1/* 2 * Copyright (c) 2006-2007 Niels Provos <provos@citi.umich.edu> 3 * Copyright (c) 2007-2012 Niels Provos and Nick Mathewson 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 event2/dns.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 * The library keeps track of the state of nameservers and will avoid 62 * them when they go down. Otherwise it will round robin between them. 63 * 64 * Quick start guide: 65 * #include "evdns.h" 66 * void callback(int result, char type, int count, int ttl, 67 * void *addresses, void *arg); 68 * evdns_resolv_conf_parse(DNS_OPTIONS_ALL, "/etc/resolv.conf"); 69 * evdns_resolve("www.hostname.com", 0, callback, NULL); 70 * 71 * When the lookup is complete the callback function is called. The 72 * first argument will be one of the DNS_ERR_* defines in evdns.h. 73 * Hopefully it will be DNS_ERR_NONE, in which case type will be 74 * DNS_IPv4_A, count will be the number of IP addresses, ttl is the time 75 * which the data can be cached for (in seconds), addresses will point 76 * to an array of uint32_t's and arg will be whatever you passed to 77 * evdns_resolve. 78 * 79 * Searching: 80 * 81 * In order for this library to be a good replacement for glibc's resolver it 82 * supports searching. This involves setting a list of default domains, in 83 * which names will be queried for. The number of dots in the query name 84 * determines the order in which this list is used. 85 * 86 * Searching appears to be a single lookup from the point of view of the API, 87 * although many DNS queries may be generated from a single call to 88 * evdns_resolve. Searching can also drastically slow down the resolution 89 * of names. 90 * 91 * To disable searching: 92 * 1. Never set it up. If you never call evdns_resolv_conf_parse or 93 * evdns_search_add then no searching will occur. 94 * 95 * 2. If you do call evdns_resolv_conf_parse then don't pass 96 * DNS_OPTION_SEARCH (or DNS_OPTIONS_ALL, which implies it). 97 * 98 * 3. When calling evdns_resolve, pass the DNS_QUERY_NO_SEARCH flag. 99 * 100 * The order of searches depends on the number of dots in the name. If the 101 * number is greater than the ndots setting then the names is first tried 102 * globally. Otherwise each search domain is appended in turn. 103 * 104 * The ndots setting can either be set from a resolv.conf, or by calling 105 * evdns_search_ndots_set. 106 * 107 * For example, with ndots set to 1 (the default) and a search domain list of 108 * ["myhome.net"]: 109 * Query: www 110 * Order: www.myhome.net, www. 111 * 112 * Query: www.abc 113 * Order: www.abc., www.abc.myhome.net 114 * 115 * Internals: 116 * 117 * Requests are kept in two queues. The first is the inflight queue. In 118 * this queue requests have an allocated transaction id and nameserver. 119 * They will soon be transmitted if they haven't already been. 120 * 121 * The second is the waiting queue. The size of the inflight ring is 122 * limited and all other requests wait in waiting queue for space. This 123 * bounds the number of concurrent requests so that we don't flood the 124 * nameserver. Several algorithms require a full walk of the inflight 125 * queue and so bounding its size keeps thing going nicely under huge 126 * (many thousands of requests) loads. 127 * 128 * If a nameserver loses too many requests it is considered down and we 129 * try not to use it. After a while we send a probe to that nameserver 130 * (a lookup for google.com) and, if it replies, we consider it working 131 * again. If the nameserver fails a probe we wait longer to try again 132 * with the next probe. 