1 /**
2 * @file
3 * DNS - host name to IP address resolver.
4 *
5 */
6
7 /**
8
9 * This file implements a DNS host name to IP address resolver.
10
11 * Port to lwIP from uIP
12 * by Jim Pettinato April 2007
13
14 * uIP version Copyright (c) 2002-2003, Adam Dunkels.
15 * All rights reserved.
16 *
17 * Redistribution and use in source and binary forms, with or without
18 * modification, are permitted provided that the following conditions
19 * are met:
20 * 1. Redistributions of source code must retain the above copyright
21 * notice, this list of conditions and the following disclaimer.
22 * 2. Redistributions in binary form must reproduce the above copyright
23 * notice, this list of conditions and the following disclaimer in the
24 * documentation and/or other materials provided with the distribution.
25 * 3. The name of the author may not be used to endorse or promote
26 * products derived from this software without specific prior
27 * written permission.
28 *
29 * THIS SOFTWARE IS PROVIDED BY THE AUTHOR ``AS IS'' AND ANY EXPRESS
30 * OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED
31 * WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
32 * ARE DISCLAIMED. IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR ANY
33 * DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
34 * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE
35 * GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS
36 * INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY,
37 * WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING
38 * NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF THIS
39 * SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
40 *
41 *
42 * DNS.C
43 *
44 * The lwIP DNS resolver functions are used to lookup a host name and
45 * map it to a numerical IP address. It maintains a list of resolved
46 * hostnames that can be queried with the dns_lookup() function.
47 * New hostnames can be resolved using the dns_query() function.
48 *
49 * The lwIP version of the resolver also adds a non-blocking version of
50 * gethostbyname() that will work with a raw API application. This function
51 * checks for an IP address string first and converts it if it is valid.
52 * gethostbyname() then does a dns_lookup() to see if the name is
53 * already in the table. If so, the IP is returned. If not, a query is
54 * issued and the function returns with a ERR_INPROGRESS status. The app
55 * using the dns client must then go into a waiting state.
56 *
57 * Once a hostname has been resolved (or found to be non-existent),
58 * the resolver code calls a specified callback function (which
59 * must be implemented by the module that uses the resolver).
60 */
61
62 /*-----------------------------------------------------------------------------
63 * RFC 1035 - Domain names - implementation and specification
64 * RFC 2181 - Clarifications to the DNS Specification
65 *----------------------------------------------------------------------------*/
66
67 /** @todo: define good default values (rfc compliance) */
68 /** @todo: improve answer parsing, more checkings... */
69 /** @todo: check RFC1035 - 7.3. Processing responses */
70
71 /*-----------------------------------------------------------------------------
72 * Includes
73 *----------------------------------------------------------------------------*/
74
75 #include "lwip/opt.h"
76
77 #if LWIP_DNS /* don't build if not configured for use in lwipopts.h */
78
79 #include "lwip/udp.h"
80 #include "lwip/mem.h"
81 #include "lwip/memp.h"
82 #include "lwip/dns.h"
83
84 #include <string.h>
85
86 /** DNS server IP address */
87 #ifndef DNS_SERVER_ADDRESS
88 #define DNS_SERVER_ADDRESS(ipaddr) (ip4_addr_set_u32(ipaddr, ipaddr_addr("208.67.222.222"))) /* resolver1.opendns.com */
89 #endif
90
91 /** DNS server port address */
92 #ifndef DNS_SERVER_PORT
93 #define DNS_SERVER_PORT 53
94 #endif
95
96 /** DNS maximum number of retries when asking for a name, before "timeout". */
97 #ifndef DNS_MAX_RETRIES
98 #define DNS_MAX_RETRIES 4
99 #endif
100
101 /** DNS resource record max. TTL (one week as default) */
102 #ifndef DNS_MAX_TTL
103 #define DNS_MAX_TTL 604800
104 #endif
105
106 /* DNS protocol flags */
107 #define DNS_FLAG1_RESPONSE 0x80
108 #define DNS_FLAG1_OPCODE_STATUS 0x10
109 #define DNS_FLAG1_OPCODE_INVERSE 0x08
110 #define DNS_FLAG1_OPCODE_STANDARD 0x00
111 #define DNS_FLAG1_AUTHORATIVE 0x04
112 #define DNS_FLAG1_TRUNC 0x02
113 #define DNS_FLAG1_RD 0x01
114 #define DNS_FLAG2_RA 0x80
115 #define DNS_FLAG2_ERR_MASK 0x0f
116 #define DNS_FLAG2_ERR_NONE 0x00
117 #define DNS_FLAG2_ERR_NAME 0x03
118
119 /* DNS protocol states */
120 #define DNS_STATE_UNUSED 0
121 #define DNS_STATE_NEW 1
122 #define DNS_STATE_ASKING 2
123 #define DNS_STATE_DONE 3
124
125 #ifdef PACK_STRUCT_USE_INCLUDES
126 # include "arch/bpstruct.h"
127 #endif
128 PACK_STRUCT_BEGIN
129 /** DNS message header */
130 struct dns_hdr {
131 PACK_STRUCT_FIELD(u16_t id);
132 PACK_STRUCT_FIELD(u8_t flags1);
133 PACK_STRUCT_FIELD(u8_t flags2);
134 PACK_STRUCT_FIELD(u16_t numquestions);
135 PACK_STRUCT_FIELD(u16_t numanswers);
136 PACK_STRUCT_FIELD(u16_t numauthrr);
137 PACK_STRUCT_FIELD(u16_t numextrarr);
138 } PACK_STRUCT_STRUCT;
139 PACK_STRUCT_END
140 #ifdef PACK_STRUCT_USE_INCLUDES
141 # include "arch/epstruct.h"
142 #endif
143 #define SIZEOF_DNS_HDR 12
144
145 /** DNS query message structure.
