1 /* 2 * Copyright (c) 2006 Niels Provos <provos@citi.umich.edu> 3 * All rights reserved. 4 * 5 * Redistribution and use in source and binary forms, with or without 6 * modification, are permitted provided that the following conditions 7 * are met: 8 * 1. Redistributions of source code must retain the above copyright 9 * notice, this list of conditions and the following disclaimer. 10 * 2. Redistributions in binary form must reproduce the above copyright 11 * notice, this list of conditions and the following disclaimer in the 12 * documentation and/or other materials provided with the distribution. 13 * 3. The name of the author may not be used to endorse or promote products 14 * derived from this software without specific prior written permission. 15 * 16 * THIS SOFTWARE IS PROVIDED BY THE AUTHOR ``AS IS'' AND ANY EXPRESS OR 17 * IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES 18 * OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE DISCLAIMED. 19 * IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR ANY DIRECT, INDIRECT, 20 * INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT 21 * NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, 22 * DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY 23 * THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT 24 * (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF 25 * THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE. 26 */ 27 28 /* 29 * The original DNS code is due to Adam Langley with heavy 30 * modifications by Nick Mathewson. Adam put his DNS software in the 31 * public domain. You can find his original copyright below. Please, 32 * aware that the code as part of libevent is governed by the 3-clause 33 * BSD license above. 34 * 35 * This software is Public Domain. To view a copy of the public domain dedication, 36 * visit http://creativecommons.org/licenses/publicdomain/ or send a letter to 37 * Creative Commons, 559 Nathan Abbott Way, Stanford, California 94305, USA. 38 * 39 * I ask and expect, but do not require, that all derivative works contain an 40 * attribution similar to: 41 * Parts developed by Adam Langley <agl@imperialviolet.org> 42 * 43 * You may wish to replace the word "Parts" with something else depending on 44 * the amount of original code. 45 * 46 * (Derivative works does not include programs which link against, run or include 47 * the source verbatim in their source distributions) 48 */ 49 50 /** @file evdns.h 51 * 52 * Welcome, gentle reader 53 * 54 * Async DNS lookups are really a whole lot harder than they should be, 55 * mostly stemming from the fact that the libc resolver has never been 56 * very good at them. Before you use this library you should see if libc 57 * can do the job for you with the modern async call getaddrinfo_a 58 * (see http://www.imperialviolet.org/page25.html#e498). Otherwise, 59 * please continue. 60 * 61 * This code is based on libevent and you must call event_init before 62 * any of the APIs in this file. You must also seed the OpenSSL random 63 * source if you are using OpenSSL for ids (see below). 64 * 65 * This library is designed to be included and shipped with your source 66 * code. You statically link with it. You should also test for the 67 * existence of strtok_r and define HAVE_STRTOK_R if you have it. 68 * 69 * The DNS protocol requires a good source of id numbers and these 70 * numbers should be unpredictable for spoofing reasons. There are 71 * three methods for generating them here and you must define exactly 72 * one of them. In increasing order of preference: 73 * 74 * DNS_USE_GETTIMEOFDAY_FOR_ID: 75 * Using the bottom 16 bits of the usec result from gettimeofday. This 76 * is a pretty poor solution but should work anywhere. 77 * DNS_USE_CPU_CLOCK_FOR_ID: 78 * Using the bottom 16 bits of the nsec result from the CPU's time 79 * counter. This is better, but may not work everywhere. Requires 80 * POSIX realtime support and you'll need to link against -lrt on 81 * glibc systems at least. 