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   PACK_STRUCT_FIELD(u16_t id);
00135   PACK_STRUCT_FIELD(u8_t flags1);
00136   PACK_STRUCT_FIELD(u8_t flags2);
00137   PACK_STRUCT_FIELD(u16_t numquestions);
00138   PACK_STRUCT_FIELD(u16_t numanswers);
00139   PACK_STRUCT_FIELD(u16_t numauthrr);
00140   PACK_STRUCT_FIELD(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   PACK_STRUCT_FIELD(u16_t type);
00157   PACK_STRUCT_FIELD(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   PACK_STRUCT_FIELD(u16_t type);
00174   PACK_STRUCT_FIELD(u16_t class);
00175   PACK_STRUCT_FIELD(u32_t ttl);
00176   PACK_STRUCT_FIELD(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 /** Local host-list. For hostnames in this list, no
00212  *  external name resolution is performed */
00213 static struct local_hostlist_entry *local_hostlist_dynamic;
00214 #else /* DNS_LOCAL_HOSTLIST_IS_DYNAMIC */
00215 
00216 /** Defining this allows the local_hostlist_static to be placed in a different
00217  * linker section (e.g. FLASH) */
00218 #ifndef DNS_LOCAL_HOSTLIST_STORAGE_PRE
00219 #define DNS_LOCAL_HOSTLIST_STORAGE_PRE static
00220 #endif /* DNS_LOCAL_HOSTLIST_STORAGE_PRE */
00221 /** Defining this allows the local_hostlist_static to be placed in a different
00222  * linker section (e.g. FLASH) */
00223 #ifndef DNS_LOCAL_HOSTLIST_STORAGE_POST
00224 #define DNS_LOCAL_HOSTLIST_STORAGE_POST
00225 #endif /* DNS_LOCAL_HOSTLIST_STORAGE_POST */
00226 DNS_LOCAL_HOSTLIST_STORAGE_PRE struct local_hostlist_entry local_hostlist_static[]
00227   DNS_LOCAL_HOSTLIST_STORAGE_POST = DNS_LOCAL_HOSTLIST_INIT;
00228 
00229 #endif /* DNS_LOCAL_HOSTLIST_IS_DYNAMIC */
00230 
00231 static void dns_init_local();
00232 #endif /* DNS_LOCAL_HOSTLIST */
00233 
00234 
00235 /* forward declarations */
00236 static void dns_recv(void *s, struct udp_pcb *pcb, struct pbuf *p, struct ip_addr *addr, u16_t port);
00237 static void dns_check_entries(void);
00238 
00239 /*-----------------------------------------------------------------------------
00240  * Globales
00241  *----------------------------------------------------------------------------*/
00242 
00243 /* DNS variables */
00244 static struct udp_pcb        *dns_pcb;
00245 static u8_t                   dns_seqno;
00246 static struct dns_table_entry dns_table[DNS_TABLE_SIZE] MEM_POSITION;
00247 static struct ip_addr         dns_servers[DNS_MAX_SERVERS] MEM_POSITION;
00248 
00249 #if (DNS_USES_STATIC_BUF == 1)
00250 static u8_t                   dns_payload[DNS_MSG_SIZE] MEM_POSITION;
00251 #endif /* (DNS_USES_STATIC_BUF == 1) */
00252 
00253 /**
00254  * Initialize the resolver: set up the UDP pcb and configure the default server
00255  * (DNS_SERVER_ADDRESS).
00256  */
00257 void
00258 dns_init()
00259 {
00260   struct ip_addr dnsserver;
00261   
00262   /* initialize default DNS server address */
00263   dnsserver.addr = DNS_SERVER_ADDRESS;
00264 
00265   LWIP_DEBUGF(DNS_DEBUG, ("dns_init: initializing\n"));
00266 
00267   /* if dns client not yet initialized... */
00268   if (dns_pcb == NULL) {
00269     dns_pcb = udp_new();
00270 
00271     if (dns_pcb != NULL) {
00272       /* initialize DNS table not needed (initialized to zero since it is a
00273        * global variable) */
00274       LWIP_ASSERT("For implicit initialization to work, DNS_STATE_UNUSED needs to be 0",
00275         DNS_STATE_UNUSED == 0);
00276 
00277       /* initialize DNS client */
00278       udp_bind(dns_pcb, IP_ADDR_ANY, 0);
00279       udp_recv(dns_pcb, dns_recv, NULL);
00280 
00281       /* initialize default DNS primary server */
00282       dns_setserver(0, &dnsserver);
00283     }
00284   }
00285 #if DNS_LOCAL_HOSTLIST
00286   dns_init_local();
00287 #endif
00288 }
00289 
00290 /**
00291  * Initialize one of the DNS servers.