146 No packing needed: only used locally on the stack. */
147 struct dns_query {
148 /* DNS query record starts with either a domain name or a pointer
149 to a name already present somewhere in the packet. */
150 u16_t type;
151 u16_t cls;
152 };
153 #define SIZEOF_DNS_QUERY 4
154
155 /** DNS answer message structure.
156 No packing needed: only used locally on the stack. */
157 struct dns_answer {
158 /* DNS answer record starts with either a domain name or a pointer
159 to a name already present somewhere in the packet. */
160 u16_t type;
161 u16_t cls;
162 u32_t ttl;
163 u16_t len;
164 };
165 #define SIZEOF_DNS_ANSWER 10
166
167 /** DNS table entry */
168 struct dns_table_entry {
169 u8_t state;
170 u8_t numdns;
171 u8_t tmr;
172 u8_t retries;
173 u8_t seqno;
174 u8_t err;
175 u32_t ttl;
176 char name[DNS_MAX_NAME_LENGTH];
177 ip_addr_t ipaddr;
178 /* pointer to callback on DNS query done */
179 dns_found_callback found;
180 void *arg;
181 };
182
183 #if DNS_LOCAL_HOSTLIST
184
185 #if DNS_LOCAL_HOSTLIST_IS_DYNAMIC
186 /** Local host-list. For hostnames in this list, no
187 * external name resolution is performed */
188 static struct local_hostlist_entry *local_hostlist_dynamic;
189 #else /* DNS_LOCAL_HOSTLIST_IS_DYNAMIC */
190
191 /** Defining this allows the local_hostlist_static to be placed in a different
192 * linker section (e.g. FLASH) */
193 #ifndef DNS_LOCAL_HOSTLIST_STORAGE_PRE
194 #define DNS_LOCAL_HOSTLIST_STORAGE_PRE static
195 #endif /* DNS_LOCAL_HOSTLIST_STORAGE_PRE */
196 /** Defining this allows the local_hostlist_static to be placed in a different
197 * linker section (e.g. FLASH) */
198 #ifndef DNS_LOCAL_HOSTLIST_STORAGE_POST
199 #define DNS_LOCAL_HOSTLIST_STORAGE_POST
200 #endif /* DNS_LOCAL_HOSTLIST_STORAGE_POST */
201 DNS_LOCAL_HOSTLIST_STORAGE_PRE struct local_hostlist_entry local_hostlist_static[]
202 DNS_LOCAL_HOSTLIST_STORAGE_POST = DNS_LOCAL_HOSTLIST_INIT;
203
204 #endif /* DNS_LOCAL_HOSTLIST_IS_DYNAMIC */
205
206 static void dns_init_local();
207 #endif /* DNS_LOCAL_HOSTLIST */
208
209
210 /* forward declarations */
211 static void dns_recv(void *s, struct udp_pcb *pcb, struct pbuf *p, ip_addr_t *addr, u16_t port);
212 static void dns_check_entries(void);
213
214 /*-----------------------------------------------------------------------------
215 * Globales
216 *----------------------------------------------------------------------------*/
217
218 /* DNS variables */
219 static struct udp_pcb *dns_pcb;
220 static u8_t dns_seqno;
221 static struct dns_table_entry dns_table[DNS_TABLE_SIZE];
222 static ip_addr_t dns_servers[DNS_MAX_SERVERS];
223 /** Contiguous buffer for processing responses */
224 static u8_t dns_payload_buffer[LWIP_MEM_ALIGN_BUFFER(DNS_MSG_SIZE)];
225 static u8_t* dns_payload;
226
227 /**
228 * Initialize the resolver: set up the UDP pcb and configure the default server
229 * (DNS_SERVER_ADDRESS).
230 */
231 void
dns_init()232 dns_init()
233 {
234 ip_addr_t dnsserver;
235
236 dns_payload = (u8_t *)LWIP_MEM_ALIGN(dns_payload_buffer);
237
238 /* initialize default DNS server address */
239 DNS_SERVER_ADDRESS(&dnsserver);
240
241 LWIP_DEBUGF(DNS_DEBUG, ("dns_init: initializing\n"));
242
243 /* if dns client not yet initialized... */
244 if (dns_pcb == NULL) {
245 dns_pcb = udp_new();
246
247 if (dns_pcb != NULL) {
248 /* initialize DNS table not needed (initialized to zero since it is a
249 * global variable) */
250 LWIP_ASSERT("For implicit initialization to work, DNS_STATE_UNUSED needs to be 0",
251 DNS_STATE_UNUSED == 0);
252
253 /* initialize DNS client */
254 udp_bind(dns_pcb, IP_ADDR_ANY, 0);
255 udp_recv(dns_pcb, dns_recv, NULL);
256
257 /* initialize default DNS primary server */
258 dns_setserver(0, &dnsserver);
259 }
260 }
261 #if DNS_LOCAL_HOSTLIST
262 dns_init_local();
263 #endif
264 }
265
266 /**
267 * Initialize one of the DNS servers.
