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/memp.h"
00082 #include "lwip/dns.h"
00083 #include "lwip/debug.h"
00084 
00085 #include <string.h>
00086 
00087 /** DNS server IP address */
00088 #ifndef DNS_SERVER_ADDRESS
00089 #define DNS_SERVER_ADDRESS(ipaddr)        (ip4_addr_set_u32(ipaddr, ipaddr_addr("208.67.222.222"))) /* resolver1.opendns.com */
00090 #endif
00091 
00092 /** DNS server port address */
00093 #ifndef DNS_SERVER_PORT
00094 #define DNS_SERVER_PORT           53
00095 #endif
00096 
00097 /** DNS maximum number of retries when asking for a name, before "timeout". */
00098 #ifndef DNS_MAX_RETRIES
00099 #define DNS_MAX_RETRIES           4
00100 #endif
00101 
00102 /** DNS resource record max. TTL (one week as default) */
00103 #ifndef DNS_MAX_TTL
00104 #define DNS_MAX_TTL               604800
00105 #endif
00106 
00107 /* DNS protocol flags */
00108 #define DNS_FLAG1_RESPONSE        0x80
00109 #define DNS_FLAG1_OPCODE_STATUS   0x10
00110 #define DNS_FLAG1_OPCODE_INVERSE  0x08
00111 #define DNS_FLAG1_OPCODE_STANDARD 0x00
00112 #define DNS_FLAG1_AUTHORATIVE     0x04
00113 #define DNS_FLAG1_TRUNC           0x02
00114 #define DNS_FLAG1_RD              0x01
00115 #define DNS_FLAG2_RA              0x80
00116 #define DNS_FLAG2_ERR_MASK        0x0f
00117 #define DNS_FLAG2_ERR_NONE        0x00
00118 #define DNS_FLAG2_ERR_NAME        0x03
00119 
00120 /* DNS protocol states */
00121 #define DNS_STATE_UNUSED          0
00122 #define DNS_STATE_NEW             1
00123 #define DNS_STATE_ASKING          2
00124 #define DNS_STATE_DONE            3
00125 
00126 #ifdef PACK_STRUCT_USE_INCLUDES
00127 #  include "arch/bpstruct.h"
00128 #endif
00129 PACK_STRUCT_BEGIN
00130 /** DNS message header */
00131 struct dns_hdr {
00132   PACK_STRUCT_FIELD(u16_t id);
00133   PACK_STRUCT_FIELD(u8_t flags1);
00134   PACK_STRUCT_FIELD(u8_t flags2);
00135   PACK_STRUCT_FIELD(u16_t numquestions);
00136   PACK_STRUCT_FIELD(u16_t numanswers);
00137   PACK_STRUCT_FIELD(u16_t numauthrr);
00138   PACK_STRUCT_FIELD(u16_t numextrarr);
00139 } PACK_STRUCT_STRUCT;
00140 PACK_STRUCT_END
00141 #ifdef PACK_STRUCT_USE_INCLUDES
00142 #  include "arch/epstruct.h"
00143 #endif
00144 #define SIZEOF_DNS_HDR 12
00145 
00146 /** DNS query message structure.
00147     No packing needed: only used locally on the stack. */
00148 struct dns_query {
00149   /* DNS query record starts with either a domain name or a pointer
00150      to a name already present somewhere in the packet. */
00151   u16_t type;
00152   u16_t cls;
00153 };
00154 #define SIZEOF_DNS_QUERY 4
00155 
00156 /** DNS answer message structure.
