another bunch of include removals (errno.h and asterisk/logger.h)
[asterisk/asterisk.git] / main / srv.c
1 /*
2  * Asterisk -- An open source telephony toolkit.
3  *
4  * Copyright (C) 1999 - 2005, Digium, Inc.
5  *
6  * Mark Spencer <markster@digium.com>
7  *
8  * Funding provided by nic.at
9  *
10  * See http://www.asterisk.org for more information about
11  * the Asterisk project. Please do not directly contact
12  * any of the maintainers of this project for assistance;
13  * the project provides a web site, mailing lists and IRC
14  * channels for your use.
15  *
16  * This program is free software, distributed under the terms of
17  * the GNU General Public License Version 2. See the LICENSE file
18  * at the top of the source tree.
19  */
20
21 /*! \file
22  *
23  * \brief DNS SRV Record Lookup Support for Asterisk
24  *
25  * \author Mark Spencer <markster@digium.com>
26  * 
27  * \arg See also \ref AstENUM
28  *
29  * \note Funding provided by nic.at
30  */
31
32 #include "asterisk.h"
33
34 ASTERISK_FILE_VERSION(__FILE__, "$Revision$")
35
36 #include <netinet/in.h>
37 #include <arpa/nameser.h>
38 #ifdef __APPLE__
39 #if __APPLE_CC__ >= 1495
40 #include <arpa/nameser_compat.h>
41 #endif
42 #endif
43 #include <resolv.h>
44
45 #include "asterisk/channel.h"
46 #include "asterisk/srv.h"
47 #include "asterisk/dns.h"
48 #include "asterisk/options.h"
49 #include "asterisk/utils.h"
50 #include "asterisk/linkedlists.h"
51
52 #ifdef __APPLE__
53 #undef T_SRV
54 #define T_SRV 33
55 #endif
56
57 struct srv_entry {
58         unsigned short priority;
59         unsigned short weight;
60         unsigned short port;
61         unsigned int weight_sum;
62         AST_LIST_ENTRY(srv_entry) list;
63         char host[1];
64 };
65
66 struct srv_context {
67         unsigned int have_weights:1;
68         AST_LIST_HEAD_NOLOCK(srv_entries, srv_entry) entries;
69 };
70
71 static int parse_srv(unsigned char *answer, int len, unsigned char *msg, struct srv_entry **result)
72 {
73         struct srv {
74                 unsigned short priority;
75                 unsigned short weight;
76                 unsigned short port;
77         } __attribute__ ((__packed__)) *srv = (struct srv *) answer;
78
79         int res = 0;
80         char repl[256] = "";
81         struct srv_entry *entry;
82
83         if (len < sizeof(*srv))
84                 return -1;
85
86         answer += sizeof(*srv);
87         len -= sizeof(*srv);
88
89         if ((res = dn_expand(msg, answer + len, answer, repl, sizeof(repl) - 1)) <= 0) {
90                 ast_log(LOG_WARNING, "Failed to expand hostname\n");
91                 return -1;
92         }
93
94         /* the magic value "." for the target domain means that this service
95            is *NOT* available at the domain we searched */
96         if (!strcmp(repl, "."))
97                 return -1;
98
99         if (!(entry = ast_calloc(1, sizeof(*entry) + strlen(repl))))
100                 return -1;
101         
102         entry->priority = ntohs(srv->priority);
103         entry->weight = ntohs(srv->weight);
104         entry->port = ntohs(srv->port);
105         strcpy(entry->host, repl);
106
107         *result = entry;
108         
109         return 0;
110 }
111
112 static int srv_callback(void *context, unsigned char *answer, int len, unsigned char *fullanswer)
113 {
114         struct srv_context *c = (struct srv_context *) context;
115         struct srv_entry *entry = NULL;
116         struct srv_entry *current;
117
118         if (parse_srv(answer, len, fullanswer, &entry))
119                 return -1;
120
121         if (entry->weight)
122                 c->have_weights = 1;
123
124         AST_LIST_TRAVERSE_SAFE_BEGIN(&c->entries, current, list) {
125                 /* insert this entry just before the first existing
126                    entry with a higher priority */
127                 if (current->priority <= entry->priority)
128                         continue;
129
130                 AST_LIST_INSERT_BEFORE_CURRENT(entry, list);
131                 entry = NULL;
132                 break;
133         }
134         AST_LIST_TRAVERSE_SAFE_END;
135
136         /* if we didn't find a place to insert the entry before an existing
137            entry, then just add it to the end */
138         if (entry)
139                 AST_LIST_INSERT_TAIL(&c->entries, entry, list);
140
141         return 1;
142 }
143
144 /* Do the bizarre SRV record weight-handling algorithm
145    involving sorting and random number generation...