268 *
269 * @param numdns the index of the DNS server to set must be < DNS_MAX_SERVERS
270 * @param dnsserver IP address of the DNS server to set
271 */
272 void
dns_setserver(u8_t numdns,ip_addr_t * dnsserver)273 dns_setserver(u8_t numdns, ip_addr_t *dnsserver)
274 {
275 /*
276 * hpa: the lwip code has the dnsserver->addr != 0 test, but that would
277 * seem to indicate that there is no way to cancel a previously given
278 * DNS server...
279 */
280 if ((numdns < DNS_MAX_SERVERS) && (dns_pcb != NULL) &&
281 (dnsserver != NULL) /* && !ip_addr_isany(dnsserver) */) {
282 dns_servers[numdns] = (*dnsserver);
283 }
284 }
285
286 /**
287 * Obtain one of the currently configured DNS server.
288 *
289 * @param numdns the index of the DNS server
290 * @return IP address of the indexed DNS server or "ip_addr_any" if the DNS
291 * server has not been configured.
292 */
293 ip_addr_t
dns_getserver(u8_t numdns)294 dns_getserver(u8_t numdns)
295 {
296 if (numdns < DNS_MAX_SERVERS) {
297 return dns_servers[numdns];
298 } else {
299 return *IP_ADDR_ANY;
300 }
301 }
302
303 /**
304 * The DNS resolver client timer - handle retries and timeouts and should
305 * be called every DNS_TMR_INTERVAL milliseconds (every second by default).
306 */
307 void
dns_tmr(void)308 dns_tmr(void)
309 {
310 if (dns_pcb != NULL) {
311 LWIP_DEBUGF(DNS_DEBUG, ("dns_tmr: dns_check_entries\n"));
312 dns_check_entries();
313 }
314 }
315
316 #if DNS_LOCAL_HOSTLIST
317 static void
dns_init_local()318 dns_init_local()
319 {
320 #if DNS_LOCAL_HOSTLIST_IS_DYNAMIC && defined(DNS_LOCAL_HOSTLIST_INIT)
321 int i;
322 struct local_hostlist_entry *entry;
323 /* Dynamic: copy entries from DNS_LOCAL_HOSTLIST_INIT to list */
324 struct local_hostlist_entry local_hostlist_init[] = DNS_LOCAL_HOSTLIST_INIT;
325 size_t namelen;
326 for (i = 0; i < sizeof(local_hostlist_init) / sizeof(struct local_hostlist_entry); i++) {
327 struct local_hostlist_entry *init_entry = &local_hostlist_init[i];
328 LWIP_ASSERT("invalid host name (NULL)", init_entry->name != NULL);
329 namelen = strlen(init_entry->name);
330 LWIP_ASSERT("namelen <= DNS_LOCAL_HOSTLIST_MAX_NAMELEN", namelen <= DNS_LOCAL_HOSTLIST_MAX_NAMELEN);
331 entry = (struct local_hostlist_entry *)memp_malloc(MEMP_LOCALHOSTLIST);
332 LWIP_ASSERT("mem-error in dns_init_local", entry != NULL);
333 if (entry != NULL) {
334 entry->name = (char*)entry + sizeof(struct local_hostlist_entry);
335 MEMCPY((char*)entry->name, init_entry->name, namelen);
336 ((char*)entry->name)[namelen] = 0;
337 entry->addr = init_entry->addr;
338 entry->next = local_hostlist_dynamic;
339 local_hostlist_dynamic = entry;
340 }
341 }
342 #endif /* DNS_LOCAL_HOSTLIST_IS_DYNAMIC && defined(DNS_LOCAL_HOSTLIST_INIT) */
343 }
344
345 /**
346 * Scans the local host-list for a hostname.
347 *
348 * @param hostname Hostname to look for in the local host-list
349 * @return The first IP address for the hostname in the local host-list or
350 * IPADDR_NONE if not found.
