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1 /*
2  * Copyright (c) 2006 Niels Provos <provos@citi.umich.edu>
3  * All rights reserved.
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 evdns.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  * This code is based on libevent and you must call event_init before
62  * any of the APIs in this file. You must also seed the OpenSSL random
63  * source if you are using OpenSSL for ids (see below).
64  *
65  * This library is designed to be included and shipped with your source
66  * code. You statically link with it. You should also test for the
67  * existence of strtok_r and define HAVE_STRTOK_R if you have it.
68  *
69  * The DNS protocol requires a good source of id numbers and these
70  * numbers should be unpredictable for spoofing reasons. There are
71  * three methods for generating them here and you must define exactly
72  * one of them. In increasing order of preference:
73  *
74  * DNS_USE_GETTIMEOFDAY_FOR_ID:
75  *   Using the bottom 16 bits of the usec result from gettimeofday. This
76  *   is a pretty poor solution but should work anywhere.
77  * DNS_USE_CPU_CLOCK_FOR_ID:
78  *   Using the bottom 16 bits of the nsec result from the CPU's time
79  *   counter. This is better, but may not work everywhere. Requires
80  *   POSIX realtime support and you'll need to link against -lrt on
81  *   glibc systems at least.
82  * DNS_USE_OPENSSL_FOR_ID:
83  *   Uses the OpenSSL RAND_bytes call to generate the data. You must
84  *   have seeded the pool before making any calls to this library.
85  *
86  * The library keeps track of the state of nameservers and will avoid
87  * them when they go down. Otherwise it will round robin between them.
88  *
89  * Quick start guide:
90  *   #include "evdns.h"
91  *   void callback(int result, char type, int count, int ttl,
92  *		 void *addresses, void *arg);
93  *   evdns_resolv_conf_parse(DNS_OPTIONS_ALL, "/etc/resolv.conf");
94  *   evdns_resolve("www.hostname.com", 0, callback, NULL);
95  *
96  * When the lookup is complete the callback function is called. The
97  * first argument will be one of the DNS_ERR_* defines in evdns.h.
98  * Hopefully it will be DNS_ERR_NONE, in which case type will be
99  * DNS_IPv4_A, count will be the number of IP addresses, ttl is the time
100  * which the data can be cached for (in seconds), addresses will point
101  * to an array of uint32_t's and arg will be whatever you passed to
102  * evdns_resolve.
103  *
104  * Searching:
105  *
106  * In order for this library to be a good replacement for glibc's resolver it
107  * supports searching. This involves setting a list of default domains, in
108  * which names will be queried for. The number of dots in the query name
109  * determines the order in which this list is used.
110  *
111  * Searching appears to be a single lookup from the point of view of the API,
112  * although many DNS queries may be generated from a single call to
113  * evdns_resolve. Searching can also drastically slow down the resolution
114  * of names.
115  *
116  * To disable searching:
117  *   1. Never set it up. If you never call evdns_resolv_conf_parse or
118  *   evdns_search_add then no searching will occur.
119  *
120  *   2. If you do call evdns_resolv_conf_parse then don't pass
121  *   DNS_OPTION_SEARCH (or DNS_OPTIONS_ALL, which implies it).
122  *
123  *   3. When calling evdns_resolve, pass the DNS_QUERY_NO_SEARCH flag.
124  *
125  * The order of searches depends on the number of dots in the name. If the
126  * number is greater than the ndots setting then the names is first tried
127  * globally. Otherwise each search domain is appended in turn.
128  *
129  * The ndots setting can either be set from a resolv.conf, or by calling
130  * evdns_search_ndots_set.
131  *
132  * For example, with ndots set to 1 (the default) and a search domain list of
133  * ["myhome.net"]:
134  *  Query: www
135  *  Order: www.myhome.net, www.
136  *
137  *  Query: www.abc
138  *  Order: www.abc., www.abc.myhome.net
139  *
140  * Internals:
141  *
142  * Requests are kept in two queues. The first is the inflight queue. In
143  * this queue requests have an allocated transaction id and nameserver.
144  * They will soon be transmitted if they haven't already been.
145  *
146  * The second is the waiting queue. The size of the inflight ring is
147  * limited and all other requests wait in waiting queue for space. This
148  * bounds the number of concurrent requests so that we don't flood the
149  * nameserver. Several algorithms require a full walk of the inflight
150  * queue and so bounding its size keeps thing going nicely under huge
151  * (many thousands of requests) loads.
