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
141 extern "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  */
201 typedef void (*evdns_callback_type) (int result, char type, int count, int ttl, void *addresses, void *arg);
202 
203 struct evdns_base;
204 struct event_base;
205 
206 /** Flag for evdns_base_new: process resolv.conf.  */
207 #define EVDNS_BASE_INITIALIZE_NAMESERVERS 1
208 /** Flag for evdns_base_new: Do not prevent the libevent event loop from
209  * exiting when we have no active dns requests. */
210 #define EVDNS_BASE_DISABLE_WHEN_INACTIVE 0x8000
211 
212 /**
213   Initialize the asynchronous DNS library.
214 
215   This function initializes support for non-blocking name resolution by
216   calling evdns_resolv_conf_parse() on UNIX and
217   evdns_config_windows_nameservers() on Windows.
218 
219   @param event_base the event base to associate the dns client with
220   @param flags any of EVDNS_BASE_INITIALIZE_NAMESERVERS|
221     EVDNS_BASE_DISABLE_WHEN_INACTIVE
222   @return evdns_base object if successful, or NULL if an error occurred.
223   @see evdns_base_free()
224  */
225 EVENT2_EXPORT_SYMBOL
226 struct evdns_base * evdns_base_new(struct event_base *event_base, int initialize_nameservers);
227 
228 
229 /**
230   Shut down the asynchronous DNS resolver and terminate all active requests.
231 
232   If the 'fail_requests' option is enabled, all active requests will return
233   an empty result with the error flag set to DNS_ERR_SHUTDOWN. Otherwise,
234   the requests will be silently discarded.
235 
236   @param evdns_base the evdns base to free
237   @param fail_requests if zero, active requests will be aborted; if non-zero,
238 		active requests will return DNS_ERR_SHUTDOWN.
239   @see evdns_base_new()
240  */
241 EVENT2_EXPORT_SYMBOL
242 void evdns_base_free(struct evdns_base *base, int fail_requests);
243 
244 /**
245    Remove all hosts entries that have been loaded into the event_base via
246    evdns_base_load_hosts or via event_base_resolv_conf_parse.
247 
248    @param evdns_base the evdns base to remove outdated host addresses from
249  */
250 EVENT2_EXPORT_SYMBOL
251 void evdns_base_clear_host_addresses(struct evdns_base *base);
252 
253 /**
254   Convert a DNS error code to a string.
255 
256   @param err the DNS error code
257   @return a string containing an explanation of the error code
258 */
259 EVENT2_EXPORT_SYMBOL
260 const char *evdns_err_to_string(int err);
261 
262 
263 /**
264   Add a nameserver.
265 
266   The address should be an IPv4 address in network byte order.
267   The type of address is chosen so that it matches in_addr.s_addr.
268 
269   @param base the evdns_base to which to add the name server
270   @param address an IP address in network byte order
271   @return 0 if successful, or -1 if an error occurred
272   @see evdns_base_nameserver_ip_add()
273  */
274 EVENT2_EXPORT_SYMBOL
275 int evdns_base_nameserver_add(struct evdns_base *base,
276     unsigned long int address);
277 
278 /**
279   Get the number of configured nameservers.
280 
281   This returns the number of configured nameservers (not necessarily the
282   number of running nameservers).  This is useful for double-checking
283   whether our calls to the various nameserver configuration functions
284   have been successful.
285 
286   @param base the evdns_base to which to apply this operation
287   @return the number of configured nameservers
288   @see evdns_base_nameserver_add()
289  */
290 EVENT2_EXPORT_SYMBOL
291 int evdns_base_count_nameservers(struct evdns_base *base);
292 
293 /**
294   Remove all configured nameservers, and suspend all pending resolves.
295 
296   Resolves will not necessarily be re-attempted until evdns_base_resume() is called.
297 
298   @param base the evdns_base to which to apply this operation
299   @return 0 if successful, or -1 if an error occurred
300   @see evdns_base_resume()
301  */
302 EVENT2_EXPORT_SYMBOL
303 int evdns_base_clear_nameservers_and_suspend(struct evdns_base *base);
304 
305 
306 /**
307   Resume normal operation and continue any suspended resolve requests.
308 
309   Re-attempt resolves left in limbo after an earlier call to
310   evdns_base_clear_nameservers_and_suspend().
