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# Content
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 /*
51 * Welcome, gentle reader
52 *
53 * Async DNS lookups are really a whole lot harder than they should be,
54 * mostly stemming from the fact that the libc resolver has never been
55 * very good at them. Before you use this library you should see if libc
56 * can do the job for you with the modern async call getaddrinfo_a
57 * (see http://www.imperialviolet.org/page25.html#e498). Otherwise,
58 * please continue.
59 *
60 * This code is based on libevent and you must call event_init before
61 * any of the APIs in this file. You must also seed the OpenSSL random
62 * source if you are using OpenSSL for ids (see below).
63 *
64 * This library is designed to be included and shipped with your source
65 * code. You statically link with it. You should also test for the
66 * existence of strtok_r and define HAVE_STRTOK_R if you have it.
67 *
68 * The DNS protocol requires a good source of id numbers and these
69 * numbers should be unpredictable for spoofing reasons. There are
70 * three methods for generating them here and you must define exactly
71 * one of them. In increasing order of preference:
72 *
73 * DNS_USE_GETTIMEOFDAY_FOR_ID:
74 * Using the bottom 16 bits of the usec result from gettimeofday. This
75 * is a pretty poor solution but should work anywhere.
76 * DNS_USE_CPU_CLOCK_FOR_ID:
77 * Using the bottom 16 bits of the nsec result from the CPU's time
78 * counter. This is better, but may not work everywhere. Requires
79 * POSIX realtime support and you'll need to link against -lrt on
80 * glibc systems at least.
81 * DNS_USE_OPENSSL_FOR_ID:
82 * Uses the OpenSSL RAND_bytes call to generate the data. You must
83 * have seeded the pool before making any calls to this library.
84 *
85 * The library keeps track of the state of nameservers and will avoid
86 * them when they go down. Otherwise it will round robin between them.
87 *
88 * Quick start guide:
89 * #include "evdns.h"
90 * void callback(int result, char type, int count, int ttl,
91 * void *addresses, void *arg);
92 * evdns_resolv_conf_parse(DNS_OPTIONS_ALL, "/etc/resolv.conf");
93 * evdns_resolve("www.hostname.com", 0, callback, NULL);
94 *
95 * When the lookup is complete the callback function is called. The
96 * first argument will be one of the DNS_ERR_* defines in evdns.h.
97 * Hopefully it will be DNS_ERR_NONE, in which case type will be
98 * DNS_IPv4_A, count will be the number of IP addresses, ttl is the time
99 * which the data can be cached for (in seconds), addresses will point
100 * to an array of uint32_t's and arg will be whatever you passed to
101 * evdns_resolve.
102 *
103 * Searching:
104 *
105 * In order for this library to be a good replacement for glibc's resolver it
106 * supports searching. This involves setting a list of default domains, in
107 * which names will be queried for. The number of dots in the query name
108 * determines the order in which this list is used.
109 *
110 * Searching appears to be a single lookup from the point of view of the API,
111 * although many DNS queries may be generated from a single call to
112 * evdns_resolve. Searching can also drastically slow down the resolution
113 * of names.
114 *
115 * To disable searching:
116 * 1. Never set it up. If you never call evdns_resolv_conf_parse or
117 * evdns_search_add then no searching will occur.
118 *
119 * 2. If you do call evdns_resolv_conf_parse then don't pass
120 * DNS_OPTION_SEARCH (or DNS_OPTIONS_ALL, which implies it).
121 *
122 * 3. When calling evdns_resolve, pass the DNS_QUERY_NO_SEARCH flag.
123 *
124 * The order of searches depends on the number of dots in the name. If the
125 * number is greater than the ndots setting then the names is first tried
126 * globally. Otherwise each search domain is appended in turn.
127 *
128 * The ndots setting can either be set from a resolv.conf, or by calling
129 * evdns_search_ndots_set.
130 *
131 * For example, with ndots set to 1 (the default) and a search domain list of
132 * ["myhome.net"]:
133 * Query: www
134 * Order: www.myhome.net, www.
135 *
136 * Query: www.abc
137 * Order: www.abc., www.abc.myhome.net
138 *
139 * API reference:
140 *
141 * int evdns_nameserver_add(unsigned long int address)
142 * Add a nameserver. The address should be an IP address in
143 * network byte order. The type of address is chosen so that
144 * it matches in_addr.s_addr.
145 * Returns non-zero on error.
146 *
147 * int evdns_nameserver_ip_add(const char *ip_as_string)
148 * This wraps the above function by parsing a string as an IP
149 * address and adds it as a nameserver.
150 * Returns non-zero on error
151 *
152 * int evdns_resolve(const char *name, int flags,
153 * evdns_callback_type callback,
154 * void *ptr)
155 * Resolve a name. The name parameter should be a DNS name.