00292  *
00293  * @param numdns the index of the DNS server to set must be < DNS_MAX_SERVERS
00294  * @param dnsserver IP address of the DNS server to set
00295  */
00296 void
00297 dns_setserver(u8_t numdns, struct ip_addr *dnsserver)
00298 {
00299   if ((numdns < DNS_MAX_SERVERS) && (dns_pcb != NULL) &&
00300       (dnsserver != NULL) && (dnsserver->addr !=0 )) {
00301     dns_servers[numdns] = (*dnsserver);
00302   }
00303 }
00304 
00305 /**
00306  * Obtain one of the currently configured DNS server.
00307  *
00308  * @param numdns the index of the DNS server
00309  * @return IP address of the indexed DNS server or "ip_addr_any" if the DNS
00310  *         server has not been configured.
00311  */
00312 struct ip_addr
00313 dns_getserver(u8_t numdns)
00314 {
00315   if (numdns < DNS_MAX_SERVERS) {
00316     return dns_servers[numdns];
00317   } else {
00318     return *IP_ADDR_ANY;
00319   }
00320 }
00321 
00322 /**
00323  * The DNS resolver client timer - handle retries and timeouts and should
00324  * be called every DNS_TMR_INTERVAL milliseconds (every second by default).
00325  */
00326 void
00327 dns_tmr(void)
00328 {
00329   if (dns_pcb != NULL) {
00330     LWIP_DEBUGF(DNS_DEBUG, ("dns_tmr: dns_check_entries\n"));
00331     dns_check_entries();
00332   }
00333 }
00334 
00335 #if DNS_LOCAL_HOSTLIST
00336 static void
00337 dns_init_local()
00338 {
00339 #if DNS_LOCAL_HOSTLIST_IS_DYNAMIC && defined(DNS_LOCAL_HOSTLIST_INIT)
00340   int i;
00341   struct local_hostlist_entry *entry;
00342   /* Dynamic: copy entries from DNS_LOCAL_HOSTLIST_INIT to list */
00343   struct local_hostlist_entry local_hostlist_init[] = DNS_LOCAL_HOSTLIST_INIT;
00344   for (i = 0; i < sizeof(local_hostlist_init) / sizeof(struct local_hostlist_entry); i++) {
00345     entry = mem_malloc(sizeof(struct local_hostlist_entry));
00346     LWIP_ASSERT("mem-error in dns_init_local", entry != NULL);
00347     if (entry != NULL) {
00348       struct local_hostlist_entry *init_entry = &local_hostlist_init[i];
00349       entry->name = init_entry->name;
00350       entry->addr = init_entry->addr;
00351       entry->next = local_hostlist_dynamic;
00352       local_hostlist_dynamic = entry;
00353     }
00354   }
00355 #endif /* DNS_LOCAL_HOSTLIST_IS_DYNAMIC && defined(DNS_LOCAL_HOSTLIST_INIT) */
00356 }
00357 
00358 /**
00359  * Scans the local host-list for a hostname.
00360  *
00361  * @param hostname Hostname to look for in the local host-list
00362  * @return The first IP address for the hostname in the local host-list or
00363  *         INADDR_NONE if not found.
