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/* $Id: dnscache.c,v 1.10 2001-08-29 03:57:51 rjkaes Exp $
*
* This is a caching DNS system. When a host name is needed we look it up here
* and see if there is already an answer for it. The domains are placed in a
* hashed linked list. If the name is not here, then we need to look it up and
* add it to the system. This really speeds up the connection to servers since
* the DNS name does not need to be looked up each time. It's kind of cool. :)
*
* Copyright (C) 1999 Robert James Kaes (rjkaes@flarenet.com)
* Copyright (C) 2000 Chris Lightfoot (chris@ex-parrot.com)
*
* This program is free software; you can redistribute it and/or modify it
* under the terms of the GNU General Public License as published by the
* Free Software Foundation; either version 2, or (at your option) any
* later version.
*
* This program is distributed in the hope that it will be useful, but
* WITHOUT ANY WARRANTY; without even the implied warranty of
* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
* General Public License for more details.
*/
#ifdef HAVE_CONFIG_H
# include <config.h>
#endif
#include <sys/types.h>
#include <assert.h>
#include <ctype.h>
#include <unistd.h>
#include "dnscache.h"
#include "log.h"
#include "ternary.h"
#include "utils.h"
/*
* The mutex is used for locking around accesses to the ternary tree.
*/
static pthread_mutex_t mutex = PTHREAD_MUTEX_INITIALIZER;
#define LOCK() pthread_mutex_lock(&mutex);
#define UNLOCK() pthread_mutex_unlock(&mutex);
#define DNSEXPIRE (5 * 60)
struct dnscache_s {
struct in_addr ipaddr;
time_t expire;
};
static TERNARY dns_tree = -1;
/*
* Insert the data into the DNS tree.
*/
static int insert_data(char *domain, struct dnscache_s *newptr)
{
int ret;
LOCK();
ret = ternary_insert(dns_tree, domain, newptr);
UNLOCK();
return ret;
}
static int dns_lookup(struct in_addr *addr, char *domain)
{
int ret;
struct dnscache_s *ptr;
assert(addr != NULL);
assert(domain != NULL);
LOCK();
ret = ternary_search(dns_tree, domain, (void *)&ptr);
if (TE_ISERROR(ret)
|| difftime(time(NULL), ptr->expire) > DNSEXPIRE) {
UNLOCK();
return -1;
}
memcpy(addr, &ptr->ipaddr, sizeof(struct in_addr));
UNLOCK();
return 0;
}
static int dns_insert(struct in_addr *addr, char *domain)
{
struct dnscache_s *newptr;
int ret;
assert(addr != NULL);
assert(domain != NULL);
DEBUG2("Inserting [%s] into DNS cache", domain);
if (!(newptr = malloc(sizeof(struct dnscache_s)))) {
return -1;
}
memcpy(&newptr->ipaddr, addr, sizeof(struct in_addr));
newptr->expire = time(NULL);
ret = insert_data(domain, newptr);
if (TE_ISERROR(ret)) {
if (ret == TE_EXISTS) {
/*
* The value already exists. First search for the
* value and then delete the data before inserting
* the new value.
*/
struct dnscache_s *existing;
DEBUG2("[%s] already exists in DNS cache", domain);
LOCK();
ret = ternary_search(dns_tree, domain, (void *)&existing);
UNLOCK();
if (TE_ISERROR(ret))
goto INSERT_ERROR;
safefree(existing);
ret = insert_data(domain, newptr);
if (TE_ISERROR(ret))
goto INSERT_ERROR;
} else {
INSERT_ERROR:
safefree(newptr);
return -1;
}
}
return 0;
}
int dnscache(struct in_addr *addr, char *domain)
{
struct hostent *resolv;
assert(addr != NULL);
assert(domain != NULL);
/* If the DNS tree doesn't exist, build a new one */
LOCK();
if (dns_tree < 0)
dns_tree = ternary_new();
UNLOCK();
if (inet_aton(domain, (struct in_addr *)addr) != 0)
return 0;
/* Well, we're not dotted-decimal so we need to look it up */
if (dns_lookup(addr, domain) == 0)
return 0;
/* Okay, so not in the list... need to actually look it up. */
LOCK();
if (!(resolv = gethostbyname(domain))) {
UNLOCK();
return -1;
}
memcpy(addr, resolv->h_addr_list[0], (size_t)resolv->h_length);
UNLOCK();
dns_insert(addr, domain);
return 0;
}
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