Fri Jul 24 00:41:41 2009

Asterisk developer's documentation


dns.c File Reference

DNS Support for Asterisk. More...

#include "asterisk.h"
#include "asterisk/network.h"
#include <arpa/nameser.h>
#include <resolv.h>
#include "asterisk/channel.h"
#include "asterisk/dns.h"
#include "asterisk/endian.h"

Go to the source code of this file.

Data Structures

struct  dn_answer
struct  dns_HEADER

Defines

#define MAX_SIZE   4096

Functions

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).
static int dns_parse_answer (void *context, int class, int type, unsigned char *answer, int len, int(*callback)(void *context, unsigned char *answer, int len, unsigned char *fullanswer))
 Parse DNS lookup result, call callback.
static int skip_name (unsigned char *s, int len)


Detailed Description

DNS Support for Asterisk.

Author:
Thorsten Lockert <tholo@trollphone.org>
Reference

Definition in file dns.c.


Define Documentation

#define MAX_SIZE   4096

Definition at line 44 of file dns.c.

Referenced by ast_search_dns().


Function Documentation

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

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

Note:
Asterisk DNS is synchronus at this time. This means that if your DNS does not work properly, Asterisk might not start properly or a channel may lock.

Definition at line 255 of file dns.c.

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

Referenced by ast_get_enum(), ast_get_srv(), blr_ebl(), and blr_txt().

00258 {
00259 #ifdef HAVE_RES_NINIT
00260    struct __res_state dnsstate;
00261 #endif
00262    unsigned char answer[MAX_SIZE];
00263    int res, ret = -1;
00264 
00265 #ifdef HAVE_RES_NINIT
00266    memset(&dnsstate, 0, sizeof(dnsstate));
00267    res_ninit(&dnsstate);
00268    res = res_nsearch(&dnsstate, dname, class, type, answer, sizeof(answer));
00269 #else
00270    ast_mutex_lock(&res_lock);
00271    res_init();
00272    res = res_search(dname, class, type, answer, sizeof(answer));
00273 #endif
00274    if (res > 0) {
00275       if ((res = dns_parse_answer(context, class, type, answer, res, callback)) < 0) {
00276          ast_log(LOG_WARNING, "DNS Parse error for %s\n", dname);
00277          ret = -1;
00278       } else if (res == 0) {
00279          ast_debug(1, "No matches found in DNS for %s\n", dname);
00280          ret = 0;
00281       } else
00282          ret = 1;
00283    }
00284 #ifdef HAVE_RES_NINIT
00285 #ifdef HAVE_RES_NDESTROY
00286    res_ndestroy(&dnsstate);
00287 #else
00288    res_nclose(&dnsstate);
00289 #endif
00290 #else
00291 #ifndef __APPLE__
00292    res_close();
00293 #endif
00294    ast_mutex_unlock(&res_lock);
00295 #endif
00296 
00297    return ret;
00298 }

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

Parse DNS lookup result, call callback.

Definition at line 185 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().

00188 {
00189    unsigned char *fullanswer = answer;
00190    struct dn_answer *ans;
00191    dns_HEADER *h;
00192    int ret = 0;
00193    int res;
00194    int x;
00195 
00196    h = (dns_HEADER *)answer;
00197    answer += sizeof(dns_HEADER);
00198    len -= sizeof(dns_HEADER);
00199 
00200    for (x = 0; x < ntohs(h->qdcount); x++) {
00201       if ((res = skip_name(answer, len)) < 0) {
00202          ast_log(LOG_WARNING, "Couldn't skip over name\n");
00203          return -1;
00204       }
00205       answer += res + 4;   /* Skip name and QCODE / QCLASS */
00206       len -= res + 4;
00207       if (len < 0) {
00208          ast_log(LOG_WARNING, "Strange query size\n");
00209          return -1;
00210       }
00211    }
00212 
00213    for (x = 0; x < ntohs(h->ancount); x++) {
00214       if ((res = skip_name(answer, len)) < 0) {
00215          ast_log(LOG_WARNING, "Failed skipping name\n");
00216          return -1;
00217       }
00218       answer += res;
00219       len -= res;
00220       ans = (struct dn_answer *)answer;
00221       answer += sizeof(struct dn_answer);
00222       len -= sizeof(struct dn_answer);
00223       if (len < 0) {
00224          ast_log(LOG_WARNING, "Strange result size\n");
00225          return -1;
00226       }
00227       if (len < 0) {
00228          ast_log(LOG_WARNING, "Length exceeds frame\n");
00229          return -1;
00230       }
00231 
00232       if (ntohs(ans->class) == class && ntohs(ans->rtype) == type) {
00233          if (callback) {
00234             if ((res = callback(context, answer, ntohs(ans->size), fullanswer)) < 0) {
00235                ast_log(LOG_WARNING, "Failed to parse result\n");
00236                return -1;
00237             }
00238             ret = 1;
00239          }
00240       }
00241       answer += ntohs(ans->size);
00242       len -= ntohs(ans->size);
00243    }
00244    return ret;
00245 }

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

Definition at line 161 of file dns.c.

Referenced by dns_parse_answer().

00162 {
00163    int x = 0;
00164 
00165    while (x < len) {
00166       if (*s == '\0') {
00167          s++;
00168          x++;
00169          break;
00170       }
00171       if ((*s & 0xc0) == 0xc0) {
00172          s += 2;
00173          x += 2;
00174          break;
00175       }
00176       x += *s + 1;
00177       s += *s + 1;
00178    }
00179    if (x >= len)
00180       return -1;
00181    return x;
00182 }


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