538     if ((n & 0xc0) == 0xc0) {
00539       /* Compressed name */
00540       break;
00541     } else {
00542       /* Not compressed name */
00543       while (n > 0) {
00544         ++query;
00545         --n;
00546       };
00547     }
00548   } while (*query != 0);
00549 
00550   return query + 1;
00551 }
00552 
00553 /**
00554  * Send a DNS query packet.
00555  *
00556  * @param numdns index of the DNS server in the dns_servers table
00557  * @param name hostname to query
00558  * @param id index of the hostname in dns_table, used as transaction ID in the
00559  *        DNS query packet
00560  * @return ERR_OK if packet is sent; an err_t indicating the problem otherwise
00561  */
00562 static err_t
00563 dns_send(u8_t numdns, const char* name, u8_t id)
00564 {
00565   err_t err;
00566   struct dns_hdr *hdr;
00567   struct dns_query qry;
00568   struct pbuf *p;
00569   char *query, *nptr;
00570   const char *pHostname;
00571   u8_t n;
00572 
00573   LWIP_DEBUGF(DNS_DEBUG, ("dns_send: dns_servers[%"U16_F"] \"%s\": request\n",
00574               (u16_t)(numdns), name));
00575   LWIP_ASSERT("dns server out of array", numdns < DNS_MAX_SERVERS);
00576   LWIP_ASSERT("dns server has no IP address set", dns_servers[numdns].addr != 0);
00577 
00578   /* if here, we have either a new query or a retry on a previous query to process */
00579   p = pbuf_alloc(PBUF_TRANSPORT, SIZEOF_DNS_HDR + DNS_MAX_NAME_LENGTH +
00580                  SIZEOF_DNS_QUERY, PBUF_RAM);
00581   if (p != NULL) {
00582     LWIP_ASSERT("pbuf must be in one piece", p->next == NULL);
00583     /* fill dns header */
00584     hdr = (struct dns_hdr*)p->payload;
00585     memset(hdr, 0, SIZEOF_DNS_HDR);
00586     hdr->id = htons(id);
00587     hdr->flags1 = DNS_FLAG1_RD;
00588     hdr->numquestions = htons(1);
00589     query = (char*)hdr + SIZEOF_DNS_HDR;
00590     pHostname = name;
00591     --pHostname;
00592 
00593     /* convert hostname into suitable query format. */
00594     do {
00595       ++pHostname;
00596       nptr = query;
00597       ++query;
00598       for(n = 0; *pHostname != '.' && *pHostname != 0; ++pHostname) {
00599         *query = *pHostname;
00600         ++query;
00601         ++n;
00602       }
00603       *nptr = n;
00604     } while(*pHostname != 0);
00605     *query++='\0';
00606 
00607     /* fill dns query */
00608     qry.type  = htons(DNS_RRTYPE_A);
00609     qry.class = htons(DNS_RRCLASS_IN);
00610     MEMCPY( query, &qry, SIZEOF_DNS_QUERY);
00611 
00612     /* resize pbuf to the exact dns query */
00613     pbuf_realloc(p, (query + SIZEOF_DNS_QUERY) - ((char*)(p->payload)));
00614 
00615     /* connect to the server for faster receiving */
00616     udp_connect(dns_pcb, &dns_servers[numdns], DNS_SERVER_PORT);
00617     /* send dns packet */
00618     err = udp_sendto(dns_pcb, p, &dns_servers[numdns], DNS_SERVER_PORT);
00619 
00620     /* free pbuf */
00621     pbuf_free(p);
00622   } else {
00623     err = ERR_MEM;
00624   }
00625 
00626   return err;
00627 }
00628 
00629 /**
00630  * dns_check_entry() - see if pEntry has not yet been queried and, if so, sends out a query.