351 */
352 static u32_t
dns_lookup_local(const char * hostname)353 dns_lookup_local(const char *hostname)
354 {
355 #if DNS_LOCAL_HOSTLIST_IS_DYNAMIC
356 struct local_hostlist_entry *entry = local_hostlist_dynamic;
357 while(entry != NULL) {
358 if(strcmp(entry->name, hostname) == 0) {
359 return ip4_addr_get_u32(&entry->addr);
360 }
361 entry = entry->next;
362 }
363 #else /* DNS_LOCAL_HOSTLIST_IS_DYNAMIC */
364 int i;
365 for (i = 0; i < sizeof(local_hostlist_static) / sizeof(struct local_hostlist_entry); i++) {
366 if(strcmp(local_hostlist_static[i].name, hostname) == 0) {
367 return ip4_addr_get_u32(&local_hostlist_static[i].addr);
368 }
369 }
370 #endif /* DNS_LOCAL_HOSTLIST_IS_DYNAMIC */
371 return IPADDR_NONE;
372 }
373
374 #if DNS_LOCAL_HOSTLIST_IS_DYNAMIC
375 /** Remove all entries from the local host-list for a specific hostname
376 * and/or IP addess
377 *
378 * @param hostname hostname for which entries shall be removed from the local
379 * host-list
380 * @param addr address for which entries shall be removed from the local host-list
381 * @return the number of removed entries
382 */
383 int
dns_local_removehost(const char * hostname,const ip_addr_t * addr)384 dns_local_removehost(const char *hostname, const ip_addr_t *addr)
385 {
386 int removed = 0;
387 struct local_hostlist_entry *entry = local_hostlist_dynamic;
388 struct local_hostlist_entry *last_entry = NULL;
389 while (entry != NULL) {
390 if (((hostname == NULL) || !strcmp(entry->name, hostname)) &&
391 ((addr == NULL) || ip_addr_cmp(&entry->addr, addr))) {
392 struct local_hostlist_entry *free_entry;
393 if (last_entry != NULL) {
394 last_entry->next = entry->next;
395 } else {
396 local_hostlist_dynamic = entry->next;
397 }
398 free_entry = entry;
399 entry = entry->next;
400 memp_free(MEMP_LOCALHOSTLIST, free_entry);
401 removed++;
402 } else {
403 last_entry = entry;
404 entry = entry->next;
405 }
406 }
407 return removed;
408 }
409
410 /**
411 * Add a hostname/IP address pair to the local host-list.
412 * Duplicates are not checked.
413 *
414 * @param hostname hostname of the new entry
415 * @param addr IP address of the new entry
416 * @return ERR_OK if succeeded or ERR_MEM on memory error
417 */
418 err_t
dns_local_addhost(const char * hostname,const ip_addr_t * addr)419 dns_local_addhost(const char *hostname, const ip_addr_t *addr)
420 {
421 struct local_hostlist_entry *entry;
422 size_t namelen;
423 LWIP_ASSERT("invalid host name (NULL)", hostname != NULL);
424 namelen = strlen(hostname);
425 LWIP_ASSERT("namelen <= DNS_LOCAL_HOSTLIST_MAX_NAMELEN", namelen <= DNS_LOCAL_HOSTLIST_MAX_NAMELEN);
426 entry = (struct local_hostlist_entry *)memp_malloc(MEMP_LOCALHOSTLIST);
427 if (entry == NULL) {
428 return ERR_MEM;
429 }
430 entry->name = (char*)entry + sizeof(struct local_hostlist_entry);
431 MEMCPY((char*)entry->name, hostname, namelen);
432 ((char*)entry->name)[namelen] = 0;
433 ip_addr_copy(entry->addr, *addr);
434 entry->next = local_hostlist_dynamic;
435 local_hostlist_dynamic = entry;
436 return ERR_OK;
437 }
438 #endif /* DNS_LOCAL_HOSTLIST_IS_DYNAMIC*/
439 #endif /* DNS_LOCAL_HOSTLIST */
440
441 /**
442 * Look up a hostname in the array of known hostnames.
443 *
444 * @note This function only looks in the internal array of known
445 * hostnames, it does not send out a query for the hostname if none
446 * was found. The function dns_enqueue() can be used to send a query
447 * for a hostname.
448 *
449 * @param name the hostname to look up
450 * @return the hostname's IP address, as u32_t (instead of ip_addr_t to
451 * better check for failure: != IPADDR_NONE) or IPADDR_NONE if the hostname
452 * was not found in the cached dns_table.
453 */
454 static u32_t
dns_lookup(const char * name)455 dns_lookup(const char *name)
456 {
457 u8_t i;
458 #if DNS_LOCAL_HOSTLIST || defined(DNS_LOOKUP_LOCAL_EXTERN)
459 u32_t addr;
460 #endif /* DNS_LOCAL_HOSTLIST || defined(DNS_LOOKUP_LOCAL_EXTERN) */
461 #if DNS_LOCAL_HOSTLIST
462 if ((addr = dns_lookup_local(name)) != IPADDR_NONE) {
463 return addr;
464 }
465 #endif /* DNS_LOCAL_HOSTLIST */
466 #ifdef DNS_LOOKUP_LOCAL_EXTERN
467 if((addr = DNS_LOOKUP_LOCAL_EXTERN(name)) != IPADDR_NONE) {
468 return addr;
469 }
470 #endif /* DNS_LOOKUP_LOCAL_EXTERN */
471
472 /* Walk through name list, return entry if found. If not, return NULL. */
473 for (i = 0; i < DNS_TABLE_SIZE; ++i) {
474 if ((dns_table[i].state == DNS_STATE_DONE) &&
475 (strcmp(name, dns_table[i].name) == 0)) {
476 LWIP_DEBUGF(DNS_DEBUG, ("dns_lookup: \"%s\": found = ", name));
477 ip_addr_debug_print(DNS_DEBUG, &(dns_table[i].ipaddr));
478 LWIP_DEBUGF(DNS_DEBUG, ("\n"));
479 return ip4_addr_get_u32(&dns_table[i].ipaddr);
480 }
481 }
482
483 return IPADDR_NONE;
484 }
485
486 #if DNS_DOES_NAME_CHECK
487 /**
488 * Compare the "dotted" name "query" with the encoded name "response"
489 * to make sure an answer from the DNS server matches the current dns_table
490 * entry (otherwise, answers might arrive late for hostname not on the list
491 * any more).