00364  */
00365 static u32_t
00366 dns_lookup_local(const char *hostname)
00367 {
00368 #if DNS_LOCAL_HOSTLIST_IS_DYNAMIC
00369   struct local_hostlist_entry *entry = local_hostlist_dynamic;
00370   while(entry != NULL) {
00371     if(strcmp(entry->name, hostname) == 0) {
00372       return entry->addr;
00373     }
00374     entry = entry->next;
00375   }
00376 #else /* DNS_LOCAL_HOSTLIST_IS_DYNAMIC */
00377   int i;
00378   for (i = 0; i < sizeof(local_hostlist_static) / sizeof(struct local_hostlist_entry); i++) {
00379     if(strcmp(local_hostlist_static[i].name, hostname) == 0) {
00380       return local_hostlist_static[i].addr;
00381     }
00382   }
00383 #endif /* DNS_LOCAL_HOSTLIST_IS_DYNAMIC */
00384   return INADDR_NONE;
00385 }
00386 
00387 #if DNS_LOCAL_HOSTLIST_IS_DYNAMIC
00388 /** Remove all entries from the local host-list for a specific hostname
00389  * and/or IP addess
00390  *
00391  * @param hostname hostname for which entries shall be removed from the local
00392  *                 host-list
00393  * @param addr address for which entries shall be removed from the local host-list
00394  * @return the number of removed entries
00395  */
00396 int
00397 dns_local_removehost(const char *hostname, const struct ip_addr *addr)
00398 {
00399   int removed = 0;
00400   struct local_hostlist_entry *entry = local_hostlist_dynamic;
00401   struct local_hostlist_entry *last_entry = NULL;
00402   while (entry != NULL) {
00403     if (((hostname == NULL) || !strcmp(entry->name, hostname)) &&
00404         ((addr == NULL) || (entry->addr == addr->addr))) {
00405       struct local_hostlist_entry *free_entry;
00406       if (last_entry != NULL) {
00407         last_entry->next = entry->next;
00408       } else {
00409         local_hostlist_dynamic = entry->next;
00410       }
00411       free_entry = entry;
00412       entry = entry->next;
00413       mem_free(free_entry);
00414       removed++;
00415     } else {
00416       last_entry = entry;
00417       entry = entry->next;
00418     }
00419   }
00420   return removed;
00421 }
00422 
00423 /**
00424  * Add a hostname/IP address pair to the local host-list.
00425  * Duplicates are not checked.
00426  *
00427  * @param hostname hostname of the new entry
00428  * @param addr IP address of the new entry
00429  * @return ERR_OK if succeeded or ERR_MEM on memory error
00430  */
00431 err_t
00432 dns_local_addhost(const char *hostname, const struct ip_addr *addr)
00433 {
00434   struct local_hostlist_entry *entry;
00435   entry = mem_malloc(sizeof(struct local_hostlist_entry));
00436   if (entry == NULL) {
00437     return ERR_MEM;
00438   }
00439   entry->name = hostname;
00440   entry->addr = addr->addr;
00441   entry->next = local_hostlist_dynamic;
00442   local_hostlist_dynamic = entry;
00443   return ERR_OK;
00444 }
00445 #endif /* DNS_LOCAL_HOSTLIST_IS_DYNAMIC*/
00446 #endif /* DNS_LOCAL_HOSTLIST */
00447 
00448 /**
00449  * Look up a hostname in the array of known hostnames.
00450  *
00451  * @note This function only looks in the internal array of known
00452  * hostnames, it does not send out a query for the hostname if none
00453  * was found. The function dns_enqueue() can be used to send a query
00454  * for a hostname.
00455  *
00456  * @param name the hostname to look up
00457  * @return the hostname's IP address, as u32_t (instead of struct ip_addr to
00458  *         better check for failure: != INADDR_NONE) or INADDR_NONE if the hostname
00459  *         was not found in the cached dns_table.
00460  */
00461 static u32_t
00462 dns_lookup(const char *name)
00463 {
00464   u8_t i;
00465 #if DNS_LOCAL_HOSTLIST || defined(DNS_LOOKUP_LOCAL_EXTERN)
00466   u32_t addr;
00467 #endif /* DNS_LOCAL_HOSTLIST || defined(DNS_LOOKUP_LOCAL_EXTERN) */
00468 #if DNS_LOCAL_HOSTLIST
00469   if ((addr = dns_lookup_local(name)) != INADDR_NONE) {
00470     return addr;
00471   }
00472 #endif /* DNS_LOCAL_HOSTLIST */
00473 #ifdef DNS_LOOKUP_LOCAL_EXTERN
00474   if((addr = DNS_LOOKUP_LOCAL_EXTERN(name)) != INADDR_NONE) {
00475     return addr;
00476   }
00477 #endif /* DNS_LOOKUP_LOCAL_EXTERN */
00478 
00479   /* Walk through name list, return entry if found. If not, return NULL. */
00480   for (i = 0; i < DNS_TABLE_SIZE; ++i) {
00481     if ((dns_table[i].state == DNS_STATE_DONE) &&
00482         (strcmp(name, dns_table[i].name) == 0)) {
00483       LWIP_DEBUGF(DNS_DEBUG, ("dns_lookup: \"%s\": found = ", name));
00484       ip_addr_debug_print(DNS_DEBUG, &(dns_table[i].ipaddr));
00485       LWIP_DEBUGF(DNS_DEBUG, ("\n"));
00486       return dns_table[i].ipaddr.addr;
00487     }
00488   }
00489 
00490   return INADDR_NONE;
00491 }
00492 
00493 #if DNS_DOES_NAME_CHECK
00494 /**
00495  * Compare the "dotted" name "query" with the encoded name "response"
00496  * to make sure an answer from the DNS server matches the current dns_table
00497  * entry (otherwise, answers might arrive late for hostname not on the list
00498  * any more).