00157     No packing needed: only used locally on the stack. */
00158 struct dns_answer {
00159   /* DNS answer record starts with either a domain name or a pointer
00160      to a name already present somewhere in the packet. */
00161   u16_t type;
00162   u16_t cls;
00163   u32_t ttl;
00164   u16_t len;
00165 };
00166 #define SIZEOF_DNS_ANSWER 10
00167 
00168 /** DNS table entry */
00169 struct dns_table_entry {
00170   u8_t  state;
00171   u8_t  numdns;
00172   u8_t  tmr;
00173   u8_t  retries;
00174   u8_t  seqno;
00175   u8_t  err;
00176   u32_t ttl;
00177   char name[DNS_MAX_NAME_LENGTH];
00178   ip_addr_t ipaddr;
00179   /* pointer to callback on DNS query done */
00180   dns_found_callback found;
00181   void *arg;
00182 };
00183 
00184 #if DNS_LOCAL_HOSTLIST
00185 
00186 #if DNS_LOCAL_HOSTLIST_IS_DYNAMIC
00187 /** Local host-list. For hostnames in this list, no
00188  *  external name resolution is performed */
00189 static struct local_hostlist_entry *local_hostlist_dynamic;
00190 #else /* DNS_LOCAL_HOSTLIST_IS_DYNAMIC */
00191 
00192 /** Defining this allows the local_hostlist_static to be placed in a different
00193  * linker section (e.g. FLASH) */
00194 #ifndef DNS_LOCAL_HOSTLIST_STORAGE_PRE
00195 #define DNS_LOCAL_HOSTLIST_STORAGE_PRE static
00196 #endif /* DNS_LOCAL_HOSTLIST_STORAGE_PRE */
00197 /** Defining this allows the local_hostlist_static to be placed in a different
00198  * linker section (e.g. FLASH) */
00199 #ifndef DNS_LOCAL_HOSTLIST_STORAGE_POST
00200 #define DNS_LOCAL_HOSTLIST_STORAGE_POST
00201 #endif /* DNS_LOCAL_HOSTLIST_STORAGE_POST */
00202 DNS_LOCAL_HOSTLIST_STORAGE_PRE struct local_hostlist_entry local_hostlist_static[]
00203   DNS_LOCAL_HOSTLIST_STORAGE_POST = DNS_LOCAL_HOSTLIST_INIT;
00204 
00205 #endif /* DNS_LOCAL_HOSTLIST_IS_DYNAMIC */
00206 
00207 static void dns_init_local();
00208 #endif /* DNS_LOCAL_HOSTLIST */
00209 
00210 
00211 /* forward declarations */
00212 static void dns_recv(void *s, struct udp_pcb *pcb, struct pbuf *p, ip_addr_t *addr, u16_t port);
00213 static void dns_check_entries(void);
00214 
00215 /*-----------------------------------------------------------------------------
00216  * Globales
00217  *----------------------------------------------------------------------------*/
00218 
00219 /* DNS variables */
00220 static struct udp_pcb        *dns_pcb;
00221 static u8_t                   dns_seqno;
00222 static struct dns_table_entry dns_table[DNS_TABLE_SIZE];
00223 static ip_addr_t              dns_servers[DNS_MAX_SERVERS];
00224 /** Contiguous buffer for processing responses */
00225 static u8_t                   dns_payload_buffer[LWIP_MEM_ALIGN_BUFFER(DNS_MSG_SIZE)];
00226 static u8_t*                  dns_payload;
00227 
00228 /**
00229  * Initialize the resolver: set up the UDP pcb and configure the default server
00230  * (DNS_SERVER_ADDRESS).
00231  */
00232 void
00233 dns_init()
00234 {
00235   ip_addr_t dnsserver;
00236 
00237   dns_payload = (u8_t *)LWIP_MEM_ALIGN(dns_payload_buffer);
00238   
00239   /* initialize default DNS server address */
00240   DNS_SERVER_ADDRESS(&dnsserver);
00241 
00242   LWIP_DEBUGF(DNS_DEBUG, ("dns_init: initializing\n"));
00243 
00244   /* if dns client not yet initialized... */
00245   if (dns_pcb == NULL) {
00246     dns_pcb = udp_new();
00247 
00248     if (dns_pcb != NULL) {
00249       /* initialize DNS table not needed (initialized to zero since it is a
00250        * global variable) */
00251       LWIP_ASSERT("For implicit initialization to work, DNS_STATE_UNUSED needs to be 0",
00252         DNS_STATE_UNUSED == 0);
00253 
00254       /* initialize DNS client */
00255       udp_bind(dns_pcb, IP_ADDR_ANY, 0);
00256       udp_recv(dns_pcb, dns_recv, NULL);
00257 
00258       /* initialize default DNS primary server */
00259       dns_setserver(0, &dnsserver);
00260     }
00261   }
00262 #if DNS_LOCAL_HOSTLIST
00263   dns_init_local();
00264 #endif
00265 }
00266 
00267 /**
00268  * Initialize one of the DNS servers.
00269  *
00270  * @param numdns the index of the DNS server to set must be < DNS_MAX_SERVERS
00271  * @param dnsserver IP address of the DNS server to set
00272  */
00273 void
00274 dns_setserver(u8_t numdns, ip_addr_t *dnsserver)
00275 {
00276   if ((numdns < DNS_MAX_SERVERS) && (dns_pcb != NULL) &&
00277       (dnsserver != NULL) && !ip_addr_isany(dnsserver)) {
00278     dns_servers[numdns] = (*dnsserver);
00279   }
00280 }
00281 
00282 /**
00283  * Obtain one of the currently configured DNS server.
00284  *
00285  * @param numdns the index of the DNS server
00286  * @return IP address of the indexed DNS server or "ip_addr_any" if the DNS
00287  *         server has not been configured.
00288  */
00289 ip_addr_t
00290 dns_getserver(u8_t numdns)
00291 {
00292   if (numdns < DNS_MAX_SERVERS) {
00293     return dns_servers[numdns];
00294   } else {
00295     return *IP_ADDR_ANY;
00296   }
00297 }
00298 
00299 /**
00300  * The DNS resolver client timer - handle retries and timeouts and should
00301  * be called every DNS_TMR_INTERVAL milliseconds (every second by default).