492 *
493 * @param query hostname (not encoded) from the dns_table
494 * @param response encoded hostname in the DNS response
495 * @return 0: names equal; 1: names differ
496 */
497 static u8_t
dns_compare_name(unsigned char * query,unsigned char * response)498 dns_compare_name(unsigned char *query, unsigned char *response)
499 {
500 unsigned char n;
501
502 do {
503 n = *response++;
504 /** @see RFC 1035 - 4.1.4. Message compression */
505 if ((n & 0xc0) == 0xc0) {
506 /* Compressed name */
507 break;
508 } else {
509 /* Not compressed name */
510 while (n > 0) {
511 if ((*query) != (*response)) {
512 return 1;
513 }
514 ++response;
515 ++query;
516 --n;
517 };
518 ++query;
519 }
520 } while (*response != 0);
521
522 return 0;
523 }
524 #endif /* DNS_DOES_NAME_CHECK */
525
526 /**
527 * Walk through a compact encoded DNS name and return the end of the name.
528 *
529 * @param query encoded DNS name in the DNS server response
530 * @return end of the name
531 */
532 static unsigned char *
dns_parse_name(unsigned char * query)533 dns_parse_name(unsigned char *query)
534 {
535 unsigned char n;
536
537 do {
538 n = *query++;
539 /** @see RFC 1035 - 4.1.4. Message compression */
540 if ((n & 0xc0) == 0xc0) {
541 /* Compressed name */
542 break;
543 } else {
544 /* Not compressed name */
545 while (n > 0) {
546 ++query;
547 --n;
548 };
549 }
550 } while (*query != 0);
551
552 return query + 1;
553 }
554
555 /**
556 * Send a DNS query packet.
557 *
558 * @param numdns index of the DNS server in the dns_servers table
559 * @param name hostname to query
560 * @param id index of the hostname in dns_table, used as transaction ID in the
561 * DNS query packet
562 * @return ERR_OK if packet is sent; an err_t indicating the problem otherwise
563 */
564 static err_t
dns_send(u8_t numdns,const char * name,u8_t id)565 dns_send(u8_t numdns, const char* name, u8_t id)
566 {
567 err_t err;
568 struct dns_hdr *hdr;
569 struct dns_query qry;
570 struct pbuf *p;
571 char *query, *nptr;
572 const char *pHostname;
573 u8_t n;
574
575 LWIP_DEBUGF(DNS_DEBUG, ("dns_send: dns_servers[%"U16_F"] \"%s\": request\n",
576 (u16_t)(numdns), name));
577 LWIP_ASSERT("dns server out of array", numdns < DNS_MAX_SERVERS);
578 LWIP_ASSERT("dns server has no IP address set", !ip_addr_isany(&dns_servers[numdns]));
579
580 /* if here, we have either a new query or a retry on a previous query to process */
581 p = pbuf_alloc(PBUF_TRANSPORT, SIZEOF_DNS_HDR + DNS_MAX_NAME_LENGTH +
582 SIZEOF_DNS_QUERY, PBUF_RAM);
583 if (p != NULL) {
584 LWIP_ASSERT("pbuf must be in one piece", p->next == NULL);
585 /* fill dns header */
586 hdr = (struct dns_hdr*)p->payload;
587 memset(hdr, 0, SIZEOF_DNS_HDR);
588 hdr->id = htons(id);
589 hdr->flags1 = DNS_FLAG1_RD;
590 hdr->numquestions = PP_HTONS(1);
591 query = (char*)hdr + SIZEOF_DNS_HDR;
592 pHostname = name;
593 --pHostname;
594
595 /* convert hostname into suitable query format. */
596 do {
597 ++pHostname;
598 nptr = query;
599 ++query;
600 for(n = 0; *pHostname != '.' && *pHostname != 0; ++pHostname) {
601 *query = *pHostname;
602 ++query;
603 ++n;
604 }
605 *nptr = n;
606 } while(*pHostname != 0);
607 *query++='\0';
608
609 /* fill dns query */
610 qry.type = PP_HTONS(DNS_RRTYPE_A);
611 qry.cls = PP_HTONS(DNS_RRCLASS_IN);
612 SMEMCPY(query, &qry, SIZEOF_DNS_QUERY);
613
614 /* resize pbuf to the exact dns query */
615 pbuf_realloc(p, (u16_t)((query + SIZEOF_DNS_QUERY) - ((char*)(p->payload))));
616
617 /* connect to the server for faster receiving */
618 udp_connect(dns_pcb, &dns_servers[numdns], DNS_SERVER_PORT);
619 /* send dns packet */
620 err = udp_sendto(dns_pcb, p, &dns_servers[numdns], DNS_SERVER_PORT);
621
622 /* free pbuf */
623 pbuf_free(p);
624 } else {
625 err = ERR_MEM;
626 }
627
628 return err;
629 }
630
631 /**
632 * dns_check_entry() - see if pEntry has not yet been queried and, if so, sends out a query.
