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/* $Id: dnscache.c,v 1.2 2000-03-11 20:37:44 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 <defines.h>
#endif
#include <stdlib.h>
#include <string.h>
#include <netdb.h>
#include <time.h>
#include <sys/socket.h>
#include <netinet/in.h>
#include <arpa/inet.h>
#include <assert.h>
#include <ctype.h>
#include "utils.h"
#include "dnscache.h"
#define HASH_BOX 25
#define DNSEXPIRE (5 * 60)
struct dnscache_s {
struct in_addr ipaddr;
char *domain;
time_t expire;
struct dnscache_s *next;
};
struct dnscache_s *cache[HASH_BOX];
static unsigned int hash(unsigned char *keystr, unsigned int box)
{
unsigned long hashc = 0;
unsigned char ch;
assert(keystr);
assert(box > 0);
while ((ch = *keystr++))
hashc += tolower(ch);
return hashc % box;
}
int lookup(struct in_addr *addr, char *domain)
{
unsigned int box = hash(domain, HASH_BOX);
struct dnscache_s **rptr = &cache[box];
struct dnscache_s *ptr = cache[box];
assert(domain);
while (ptr && strcasecmp(ptr->domain, domain)) {
rptr = &ptr->next;
ptr = ptr->next;
}
if (ptr && !strcasecmp(ptr->domain, domain)) {
/* Woohoo... found it. Make sure it hasn't expired */
if (difftime(time(NULL), ptr->expire) > DNSEXPIRE) {
/* Oops... expired */
*rptr = ptr->next;
safefree(ptr->domain);
safefree(ptr);
return -1;
}
/* chris - added this so that the routine can be used to just
* look stuff up.
*/
if (addr)
*addr = ptr->ipaddr;
return 0;
}
return -1;
}
int insert(struct in_addr *addr, char *domain)
{
unsigned int box = hash(domain, HASH_BOX);
struct dnscache_s **rptr = &cache[box];
struct dnscache_s *ptr = cache[box];
struct dnscache_s *newptr;
assert(addr);
assert(domain);
while (ptr) {
rptr = &ptr->next;
ptr = ptr->next;
}
if (!(newptr = xmalloc(sizeof(struct dnscache_s)))) {
return -1;
}
if (!(newptr->domain = xstrdup(domain))) {
safefree(newptr);
return -1;
}
newptr->ipaddr = *addr;
newptr->expire = time(NULL);
*rptr = newptr;
newptr->next = ptr;
return 0;
}
int dnscache(struct in_addr *addr, char *domain)
{
struct hostent *resolv;
assert(addr);
assert(domain);
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 (lookup(addr, domain) == 0)
return 0;
/* Okay, so not in the list... need to actually look it up. */
if (!(resolv = gethostbyname(domain)))
return -1;
memcpy(addr, resolv->h_addr_list[0], resolv->h_length);
insert(addr, domain);
return 0;
}
static void dnsdelete(unsigned int c, struct dnscache_s *del)
{
struct dnscache_s **rptr;
struct dnscache_s *ptr;
assert(c > 0);
assert(del);
rptr = &cache[c];
ptr = cache[c];
while (ptr && (ptr != del)) {
rptr = &ptr->next;
ptr = ptr->next;
}
if (ptr == del) {
*rptr = ptr->next;
safefree(ptr->domain);
safefree(ptr);
}
}
void dnsclean(void)
{
unsigned int c;
struct dnscache_s *ptr, *tmp;
for (c = 0; c < HASH_BOX; c++) {
ptr = cache[c];
while (ptr) {
tmp = ptr->next;
if (difftime(time(NULL), ptr->expire) > DNSEXPIRE)
dnsdelete(c, ptr);
ptr = tmp;
}
}
}
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