00302  */
00303 void
00304 dns_tmr(void)
00305 {
00306   if (dns_pcb != NULL) {
00307     LWIP_DEBUGF(DNS_DEBUG, ("dns_tmr: dns_check_entries\n"));
00308     dns_check_entries();
00309   }
00310 }
00311 
00312 #if DNS_LOCAL_HOSTLIST
00313 static void
00314 dns_init_local()
00315 {
00316 #if DNS_LOCAL_HOSTLIST_IS_DYNAMIC && defined(DNS_LOCAL_HOSTLIST_INIT)
00317   int i;
00318   struct local_hostlist_entry *entry;
00319   /* Dynamic: copy entries from DNS_LOCAL_HOSTLIST_INIT to list */
00320   struct local_hostlist_entry local_hostlist_init[] = DNS_LOCAL_HOSTLIST_INIT;
00321   size_t namelen;
00322   for (i = 0; i < sizeof(local_hostlist_init) / sizeof(struct local_hostlist_entry); i++) {
00323     struct local_hostlist_entry *init_entry = &local_hostlist_init[i];
00324     LWIP_ASSERT("invalid host name (NULL)", init_entry->name != NULL);
00325     namelen = strlen(init_entry->name);
00326     LWIP_ASSERT("namelen <= DNS_LOCAL_HOSTLIST_MAX_NAMELEN", namelen <= DNS_LOCAL_HOSTLIST_MAX_NAMELEN);
00327     entry = (struct local_hostlist_entry *)memp_malloc(MEMP_LOCALHOSTLIST);
00328     LWIP_ASSERT("mem-error in dns_init_local", entry != NULL);
00329     if (entry != NULL) {
00330       entry->name = (char*)entry + sizeof(struct local_hostlist_entry);
00331       MEMCPY((char*)entry->name, init_entry->name, namelen);
00332       ((char*)entry->name)[namelen] = 0;
00333       entry->addr = init_entry->addr;
00334       entry->next = local_hostlist_dynamic;
00335       local_hostlist_dynamic = entry;
00336     }
00337   }
00338 #endif /* DNS_LOCAL_HOSTLIST_IS_DYNAMIC && defined(DNS_LOCAL_HOSTLIST_INIT) */
00339 }
00340 
00341 /**
00342  * Scans the local host-list for a hostname.
00343  *
00344  * @param hostname Hostname to look for in the local host-list
00345  * @return The first IP address for the hostname in the local host-list or
00346  *         IPADDR_NONE if not found.
00347  */
00348 static u32_t
00349 dns_lookup_local(const char *hostname)
00350 {
00351 #if DNS_LOCAL_HOSTLIST_IS_DYNAMIC
00352   struct local_hostlist_entry *entry = local_hostlist_dynamic;
00353   while(entry != NULL) {
00354     if(strcmp(entry->name, hostname) == 0) {
00355       return ip4_addr_get_u32(&entry->addr);
00356     }
00357     entry = entry->next;
00358   }
00359 #else /* DNS_LOCAL_HOSTLIST_IS_DYNAMIC */
00360   int i;
00361   for (i = 0; i < sizeof(local_hostlist_static) / sizeof(struct local_hostlist_entry); i++) {
00362     if(strcmp(local_hostlist_static[i].name, hostname) == 0) {
00363       return ip4_addr_get_u32(&local_hostlist_static[i].addr);
00364     }
00365   }
00366 #endif /* DNS_LOCAL_HOSTLIST_IS_DYNAMIC */
00367   return IPADDR_NONE;
00368 }
00369 
00370 #if DNS_LOCAL_HOSTLIST_IS_DYNAMIC
00371 /** Remove all entries from the local host-list for a specific hostname
00372  * and/or IP addess
00373  *
00374  * @param hostname hostname for which entries shall be removed from the local
00375  *                 host-list
00376  * @param addr address for which entries shall be removed from the local host-list
00377  * @return the number of removed entries
00378  */
00379 int
00380 dns_local_removehost(const char *hostname, const ip_addr_t *addr)
00381 {
00382   int removed = 0;
00383   struct local_hostlist_entry *entry = local_hostlist_dynamic;
00384   struct local_hostlist_entry *last_entry = NULL;
00385   while (entry != NULL) {
00386     if (((hostname == NULL) || !strcmp(entry->name, hostname)) &&
00387         ((addr == NULL) || ip_addr_cmp(&entry->addr, addr))) {
00388       struct local_hostlist_entry *free_entry;
00389       if (last_entry != NULL) {
00390         last_entry->next = entry->next;
00391       } else {
00392         local_hostlist_dynamic = entry->next;
00393       }
00394       free_entry = entry;
00395       entry = entry->next;
00396       memp_free(MEMP_LOCALHOSTLIST, free_entry);
00397       removed++;
00398     } else {
00399       last_entry = entry;
00400       entry = entry->next;
00401     }
00402   }
00403   return removed;
00404 }
00405 
00406 /**
00407  * Add a hostname/IP address pair to the local host-list.
