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