Asterisk - The Open Source Telephony Project  GIT-master-a1fa8df
srv.c
Go to the documentation of this file.
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 /*** MODULEINFO
33  <support_level>core</support_level>
34  ***/
35 
36 #include "asterisk.h"
37 
38 #include <netinet/in.h>
39 #include <arpa/nameser.h>
40 #ifdef __APPLE__
41 #include <arpa/nameser_compat.h>
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/utils.h"
49 #include "asterisk/linkedlists.h"
50 
51 #ifdef __APPLE__
52 #undef T_SRV
53 #define T_SRV 33
54 #endif
55 
56 struct srv_entry {
57  unsigned short priority;
58  unsigned short weight;
59  unsigned short port;
60  unsigned int weight_sum;
62  char host[1];
63 };
64 
65 struct srv_context {
66  unsigned int have_weights:1;
67  struct srv_entry *prev;
68  unsigned int num_records;
70 };
71 
72 static int parse_srv(unsigned char *answer, int len, unsigned char *msg, struct srv_entry **result)
73 {
74  struct srv {
75  unsigned short priority;
76  unsigned short weight;
77  unsigned short port;
78  } __attribute__((__packed__)) *srv = (struct srv *) answer;
79 
80  int res = 0;
81  char repl[256] = "";
82  struct srv_entry *entry;
83 
84  if (len < sizeof(*srv))
85  return -1;
86 
87  answer += sizeof(*srv);
88  len -= sizeof(*srv);
89 
90  if ((res = dn_expand(msg, answer + len, answer, repl, sizeof(repl) - 1)) <= 0) {
91  ast_log(LOG_WARNING, "Failed to expand hostname\n");
92  return -1;
93  }
94 
95  /* the magic value "." for the target domain means that this service
96  is *NOT* available at the domain we searched */
97  if (!strcmp(repl, "."))
98  return -1;
99 
100  if (!(entry = ast_calloc(1, sizeof(*entry) + strlen(repl))))
101  return -1;
102 
103  entry->priority = ntohs(srv->priority);
104  entry->weight = ntohs(srv->weight);
105  entry->port = ntohs(srv->port);
106  strcpy(entry->host, repl);
107 
108  *result = entry;
109 
110  return 0;
111 }
112 
113 static int srv_callback(void *context, unsigned char *answer, int len, unsigned char *fullanswer)
114 {
115  struct srv_context *c = (struct srv_context *) context;
116  struct srv_entry *entry = NULL;
117  struct srv_entry *current;
118 
119  if (parse_srv(answer, len, fullanswer, &entry))
120  return -1;
121 
122  if (entry->weight)
123  c->have_weights = 1;
124 
125  AST_LIST_TRAVERSE_SAFE_BEGIN(&c->entries, current, list) {
126  /* insert this entry just before the first existing
127  entry with a higher priority */
128  if (current->priority <= entry->priority)
129  continue;
130 
132  entry = NULL;
133  break;
134  }
136 
137  /* if we didn't find a place to insert the entry before an existing
138  entry, then just add it to the end */
139  if (entry)
140  AST_LIST_INSERT_TAIL(&c->entries, entry, list);
141 
142  return 0;
143 }
144 
145 /* Do the bizarre SRV record weight-handling algorithm
146  involving sorting and random number generation...
147 
148  See RFC 2782 if you want know why this code does this
149 */
150 static void process_weights(struct srv_context *context)
151 {
152  struct srv_entry *current;
153  struct srv_entries newlist = AST_LIST_HEAD_NOLOCK_INIT_VALUE;
154 
155  while (AST_LIST_FIRST(&context->entries)) {
156  unsigned int random_weight;
157  unsigned int weight_sum;
158  unsigned short cur_priority = AST_LIST_FIRST(&context->entries)->priority;
159  struct srv_entries temp_list = AST_LIST_HEAD_NOLOCK_INIT_VALUE;
160  weight_sum = 0;
161 
162  AST_LIST_TRAVERSE_SAFE_BEGIN(&context->entries, current, list) {
163  if (current->priority != cur_priority)
164  break;
165 
166  AST_LIST_MOVE_CURRENT(&temp_list, list);
167  }
169 
170  while (AST_LIST_FIRST(&temp_list)) {
171  weight_sum = 0;
172  AST_LIST_TRAVERSE(&temp_list, current, list)
173  current->weight_sum = weight_sum += current->weight;
174 
175  /* if all the remaining entries have weight == 0,
176  then just append them to the result list and quit */
177  if (weight_sum == 0) {
178  AST_LIST_APPEND_LIST(&newlist, &temp_list, list);
179  break;
180  }
181 
182  random_weight = 1 + (unsigned int) ((float) weight_sum * (ast_random() / ((float) RAND_MAX + 1.0)));
183 
184  AST_LIST_TRAVERSE_SAFE_BEGIN(&temp_list, current, list) {
185  if (current->weight < random_weight)
186  continue;
187 