00408  * Duplicates are not checked.
00409  *
00410  * @param hostname hostname of the new entry
00411  * @param addr IP address of the new entry
00412  * @return ERR_OK if succeeded or ERR_MEM on memory error
00413  */
00414 err_t
00415 dns_local_addhost(const char *hostname, const ip_addr_t *addr)
00416 {
00417   struct local_hostlist_entry *entry;
00418   size_t namelen;
00419   LWIP_ASSERT("invalid host name (NULL)", hostname != NULL);
00420   namelen = strlen(hostname);
00421   LWIP_ASSERT("namelen <= DNS_LOCAL_HOSTLIST_MAX_NAMELEN", namelen <= DNS_LOCAL_HOSTLIST_MAX_NAMELEN);
00422   entry = (struct local_hostlist_entry *)memp_malloc(MEMP_LOCALHOSTLIST);
00423   if (entry == NULL) {
00424     return ERR_MEM;
00425   }
00426   entry->name = (char*)entry + sizeof(struct local_hostlist_entry);
00427   MEMCPY((char*)entry->name, hostname, namelen);
00428   ((char*)entry->name)[namelen] = 0;
00429   ip_addr_copy(entry->addr, *addr);
00430   entry->next = local_hostlist_dynamic;
00431   local_hostlist_dynamic = entry;
00432   return ERR_OK;
00433 }
00434 #endif /* DNS_LOCAL_HOSTLIST_IS_DYNAMIC*/
00435 #endif /* DNS_LOCAL_HOSTLIST */
00436 
00437 /**
00438  * Look up a hostname in the array of known hostnames.
00439  *
00440  * @note This function only looks in the internal array of known
00441  * hostnames, it does not send out a query for the hostname if none
00442  * was found. The function dns_enqueue() can be used to send a query
00443  * for a hostname.
00444  *
00445  * @param name the hostname to look up
00446  * @return the hostname's IP address, as u32_t (instead of ip_addr_t to
00447  *         better check for failure: != IPADDR_NONE) or IPADDR_NONE if the hostname
00448  *         was not found in the cached dns_table.
00449  */
00450 static u32_t
00451 dns_lookup(const char *name)
00452 {
00453   u8_t i;
00454 #if DNS_LOCAL_HOSTLIST || defined(DNS_LOOKUP_LOCAL_EXTERN)
00455   u32_t addr;
00456 #endif /* DNS_LOCAL_HOSTLIST || defined(DNS_LOOKUP_LOCAL_EXTERN) */
00457 #if DNS_LOCAL_HOSTLIST
00458   if ((addr = dns_lookup_local(name)) != IPADDR_NONE) {
00459     return addr;
00460   }
00461 #endif /* DNS_LOCAL_HOSTLIST */
00462 #ifdef DNS_LOOKUP_LOCAL_EXTERN
00463   if((addr = DNS_LOOKUP_LOCAL_EXTERN(name)) != IPADDR_NONE) {
00464     return addr;
00465   }
00466 #endif /* DNS_LOOKUP_LOCAL_EXTERN */
00467 
00468   /* Walk through name list, return entry if found. If not, return NULL. */
00469   for (i = 0; i < DNS_TABLE_SIZE; ++i) {
00470     if ((dns_table[i].state == DNS_STATE_DONE) &&
00471         (strcmp(name, dns_table[i].name) == 0)) {
00472       LWIP_DEBUGF(DNS_DEBUG, ("dns_lookup: \"%s\": found = ", name));
00473       ip_addr_debug_print(DNS_DEBUG, &(dns_table[i].ipaddr));
00474       LWIP_DEBUGF(DNS_DEBUG, ("\n"));
00475       return ip4_addr_get_u32(&dns_table[i].ipaddr);
00476     }
00477   }
00478 
00479   return IPADDR_NONE;
00480 }
00481 
00482 #if DNS_DOES_NAME_CHECK
00483 /**
00484  * Compare the "dotted" name "query" with the encoded name "response"
00485  * to make sure an answer from the DNS server matches the current dns_table
00486  * entry (otherwise, answers might arrive late for hostname not on the list
00487  * any more).
00488  *
00489  * @param query hostname (not encoded) from the dns_table
00490  * @param response encoded hostname in the DNS response
00491  * @return 0: names equal; 1: names differ
00492  */
00493 static u8_t
00494 dns_compare_name(unsigned char *query, unsigned char *response)
00495 {
00496   unsigned char n;
00497 
00498   do {
00499     n = *response++;
00500     /** @see RFC 1035 - 4.1.4. Message compression */
00501     if ((n & 0xc0) == 0xc0) {
00502       /* Compressed name */
00503       break;
00504     } else {
00505       /* Not compressed name */
00506       while (n > 0) {
00507         if ((*query) != (*response)) {
00508           return 1;
00509         }
00510         ++response;
00511         ++query;
00512         --n;
00513       };
00514       ++query;
00515     }
00516   } while (*response != 0);
00517 
00518   return 0;
00519 }
00520 #endif /* DNS_DOES_NAME_CHECK */
00521 
00522 /**
00523  * Walk through a compact encoded DNS name and return the end of the name.
