dns.h revision 1.1.1.2
1/* $NetBSD: dns.h,v 1.1.1.2 2015/01/29 06:38:28 spz Exp $ */ 2/* $NetBSD: dns.h,v 1.1.1.2 2015/01/29 06:38:28 spz Exp $ */ 3/* 4 * Copyright (c) 2006-2007 Niels Provos <provos@citi.umich.edu> 5 * Copyright (c) 2007-2012 Niels Provos and Nick Mathewson 6 * 7 * Redistribution and use in source and binary forms, with or without 8 * modification, are permitted provided that the following conditions 9 * are met: 10 * 1. Redistributions of source code must retain the above copyright 11 * notice, this list of conditions and the following disclaimer. 12 * 2. Redistributions in binary form must reproduce the above copyright 13 * notice, this list of conditions and the following disclaimer in the 14 * documentation and/or other materials provided with the distribution. 15 * 3. The name of the author may not be used to endorse or promote products 16 * derived from this software without specific prior written permission. 17 * 18 * THIS SOFTWARE IS PROVIDED BY THE AUTHOR ``AS IS'' AND ANY EXPRESS OR 19 * IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES 20 * OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE DISCLAIMED. 21 * IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR ANY DIRECT, INDIRECT, 22 * INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT 23 * NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, 24 * DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY 25 * THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT 26 * (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF 27 * THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE. 28 */ 29 30/* 31 * The original DNS code is due to Adam Langley with heavy 32 * modifications by Nick Mathewson. Adam put his DNS software in the 33 * public domain. You can find his original copyright below. Please, 34 * aware that the code as part of Libevent is governed by the 3-clause 35 * BSD license above. 36 * 37 * This software is Public Domain. To view a copy of the public domain dedication, 38 * visit http://creativecommons.org/licenses/publicdomain/ or send a letter to 39 * Creative Commons, 559 Nathan Abbott Way, Stanford, California 94305, USA. 40 * 41 * I ask and expect, but do not require, that all derivative works contain an 42 * attribution similar to: 43 * Parts developed by Adam Langley <agl@imperialviolet.org> 44 * 45 * You may wish to replace the word "Parts" with something else depending on 46 * the amount of original code. 47 * 48 * (Derivative works does not include programs which link against, run or include 49 * the source verbatim in their source distributions) 50 */ 51 52/** @file event2/dns.h 53 * 54 * Welcome, gentle reader 55 * 56 * Async DNS lookups are really a whole lot harder than they should be, 57 * mostly stemming from the fact that the libc resolver has never been 58 * very good at them. Before you use this library you should see if libc 59 * can do the job for you with the modern async call getaddrinfo_a 60 * (see http://www.imperialviolet.org/page25.html#e498). Otherwise, 61 * please continue. 62 * 63 * The library keeps track of the state of nameservers and will avoid 64 * them when they go down. Otherwise it will round robin between them. 65 * 66 * Quick start guide: 67 * #include "evdns.h" 68 * void callback(int result, char type, int count, int ttl, 69 * void *addresses, void *arg); 70 * evdns_resolv_conf_parse(DNS_OPTIONS_ALL, "/etc/resolv.conf"); 71 * evdns_resolve("www.hostname.com", 0, callback, NULL); 72 * 73 * When the lookup is complete the callback function is called. The 74 * first argument will be one of the DNS_ERR_* defines in evdns.h. 75 * Hopefully it will be DNS_ERR_NONE, in which case type will be 76 * DNS_IPv4_A, count will be the number of IP addresses, ttl is the time 77 * which the data can be cached for (in seconds), addresses will point 78 * to an array of uint32_t's and arg will be whatever you passed to 79 * evdns_resolve. 