dns.h revision 1.1.1.1
1/* $NetBSD: dns.h,v 1.1.1.1 2013/04/11 16:43:35 christos Exp $ */ 2/* 3 * Copyright (c) 2006-2007 Niels Provos <provos@citi.umich.edu> 4 * Copyright (c) 2007-2012 Niels Provos and Nick Mathewson 5 * 6 * Redistribution and use in source and binary forms, with or without 7 * modification, are permitted provided that the following conditions 8 * are met: 9 * 1. Redistributions of source code must retain the above copyright 10 * notice, this list of conditions and the following disclaimer. 11 * 2. Redistributions in binary form must reproduce the above copyright 12 * notice, this list of conditions and the following disclaimer in the 13 * documentation and/or other materials provided with the distribution. 14 * 3. The name of the author may not be used to endorse or promote products 15 * derived from this software without specific prior written permission. 16 * 17 * THIS SOFTWARE IS PROVIDED BY THE AUTHOR ``AS IS'' AND ANY EXPRESS OR 18 * IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES 19 * OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE DISCLAIMED. 20 * IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR ANY DIRECT, INDIRECT, 21 * INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT 22 * NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, 23 * DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY 24 * THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT 25 * (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF 26 * THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE. 27 */ 28 29/* 30 * The original DNS code is due to Adam Langley with heavy 31 * modifications by Nick Mathewson. Adam put his DNS software in the 32 * public domain. You can find his original copyright below. Please, 33 * aware that the code as part of Libevent is governed by the 3-clause 34 * BSD license above. 35 * 36 * This software is Public Domain. To view a copy of the public domain dedication, 37 * visit http://creativecommons.org/licenses/publicdomain/ or send a letter to 38 * Creative Commons, 559 Nathan Abbott Way, Stanford, California 94305, USA. 39 * 40 * I ask and expect, but do not require, that all derivative works contain an 41 * attribution similar to: 42 * Parts developed by Adam Langley <agl@imperialviolet.org> 43 * 44 * You may wish to replace the word "Parts" with something else depending on 45 * the amount of original code. 46 * 47 * (Derivative works does not include programs which link against, run or include 48 * the source verbatim in their source distributions) 49 */ 50 51/** @file event2/dns.h 52 * 53 * Welcome, gentle reader 54 * 55 * Async DNS lookups are really a whole lot harder than they should be, 56 * mostly stemming from the fact that the libc resolver has never been 57 * very good at them. Before you use this library you should see if libc 58 * can do the job for you with the modern async call getaddrinfo_a 59 * (see http://www.imperialviolet.org/page25.html#e498). Otherwise, 60 * please continue. 61 * 62 * The library keeps track of the state of nameservers and will avoid 63 * them when they go down. Otherwise it will round robin between them. 64 * 65 * Quick start guide: 66 * #include "evdns.h" 67 * void callback(int result, char type, int count, int ttl, 68 * void *addresses, void *arg); 69 * evdns_resolv_conf_parse(DNS_OPTIONS_ALL, "/etc/resolv.conf"); 70 * evdns_resolve("www.hostname.com", 0, callback, NULL); 71 * 72 * When the lookup is complete the callback function is called. The 73 * first argument will be one of the DNS_ERR_* defines in evdns.h. 74 * Hopefully it will be DNS_ERR_NONE, in which case type will be 75 * DNS_IPv4_A, count will be the number of IP addresses, ttl is the time 76 * which the data can be cached for (in seconds), addresses will point 77 * to an array of uint32_t's and arg will be whatever you passed to 78 * evdns_resolve. 79 * 80 * Searching: 81 * 82 * In order for this library to be a good replacement for glibc's resolver it 83 * supports searching. This involves setting a list of default domains, in 84 * which names will be queried for. The number of dots in the query name 85 * determines the order in which this list is used. 86 * 87 * Searching appears to be a single lookup from the point of view of the API, 88 * although many DNS queries may be generated from a single call to 89 * evdns_resolve. Searching can also drastically slow down the resolution 90 * of names. 