82 * DNS_USE_OPENSSL_FOR_ID: 83 * Uses the OpenSSL RAND_bytes call to generate the data. You must 84 * have seeded the pool before making any calls to this library. 85 * 86 * The library keeps track of the state of nameservers and will avoid 87 * them when they go down. Otherwise it will round robin between them. 88 * 89 * Quick start guide: 90 * #include "evdns.h" 91 * void callback(int result, char type, int count, int ttl, 92 * void *addresses, void *arg); 93 * evdns_resolv_conf_parse(DNS_OPTIONS_ALL, "/etc/resolv.conf"); 94 * evdns_resolve("www.hostname.com", 0, callback, NULL); 95 * 96 * When the lookup is complete the callback function is called. The 97 * first argument will be one of the DNS_ERR_* defines in evdns.h. 98 * Hopefully it will be DNS_ERR_NONE, in which case type will be 99 * DNS_IPv4_A, count will be the number of IP addresses, ttl is the time 100 * which the data can be cached for (in seconds), addresses will point 101 * to an array of uint32_t's and arg will be whatever you passed to 102 * evdns_resolve. 103 * 104 * Searching: 105 * 106 * In order for this library to be a good replacement for glibc's resolver it 107 * supports searching. This involves setting a list of default domains, in 108 * which names will be queried for. The number of dots in the query name 109 * determines the order in which this list is used. 110 * 111 * Searching appears to be a single lookup from the point of view of the API, 112 * although many DNS queries may be generated from a single call to 113 * evdns_resolve. Searching can also drastically slow down the resolution 114 * of names. 115 * 116 * To disable searching: 117 * 1. Never set it up. If you never call evdns_resolv_conf_parse or 118 * evdns_search_add then no searching will occur. 119 * 120 * 2. If you do call evdns_resolv_conf_parse then don't pass 121 * DNS_OPTION_SEARCH (or DNS_OPTIONS_ALL, which implies it). 122 * 123 * 3. When calling evdns_resolve, pass the DNS_QUERY_NO_SEARCH flag. 124 * 125 * The order of searches depends on the number of dots in the name. If the 126 * number is greater than the ndots setting then the names is first tried 127 * globally. Otherwise each search domain is appended in turn. 128 * 129 * The ndots setting can either be set from a resolv.conf, or by calling 130 * evdns_search_ndots_set. 131 * 132 * For example, with ndots set to 1 (the default) and a search domain list of 133 * ["myhome.net"]: 134 * Query: www 135 * Order: www.myhome.net, www. 136 * 137 * Query: www.abc 138 * Order: www.abc., www.abc.myhome.net 139 * 140 * Internals: 141 * 142 * Requests are kept in two queues. The first is the inflight queue. In 143 * this queue requests have an allocated transaction id and nameserver. 144 * They will soon be transmitted if they haven't already been. 145 * 146 * The second is the waiting queue. The size of the inflight ring is 147 * limited and all other requests wait in waiting queue for space. This 148 * bounds the number of concurrent requests so that we don't flood the 149 * nameserver. Several algorithms require a full walk of the inflight 150 * queue and so bounding its size keeps thing going nicely under huge 151 * (many thousands of requests) loads. 152 * 153 * If a nameserver loses too many requests it is considered down and we 154 * try not to use it. After a while we send a probe to that nameserver 155 * (a lookup for google.com) and, if it replies, we consider it working 156 * again. If the nameserver fails a probe we wait longer to try again 157 * with the next probe. 