Sat Nov 1 06:31:02 2008

Asterisk developer's documentation

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dns.c File Reference

DNS Support for Asterisk. More...

#include <sys/types.h>
#include <sys/socket.h>
#include <netinet/in.h>
#include <arpa/nameser.h>
#include <resolv.h>
#include <unistd.h>
#include "asterisk.h"
#include "asterisk/logger.h"
#include "asterisk/channel.h"
#include "asterisk/dns.h"
#include "asterisk/endian.h"

Include dependency graph for dns.c:

Go to the source code of this file.

Data Structures
struct	dn_answer
struct	dns_HEADER
Defines
#define	MAX_SIZE   4096
Functions
	AST_MUTEX_DEFINE_STATIC (res_lock)
int	ast_search_dns (void *context, const char *dname, int class, int type, int(*callback)(void *context, char *answer, int len, char *fullanswer))
	Perform DNS lookup (used by enum and SRV lookups).
static int	dns_parse_answer (void *context, int class, int type, char *answer, int len, int(*callback)(void *context, char *answer, int len, char *fullanswer))
static int	skip_name (char *s, int len)
Variables
dn_answer	__packed__

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Detailed Description

DNS Support for Asterisk.

Author:

Thorsten Lockert <tholo@trollphone.org>

Definition in file dns.c.

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Define Documentation

#define MAX_SIZE   4096

Definition at line 44 of file dns.c.

Referenced by ast_search_dns().

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Function Documentation

AST_MUTEX_DEFINE_STATIC

(

res_lock

)

int ast_search_dns	(	void *	context,
		const char *	dname,
		int	class,
		int	type,
		int(*)(void *context, char *answer, int len, char *fullanswer)	callback
	)

Perform DNS lookup (used by enum and SRV lookups).

Parameters:

	context
	dname	Domain name to lookup (host, SRV domain, TXT record name)
	class	Record Class (see "man res_search")
	type	Record type (see "man res_search")
	callback	Callback function for handling DNS result

Definition at line 248 of file dns.c.

References ast_log(), ast_mutex_lock(), ast_mutex_unlock(), dns_parse_answer(), LOG_DEBUG, LOG_WARNING, and MAX_SIZE.

Referenced by ast_get_enum(), ast_get_srv(), and ast_get_txt().

{
#ifdef HAS_RES_NINIT
   struct __res_state dnsstate;
#endif
   char answer[MAX_SIZE];
   int res, ret = -1;

#ifdef HAS_RES_NINIT
#ifdef MAKE_VALGRIND_HAPPY
   memset(&dnsstate, 0, sizeof(dnsstate));
#endif   
   res_ninit(&dnsstate);
   res = res_nsearch(&dnsstate, dname, class, type, (unsigned char *)answer, sizeof(answer));
#else
   ast_mutex_lock(&res_lock);
   res_init();
   res = res_search(dname, class, type, answer, sizeof(answer));
#endif
   if (res > 0) {
      if ((res = dns_parse_answer(context, class, type, answer, res, callback)) < 0) {
         ast_log(LOG_WARNING, "DNS Parse error for %s\n", dname);
         ret = -1;
      }
      else if (ret == 0) {
         ast_log(LOG_DEBUG, "No matches found in DNS for %s\n", dname);
         ret = 0;
      }
      else
         ret = 1;
   }
#ifdef HAS_RES_NINIT
#ifdef HAS_RES_NDESTROY
   res_ndestroy(&dnsstate);
#else
   res_nclose(&dnsstate);
#endif
#else
#ifndef __APPLE__
   res_close();
#endif
   ast_mutex_unlock(&res_lock);
#endif
   return ret;
}

static int dns_parse_answer	(	void *	context,
		int	class,
		int	type,
		char *	answer,
		int	len,
		int(*)(void *context, char *answer, int len, char *fullanswer)	callback
	)			[static]

Definition at line 173 of file dns.c.

References dns_HEADER::ancount, ast_log(), dn_answer::class, LOG_WARNING, dns_HEADER::qdcount, dn_answer::rtype, dn_answer::size, and skip_name().

Referenced by ast_search_dns().

{
   char *fullanswer = answer;
   struct dn_answer *ans;
   dns_HEADER *h;
   int res;
   int x;

   h = (dns_HEADER *)answer;
   answer += sizeof(dns_HEADER);
   len -= sizeof(dns_HEADER);

   for (x = 0; x < ntohs(h->qdcount); x++) {
      if ((res = skip_name(answer, len)) < 0) {
         ast_log(LOG_WARNING, "Couldn't skip over name\n");
         return -1;
      }
      answer += res + 4;   /* Skip name and QCODE / QCLASS */
      len -= res + 4;
      if (len < 0) {
         ast_log(LOG_WARNING, "Strange query size\n");
         return -1;
      }
   }

   for (x = 0; x < ntohs(h->ancount); x++) {
      if ((res = skip_name(answer, len)) < 0) {
         ast_log(LOG_WARNING, "Failed skipping name\n");
         return -1;
      }
      answer += res;
      len -= res;
      ans = (struct dn_answer *)answer;
      answer += sizeof(struct dn_answer);
      len -= sizeof(struct dn_answer);
      if (len < 0) {
         ast_log(LOG_WARNING, "Strange result size\n");
         return -1;
      }
      if (len < 0) {
         ast_log(LOG_WARNING, "Length exceeds frame\n");
         return -1;
      }

      if (ntohs(ans->class) == class && ntohs(ans->rtype) == type) {
         if (callback) {
            if ((res = callback(context, answer, ntohs(ans->size), fullanswer)) < 0) {
               ast_log(LOG_WARNING, "Failed to parse result\n");
               return -1;
            }
            if (res > 0)
               return 1;
         }
      }
      answer += ntohs(ans->size);
      len -= ntohs(ans->size);
   }
   return 0;
}

static int skip_name	(	char *	s,
		int	len
	)			[static]

Definition at line 149 of file dns.c.

Referenced by dns_parse_answer().

{
   int x = 0;

   while (x < len) {
      if (*s == '\0') {
         s++;
         x++;
         break;
      }
      if ((*s & 0xc0) == 0xc0) {
         s += 2;
         x += 2;
         break;
      }
      x += *s + 1;
      s += *s + 1;
   }
   if (x >= len)
      return -1;
   return x;
}

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Variable Documentation

struct dn_answer __packed__

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