2 * Copyright (c) 2006-2007 Niels Provos <provos@citi.umich.edu>
3 * Copyright (c) 2007-2012 Niels Provos and Nick Mathewson
5 * Redistribution and use in source and binary forms, with or without
6 * modification, are permitted provided that the following conditions
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.
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.
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
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.
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>
43 * You may wish to replace the word "Parts" with something else depending on
44 * the amount of original code.
46 * (Derivative works does not include programs which link against, run or include
47 * the source verbatim in their source distributions)
50 /** @file event2/dns.h
52 * Welcome, gentle reader
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,
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.
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);
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
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.
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
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.
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).
98 * 3. When calling evdns_resolve, pass the DNS_QUERY_NO_SEARCH flag.
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.
104 * The ndots setting can either be set from a resolv.conf, or by calling
105 * evdns_search_ndots_set.
107 * For example, with ndots set to 1 (the default) and a search domain list of
110 * Order: www.myhome.net, www.
113 * Order: www.abc., www.abc.myhome.net
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.
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.
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.
135 #ifndef EVENT2_DNS_H_INCLUDED_
136 #define EVENT2_DNS_H_INCLUDED_
138 #include <event2/visibility.h>
144 /* For integer types. */
145 #include <event2/util.h>
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
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
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
178 #define DNS_IPv6_AAAA 3
180 #define DNS_QUERY_NO_SEARCH 1
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:
188 * - getaddrinfo-allow-skew:
193 * - initial-probe-timeout:
195 #define DNS_OPTION_MISC 4
196 /* Load hosts file (i.e. "/etc/hosts") */
197 #define DNS_OPTION_HOSTSFILE 8
200 * - DNS_OPTION_SEARCH
201 * - DNS_OPTION_NAMESERVERS
203 * - DNS_OPTION_HOSTSFILE
205 #define DNS_OPTIONS_ALL ( \
206 DNS_OPTION_SEARCH | \
207 DNS_OPTION_NAMESERVERS | \
209 DNS_OPTION_HOSTSFILE | \
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
216 /* Obsolete name for DNS_QUERY_NO_SEARCH */
217 #define DNS_NO_SEARCH DNS_QUERY_NO_SEARCH
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.
229 typedef void (*evdns_callback_type) (int result, char type, int count, int ttl, void *addresses, void *arg);
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
245 Initialize the asynchronous DNS library.
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.
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()
258 struct evdns_base * evdns_base_new(struct event_base *event_base, int initialize_nameservers);
262 Shut down the asynchronous DNS resolver and terminate all active requests.
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.
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()
274 void evdns_base_free(struct evdns_base *base, int fail_requests);
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.
280 @param evdns_base the evdns base to remove outdated host addresses from
283 void evdns_base_clear_host_addresses(struct evdns_base *base);
286 Convert a DNS error code to a string.
288 @param err the DNS error code
289 @return a string containing an explanation of the error code
292 const char *evdns_err_to_string(int err);
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.
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()
307 int evdns_base_nameserver_add(struct evdns_base *base,
308 unsigned long int address);
311 Get the number of configured nameservers.
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.
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()
323 int evdns_base_count_nameservers(struct evdns_base *base);
326 Remove all configured nameservers, and suspend all pending resolves.
328 Resolves will not necessarily be re-attempted until evdns_base_resume() is called.
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()
335 int evdns_base_clear_nameservers_and_suspend(struct evdns_base *base);
339 Resume normal operation and continue any suspended resolve requests.
341 Re-attempt resolves left in limbo after an earlier call to
342 evdns_base_clear_nameservers_and_suspend().
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()
349 int evdns_base_resume(struct evdns_base *base);
352 Add a nameserver by string address.
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:
362 If no port is specified, it defaults to 53.
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()
369 int evdns_base_nameserver_ip_add(struct evdns_base *base,
370 const char *ip_as_string);
373 Add a nameserver by sockaddr.
377 evdns_base_nameserver_sockaddr_add(struct evdns_base *base,
378 const struct sockaddr *sa, ev_socklen_t len, unsigned flags);
380 struct evdns_request;
383 Lookup an A record for a given name.
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()
394 struct evdns_request *evdns_base_resolve_ipv4(struct evdns_base *base, const char *name, int flags, evdns_callback_type callback, void *ptr);
397 Lookup an AAAA record for a given name.
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()
408 struct evdns_request *evdns_base_resolve_ipv6(struct evdns_base *base, const char *name, int flags, evdns_callback_type callback, void *ptr);
414 Lookup a PTR record for a given IP address.
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()
425 struct evdns_request *evdns_base_resolve_reverse(struct evdns_base *base, const struct in_addr *in, int flags, evdns_callback_type callback, void *ptr);
429 Lookup a PTR record for a given IPv6 address.
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()
440 struct evdns_request *evdns_base_resolve_reverse_ipv6(struct evdns_base *base, const struct in6_addr *in, int flags, evdns_callback_type callback, void *ptr);
443 Cancels a pending DNS resolution request.
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
450 void evdns_cancel_request(struct evdns_base *base, struct evdns_request *req);
453 Set the value of a configuration option.
455 The currently available configuration options are:
457 ndots, timeout, max-timeouts, max-inflight, attempts, randomize-case,
458 bind-to, initial-probe-timeout, getaddrinfo-allow-skew.