311 
312   @param base the evdns_base to which to apply this operation
313   @return 0 if successful, or -1 if an error occurred
314   @see evdns_base_clear_nameservers_and_suspend()
315  */
316 EVENT2_EXPORT_SYMBOL
317 int evdns_base_resume(struct evdns_base *base);
318 
319 /**
320   Add a nameserver by string address.
321 
322   This function parses a n IPv4 or IPv6 address from a string and adds it as a
323   nameserver.  It supports the following formats:
324   - [IPv6Address]:port
325   - [IPv6Address]
326   - IPv6Address
327   - IPv4Address:port
328   - IPv4Address
329 
330   If no port is specified, it defaults to 53.
331 
332   @param base the evdns_base to which to apply this operation
333   @return 0 if successful, or -1 if an error occurred
334   @see evdns_base_nameserver_add()
335  */
336 EVENT2_EXPORT_SYMBOL
337 int evdns_base_nameserver_ip_add(struct evdns_base *base,
338     const char *ip_as_string);
339 
340 /**
341    Add a nameserver by sockaddr.
342  **/
343 EVENT2_EXPORT_SYMBOL
344 int
345 evdns_base_nameserver_sockaddr_add(struct evdns_base *base,
346     const struct sockaddr *sa, ev_socklen_t len, unsigned flags);
347 
348 struct evdns_request;
349 
350 /**
351   Lookup an A record for a given name.
352 
353   @param base the evdns_base to which to apply this operation
354   @param name a DNS hostname
355   @param flags either 0, or DNS_QUERY_NO_SEARCH to disable searching for this query.
356   @param callback a callback function to invoke when the request is completed
357   @param ptr an argument to pass to the callback function
358   @return an evdns_request object if successful, or NULL if an error occurred.
359   @see evdns_resolve_ipv6(), evdns_resolve_reverse(), evdns_resolve_reverse_ipv6(), evdns_cancel_request()
360  */
361 EVENT2_EXPORT_SYMBOL
362 struct evdns_request *evdns_base_resolve_ipv4(struct evdns_base *base, const char *name, int flags, evdns_callback_type callback, void *ptr);
363 
364 /**
365   Lookup an AAAA record for a given name.
366 
367   @param base the evdns_base to which to apply this operation
368   @param name a DNS hostname
369   @param flags either 0, or DNS_QUERY_NO_SEARCH to disable searching for this query.
370   @param callback a callback function to invoke when the request is completed
371   @param ptr an argument to pass to the callback function
372   @return an evdns_request object if successful, or NULL if an error occurred.
373   @see evdns_resolve_ipv4(), evdns_resolve_reverse(), evdns_resolve_reverse_ipv6(), evdns_cancel_request()
374  */
375 EVENT2_EXPORT_SYMBOL
376 struct evdns_request *evdns_base_resolve_ipv6(struct evdns_base *base, const char *name, int flags, evdns_callback_type callback, void *ptr);
377 
378 struct in_addr;
379 struct in6_addr;
380 
381 /**
382   Lookup a PTR record for a given IP address.
383 
384   @param base the evdns_base to which to apply this operation
385   @param in an IPv4 address
386   @param flags either 0, or DNS_QUERY_NO_SEARCH to disable searching for this query.
387   @param callback a callback function to invoke when the request is completed
388   @param ptr an argument to pass to the callback function
389   @return an evdns_request object if successful, or NULL if an error occurred.
390   @see evdns_resolve_reverse_ipv6(), evdns_cancel_request()
391  */
392 EVENT2_EXPORT_SYMBOL
393 struct evdns_request *evdns_base_resolve_reverse(struct evdns_base *base, const struct in_addr *in, int flags, evdns_callback_type callback, void *ptr);
394 
395 
396 /**
397   Lookup a PTR record for a given IPv6 address.
398 
399   @param base the evdns_base to which to apply this operation
400   @param in an IPv6 address
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_reverse_ipv6(), evdns_cancel_request()
406  */
407 EVENT2_EXPORT_SYMBOL
408 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);
409 
410 /**
411   Cancels a pending DNS resolution request.
412 
413   @param base the evdns_base that was used to make the request
414   @param req the evdns_request that was returned by calling a resolve function
415   @see evdns_base_resolve_ipv4(), evdns_base_resolve_ipv6, evdns_base_resolve_reverse
416 */
417 EVENT2_EXPORT_SYMBOL
418 void evdns_cancel_request(struct evdns_base *base, struct evdns_request *req);
419 
420 /**
421   Set the value of a configuration option.
422 
423   The currently available configuration options are:
424 
425     ndots, timeout, max-timeouts, max-inflight, attempts, randomize-case,
426     bind-to, initial-probe-timeout, getaddrinfo-allow-skew.
