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dns.c File Reference

Detailed Description

DNS Support for Asterisk.

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

Definition in file dns.c.

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

Variables

dn_answer __packed__

Define Documentation

#define MAX_SIZE   4096
 

Definition at line 49 of file dns.c.

Referenced by ast_search_dns().

Function Documentation

AST_MUTEX_DEFINE_STATIC (  res_lock   ) 
 

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 189 of file dns.c.

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

Referenced by ast_get_enum(), and ast_get_srv().

00192 {
00193 #if HAVE_RES_NINIT
00194    struct __res_state dnsstate;
00195 #endif
00196    unsigned char answer[MAX_SIZE];
00197    int res, ret = -1;
00198 
00199 #if HAVE_RES_NINIT
00200    res_ninit(&dnsstate);
00201    res = res_nsearch(&dnsstate, dname, class, type, answer, sizeof(answer));
00202 #else
00203    ast_mutex_lock(&res_lock);
00204    res_init();
00205    res = res_search(dname, class, type, answer, sizeof(answer));
00206 #endif
00207    if (res > 0) {
00208       if ((res = dns_parse_answer(context, class, type, answer, res, callback)) < 0) {
00209          ast_log(LOG_WARNING, "DNS Parse error for %s\n", dname);
00210          ret = -1;
00211       }
00212       else if (ret == 0) {
00213          if (option_debug)
00214             ast_log(LOG_DEBUG, "No matches found in DNS for %s\n", dname);
00215          ret = 0;
00216       }
00217       else
00218          ret = 1;
00219    }
00220 #if HAVE_RES_NINIT
00221    res_nclose(&dnsstate);
00222 #else
00223 #ifndef __APPLE__
00224    res_close();
00225 #endif
00226    ast_mutex_unlock(&res_lock);
00227 #endif
00228 
00229    return ret;
00230 }

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 119 of file dns.c.

References ast_log(), LOG_WARNING, dns_HEADER::qdcount, and skip_name().

Referenced by ast_search_dns().

00122 {
00123    unsigned char *fullanswer = answer;
00124    struct dn_answer *ans;
00125    dns_HEADER *h;
00126    int res;
00127    int x;
00128 
00129    h = (dns_HEADER *)answer;
00130    answer += sizeof(dns_HEADER);
00131    len -= sizeof(dns_HEADER);
00132 
00133    for (x = 0; x < ntohs(h->qdcount); x++) {
00134       if ((res = skip_name(answer, len)) < 0) {
00135          ast_log(LOG_WARNING, "Couldn't skip over name\n");
00136          return -1;
00137       }
00138       answer += res + 4;   /* Skip name and QCODE / QCLASS */
00139       len -= res + 4;
00140       if (len < 0) {
00141          ast_log(LOG_WARNING, "Strange query size\n");
00142          return -1;
00143       }
00144    }
00145 
00146    for (x = 0; x < ntohs(h->ancount); x++) {
00147       if ((res = skip_name(answer, len)) < 0) {
00148          ast_log(LOG_WARNING, "Failed skipping name\n");
00149          return -1;
00150       }
00151       answer += res;
00152       len -= res;
00153       ans = (struct dn_answer *)answer;
00154       answer += sizeof(struct dn_answer);
00155       len -= sizeof(struct dn_answer);
00156       if (len < 0) {
00157          ast_log(LOG_WARNING, "Strange result size\n");
00158          return -1;
00159       }
00160       if (len < 0) {
00161          ast_log(LOG_WARNING, "Length exceeds frame\n");
00162          return -1;
00163       }
00164 
00165       if (ntohs(ans->class) == class && ntohs(ans->rtype) == type) {
00166          if (callback) {
00167             if ((res = callback(context, answer, ntohs(ans->size), fullanswer)) < 0) {
00168                ast_log(LOG_WARNING, "Failed to parse result\n");
00169                return -1;
00170             }
00171             if (res > 0)
00172                return 1;
00173          }
00174       }
00175       answer += ntohs(ans->size);
00176       len -= ntohs(ans->size);
00177    }
00178    return 0;
00179 }

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

Definition at line 95 of file dns.c.

Referenced by dns_parse_answer().

00096 {
00097    int x = 0;
00098 
00099    while (x < len) {
00100       if (*s == '\0') {
00101          s++;
00102          x++;
00103          break;
00104       }
00105       if ((*s & 0xc0) == 0xc0) {
00106          s += 2;
00107          x += 2;
00108          break;
00109       }
00110       x += *s + 1;
00111       s += *s + 1;
00112    }
00113    if (x >= len)
00114       return -1;
00115    return x;
00116 }

Variable Documentation

struct dn_answer __packed__
 

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