00631  * Check an entry in the dns_table:
00632  * - send out query for new entries
00633  * - retry old pending entries on timeout (also with different servers)
00634  * - remove completed entries from the table if their TTL has expired
00635  *
00636  * @param i index of the dns_table entry to check
00637  */
00638 static void
00639 dns_check_entry(u8_t i)
00640 {
00641   struct dns_table_entry *pEntry = &dns_table[i];
00642 
00643   LWIP_ASSERT("array index out of bounds", i < DNS_TABLE_SIZE);
00644 
00645   switch(pEntry->state) {
00646 
00647     case DNS_STATE_NEW: {
00648       /* initialize new entry */
00649       pEntry->state   = DNS_STATE_ASKING;
00650       pEntry->numdns  = 0;
00651       pEntry->tmr     = 1;
00652       pEntry->retries = 0;
00653       
00654       /* send DNS packet for this entry */
00655       dns_send(pEntry->numdns, pEntry->name, i);
00656       break;
00657     }
00658 
00659     case DNS_STATE_ASKING: {
00660       if (--pEntry->tmr == 0) {
00661         if (++pEntry->retries == DNS_MAX_RETRIES) {
00662           if ((pEntry->numdns+1<DNS_MAX_SERVERS) && (dns_servers[pEntry->numdns+1].addr!=0)) {
00663             /* change of server */
00664             pEntry->numdns++;
00665             pEntry->tmr     = 1;
00666             pEntry->retries = 0;
00667             break;
00668           } else {
00669             LWIP_DEBUGF(DNS_DEBUG, ("dns_check_entry: \"%s\": timeout\n", pEntry->name));
00670             /* call specified callback function if provided */
00671             if (pEntry->found)
00672               (*pEntry->found)(pEntry->name, NULL, pEntry->arg);
00673             /* flush this entry */
00674             pEntry->state   = DNS_STATE_UNUSED;
00675             pEntry->found   = NULL;
00676             break;
00677           }
00678         }
00679 
00680         /* wait longer for the next retry */
00681         pEntry->tmr = pEntry->retries;
00682 
00683         /* send DNS packet for this entry */
00684         dns_send(pEntry->numdns, pEntry->name, i);
00685       }
00686       break;
00687     }
00688 
00689     case DNS_STATE_DONE: {
00690       /* if the time to live is nul */
00691       if (--pEntry->ttl == 0) {
00692         LWIP_DEBUGF(DNS_DEBUG, ("dns_check_entry: \"%s\": flush\n", pEntry->name));
00693         /* flush this entry */
00694         pEntry->state = DNS_STATE_UNUSED;
00695         pEntry->found = NULL;
00696       }
00697       break;
00698     }
00699     case DNS_STATE_UNUSED:
00700       /* nothing to do */
00701       break;
00702     default:
00703       LWIP_ASSERT("unknown dns_table entry state:", 0);
00704       break;
00705   }
00706 }
00707 
00708 /**
00709  * Call dns_check_entry for each entry in dns_table - check all entries.
00710  */
00711 static void
00712 dns_check_entries(void)
00713 {
00714   u8_t i;
00715 
00716   for (i = 0; i < DNS_TABLE_SIZE; ++i) {
00717     dns_check_entry(i);
00718   }
00719 }
00720 
00721 /**
00722  * Receive input function for DNS response packets arriving for the dns UDP pcb.
00723  *
00724  * @params see udp.h
00725  */
00726 static void
00727 dns_recv(void *arg, struct udp_pcb *pcb, struct pbuf *p, struct ip_addr *addr, u16_t port)
00728 {
00729   u8_t i;
00730   char *pHostname;
00731   struct dns_hdr *hdr;
00732   struct dns_answer ans;
00733   struct dns_table_entry *pEntry;
00734   u8_t nquestions, nanswers;
00735 #if (DNS_USES_STATIC_BUF == 0)
00736   u8_t dns_payload[DNS_MSG_SIZE];
00737 #endif /* (DNS_USES_STATIC_BUF == 0) */
00738 #if (DNS_USES_STATIC_BUF == 2)
00739   u8_t* dns_payload;
00740 #endif /* (DNS_USES_STATIC_BUF == 2) */
00741 
00742   LWIP_UNUSED_ARG(arg);
00743   LWIP_UNUSED_ARG(pcb);
00744   LWIP_UNUSED_ARG(addr);
00745   LWIP_UNUSED_ARG(port);
00746 
00747   /* is the dns message too big ? */
00748   if (p->tot_len > DNS_MSG_SIZE) {
00749     LWIP_DEBUGF(DNS_DEBUG, ("dns_recv: pbuf too big\n"));
00750     /* free pbuf and return */
00751     goto memerr1;
00752   }
00753 
00754   /* is the dns message big enough ? */
00755   if (p->tot_len < (SIZEOF_DNS_HDR + SIZEOF_DNS_QUERY + SIZEOF_DNS_ANSWER)) {
00756     LWIP_DEBUGF(DNS_DEBUG, ("dns_recv: pbuf too small\n"));
00757     /* free pbuf and return */
00758     goto memerr1;
00759   }
00760 
00761 #if (DNS_USES_STATIC_BUF == 2)
00762   dns_payload = mem_malloc(p->tot_len);
00763   if (dns_payload == NULL) {
00764     LWIP_DEBUGF(DNS_DEBUG, ("dns_recv: mem_malloc error\n"));
00765     /* free pbuf and return */
00766     goto memerr1;
00767   }
00768 #endif /* (DNS_USES_STATIC_BUF == 2) */
00769 
00770   /* copy dns payload inside static buffer for processing */ 
00771   if (pbuf_copy_partial(p, dns_payload, p->tot_len, 0) == p->tot_len) {