156 * The flags parameter should be 0, or DNS_QUERY_NO_SEARCH
157 * which disables searching for this query. (see defn of
158 * searching above).
159 *
160 * The callback argument is a function which is called when
161 * this query completes and ptr is an argument which is passed
162 * to that callback function.
163 *
164 * Returns non-zero on error
165 *
166 * void evdns_search_clear()
167 * Clears the list of search domains
168 *
169 * void evdns_search_add(const char *domain)
170 * Add a domain to the list of search domains
171 *
172 * void evdns_search_ndots_set(int ndots)
173 * Set the number of dots which, when found in a name, causes
174 * the first query to be without any search domain.
175 *
176 * int evdns_count_nameservers(void)
177 * Return the number of configured nameservers (not necessarily the
178 * number of running nameservers). This is useful for double-checking
179 * whether our calls to the various nameserver configuration functions
180 * have been successful.
181 *
182 * int evdns_clear_nameservers_and_suspend(void)
183 * Remove all currently configured nameservers, and suspend all pending
184 * resolves. Resolves will not necessarily be re-attempted until
185 * evdns_resume() is called.
186 *
187 * int evdns_resume(void)
188 * Re-attempt resolves left in limbo after an earlier call to
189 * evdns_clear_nameservers_and_suspend().
190 *
191 * int evdns_config_windows_nameservers(void)
192 * Attempt to configure a set of nameservers based on platform settings on
193 * a win32 host. Preferentially tries to use GetNetworkParams; if that fails,
194 * looks in the registry. Returns 0 on success, nonzero on failure.
195 *
196 * int evdns_resolv_conf_parse(int flags, const char *filename)
197 * Parse a resolv.conf like file from the given filename.
198 *
199 * See the man page for resolv.conf for the format of this file.
200 * The flags argument determines what information is parsed from
201 * this file:
202 * DNS_OPTION_SEARCH - domain, search and ndots options
203 * DNS_OPTION_NAMESERVERS - nameserver lines
204 * DNS_OPTION_MISC - timeout and attempts options
205 * DNS_OPTIONS_ALL - all of the above
206 * The following directives are not parsed from the file:
207 * sortlist, rotate, no-check-names, inet6, debug
208 *
209 * Returns non-zero on error:
210 * 0 no errors
211 * 1 failed to open file
212 * 2 failed to stat file
213 * 3 file too large
214 * 4 out of memory
215 * 5 short read from file
216 * 6 no nameservers in file
217 *
218 * Internals:
219 *
220 * Requests are kept in two queues. The first is the inflight queue. In
221 * this queue requests have an allocated transaction id and nameserver.
222 * They will soon be transmitted if they haven't already been.
223 *
224 * The second is the waiting queue. The size of the inflight ring is
225 * limited and all other requests wait in waiting queue for space. This
226 * bounds the number of concurrent requests so that we don't flood the
227 * nameserver. Several algorithms require a full walk of the inflight
228 * queue and so bounding its size keeps thing going nicely under huge
229 * (many thousands of requests) loads.
230 *
231 * If a nameserver loses too many requests it is considered down and we
232 * try not to use it. After a while we send a probe to that nameserver
233 * (a lookup for google.com) and, if it replies, we consider it working
234 * again. If the nameserver fails a probe we wait longer to try again
235 * with the next probe.
236 */
237
238 #ifndef EVENTDNS_H
239 #define EVENTDNS_H
240
241 #ifdef __cplusplus
242 extern "C" {
243 #endif
244
245 /* Error codes 0-5 are as described in RFC 1035. */
246 #define DNS_ERR_NONE 0
247 /* The name server was unable to interpret the query */
248 #define DNS_ERR_FORMAT 1
249 /* The name server was unable to process this query due to a problem with the
250 * name server */
251 #define DNS_ERR_SERVERFAILED 2
252 /* The domain name does not exist */
253 #define DNS_ERR_NOTEXIST 3
254 /* The name server does not support the requested kind of query */
255 #define DNS_ERR_NOTIMPL 4
256 /* The name server refuses to reform the specified operation for policy
257 * reasons */
258 #define DNS_ERR_REFUSED 5
259 /* The reply was truncated or ill-formated */
260 #define DNS_ERR_TRUNCATED 65
261 /* An unknown error occurred */
262 #define DNS_ERR_UNKNOWN 66
263 /* Communication with the server timed out */
264 #define DNS_ERR_TIMEOUT 67
265 /* The request was canceled because the DNS subsystem was shut down. */
266 #define DNS_ERR_SHUTDOWN 68
267
268 #define DNS_IPv4_A 1
269 #define DNS_PTR 2
270 #define DNS_IPv6_AAAA 3
271
272 #define DNS_QUERY_NO_SEARCH 1
273
274 #define DNS_OPTION_SEARCH 1
275 #define DNS_OPTION_NAMESERVERS 2
276 #define DNS_OPTION_MISC 4
277 #define DNS_OPTIONS_ALL 7
278
279 /*
280 * The callback that contains the results from a lookup.