80 * 81 * Searching: 82 * 83 * In order for this library to be a good replacement for glibc's resolver it 84 * supports searching. This involves setting a list of default domains, in 85 * which names will be queried for. The number of dots in the query name 86 * determines the order in which this list is used. 87 * 88 * Searching appears to be a single lookup from the point of view of the API, 89 * although many DNS queries may be generated from a single call to 90 * evdns_resolve. Searching can also drastically slow down the resolution 91 * of names. 92 * 93 * To disable searching: 94 * 1. Never set it up. If you never call evdns_resolv_conf_parse or 95 * evdns_search_add then no searching will occur. 96 * 97 * 2. If you do call evdns_resolv_conf_parse then don't pass 98 * DNS_OPTION_SEARCH (or DNS_OPTIONS_ALL, which implies it). 99 * 100 * 3. When calling evdns_resolve, pass the DNS_QUERY_NO_SEARCH flag. 101 * 102 * The order of searches depends on the number of dots in the name. If the 103 * number is greater than the ndots setting then the names is first tried 104 * globally. Otherwise each search domain is appended in turn. 105 * 106 * The ndots setting can either be set from a resolv.conf, or by calling 107 * evdns_search_ndots_set. 108 * 109 * For example, with ndots set to 1 (the default) and a search domain list of 110 * ["myhome.net"]: 111 * Query: www 112 * Order: www.myhome.net, www. 113 * 114 * Query: www.abc 115 * Order: www.abc., www.abc.myhome.net 116 * 117 * Internals: 118 * 119 * Requests are kept in two queues. The first is the inflight queue. In 120 * this queue requests have an allocated transaction id and nameserver. 121 * They will soon be transmitted if they haven't already been. 122 * 123 * The second is the waiting queue. The size of the inflight ring is 124 * limited and all other requests wait in waiting queue for space. This 125 * bounds the number of concurrent requests so that we don't flood the 126 * nameserver. Several algorithms require a full walk of the inflight 127 * queue and so bounding its size keeps thing going nicely under huge 128 * (many thousands of requests) loads. 129 * 130 * If a nameserver loses too many requests it is considered down and we 131 * try not to use it. After a while we send a probe to that nameserver 132 * (a lookup for google.com) and, if it replies, we consider it working 133 * again. If the nameserver fails a probe we wait longer to try again 134 * with the next probe. 135 */ 136 137#ifndef _EVENT2_DNS_H_ 138#define _EVENT2_DNS_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#define DNS_OPTION_SEARCH 1 183#define DNS_OPTION_NAMESERVERS 2 184#define DNS_OPTION_MISC 4 185#define DNS_OPTION_HOSTSFILE 8 186#define DNS_OPTIONS_ALL 15 187 188/* Obsolete name for DNS_QUERY_NO_SEARCH */ 189#define DNS_NO_SEARCH DNS_QUERY_NO_SEARCH 190 191/** 192 * The callback that contains the results from a lookup. 193 * - result is one of the DNS_ERR_* values (DNS_ERR_NONE for success) 194 * - type is either DNS_IPv4_A or DNS_PTR or DNS_IPv6_AAAA 195 * - count contains the number of addresses of form type 196 * - ttl is the number of seconds the resolution may be cached for. 197 * - addresses needs to be cast according to type. It will be an array of 198 * 4-byte sequences for ipv4, or an array of 16-byte sequences for ipv6, 199 * or a nul-terminated string for PTR. 200 */ 201typedef void (*evdns_callback_type) (int result, char type, int count, int ttl, void *addresses, void *arg); 202 203struct evdns_base; 204struct event_base; 205 206/** 207 Initialize the asynchronous DNS library. 208 209 This function initializes support for non-blocking name resolution by 210 calling evdns_resolv_conf_parse() on UNIX and 211 evdns_config_windows_nameservers() on Windows. 212 213 @param event_base the event base to associate the dns client with 214 @param initialize_nameservers 1 if resolve.conf processing should occur 215 @return evdns_base object if successful, or NULL if an error occurred. 216 @see evdns_base_free() 217 */ 218struct evdns_base * evdns_base_new(struct event_base *event_base, int initialize_nameservers); 219 220 221/** 222 Shut down the asynchronous DNS resolver and terminate all active requests. 