00499  *
00500  * @param query hostname (not encoded) from the dns_table
00501  * @param response encoded hostname in the DNS response
00502  * @return 0: names equal; 1: names differ
00503  */
00504 static u8_t
00505 dns_compare_name(unsigned char *query, unsigned char *response)
00506 {
00507   unsigned char n;
00508 
00509   do {
00510     n = *response++;
00511     /** @see RFC 1035 - 4.1.4. Message compression */
00512     if ((n & 0xc0) == 0xc0) {
00513       /* Compressed name */
00514       break;
00515     } else {
00516       /* Not compressed name */
00517       while (n > 0) {
00518         if ((*query) != (*response)) {
00519           return 1;
00520         }
00521         ++response;
00522         ++query;
00523         --n;
00524       };
00525       ++query;
00526     }
00527   } while (*response != 0);
00528 
00529   return 0;
00530 }
00531 #endif /* DNS_DOES_NAME_CHECK */
00532 
00533 /**
00534  * Walk through a compact encoded DNS name and return the end of the name.
00535  *
00536  * @param query encoded DNS name in the DNS server response
00537  * @return end of the name
00538  */
00539 static unsigned char *
00540 dns_parse_name(unsigned char *query)
00541 {
00542   unsigned char n;
00543 
00544   do {
00545     n = *query++;
00546     /** @see RFC 1035 - 4.1.4. Message compression */
00547     if ((n & 0xc0) == 0xc0) {
00548       /* Compressed name */
00549       break;
00550     } else {
00551       /* Not compressed name */
00552       while (n > 0) {
00553         ++query;
00554         --n;
00555       };
00556     }
00557   } while (*query != 0);
00558 
00559   return query + 1;
00560 }
00561 
00562 /**
00563  * Send a DNS query packet.
00564  *
00565  * @param numdns index of the DNS server in the dns_servers table
00566  * @param name hostname to query
00567  * @param id index of the hostname in dns_table, used as transaction ID in the
00568  *        DNS query packet
00569  * @return ERR_OK if packet is sent; an err_t indicating the problem otherwise
00570  */
00571 static err_t
00572 dns_send(u8_t numdns, const char* name, u8_t id)
00573 {
00574   err_t err;
00575   struct dns_hdr *hdr;
00576   struct dns_query qry;
00577   struct pbuf *p;
00578   char *query, *nptr;
00579   const char *pHostname;
00580   u8_t n;
00581 
00582   LWIP_DEBUGF(DNS_DEBUG, ("dns_send: dns_servers[%"U16_F"] \"%s\": request\n",
00583               (u16_t)(numdns), name));
00584   LWIP_ASSERT("dns server out of array", numdns < DNS_MAX_SERVERS);
00585   LWIP_ASSERT("dns server has no IP address set", dns_servers[numdns].addr != 0);
00586 
00587   /* if here, we have either a new query or a retry on a previous query to process */
00588   p = pbuf_alloc(PBUF_TRANSPORT, SIZEOF_DNS_HDR + DNS_MAX_NAME_LENGTH +
00589                  SIZEOF_DNS_QUERY, PBUF_RAM);
00590   if (p != NULL) {
00591     LWIP_ASSERT("pbuf must be in one piece", p->next == NULL);
00592     /* fill dns header */
00593     hdr = (struct dns_hdr*)p->payload;
00594     memset(hdr, 0, SIZEOF_DNS_HDR);
00595     hdr->id = htons(id);
00596     hdr->flags1 = DNS_FLAG1_RD;
00597     hdr->numquestions = htons(1);
00598     query = (char*)hdr + SIZEOF_DNS_HDR;
00599     pHostname = name;
00600     --pHostname;
00601 
00602     /* convert hostname into suitable query format. */
00603     do {
00604       ++pHostname;
00605       nptr = query;
00606       ++query;
00607       for(n = 0; *pHostname != '.' && *pHostname != 0; ++pHostname) {
00608         *query = *pHostname;
00609         ++query;
00610         ++n;
00611       }
00612       *nptr = n;
00613     } while(*pHostname != 0);