00524  *
00525  * @param query encoded DNS name in the DNS server response
00526  * @return end of the name
00527  */
00528 static unsigned char *
00529 dns_parse_name(unsigned char *query)
00530 {
00531   unsigned char n;
00532 
00533   do {
00534     n = *query++;
00535     /** @see RFC 1035 - 4.1.4. Message compression */
00536     if ((n & 0xc0) == 0xc0) {
00537       /* Compressed name */
00538       break;
00539     } else {
00540       /* Not compressed name */
00541       while (n > 0) {
00542         ++query;
00543         --n;
00544       };
00545     }
00546   } while (*query != 0);
00547 
00548   return query + 1;
00549 }
00550 
00551 /**
00552  * Send a DNS query packet.
00553  *
00554  * @param numdns index of the DNS server in the dns_servers table
00555  * @param name hostname to query
00556  * @param id index of the hostname in dns_table, used as transaction ID in the
00557  *        DNS query packet
00558  * @return ERR_OK if packet is sent; an err_t indicating the problem otherwise
00559  */
00560 static err_t
00561 dns_send(u8_t numdns, const char* name, u8_t id)
00562 {
00563   err_t err;
00564   struct dns_hdr *hdr;
00565   struct dns_query qry;
00566   struct pbuf *p;
00567   char *query, *nptr;
00568   const char *pHostname;
00569   u8_t n;
00570 
00571   LWIP_DEBUGF(DNS_DEBUG, ("dns_send: dns_servers[%"U16_F"] \"%s\": request\n",
00572               (u16_t)(numdns), name));
00573   LWIP_ASSERT("dns server out of array", numdns < DNS_MAX_SERVERS);
00574   LWIP_ASSERT("dns server has no IP address set", !ip_addr_isany(&dns_servers[numdns]));
00575 
00576   /* if here, we have either a new query or a retry on a previous query to process */
00577   p = pbuf_alloc(PBUF_TRANSPORT, SIZEOF_DNS_HDR + DNS_MAX_NAME_LENGTH +
00578                  SIZEOF_DNS_QUERY, PBUF_RAM);
00579   if (p != NULL) {
00580     LWIP_ASSERT("pbuf must be in one piece", p->next == NULL);
00581     /* fill dns header */
00582     hdr = (struct dns_hdr*)p->payload;
00583     memset(hdr, 0, SIZEOF_DNS_HDR);
00584     hdr->id = htons(id);
00585     hdr->flags1 = DNS_FLAG1_RD;
00586     hdr->numquestions = PP_HTONS(1);
00587     query = (char*)hdr + SIZEOF_DNS_HDR;
00588     pHostname = name;
00589     --pHostname;
00590 
00591     /* convert hostname into suitable query format. */
00592     do {
00593       ++pHostname;
00594       nptr = query;
00595       ++query;
00596       for(n = 0; *pHostname != '.' && *pHostname != 0; ++pHostname) {
00597         *query = *pHostname;
00598         ++query;
00599         ++n;
00600       }
00601       *nptr = n;
00602     } while(*pHostname != 0);
00603     *query++='\0';
00604 
00605     /* fill dns query */
00606     qry.type = PP_HTONS(DNS_RRTYPE_A);
00607     qry.cls = PP_HTONS(DNS_RRCLASS_IN);
00608     SMEMCPY(query, &qry, SIZEOF_DNS_QUERY);
00609 
00610     /* resize pbuf to the exact dns query */
00611     pbuf_realloc(p, (u16_t)((query + SIZEOF_DNS_QUERY) - ((char*)(p->payload))));
00612 
00613     /* connect to the server for faster receiving */
00614     udp_connect(dns_pcb, &dns_servers[numdns], DNS_SERVER_PORT);
00615     /* send dns packet */
00616     err = udp_sendto(dns_pcb, p, &dns_servers[numdns], DNS_SERVER_PORT);
00617 
00618     /* free pbuf */
00619     pbuf_free(p);
00620   } else {
00621     err = ERR_MEM;
00622   }
00623 
00624   return err;
00625 }
00626 
00627 /**
00628  * dns_check_entry() - see if pEntry has not yet been queried and, if so, sends out a query.