91 * 92 * To disable searching: 93 * 1. Never set it up. If you never call evdns_resolv_conf_parse or 94 * evdns_search_add then no searching will occur. 95 * 96 * 2. If you do call evdns_resolv_conf_parse then don't pass 97 * DNS_OPTION_SEARCH (or DNS_OPTIONS_ALL, which implies it). 98 * 99 * 3. When calling evdns_resolve, pass the DNS_QUERY_NO_SEARCH flag. 100 * 101 * The order of searches depends on the number of dots in the name. If the 102 * number is greater than the ndots setting then the names is first tried 103 * globally. Otherwise each search domain is appended in turn. 104 * 105 * The ndots setting can either be set from a resolv.conf, or by calling 106 * evdns_search_ndots_set. 107 * 108 * For example, with ndots set to 1 (the default) and a search domain list of 109 * ["myhome.net"]: 110 * Query: www 111 * Order: www.myhome.net, www. 112 * 113 * Query: www.abc 114 * Order: www.abc., www.abc.myhome.net 115 * 116 * Internals: 117 * 118 * Requests are kept in two queues. The first is the inflight queue. In 119 * this queue requests have an allocated transaction id and nameserver. 120 * They will soon be transmitted if they haven't already been. 121 * 122 * The second is the waiting queue. The size of the inflight ring is 123 * limited and all other requests wait in waiting queue for space. This 124 * bounds the number of concurrent requests so that we don't flood the 125 * nameserver. Several algorithms require a full walk of the inflight 126 * queue and so bounding its size keeps thing going nicely under huge 127 * (many thousands of requests) loads. 128 * 129 * If a nameserver loses too many requests it is considered down and we 130 * try not to use it. After a while we send a probe to that nameserver 131 * (a lookup for google.com) and, if it replies, we consider it working 132 * again. If the nameserver fails a probe we wait longer to try again 133 * with the next probe. 134 */ 135 136#ifndef _EVENT2_DNS_H_ 137#define _EVENT2_DNS_H_ 138 139#ifdef __cplusplus 140extern "C" { 141#endif 142 143/* For integer types. */ 144#include <event2/util.h> 145 146/** Error codes 0-5 are as described in RFC 1035. */ 147#define DNS_ERR_NONE 0 148/** The name server was unable to interpret the query */ 149#define DNS_ERR_FORMAT 1 150/** The name server was unable to process this query due to a problem with the 151 * name server */ 152#define DNS_ERR_SERVERFAILED 2 153/** The domain name does not exist */ 154#define DNS_ERR_NOTEXIST 3 155/** The name server does not support the requested kind of query */ 156#define DNS_ERR_NOTIMPL 4 157/** The name server refuses to reform the specified operation for policy 158 * reasons */ 159#define DNS_ERR_REFUSED 5 160/** The reply was truncated or ill-formatted */ 161#define DNS_ERR_TRUNCATED 65 162/** An unknown error occurred */ 163#define DNS_ERR_UNKNOWN 66 164/** Communication with the server timed out */ 165#define DNS_ERR_TIMEOUT 67 166/** The request was canceled because the DNS subsystem was shut down. */ 167#define DNS_ERR_SHUTDOWN 68 168/** The request was canceled via a call to evdns_cancel_request */ 169#define DNS_ERR_CANCEL 69 170/** There were no answers and no error condition in the DNS packet. 171 * This can happen when you ask for an address that exists, but a record 172 * type that doesn't. */ 173#define DNS_ERR_NODATA 70 174 175#define DNS_IPv4_A 1 176#define DNS_PTR 2 177#define DNS_IPv6_AAAA 3 178 179#define DNS_QUERY_NO_SEARCH 1 180 181#define DNS_OPTION_SEARCH 1 182#define DNS_OPTION_NAMESERVERS 2 183#define DNS_OPTION_MISC 4 184#define DNS_OPTION_HOSTSFILE 8 185#define DNS_OPTIONS_ALL 15 186 187/* Obsolete name for DNS_QUERY_NO_SEARCH */ 188#define DNS_NO_SEARCH DNS_QUERY_NO_SEARCH 189 190/** 191 * The callback that contains the results from a lookup. 192 * - result is one of the DNS_ERR_* values (DNS_ERR_NONE for success) 193 * - type is either DNS_IPv4_A or DNS_PTR or DNS_IPv6_AAAA 194 * - count contains the number of addresses of form type 195 * - ttl is the number of seconds the resolution may be cached for. 196 * - addresses needs to be cast according to type. It will be an array of 197 * 4-byte sequences for ipv4, or an array of 16-byte sequences for ipv6, 198 * or a nul-terminated string for PTR. 199 */ 200typedef void (*evdns_callback_type) (int result, char type, int count, int ttl, void *addresses, void *arg); 201 202struct evdns_base; 203struct event_base; 204 205/** 206 Initialize the asynchronous DNS library. 