146
147    See RFC 2782 if you want know why this code does this
148 */
149 static void process_weights(struct srv_context *context)
150 {
151         struct srv_entry *current;
152         struct srv_entries newlist = AST_LIST_HEAD_NOLOCK_INIT_VALUE;
153
154         while (AST_LIST_FIRST(&context->entries)) {
155                 unsigned int random_weight;
156                 unsigned int weight_sum;
157                 unsigned short cur_priority = AST_LIST_FIRST(&context->entries)->priority;
158                 struct srv_entries temp_list = AST_LIST_HEAD_NOLOCK_INIT_VALUE;
159                 weight_sum = 0;
160
161                 AST_LIST_TRAVERSE_SAFE_BEGIN(&context->entries, current, list) {
162                         if (current->priority != cur_priority)
163                                 break;
164
165                         AST_LIST_MOVE_CURRENT(&temp_list, list);
166                 }
167                 AST_LIST_TRAVERSE_SAFE_END;
168
169                 while (AST_LIST_FIRST(&temp_list)) {
170                         weight_sum = 0;
171                         AST_LIST_TRAVERSE(&temp_list, current, list)
172                                 current->weight_sum = weight_sum += current->weight;
173
174                         /* if all the remaining entries have weight == 0,
175                            then just append them to the result list and quit */
176                         if (weight_sum == 0) {
177                                 AST_LIST_APPEND_LIST(&newlist, &temp_list, list);
178                                 break;
179                         }
180
181                         random_weight = 1 + (unsigned int) ((float) weight_sum * (ast_random() / ((float) RAND_MAX + 1.0)));
182
183                         AST_LIST_TRAVERSE_SAFE_BEGIN(&temp_list, current, list) {
184                                 if (current->weight < random_weight)
185                                         continue;
186
187                                 AST_LIST_MOVE_CURRENT(&newlist, list);
188                                 break;
189                         }
190                         AST_LIST_TRAVERSE_SAFE_END;
191                 }
192
193         }
194
195         /* now that the new list has been ordered,
196            put it in place */
197
198         AST_LIST_APPEND_LIST(&context->entries, &newlist, list);
199 }
200
201 int ast_get_srv(struct ast_channel *chan, char *host, int hostlen, int *port, const char *service)
202 {
203         struct srv_context context = { .entries = AST_LIST_HEAD_NOLOCK_INIT_VALUE };
204         struct srv_entry *current;
205         int ret;
206
207         if (chan && ast_autoservice_start(chan) < 0)
208                 return -1;
209
210         ret = ast_search_dns(&context, service, C_IN, T_SRV, srv_callback);
211
212         if (context.have_weights)
213                 process_weights(&context);
214
215         if (chan)
216                 ret |= ast_autoservice_stop(chan);
217
218         /* TODO: there could be a "." entry in the returned list of
219            answers... if so, this requires special handling */
220
221         /* the list of entries will be sorted in the proper selection order
222            already, so we just need the first one (if any) */
223
224         if ((ret > 0) && (current = AST_LIST_REMOVE_HEAD(&context.entries, list))) {
225                 ast_copy_string(host, current->host, hostlen);
226                 *port = current->port;
227                 ast_free(current);
228                 if (option_verbose > 3) {
229                         ast_verbose(VERBOSE_PREFIX_3 "ast_get_srv: SRV lookup for '%s' mapped to host %s, port %d\n",
230                                     service, host, *port);
231                 }
232         } else {
233                 host[0] = '\0';
234                 *port = -1;
235         }
236
237         while ((current = AST_LIST_REMOVE_HEAD(&context.entries, list)))
238                 ast_free(current);
239
240         return ret;
241 }