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)
void	ast_srv_cleanup (struct srv_context **context)
	Cleanup resources associated with ast_srv_lookup.
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.
unsigned int	ast_srv_get_record_count (struct srv_context *context)
	Get the number of records for a given SRV context.
int	ast_srv_lookup (struct srv_context *context, const char service, const char *host, unsigned short port)
	Retrieve set of SRV lookups, in order.
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 259 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;
}

void ast_srv_cleanup ( struct srv_context ** context )

Cleanup resources associated with ast_srv_lookup.

Parameters:

context Pointer passed into ast_srv_lookup

Definition at line 247 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().

{
   const char *host;
   unsigned short port;

   if (*context) {
      /* We have a context to clean up. */
      while (!(ast_srv_lookup(context, NULL, &host, &port))) {
      }
   }
}

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:

	context	The context returned by ast_srv_lookup
	record_num	The 1-indexed record number to retrieve
[out]	host	The host portion of the record
[out]	port	The port portion of the record
[out]	priority	The priority portion of the record
[out]	weight	The weight portion of the record

Return values:

-1	Failed to retrieve information. Likely due to an out of range record_num
0	Success

Definition at line 308 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().

{
   int i = 1;
   int res = -1;
   struct srv_entry *entry;

   if (record_num < 1 || record_num > context->num_records) {
      return res;
   }

   AST_LIST_TRAVERSE(&context->entries, entry, list) {
      if (i == record_num) {
         *host = entry->host;
         *port = entry->port;
         *priority = entry->priority;
         *weight = entry->weight;
         res = 0;
         break;
      }
      ++i;
   }

   return res;
}

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:

context The context returned by ast_srv_lookup

Returns:: Number of records in context

Definition at line 303 of file srv.c.

References srv_context::num_records.

Referenced by srv_result_read().

{
   return context->num_records;
}

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]	context	A pointer in which to hold the result
[in]	service	The service name to look up
[out]	host	Result host
[out]	port	Associated TCP portnum

Return values:

-1	Query failed
0	Result exists in host and port
1	No more results

Definition at line 202 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().

{
   struct srv_entry *cur;

   if (*context == NULL) {
      if (!(*context = ast_calloc(1, sizeof(struct srv_context)))) {
         return -1;
      }
      AST_LIST_HEAD_INIT_NOLOCK(&(*context)->entries);

      if ((ast_search_dns(*context, service, C_IN, T_SRV, srv_callback)) < 0) {
         ast_free(*context);
         *context = NULL;
         return -1;
      }

      if ((*context)->have_weights) {
         process_weights(*context);
      }

      (*context)->prev = AST_LIST_FIRST(&(*context)->entries);
      *host = (*context)->prev->host;
      *port = (*context)->prev->port;
      AST_LIST_TRAVERSE(&(*context)->entries, cur, list) {
         ++((*context)->num_records);
      }
      return 0;
   }

   if (((*context)->prev = AST_LIST_NEXT((*context)->prev, list))) {
      /* Retrieve next item in result */
      *host = (*context)->prev->host;
      *port = (*context)->prev->port;
      return 0;
   } else {
      /* No more results */
      while ((cur = AST_LIST_REMOVE_HEAD(&(*context)->entries, list))) {
         ast_free(cur);
      }
      ast_free(*context);
      *context = NULL;
      return 1;
   }
}

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

Definition at line 72 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 150 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(), and ast_srv_lookup().

{
   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 113 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(), and ast_srv_lookup().

{
   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