158 */ 159 160 #ifndef EVENTDNS_H 161 #define EVENTDNS_H 162 163 #ifdef __cplusplus 164 extern "C" { 165 #endif 166 167 /* For integer types. */ 168 #include <evutil.h> 169 170 /** Error codes 0-5 are as described in RFC 1035. */ 171 #define DNS_ERR_NONE 0 172 /** The name server was unable to interpret the query */ 173 #define DNS_ERR_FORMAT 1 174 /** The name server was unable to process this query due to a problem with the 175 * name server */ 176 #define DNS_ERR_SERVERFAILED 2 177 /** The domain name does not exist */ 178 #define DNS_ERR_NOTEXIST 3 179 /** The name server does not support the requested kind of query */ 180 #define DNS_ERR_NOTIMPL 4 181 /** The name server refuses to reform the specified operation for policy 182 * reasons */ 183 #define DNS_ERR_REFUSED 5 184 /** The reply was truncated or ill-formated */ 185 #define DNS_ERR_TRUNCATED 65 186 /** An unknown error occurred */ 187 #define DNS_ERR_UNKNOWN 66 188 /** Communication with the server timed out */ 189 #define DNS_ERR_TIMEOUT 67 190 /** The request was canceled because the DNS subsystem was shut down. */ 191 #define DNS_ERR_SHUTDOWN 68 192 193 #define DNS_IPv4_A 1 194 #define DNS_PTR 2 195 #define DNS_IPv6_AAAA 3 196 197 #define DNS_QUERY_NO_SEARCH 1 198 199 #define DNS_OPTION_SEARCH 1 200 #define DNS_OPTION_NAMESERVERS 2 201 #define DNS_OPTION_MISC 4 202 #define DNS_OPTIONS_ALL 7 203 204 /** 205 * The callback that contains the results from a lookup. 206 * - type is either DNS_IPv4_A or DNS_PTR or DNS_IPv6_AAAA 207 * - count contains the number of addresses of form type 208 * - ttl is the number of seconds the resolution may be cached for. 209 * - addresses needs to be cast according to type 210 */ 211 typedef void (*evdns_callback_type) (int result, char type, int count, int ttl, void *addresses, void *arg); 212 213 /** 214 Initialize the asynchronous DNS library. 215 216 This function initializes support for non-blocking name resolution by 217 calling evdns_resolv_conf_parse() on UNIX and 218 evdns_config_windows_nameservers() on Windows. 219 220 @return 0 if successful, or -1 if an error occurred 221 @see evdns_shutdown() 222 */ 223 int evdns_init(void); 224 225 226 /** 227 Shut down the asynchronous DNS resolver and terminate all active requests. 228 229 If the 'fail_requests' option is enabled, all active requests will return 230 an empty result with the error flag set to DNS_ERR_SHUTDOWN. Otherwise, 231 the requests will be silently discarded. 232 233 @param fail_requests if zero, active requests will be aborted; if non-zero, 234 active requests will return DNS_ERR_SHUTDOWN. 235 @see evdns_init() 236 */ 237 void evdns_shutdown(int fail_requests); 238 239 240 /** 241 Convert a DNS error code to a string. 242 243 @param err the DNS error code 244 @return a string containing an explanation of the error code 245 */ 246 const char *evdns_err_to_string(int err); 247 248 249 /** 250 Add a nameserver. 251 252 The address should be an IPv4 address in network byte order. 253 The type of address is chosen so that it matches in_addr.s_addr. 254 255 @param address an IP address in network byte order 256 @return 0 if successful, or -1 if an error occurred 257 @see evdns_nameserver_ip_add() 258 */ 259 int evdns_nameserver_add(unsigned long int address); 260 261 262 /** 263 Get the number of configured nameservers. 264 265 This returns the number of configured nameservers (not necessarily the 266 number of running nameservers). This is useful for double-checking 267 whether our calls to the various nameserver configuration functions 268 have been successful. 269 270 @return the number of configured nameservers 271 @see evdns_nameserver_add() 272 */ 273 int evdns_count_nameservers(void); 274 275 276 /** 277 Remove all configured nameservers, and suspend all pending resolves. 278 279 Resolves will not necessarily be re-attempted until evdns_resume() is called. 280 281 @return 0 if successful, or -1 if an error occurred 282 @see evdns_resume() 283 */ 284 int evdns_clear_nameservers_and_suspend(void); 285 286 287 /** 288 Resume normal operation and continue any suspended resolve requests. 289 290 Re-attempt resolves left in limbo after an earlier call to 291 evdns_clear_nameservers_and_suspend(). 292 293 @return 0 if successful, or -1 if an error occurred 294 @see evdns_clear_nameservers_and_suspend() 295 */ 296 int evdns_resume(void); 297 298 299 /** 300 Add a nameserver. 301 302 This wraps the evdns_nameserver_add() function by parsing a string as an IP 303 address and adds it as a nameserver. 