00614     *query++='\0';
00615 
00616     /* fill dns query */
00617     qry.type  = htons(DNS_RRTYPE_A);
00618     qry.class = htons(DNS_RRCLASS_IN);
00619     MEMCPY( query, &qry, SIZEOF_DNS_QUERY);
00620 
00621     /* resize pbuf to the exact dns query */
00622     pbuf_realloc(p, (query + SIZEOF_DNS_QUERY) - ((char*)(p->payload)));
00623 
00624     /* connect to the server for faster receiving */
00625     udp_connect(dns_pcb, &dns_servers[numdns], DNS_SERVER_PORT);
00626     /* send dns packet */
00627     err = udp_sendto(dns_pcb, p, &dns_servers[numdns], DNS_SERVER_PORT);
00628 
00629     /* free pbuf */
00630     pbuf_free(p);
00631   } else {
00632     err = ERR_MEM;
00633   }
00634 
00635   return err;
00636 }
00637 
00638 /**
00639  * dns_check_entry() - see if pEntry has not yet been queried and, if so, sends out a query.
00640  * Check an entry in the dns_table:
00641  * - send out query for new entries
00642  * - retry old pending entries on timeout (also with different servers)
00643  * - remove completed entries from the table if their TTL has expired
00644  *
00645  * @param i index of the dns_table entry to check
00646  */
00647 static void
00648 dns_check_entry(u8_t i)
00649 {
00650   struct dns_table_entry *pEntry = &dns_table[i];
00651 
00652   LWIP_ASSERT("array index out of bounds", i < DNS_TABLE_SIZE);
00653 
00654   switch(pEntry->state) {
00655 
00656     case DNS_STATE_NEW: {
00657       /* initialize new entry */
00658       pEntry->state   = DNS_STATE_ASKING;
00659       pEntry->numdns  = 0;
00660       pEntry->tmr     = 1;
00661       pEntry->retries = 0;
00662       
00663       /* send DNS packet for this entry */
00664       dns_send(pEntry->numdns, pEntry->name, i);
00665       break;
00666     }
00667 
00668     case DNS_STATE_ASKING: {
00669       if (--pEntry->tmr == 0) {
00670         if (++pEntry->retries == DNS_MAX_RETRIES) {
00671           if ((pEntry->numdns+1<DNS_MAX_SERVERS) && (dns_servers[pEntry->numdns+1].addr!=0)) {
00672             /* change of server */
00673             pEntry->numdns++;
00674             pEntry->tmr     = 1;
00675             pEntry->retries = 0;
00676             break;
00677           } else {
00678             LWIP_DEBUGF(DNS_DEBUG, ("dns_check_entry: \"%s\": timeout\n", pEntry->name));
00679             /* call specified callback function if provided */
00680             if (pEntry->found)
00681               (*pEntry->found)(pEntry->name, NULL, pEntry->arg);
00682             /* flush this entry */
00683             pEntry->state   = DNS_STATE_UNUSED;
00684             pEntry->found   = NULL;
00685             break;
00686           }
00687         }
00688 
00689         /* wait longer for the next retry */
00690         pEntry->tmr = pEntry->retries;
00691 
00692         /* send DNS packet for this entry */
00693         dns_send(pEntry->numdns, pEntry->name, i);
00694       }
00695       break;
00696     }
00697 
00698     case DNS_STATE_DONE: {
00699       /* if the time to live is nul */
00700       if (--pEntry->ttl == 0) {
00701         LWIP_DEBUGF(DNS_DEBUG, ("dns_check_entry: \"%s\": flush\n", pEntry->name));
00702         /* flush this entry */
00703         pEntry->state = DNS_STATE_UNUSED;
00704         pEntry->found = NULL;
00705       }
00706       break;
00707     }
00708     case DNS_STATE_UNUSED:
00709       /* nothing to do */
00710       break;
00711     default:
00712       LWIP_ASSERT("unknown dns_table entry state:", 0);
00713       break;
00714   }
00715 }
00716 
00717 /**
00718  * Call dns_check_entry for each entry in dns_table - check all entries.
