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/***************************************************************************
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* Copyright (c) 2001 BalaBit IT Ltd.
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* This program is free software; you can redistribute it and/or modify
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* it under the terms of the GNU General Public License as published by
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* the Free Software Foundation; either version 2 of the License, or
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* (at your option) any later version.
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* This program is distributed in the hope that it will be useful,
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* but WITHOUT ANY WARRANTY; without even the implied warranty of
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* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
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* GNU General Public License for more details.
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* You should have received a copy of the GNU General Public License
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* along with this program; if not, write to the Free Software
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* Foundation, Inc., 675 Mass Ave, Cambridge, MA 02139, USA.
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* Inspired by nsyslog, originally written by Darren Reed.
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* $Id: nscache.c,v 1.4 2001/05/14 09:07:25 bazsi Exp $
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***************************************************************************/
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* Copyright (c) 2001 Ga�l Roualland <gael.roualland@iname.com>
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* All rights reserved.
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* Redistribution and use in source and binary forms, with or without
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* modification, are permitted provided that the following conditions
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* 1. Redistributions of source code must retain the above copyright
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* notice, this list of conditions and the following disclaimer.
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* 2. Redistributions in binary form must reproduce the above copyright
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* notice, this list of conditions and the following disclaimer in the
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* documentation and/or other materials provided with the distribution.
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* 3. Neither the name of the author nor the names of its contributors
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* may be used to endorse or promote products derived from this software
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* without specific prior written permission.
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* THIS SOFTWARE IS PROVIDED BY THE AUTHOR AND CONTRIBUTORS `AS IS'' AND
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* ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
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* IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
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* ARE DISCLAIMED. IN NO EVENT SHALL THE AUTHOR OR CONTRIBUTORS BE LIABLE
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* FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
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* DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
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* OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
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* HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
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* LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
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* OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
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#include <netinet/in.h>
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#include <arpa/inet.h>
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#include <sys/socket.h>
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/* Simple NS cache, using a flat hash table (NOT thread safe).
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* This is designed to be used with a fixed set of ip adresses.
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* Inspired from similar caches in ippl, iplog...
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* The size of the cache must be a primary number for good
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* performance and somewhat larger than the maximum number
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* of estimated entries. If more entries than available in the
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* cache are used at the same time it will perform very poorly.
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struct nsentry * entries;
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struct nscache *nscache_new(int size, int expire, int expire_failed)
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struct nscache * cache;
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if ((cache = malloc(sizeof(struct nscache))) == NULL)
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/* check args for reasonnable values
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0 for expire_failed means not to cache failures */
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cache->size = (size < 10) ? 10 : size;
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cache->expire = (expire < 10) ? 10 : expire;
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cache->expire_failed = (expire_failed < 0) ? 0 : expire_failed;
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if ((cache->entries =
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malloc(cache->size * sizeof(struct nsentry))) == NULL) {
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for (i = 0; i < cache->size; i++) {
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cache->entries[i].addr.s_addr = 0;
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cache->entries[i].name = NULL;
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cache->entries[i].expire = 0;
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cache->entries[i].used = 0;
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fprintf(stderr, "initialising nscache: %d entries, %d/%d expiration.\n",
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cache->size, cache->expire, cache->expire_failed);
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cache->hits = cache->misses = 0;
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void nscache_free(struct nscache * cache)
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if (cache->entries == NULL) {
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fprintf(stderr, "destroying nscache: %d entries, %d hits, %d misses.\n",
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cache->size, cache->hits, cache->misses);
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for (i = 0; i < cache->size; i++) {
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if (cache->entries[i].name != NULL)
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free(cache->entries[i].name);
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free(cache->entries);
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static char *nsresolve(struct in_addr addr)
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struct hostent *host;
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if ((host = gethostbyaddr((char *) &addr,
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sizeof(struct in_addr),
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host->h_name != NULL)
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char *nscache_lookup(struct nscache * cache, struct in_addr in)
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time_t now = time(NULL);
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time_t oldest = now + 1;
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if (cache == NULL || cache->entries == NULL) /* be safe.. */
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return nsresolve(in);
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k = h = ntohl(in.s_addr) % (cache->size - 1) + 1;
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if (cache->entries[k].expire > 0 &&
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cache->entries[k].addr.s_addr == in.s_addr) { /* found it! */
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if (now > cache->entries[k].expire) {
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/* entry has expired, update it */
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fprintf(stderr, "%s... updating entry %d (%d > %d).\n",
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inet_ntoa(in), k, (int) now,
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(int) cache->entries[k].expire);
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fprintf(stderr, "%s... found on %d: %s (%d iters, %d/%d)\n",
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inet_ntoa(in), k, cache->entries[k].name,
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iter, (int) now, (int) cache->entries[k].expire);
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cache->entries[k].used = now;
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return cache->entries[k].name;
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if (new < 0) { /* no empty entries found yet */
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if (cache->entries[k].expire < now) {
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new = k; /* use this to save new entry if not found */
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if (cache->entries[k].expire < 1)
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break; /* never used */
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if (cache->entries[k].used < oldest) {
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oldest = cache->entries[k].used;
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k = (h + k) % cache->size;
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if (new < 0) { /* no place to save ? use oldest. */
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old = 0; /* shouldn't happen.. */
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fprintf(stderr, "%s... old entry %d will be replaced.\n",
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inet_ntoa(cache->entries[old].addr), old);
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fprintf(stderr, "%s... adding as %d (%d iters).\n",
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inet_ntoa(in), new, iter);
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if (cache->entries[new].name != NULL)
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free (cache->entries[new].name);
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if ((host = nsresolve(in)) != NULL) {
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cache->entries[new].name = strdup(host);
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cache->entries[new].expire =
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cache->entries[new].name = NULL;
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cache->entries[new].expire =
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now + cache->expire_failed;
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cache->entries[new].addr.s_addr = in.s_addr;
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return cache->entries[new].name;
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void nscache_dump(struct nscache * cache)
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fprintf(stderr, "nscache contents:\n");
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for (i = 0; i < cache->size; i++) {
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if (cache->entries[i].used > 0)
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fprintf(stderr, " %5d %-16s %09d/%09d %s\n",
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i, inet_ntoa(cache->entries[i].addr),
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(int) cache->entries[i].used,
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(int) cache->entries[i].expire,
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cache->entries[i].name);
added
removed
src/nscache.c
