DNS SRV Record Lookup Support for Asterisk. More...

#include "asterisk.h"
#include <netinet/in.h>
#include <arpa/nameser.h>
#include <resolv.h>
#include "asterisk/channel.h"
#include "asterisk/srv.h"
#include "asterisk/dns.h"
#include "asterisk/utils.h"
#include "asterisk/linkedlists.h"

Include dependency graph for srv.c:

Go to the source code of this file.

Data Structures
struct	srv_context
struct	srv_context::srv_entries
struct	srv_entry
Functions
int	ast_get_srv (struct ast_channel chan, char host, int hostlen, int port, const char service)
static int	parse_srv (unsigned char answer, int len, unsigned char msg, struct srv_entry **result)
static void	process_weights (struct srv_context *context)
static int	srv_callback (void context, unsigned char answer, int len, unsigned char *fullanswer)

Detailed Description

DNS SRV Record Lookup Support for Asterisk.

Author:: Mark Spencer <markster@digium.com>

See also ENUM

Note:: Funding provided by nic.at

Definition in file srv.c.

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:

chan	Ast channel
host	host name (return value)
hostlen	Length of string "host"
port	Port number (return value)
service	Service tag for SRV lookup (like "_sip._udp" or "_stun._udp"

Definition at line 200 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().

{
   struct srv_context context = { .entries = AST_LIST_HEAD_NOLOCK_INIT_VALUE };
   struct srv_entry *current;
   int ret;

   if (chan && ast_autoservice_start(chan) < 0)
      return -1;

   ret = ast_search_dns(&context, service, C_IN, T_SRV, srv_callback);

   if (context.have_weights)
      process_weights(&context);

   if (chan)
      ret |= ast_autoservice_stop(chan);

   /* TODO: there could be a "." entry in the returned list of
      answers... if so, this requires special handling */

   /* the list of entries will be sorted in the proper selection order
      already, so we just need the first one (if any) */

   if ((ret > 0) && (current = AST_LIST_REMOVE_HEAD(&context.entries, list))) {
      ast_copy_string(host, current->host, hostlen);
      *port = current->port;
      ast_free(current);
      ast_verb(4, "ast_get_srv: SRV lookup for '%s' mapped to host %s, port %d\n",
                service, host, *port);
   } else {
      host[0] = '\0';
      *port = -1;
   }

   while ((current = AST_LIST_REMOVE_HEAD(&context.entries, list)))
      ast_free(current);

   return ret;
}

static int parse_srv	(	unsigned char *	answer,
		int	len,
		unsigned char *	msg,
		struct srv_entry **	result
	)		`[static]`

Definition at line 70 of file srv.c.

References ast_calloc, ast_log(), srv_entry::host, LOG_WARNING, srv_entry::port, srv_entry::priority, and srv_entry::weight.

Referenced by srv_callback().

{
   struct srv {
      unsigned short priority;
      unsigned short weight;
      unsigned short port;
   } __attribute__((__packed__)) *srv = (struct srv *) answer;

   int res = 0;
   char repl[256] = "";
   struct srv_entry *entry;

   if (len < sizeof(*srv))
      return -1;

   answer += sizeof(*srv);
   len -= sizeof(*srv);

   if ((res = dn_expand(msg, answer + len, answer, repl, sizeof(repl) - 1)) <= 0) {
      ast_log(LOG_WARNING, "Failed to expand hostname\n");
      return -1;
   }

   /* the magic value "." for the target domain means that this service
      is *NOT* available at the domain we searched */
   if (!strcmp(repl, "."))
      return -1;

   if (!(entry = ast_calloc(1, sizeof(*entry) + strlen(repl))))
      return -1;
   
   entry->priority = ntohs(srv->priority);
   entry->weight = ntohs(srv->weight);
   entry->port = ntohs(srv->port);
   strcpy(entry->host, repl);

   *result = entry;
   
   return 0;
}

static void process_weights ( struct srv_context * context ) [static]

Definition at line 148 of file srv.c.

References AST_LIST_APPEND_LIST, AST_LIST_FIRST, AST_LIST_HEAD_NOLOCK_INIT_VALUE, AST_LIST_MOVE_CURRENT, AST_LIST_TRAVERSE, AST_LIST_TRAVERSE_SAFE_BEGIN, AST_LIST_TRAVERSE_SAFE_END, ast_random(), srv_context::entries, srv_entry::priority, srv_entry::weight, and srv_entry::weight_sum.

Referenced by ast_get_srv().

{
   struct srv_entry *current;
   struct srv_entries newlist = AST_LIST_HEAD_NOLOCK_INIT_VALUE;

   while (AST_LIST_FIRST(&context->entries)) {
      unsigned int random_weight;
      unsigned int weight_sum;
      unsigned short cur_priority = AST_LIST_FIRST(&context->entries)->priority;
      struct srv_entries temp_list = AST_LIST_HEAD_NOLOCK_INIT_VALUE;
      weight_sum = 0;

      AST_LIST_TRAVERSE_SAFE_BEGIN(&context->entries, current, list) {
         if (current->priority != cur_priority)
            break;

         AST_LIST_MOVE_CURRENT(&temp_list, list);
      }
      AST_LIST_TRAVERSE_SAFE_END;

      while (AST_LIST_FIRST(&temp_list)) {
         weight_sum = 0;
         AST_LIST_TRAVERSE(&temp_list, current, list)
            current->weight_sum = weight_sum += 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 (current->weight < 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(&context->entries, &newlist, list);
}

static int srv_callback	(	void *	context,
		unsigned char *	answer,
		int	len,
		unsigned char *	fullanswer
	)		`[static]`

Definition at line 111 of file srv.c.

References AST_LIST_INSERT_BEFORE_CURRENT, AST_LIST_INSERT_TAIL, AST_LIST_TRAVERSE_SAFE_BEGIN, AST_LIST_TRAVERSE_SAFE_END, srv_context::entries, srv_context::have_weights, parse_srv(), srv_entry::priority, and srv_entry::weight.

Referenced by ast_get_srv().

{
   struct srv_context *c = (struct srv_context *) context;
   struct srv_entry *entry = NULL;
   struct srv_entry *current;

   if (parse_srv(answer, len, fullanswer, &entry))
      return -1;

   if (entry->weight)
      c->have_weights = 1;

   AST_LIST_TRAVERSE_SAFE_BEGIN(&c->entries, current, list) {
      /* insert this entry just before the first existing
         entry with a higher priority */
      if (current->priority <= entry->priority)
         continue;

      AST_LIST_INSERT_BEFORE_CURRENT(entry, list);
      entry = NULL;
      break;
   }
   AST_LIST_TRAVERSE_SAFE_END;

   /* if we didn't find a place to insert the entry before an existing
      entry, then just add it to the end */
   if (entry)
      AST_LIST_INSERT_TAIL(&c->entries, entry, list);

   return 0;
}

Asterisk developer's documentation

Data Structures

Functions

Detailed Description

Function Documentation