00629  * Check an entry in the dns_table:
00630  * - send out query for new entries
00631  * - retry old pending entries on timeout (also with different servers)
00632  * - remove completed entries from the table if their TTL has expired
00633  *
00634  * @param i index of the dns_table entry to check
00635  */
00636 static void
00637 dns_check_entry(u8_t i)
00638 {
00639   err_t err;
00640   struct dns_table_entry *pEntry = &dns_table[i];
00641 
00642   LWIP_ASSERT("array index out of bounds", i < DNS_TABLE_SIZE);
00643 
00644   switch(pEntry->state) {
00645 
00646     case DNS_STATE_NEW: {
00647       /* initialize new entry */
00648       pEntry->state   = DNS_STATE_ASKING;
00649       pEntry->numdns  = 0;
00650       pEntry->tmr     = 1;
00651       pEntry->retries = 0;
00652       
00653       /* send DNS packet for this entry */
00654       err = dns_send(pEntry->numdns, pEntry->name, i);
00655       if (err != ERR_OK) {
00656         LWIP_DEBUGF(DNS_DEBUG | LWIP_DBG_LEVEL_WARNING,
00657                     ("dns_send returned error: %d\n", err));
00658       }
00659       break;
00660     }
00661 
00662     case DNS_STATE_ASKING: {
00663       if (--pEntry->tmr == 0) {
00664         if (++pEntry->retries == DNS_MAX_RETRIES) {
00665           if ((pEntry->numdns+1<DNS_MAX_SERVERS) && !ip_addr_isany(&dns_servers[pEntry->numdns+1])) {
00666             /* change of server */
00667             pEntry->numdns++;
00668             pEntry->tmr     = 1;
00669             pEntry->retries = 0;
00670             break;
00671           } else {
00672             LWIP_DEBUGF(DNS_DEBUG, ("dns_check_entry: \"%s\": timeout\n", pEntry->name));
00673             /* call specified callback function if provided */
00674             if (pEntry->found)
00675               (*pEntry->found)(pEntry->name, NULL, pEntry->arg);
00676             /* flush this entry */
00677             pEntry->state   = DNS_STATE_UNUSED;
00678             pEntry->found   = NULL;
00679             break;
00680           }
00681         }
00682 
00683         /* wait longer for the next retry */
00684         pEntry->tmr = pEntry->retries;
00685 
00686         /* send DNS packet for this entry */
00687         err = dns_send(pEntry->numdns, pEntry->name, i);
00688         if (err != ERR_OK) {
00689           LWIP_DEBUGF(DNS_DEBUG | LWIP_DBG_LEVEL_WARNING,
00690                       ("dns_send returned error: %d\n", err));
00691         }
00692       }
00693       break;
00694     }
00695 
00696     case DNS_STATE_DONE: {
00697       /* if the time to live is nul */
00698       if (--pEntry->ttl == 0) {
00699         LWIP_DEBUGF(DNS_DEBUG, ("dns_check_entry: \"%s\": flush\n", pEntry->name));
00700         /* flush this entry */
00701         pEntry->state = DNS_STATE_UNUSED;
00702         pEntry->found = NULL;
00703       }
00704       break;
00705     }
00706     case DNS_STATE_UNUSED:
00707       /* nothing to do */
00708       break;
00709     default:
00710       LWIP_ASSERT("unknown dns_table entry state:", 0);
00711       break;
00712   }
00713 }
00714 
00715 /**
00716  * Call dns_check_entry for each entry in dns_table - check all entries.
00717  */
00718 static void
00719 dns_check_entries(void)
00720 {
00721   u8_t i;
00722 
00723   for (i = 0; i < DNS_TABLE_SIZE; ++i) {
00724     dns_check_entry(i);
00725   }
00726 }
00727 
00728 /**
00729  * Receive input function for DNS response packets arriving for the dns UDP pcb.
00730  *
00731  * @params see udp.h
00732  */
00733 static void
00734 dns_recv(void *arg, struct udp_pcb *pcb, struct pbuf *p, ip_addr_t *addr, u16_t port)
00735 {
00736   u16_t i;
00737   char *pHostname;
00738   struct dns_hdr *hdr;
00739   struct dns_answer ans;
00740   struct dns_table_entry *pEntry;
00741   u16_t nquestions, nanswers;
00742 
00743   LWIP_UNUSED_ARG(arg);
00744   LWIP_UNUSED_ARG(pcb);
00745   LWIP_UNUSED_ARG(addr);
00746   LWIP_UNUSED_ARG(port);
00747 
00748   /* is the dns message too big ? */
00749   if (p->tot_len > DNS_MSG_SIZE) {
00750     LWIP_DEBUGF(DNS_DEBUG, ("dns_recv: pbuf too big\n"));
00751     /* free pbuf and return */
00752     goto memerr;
00753   }
00754 
00755   /* is the dns message big enough ? */
00756   if (p->tot_len < (SIZEOF_DNS_HDR + SIZEOF_DNS_QUERY + SIZEOF_DNS_ANSWER)) {
00757     LWIP_DEBUGF(DNS_DEBUG, ("dns_recv: pbuf too small\n"));
00758     /* free pbuf and return */
00759     goto memerr;
00760   }
00761 
00762   /* copy dns payload inside static buffer for processing */ 
00763   if (pbuf_copy_partial(p, dns_payload, p->tot_len, 0) == p->tot_len) {