460 In versions before Libevent 2.0.3-alpha, the option name needed to end with
463 @param base the evdns_base to which to apply this operation
464 @param option the name of the configuration option to be modified
465 @param val the value to be set
466 @return 0 if successful, or -1 if an error occurred
469 int evdns_base_set_option(struct evdns_base *base, const char *option, const char *val);
473 Parse a resolv.conf file.
475 The 'flags' parameter determines what information is parsed from the
476 resolv.conf file. See the man page for resolv.conf for the format of this
479 The following directives are not parsed from the file: sortlist, rotate,
480 no-check-names, inet6, debug.
482 If this function encounters an error, the possible return values are: 1 =
483 failed to open file, 2 = failed to stat file, 3 = file too large, 4 = out of
484 memory, 5 = short read from file, 6 = no nameservers listed in the file
486 @param base the evdns_base to which to apply this operation
487 @param flags any of DNS_OPTION_NAMESERVERS|DNS_OPTION_SEARCH|DNS_OPTION_MISC|
488 DNS_OPTION_HOSTSFILE|DNS_OPTIONS_ALL|DNS_OPTION_NAMESERVERS_NO_DEFAULT
489 @param filename the path to the resolv.conf file
490 @return 0 if successful, or various positive error codes if an error
492 @see resolv.conf(3), evdns_config_windows_nameservers()
495 int evdns_base_resolv_conf_parse(struct evdns_base *base, int flags, const char *const filename);
498 Load an /etc/hosts-style file from 'hosts_fname' into 'base'.
500 If hosts_fname is NULL, add minimal entries for localhost, and nothing
503 Note that only evdns_getaddrinfo uses the /etc/hosts entries.
505 This function does not replace previously loaded hosts entries; to do that,
506 call evdns_base_clear_host_addresses first.
508 Return 0 on success, negative on failure.
511 int evdns_base_load_hosts(struct evdns_base *base, const char *hosts_fname);
513 #if defined(EVENT_IN_DOXYGEN_) || defined(_WIN32)
515 Obtain nameserver information using the Windows API.
517 Attempt to configure a set of nameservers based on platform settings on
518 a win32 host. Preferentially tries to use GetNetworkParams; if that fails,
519 looks in the registry.
521 @return 0 if successful, or -1 if an error occurred
522 @see evdns_resolv_conf_parse()
525 int evdns_base_config_windows_nameservers(struct evdns_base *);
526 #define EVDNS_BASE_CONFIG_WINDOWS_NAMESERVERS_IMPLEMENTED
531 Clear the list of search domains.
534 void evdns_base_search_clear(struct evdns_base *base);
538 Add a domain to the list of search domains
540 @param domain the domain to be added to the search list
543 void evdns_base_search_add(struct evdns_base *base, const char *domain);
547 Set the 'ndots' parameter for searches.
549 Sets the number of dots which, when found in a name, causes
550 the first query to be without any search domain.
552 @param ndots the new ndots parameter
555 void evdns_base_search_ndots_set(struct evdns_base *base, const int ndots);
558 A callback that is invoked when a log message is generated
560 @param is_warning indicates if the log message is a 'warning'
561 @param msg the content of the log message
563 typedef void (*evdns_debug_log_fn_type)(int is_warning, const char *msg);
567 Set the callback function to handle DNS log messages. If this
568 callback is not set, evdns log messages are handled with the regular
569 Libevent logging system.
571 @param fn the callback to be invoked when a log message is generated
574 void evdns_set_log_fn(evdns_debug_log_fn_type fn);
577 Set a callback that will be invoked to generate transaction IDs. By
578 default, we pick transaction IDs based on the current clock time, which
581 @param fn the new callback, or NULL to use the default.
583 NOTE: This function has no effect in Libevent 2.0.4-alpha and later,
584 since Libevent now provides its own secure RNG.
587 void evdns_set_transaction_id_fn(ev_uint16_t (*fn)(void));
590 Set a callback used to generate random bytes. By default, we use
591 the same function as passed to evdns_set_transaction_id_fn to generate
592 bytes two at a time. If a function is provided here, it's also used
593 to generate transaction IDs.
595 NOTE: This function has no effect in Libevent 2.0.4-alpha and later,
596 since Libevent now provides its own secure RNG.
599 void evdns_set_random_bytes_fn(void (*fn)(char *, size_t));
602 * Functions used to implement a DNS server.
605 struct evdns_server_request;
606 struct evdns_server_question;
609 A callback to implement a DNS server. The callback function receives a DNS
610 request. It should then optionally add a number of answers to the reply
611 using the evdns_server_request_add_*_reply functions, before calling either
612 evdns_server_request_respond to send the reply back, or
613 evdns_server_request_drop to decline to answer the request.