133 */ 134 135#ifndef EVENT2_DNS_H_INCLUDED_ 136#define EVENT2_DNS_H_INCLUDED_ 137 138#include <event2/visibility.h> 139 140#ifdef __cplusplus 141extern "C" { 142#endif 143 144/* For integer types. */ 145#include <event2/util.h> 146 147/** Error codes 0-5 are as described in RFC 1035. */ 148#define DNS_ERR_NONE 0 149/** The name server was unable to interpret the query */ 150#define DNS_ERR_FORMAT 1 151/** The name server was unable to process this query due to a problem with the 152 * name server */ 153#define DNS_ERR_SERVERFAILED 2 154/** The domain name does not exist */ 155#define DNS_ERR_NOTEXIST 3 156/** The name server does not support the requested kind of query */ 157#define DNS_ERR_NOTIMPL 4 158/** The name server refuses to reform the specified operation for policy 159 * reasons */ 160#define DNS_ERR_REFUSED 5 161/** The reply was truncated or ill-formatted */ 162#define DNS_ERR_TRUNCATED 65 163/** An unknown error occurred */ 164#define DNS_ERR_UNKNOWN 66 165/** Communication with the server timed out */ 166#define DNS_ERR_TIMEOUT 67 167/** The request was canceled because the DNS subsystem was shut down. */ 168#define DNS_ERR_SHUTDOWN 68 169/** The request was canceled via a call to evdns_cancel_request */ 170#define DNS_ERR_CANCEL 69 171/** There were no answers and no error condition in the DNS packet. 172 * This can happen when you ask for an address that exists, but a record 173 * type that doesn't. */ 174#define DNS_ERR_NODATA 70 175 176#define DNS_IPv4_A 1 177#define DNS_PTR 2 178#define DNS_IPv6_AAAA 3 179 180#define DNS_QUERY_NO_SEARCH 1 181 182/* Allow searching */ 183#define DNS_OPTION_SEARCH 1 184/* Parse "nameserver" and add default if no such section */ 185#define DNS_OPTION_NAMESERVERS 2 186/* Parse additional options like: 187 * - timeout: 188 * - getaddrinfo-allow-skew: 189 * - max-timeouts: 190 * - max-inflight: 191 * - attempts: 192 * - randomize-case: 193 * - initial-probe-timeout: 194 */ 195#define DNS_OPTION_MISC 4 196/* Load hosts file (i.e. "/etc/hosts") */ 197#define DNS_OPTION_HOSTSFILE 8 198/** 199 * All above: 200 * - DNS_OPTION_SEARCH 201 * - DNS_OPTION_NAMESERVERS 202 * - DNS_OPTION_MISC 203 * - DNS_OPTION_HOSTSFILE 204 */ 205#define DNS_OPTIONS_ALL ( \ 206 DNS_OPTION_SEARCH | \ 207 DNS_OPTION_NAMESERVERS | \ 208 DNS_OPTION_MISC | \ 209 DNS_OPTION_HOSTSFILE | \ 210 0 \ 211) 212/* Do not "default" nameserver (i.e. "127.0.0.1:53") if there is no nameservers 213 * in resolv.conf, (iff DNS_OPTION_NAMESERVERS is set) */ 214#define DNS_OPTION_NAMESERVERS_NO_DEFAULT 16 215 216/* Obsolete name for DNS_QUERY_NO_SEARCH */ 217#define DNS_NO_SEARCH DNS_QUERY_NO_SEARCH 218 219/** 220 * The callback that contains the results from a lookup. 221 * - result is one of the DNS_ERR_* values (DNS_ERR_NONE for success) 222 * - type is either DNS_IPv4_A or DNS_PTR or DNS_IPv6_AAAA 223 * - count contains the number of addresses of form type 224 * - ttl is the number of seconds the resolution may be cached for. 225 * - addresses needs to be cast according to type. It will be an array of 226 * 4-byte sequences for ipv4, or an array of 16-byte sequences for ipv6, 227 * or a nul-terminated string for PTR. 228 */ 229typedef void (*evdns_callback_type) (int result, char type, int count, int ttl, void *addresses, void *arg); 230 231struct evdns_base; 232struct event_base; 233 234/** Flag for evdns_base_new: process resolv.conf. */ 235#define EVDNS_BASE_INITIALIZE_NAMESERVERS 1 236/** Flag for evdns_base_new: Do not prevent the libevent event loop from 237 * exiting when we have no active dns requests. */ 238#define EVDNS_BASE_DISABLE_WHEN_INACTIVE 0x8000 239/** Flag for evdns_base_new: If EVDNS_BASE_INITIALIZE_NAMESERVERS isset, do not 240 * add default nameserver if there are no nameservers in resolv.conf 241 * @see DNS_OPTION_NAMESERVERS_NO_DEFAULT */ 242#define EVDNS_BASE_NAMESERVERS_NO_DEFAULT 0x10000 243 244/** 245 Initialize the asynchronous DNS library. 246 247 This function initializes support for non-blocking name resolution by 248 calling evdns_resolv_conf_parse() on UNIX and 249 evdns_config_windows_nameservers() on Windows. 