aboutsummaryrefslogtreecommitdiff
path: root/src/or/eventdns.h
blob: bf3b64d08a873ab3ca027d7d8da5c36074c94931 (plain)
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
159
160
161
162
163
164
165
166
167
168
169
170
171
172
173
174
175
176
177
178
179
180
181
182
183
184
185
186
187
188
189
190
191
192
193
194
195
196
197
198
199
200
201
202
203
204
205
206
207
208
209
210
211
212
213
214
215
216
217
218
219
220
221
222
223
224
225
226
227
228
229
230
231
232
233
234
235
236
237
238
239
240
241
242
243
244
245
246
247
248
249
250
251
252
253
254
255
256
257
258
259
260
261
262
263
264
265
266
267
268
269
270
271
272
273
274
275
276
277
278
279
280
281
282
283
284
285
286
287
288
289
290
291
292
293
294
295
296
297
298
299
300
301
302
303
304
305
306
307
308
309
310
311
312
313
314
315
316
317
318
319
320
321
322
323
324
325
326
327
328
329
330
331
332
333
334
335
336
337
/*
 * The original DNS code is due to Adam Langley with heavy
 * modifications by Nick Mathewson.  Adam put his DNS software in the
 * public domain.  You can find his original copyright below.  Please,
 * aware that the code as part of libevent is governed by the 3-clause
 * BSD license above.
 *
 * This software is Public Domain. To view a copy of the public domain dedication,
 * visit http://creativecommons.org/licenses/publicdomain/ or send a letter to
 * Creative Commons, 559 Nathan Abbott Way, Stanford, California 94305, USA.
 *
 * I ask and expect, but do not require, that all derivative works contain an
 * attribution similar to:
 *	Parts developed by Adam Langley <agl@imperialviolet.org>
 *
 * You may wish to replace the word "Parts" with something else depending on
 * the amount of original code.
 *
 * (Derivative works does not include programs which link against, run or include
 * the source verbatim in their source distributions)
 */