615 @param req A newly received request
616 @param user_data A pointer that was passed to
617 evdns_add_server_port_with_base().
619 typedef void (*evdns_request_callback_fn_type)(struct evdns_server_request *, void *);
620 #define EVDNS_ANSWER_SECTION 0
621 #define EVDNS_AUTHORITY_SECTION 1
622 #define EVDNS_ADDITIONAL_SECTION 2
624 #define EVDNS_TYPE_A 1
625 #define EVDNS_TYPE_NS 2
626 #define EVDNS_TYPE_CNAME 5
627 #define EVDNS_TYPE_SOA 6
628 #define EVDNS_TYPE_PTR 12
629 #define EVDNS_TYPE_MX 15
630 #define EVDNS_TYPE_TXT 16
631 #define EVDNS_TYPE_AAAA 28
633 #define EVDNS_QTYPE_AXFR 252
634 #define EVDNS_QTYPE_ALL 255
636 #define EVDNS_CLASS_INET 1
638 /* flags that can be set in answers; as part of the err parameter */
639 #define EVDNS_FLAGS_AA 0x400
640 #define EVDNS_FLAGS_RD 0x080
642 /** Create a new DNS server port.
644 @param base The event base to handle events for the server port.
645 @param socket A UDP socket to accept DNS requests.
646 @param flags Always 0 for now.
647 @param callback A function to invoke whenever we get a DNS request
649 @param user_data Data to pass to the callback.
650 @return an evdns_server_port structure for this server port or NULL if
654 struct 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);
655 /** Close down a DNS server port, and free associated structures. */
657 void evdns_close_server_port(struct evdns_server_port *port);
659 /** Sets some flags in a reply we're building.
660 Allows setting of the AA or RD flags
663 void evdns_server_request_set_flags(struct evdns_server_request *req, int flags);
665 /* Functions to add an answer to an in-progress DNS reply.
668 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);
670 int evdns_server_request_add_a_reply(struct evdns_server_request *req, const char *name, int n, const void *addrs, int ttl);
672 int evdns_server_request_add_aaaa_reply(struct evdns_server_request *req, const char *name, int n, const void *addrs, int ttl);
674 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);
676 int evdns_server_request_add_cname_reply(struct evdns_server_request *req, const char *name, const char *cname, int ttl);
679 Send back a response to a DNS request, and free the request structure.
682 int evdns_server_request_respond(struct evdns_server_request *req, int err);
684 Free a DNS request without sending back a reply.
687 int evdns_server_request_drop(struct evdns_server_request *req);
690 Get the address that made a DNS request.
693 int evdns_server_request_get_requesting_addr(struct evdns_server_request *req, struct sockaddr *sa, int addr_len);
695 /** Callback for evdns_getaddrinfo. */
696 typedef void (*evdns_getaddrinfo_cb)(int result, struct evutil_addrinfo *res, void *arg);
699 struct evdns_getaddrinfo_request;
700 /** Make a non-blocking getaddrinfo request using the dns_base in 'dns_base'.
702 * If we can answer the request immediately (with an error or not!), then we
703 * invoke cb immediately and return NULL. Otherwise we return
704 * an evdns_getaddrinfo_request and invoke cb later.
706 * When the callback is invoked, we pass as its first argument the error code
707 * that getaddrinfo would return (or 0 for no error). As its second argument,
708 * we pass the evutil_addrinfo structures we found (or NULL on error). We
709 * pass 'arg' as the third argument.
713 * - The AI_V4MAPPED and AI_ALL flags are not currently implemented.
714 * - For ai_socktype, we only handle SOCKTYPE_STREAM, SOCKTYPE_UDP, and 0.
715 * - For ai_protocol, we only handle IPPROTO_TCP, IPPROTO_UDP, and 0.
718 struct evdns_getaddrinfo_request *evdns_getaddrinfo(
719 struct evdns_base *dns_base,
720 const char *nodename, const char *servname,
721 const struct evutil_addrinfo *hints_in,
722 evdns_getaddrinfo_cb cb, void *arg);
724 /* Cancel an in-progress evdns_getaddrinfo. This MUST NOT be called after the
725 * getaddrinfo's callback has been invoked. The resolves will be canceled,
726 * and the callback will be invoked with the error EVUTIL_EAI_CANCEL. */
728 void evdns_getaddrinfo_cancel(struct evdns_getaddrinfo_request *req);
731 Retrieve the address of the 'idx'th configured nameserver.
733 @param base The evdns_base to examine.
734 @param idx The index of the nameserver to get the address of.
735 @param sa A location to receive the server's address.
736 @param len The number of bytes available at sa.
738 @return the number of bytes written into sa on success. On failure, returns
739 -1 if idx is greater than the number of configured nameservers, or a
740 value greater than 'len' if len was not high enough.
743 int evdns_base_get_nameserver_addr(struct evdns_base *base, int idx,
744 struct sockaddr *sa, ev_socklen_t len);
750 #endif /* !EVENT2_DNS_H_INCLUDED_ */