633 * Check an entry in the dns_table:
634 * - send out query for new entries
635 * - retry old pending entries on timeout (also with different servers)
636 * - remove completed entries from the table if their TTL has expired
637 *
638 * @param i index of the dns_table entry to check
639 */
640 static void
dns_check_entry(u8_t i)641 dns_check_entry(u8_t i)
642 {
643 err_t err;
644 struct dns_table_entry *pEntry = &dns_table[i];
645
646 LWIP_ASSERT("array index out of bounds", i < DNS_TABLE_SIZE);
647
648 switch(pEntry->state) {
649
650 case DNS_STATE_NEW: {
651 /* initialize new entry */
652 pEntry->state = DNS_STATE_ASKING;
653 pEntry->numdns = 0;
654 pEntry->tmr = 1;
655 pEntry->retries = 0;
656
657 /* send DNS packet for this entry */
658 err = dns_send(pEntry->numdns, pEntry->name, i);
659 if (err != ERR_OK) {
660 LWIP_DEBUGF(DNS_DEBUG | LWIP_DBG_LEVEL_WARNING,
661 ("dns_send returned error: %s\n", lwip_strerr(err)));
662 }
663 break;
664 }
665
666 case DNS_STATE_ASKING: {
667 if (--pEntry->tmr == 0) {
668 if (++pEntry->retries == DNS_MAX_RETRIES) {
669 if ((pEntry->numdns+1<DNS_MAX_SERVERS) && !ip_addr_isany(&dns_servers[pEntry->numdns+1])) {
670 /* change of server */
671 pEntry->numdns++;
672 pEntry->tmr = 1;
673 pEntry->retries = 0;
674 break;
675 } else {
676 LWIP_DEBUGF(DNS_DEBUG, ("dns_check_entry: \"%s\": timeout\n", pEntry->name));
677 /* call specified callback function if provided */
678 if (pEntry->found)
679 (*pEntry->found)(pEntry->name, NULL, pEntry->arg);
680 /* flush this entry */
681 pEntry->state = DNS_STATE_UNUSED;
682 pEntry->found = NULL;
683 break;
684 }
685 }
686
687 /* wait longer for the next retry */
688 pEntry->tmr = pEntry->retries;
689
690 /* send DNS packet for this entry */
691 err = dns_send(pEntry->numdns, pEntry->name, i);
692 if (err != ERR_OK) {
693 LWIP_DEBUGF(DNS_DEBUG | LWIP_DBG_LEVEL_WARNING,
694 ("dns_send returned error: %s\n", lwip_strerr(err)));
695 }
696 }
697 break;
698 }
699
700 case DNS_STATE_DONE: {
701 /* if the time to live is nul */
702 if (--pEntry->ttl == 0) {
703 LWIP_DEBUGF(DNS_DEBUG, ("dns_check_entry: \"%s\": flush\n", pEntry->name));
704 /* flush this entry */
705 pEntry->state = DNS_STATE_UNUSED;
706 pEntry->found = NULL;
707 }
708 break;
709 }
710 case DNS_STATE_UNUSED:
711 /* nothing to do */
712 break;
713 default:
714 LWIP_ASSERT("unknown dns_table entry state:", 0);
715 break;
716 }
717 }
718
719 /**
720 * Call dns_check_entry for each entry in dns_table - check all entries.
721 */
722 static void
dns_check_entries(void)723 dns_check_entries(void)
724 {
725 u8_t i;
726
727 for (i = 0; i < DNS_TABLE_SIZE; ++i) {
728 dns_check_entry(i);
729 }
730 }
731
732 /**
733 * Receive input function for DNS response packets arriving for the dns UDP pcb.