281 * - type is either DNS_IPv4_A or DNS_PTR or DNS_IPv6_AAAA
282 * - count contains the number of addresses of form type
283 * - ttl is the number of seconds the resolution may be cached for.
284 * - addresses needs to be cast according to type
285 */
286 typedef void (*evdns_callback_type) (int result, char type, int count, int ttl, void *addresses, void *arg);
287
288 int evdns_init(void);
289 void evdns_shutdown(int fail_requests);
290 const char *evdns_err_to_string(int err);
291 int evdns_nameserver_add(unsigned long int address);
292 int evdns_count_nameservers(void);
293 int evdns_clear_nameservers_and_suspend(void);
294 int evdns_resume(void);
295 int evdns_nameserver_ip_add(const char *ip_as_string);
296 int evdns_resolve_ipv4(const char *name, int flags, evdns_callback_type callback, void *ptr);
297 int evdns_resolve_ipv6(const char *name, int flags, evdns_callback_type callback, void *ptr);
298 struct in_addr;
299 struct in6_addr;
300 int evdns_resolve_reverse(struct in_addr *in, int flags, evdns_callback_type callback, void *ptr);
301 int evdns_resolve_reverse_ipv6(struct in6_addr *in, int flags, evdns_callback_type callback, void *ptr);
302 int evdns_set_option(const char *option, const char *val, int flags);
303 int evdns_resolv_conf_parse(int flags, const char *);
304 #ifdef MS_WINDOWS
305 int evdns_config_windows_nameservers(void);
306 #endif
307 void evdns_search_clear(void);
308 void evdns_search_add(const char *domain);
309 void evdns_search_ndots_set(const int ndots);
310
311 typedef void (*evdns_debug_log_fn_type)(int is_warning, const char *msg);
312 void evdns_set_log_fn(evdns_debug_log_fn_type fn);
313
314 #define DNS_NO_SEARCH 1
315
316 #ifdef __cplusplus
317 }
318 #endif
319
320 /*
321 * Structures and functions used to implement a DNS server.
322 */
323
324 struct evdns_server_request {
325 int flags;
326 int nquestions;
327 struct evdns_server_question **questions;
328 };
329 struct evdns_server_question {
330 int type;
331 int class;
332 char name[1];
333 };
334 typedef void (*evdns_request_callback_fn_type)(struct evdns_server_request *, void *);
335 #define EVDNS_ANSWER_SECTION 0
336 #define EVDNS_AUTHORITY_SECTION 1
337 #define EVDNS_ADDITIONAL_SECTION 2
338
339 #define EVDNS_TYPE_A 1
340 #define EVDNS_TYPE_NS 2
341 #define EVDNS_TYPE_CNAME 5
342 #define EVDNS_TYPE_SOA 6
343 #define EVDNS_TYPE_PTR 12
344 #define EVDNS_TYPE_MX 15
345 #define EVDNS_TYPE_TXT 16
346 #define EVDNS_TYPE_AAAA 28
347
348 #define EVDNS_QTYPE_AXFR 252
349 #define EVDNS_QTYPE_ALL 255
350
351 #define EVDNS_CLASS_INET 1
352
353 struct evdns_server_port *evdns_add_server_port(int socket, int is_tcp, evdns_request_callback_fn_type callback, void *user_data);
354 void evdns_close_server_port(struct evdns_server_port *port);
355
356 int evdns_server_request_add_reply(struct evdns_server_request *req, int section, const char *name, int type, int class, int ttl, int datalen, int is_name, const char *data);
357 int evdns_server_request_add_a_reply(struct evdns_server_request *req, const char *name, int n, void *addrs, int ttl);
358 int evdns_server_request_add_aaaa_reply(struct evdns_server_request *req, const char *name, int n, void *addrs, int ttl);
359 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);
360 int evdns_server_request_add_cname_reply(struct evdns_server_request *req, const char *name, const char *cname, int ttl);
361
362 int evdns_server_request_respond(struct evdns_server_request *req, int err);
363 int evdns_server_request_drop(struct evdns_server_request *req);
364 struct sockaddr;
365 int evdns_server_request_get_requesting_addr(struct evdns_server_request *_req, struct sockaddr *sa, int addr_len);
366
367 #endif /* !EVENTDNS_H */