427 
428   In versions before Libevent 2.0.3-alpha, the option name needed to end with
429   a colon.
430 
431   @param base the evdns_base to which to apply this operation
432   @param option the name of the configuration option to be modified
433   @param val the value to be set
434   @return 0 if successful, or -1 if an error occurred
435  */
436 EVENT2_EXPORT_SYMBOL
437 int evdns_base_set_option(struct evdns_base *base, const char *option, const char *val);
438 
439 
440 /**
441   Parse a resolv.conf file.
442 
443   The 'flags' parameter determines what information is parsed from the
444   resolv.conf file. See the man page for resolv.conf for the format of this
445   file.
446 
447   The following directives are not parsed from the file: sortlist, rotate,
448   no-check-names, inet6, debug.
449 
450   If this function encounters an error, the possible return values are: 1 =
451   failed to open file, 2 = failed to stat file, 3 = file too large, 4 = out of
452   memory, 5 = short read from file, 6 = no nameservers listed in the file
453 
454   @param base the evdns_base to which to apply this operation
455   @param flags any of DNS_OPTION_NAMESERVERS|DNS_OPTION_SEARCH|DNS_OPTION_MISC|
456     DNS_OPTION_HOSTSFILE|DNS_OPTIONS_ALL
457   @param filename the path to the resolv.conf file
458   @return 0 if successful, or various positive error codes if an error
459     occurred (see above)
460   @see resolv.conf(3), evdns_config_windows_nameservers()
461  */
462 EVENT2_EXPORT_SYMBOL
463 int evdns_base_resolv_conf_parse(struct evdns_base *base, int flags, const char *const filename);
464 
465 /**
466    Load an /etc/hosts-style file from 'hosts_fname' into 'base'.
467 
468    If hosts_fname is NULL, add minimal entries for localhost, and nothing
469    else.
470 
471    Note that only evdns_getaddrinfo uses the /etc/hosts entries.
472 
473    This function does not replace previously loaded hosts entries; to do that,
474    call evdns_base_clear_host_addresses first.
475 
476    Return 0 on success, negative on failure.
477 */
478 EVENT2_EXPORT_SYMBOL
479 int evdns_base_load_hosts(struct evdns_base *base, const char *hosts_fname);
480 
481 /**
482   Obtain nameserver information using the Windows API.
483 
484   Attempt to configure a set of nameservers based on platform settings on
485   a win32 host.  Preferentially tries to use GetNetworkParams; if that fails,
486   looks in the registry.
487 
488   @return 0 if successful, or -1 if an error occurred
489   @see evdns_resolv_conf_parse()
490  */
491 #ifdef _WIN32
492 EVENT2_EXPORT_SYMBOL
493 int evdns_base_config_windows_nameservers(struct evdns_base *);
494 #define EVDNS_BASE_CONFIG_WINDOWS_NAMESERVERS_IMPLEMENTED
495 #endif
496 
497 
498 /**
499   Clear the list of search domains.
500  */
501 EVENT2_EXPORT_SYMBOL
502 void evdns_base_search_clear(struct evdns_base *base);
503 
504 
505 /**
506   Add a domain to the list of search domains
507 
508   @param domain the domain to be added to the search list
509  */
510 EVENT2_EXPORT_SYMBOL
511 void evdns_base_search_add(struct evdns_base *base, const char *domain);
512 
513 
514 /**
515   Set the 'ndots' parameter for searches.
516 
517   Sets the number of dots which, when found in a name, causes
518   the first query to be without any search domain.