00719  */
00720 static void
00721 dns_check_entries(void)
00722 {
00723   u8_t i;
00724 
00725   for (i = 0; i < DNS_TABLE_SIZE; ++i) {
00726     dns_check_entry(i);
00727   }
00728 }
00729 
00730 /**
00731  * Receive input function for DNS response packets arriving for the dns UDP pcb.
00732  *
00733  * @params see udp.h
00734  */
00735 static void
00736 dns_recv(void *arg, struct udp_pcb *pcb, struct pbuf *p, struct ip_addr *addr, u16_t port)
00737 {
00738   u8_t i;
00739   char *pHostname;
00740   struct dns_hdr *hdr;
00741   struct dns_answer ans;
00742   struct dns_table_entry *pEntry;
00743   u8_t nquestions, nanswers;
00744 #if (DNS_USES_STATIC_BUF == 0)
00745   u8_t dns_payload[DNS_MSG_SIZE];
00746 #endif /* (DNS_USES_STATIC_BUF == 0) */
00747 #if (DNS_USES_STATIC_BUF == 2)
00748   u8_t* dns_payload;
00749 #endif /* (DNS_USES_STATIC_BUF == 2) */
00750 
00751   LWIP_UNUSED_ARG(arg);
00752   LWIP_UNUSED_ARG(pcb);
00753   LWIP_UNUSED_ARG(addr);
00754   LWIP_UNUSED_ARG(port);
00755 
00756   /* is the dns message too big ? */
00757   if (p->tot_len > DNS_MSG_SIZE) {
00758     LWIP_DEBUGF(DNS_DEBUG, ("dns_recv: pbuf too big\n"));
00759     /* free pbuf and return */
00760     goto memerr1;
00761   }
00762 
00763   /* is the dns message big enough ? */
00764   if (p->tot_len < (SIZEOF_DNS_HDR + SIZEOF_DNS_QUERY + SIZEOF_DNS_ANSWER)) {
00765     LWIP_DEBUGF(DNS_DEBUG, ("dns_recv: pbuf too small\n"));
00766     /* free pbuf and return */
00767     goto memerr1;
00768   }
00769 
00770 #if (DNS_USES_STATIC_BUF == 2)
00771   dns_payload = mem_malloc(p->tot_len);
00772   if (dns_payload == NULL) {
00773     LWIP_DEBUGF(DNS_DEBUG, ("dns_recv: mem_malloc error\n"));
00774     /* free pbuf and return */
00775     goto memerr1;
00776   }
00777 #endif /* (DNS_USES_STATIC_BUF == 2) */
00778 
00779   /* copy dns payload inside static buffer for processing */ 
00780   if (pbuf_copy_partial(p, dns_payload, p->tot_len, 0) == p->tot_len) {
00781     /* The ID in the DNS header should be our entry into the name table. */
00782     hdr = (struct dns_hdr*)dns_payload;
00783     i = htons(hdr->id);
00784     if (i < DNS_TABLE_SIZE) {
00785       pEntry = &dns_table[i];
00786       if(pEntry->state == DNS_STATE_ASKING) {
00787         /* This entry is now completed. */
00788         pEntry->state = DNS_STATE_DONE;
00789         pEntry->err   = hdr->flags2 & DNS_FLAG2_ERR_MASK;
00790 
00791         /* We only care about the question(s) and the answers. The authrr
00792            and the extrarr are simply discarded. */
00793         nquestions = htons(hdr->numquestions);
00794         nanswers   = htons(hdr->numanswers);
00795 
00796         /* Check for error. If so, call callback to inform. */
00797         if (((hdr->flags1 & DNS_FLAG1_RESPONSE) == 0) || (pEntry->err != 0) || (nquestions != 1)) {
00798           LWIP_DEBUGF(DNS_DEBUG, ("dns_recv: \"%s\": error in flags\n", pEntry->name));
00799           /* call callback to indicate error, clean up memory and return */
00800           goto responseerr;
00801         }
00802 
00803 #if DNS_DOES_NAME_CHECK
00804         /* Check if the name in the "question" part match with the name in the entry. */
00805         if (dns_compare_name((unsigned char *)(pEntry->name), (unsigned char *)dns_payload + SIZEOF_DNS_HDR) != 0) {