304 305 @return 0 if successful, or -1 if an error occurred 306 @see evdns_nameserver_add() 307 */ 308 int evdns_nameserver_ip_add(const char *ip_as_string); 309 310 311 /** 312 Lookup an A record for a given name. 313 314 @param name a DNS hostname 315 @param flags either 0, or DNS_QUERY_NO_SEARCH to disable searching for this query. 316 @param callback a callback function to invoke when the request is completed 317 @param ptr an argument to pass to the callback function 318 @return 0 if successful, or -1 if an error occurred 319 @see evdns_resolve_ipv6(), evdns_resolve_reverse(), evdns_resolve_reverse_ipv6() 320 */ 321 int evdns_resolve_ipv4(const char *name, int flags, evdns_callback_type callback, void *ptr); 322 323 324 /** 325 Lookup an AAAA record for a given name. 326 327 @param name a DNS hostname 328 @param flags either 0, or DNS_QUERY_NO_SEARCH to disable searching for this query. 329 @param callback a callback function to invoke when the request is completed 330 @param ptr an argument to pass to the callback function 331 @return 0 if successful, or -1 if an error occurred 332 @see evdns_resolve_ipv4(), evdns_resolve_reverse(), evdns_resolve_reverse_ipv6() 333 */ 334 int evdns_resolve_ipv6(const char *name, int flags, evdns_callback_type callback, void *ptr); 335 336 struct in_addr; 337 struct in6_addr; 338 339 /** 340 Lookup a PTR record for a given IP address. 341 342 @param in an IPv4 address 343 @param flags either 0, or DNS_QUERY_NO_SEARCH to disable searching for this query. 344 @param callback a callback function to invoke when the request is completed 345 @param ptr an argument to pass to the callback function 346 @return 0 if successful, or -1 if an error occurred 347 @see evdns_resolve_reverse_ipv6() 348 */ 349 int evdns_resolve_reverse(const struct in_addr *in, int flags, evdns_callback_type callback, void *ptr); 350 351 352 /** 353 Lookup a PTR record for a given IPv6 address. 354 355 @param in an IPv6 address 356 @param flags either 0, or DNS_QUERY_NO_SEARCH to disable searching for this query. 357 @param callback a callback function to invoke when the request is completed 358 @param ptr an argument to pass to the callback function 359 @return 0 if successful, or -1 if an error occurred 360 @see evdns_resolve_reverse_ipv6() 361 */ 362 int evdns_resolve_reverse_ipv6(const struct in6_addr *in, int flags, evdns_callback_type callback, void *ptr); 363 364 365 /** 366 Set the value of a configuration option. 367 368 The currently available configuration options are: 369 370 ndots, timeout, max-timeouts, max-inflight, and attempts 371 372 @param option the name of the configuration option to be modified 373 @param val the value to be set 374 @param flags either 0 | DNS_OPTION_SEARCH | DNS_OPTION_MISC 375 @return 0 if successful, or -1 if an error occurred 376 */ 377 int evdns_set_option(const char *option, const char *val, int flags); 378 379 380 /** 381 Parse a resolv.conf file. 382 383 The 'flags' parameter determines what information is parsed from the 384 resolv.conf file. See the man page for resolv.conf for the format of this 385 file. 386 387 The following directives are not parsed from the file: sortlist, rotate, 388 no-check-names, inet6, debug. 389 390 If this function encounters an error, the possible return values are: 1 = 391 failed to open file, 2 = failed to stat file, 3 = file too large, 4 = out of 392 memory, 5 = short read from file, 6 = no nameservers listed in the file 393 394 @param flags any of DNS_OPTION_NAMESERVERS|DNS_OPTION_SEARCH|DNS_OPTION_MISC| 395 DNS_OPTIONS_ALL 396 @param filename the path to the resolv.conf file 397 @return 0 if successful, or various positive error codes if an error 398 occurred (see above) 399 @see resolv.conf(3), evdns_config_windows_nameservers() 400 */ 401 int evdns_resolv_conf_parse(int flags, const char *const filename); 402 403 404 /** 405 Obtain nameserver information using the Windows API. 406 407 Attempt to configure a set of nameservers based on platform settings on 408 a win32 host. Preferentially tries to use GetNetworkParams; if that fails, 409 looks in the registry. 