250 251 @param event_base the event base to associate the dns client with 252 @param flags any of EVDNS_BASE_INITIALIZE_NAMESERVERS| 253 EVDNS_BASE_DISABLE_WHEN_INACTIVE|EVDNS_BASE_NAMESERVERS_NO_DEFAULT 254 @return evdns_base object if successful, or NULL if an error occurred. 255 @see evdns_base_free() 256 */ 257EVENT2_EXPORT_SYMBOL 258struct evdns_base * evdns_base_new(struct event_base *event_base, int initialize_nameservers); 259 260 261/** 262 Shut down the asynchronous DNS resolver and terminate all active requests. 263 264 If the 'fail_requests' option is enabled, all active requests will return 265 an empty result with the error flag set to DNS_ERR_SHUTDOWN. Otherwise, 266 the requests will be silently discarded. 267 268 @param evdns_base the evdns base to free 269 @param fail_requests if zero, active requests will be aborted; if non-zero, 270 active requests will return DNS_ERR_SHUTDOWN. 271 @see evdns_base_new() 272 */ 273EVENT2_EXPORT_SYMBOL 274void evdns_base_free(struct evdns_base *base, int fail_requests); 275 276/** 277 Remove all hosts entries that have been loaded into the event_base via 278 evdns_base_load_hosts or via event_base_resolv_conf_parse. 279 280 @param evdns_base the evdns base to remove outdated host addresses from 281 */ 282EVENT2_EXPORT_SYMBOL 283void evdns_base_clear_host_addresses(struct evdns_base *base); 284 285/** 286 Convert a DNS error code to a string. 287 288 @param err the DNS error code 289 @return a string containing an explanation of the error code 290*/ 291EVENT2_EXPORT_SYMBOL 292const char *evdns_err_to_string(int err); 293 294 295/** 296 Add a nameserver. 297 298 The address should be an IPv4 address in network byte order. 299 The type of address is chosen so that it matches in_addr.s_addr. 300 301 @param base the evdns_base to which to add the name server 302 @param address an IP address in network byte order 303 @return 0 if successful, or -1 if an error occurred 304 @see evdns_base_nameserver_ip_add() 305 */ 306EVENT2_EXPORT_SYMBOL 307int evdns_base_nameserver_add(struct evdns_base *base, 308 unsigned long int address); 309 310/** 311 Get the number of configured nameservers. 312 313 This returns the number of configured nameservers (not necessarily the 314 number of running nameservers). This is useful for double-checking 315 whether our calls to the various nameserver configuration functions 316 have been successful. 317 318 @param base the evdns_base to which to apply this operation 319 @return the number of configured nameservers 320 @see evdns_base_nameserver_add() 321 */ 322EVENT2_EXPORT_SYMBOL 323int evdns_base_count_nameservers(struct evdns_base *base); 324 325/** 326 Remove all configured nameservers, and suspend all pending resolves. 327 328 Resolves will not necessarily be re-attempted until evdns_base_resume() is called. 329 330 @param base the evdns_base to which to apply this operation 331 @return 0 if successful, or -1 if an error occurred 332 @see evdns_base_resume() 333 */ 334EVENT2_EXPORT_SYMBOL 335int evdns_base_clear_nameservers_and_suspend(struct evdns_base *base); 336 337 338/** 339 Resume normal operation and continue any suspended resolve requests. 340 341 Re-attempt resolves left in limbo after an earlier call to 342 evdns_base_clear_nameservers_and_suspend(). 343 344 @param base the evdns_base to which to apply this operation 345 @return 0 if successful, or -1 if an error occurred 346 @see evdns_base_clear_nameservers_and_suspend() 347 */ 348EVENT2_EXPORT_SYMBOL 349int evdns_base_resume(struct evdns_base *base); 350 351/** 352 Add a nameserver by string address. 353 354 This function parses a n IPv4 or IPv6 address from a string and adds it as a 355 nameserver. It supports the following formats: 356 - [IPv6Address]:port 357 - [IPv6Address] 358 - IPv6Address 359 - IPv4Address:port 360 - IPv4Address 361 362 If no port is specified, it defaults to 53. 