207 208 This function initializes support for non-blocking name resolution by 209 calling evdns_resolv_conf_parse() on UNIX and 210 evdns_config_windows_nameservers() on Windows. 211 212 @param event_base the event base to associate the dns client with 213 @param initialize_nameservers 1 if resolve.conf processing should occur 214 @return evdns_base object if successful, or NULL if an error occurred. 215 @see evdns_base_free() 216 */ 217struct evdns_base * evdns_base_new(struct event_base *event_base, int initialize_nameservers); 218 219 220/** 221 Shut down the asynchronous DNS resolver and terminate all active requests. 222 223 If the 'fail_requests' option is enabled, all active requests will return 224 an empty result with the error flag set to DNS_ERR_SHUTDOWN. Otherwise, 225 the requests will be silently discarded. 226 227 @param evdns_base the evdns base to free 228 @param fail_requests if zero, active requests will be aborted; if non-zero, 229 active requests will return DNS_ERR_SHUTDOWN. 230 @see evdns_base_new() 231 */ 232void evdns_base_free(struct evdns_base *base, int fail_requests); 233 234/** 235 Convert a DNS error code to a string. 236 237 @param err the DNS error code 238 @return a string containing an explanation of the error code 239*/ 240const char *evdns_err_to_string(int err); 241 242 243/** 244 Add a nameserver. 245 246 The address should be an IPv4 address in network byte order. 247 The type of address is chosen so that it matches in_addr.s_addr. 248 249 @param base the evdns_base to which to add the name server 250 @param address an IP address in network byte order 251 @return 0 if successful, or -1 if an error occurred 252 @see evdns_base_nameserver_ip_add() 253 */ 254int evdns_base_nameserver_add(struct evdns_base *base, 255 unsigned long int address); 256 257/** 258 Get the number of configured nameservers. 259 260 This returns the number of configured nameservers (not necessarily the 261 number of running nameservers). This is useful for double-checking 262 whether our calls to the various nameserver configuration functions 263 have been successful. 264 265 @param base the evdns_base to which to apply this operation 266 @return the number of configured nameservers 267 @see evdns_base_nameserver_add() 268 */ 269int evdns_base_count_nameservers(struct evdns_base *base); 270 271/** 272 Remove all configured nameservers, and suspend all pending resolves. 273 274 Resolves will not necessarily be re-attempted until evdns_base_resume() is called. 275 276 @param base the evdns_base to which to apply this operation 277 @return 0 if successful, or -1 if an error occurred 278 @see evdns_base_resume() 279 */ 280int evdns_base_clear_nameservers_and_suspend(struct evdns_base *base); 281 282 283/** 284 Resume normal operation and continue any suspended resolve requests. 285 286 Re-attempt resolves left in limbo after an earlier call to 287 evdns_base_clear_nameservers_and_suspend(). 288 289 @param base the evdns_base to which to apply this operation 290 @return 0 if successful, or -1 if an error occurred 291 @see evdns_base_clear_nameservers_and_suspend() 292 */ 293int evdns_base_resume(struct evdns_base *base); 294 295/** 296 Add a nameserver by string address. 297 298 This function parses a n IPv4 or IPv6 address from a string and adds it as a 299 nameserver. It supports the following formats: 300 - [IPv6Address]:port 301 - [IPv6Address] 302 - IPv6Address 303 - IPv4Address:port 304 - IPv4Address 305 306 If no port is specified, it defaults to 53. 307 308 @param base the evdns_base to which to apply this operation 309 @return 0 if successful, or -1 if an error occurred 310 @see evdns_base_nameserver_add() 311 */ 312int evdns_base_nameserver_ip_add(struct evdns_base *base, 313 const char *ip_as_string); 314 315/** 316 Add a nameserver by sockaddr. 