410 411 @return 0 if successful, or -1 if an error occurred 412 @see evdns_resolv_conf_parse() 413 */ 414 #ifdef WIN32 415 int evdns_config_windows_nameservers(void); 416 #endif 417 418 419 /** 420 Clear the list of search domains. 421 */ 422 void evdns_search_clear(void); 423 424 425 /** 426 Add a domain to the list of search domains 427 428 @param domain the domain to be added to the search list 429 */ 430 void evdns_search_add(const char *domain); 431 432 433 /** 434 Set the 'ndots' parameter for searches. 435 436 Sets the number of dots which, when found in a name, causes 437 the first query to be without any search domain. 438 439 @param ndots the new ndots parameter 440 */ 441 void evdns_search_ndots_set(const int ndots); 442 443 /** 444 A callback that is invoked when a log message is generated 445 446 @param is_warning indicates if the log message is a 'warning' 447 @param msg the content of the log message 448 */ 449 typedef void (*evdns_debug_log_fn_type)(int is_warning, const char *msg); 450 451 452 /** 453 Set the callback function to handle log messages. 454 455 @param fn the callback to be invoked when a log message is generated 456 */ 457 void evdns_set_log_fn(evdns_debug_log_fn_type fn); 458 459 /** 460 Set a callback that will be invoked to generate transaction IDs. By 461 default, we pick transaction IDs based on the current clock time. 462 463 @param fn the new callback, or NULL to use the default. 464 */ 465 void evdns_set_transaction_id_fn(ev_uint16_t (*fn)(void)); 466 467 #define DNS_NO_SEARCH 1 468 469 /* 470 * Structures and functions used to implement a DNS server. 471 */ 472 473 struct evdns_server_request { 474 int flags; 475 int nquestions; 476 struct evdns_server_question **questions; 477 }; 478 struct evdns_server_question { 479 int type; 480 #ifdef __cplusplus 481 int dns_question_class; 482 #else 483 /* You should refer to this field as "dns_question_class". The 484 * name "class" works in C for backward compatibility, and will be 485 * removed in a future version. (1.5 or later). */ 486 int class; 487 #define dns_question_class class 488 #endif 489 char name[1]; 490 }; 491 typedef void (*evdns_request_callback_fn_type)(struct evdns_server_request *, void *); 492 #define EVDNS_ANSWER_SECTION 0 493 #define EVDNS_AUTHORITY_SECTION 1 494 #define EVDNS_ADDITIONAL_SECTION 2 495 496 #define EVDNS_TYPE_A 1 497 #define EVDNS_TYPE_NS 2 498 #define EVDNS_TYPE_CNAME 5 499 #define EVDNS_TYPE_SOA 6 500 #define EVDNS_TYPE_PTR 12 501 #define EVDNS_TYPE_MX 15 502 #define EVDNS_TYPE_TXT 16 503 #define EVDNS_TYPE_AAAA 28 504 505 #define EVDNS_QTYPE_AXFR 252 506 #define EVDNS_QTYPE_ALL 255 507 508 #define EVDNS_CLASS_INET 1 509 510 struct evdns_server_port *evdns_add_server_port(int socket, int is_tcp, evdns_request_callback_fn_type callback, void *user_data); 511 void evdns_close_server_port(struct evdns_server_port *port); 512 513 int evdns_server_request_add_reply(struct evdns_server_request *req, int section, const char *name, int type, int dns_class, int ttl, int datalen, int is_name, const char *data); 514 int evdns_server_request_add_a_reply(struct evdns_server_request *req, const char *name, int n, void *addrs, int ttl); 515 int evdns_server_request_add_aaaa_reply(struct evdns_server_request *req, const char *name, int n, void *addrs, int ttl); 516 int evdns_server_request_add_ptr_reply(struct evdns_server_request *req, struct in_addr *in, const char *inaddr_name, const char *hostname, int ttl); 517 int evdns_server_request_add_cname_reply(struct evdns_server_request *req, const char *name, const char *cname, int ttl); 518 519 int evdns_server_request_respond(struct evdns_server_request *req, int err); 520 int evdns_server_request_drop(struct evdns_server_request *req); 521 struct sockaddr; 522 int evdns_server_request_get_requesting_addr(struct evdns_server_request *_req, struct sockaddr *sa, int addr_len); 523 524 #ifdef __cplusplus 525 } 526 #endif 527 528 #endif /* !EVENTDNS_H */ 529