734 *
735 * @params see udp.h
736 */
737 static void
dns_recv(void * arg,struct udp_pcb * pcb,struct pbuf * p,ip_addr_t * addr,u16_t port)738 dns_recv(void *arg, struct udp_pcb *pcb, struct pbuf *p, ip_addr_t *addr, u16_t port)
739 {
740 u16_t i;
741 char *pHostname;
742 struct dns_hdr *hdr;
743 struct dns_answer ans;
744 struct dns_table_entry *pEntry;
745 u16_t nquestions, nanswers;
746
747 LWIP_UNUSED_ARG(arg);
748 LWIP_UNUSED_ARG(pcb);
749 LWIP_UNUSED_ARG(addr);
750 LWIP_UNUSED_ARG(port);
751
752 /* is the dns message too big ? */
753 if (p->tot_len > DNS_MSG_SIZE) {
754 LWIP_DEBUGF(DNS_DEBUG, ("dns_recv: pbuf too big\n"));
755 /* free pbuf and return */
756 goto memerr;
757 }
758
759 /* is the dns message big enough ? */
760 if (p->tot_len < (SIZEOF_DNS_HDR + SIZEOF_DNS_QUERY + SIZEOF_DNS_ANSWER)) {
761 LWIP_DEBUGF(DNS_DEBUG, ("dns_recv: pbuf too small\n"));
762 /* free pbuf and return */
763 goto memerr;
764 }
765
766 /* copy dns payload inside static buffer for processing */
767 if (pbuf_copy_partial(p, dns_payload, p->tot_len, 0) == p->tot_len) {
768 /* The ID in the DNS header should be our entry into the name table. */
769 hdr = (struct dns_hdr*)dns_payload;
770 i = htons(hdr->id);
771 if (i < DNS_TABLE_SIZE) {
772 pEntry = &dns_table[i];
773 if(pEntry->state == DNS_STATE_ASKING) {
774 /* This entry is now completed. */
775 pEntry->state = DNS_STATE_DONE;
776 pEntry->err = hdr->flags2 & DNS_FLAG2_ERR_MASK;
777
778 /* We only care about the question(s) and the answers. The authrr
779 and the extrarr are simply discarded. */
780 nquestions = htons(hdr->numquestions);
781 nanswers = htons(hdr->numanswers);
782
783 /* Check for error. If so, call callback to inform. */
784 if (((hdr->flags1 & DNS_FLAG1_RESPONSE) == 0) || (pEntry->err != 0) || (nquestions != 1)) {
785 LWIP_DEBUGF(DNS_DEBUG, ("dns_recv: \"%s\": error in flags\n", pEntry->name));
786 /* call callback to indicate error, clean up memory and return */
787 goto responseerr;
788 }
789
790 #if DNS_DOES_NAME_CHECK
791 /* Check if the name in the "question" part match with the name in the entry. */
792 if (dns_compare_name((unsigned char *)(pEntry->name), (unsigned char *)dns_payload + SIZEOF_DNS_HDR) != 0) {
793 LWIP_DEBUGF(DNS_DEBUG, ("dns_recv: \"%s\": response not match to query\n", pEntry->name));
794 /* call callback to indicate error, clean up memory and return */
795 goto responseerr;
796 }
797 #endif /* DNS_DOES_NAME_CHECK */
798
799 /* Skip the name in the "question" part */
800 pHostname = (char *) dns_parse_name((unsigned char *)dns_payload + SIZEOF_DNS_HDR) + SIZEOF_DNS_QUERY;
801
802 while (nanswers > 0) {
803 /* skip answer resource record's host name */
804 pHostname = (char *) dns_parse_name((unsigned char *)pHostname);
805
806 /* Check for IP address type and Internet class. Others are discarded. */
807 SMEMCPY(&ans, pHostname, SIZEOF_DNS_ANSWER);
808 if((ans.type == PP_HTONS(DNS_RRTYPE_A)) && (ans.cls == PP_HTONS(DNS_RRCLASS_IN)) &&
809 (ans.len == PP_HTONS(sizeof(ip_addr_t))) ) {
810 /* read the answer resource record's TTL, and maximize it if needed */
811 pEntry->ttl = ntohl(ans.ttl);
812 if (pEntry->ttl > DNS_MAX_TTL) {
813 pEntry->ttl = DNS_MAX_TTL;
814 }
815 /* read the IP address after answer resource record's header */
816 SMEMCPY(&(pEntry->ipaddr), (pHostname+SIZEOF_DNS_ANSWER), sizeof(ip_addr_t));
817 LWIP_DEBUGF(DNS_DEBUG, ("dns_recv: \"%s\": response = ", pEntry->name));
818 ip_addr_debug_print(DNS_DEBUG, (&(pEntry->ipaddr)));
819 LWIP_DEBUGF(DNS_DEBUG, ("\n"));
820 /* call specified callback function if provided */
821 if (pEntry->found) {
822 (*pEntry->found)(pEntry->name, &pEntry->ipaddr, pEntry->arg);
823 }
824 /* deallocate memory and return */
825 goto memerr;
826 } else {
827 pHostname = pHostname + SIZEOF_DNS_ANSWER + htons(ans.len);
828 }
829 --nanswers;
830 }
831 LWIP_DEBUGF(DNS_DEBUG, ("dns_recv: \"%s\": error in response\n", pEntry->name));
832 /* call callback to indicate error, clean up memory and return */
833 goto responseerr;
834 }
835 }
836 }
837
838 /* deallocate memory and return */
839 goto memerr;
840
841 responseerr:
842 /* ERROR: call specified callback function with NULL as name to indicate an error */
843 if (pEntry->found) {
844 (*pEntry->found)(pEntry->name, NULL, pEntry->arg);
845 }
846 /* flush this entry */
847 pEntry->state = DNS_STATE_UNUSED;
848 pEntry->found = NULL;
849
850 memerr:
851 /* free pbuf */
852 pbuf_free(p);
853 return;
854 }
855
856 /**
857 * Queues a new hostname to resolve and sends out a DNS query for that hostname
858 *
859 * @param name the hostname that is to be queried
860 * @param found a callback founction to be called on success, failure or timeout
861 * @param callback_arg argument to pass to the callback function
862 * @return @return a err_t return code.
