dns_srv.c File Reference

DNS SRV Record Support. More...

#include "asterisk.h"
#include <netinet/in.h>
#include <arpa/nameser.h>
#include <resolv.h>
#include "asterisk/dns_core.h"
#include "asterisk/dns_srv.h"
#include "asterisk/linkedlists.h"
#include "asterisk/dns_internal.h"
#include "asterisk/utils.h"

Include dependency graph for dns_srv.c:

Go to the source code of this file.

Functions
const char *	ast_dns_srv_get_host (const struct ast_dns_record *record)
	Get the hostname from an SRV record. More...
unsigned short	ast_dns_srv_get_port (const struct ast_dns_record *record)
	Get the port from an SRV record. More...
unsigned short	ast_dns_srv_get_priority (const struct ast_dns_record *record)
	Get the priority from an SRV record. More...
unsigned short	ast_dns_srv_get_weight (const struct ast_dns_record *record)
	Get the weight from an SRV record. More...
struct ast_dns_record *	dns_srv_alloc (struct ast_dns_query *query, const char *data, const size_t size)
	Allocate and parse a DNS SRV record. More...
void	dns_srv_sort (struct ast_dns_result *result)
	Sort the SRV records on a result. More...

Detailed Description

DNS SRV Record Support.

Author

Joshua Colp jcolp.nosp@m.@dig.nosp@m.ium.c.nosp@m.om

Definition in file dns_srv.c.

Function Documentation

ast_dns_srv_get_host()

const char* ast_dns_srv_get_host

(

const struct ast_dns_record *

record

)

Get the hostname from an SRV record.

Parameters

record

The DNS record

Returns

the hostname

Definition at line 188 of file dns_srv.c.

References ast_assert, ast_dns_record_get_rr_type(), and ast_dns_srv_record::host.

Referenced by AST_TEST_DEFINE(), nominal_test(), and sip_resolve_callback().

{
   struct ast_dns_srv_record *srv = (struct ast_dns_srv_record *) record;

   ast_assert(ast_dns_record_get_rr_type(record) == T_SRV);
   return srv->host;
}

ast_dns_srv_get_port()

unsigned short ast_dns_srv_get_port

(

const struct ast_dns_record *

record

)

Get the port from an SRV record.

Parameters

record

The DNS record

Returns

the port

Definition at line 212 of file dns_srv.c.

References ast_assert, ast_dns_record_get_rr_type(), and ast_dns_srv_record::port.

Referenced by AST_TEST_DEFINE(), nominal_test(), and sip_resolve_callback().

{
   struct ast_dns_srv_record *srv = (struct ast_dns_srv_record *) record;

   ast_assert(ast_dns_record_get_rr_type(record) == T_SRV);
   return srv->port;
}

ast_dns_srv_get_priority()

unsigned short ast_dns_srv_get_priority

(

const struct ast_dns_record *

record

)

Get the priority from an SRV record.

Parameters

record

The DNS record

Returns

the priority

Definition at line 196 of file dns_srv.c.

References ast_assert, ast_dns_record_get_rr_type(), and ast_dns_srv_record::priority.

Referenced by AST_TEST_DEFINE(), and nominal_test().

{
   struct ast_dns_srv_record *srv = (struct ast_dns_srv_record *) record;

   ast_assert(ast_dns_record_get_rr_type(record) == T_SRV);
   return srv->priority;
}

ast_dns_srv_get_weight()

unsigned short ast_dns_srv_get_weight

(

const struct ast_dns_record *

record

)

Get the weight from an SRV record.

Parameters

record

The DNS record

Returns

the weight

Definition at line 204 of file dns_srv.c.

References ast_assert, ast_dns_record_get_rr_type(), and ast_dns_srv_record::weight.

Referenced by AST_TEST_DEFINE(), and nominal_test().

{
   struct ast_dns_srv_record *srv = (struct ast_dns_srv_record *) record;

   ast_assert(ast_dns_record_get_rr_type(record) == T_SRV);
   return srv->weight;
}

dns_srv_alloc()

struct ast_dns_record* dns_srv_alloc	(	struct ast_dns_query *	query,
		const char *	data,
		const size_t	size
	)

Allocate and parse a DNS SRV record.

Parameters

query	The DNS query
data	This specific SRV record
size	The size of the SRV record

Return values

non-NULL	success
NULL	failure

Definition at line 42 of file dns_srv.c.

References ast_dns_result::answer, ast_dns_result::answer_size, ast_assert, ast_calloc, ast_copy_string(), ast_log, ast_dns_srv_record::data, ast_dns_record::data_ptr, dns_find_record(), dns_parse_short(), errno, ast_dns_srv_record::generic, host, ast_dns_srv_record::host, LOG_ERROR, NULL, ast_dns_srv_record::port, priority, ast_dns_srv_record::priority, ast_dns_query::result, ast_dns_srv_record::weight, and weight.