152  *
153  * If a nameserver loses too many requests it is considered down and we
154  * try not to use it. After a while we send a probe to that nameserver
155  * (a lookup for google.com) and, if it replies, we consider it working
156  * again. If the nameserver fails a probe we wait longer to try again
157  * with the next probe.
158  */
159 
160 #ifndef EVENTDNS_H
161 #define EVENTDNS_H
162 
163 #ifdef __cplusplus
164 extern "C" {
165 #endif
166 
167 /* For integer types. */
168 #include <evutil.h>
169 
170 /** Error codes 0-5 are as described in RFC 1035. */
171 #define DNS_ERR_NONE 0
172 /** The name server was unable to interpret the query */
173 #define DNS_ERR_FORMAT 1
174 /** The name server was unable to process this query due to a problem with the
175  * name server */
176 #define DNS_ERR_SERVERFAILED 2
177 /** The domain name does not exist */
178 #define DNS_ERR_NOTEXIST 3
179 /** The name server does not support the requested kind of query */
180 #define DNS_ERR_NOTIMPL 4
181 /** The name server refuses to reform the specified operation for policy
182  * reasons */
183 #define DNS_ERR_REFUSED 5
184 /** The reply was truncated or ill-formated */
185 #define DNS_ERR_TRUNCATED 65
186 /** An unknown error occurred */
187 #define DNS_ERR_UNKNOWN 66
188 /** Communication with the server timed out */
189 #define DNS_ERR_TIMEOUT 67
190 /** The request was canceled because the DNS subsystem was shut down. */
191 #define DNS_ERR_SHUTDOWN 68
192 
193 #define DNS_IPv4_A 1
194 #define DNS_PTR 2
195 #define DNS_IPv6_AAAA 3
196 
197 #define DNS_QUERY_NO_SEARCH 1
198 
199 #define DNS_OPTION_SEARCH 1
200 #define DNS_OPTION_NAMESERVERS 2
201 #define DNS_OPTION_MISC 4
202 #define DNS_OPTIONS_ALL 7
203 
204 /**
205  * The callback that contains the results from a lookup.
206  * - type is either DNS_IPv4_A or DNS_PTR or DNS_IPv6_AAAA
207  * - count contains the number of addresses of form type
208  * - ttl is the number of seconds the resolution may be cached for.
209  * - addresses needs to be cast according to type
210  */
211 typedef void (*evdns_callback_type) (int result, char type, int count, int ttl, void *addresses, void *arg);
212 
213 /**
214   Initialize the asynchronous DNS library.
215 
216   This function initializes support for non-blocking name resolution by
217   calling evdns_resolv_conf_parse() on UNIX and
218   evdns_config_windows_nameservers() on Windows.
219 
220   @return 0 if successful, or -1 if an error occurred
221   @see evdns_shutdown()
222  */
223 int evdns_init(void);
224 
225 
226 /**
227   Shut down the asynchronous DNS resolver and terminate all active requests.
228 
229   If the 'fail_requests' option is enabled, all active requests will return
230   an empty result with the error flag set to DNS_ERR_SHUTDOWN. Otherwise,
231   the requests will be silently discarded.
232 
233   @param fail_requests if zero, active requests will be aborted; if non-zero,
234 		active requests will return DNS_ERR_SHUTDOWN.
235   @see evdns_init()
236  */
237 void evdns_shutdown(int fail_requests);
238 
239 
240 /**
241   Convert a DNS error code to a string.
242 
243   @param err the DNS error code
244   @return a string containing an explanation of the error code
245 */
246 const char *evdns_err_to_string(int err);
247 
248 
249 /**
250   Add a nameserver.
251 
252   The address should be an IPv4 address in network byte order.
253   The type of address is chosen so that it matches in_addr.s_addr.
254 
255   @param address an IP address in network byte order
256   @return 0 if successful, or -1 if an error occurred
257   @see evdns_nameserver_ip_add()
258  */
259 int evdns_nameserver_add(unsigned long int address);
260 
261 
262 /**
263   Get the number of configured nameservers.
264 
265   This returns the number of configured nameservers (not necessarily the
266   number of running nameservers).  This is useful for double-checking
267   whether our calls to the various nameserver configuration functions
268   have been successful.
