Wed Jan 8 2020 09:50:21

Asterisk developer's documentation


srv.h File Reference

Support for DNS SRV records, used in to locate SIP services. More...

Go to the source code of this file.

Functions

int ast_get_srv (struct ast_channel *chan, char *host, int hostlen, int *port, const char *service)
 
void ast_srv_cleanup (struct srv_context **context)
 Cleanup resources associated with ast_srv_lookup. More...
 
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. More...
 
unsigned int ast_srv_get_record_count (struct srv_context *context)
 Get the number of records for a given SRV context. More...
 
int ast_srv_lookup (struct srv_context **context, const char *service, const char **host, unsigned short *port)
 Retrieve set of SRV lookups, in order. More...
 

Detailed Description

Support for DNS SRV records, used in to locate SIP services.

Note
Note: This SRV record support will respect the priority and weight elements of the records that are returned, but there are no provisions for retrying or failover between records.

Definition in file srv.h.

Function Documentation

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 Only do SRV record lookup if you get a domain without a port. If you get a port #, it's a DNS host name.

Parameters
chanAst channel
hosthost name (return value)
hostlenLength of string "host"
portPort number (return value)
serviceService tag for SRV lookup (like "_sip._udp" or "_stun._udp"

Definition at line 263 of file srv.c.

References ast_autoservice_start(), ast_autoservice_stop(), ast_copy_string(), ast_free, AST_LIST_HEAD_NOLOCK_INIT_VALUE, AST_LIST_REMOVE_HEAD, ast_search_dns(), ast_verb, srv_context::entries, srv_context::have_weights, srv_entry::host, srv_entry::port, process_weights(), and srv_callback().

Referenced by ast_get_ip_or_srv(), and create_addr().

264 {
265  struct srv_context context = { .entries = AST_LIST_HEAD_NOLOCK_INIT_VALUE };
266  struct srv_entry *current;
267  int ret;
268 
269  if (chan && ast_autoservice_start(chan) < 0) {
270  return -1;
271  }
272 
273  ret = ast_search_dns(&context, service, C_IN, T_SRV, srv_callback);
274 
275  if (context.have_weights) {
276  process_weights(&context);
277  }
278 
279  if (chan) {
280  ret |= ast_autoservice_stop(chan);
281  }
282 
283  /* TODO: there could be a "." entry in the returned list of
284  answers... if so, this requires special handling */
285 
286  /* the list of entries will be sorted in the proper selection order
287  already, so we just need the first one (if any) */
288 
289  if ((ret > 0) && (current = AST_LIST_REMOVE_HEAD(&context.entries, list))) {
290  ast_copy_string(host, current->host, hostlen);
291  *port = current->port;
292  ast_free(current);
293  ast_verb(4, "ast_get_srv: SRV lookup for '%s' mapped to host %s, port %d\n",
294  service, host, *port);
295  } else {
296  host[0] = '\0';
297  *port = -1;
298  }
299 
300  while ((current = AST_LIST_REMOVE_HEAD(&context.entries, list))) {
301  ast_free(current);
302  }
303 
304  return ret;
305 }
unsigned int have_weights
Definition: srv.c:70
int ast_autoservice_start(struct ast_channel *chan)
Automatically service a channel for us...
Definition: autoservice.c:179
char host[1]
Definition: srv.c:66
struct srv_entry::@300 list
static void process_weights(struct srv_context *context)
Definition: srv.c:154
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:259
enum ast_cc_service_type service
Definition: chan_sip.c:821
#define ast_verb(level,...)
Definition: logger.h:243
unsigned short port
Definition: srv.c:63
struct srv_context::srv_entries entries
#define AST_LIST_REMOVE_HEAD(head, field)
Removes and returns the head entry from a list.
Definition: linkedlists.h:818
int ast_autoservice_stop(struct ast_channel *chan)
Stop servicing a channel for us...
Definition: autoservice.c:238
Definition: srv.c:60
#define ast_free(a)
Definition: astmm.h:97
#define AST_LIST_HEAD_NOLOCK_INIT_VALUE
Defines initial values for a declaration of AST_LIST_HEAD_NOLOCK.
Definition: linkedlists.h:251
void ast_copy_string(char *dst, const char *src, size_t size)
Size-limited null-terminating string copy.
Definition: strings.h:223
static char context[AST_MAX_CONTEXT]
Definition: chan_alsa.c:107
static int srv_callback(void *context, unsigned char *answer, int len, unsigned char *fullanswer)
Definition: srv.c:117
void ast_srv_cleanup ( struct srv_context **  context)

Cleanup resources associated with ast_srv_lookup.

Parameters
contextPointer passed into ast_srv_lookup

Definition at line 251 of file srv.c.

References ast_srv_lookup(), srv_entry::host, and srv_entry::port.

Referenced by launch_ha_netscript(), srds_destroy_cb(), and srv_datastore_setup().

252 {
253  const char *host;
254  unsigned short port;
255 
256  if (*context) {
257  /* We have a context to clean up. */
258  while (!(ast_srv_lookup(context, NULL, &host, &port))) {
259  }
260  }
261 }
char host[1]
Definition: srv.c:66
unsigned short port
Definition: srv.c:63
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:206
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.

After calling ast_srv_lookup, the srv_context will contain the data from several records. You can retrieve the data of a specific one by asking for a specific record number. The records are sorted based on priority and secondarily based on weight. See RFC 2782 for the exact sorting rules.