223 224 If the 'fail_requests' option is enabled, all active requests will return 225 an empty result with the error flag set to DNS_ERR_SHUTDOWN. Otherwise, 226 the requests will be silently discarded. 227 228 @param evdns_base the evdns base to free 229 @param fail_requests if zero, active requests will be aborted; if non-zero, 230 active requests will return DNS_ERR_SHUTDOWN. 231 @see evdns_base_new() 232 */ 233void evdns_base_free(struct evdns_base *base, int fail_requests); 234 235/** 236 Convert a DNS error code to a string. 237 238 @param err the DNS error code 239 @return a string containing an explanation of the error code 240*/ 241const char *evdns_err_to_string(int err); 242 243 244/** 245 Add a nameserver. 246 247 The address should be an IPv4 address in network byte order. 248 The type of address is chosen so that it matches in_addr.s_addr. 249 250 @param base the evdns_base to which to add the name server 251 @param address an IP address in network byte order 252 @return 0 if successful, or -1 if an error occurred 253 @see evdns_base_nameserver_ip_add() 254 */ 255int evdns_base_nameserver_add(struct evdns_base *base, 256 unsigned long int address); 257 258/** 259 Get the number of configured nameservers. 260 261 This returns the number of configured nameservers (not necessarily the 262 number of running nameservers). This is useful for double-checking 263 whether our calls to the various nameserver configuration functions 264 have been successful. 265 266 @param base the evdns_base to which to apply this operation 267 @return the number of configured nameservers 268 @see evdns_base_nameserver_add() 269 */ 270int evdns_base_count_nameservers(struct evdns_base *base); 271 272/** 273 Remove all configured nameservers, and suspend all pending resolves. 274 275 Resolves will not necessarily be re-attempted until evdns_base_resume() is called. 276 277 @param base the evdns_base to which to apply this operation 278 @return 0 if successful, or -1 if an error occurred 279 @see evdns_base_resume() 280 */ 281int evdns_base_clear_nameservers_and_suspend(struct evdns_base *base); 282 283 284/** 285 Resume normal operation and continue any suspended resolve requests. 286 287 Re-attempt resolves left in limbo after an earlier call to 288 evdns_base_clear_nameservers_and_suspend(). 289 290 @param base the evdns_base to which to apply this operation 291 @return 0 if successful, or -1 if an error occurred 292 @see evdns_base_clear_nameservers_and_suspend() 293 */ 294int evdns_base_resume(struct evdns_base *base); 295 296/** 297 Add a nameserver by string address. 298 299 This function parses a n IPv4 or IPv6 address from a string and adds it as a 300 nameserver. It supports the following formats: 301 - [IPv6Address]:port 302 - [IPv6Address] 303 - IPv6Address 304 - IPv4Address:port 305 - IPv4Address 306 307 If no port is specified, it defaults to 53. 308 309 @param base the evdns_base to which to apply this operation 310 @return 0 if successful, or -1 if an error occurred 311 @see evdns_base_nameserver_add() 312 */ 313int evdns_base_nameserver_ip_add(struct evdns_base *base, 314 const char *ip_as_string); 315 316/** 317 Add a nameserver by sockaddr. 318 **/ 319int 320evdns_base_nameserver_sockaddr_add(struct evdns_base *base, 321 const struct sockaddr *sa, ev_socklen_t len, unsigned flags); 322 323struct evdns_request; 324 325/** 326 Lookup an A record for a given name. 327 328 @param base the evdns_base to which to apply this operation 329 @param name a DNS hostname 330 @param flags either 0, or DNS_QUERY_NO_SEARCH to disable searching for this query. 331 @param callback a callback function to invoke when the request is completed 332 @param ptr an argument to pass to the callback function 333 @return an evdns_request object if successful, or NULL if an error occurred. 