363 364 @param base the evdns_base to which to apply this operation 365 @return 0 if successful, or -1 if an error occurred 366 @see evdns_base_nameserver_add() 367 */ 368EVENT2_EXPORT_SYMBOL 369int evdns_base_nameserver_ip_add(struct evdns_base *base, 370 const char *ip_as_string); 371 372/** 373 Add a nameserver by sockaddr. 374 **/ 375EVENT2_EXPORT_SYMBOL 376int 377evdns_base_nameserver_sockaddr_add(struct evdns_base *base, 378 const struct sockaddr *sa, ev_socklen_t len, unsigned flags); 379 380struct evdns_request; 381 382/** 383 Lookup an A record for a given name. 384 385 @param base the evdns_base to which to apply this operation 386 @param name a DNS hostname 387 @param flags either 0, or DNS_QUERY_NO_SEARCH to disable searching for this query. 388 @param callback a callback function to invoke when the request is completed 389 @param ptr an argument to pass to the callback function 390 @return an evdns_request object if successful, or NULL if an error occurred. 391 @see evdns_resolve_ipv6(), evdns_resolve_reverse(), evdns_resolve_reverse_ipv6(), evdns_cancel_request() 392 */ 393EVENT2_EXPORT_SYMBOL 394struct evdns_request *evdns_base_resolve_ipv4(struct evdns_base *base, const char *name, int flags, evdns_callback_type callback, void *ptr); 395 396/** 397 Lookup an AAAA record for a given name. 398 399 @param base the evdns_base to which to apply this operation 400 @param name a DNS hostname 401 @param flags either 0, or DNS_QUERY_NO_SEARCH to disable searching for this query. 402 @param callback a callback function to invoke when the request is completed 403 @param ptr an argument to pass to the callback function 404 @return an evdns_request object if successful, or NULL if an error occurred. 405 @see evdns_resolve_ipv4(), evdns_resolve_reverse(), evdns_resolve_reverse_ipv6(), evdns_cancel_request() 406 */ 407EVENT2_EXPORT_SYMBOL 408struct evdns_request *evdns_base_resolve_ipv6(struct evdns_base *base, const char *name, int flags, evdns_callback_type callback, void *ptr); 409 410struct in_addr; 411struct in6_addr; 412 413/** 414 Lookup a PTR record for a given IP address. 415 416 @param base the evdns_base to which to apply this operation 417 @param in an IPv4 address 418 @param flags either 0, or DNS_QUERY_NO_SEARCH to disable searching for this query. 419 @param callback a callback function to invoke when the request is completed 420 @param ptr an argument to pass to the callback function 421 @return an evdns_request object if successful, or NULL if an error occurred. 422 @see evdns_resolve_reverse_ipv6(), evdns_cancel_request() 423 */ 424EVENT2_EXPORT_SYMBOL 425struct evdns_request *evdns_base_resolve_reverse(struct evdns_base *base, const struct in_addr *in, int flags, evdns_callback_type callback, void *ptr); 426 427 428/** 429 Lookup a PTR record for a given IPv6 address. 430 431 @param base the evdns_base to which to apply this operation 432 @param in an IPv6 address 433 @param flags either 0, or DNS_QUERY_NO_SEARCH to disable searching for this query. 434 @param callback a callback function to invoke when the request is completed 435 @param ptr an argument to pass to the callback function 436 @return an evdns_request object if successful, or NULL if an error occurred. 437 @see evdns_resolve_reverse_ipv6(), evdns_cancel_request() 438 */ 439EVENT2_EXPORT_SYMBOL 440struct evdns_request *evdns_base_resolve_reverse_ipv6(struct evdns_base *base, const struct in6_addr *in, int flags, evdns_callback_type callback, void *ptr); 441 442/** 443 Cancels a pending DNS resolution request. 