317 **/ 318int 319evdns_base_nameserver_sockaddr_add(struct evdns_base *base, 320 const struct sockaddr *sa, ev_socklen_t len, unsigned flags); 321 322struct evdns_request; 323 324/** 325 Lookup an A record for a given name. 326 327 @param base the evdns_base to which to apply this operation 328 @param name a DNS hostname 329 @param flags either 0, or DNS_QUERY_NO_SEARCH to disable searching for this query. 330 @param callback a callback function to invoke when the request is completed 331 @param ptr an argument to pass to the callback function 332 @return an evdns_request object if successful, or NULL if an error occurred. 333 @see evdns_resolve_ipv6(), evdns_resolve_reverse(), evdns_resolve_reverse_ipv6(), evdns_cancel_request() 334 */ 335struct evdns_request *evdns_base_resolve_ipv4(struct evdns_base *base, const char *name, int flags, evdns_callback_type callback, void *ptr); 336 337/** 338 Lookup an AAAA record for a given name. 339 340 @param base the evdns_base to which to apply this operation 341 @param name a DNS hostname 342 @param flags either 0, or DNS_QUERY_NO_SEARCH to disable searching for this query. 343 @param callback a callback function to invoke when the request is completed 344 @param ptr an argument to pass to the callback function 345 @return an evdns_request object if successful, or NULL if an error occurred. 346 @see evdns_resolve_ipv4(), evdns_resolve_reverse(), evdns_resolve_reverse_ipv6(), evdns_cancel_request() 347 */ 348struct evdns_request *evdns_base_resolve_ipv6(struct evdns_base *base, const char *name, int flags, evdns_callback_type callback, void *ptr); 349 350struct in_addr; 351struct in6_addr; 352 353/** 354 Lookup a PTR record for a given IP address. 355 356 @param base the evdns_base to which to apply this operation 357 @param in an IPv4 address 358 @param flags either 0, or DNS_QUERY_NO_SEARCH to disable searching for this query. 359 @param callback a callback function to invoke when the request is completed 360 @param ptr an argument to pass to the callback function 361 @return an evdns_request object if successful, or NULL if an error occurred. 362 @see evdns_resolve_reverse_ipv6(), evdns_cancel_request() 363 */ 364struct evdns_request *evdns_base_resolve_reverse(struct evdns_base *base, const struct in_addr *in, int flags, evdns_callback_type callback, void *ptr); 365 366 367/** 368 Lookup a PTR record for a given IPv6 address. 369 370 @param base the evdns_base to which to apply this operation 371 @param in an IPv6 address 372 @param flags either 0, or DNS_QUERY_NO_SEARCH to disable searching for this query. 373 @param callback a callback function to invoke when the request is completed 374 @param ptr an argument to pass to the callback function 375 @return an evdns_request object if successful, or NULL if an error occurred. 376 @see evdns_resolve_reverse_ipv6(), evdns_cancel_request() 377 */ 378struct evdns_request *evdns_base_resolve_reverse_ipv6(struct evdns_base *base, const struct in6_addr *in, int flags, evdns_callback_type callback, void *ptr); 379 380/** 381 Cancels a pending DNS resolution request. 382 383 @param base the evdns_base that was used to make the request 384 @param req the evdns_request that was returned by calling a resolve function 385 @see evdns_base_resolve_ipv4(), evdns_base_resolve_ipv6, evdns_base_resolve_reverse 386*/ 387void evdns_cancel_request(struct evdns_base *base, struct evdns_request *req); 388 389/** 390 Set the value of a configuration option. 391 392 The currently available configuration options are: 393 394 ndots, timeout, max-timeouts, max-inflight, attempts, randomize-case, 395 bind-to, initial-probe-timeout, getaddrinfo-allow-skew. 396 397 In versions before Libevent 2.0.3-alpha, the option name needed to end with 398 a colon. 399 400 @param base the evdns_base to which to apply this operation 401 @param option the name of the configuration option to be modified 402 @param val the value to be set 403 @return 0 if successful, or -1 if an error occurred 404 */ 405int evdns_base_set_option(struct evdns_base *base, const char *option, const char *val); 406 407 408/** 409 Parse a resolv.conf file. 410 411 The 'flags' parameter determines what information is parsed from the 412 resolv.conf file. See the man page for resolv.conf for the format of this 413 file. 414 415 The following directives are not parsed from the file: sortlist, rotate, 416 no-check-names, inet6, debug. 