188  AST_LIST_MOVE_CURRENT(&newlist, list);
189  break;
190  }
192  }
193 
194  }
195 
196  /* now that the new list has been ordered,
197  put it in place */
198 
199  AST_LIST_APPEND_LIST(&context->entries, &newlist, list);
200 }
201 
202 int ast_srv_lookup(struct srv_context **context, const char *service, const char **host, unsigned short *port)
203 {
204  struct srv_entry *cur;
205 
206  if (*context == NULL) {
207  if (!(*context = ast_calloc(1, sizeof(struct srv_context)))) {
208  return -1;
209  }
210  AST_LIST_HEAD_INIT_NOLOCK(&(*context)->entries);
211 
212  if (((ast_search_dns(*context, service, C_IN, T_SRV, srv_callback)) < 1) ||
213  AST_LIST_EMPTY(&(*context)->entries)) {
214  ast_free(*context);
215  *context = NULL;
216  return -1;
217  }
218 
219  if ((*context)->have_weights) {
220  process_weights(*context);
221  }
222 
223  (*context)->prev = AST_LIST_FIRST(&(*context)->entries);
224  *host = (*context)->prev->host;
225  *port = (*context)->prev->port;
226  AST_LIST_TRAVERSE(&(*context)->entries, cur, list) {
227  ++((*context)->num_records);
228  }
229  return 0;
230  }
231 
232  if (((*context)->prev = AST_LIST_NEXT((*context)->prev, list))) {
233  /* Retrieve next item in result */
234  *host = (*context)->prev->host;
235  *port = (*context)->prev->port;
236  return 0;
237  } else {
238  /* No more results */
239  while ((cur = AST_LIST_REMOVE_HEAD(&(*context)->entries, list))) {
240  ast_free(cur);
241  }
242  ast_free(*context);
243  *context = NULL;
244  return 1;
245  }
246 }
247 
249 {
250  const char *host;
251  unsigned short port;
252 
253  if (*context) {
254  /* We have a context to clean up. */
255  while (!(ast_srv_lookup(context, NULL, &host, &port))) {
256  }
257  }
258 }
259 
260 int ast_get_srv(struct ast_channel *chan, char *host, int hostlen, int *port, const char *service)
261 {
262  struct srv_context context = { .entries = AST_LIST_HEAD_NOLOCK_INIT_VALUE };
263  struct srv_entry *current;
264  int ret;
265 
266  if (chan && ast_autoservice_start(chan) < 0) {
267  return -1;
268  }
269 
270  ret = ast_search_dns(&context, service, C_IN, T_SRV, srv_callback);
271 
272  if (context.have_weights) {
273  process_weights(&context);
274  }
275 
276  if (chan) {
277  ret |= ast_autoservice_stop(chan);
278  }
279 
280  /* TODO: there could be a "." entry in the returned list of
281  answers... if so, this requires special handling */
282 
283  /* the list of entries will be sorted in the proper selection order
284  already, so we just need the first one (if any) */
285 
286  if ((ret > 0) && (current = AST_LIST_REMOVE_HEAD(&context.entries, list))) {
287  ast_copy_string(host, current->host, hostlen);
288  *port = current->port;
289  ast_free(current);
290  ast_debug(4, "ast_get_srv: SRV lookup for '%s' mapped to host %s, port %d\n",
291  service, host, *port);
292  } else {
293  host[0] = '\0';
294  *port = -1;
295  }
296 
297  while ((current = AST_LIST_REMOVE_HEAD(&context.entries, list))) {
298  ast_free(current);
299  }
300 
301  return ret;
302 }
303 
305 {
306  return context->num_records;
307 }
308 
309 int ast_srv_get_nth_record(struct srv_context *context, int record_num, const char **host,
310  unsigned short *port, unsigned short *priority, unsigned short *weight)
311 {
312  int i = 1;
313  int res = -1;
314  struct srv_entry *entry;
315 
316  if (record_num < 1 || record_num > context->num_records) {
317  return res;
318  }
319 
320  AST_LIST_TRAVERSE(&context->entries, entry, list) {
321  if (i == record_num) {
322  *host = entry->host;
323  *port = entry->port;
324  *priority = entry->priority;
325  *weight = entry->weight;
326  res = 0;
327  break;
328  }
329  ++i;
330  }
331 
332  return res;
333 }
unsigned int have_weights
Definition: srv.c:66
Main Channel structure associated with a channel.
struct srv_entry * prev
Definition: srv.c:67
void ast_srv_cleanup(struct srv_context **context)
Cleanup resources associated with ast_srv_lookup.
Definition: srv.c:248
Asterisk main include file. File version handling, generic pbx functions.
#define AST_LIST_FIRST(head)
Returns the first entry contained in a list.
Definition: linkedlists.h:420
int ast_autoservice_start(struct ast_channel *chan)
Automatically service a channel for us...