{
   uint16_t priority;
   uint16_t weight;
   uint16_t port;
   const char *ptr;
   const char *end_of_record;
   struct ast_dns_srv_record *srv;
   int host_size;
   char host[NI_MAXHOST] = "";
   size_t host_len;

   ptr = dns_find_record(data, size, query->result->answer, query->result->answer_size);
   ast_assert(ptr != NULL);

   end_of_record = ptr + size;

   /* PRIORITY */
   ptr += dns_parse_short((unsigned char *) ptr, &priority);
   if (ptr >= end_of_record) {
      return NULL;
   }

   /* WEIGHT */
   ptr += dns_parse_short((unsigned char *) ptr, &weight);
   if (ptr >= end_of_record) {
      return NULL;
   }

   /* PORT */
   ptr += dns_parse_short((unsigned char *) ptr, &port);
   if (ptr >= end_of_record) {
      return NULL;
   }

   /*
    * The return value from dn_expand represents the size of the replacement
    * in the buffer which MAY be compressed.  Since the expanded replacement
    * is NULL terminated, you can use strlen() to get the expanded size.
    */
   host_size = dn_expand((unsigned char *)query->result->answer,
      (unsigned char *) end_of_record, (unsigned char *) ptr, host, sizeof(host) - 1);
   if (host_size < 0) {
      ast_log(LOG_ERROR, "Failed to expand domain name: %s\n", strerror(errno));
      return NULL;
   }

   if (!strcmp(host, ".")) {
      return NULL;
   }

   host_len = strlen(host) + 1;
   srv = ast_calloc(1, sizeof(*srv) + size + host_len);
   if (!srv) {
      return NULL;
   }

   srv->priority = priority;
   srv->weight = weight;
   srv->port = port;

   srv->host = srv->data + size;
   ast_copy_string((char *)srv->host, host, host_len); /* SAFE */
   srv->generic.data_ptr = srv->data;

   return (struct ast_dns_record *)srv;
}

dns_srv_sort()

void dns_srv_sort

(

struct ast_dns_result *

result

)

Sort the SRV records on a result.

Parameters

result

The DNS result

Definition at line 113 of file dns_srv.c.

References AST_LIST_APPEND_LIST, AST_LIST_FIRST, AST_LIST_HEAD_NOLOCK_INIT_VALUE, AST_LIST_INSERT_HEAD, AST_LIST_INSERT_TAIL, AST_LIST_MOVE_CURRENT, AST_LIST_REMOVE_CURRENT, AST_LIST_TRAVERSE, AST_LIST_TRAVERSE_SAFE_BEGIN, AST_LIST_TRAVERSE_SAFE_END, ast_random(), priority, ast_dns_result::records, weight, and ast_dns_srv_record::weight_sum.

{
   struct ast_dns_record *current;
   struct dns_records newlist = AST_LIST_HEAD_NOLOCK_INIT_VALUE;

   while (AST_LIST_FIRST(&result->records)) {
      unsigned short cur_priority = ((struct ast_dns_srv_record *)(AST_LIST_FIRST(&result->records)))->priority;
      struct dns_records temp_list = AST_LIST_HEAD_NOLOCK_INIT_VALUE;

      /* Find the lowest current priority to work on, but if the priority is already zero there is no lower priority */
      if (cur_priority) {
         AST_LIST_TRAVERSE(&result->records, current, list) {
            if (((struct ast_dns_srv_record *)current)->priority < cur_priority) {
               cur_priority = ((struct ast_dns_srv_record *)current)->priority;
            }
         }
      }

      /* Find all records which match this priority */
      AST_LIST_TRAVERSE_SAFE_BEGIN(&result->records, current, list) {
         if (((struct ast_dns_srv_record *)current)->priority != cur_priority) {
            continue;
         }

         AST_LIST_REMOVE_CURRENT(list);

         /* Records with a weight of zero must always be at the head */
         if (((struct ast_dns_srv_record *)current)->weight == 0) {
            AST_LIST_INSERT_HEAD(&temp_list, current, list);
         } else {
            AST_LIST_INSERT_TAIL(&temp_list, current, list);
         }
      }
      AST_LIST_TRAVERSE_SAFE_END;

      /* Apply weighting - as each record is passed the sum of all previous weights (plus its own) is stored away, and then a random weight
       * is calculated. The first record with a weight sum greater than the random weight is put in the new list and the whole thing starts
       * once again.
       */
      while (AST_LIST_FIRST(&temp_list)) {
         unsigned int weight_sum = 0;
         unsigned int random_weight;

         AST_LIST_TRAVERSE(&temp_list, current, list) {
            ((struct ast_dns_srv_record *)current)->weight_sum = weight_sum += ((struct ast_dns_srv_record *)current)->weight;
         }

         /* if all the remaining entries have weight == 0,
            then just append them to the result list and quit */
         if (weight_sum == 0) {
            AST_LIST_APPEND_LIST(&newlist, &temp_list, list);
            break;
         }

         random_weight = 1 + (unsigned int) ((float) weight_sum * (ast_random() / ((float) RAND_MAX + 1.0)));

         AST_LIST_TRAVERSE_SAFE_BEGIN(&temp_list, current, list) {
            if (((struct ast_dns_srv_record *)current)->weight_sum < random_weight) {
               continue;
            }

            AST_LIST_MOVE_CURRENT(&newlist, list);
            break;
         }
         AST_LIST_TRAVERSE_SAFE_END;
      }

   }

   /* now that the new list has been ordered,
      put it in place */

   AST_LIST_APPEND_LIST(&result->records, &newlist, list);
}