00764     /* The ID in the DNS header should be our entry into the name table. */
00765     hdr = (struct dns_hdr*)dns_payload;
00766     i = htons(hdr->id);
00767     if (i < DNS_TABLE_SIZE) {
00768       pEntry = &dns_table[i];
00769       if(pEntry->state == DNS_STATE_ASKING) {
00770         /* This entry is now completed. */
00771         pEntry->state = DNS_STATE_DONE;
00772         pEntry->err   = hdr->flags2 & DNS_FLAG2_ERR_MASK;
00773 
00774         /* We only care about the question(s) and the answers. The authrr
00775            and the extrarr are simply discarded. */
00776         nquestions = htons(hdr->numquestions);
00777         nanswers   = htons(hdr->numanswers);
00778 
00779         /* Check for error. If so, call callback to inform. */
00780         if (((hdr->flags1 & DNS_FLAG1_RESPONSE) == 0) || (pEntry->err != 0) || (nquestions != 1)) {
00781           LWIP_DEBUGF(DNS_DEBUG, ("dns_recv: \"%s\": error in flags\n", pEntry->name));
00782           /* call callback to indicate error, clean up memory and return */
00783           goto responseerr;
00784         }
00785 
00786 #if DNS_DOES_NAME_CHECK
00787         /* Check if the name in the "question" part match with the name in the entry. */
00788         if (dns_compare_name((unsigned char *)(pEntry->name), (unsigned char *)dns_payload + SIZEOF_DNS_HDR) != 0) {
00789           LWIP_DEBUGF(DNS_DEBUG, ("dns_recv: \"%s\": response not match to query\n", pEntry->name));
00790           /* call callback to indicate error, clean up memory and return */
00791           goto responseerr;
00792         }
00793 #endif /* DNS_DOES_NAME_CHECK */
00794 
00795         /* Skip the name in the "question" part */
00796         pHostname = (char *) dns_parse_name((unsigned char *)dns_payload + SIZEOF_DNS_HDR) + SIZEOF_DNS_QUERY;
00797 
00798         while (nanswers > 0) {
00799           /* skip answer resource record's host name */
00800           pHostname = (char *) dns_parse_name((unsigned char *)pHostname);
00801 
00802           /* Check for IP address type and Internet class. Others are discarded. */
00803           SMEMCPY(&ans, pHostname, SIZEOF_DNS_ANSWER);
00804           if((ans.type == PP_HTONS(DNS_RRTYPE_A)) && (ans.cls == PP_HTONS(DNS_RRCLASS_IN)) &&
00805              (ans.len == PP_HTONS(sizeof(ip_addr_t))) ) {
00806             /* read the answer resource record's TTL, and maximize it if needed */
00807             pEntry->ttl = ntohl(ans.ttl);
00808             if (pEntry->ttl > DNS_MAX_TTL) {
00809               pEntry->ttl = DNS_MAX_TTL;
00810             }
00811             /* read the IP address after answer resource record's header */
00812             SMEMCPY(&(pEntry->ipaddr), (pHostname+SIZEOF_DNS_ANSWER), sizeof(ip_addr_t));
00813             LWIP_DEBUGF(DNS_DEBUG, ("dns_recv: \"%s\": response = ", pEntry->name));
00814             ip_addr_debug_print(DNS_DEBUG, (&(pEntry->ipaddr)));
00815             LWIP_DEBUGF(DNS_DEBUG, ("\n"));
00816             /* call specified callback function if provided */
00817             if (pEntry->found) {
00818               (*pEntry->found)(pEntry->name, &pEntry->ipaddr, pEntry->arg);
00819             }
00820             /* deallocate memory and return */
00821             goto memerr;
00822           } else {
00823             pHostname = pHostname + SIZEOF_DNS_ANSWER + htons(ans.len);
00824           }
00825           --nanswers;
00826         }
00827         LWIP_DEBUGF(DNS_DEBUG, ("dns_recv: \"%s\": error in response\n", pEntry->name));
00828         /* call callback to indicate error, clean up memory and return */
00829         goto responseerr;
00830       }
00831     }
00832   }
00833 
00834   /* deallocate memory and return */
00835   goto memerr;
00836 
00837 responseerr:
00838   /* ERROR: call specified callback function with NULL as name to indicate an error */
00839   if (pEntry->found) {
00840     (*pEntry->found)(pEntry->name, NULL, pEntry->arg);
00841   }
00842   /* flush this entry */
00843   pEntry->state = DNS_STATE_UNUSED;
00844   pEntry->found = NULL;
00845 
00846 memerr:
00847   /* free pbuf */
00848   pbuf_free(p);
00849   return;
00850 }
00851 
00852 /**
00853  * Queues a new hostname to resolve and sends out a DNS query for that hostname
00854  *
00855  * @param name the hostname that is to be queried
00856  * @param found a callback founction to be called on success, failure or timeout
00857  * @param callback_arg argument to pass to the callback function
00858  * @return @return a err_t return code.