417 418 If this function encounters an error, the possible return values are: 1 = 419 failed to open file, 2 = failed to stat file, 3 = file too large, 4 = out of 420 memory, 5 = short read from file, 6 = no nameservers listed in the file 421 422 @param base the evdns_base to which to apply this operation 423 @param flags any of DNS_OPTION_NAMESERVERS|DNS_OPTION_SEARCH|DNS_OPTION_MISC| 424 DNS_OPTIONS_HOSTSFILE|DNS_OPTIONS_ALL 425 @param filename the path to the resolv.conf file 426 @return 0 if successful, or various positive error codes if an error 427 occurred (see above) 428 @see resolv.conf(3), evdns_config_windows_nameservers() 429 */ 430int evdns_base_resolv_conf_parse(struct evdns_base *base, int flags, const char *const filename); 431 432/** 433 Load an /etc/hosts-style file from 'hosts_fname' into 'base'. 434 435 If hosts_fname is NULL, add minimal entries for localhost, and nothing 436 else. 437 438 Note that only evdns_getaddrinfo uses the /etc/hosts entries. 439 440 Return 0 on success, negative on failure. 441*/ 442int evdns_base_load_hosts(struct evdns_base *base, const char *hosts_fname); 443 444/** 445 Obtain nameserver information using the Windows API. 446 447 Attempt to configure a set of nameservers based on platform settings on 448 a win32 host. Preferentially tries to use GetNetworkParams; if that fails, 449 looks in the registry. 450 451 @return 0 if successful, or -1 if an error occurred 452 @see evdns_resolv_conf_parse() 453 */ 454#ifdef WIN32 455int evdns_base_config_windows_nameservers(struct evdns_base *); 456#define EVDNS_BASE_CONFIG_WINDOWS_NAMESERVERS_IMPLEMENTED 457#endif 458 459 460/** 461 Clear the list of search domains. 462 */ 463void evdns_base_search_clear(struct evdns_base *base); 464 465 466/** 467 Add a domain to the list of search domains 468 469 @param domain the domain to be added to the search list 470 */ 471void evdns_base_search_add(struct evdns_base *base, const char *domain); 472 473 474/** 475 Set the 'ndots' parameter for searches. 476 477 Sets the number of dots which, when found in a name, causes 478 the first query to be without any search domain. 479 480 @param ndots the new ndots parameter 481 */ 482void evdns_base_search_ndots_set(struct evdns_base *base, const int ndots); 483 484/** 485 A callback that is invoked when a log message is generated 486 487 @param is_warning indicates if the log message is a 'warning' 488 @param msg the content of the log message 489 */ 490typedef void (*evdns_debug_log_fn_type)(int is_warning, const char *msg); 491 492 493/** 494 Set the callback function to handle DNS log messages. If this 495 callback is not set, evdns log messages are handled with the regular 496 Libevent logging system. 497 498 @param fn the callback to be invoked when a log message is generated 499 */ 500void evdns_set_log_fn(evdns_debug_log_fn_type fn); 501 502/** 503 Set a callback that will be invoked to generate transaction IDs. By 504 default, we pick transaction IDs based on the current clock time, which 505 is bad for security. 506 507 @param fn the new callback, or NULL to use the default. 508 509 NOTE: This function has no effect in Libevent 2.0.4-alpha and later, 510 since Libevent now provides its own secure RNG. 511 */ 512void evdns_set_transaction_id_fn(ev_uint16_t (*fn)(void)); 513 514/** 515 Set a callback used to generate random bytes. By default, we use 516 the same function as passed to evdns_set_transaction_id_fn to generate 517 bytes two at a time. If a function is provided here, it's also used 518 to generate transaction IDs. 519 520 NOTE: This function has no effect in Libevent 2.0.4-alpha and later, 521 since Libevent now provides its own secure RNG. 522*/ 523void evdns_set_random_bytes_fn(void (*fn)(char *, size_t)); 524 525/* 526 * Functions used to implement a DNS server. 527 */ 528 529struct evdns_server_request; 530struct evdns_server_question; 531 532/** 533 A callback to implement a DNS server. The callback function receives a DNS 534 request. It should then optionally add a number of answers to the reply 535 using the evdns_server_request_add_*_reply functions, before calling either 536 evdns_server_request_respond to send the reply back, or 537 evdns_server_request_drop to decline to answer the request. 538 539 @param req A newly received request 540 @param user_data A pointer that was passed to 541 evdns_add_server_port_with_base(). 