863 */
864 static err_t
dns_enqueue(const char * name,dns_found_callback found,void * callback_arg)865 dns_enqueue(const char *name, dns_found_callback found, void *callback_arg)
866 {
867 u8_t i;
868 u8_t lseq, lseqi;
869 struct dns_table_entry *pEntry = NULL;
870 size_t namelen;
871
872 /* search an unused entry, or the oldest one */
873 lseq = lseqi = 0;
874 for (i = 0; i < DNS_TABLE_SIZE; ++i) {
875 pEntry = &dns_table[i];
876 /* is it an unused entry ? */
877 if (pEntry->state == DNS_STATE_UNUSED)
878 break;
879
880 /* check if this is the oldest completed entry */
881 if (pEntry->state == DNS_STATE_DONE) {
882 if ((dns_seqno - pEntry->seqno) > lseq) {
883 lseq = dns_seqno - pEntry->seqno;
884 lseqi = i;
885 }
886 }
887 }
888
889 /* if we don't have found an unused entry, use the oldest completed one */
890 if (i == DNS_TABLE_SIZE) {
891 if ((lseqi >= DNS_TABLE_SIZE) || (dns_table[lseqi].state != DNS_STATE_DONE)) {
892 /* no entry can't be used now, table is full */
893 LWIP_DEBUGF(DNS_DEBUG, ("dns_enqueue: \"%s\": DNS entries table is full\n", name));
894 return ERR_MEM;
895 } else {
896 /* use the oldest completed one */
897 i = lseqi;
898 pEntry = &dns_table[i];
899 }
900 }
901
902 /* use this entry */
903 LWIP_DEBUGF(DNS_DEBUG, ("dns_enqueue: \"%s\": use DNS entry %"U16_F"\n", name, (u16_t)(i)));
904
905 /* fill the entry */
906 pEntry->state = DNS_STATE_NEW;
907 pEntry->seqno = dns_seqno++;
908 pEntry->found = found;
909 pEntry->arg = callback_arg;
910 namelen = LWIP_MIN(strlen(name), DNS_MAX_NAME_LENGTH-1);
911 MEMCPY(pEntry->name, name, namelen);
912 pEntry->name[namelen] = 0;
913
914 /* force to send query without waiting timer */
915 dns_check_entry(i);
916
917 /* dns query is enqueued */
918 return ERR_INPROGRESS;
919 }
920
921 /**
922 * Resolve a hostname (string) into an IP address.
923 * NON-BLOCKING callback version for use with raw API!!!
924 *
925 * Returns immediately with one of err_t return codes:
926 * - ERR_OK if hostname is a valid IP address string or the host
927 * name is already in the local names table.
928 * - ERR_INPROGRESS enqueue a request to be sent to the DNS server
929 * for resolution if no errors are present.
930 * - ERR_ARG: dns client not initialized or invalid hostname
931 *
932 * @param hostname the hostname that is to be queried
933 * @param addr pointer to a ip_addr_t where to store the address if it is already
934 * cached in the dns_table (only valid if ERR_OK is returned!)
935 * @param found a callback function to be called on success, failure or timeout (only if
936 * ERR_INPROGRESS is returned!)
937 * @param callback_arg argument to pass to the callback function
938 * @return a err_t return code.
939 */
940 err_t
dns_gethostbyname(const char * hostname,ip_addr_t * addr,dns_found_callback found,void * callback_arg)941 dns_gethostbyname(const char *hostname, ip_addr_t *addr, dns_found_callback found,
942 void *callback_arg)
943 {
944 u32_t ipaddr;
945 /* not initialized or no valid server yet, or invalid addr pointer
946 * or invalid hostname or invalid hostname length */
947 if ((dns_pcb == NULL) || (addr == NULL) ||
948 (!hostname) || (!hostname[0]) ||
949 (strlen(hostname) >= DNS_MAX_NAME_LENGTH)) {
950 return ERR_ARG;
951 }
952
953 #if LWIP_HAVE_LOOPIF
954 if (strcmp(hostname, "localhost")==0) {
955 ip_addr_set_loopback(addr);
956 return ERR_OK;
957 }
958 #endif /* LWIP_HAVE_LOOPIF */
959
960 /* host name already in octet notation? set ip addr and return ERR_OK */
961 ipaddr = ipaddr_addr(hostname);
962 if (ipaddr == IPADDR_NONE) {
963 /* already have this address cached? */
964 ipaddr = dns_lookup(hostname);
965 }
966 if (ipaddr != IPADDR_NONE) {
967 ip4_addr_set_u32(addr, ipaddr);
968 return ERR_OK;
969 }
970
971 /* queue query with specified callback */
972 return dns_enqueue(hostname, found, callback_arg);
973 }
974
975 #endif /* LWIP_DNS */
976