/*
 * Welcome, gentle reader
 *
 * Async DNS lookups are really a whole lot harder than they should be,
 * mostly stemming from the fact that the libc resolver has never been
 * very good at them. Before you use this library you should see if libc
 * can do the job for you with the modern async call getaddrinfo_a
 * (see http://www.imperialviolet.org/page25.html#e498). Otherwise,
 * please continue.
 *
 * This code is based on libevent and you must call event_init before
 * any of the APIs in this file. You must also seed the OpenSSL random
 * source if you are using OpenSSL for ids (see below).
 *
 * This library is designed to be included and shipped with your source
 * code. You statically link with it. You should also test for the
 * existence of strtok_r and define HAVE_STRTOK_R if you have it.
 *
 * The DNS protocol requires a good source of id numbers and these
 * numbers should be unpredictable for spoofing reasons. There are
 * three methods for generating them here and you must define exactly
 * one of them. In increasing order of preference:
 *
 * DNS_USE_GETTIMEOFDAY_FOR_ID:
 *   Using the bottom 16 bits of the usec result from gettimeofday. This
 *   is a pretty poor solution but should work anywhere.
 * DNS_USE_CPU_CLOCK_FOR_ID:
 *  Using the bottom 16 bits of the nsec result from the CPU's time
 *  counter. This is better, but may not work everywhere. Requires
 *  POSIX realtime support and you'll need to link against -lrt on
 *  glibc systems at least.
 * DNS_USE_OPENSSL_FOR_ID:
 *  Uses the OpenSSL RAND_bytes call to generate the data. You must
 *  have seeded the pool before making any calls to this library.
 *
 * The library keeps track of the state of nameservers and will avoid
 * them when they go down. Otherwise it will round robin between them.
 *
 * Quick start guide:
 *	 #include "evdns.h"
 *	 void callback(int result, char type, int count, int ttl,
 *     void *addresses, void *arg);
 *	 evdns_resolv_conf_parse(DNS_OPTIONS_ALL, "/etc/resolv.conf");
 *	 evdns_resolve("www.hostname.com", 0, callback, NULL);
 *
 * When the lookup is complete the callback function is called. The
 * first argument will be one of the DNS_ERR_* defines in evdns.h.
 * Hopefully it will be DNS_ERR_NONE, in which case type will be
 * DNS_IPv4_A, count will be the number of IP addresses, ttl is the time
 * which the data can be cached for (in seconds), addresses will point
 * to an array of uint32_t's and arg will be whatever you passed to
 * evdns_resolve.
 *
 * Searching:
 *
 * In order for this library to be a good replacement for glibc's resolver it
 * supports searching. This involves setting a list of default domains, in
 * which names will be queried for. The number of dots in the query name
 * determines the order in which this list is used.
 *
 * Searching appears to be a single lookup from the point of view of the API,
 * although many DNS queries may be generated from a single call to
 * evdns_resolve. Searching can also drastically slow down the resolution
 * of names.
 *
 * To disable searching:
 *	 1. Never set it up. If you never call evdns_resolv_conf_parse or
 *   evdns_search_add then no searching will occur.
 *
 *	 2. If you do call evdns_resolv_conf_parse then don't pass
 *   DNS_OPTION_SEARCH (or DNS_OPTIONS_ALL, which implies it).
 *
 *	 3. When calling evdns_resolve, pass the DNS_QUERY_NO_SEARCH flag.
 *
 * The order of searches depends on the number of dots in the name. If the
 * number is greater than the ndots setting then the names is first tried
 * globally. Otherwise each search domain is appended in turn.
 *
 * The ndots setting can either be set from a resolv.conf, or by calling
 * evdns_search_ndots_set.
 *
 * For example, with ndots set to 1 (the default) and a search domain list of
 * ["myhome.net"]:
 *	Query: www
 *	Order: www.myhome.net, www.
 *
 *	Query: www.abc
 *	Order: www.abc., www.abc.myhome.net
 *
 * API reference:
 *
 * int evdns_nameserver_add(uint32_t address)
 *	 Add a nameserver. The address should be an IP address in
 *	 network byte order. The type of address is chosen so that
 *	 it matches in_addr.s_addr.
 *	 Returns non-zero on error.
 *
 * int evdns_nameserver_ip_add(const char *ip_as_string)
 *	 This wraps the above function by parsing a string as an IP
 *	 address and adds it as a nameserver.
 *	 Returns non-zero on error
 *
 * int evdns_resolve(const char *name, int flags,
 *	      evdns_callback_type callback,
 *	      void *ptr)
 *	 Resolve a name. The name parameter should be a DNS name.
 *	 The flags parameter should be 0, or DNS_QUERY_NO_SEARCH
 *	 which disables searching for this query. (see defn of
 *	 searching above).
 *
 *	 The callback argument is a function which is called when
 *	 this query completes and ptr is an argument which is passed
 *	 to that callback function.
 *
 *	 Returns non-zero on error
 *
 * void evdns_search_clear()
 *	 Clears the list of search domains
 *
 * void evdns_search_add(const char *domain)
 *	 Add a domain to the list of search domains
 *
 * void evdns_search_ndots_set(int ndots)
 *	 Set the number of dots which, when found in a name, causes
 *	 the first query to be without any search domain.
 *
 * int evdns_count_nameservers(void)
 *	 Return the number of configured nameservers (not necessarily the
 *	 number of running nameservers).  This is useful for double-checking
 *	 whether our calls to the various nameserver configuration functions
 *	 have been successful.
 *
 * int evdns_clear_nameservers_and_suspend(void)
 *	 Remove all currently configured nameservers, and suspend all pending
 *	 resolves.	Resolves will not necessarily be re-attempted until
 *	 evdns_resume() is called.
 *
 * int evdns_resume(void)
 *	 Re-attempt resolves left in limbo after an earlier call to
 *	 evdns_clear_nameservers_and_suspend().
 *
 * int evdns_config_windows_nameservers(void)
 *	 Attempt to configure a set of nameservers based on platform settings on
 *	 a win32 host.	Preferentially tries to use GetNetworkParams; if that fails,
 *	 looks in the registry.	 Returns 0 on success, nonzero on failure.
 *
 * int evdns_resolv_conf_parse(int flags, const char *filename)
 *	 Parse a resolv.conf like file from the given filename.
 *
 *	 See the man page for resolv.conf for the format of this file.
 *	 The flags argument determines what information is parsed from
 *	 this file:
 *	   DNS_OPTION_SEARCH - domain, search and ndots options
 *	   DNS_OPTION_NAMESERVERS - nameserver lines
 *	   DNS_OPTION_MISC - timeout and attempts options
 *	   DNS_OPTIONS_ALL - all of the above
 *	 The following directives are not parsed from the file:
 *	   sortlist, rotate, no-check-names, inet6, debug
 *
 *	 Returns non-zero on error:
 *	  0 no errors
 *	  1 failed to open file
 *	  2 failed to stat file
 *	  3 file too large
 *	  4 out of memory
 *	  5 short read from file
 *        6 no nameservers in file
 *
 * Internals:
 *
 * Requests are kept in two queues. The first is the inflight queue. In
 * this queue requests have an allocated transaction id and nameserver.
 * They will soon be transmitted if they haven't already been.
 *
 * The second is the waiting queue. The size of the inflight ring is
 * limited and all other requests wait in waiting queue for space. This
 * bounds the number of concurrent requests so that we don't flood the
 * nameserver. Several algorithms require a full walk of the inflight
 * queue and so bounding its size keeps thing going nicely under huge
 * (many thousands of requests) loads.
 *
 * If a nameserver loses too many requests it is considered down and we
 * try not to use it. After a while we send a probe to that nameserver
 * (a lookup for google.com) and, if it replies, we consider it working
 * again. If the nameserver fails a probe we wait longer to try again
 * with the next probe.
 */