334 @see evdns_resolve_ipv6(), evdns_resolve_reverse(), evdns_resolve_reverse_ipv6(), evdns_cancel_request() 335 */ 336struct evdns_request *evdns_base_resolve_ipv4(struct evdns_base *base, const char *name, int flags, evdns_callback_type callback, void *ptr); 337 338/** 339 Lookup an AAAA record for a given name. 340 341 @param base the evdns_base to which to apply this operation 342 @param name a DNS hostname 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 an evdns_request object if successful, or NULL if an error occurred. 347 @see evdns_resolve_ipv4(), evdns_resolve_reverse(), evdns_resolve_reverse_ipv6(), evdns_cancel_request() 348 */ 349struct evdns_request *evdns_base_resolve_ipv6(struct evdns_base *base, const char *name, int flags, evdns_callback_type callback, void *ptr); 350 351struct in_addr; 352struct in6_addr; 353 354/** 355 Lookup a PTR record for a given IP address. 356 357 @param base the evdns_base to which to apply this operation 358 @param in an IPv4 address 359 @param flags either 0, or DNS_QUERY_NO_SEARCH to disable searching for this query. 360 @param callback a callback function to invoke when the request is completed 361 @param ptr an argument to pass to the callback function 362 @return an evdns_request object if successful, or NULL if an error occurred. 363 @see evdns_resolve_reverse_ipv6(), evdns_cancel_request() 364 */ 365struct evdns_request *evdns_base_resolve_reverse(struct evdns_base *base, const struct in_addr *in, int flags, evdns_callback_type callback, void *ptr); 366 367 368/** 369 Lookup a PTR record for a given IPv6 address. 370 371 @param base the evdns_base to which to apply this operation 372 @param in an IPv6 address 373 @param flags either 0, or DNS_QUERY_NO_SEARCH to disable searching for this query. 374 @param callback a callback function to invoke when the request is completed 375 @param ptr an argument to pass to the callback function 376 @return an evdns_request object if successful, or NULL if an error occurred. 377 @see evdns_resolve_reverse_ipv6(), evdns_cancel_request() 378 */ 379struct evdns_request *evdns_base_resolve_reverse_ipv6(struct evdns_base *base, const struct in6_addr *in, int flags, evdns_callback_type callback, void *ptr); 380 381/** 382 Cancels a pending DNS resolution request. 383 384 @param base the evdns_base that was used to make the request 385 @param req the evdns_request that was returned by calling a resolve function 386 @see evdns_base_resolve_ipv4(), evdns_base_resolve_ipv6, evdns_base_resolve_reverse 387*/ 388void evdns_cancel_request(struct evdns_base *base, struct evdns_request *req); 389 390/** 391 Set the value of a configuration option. 392 393 The currently available configuration options are: 394 395 ndots, timeout, max-timeouts, max-inflight, attempts, randomize-case, 396 bind-to, initial-probe-timeout, getaddrinfo-allow-skew. 397 398 In versions before Libevent 2.0.3-alpha, the option name needed to end with 399 a colon. 400 401 @param base the evdns_base to which to apply this operation 402 @param option the name of the configuration option to be modified 403 @param val the value to be set 404 @return 0 if successful, or -1 if an error occurred 405 */ 406int evdns_base_set_option(struct evdns_base *base, const char *option, const char *val); 407 408 409/** 410 Parse a resolv.conf file. 411 412 The 'flags' parameter determines what information is parsed from the 413 resolv.conf file. See the man page for resolv.conf for the format of this 414 file. 415 416 The following directives are not parsed from the file: sortlist, rotate, 417 no-check-names, inet6, debug. 418 419 If this function encounters an error, the possible return values are: 1 = 420 failed to open file, 2 = failed to stat file, 3 = file too large, 4 = out of 421 memory, 5 = short read from file, 6 = no nameservers listed in the file 422 423 @param base the evdns_base to which to apply this operation 424 @param flags any of DNS_OPTION_NAMESERVERS|DNS_OPTION_SEARCH|DNS_OPTION_MISC| 425 DNS_OPTION_HOSTSFILE|DNS_OPTIONS_ALL 426 @param filename the path to the resolv.conf file 427 @return 0 if successful, or various positive error codes if an error 428 occurred (see above) 429 @see resolv.conf(3), evdns_config_windows_nameservers() 430 */ 431int evdns_base_resolv_conf_parse(struct evdns_base *base, int flags, const char *const filename); 432 433/** 434 Load an /etc/hosts-style file from 'hosts_fname' into 'base'. 