444 445 @param base the evdns_base that was used to make the request 446 @param req the evdns_request that was returned by calling a resolve function 447 @see evdns_base_resolve_ipv4(), evdns_base_resolve_ipv6, evdns_base_resolve_reverse 448*/ 449EVENT2_EXPORT_SYMBOL 450void evdns_cancel_request(struct evdns_base *base, struct evdns_request *req); 451 452/** 453 Set the value of a configuration option. 454 455 The currently available configuration options are: 456 457 ndots, timeout, max-timeouts, max-inflight, attempts, randomize-case, 458 bind-to, initial-probe-timeout, getaddrinfo-allow-skew, 459 so-rcvbuf, so-sndbuf. 460 461 In versions before Libevent 2.0.3-alpha, the option name needed to end with 462 a colon. 463 464 @param base the evdns_base to which to apply this operation 465 @param option the name of the configuration option to be modified 466 @param val the value to be set 467 @return 0 if successful, or -1 if an error occurred 468 */ 469EVENT2_EXPORT_SYMBOL 470int evdns_base_set_option(struct evdns_base *base, const char *option, const char *val); 471 472 473/** 474 Parse a resolv.conf file. 475 476 The 'flags' parameter determines what information is parsed from the 477 resolv.conf file. See the man page for resolv.conf for the format of this 478 file. 479 480 The following directives are not parsed from the file: sortlist, rotate, 481 no-check-names, inet6, debug. 482 483 If this function encounters an error, the possible return values are: 1 = 484 failed to open file, 2 = failed to stat file, 3 = file too large, 4 = out of 485 memory, 5 = short read from file, 6 = no nameservers listed in the file 486 487 @param base the evdns_base to which to apply this operation 488 @param flags any of DNS_OPTION_NAMESERVERS|DNS_OPTION_SEARCH|DNS_OPTION_MISC| 489 DNS_OPTION_HOSTSFILE|DNS_OPTIONS_ALL|DNS_OPTION_NAMESERVERS_NO_DEFAULT 490 @param filename the path to the resolv.conf file 491 @return 0 if successful, or various positive error codes if an error 492 occurred (see above) 493 @see resolv.conf(3), evdns_config_windows_nameservers() 494 */ 495EVENT2_EXPORT_SYMBOL 496int evdns_base_resolv_conf_parse(struct evdns_base *base, int flags, const char *const filename); 497 498/** 499 Load an /etc/hosts-style file from 'hosts_fname' into 'base'. 500 501 If hosts_fname is NULL, add minimal entries for localhost, and nothing 502 else. 503 504 Note that only evdns_getaddrinfo uses the /etc/hosts entries. 505 506 This function does not replace previously loaded hosts entries; to do that, 507 call evdns_base_clear_host_addresses first. 508 509 Return 0 on success, negative on failure. 510*/ 511EVENT2_EXPORT_SYMBOL 512int evdns_base_load_hosts(struct evdns_base *base, const char *hosts_fname); 513 514#if defined(EVENT_IN_DOXYGEN_) || defined(_WIN32) 515/** 516 Obtain nameserver information using the Windows API. 517 518 Attempt to configure a set of nameservers based on platform settings on 519 a win32 host. Preferentially tries to use GetNetworkParams; if that fails, 520 looks in the registry. 521 522 @return 0 if successful, or -1 if an error occurred 523 @see evdns_resolv_conf_parse() 524 */ 525EVENT2_EXPORT_SYMBOL 526int evdns_base_config_windows_nameservers(struct evdns_base *); 527#define EVDNS_BASE_CONFIG_WINDOWS_NAMESERVERS_IMPLEMENTED 528#endif 529 530 531/** 532 Clear the list of search domains. 533 */ 534EVENT2_EXPORT_SYMBOL 535void evdns_base_search_clear(struct evdns_base *base); 536 537 538/** 539 Add a domain to the list of search domains 540 541 @param domain the domain to be added to the search list 542 */ 543EVENT2_EXPORT_SYMBOL 544void evdns_base_search_add(struct evdns_base *base, const char *domain); 545 546 547/** 548 Set the 'ndots' parameter for searches. 549 550 Sets the number of dots which, when found in a name, causes 551 the first query to be without any search domain. 