Parameters
contextThe context returned by ast_srv_lookup
record_numThe 1-indexed record number to retrieve
[out]hostThe host portion of the record
[out]portThe port portion of the record
[out]priorityThe priority portion of the record
[out]weightThe weight portion of the record
Return values
-1Failed to retrieve information. Likely due to an out of range record_num
0Success

Definition at line 312 of file srv.c.

References AST_LIST_TRAVERSE, srv_context::entries, srv_entry::host, srv_context::num_records, srv_entry::port, srv_entry::priority, and srv_entry::weight.

Referenced by srv_result_read().

314 {
315  int i = 1;
316  int res = -1;
317  struct srv_entry *entry;
318 
319  if (record_num < 1 || record_num > context->num_records) {
320  return res;
321  }
322 
323  AST_LIST_TRAVERSE(&context->entries, entry, list) {
324  if (i == record_num) {
325  *host = entry->host;
326  *port = entry->port;
327  *priority = entry->priority;
328  *weight = entry->weight;
329  res = 0;
330  break;
331  }
332  ++i;
333  }
334 
335  return res;
336 }
char host[1]
Definition: srv.c:66
struct srv_entry::@300 list
unsigned short port
Definition: srv.c:63
struct srv_context::srv_entries entries
unsigned short priority
Definition: srv.c:61
unsigned int num_records
Definition: srv.c:72
#define AST_LIST_TRAVERSE(head, var, field)
Loops over (traverses) the entries in a list.
Definition: linkedlists.h:490
Definition: srv.c:60
unsigned short weight
Definition: srv.c:62
unsigned int ast_srv_get_record_count ( struct srv_context context)

Get the number of records for a given SRV context.

This is meant to be used after calling ast_srv_lookup, so that one may retrieve the number of records returned during a specific SRV lookup.

Parameters
contextThe context returned by ast_srv_lookup
Returns
Number of records in context

Definition at line 307 of file srv.c.

References srv_context::num_records.

Referenced by srv_result_read().

308 {
309  return context->num_records;
310 }
unsigned int num_records
Definition: srv.c:72
int ast_srv_lookup ( struct srv_context **  context,
const char *  service,
const char **  host,
unsigned short *  port 
)

Retrieve set of SRV lookups, in order.

Parameters
[in]contextA pointer in which to hold the result
[in]serviceThe service name to look up
[out]hostResult host
[out]portAssociated TCP portnum
Return values
-1Query failed
0Result exists in host and port
1No more results

Definition at line 206 of file srv.c.

References ast_calloc, ast_free, AST_LIST_FIRST, AST_LIST_HEAD_INIT_NOLOCK, AST_LIST_NEXT, AST_LIST_REMOVE_HEAD, AST_LIST_TRAVERSE, ast_search_dns(), process_weights(), and srv_callback().

Referenced by ast_srv_cleanup(), launch_ha_netscript(), and srv_datastore_setup().

207 {
208  struct srv_entry *cur;
209 
210  if (*context == NULL) {
211  if (!(*context = ast_calloc(1, sizeof(struct srv_context)))) {
212  return -1;
213  }
214  AST_LIST_HEAD_INIT_NOLOCK(&(*context)->entries);
215 
216  if ((ast_search_dns(*context, service, C_IN, T_SRV, srv_callback)) < 0) {
217  ast_free(*context);
218  *context = NULL;
219  return -1;
220  }
221 
222  if ((*context)->have_weights) {
223  process_weights(*context);
224  }
225 
226  (*context)->prev = AST_LIST_FIRST(&(*context)->entries);
227  *host = (*context)->prev->host;
228  *port = (*context)->prev->port;
229  AST_LIST_TRAVERSE(&(*context)->entries, cur, list) {
230  ++((*context)->num_records);
231  }
232  return 0;
233  }
234 
235  if (((*context)->prev = AST_LIST_NEXT((*context)->prev, list))) {
236  /* Retrieve next item in result */
237  *host = (*context)->prev->host;
238  *port = (*context)->prev->port;
239  return 0;
240  } else {
241  /* No more results */
242  while ((cur = AST_LIST_REMOVE_HEAD(&(*context)->entries, list))) {
243  ast_free(cur);
244  }
245  ast_free(*context);
246  *context = NULL;
247  return 1;
248  }
249 }
#define AST_LIST_FIRST(head)
Returns the first entry contained in a list.
Definition: linkedlists.h:420
char host[1]
Definition: srv.c:66
struct srv_entry::@300 list
static void process_weights(struct srv_context *context)
Definition: srv.c:154
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:259
#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:821
unsigned short port
Definition: srv.c:63
#define AST_LIST_REMOVE_HEAD(head, field)
Removes and returns the head entry from a list.
Definition: linkedlists.h:818
#define AST_LIST_TRAVERSE(head, var, field)
Loops over (traverses) the entries in a list.
Definition: linkedlists.h:490
Definition: srv.c:60
#define ast_free(a)
Definition: astmm.h:97
#define AST_LIST_HEAD_INIT_NOLOCK(head)
Initializes a list head structure.
Definition: linkedlists.h:666
#define ast_calloc(a, b)
Definition: astmm.h:82
static int srv_callback(void *context, unsigned char *answer, int len, unsigned char *fullanswer)
Definition: srv.c:117