269 
270   @return the number of configured nameservers
271   @see evdns_nameserver_add()
272  */
273 int evdns_count_nameservers(void);
274 
275 
276 /**
277   Remove all configured nameservers, and suspend all pending resolves.
278 
279   Resolves will not necessarily be re-attempted until evdns_resume() is called.
280 
281   @return 0 if successful, or -1 if an error occurred
282   @see evdns_resume()
283  */
284 int evdns_clear_nameservers_and_suspend(void);
285 
286 
287 /**
288   Resume normal operation and continue any suspended resolve requests.
289 
290   Re-attempt resolves left in limbo after an earlier call to
291   evdns_clear_nameservers_and_suspend().
292 
293   @return 0 if successful, or -1 if an error occurred
294   @see evdns_clear_nameservers_and_suspend()
295  */
296 int evdns_resume(void);
297 
298 
299 /**
300   Add a nameserver.
301 
302   This wraps the evdns_nameserver_add() function by parsing a string as an IP
303   address and adds it as a nameserver.
304 
305   @return 0 if successful, or -1 if an error occurred
306   @see evdns_nameserver_add()
307  */
308 int evdns_nameserver_ip_add(const char *ip_as_string);
309 
310 
311 /**
312   Lookup an A record for a given name.
313 
314   @param name a DNS hostname
315   @param flags either 0, or DNS_QUERY_NO_SEARCH to disable searching for this query.
316   @param callback a callback function to invoke when the request is completed
317   @param ptr an argument to pass to the callback function
318   @return 0 if successful, or -1 if an error occurred
319   @see evdns_resolve_ipv6(), evdns_resolve_reverse(), evdns_resolve_reverse_ipv6()
320  */
321 int evdns_resolve_ipv4(const char *name, int flags, evdns_callback_type callback, void *ptr);
322 
323 
324 /**
325   Lookup an AAAA record for a given name.
326 
327   @param name a DNS hostname
328   @param flags either 0, or DNS_QUERY_NO_SEARCH to disable searching for this query.
329   @param callback a callback function to invoke when the request is completed
330   @param ptr an argument to pass to the callback function
331   @return 0 if successful, or -1 if an error occurred
332   @see evdns_resolve_ipv4(), evdns_resolve_reverse(), evdns_resolve_reverse_ipv6()
333  */
334 int evdns_resolve_ipv6(const char *name, int flags, evdns_callback_type callback, void *ptr);
335 
336 struct in_addr;
337 struct in6_addr;
338 
339 /**
340   Lookup a PTR record for a given IP address.
341 
342   @param in an IPv4 address
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 0 if successful, or -1 if an error occurred
347   @see evdns_resolve_reverse_ipv6()
348  */
349 int evdns_resolve_reverse(const struct in_addr *in, int flags, evdns_callback_type callback, void *ptr);
350 
351 
352 /**
353   Lookup a PTR record for a given IPv6 address.
354 
355   @param in an IPv6 address
356   @param flags either 0, or DNS_QUERY_NO_SEARCH to disable searching for this query.
357   @param callback a callback function to invoke when the request is completed
358   @param ptr an argument to pass to the callback function
359   @return 0 if successful, or -1 if an error occurred
360   @see evdns_resolve_reverse_ipv6()
361  */
362 int evdns_resolve_reverse_ipv6(const struct in6_addr *in, int flags, evdns_callback_type callback, void *ptr);
363 
364 
365 /**
366   Set the value of a configuration option.
367 
368   The currently available configuration options are:
369 
370     ndots, timeout, max-timeouts, max-inflight, and attempts
371 
372   @param option the name of the configuration option to be modified
373   @param val the value to be set
374   @param flags either 0 | DNS_OPTION_SEARCH | DNS_OPTION_MISC
375   @return 0 if successful, or -1 if an error occurred
376  */
377 int evdns_set_option(const char *option, const char *val, int flags);
378 
379 
380 /**
381   Parse a resolv.conf file.
382 
383   The 'flags' parameter determines what information is parsed from the
384   resolv.conf file. See the man page for resolv.conf for the format of this
385   file.
386 
387   The following directives are not parsed from the file: sortlist, rotate,
388   no-check-names, inet6, debug.
389 
390   If this function encounters an error, the possible return values are: 1 =
391   failed to open file, 2 = failed to stat file, 3 = file too large, 4 = out of
392   memory, 5 = short read from file, 6 = no nameservers listed in the file
393 
394   @param flags any of DNS_OPTION_NAMESERVERS|DNS_OPTION_SEARCH|DNS_OPTION_MISC|
395          DNS_OPTIONS_ALL
396   @param filename the path to the resolv.conf file
397   @return 0 if successful, or various positive error codes if an error
398           occurred (see above)
399   @see resolv.conf(3), evdns_config_windows_nameservers()
400  */
401 int evdns_resolv_conf_parse(int flags, const char *const filename);
402 
403 
404 /**
405   Obtain nameserver information using the Windows API.
406 
407   Attempt to configure a set of nameservers based on platform settings on
408   a win32 host.  Preferentially tries to use GetNetworkParams; if that fails,
409   looks in the registry.