00772     /* The ID in the DNS header should be our entry into the name table. */
00773     hdr = (struct dns_hdr*)dns_payload;
00774     i = htons(hdr->id);
00775     if (i < DNS_TABLE_SIZE) {
00776       pEntry = &dns_table[i];
00777       if(pEntry->state == DNS_STATE_ASKING) {
00778         /* This entry is now completed. */
00779         pEntry->state = DNS_STATE_DONE;
00780         pEntry->err   = hdr->flags2 & DNS_FLAG2_ERR_MASK;
00781 
00782         /* We only care about the question(s) and the answers. The authrr
00783            and the extrarr are simply discarded. */
00784         nquestions = htons(hdr->numquestions);
00785         nanswers   = htons(hdr->numanswers);
00786 
00787         /* Check for error. If so, call callback to inform. */
00788         if (((hdr->flags1 & DNS_FLAG1_RESPONSE) == 0) || (pEntry->err != 0) || (nquestions != 1)) {
00789           LWIP_DEBUGF(DNS_DEBUG, ("dns_recv: \"%s\": error in flags\n", pEntry->name));
00790           /* call callback to indicate error, clean up memory and return */
00791           goto responseerr;
00792         }
00793 
00794 #if DNS_DOES_NAME_CHECK
00795         /* Check if the name in the "question" part match with the name in the entry. */
00796         if (dns_compare_name((unsigned char *)(pEntry->name), (unsigned char *)dns_payload + SIZEOF_DNS_HDR) != 0) {
00797           LWIP_DEBUGF(DNS_DEBUG, ("dns_recv: \"%s\": response not match to query\n", pEntry->name));
00798           /* call callback to indicate error, clean up memory and return */
00799           goto responseerr;
00800         }
00801 #endif /* DNS_DOES_NAME_CHECK */
00802 
00803         /* Skip the name in the "question" part */
00804         pHostname = (char *) dns_parse_name((unsigned char *)dns_payload + SIZEOF_DNS_HDR) + SIZEOF_DNS_QUERY;
00805 
00806         while(nanswers > 0) {
00807           /* skip answer resource record's host name */
00808           pHostname = (char *) dns_parse_name((unsigned char *)pHostname);
00809 
00810           /* Check for IP address type and Internet class. Others are discarded. */
00811           MEMCPY(&ans, pHostname, SIZEOF_DNS_ANSWER);
00812           if((ntohs(ans.type) == DNS_RRTYPE_A) && (ntohs(ans.class) == DNS_RRCLASS_IN) && (ntohs(ans.len) == sizeof(struct ip_addr)) ) {
00813             /* read the answer resource record's TTL, and maximize it if needed */
00814             pEntry->ttl = ntohl(ans.ttl);
00815             if (pEntry->ttl > DNS_MAX_TTL) {
00816               pEntry->ttl = DNS_MAX_TTL;
00817             }
00818             /* read the IP address after answer resource record's header */
00819             MEMCPY( &(pEntry->ipaddr), (pHostname+SIZEOF_DNS_ANSWER), sizeof(struct ip_addr));
00820             LWIP_DEBUGF(DNS_DEBUG, ("dns_recv: \"%s\": response = ", pEntry->name));
00821             ip_addr_debug_print(DNS_DEBUG, (&(pEntry->ipaddr)));
00822             LWIP_DEBUGF(DNS_DEBUG, ("\n"));
00823             /* call specified callback function if provided */
00824             if (pEntry->found) {
00825               (*pEntry->found)(pEntry->name, &pEntry->ipaddr, pEntry->arg);
00826             }
00827             /* deallocate memory and return */
00828             goto memerr2;
00829           } else {
00830             pHostname = pHostname + SIZEOF_DNS_ANSWER + htons(ans.len);
00831           }
00832           --nanswers;
00833         }
00834         LWIP_DEBUGF(DNS_DEBUG, ("dns_recv: \"%s\": error in response\n", pEntry->name));
00835         /* call callback to indicate error, clean up memory and return */
00836         goto responseerr;
00837       }
00838     }
00839   }
00840 
00841   /* deallocate memory and return */
00842   goto memerr2;
00843 
00844 responseerr:
00845   /* ERROR: call specified callback function with NULL as name to indicate an error */
00846   if (pEntry->found) {
00847     (*pEntry->found)(pEntry->name, NULL, pEntry->arg);
00848   }
00849   /* flush this entry */
00850   pEntry->state = DNS_STATE_UNUSED;
00851   pEntry->found = NULL;
00852 
00853 memerr2:
00854 #if (DNS_USES_STATIC_BUF == 2)
00855   /* free dns buffer */
00856   mem_free(dns_payload);
00857 #endif /* (DNS_USES_STATIC_BUF == 2) */
00858 
00859 memerr1:
00860   /* free pbuf */
00861   pbuf_free(p);
00862   return;
00863 }
00864 
00865 /**
00866  * Queues a new hostname to resolve and sends out a DNS query for that hostname
00867  *
00868  * @param name the hostname that is to be queried
00869  * @param found a callback founction to be called on success, failure or timeout
00870  * @param callback_arg argument to pass to the callback function
00871  * @return @return a err_t return code.