#ifndef _TOR_EVENTDNS_H
#define _TOR_EVENTDNS_H

/* Error codes 0-5 are as described in RFC 1035. */
#define DNS_ERR_NONE 0
/* The name server was unable to interpret the query */
#define DNS_ERR_FORMAT 1
/* The name server was unable to process this query due to a problem with the
 * name server */
#define DNS_ERR_SERVERFAILED 2
/* The domain name does not exist */
#define DNS_ERR_NOTEXIST 3
/* The name server does not support the requested kind of query */
#define DNS_ERR_NOTIMPL 4
/* The name server refuses to reform the specified operation for policy
 * reasons */
#define DNS_ERR_REFUSED 5
/* The reply was truncated or ill-formated */
#define DNS_ERR_TRUNCATED 65
/* An unknown error occurred */
#define DNS_ERR_UNKNOWN 66
/* Communication with the server timed out */
#define DNS_ERR_TIMEOUT 67
/* The request was canceled because the DNS subsystem was shut down. */
#define DNS_ERR_SHUTDOWN 68

#define DNS_IPv4_A 1
#define DNS_PTR 2
#define DNS_IPv6_AAAA 3

#define DNS_QUERY_NO_SEARCH 1

#define DNS_OPTION_SEARCH 1
#define DNS_OPTION_NAMESERVERS 2
#define DNS_OPTION_MISC 4
#define DNS_OPTIONS_ALL 7

/*
 * The callback that contains the results from a lookup.
 * - type is either DNS_IPv4_A or DNS_IPv6_AAAA or DNS_PTR
 * - count contains the number of addresses of form type
 * - ttl is the number of seconds the resolution may be cached for.
 * - addresses needs to be cast according to type
 */
typedef void (*evdns_callback_type) (int result, char type, int count, int ttl, void *addresses, void *arg);

int evdns_init(void);
void evdns_shutdown(int fail_requests);
const char *evdns_err_to_string(int err);
int evdns_nameserver_add(uint32_t address);
int evdns_count_nameservers(void);
int evdns_clear_nameservers_and_suspend(void);
int evdns_resume(void);
int evdns_nameserver_ip_add(const char *ip_as_string);
int evdns_nameserver_sockaddr_add(const struct sockaddr *sa, socklen_t len);
void evdns_set_default_outgoing_bind_address(const struct sockaddr *addr, socklen_t addrlen);
int evdns_resolve_ipv4(const char *name, int flags, evdns_callback_type callback, void *ptr);
int evdns_resolve_ipv6(const char *name, int flags, evdns_callback_type callback, void *ptr);
struct in_addr;
struct in6_addr;
int evdns_resolve_reverse(const struct in_addr *in, int flags, evdns_callback_type callback, void *ptr);
int evdns_resolve_reverse_ipv6(const struct in6_addr *in, int flags, evdns_callback_type callback, void *ptr);
int evdns_set_option(const char *option, const char *val, int flags);
int evdns_resolv_conf_parse(int flags, const char *);
#ifdef MS_WINDOWS
int evdns_config_windows_nameservers(void);
#endif
void evdns_search_clear(void);
void evdns_search_add(const char *domain);
void evdns_search_ndots_set(const int ndots);

typedef void (*evdns_debug_log_fn_type)(int is_warning, const char *msg);
void evdns_set_log_fn(evdns_debug_log_fn_type fn);

void evdns_set_transaction_id_fn(uint16_t (*fn)(void));
void evdns_set_random_bytes_fn(void (*fn)(char *, size_t));

#define DNS_NO_SEARCH 1

/* Structures and functions used to implement a DNS server. */

struct evdns_server_request {
	int flags;
	int nquestions;
	struct evdns_server_question **questions;
};
struct evdns_server_question {
	int type;
	int dns_question_class;
	char name[1];
};
typedef void (*evdns_request_callback_fn_type)(struct evdns_server_request *, void *);
#define EVDNS_ANSWER_SECTION 0
#define EVDNS_AUTHORITY_SECTION 1
#define EVDNS_ADDITIONAL_SECTION 2

#define EVDNS_TYPE_A	   1
#define EVDNS_TYPE_NS	   2
#define EVDNS_TYPE_CNAME   5
#define EVDNS_TYPE_SOA	   6
#define EVDNS_TYPE_PTR	  12
#define EVDNS_TYPE_MX	  15
#define EVDNS_TYPE_TXT	  16
#define EVDNS_TYPE_AAAA	  28

#define EVDNS_QTYPE_AXFR 252
#define EVDNS_QTYPE_ALL	 255

#define EVDNS_CLASS_INET   1

struct evdns_server_port *evdns_add_server_port(int socket, int is_tcp, evdns_request_callback_fn_type callback, void *user_data);
void evdns_close_server_port(struct evdns_server_port *port);

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);
int evdns_server_request_add_a_reply(struct evdns_server_request *req, const char *name, int n, void *addrs, int ttl);
int evdns_server_request_add_aaaa_reply(struct evdns_server_request *req, const char *name, int n, void *addrs, int ttl);
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);
int evdns_server_request_add_cname_reply(struct evdns_server_request *req, const char *name, const char *cname, int ttl);

struct sockaddr;
int evdns_server_request_get_requesting_addr(struct evdns_server_request *req, struct sockaddr *sa, int addr_len);

int evdns_server_request_respond(struct evdns_server_request *req, int err);
int evdns_server_request_drop(struct evdns_server_request *req);

#endif	// !EVENTDNS_H