519 
520   @param ndots the new ndots parameter
521  */
522 EVENT2_EXPORT_SYMBOL
523 void evdns_base_search_ndots_set(struct evdns_base *base, const int ndots);
524 
525 /**
526   A callback that is invoked when a log message is generated
527 
528   @param is_warning indicates if the log message is a 'warning'
529   @param msg the content of the log message
530  */
531 typedef void (*evdns_debug_log_fn_type)(int is_warning, const char *msg);
532 
533 
534 /**
535   Set the callback function to handle DNS log messages.  If this
536   callback is not set, evdns log messages are handled with the regular
537   Libevent logging system.
538 
539   @param fn the callback to be invoked when a log message is generated
540  */
541 EVENT2_EXPORT_SYMBOL
542 void evdns_set_log_fn(evdns_debug_log_fn_type fn);
543 
544 /**
545    Set a callback that will be invoked to generate transaction IDs.  By
546    default, we pick transaction IDs based on the current clock time, which
547    is bad for security.
548 
549    @param fn the new callback, or NULL to use the default.
550 
551    NOTE: This function has no effect in Libevent 2.0.4-alpha and later,
552    since Libevent now provides its own secure RNG.
553  */
554 EVENT2_EXPORT_SYMBOL
555 void evdns_set_transaction_id_fn(ev_uint16_t (*fn)(void));
556 
557 /**
558    Set a callback used to generate random bytes.  By default, we use
559    the same function as passed to evdns_set_transaction_id_fn to generate
560    bytes two at a time.  If a function is provided here, it's also used
561    to generate transaction IDs.
562 
563    NOTE: This function has no effect in Libevent 2.0.4-alpha and later,
564    since Libevent now provides its own secure RNG.
565 */
566 EVENT2_EXPORT_SYMBOL
567 void evdns_set_random_bytes_fn(void (*fn)(char *, size_t));
568 
569 /*
570  * Functions used to implement a DNS server.
571  */
572 
573 struct evdns_server_request;
574 struct evdns_server_question;
575 
576 /**
577    A callback to implement a DNS server.  The callback function receives a DNS
578    request.  It should then optionally add a number of answers to the reply
579    using the evdns_server_request_add_*_reply functions, before calling either
580    evdns_server_request_respond to send the reply back, or
581    evdns_server_request_drop to decline to answer the request.
582 
583    @param req A newly received request
584    @param user_data A pointer that was passed to
585       evdns_add_server_port_with_base().
586  */
587 typedef void (*evdns_request_callback_fn_type)(struct evdns_server_request *, void *);
588 #define EVDNS_ANSWER_SECTION 0
589 #define EVDNS_AUTHORITY_SECTION 1
590 #define EVDNS_ADDITIONAL_SECTION 2
591 
592 #define EVDNS_TYPE_A	   1
593 #define EVDNS_TYPE_NS	   2
594 #define EVDNS_TYPE_CNAME   5
595 #define EVDNS_TYPE_SOA	   6
596 #define EVDNS_TYPE_PTR	  12
597 #define EVDNS_TYPE_MX	  15
598 #define EVDNS_TYPE_TXT	  16
599 #define EVDNS_TYPE_AAAA	  28
600 
601 #define EVDNS_QTYPE_AXFR 252
602 #define EVDNS_QTYPE_ALL	 255
603 
604 #define EVDNS_CLASS_INET   1
605 
606 /* flags that can be set in answers; as part of the err parameter */
607 #define EVDNS_FLAGS_AA	0x400
608 #define EVDNS_FLAGS_RD	0x080
609 
610 /** Create a new DNS server port.
611 
612     @param base The event base to handle events for the server port.
613     @param socket A UDP socket to accept DNS requests.
614     @param flags Always 0 for now.
615     @param callback A function to invoke whenever we get a DNS request
616       on the socket.
617     @param user_data Data to pass to the callback.
618     @return an evdns_server_port structure for this server port.
619  */
620 EVENT2_EXPORT_SYMBOL
621 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);
622 /** Close down a DNS server port, and free associated structures. */
623 EVENT2_EXPORT_SYMBOL
624 void evdns_close_server_port(struct evdns_server_port *port);
625 
626 /** Sets some flags in a reply we're building.
627     Allows setting of the AA or RD flags
628  */
629 EVENT2_EXPORT_SYMBOL
630 void evdns_server_request_set_flags(struct evdns_server_request *req, int flags);
631 
632 /* Functions to add an answer to an in-progress DNS reply.