552 553 @param ndots the new ndots parameter 554 */ 555EVENT2_EXPORT_SYMBOL 556void evdns_base_search_ndots_set(struct evdns_base *base, const int ndots); 557 558/** 559 A callback that is invoked when a log message is generated 560 561 @param is_warning indicates if the log message is a 'warning' 562 @param msg the content of the log message 563 */ 564typedef void (*evdns_debug_log_fn_type)(int is_warning, const char *msg); 565 566 567/** 568 Set the callback function to handle DNS log messages. If this 569 callback is not set, evdns log messages are handled with the regular 570 Libevent logging system. 571 572 @param fn the callback to be invoked when a log message is generated 573 */ 574EVENT2_EXPORT_SYMBOL 575void evdns_set_log_fn(evdns_debug_log_fn_type fn); 576 577/** 578 Set a callback that will be invoked to generate transaction IDs. By 579 default, we pick transaction IDs based on the current clock time, which 580 is bad for security. 581 582 @param fn the new callback, or NULL to use the default. 583 584 NOTE: This function has no effect in Libevent 2.0.4-alpha and later, 585 since Libevent now provides its own secure RNG. 586 */ 587EVENT2_EXPORT_SYMBOL 588void evdns_set_transaction_id_fn(ev_uint16_t (*fn)(void)); 589 590/** 591 Set a callback used to generate random bytes. By default, we use 592 the same function as passed to evdns_set_transaction_id_fn to generate 593 bytes two at a time. If a function is provided here, it's also used 594 to generate transaction IDs. 595 596 NOTE: This function has no effect in Libevent 2.0.4-alpha and later, 597 since Libevent now provides its own secure RNG. 598*/ 599EVENT2_EXPORT_SYMBOL 600void evdns_set_random_bytes_fn(void (*fn)(char *, size_t)); 601 602/* 603 * Functions used to implement a DNS server. 604 */ 605 606struct evdns_server_request; 607struct evdns_server_question; 608 609/** 610 A callback to implement a DNS server. The callback function receives a DNS 611 request. It should then optionally add a number of answers to the reply 612 using the evdns_server_request_add_*_reply functions, before calling either 613 evdns_server_request_respond to send the reply back, or 614 evdns_server_request_drop to decline to answer the request. 615 616 @param req A newly received request 617 @param user_data A pointer that was passed to 618 evdns_add_server_port_with_base(). 619 */ 620typedef void (*evdns_request_callback_fn_type)(struct evdns_server_request *, void *); 621#define EVDNS_ANSWER_SECTION 0 622#define EVDNS_AUTHORITY_SECTION 1 623#define EVDNS_ADDITIONAL_SECTION 2 624 625#define EVDNS_TYPE_A 1 626#define EVDNS_TYPE_NS 2 627#define EVDNS_TYPE_CNAME 5 628#define EVDNS_TYPE_SOA 6 629#define EVDNS_TYPE_PTR 12 630#define EVDNS_TYPE_MX 15 631#define EVDNS_TYPE_TXT 16 632#define EVDNS_TYPE_AAAA 28 633 634#define EVDNS_QTYPE_AXFR 252 635#define EVDNS_QTYPE_ALL 255 636 637#define EVDNS_CLASS_INET 1 638 639/* flags that can be set in answers; as part of the err parameter */ 640#define EVDNS_FLAGS_AA 0x400 641#define EVDNS_FLAGS_RD 0x080 642 643/** Create a new DNS server port. 644 645 @param base The event base to handle events for the server port. 646 @param socket A UDP socket to accept DNS requests. 647 @param flags Always 0 for now. 648 @param callback A function to invoke whenever we get a DNS request 649 on the socket. 650 @param user_data Data to pass to the callback. 651 @return an evdns_server_port structure for this server port or NULL if 652 an error occurred. 653 */ 654EVENT2_EXPORT_SYMBOL 655struct evdns_server_port *evdns_add_server_port_with_base(struct event_base *base, evutil_socket_t socket, int flags, evdns_request_callback_fn_type callback, void *user_data); 656/** Close down a DNS server port, and free associated structures. */ 657EVENT2_EXPORT_SYMBOL 658void evdns_close_server_port(struct evdns_server_port *port); 659 660/** Sets some flags in a reply we're building. 