435 436 If hosts_fname is NULL, add minimal entries for localhost, and nothing 437 else. 438 439 Note that only evdns_getaddrinfo uses the /etc/hosts entries. 440 441 Return 0 on success, negative on failure. 442*/ 443int evdns_base_load_hosts(struct evdns_base *base, const char *hosts_fname); 444 445/** 446 Obtain nameserver information using the Windows API. 447 448 Attempt to configure a set of nameservers based on platform settings on 449 a win32 host. Preferentially tries to use GetNetworkParams; if that fails, 450 looks in the registry. 451 452 @return 0 if successful, or -1 if an error occurred 453 @see evdns_resolv_conf_parse() 454 */ 455#ifdef WIN32 456int evdns_base_config_windows_nameservers(struct evdns_base *); 457#define EVDNS_BASE_CONFIG_WINDOWS_NAMESERVERS_IMPLEMENTED 458#endif 459 460 461/** 462 Clear the list of search domains. 463 */ 464void evdns_base_search_clear(struct evdns_base *base); 465 466 467/** 468 Add a domain to the list of search domains 469 470 @param domain the domain to be added to the search list 471 */ 472void evdns_base_search_add(struct evdns_base *base, const char *domain); 473 474 475/** 476 Set the 'ndots' parameter for searches. 477 478 Sets the number of dots which, when found in a name, causes 479 the first query to be without any search domain. 480 481 @param ndots the new ndots parameter 482 */ 483void evdns_base_search_ndots_set(struct evdns_base *base, const int ndots); 484 485/** 486 A callback that is invoked when a log message is generated 487 488 @param is_warning indicates if the log message is a 'warning' 489 @param msg the content of the log message 490 */ 491typedef void (*evdns_debug_log_fn_type)(int is_warning, const char *msg); 492 493 494/** 495 Set the callback function to handle DNS log messages. If this 496 callback is not set, evdns log messages are handled with the regular 497 Libevent logging system. 498 499 @param fn the callback to be invoked when a log message is generated 500 */ 501void evdns_set_log_fn(evdns_debug_log_fn_type fn); 502 503/** 504 Set a callback that will be invoked to generate transaction IDs. By 505 default, we pick transaction IDs based on the current clock time, which 506 is bad for security. 507 508 @param fn the new callback, or NULL to use the default. 509 510 NOTE: This function has no effect in Libevent 2.0.4-alpha and later, 511 since Libevent now provides its own secure RNG. 512 */ 513void evdns_set_transaction_id_fn(ev_uint16_t (*fn)(void)); 514 515/** 516 Set a callback used to generate random bytes. By default, we use 517 the same function as passed to evdns_set_transaction_id_fn to generate 518 bytes two at a time. If a function is provided here, it's also used 519 to generate transaction IDs. 520 521 NOTE: This function has no effect in Libevent 2.0.4-alpha and later, 522 since Libevent now provides its own secure RNG. 523*/ 524void evdns_set_random_bytes_fn(void (*fn)(char *, size_t)); 525 526/* 527 * Functions used to implement a DNS server. 528 */ 529 530struct evdns_server_request; 531struct evdns_server_question; 532 533/** 534 A callback to implement a DNS server. The callback function receives a DNS 535 request. It should then optionally add a number of answers to the reply 536 using the evdns_server_request_add_*_reply functions, before calling either 537 evdns_server_request_respond to send the reply back, or 538 evdns_server_request_drop to decline to answer the request. 539 540 @param req A newly received request 541 @param user_data A pointer that was passed to 542 evdns_add_server_port_with_base(). 