00859  */
00860 static err_t
00861 dns_enqueue(const char *name, dns_found_callback found, void *callback_arg)
00862 {
00863   u8_t i;
00864   u8_t lseq, lseqi;
00865   struct dns_table_entry *pEntry = NULL;
00866   size_t namelen;
00867 
00868   /* search an unused entry, or the oldest one */
00869   lseq = lseqi = 0;
00870   for (i = 0; i < DNS_TABLE_SIZE; ++i) {
00871     pEntry = &dns_table[i];
00872     /* is it an unused entry ? */
00873     if (pEntry->state == DNS_STATE_UNUSED)
00874       break;
00875 
00876     /* check if this is the oldest completed entry */
00877     if (pEntry->state == DNS_STATE_DONE) {
00878       if ((dns_seqno - pEntry->seqno) > lseq) {
00879         lseq = dns_seqno - pEntry->seqno;
00880         lseqi = i;
00881       }
00882     }
00883   }
00884 
00885   /* if we don't have found an unused entry, use the oldest completed one */
00886   if (i == DNS_TABLE_SIZE) {
00887     if ((lseqi >= DNS_TABLE_SIZE) || (dns_table[lseqi].state != DNS_STATE_DONE)) {
00888       /* no entry can't be used now, table is full */
00889       LWIP_DEBUGF(DNS_DEBUG, ("dns_enqueue: \"%s\": DNS entries table is full\n", name));
00890       return ERR_MEM;
00891     } else {
00892       /* use the oldest completed one */
00893       i = lseqi;
00894       pEntry = &dns_table[i];
00895     }
00896   }
00897 
00898   /* use this entry */
00899   LWIP_DEBUGF(DNS_DEBUG, ("dns_enqueue: \"%s\": use DNS entry %"U16_F"\n", name, (u16_t)(i)));
00900 
00901   /* fill the entry */
00902   pEntry->state = DNS_STATE_NEW;
00903   pEntry->seqno = dns_seqno++;
00904   pEntry->found = found;
00905   pEntry->arg   = callback_arg;
00906   namelen = LWIP_MIN(strlen(name), DNS_MAX_NAME_LENGTH-1);
00907   MEMCPY(pEntry->name, name, namelen);
00908   pEntry->name[namelen] = 0;
00909 
00910   /* force to send query without waiting timer */
00911   dns_check_entry(i);
00912 
00913   /* dns query is enqueued */
00914   return ERR_INPROGRESS;
00915 }
00916 
00917 /**
00918  * Resolve a hostname (string) into an IP address.
00919  * NON-BLOCKING callback version for use with raw API!!!
00920  *
00921  * Returns immediately with one of err_t return codes:
00922  * - ERR_OK if hostname is a valid IP address string or the host
00923  *   name is already in the local names table.
00924  * - ERR_INPROGRESS enqueue a request to be sent to the DNS server
00925  *   for resolution if no errors are present.
00926  *
00927  * @param hostname the hostname that is to be queried
00928  * @param addr pointer to a ip_addr_t where to store the address if it is already
00929  *             cached in the dns_table (only valid if ERR_OK is returned!)
00930  * @param found a callback function to be called on success, failure or timeout (only if
00931  *              ERR_INPROGRESS is returned!)
00932  * @param callback_arg argument to pass to the callback function
00933  * @return a err_t return code.
00934  */
00935 err_t
00936 dns_gethostbyname(const char *hostname, ip_addr_t *addr, dns_found_callback found,
00937                   void *callback_arg)
00938 {
00939   u32_t ipaddr;
00940   /* not initialized or no valid server yet, or invalid addr pointer
00941    * or invalid hostname or invalid hostname length */
00942   if ((dns_pcb == NULL) || (addr == NULL) ||
00943       (!hostname) || (!hostname[0]) ||
00944       (strlen(hostname) >= DNS_MAX_NAME_LENGTH)) {
00945     return ERR_VAL;
00946   }
00947 
00948 #if LWIP_HAVE_LOOPIF
00949   if (strcmp(hostname, "localhost")==0) {
00950     ip_addr_set_loopback(addr);
00951     return ERR_OK;
00952   }
00953 #endif /* LWIP_HAVE_LOOPIF */
00954 
00955   /* host name already in octet notation? set ip addr and return ERR_OK */
00956   ipaddr = ipaddr_addr(hostname);
00957   if (ipaddr == IPADDR_NONE) {
00958     /* already have this address cached? */
00959     ipaddr = dns_lookup(hostname);
00960   }
00961   if (ipaddr != IPADDR_NONE) {
00962     ip4_addr_set_u32(addr, ipaddr);
00963     return ERR_OK;
00964   }
00965 
00966   /* queue query with specified callback */
00967   return dns_enqueue(hostname, found, callback_arg);
00968 }
00969 
00970 #endif /* LWIP_DNS */