00806           LWIP_DEBUGF(DNS_DEBUG, ("dns_recv: \"%s\": response not match to query\n", pEntry->name));
00807           /* call callback to indicate error, clean up memory and return */
00808           goto responseerr;
00809         }
00810 #endif /* DNS_DOES_NAME_CHECK */
00811 
00812         /* Skip the name in the "question" part */
00813         pHostname = (char *) dns_parse_name((unsigned char *)dns_payload + SIZEOF_DNS_HDR) + SIZEOF_DNS_QUERY;
00814 
00815         while(nanswers > 0) {
00816           /* skip answer resource record's host name */
00817           pHostname = (char *) dns_parse_name((unsigned char *)pHostname);
00818 
00819           /* Check for IP address type and Internet class. Others are discarded. */
00820           MEMCPY(&ans, pHostname, SIZEOF_DNS_ANSWER);
00821           if((ntohs(ans.type) == DNS_RRTYPE_A) && (ntohs(ans.class) == DNS_RRCLASS_IN) && (ntohs(ans.len) == sizeof(struct ip_addr)) ) {
00822             /* read the answer resource record's TTL, and maximize it if needed */
00823             pEntry->ttl = ntohl(ans.ttl);
00824             if (pEntry->ttl > DNS_MAX_TTL) {
00825               pEntry->ttl = DNS_MAX_TTL;
00826             }
00827             /* read the IP address after answer resource record's header */
00828             MEMCPY( &(pEntry->ipaddr), (pHostname+SIZEOF_DNS_ANSWER), sizeof(struct ip_addr));
00829             LWIP_DEBUGF(DNS_DEBUG, ("dns_recv: \"%s\": response = ", pEntry->name));
00830             ip_addr_debug_print(DNS_DEBUG, (&(pEntry->ipaddr)));
00831             LWIP_DEBUGF(DNS_DEBUG, ("\n"));
00832             /* call specified callback function if provided */
00833             if (pEntry->found) {
00834               (*pEntry->found)(pEntry->name, &pEntry->ipaddr, pEntry->arg);
00835             }
00836             /* deallocate memory and return */
00837             goto memerr2;
00838           } else {
00839             pHostname = pHostname + SIZEOF_DNS_ANSWER + htons(ans.len);
00840           }
00841           --nanswers;
00842         }
00843         LWIP_DEBUGF(DNS_DEBUG, ("dns_recv: \"%s\": error in response\n", pEntry->name));
00844         /* call callback to indicate error, clean up memory and return */
00845         goto responseerr;
00846       }
00847     }
00848   }
00849 
00850   /* deallocate memory and return */
00851   goto memerr2;
00852 
00853 responseerr:
00854   /* ERROR: call specified callback function with NULL as name to indicate an error */
00855   if (pEntry->found) {
00856     (*pEntry->found)(pEntry->name, NULL, pEntry->arg);
00857   }
00858   /* flush this entry */
00859   pEntry->state = DNS_STATE_UNUSED;
00860   pEntry->found = NULL;
00861 
00862 memerr2:
00863 #if (DNS_USES_STATIC_BUF == 2)
00864   /* free dns buffer */
00865   mem_free(dns_payload);
00866 #endif /* (DNS_USES_STATIC_BUF == 2) */
00867 
00868 memerr1:
00869   /* free pbuf */
00870   pbuf_free(p);
00871   return;
00872 }
00873 
00874 /**
00875  * Queues a new hostname to resolve and sends out a DNS query for that hostname
00876  *
00877  * @param name the hostname that is to be queried
00878  * @param found a callback founction to be called on success, failure or timeout
00879  * @param callback_arg argument to pass to the callback function
00880  * @return @return a err_t return code.