542 */ 543typedef void (*evdns_request_callback_fn_type)(struct evdns_server_request *, void *); 544#define EVDNS_ANSWER_SECTION 0 545#define EVDNS_AUTHORITY_SECTION 1 546#define EVDNS_ADDITIONAL_SECTION 2 547 548#define EVDNS_TYPE_A 1 549#define EVDNS_TYPE_NS 2 550#define EVDNS_TYPE_CNAME 5 551#define EVDNS_TYPE_SOA 6 552#define EVDNS_TYPE_PTR 12 553#define EVDNS_TYPE_MX 15 554#define EVDNS_TYPE_TXT 16 555#define EVDNS_TYPE_AAAA 28 556 557#define EVDNS_QTYPE_AXFR 252 558#define EVDNS_QTYPE_ALL 255 559 560#define EVDNS_CLASS_INET 1 561 562/* flags that can be set in answers; as part of the err parameter */ 563#define EVDNS_FLAGS_AA 0x400 564#define EVDNS_FLAGS_RD 0x080 565 566/** Create a new DNS server port. 567 568 @param base The event base to handle events for the server port. 569 @param socket A UDP socket to accept DNS requests. 570 @param flags Always 0 for now. 571 @param callback A function to invoke whenever we get a DNS request 572 on the socket. 573 @param user_data Data to pass to the callback. 574 @return an evdns_server_port structure for this server port. 575 */ 576struct 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); 577/** Close down a DNS server port, and free associated structures. */ 578void evdns_close_server_port(struct evdns_server_port *port); 579 580/** Sets some flags in a reply we're building. 581 Allows setting of the AA or RD flags 582 */ 583void evdns_server_request_set_flags(struct evdns_server_request *req, int flags); 584 585/* Functions to add an answer to an in-progress DNS reply. 586 */ 587int 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); 588int evdns_server_request_add_a_reply(struct evdns_server_request *req, const char *name, int n, const void *addrs, int ttl); 589int evdns_server_request_add_aaaa_reply(struct evdns_server_request *req, const char *name, int n, const void *addrs, int ttl); 590int evdns_server_request_add_ptr_reply(struct evdns_server_request *req, struct in_addr *in, const char *inaddr_name, const char *hostname, int ttl); 591int evdns_server_request_add_cname_reply(struct evdns_server_request *req, const char *name, const char *cname, int ttl); 592 593/** 594 Send back a response to a DNS request, and free the request structure. 595*/ 596int evdns_server_request_respond(struct evdns_server_request *req, int err); 597/** 598 Free a DNS request without sending back a reply. 599*/ 600int evdns_server_request_drop(struct evdns_server_request *req); 601struct sockaddr; 602/** 603 Get the address that made a DNS request. 604 */ 605int evdns_server_request_get_requesting_addr(struct evdns_server_request *_req, struct sockaddr *sa, int addr_len); 606 607/** Callback for evdns_getaddrinfo. */ 608typedef void (*evdns_getaddrinfo_cb)(int result, struct evutil_addrinfo *res, void *arg); 609 610struct evdns_base; 611struct evdns_getaddrinfo_request; 612/** Make a non-blocking getaddrinfo request using the dns_base in 'dns_base'. 613 * 614 * If we can answer the request immediately (with an error or not!), then we 615 * invoke cb immediately and return NULL. Otherwise we return 616 * an evdns_getaddrinfo_request and invoke cb later. 617 * 618 * When the callback is invoked, we pass as its first argument the error code 619 * that getaddrinfo would return (or 0 for no error). As its second argument, 620 * we pass the evutil_addrinfo structures we found (or NULL on error). We 621 * pass 'arg' as the third argument. 622 * 623 * Limitations: 624 * 625 * - The AI_V4MAPPED and AI_ALL flags are not currently implemented. 626 * - For ai_socktype, we only handle SOCKTYPE_STREAM, SOCKTYPE_UDP, and 0. 627 * - For ai_protocol, we only handle IPPROTO_TCP, IPPROTO_UDP, and 0. 628 */ 629struct evdns_getaddrinfo_request *evdns_getaddrinfo( 630 struct evdns_base *dns_base, 631 const char *nodename, const char *servname, 632 const struct evutil_addrinfo *hints_in, 633 evdns_getaddrinfo_cb cb, void *arg); 634 635/* Cancel an in-progress evdns_getaddrinfo. This MUST NOT be called after the 636 * getaddrinfo's callback has been invoked. The resolves will be canceled, 637 * and the callback will be invoked with the error EVUTIL_EAI_CANCEL. */ 638void evdns_getaddrinfo_cancel(struct evdns_getaddrinfo_request *req); 639 640#ifdef __cplusplus 641} 642#endif 643 644#endif /* !_EVENT2_DNS_H_ */ 645