543 */ 544typedef void (*evdns_request_callback_fn_type)(struct evdns_server_request *, void *); 545#define EVDNS_ANSWER_SECTION 0 546#define EVDNS_AUTHORITY_SECTION 1 547#define EVDNS_ADDITIONAL_SECTION 2 548 549#define EVDNS_TYPE_A 1 550#define EVDNS_TYPE_NS 2 551#define EVDNS_TYPE_CNAME 5 552#define EVDNS_TYPE_SOA 6 553#define EVDNS_TYPE_PTR 12 554#define EVDNS_TYPE_MX 15 555#define EVDNS_TYPE_TXT 16 556#define EVDNS_TYPE_AAAA 28 557 558#define EVDNS_QTYPE_AXFR 252 559#define EVDNS_QTYPE_ALL 255 560 561#define EVDNS_CLASS_INET 1 562 563/* flags that can be set in answers; as part of the err parameter */ 564#define EVDNS_FLAGS_AA 0x400 565#define EVDNS_FLAGS_RD 0x080 566 567/** Create a new DNS server port. 568 569 @param base The event base to handle events for the server port. 570 @param socket A UDP socket to accept DNS requests. 571 @param flags Always 0 for now. 572 @param callback A function to invoke whenever we get a DNS request 573 on the socket. 574 @param user_data Data to pass to the callback. 575 @return an evdns_server_port structure for this server port. 576 */ 577struct 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); 578/** Close down a DNS server port, and free associated structures. */ 579void evdns_close_server_port(struct evdns_server_port *port); 580 581/** Sets some flags in a reply we're building. 582 Allows setting of the AA or RD flags 583 */ 584void evdns_server_request_set_flags(struct evdns_server_request *req, int flags); 585 586/* Functions to add an answer to an in-progress DNS reply. 587 */ 588int 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); 589int evdns_server_request_add_a_reply(struct evdns_server_request *req, const char *name, int n, const void *addrs, int ttl); 590int evdns_server_request_add_aaaa_reply(struct evdns_server_request *req, const char *name, int n, const void *addrs, int ttl); 591int evdns_server_request_add_ptr_reply(struct evdns_server_request *req, struct in_addr *in, const char *inaddr_name, const char *hostname, int ttl); 592int evdns_server_request_add_cname_reply(struct evdns_server_request *req, const char *name, const char *cname, int ttl); 593 594/** 595 Send back a response to a DNS request, and free the request structure. 596*/ 597int evdns_server_request_respond(struct evdns_server_request *req, int err); 598/** 599 Free a DNS request without sending back a reply. 600*/ 601int evdns_server_request_drop(struct evdns_server_request *req); 602struct sockaddr; 603/** 604 Get the address that made a DNS request. 605 */ 606int evdns_server_request_get_requesting_addr(struct evdns_server_request *_req, struct sockaddr *sa, int addr_len); 607 608/** Callback for evdns_getaddrinfo. */ 609typedef void (*evdns_getaddrinfo_cb)(int result, struct evutil_addrinfo *res, void *arg); 610 611struct evdns_base; 612struct evdns_getaddrinfo_request; 613/** Make a non-blocking getaddrinfo request using the dns_base in 'dns_base'. 614 * 615 * If we can answer the request immediately (with an error or not!), then we 616 * invoke cb immediately and return NULL. Otherwise we return 617 * an evdns_getaddrinfo_request and invoke cb later. 618 * 619 * When the callback is invoked, we pass as its first argument the error code 620 * that getaddrinfo would return (or 0 for no error). As its second argument, 621 * we pass the evutil_addrinfo structures we found (or NULL on error). We 622 * pass 'arg' as the third argument. 623 * 624 * Limitations: 625 * 626 * - The AI_V4MAPPED and AI_ALL flags are not currently implemented. 627 * - For ai_socktype, we only handle SOCKTYPE_STREAM, SOCKTYPE_UDP, and 0. 628 * - For ai_protocol, we only handle IPPROTO_TCP, IPPROTO_UDP, and 0. 629 */ 630struct evdns_getaddrinfo_request *evdns_getaddrinfo( 631 struct evdns_base *dns_base, 632 const char *nodename, const char *servname, 633 const struct evutil_addrinfo *hints_in, 634 evdns_getaddrinfo_cb cb, void *arg); 635 636/* Cancel an in-progress evdns_getaddrinfo. This MUST NOT be called after the 637 * getaddrinfo's callback has been invoked. The resolves will be canceled, 638 * and the callback will be invoked with the error EVUTIL_EAI_CANCEL. */ 639void evdns_getaddrinfo_cancel(struct evdns_getaddrinfo_request *req); 640 641#ifdef __cplusplus 642} 643#endif 644 645#endif /* !_EVENT2_DNS_H_ */ 646