00872  */
00873 static err_t
00874 dns_enqueue(const char *name, dns_found_callback found, void *callback_arg)
00875 {
00876   u8_t i;
00877   u8_t lseq, lseqi;
00878   struct dns_table_entry *pEntry = NULL;
00879 
00880   /* search an unused entry, or the oldest one */
00881   lseq = lseqi = 0;
00882   for (i = 0; i < DNS_TABLE_SIZE; ++i) {
00883     pEntry = &dns_table[i];
00884     /* is it an unused entry ? */
00885     if (pEntry->state == DNS_STATE_UNUSED)
00886       break;
00887 
00888     /* check if this is the oldest completed entry */
00889     if (pEntry->state == DNS_STATE_DONE) {
00890       if ((dns_seqno - pEntry->seqno) > lseq) {
00891         lseq = dns_seqno - pEntry->seqno;
00892         lseqi = i;
00893       }
00894     }
00895   }
00896 
00897   /* if we don't have found an unused entry, use the oldest completed one */
00898   if (i == DNS_TABLE_SIZE) {
00899     if ((lseqi >= DNS_TABLE_SIZE) || (dns_table[lseqi].state != DNS_STATE_DONE)) {
00900       /* no entry can't be used now, table is full */
00901       LWIP_DEBUGF(DNS_DEBUG, ("dns_enqueue: \"%s\": DNS entries table is full\n", name));
00902       return ERR_MEM;
00903     } else {
00904       /* use the oldest completed one */
00905       i = lseqi;
00906       pEntry = &dns_table[i];
00907     }
00908   }
00909 
00910   /* use this entry */
00911   LWIP_DEBUGF(DNS_DEBUG, ("dns_enqueue: \"%s\": use DNS entry %"U16_F"\n", name, (u16_t)(i)));
00912 
00913   /* fill the entry */
00914   pEntry->state = DNS_STATE_NEW;
00915   pEntry->seqno = dns_seqno++;
00916   pEntry->found = found;
00917   pEntry->arg   = callback_arg;
00918   strcpy(pEntry->name, name);
00919 
00920   /* force to send query without waiting timer */
00921   dns_check_entry(i);
00922 
00923   /* dns query is enqueued */
00924   return ERR_INPROGRESS;
00925 }
00926 
00927 /**
00928  * Resolve a hostname (string) into an IP address.
00929  * NON-BLOCKING callback version for use with raw API!!!
00930  *
00931  * Returns immediately with one of err_t return codes:
00932  * - ERR_OK if hostname is a valid IP address string or the host
00933  *   name is already in the local names table.
00934  * - ERR_INPROGRESS enqueue a request to be sent to the DNS server
00935  *   for resolution if no errors are present.
00936  *
00937  * @param hostname the hostname that is to be queried
00938  * @param addr pointer to a struct ip_addr where to store the address if it is already
00939  *             cached in the dns_table (only valid if ERR_OK is returned!)
00940  * @param found a callback function to be called on success, failure or timeout (only if
00941  *              ERR_INPROGRESS is returned!)
00942  * @param callback_arg argument to pass to the callback function
00943  * @return a err_t return code.
00944  */
00945 err_t
00946 dns_gethostbyname(const char *hostname, struct ip_addr *addr, dns_found_callback found,
00947                   void *callback_arg)
00948 {
00949   /* not initialized or no valid server yet, or invalid addr pointer
00950    * or invalid hostname or invalid hostname length */
00951   if ((dns_pcb == NULL) || (addr == NULL) ||
00952       (!hostname) || (!hostname[0]) ||
00953       (strlen(hostname) >= DNS_MAX_NAME_LENGTH)) {
00954     return ERR_VAL;
00955   }
00956 
00957 #if LWIP_HAVE_LOOPIF
00958   if (strcmp(hostname,"localhost")==0) {
00959     addr->addr = INADDR_LOOPBACK;
00960     return ERR_OK;
00961   }
00962 #endif /* LWIP_HAVE_LOOPIF */
00963 
00964   /* host name already in octet notation? set ip addr and return ERR_OK
00965    * already have this address cached? */
00966   if (((addr->addr = inet_addr(hostname)) != INADDR_NONE) ||
00967       ((addr->addr = dns_lookup(hostname)) != INADDR_NONE)) {
00968     return ERR_OK;
00969   }
00970 
00971   /* queue query with specified callback */
00972   return dns_enqueue(hostname, found, callback_arg);
00973 }
00974 
00975 #endif /* LWIP_DNS */