Definition: autoservice.c:200
char host[1]
Definition: srv.c:62
#define LOG_WARNING
Definition: logger.h:274
static void process_weights(struct srv_context *context)
Definition: srv.c:150
Support for DNS SRV records, used in to locate SIP services.
int ast_search_dns(void *context, const char *dname, int class, int type, int(*callback)(void *context, unsigned char *answer, int len, unsigned char *fullanswer))
Perform DNS lookup (used by DNS, enum and SRV lookups)
Definition: dns.c:493
unsigned int weight_sum
Definition: srv.c:60
#define AST_LIST_NEXT(elm, field)
Returns the next entry in the list after the given entry.
Definition: linkedlists.h:438
enum ast_cc_service_type service
Definition: chan_sip.c:953
#define AST_LIST_EMPTY(head)
Checks whether the specified list contains any entries.
Definition: linkedlists.h:449
static struct test_val c
#define NULL
Definition: resample.c:96
#define AST_LIST_TRAVERSE_SAFE_END
Closes a safe loop traversal block.
Definition: linkedlists.h:614
unsigned short port
Definition: srv.c:59
Utility functions.
struct srv_context::srv_entries entries
#define ast_debug(level,...)
Log a DEBUG message.
Definition: logger.h:444
#define ast_log
Definition: astobj2.c:42
General Asterisk PBX channel definitions.
long int ast_random(void)
Definition: main/utils.c:2064
A set of macros to manage forward-linked lists.
#define AST_LIST_REMOVE_HEAD(head, field)
Removes and returns the head entry from a list.
Definition: linkedlists.h:832
AST_LIST_HEAD_NOLOCK(contactliststruct, contact)
static int answer(void *data)
Definition: chan_pjsip.c:682
struct srv_entry::@407 list
#define AST_LIST_MOVE_CURRENT(newhead, field)
Move the current list entry to another list.
Definition: linkedlists.h:581
int ast_autoservice_stop(struct ast_channel *chan)
Stop servicing a channel for us...
Definition: autoservice.c:266
#define AST_LIST_INSERT_TAIL(head, elm, field)
Appends a list entry to the tail of a list.
Definition: linkedlists.h:730
static int len(struct ast_channel *chan, const char *cmd, char *data, char *buf, size_t buflen)
unsigned short priority
Definition: srv.c:57
unsigned int num_records
Definition: srv.c:68
static int parse_srv(unsigned char *answer, int len, unsigned char *msg, struct srv_entry **result)
Definition: srv.c:72
#define AST_LIST_TRAVERSE(head, var, field)
Loops over (traverses) the entries in a list.
Definition: linkedlists.h:490
#define AST_LIST_ENTRY(type)
Declare a forward link structure inside a list entry.
Definition: linkedlists.h:409
Definition: srv.c:56
#define ast_free(a)
Definition: astmm.h:182
#define ast_calloc(num, len)
A wrapper for calloc()
Definition: astmm.h:204
#define AST_LIST_HEAD_NOLOCK_INIT_VALUE
Defines initial values for a declaration of AST_LIST_HEAD_NOLOCK.
Definition: linkedlists.h:251
unsigned int ast_srv_get_record_count(struct srv_context *context)
Get the number of records for a given SRV context.
Definition: srv.c:304
#define AST_LIST_HEAD_INIT_NOLOCK(head)
Initializes a list head structure.
Definition: linkedlists.h:680
void ast_copy_string(char *dst, const char *src, size_t size)
Size-limited null-terminating string copy.
Definition: strings.h:401
static PGresult * result
Definition: cel_pgsql.c:88
int ast_srv_lookup(struct srv_context **context, const char *service, const char **host, unsigned short *port)
Retrieve set of SRV lookups, in order.
Definition: srv.c:202
Definition: search.h:40
#define AST_LIST_TRAVERSE_SAFE_BEGIN(head, var, field)
Loops safely over (traverses) the entries in a list.
Definition: linkedlists.h:528
static char context[AST_MAX_CONTEXT]
Definition: chan_alsa.c:120
static int srv_callback(void *context, unsigned char *answer, int len, unsigned char *fullanswer)
Definition: srv.c:113
#define AST_LIST_INSERT_BEFORE_CURRENT(elm, field)
Inserts a list entry before the current entry during a traversal.
Definition: linkedlists.h:598
int ast_srv_get_nth_record(struct srv_context *context, int record_num, const char **host, unsigned short *port, unsigned short *priority, unsigned short *weight)
Retrieve details from a specific SRV record.
Definition: srv.c:309
int ast_get_srv(struct ast_channel *chan, char *host, int hostlen, int *port, const char *service)
Lookup entry in SRV records Returns 1 if found, 0 if not found, -1 on hangup.
Definition: srv.c:260
DNS support for Asterisk.
unsigned short weight
Definition: srv.c:58
#define AST_LIST_APPEND_LIST(head, list, field)
Appends a whole list to the tail of a list.
Definition: linkedlists.h:782