633  */
634 EVENT2_EXPORT_SYMBOL
635 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);
636 EVENT2_EXPORT_SYMBOL
637 int evdns_server_request_add_a_reply(struct evdns_server_request *req, const char *name, int n, const void *addrs, int ttl);
638 EVENT2_EXPORT_SYMBOL
639 int evdns_server_request_add_aaaa_reply(struct evdns_server_request *req, const char *name, int n, const void *addrs, int ttl);
640 EVENT2_EXPORT_SYMBOL
641 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);
642 EVENT2_EXPORT_SYMBOL
643 int evdns_server_request_add_cname_reply(struct evdns_server_request *req, const char *name, const char *cname, int ttl);
644 
645 /**
646    Send back a response to a DNS request, and free the request structure.
647 */
648 EVENT2_EXPORT_SYMBOL
649 int evdns_server_request_respond(struct evdns_server_request *req, int err);
650 /**
651    Free a DNS request without sending back a reply.
652 */
653 EVENT2_EXPORT_SYMBOL
654 int evdns_server_request_drop(struct evdns_server_request *req);
655 struct sockaddr;
656 /**
657     Get the address that made a DNS request.
658  */
659 EVENT2_EXPORT_SYMBOL
660 int evdns_server_request_get_requesting_addr(struct evdns_server_request *req, struct sockaddr *sa, int addr_len);
661 
662 /** Callback for evdns_getaddrinfo. */
663 typedef void (*evdns_getaddrinfo_cb)(int result, struct evutil_addrinfo *res, void *arg);
664 
665 struct evdns_base;
666 struct evdns_getaddrinfo_request;
667 /** Make a non-blocking getaddrinfo request using the dns_base in 'dns_base'.
668  *
669  * If we can answer the request immediately (with an error or not!), then we
670  * invoke cb immediately and return NULL.  Otherwise we return
671  * an evdns_getaddrinfo_request and invoke cb later.
672  *
673  * When the callback is invoked, we pass as its first argument the error code
674  * that getaddrinfo would return (or 0 for no error).  As its second argument,
675  * we pass the evutil_addrinfo structures we found (or NULL on error).  We
676  * pass 'arg' as the third argument.
677  *
678  * Limitations:
679  *
680  * - The AI_V4MAPPED and AI_ALL flags are not currently implemented.
681  * - For ai_socktype, we only handle SOCKTYPE_STREAM, SOCKTYPE_UDP, and 0.
682  * - For ai_protocol, we only handle IPPROTO_TCP, IPPROTO_UDP, and 0.
683  */
684 EVENT2_EXPORT_SYMBOL
685 struct evdns_getaddrinfo_request *evdns_getaddrinfo(
686     struct evdns_base *dns_base,
687     const char *nodename, const char *servname,
688     const struct evutil_addrinfo *hints_in,
689     evdns_getaddrinfo_cb cb, void *arg);
690 
691 /* Cancel an in-progress evdns_getaddrinfo.  This MUST NOT be called after the
692  * getaddrinfo's callback has been invoked.  The resolves will be canceled,
693  * and the callback will be invoked with the error EVUTIL_EAI_CANCEL. */
694 EVENT2_EXPORT_SYMBOL
695 void evdns_getaddrinfo_cancel(struct evdns_getaddrinfo_request *req);
696 
697 /**
698    Retrieve the address of the 'idx'th configured nameserver.
699 
700    @param base The evdns_base to examine.
701    @param idx The index of the nameserver to get the address of.
702    @param sa A location to receive the server's address.
703    @param len The number of bytes available at sa.
704 
705    @return the number of bytes written into sa on success.  On failure, returns
706      -1 if idx is greater than the number of configured nameservers, or a
707      value greater than 'len' if len was not high enough.
708  */
709 EVENT2_EXPORT_SYMBOL
710 int evdns_base_get_nameserver_addr(struct evdns_base *base, int idx,
711     struct sockaddr *sa, ev_socklen_t len);
712 
713 #ifdef __cplusplus
714 }
715 #endif
716 
717 #endif  /* !EVENT2_DNS_H_INCLUDED_ */
718