00881  */
00882 static err_t
00883 dns_enqueue(const char *name, dns_found_callback found, void *callback_arg)
00884 {
00885   u8_t i;
00886   u8_t lseq, lseqi;
00887   struct dns_table_entry *pEntry = NULL;
00888 
00889   /* search an unused entry, or the oldest one */
00890   lseq = lseqi = 0;
00891   for (i = 0; i < DNS_TABLE_SIZE; ++i) {
00892     pEntry = &dns_table[i];
00893     /* is it an unused entry ? */
00894     if (pEntry->state == DNS_STATE_UNUSED)
00895       break;
00896 
00897     /* check if this is the oldest completed entry */
00898     if (pEntry->state == DNS_STATE_DONE) {
00899       if ((dns_seqno - pEntry->seqno) > lseq) {
00900         lseq = dns_seqno - pEntry->seqno;
00901         lseqi = i;
00902       }
00903     }
00904   }
00905 
00906   /* if we don't have found an unused entry, use the oldest completed one */
00907   if (i == DNS_TABLE_SIZE) {
00908     if ((lseqi >= DNS_TABLE_SIZE) || (dns_table[lseqi].state != DNS_STATE_DONE)) {
00909       /* no entry can't be used now, table is full */
00910       LWIP_DEBUGF(DNS_DEBUG, ("dns_enqueue: \"%s\": DNS entries table is full\n", name));
00911       return ERR_MEM;
00912     } else {
00913       /* use the oldest completed one */
00914       i = lseqi;
00915       pEntry = &dns_table[i];
00916     }
00917   }
00918 
00919   /* use this entry */
00920   LWIP_DEBUGF(DNS_DEBUG, ("dns_enqueue: \"%s\": use DNS entry %"U16_F"\n", name, (u16_t)(i)));
00921 
00922   /* fill the entry */
00923   pEntry->state = DNS_STATE_NEW;
00924   pEntry->seqno = dns_seqno++;
00925   pEntry->found = found;
00926   pEntry->arg   = callback_arg;
00927   strcpy(pEntry->name, name);
00928 
00929   /* force to send query without waiting timer */
00930   dns_check_entry(i);
00931 
00932   /* dns query is enqueued */
00933   return ERR_INPROGRESS;
00934 }
00935 
00936 /**
00937  * Resolve a hostname (string) into an IP address.
00938  * NON-BLOCKING callback version for use with raw API!!!
00939  *
00940  * Returns immediately with one of err_t return codes:
00941  * - ERR_OK if hostname is a valid IP address string or the host
00942  *   name is already in the local names table.
00943  * - ERR_INPROGRESS enqueue a request to be sent to the DNS server
00944  *   for resolution if no errors are present.
00945  *
00946  * @param hostname the hostname that is to be queried
00947  * @param addr pointer to a struct ip_addr where to store the address if it is already
00948  *             cached in the dns_table (only valid if ERR_OK is returned!)
00949  * @param found a callback function to be called on success, failure or timeout (only if
00950  *              ERR_INPROGRESS is returned!)
00951  * @param callback_arg argument to pass to the callback function
00952  * @return a err_t return code.
00953  */
00954 err_t
00955 dns_gethostbyname(const char *hostname, struct ip_addr *addr, dns_found_callback found,
00956                   void *callback_arg)
00957 {
00958   /* not initialized or no valid server yet, or invalid addr pointer
00959    * or invalid hostname or invalid hostname length */
00960   if ((dns_pcb == NULL) || (addr == NULL) ||
00961       (!hostname) || (!hostname[0]) ||
00962       (strlen(hostname) >= DNS_MAX_NAME_LENGTH)) {
00963     return ERR_VAL;
00964   }
00965 
00966 #if LWIP_HAVE_LOOPIF
00967   if (strcmp(hostname,"localhost")==0) {
00968     addr->addr = htonl(INADDR_LOOPBACK);
00969     return ERR_OK;
00970   }
00971 #endif /* LWIP_HAVE_LOOPIF */
00972 
00973   /* host name already in octet notation? set ip addr and return ERR_OK
00974    * already have this address cached? */
00975   if (((addr->addr = inet_addr(hostname)) != INADDR_NONE) ||
00976       ((addr->addr = dns_lookup(hostname)) != INADDR_NONE)) {
00977     return ERR_OK;
00978   }
00979 
00980   /* queue query with specified callback */
00981   return dns_enqueue(hostname, found, callback_arg);
00982 }
00983 
00984 #endif /* LWIP_DNS */