410 
411   @return 0 if successful, or -1 if an error occurred
412   @see evdns_resolv_conf_parse()
413  */
414 #ifdef WIN32
415 int evdns_config_windows_nameservers(void);
416 #endif
417 
418 
419 /**
420   Clear the list of search domains.
421  */
422 void evdns_search_clear(void);
423 
424 
425 /**
426   Add a domain to the list of search domains
427 
428   @param domain the domain to be added to the search list
429  */
430 void evdns_search_add(const char *domain);
431 
432 
433 /**
434   Set the 'ndots' parameter for searches.
435 
436   Sets the number of dots which, when found in a name, causes
437   the first query to be without any search domain.
438 
439   @param ndots the new ndots parameter
440  */
441 void evdns_search_ndots_set(const int ndots);
442 
443 /**
444   A callback that is invoked when a log message is generated
445 
446   @param is_warning indicates if the log message is a 'warning'
447   @param msg the content of the log message
448  */
449 typedef void (*evdns_debug_log_fn_type)(int is_warning, const char *msg);
450 
451 
452 /**
453   Set the callback function to handle log messages.
454 
455   @param fn the callback to be invoked when a log message is generated
456  */
457 void evdns_set_log_fn(evdns_debug_log_fn_type fn);
458 
459 /**
460    Set a callback that will be invoked to generate transaction IDs.  By
461    default, we pick transaction IDs based on the current clock time.
462 
463    @param fn the new callback, or NULL to use the default.
464  */
465 void evdns_set_transaction_id_fn(ev_uint16_t (*fn)(void));
466 
467 #define DNS_NO_SEARCH 1
468 
469 /*
470  * Structures and functions used to implement a DNS server.
471  */
472 
473 struct evdns_server_request {
474 	int flags;
475 	int nquestions;
476 	struct evdns_server_question **questions;
477 };
478 struct evdns_server_question {
479 	int type;
480 #ifdef __cplusplus
481 	int dns_question_class;
482 #else
483 	/* You should refer to this field as "dns_question_class".  The
484 	 * name "class" works in C for backward compatibility, and will be
485 	 * removed in a future version. (1.5 or later). */
486 	int class;
487 #define dns_question_class class
488 #endif
489 	char name[1];
490 };
491 typedef void (*evdns_request_callback_fn_type)(struct evdns_server_request *, void *);
492 #define EVDNS_ANSWER_SECTION 0
493 #define EVDNS_AUTHORITY_SECTION 1
494 #define EVDNS_ADDITIONAL_SECTION 2
495 
496 #define EVDNS_TYPE_A	   1
497 #define EVDNS_TYPE_NS	   2
498 #define EVDNS_TYPE_CNAME   5
499 #define EVDNS_TYPE_SOA	   6
500 #define EVDNS_TYPE_PTR	  12
501 #define EVDNS_TYPE_MX	  15
502 #define EVDNS_TYPE_TXT	  16
503 #define EVDNS_TYPE_AAAA	  28
504 
505 #define EVDNS_QTYPE_AXFR 252
506 #define EVDNS_QTYPE_ALL	 255
507 
508 #define EVDNS_CLASS_INET   1
509 
510 struct evdns_server_port *evdns_add_server_port(int socket, int is_tcp, evdns_request_callback_fn_type callback, void *user_data);
511 void evdns_close_server_port(struct evdns_server_port *port);
512 
513 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);
514 int evdns_server_request_add_a_reply(struct evdns_server_request *req, const char *name, int n, void *addrs, int ttl);
515 int evdns_server_request_add_aaaa_reply(struct evdns_server_request *req, const char *name, int n, void *addrs, int ttl);
516 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);
517 int evdns_server_request_add_cname_reply(struct evdns_server_request *req, const char *name, const char *cname, int ttl);
518 
519 int evdns_server_request_respond(struct evdns_server_request *req, int err);
520 int evdns_server_request_drop(struct evdns_server_request *req);
521 struct sockaddr;
522 int evdns_server_request_get_requesting_addr(struct evdns_server_request *_req, struct sockaddr *sa, int addr_len);
523 
524 #ifdef __cplusplus
525 }
526 #endif
527 
528 #endif  /* !EVENTDNS_H */
529