661 Allows setting of the AA or RD flags 662 */ 663EVENT2_EXPORT_SYMBOL 664void evdns_server_request_set_flags(struct evdns_server_request *req, int flags); 665 666/* Functions to add an answer to an in-progress DNS reply. 667 */ 668EVENT2_EXPORT_SYMBOL 669int 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); 670EVENT2_EXPORT_SYMBOL 671int evdns_server_request_add_a_reply(struct evdns_server_request *req, const char *name, int n, const void *addrs, int ttl); 672EVENT2_EXPORT_SYMBOL 673int evdns_server_request_add_aaaa_reply(struct evdns_server_request *req, const char *name, int n, const void *addrs, int ttl); 674EVENT2_EXPORT_SYMBOL 675int evdns_server_request_add_ptr_reply(struct evdns_server_request *req, struct in_addr *in, const char *inaddr_name, const char *hostname, int ttl); 676EVENT2_EXPORT_SYMBOL 677int evdns_server_request_add_cname_reply(struct evdns_server_request *req, const char *name, const char *cname, int ttl); 678 679/** 680 Send back a response to a DNS request, and free the request structure. 681*/ 682EVENT2_EXPORT_SYMBOL 683int evdns_server_request_respond(struct evdns_server_request *req, int err); 684/** 685 Free a DNS request without sending back a reply. 686*/ 687EVENT2_EXPORT_SYMBOL 688int evdns_server_request_drop(struct evdns_server_request *req); 689struct sockaddr; 690/** 691 Get the address that made a DNS request. 692 */ 693EVENT2_EXPORT_SYMBOL 694int evdns_server_request_get_requesting_addr(struct evdns_server_request *req, struct sockaddr *sa, int addr_len); 695 696/** Callback for evdns_getaddrinfo. */ 697typedef void (*evdns_getaddrinfo_cb)(int result, struct evutil_addrinfo *res, void *arg); 698 699struct evdns_base; 700struct evdns_getaddrinfo_request; 701/** Make a non-blocking getaddrinfo request using the dns_base in 'dns_base'. 702 * 703 * If we can answer the request immediately (with an error or not!), then we 704 * invoke cb immediately and return NULL. Otherwise we return 705 * an evdns_getaddrinfo_request and invoke cb later. 706 * 707 * When the callback is invoked, we pass as its first argument the error code 708 * that getaddrinfo would return (or 0 for no error). As its second argument, 709 * we pass the evutil_addrinfo structures we found (or NULL on error). We 710 * pass 'arg' as the third argument. 711 * 712 * Limitations: 713 * 714 * - The AI_V4MAPPED and AI_ALL flags are not currently implemented. 715 * - For ai_socktype, we only handle SOCKTYPE_STREAM, SOCKTYPE_UDP, and 0. 716 * - For ai_protocol, we only handle IPPROTO_TCP, IPPROTO_UDP, and 0. 717 */ 718EVENT2_EXPORT_SYMBOL 719struct evdns_getaddrinfo_request *evdns_getaddrinfo( 720 struct evdns_base *dns_base, 721 const char *nodename, const char *servname, 722 const struct evutil_addrinfo *hints_in, 723 evdns_getaddrinfo_cb cb, void *arg); 724 725/* Cancel an in-progress evdns_getaddrinfo. This MUST NOT be called after the 726 * getaddrinfo's callback has been invoked. The resolves will be canceled, 727 * and the callback will be invoked with the error EVUTIL_EAI_CANCEL. */ 728EVENT2_EXPORT_SYMBOL 729void evdns_getaddrinfo_cancel(struct evdns_getaddrinfo_request *req); 730 731/** 732 Retrieve the address of the 'idx'th configured nameserver. 733 734 @param base The evdns_base to examine. 735 @param idx The index of the nameserver to get the address of. 736 @param sa A location to receive the server's address. 737 @param len The number of bytes available at sa. 738 739 @return the number of bytes written into sa on success. On failure, returns 740 -1 if idx is greater than the number of configured nameservers, or a 741 value greater than 'len' if len was not high enough. 742 */ 743EVENT2_EXPORT_SYMBOL 744int evdns_base_get_nameserver_addr(struct evdns_base *base, int idx, 745 struct sockaddr *sa, ev_socklen_t len); 746 747#ifdef __cplusplus 748} 749#endif 750 751#endif /* !EVENT2_DNS_H_INCLUDED_ */ 752