/*
 * CDDL HEADER START
 *
 * The contents of this file are subject to the terms of the
 * Common Development and Distribution License, Version 1.0 only
 * (the "License").  You may not use this file except in compliance
 * with the License.
 *
 * You can obtain a copy of the license at usr/src/OPENSOLARIS.LICENSE
 * or http://www.opensolaris.org/os/licensing.
 * See the License for the specific language governing permissions
 * and limitations under the License.
 *
 * When distributing Covered Code, include this CDDL HEADER in each
 * file and include the License file at usr/src/OPENSOLARIS.LICENSE.
 * If applicable, add the following below this CDDL HEADER, with the
 * fields enclosed by brackets "[]" replaced with your own identifying
 * information: Portions Copyright [yyyy] [name of copyright owner]
 *
 * CDDL HEADER END
 */
/*
 * Copyright 2004 Sun Microsystems, Inc.  All rights reserved.
 * Use is subject to license terms.
 */

/*
 * This module contains a cache used to optimized scope and DA
 * discovery. Entries live for a short duration only (about 10 seconds),
 * although their lifetime can be advanced somewhat by frequent use.
 * The intent is that the canonical source for DAs will always be slpd,
 * so the short lifetime of cache entries is designed to force clients
 * to consult slpd frequently so as to pick up the latest DA state
 * quickly.
 *
 * The cache is managed by a thread which monitors calls into the cache.
 * If the cache has been unused for a certain amount of time, the thread
 * frees the cache and exits.
 *
 * The cache is keyed on the queries sent to slpd to access slpd's DA
 * table. Associated with each query is a reply (in the format of an
 * on-the-wire SLP SRVRPLY message).
 * The cache is accessed by the following two functions:
 *
 * slp_find_das_cached:         searches the cache
 * slp_put_das_cached:          adds a reply to the cache
 *
 * All parameters added to the cache are copied in first, and all results
 * read from the cache are copied out, so all memory must be freed by
 * the caller.
 */

#include <stdio.h>
#include <stdlib.h>
#include <thread.h>
#include <synch.h>
#include <syslog.h>
#include <string.h>
#include <sys/types.h>
#include <time.h>
#include <errno.h>
#include <slp-internal.h>

/* These constants control the behaviour of the cache */
#define MAX_LIFETIME    25      /* max lifetime, in seconds */
#define ADVANCE_PER_USE 5       /* seconds lifetime is extended on each use */
#define INIT_LIFETIME   10      /* cache entries start with this lifetime */

/* Management thread components */
#define IDLE_TIMEOUT    30      /* thread will exit after this idle time */
static int cache_thr_running;
static mutex_t start_lock = DEFAULTMUTEX;
static int cache_called;
static cond_t cache_called_cond;
static mutex_t cache_called_lock = DEFAULTMUTEX;
static SLPError start_cache_thr();
static void *cache_thr(void *);

/* The cache and cache synchronization */
static void *da_cache;
static mutex_t cache_lock = DEFAULTMUTEX;
struct cache_entry {
        const char *query;
        const char *reply;
        unsigned int reply_len;
        time_t max_life;
        time_t expires;
};
typedef struct cache_entry cache_entry_t;

/* cache management and searching */
static int compare_entries(const void *, const void *);
static void free_cache_entry(void *, VISIT, int, void *);

/*
 * Searches the cache for the reply to 'query'. Returns the reply if
 * found, otherwise NULL.
 * The caller must free the result.
 */
char *slp_find_das_cached(const char *query) {
        cache_entry_t ce[1], **ans;
        char *reply = NULL;
        time_t now;

        if (!cache_thr_running) {
                if (start_cache_thr() != SLP_OK) {
                        return (NULL);
                }
        }

        (void) mutex_lock(&cache_lock);
        ce->query = query;

        ans = slp_tfind(ce, &da_cache, compare_entries);
        if (ans) {
                now = time(NULL);
                if ((*ans)->expires < now || (*ans)->max_life < now) {
                        goto done;
                }

                /* copy out the reply */
                if (!(reply = malloc((*ans)->reply_len))) {
                        slp_err(LOG_CRIT, 0, "slp_find_das_cached",
                                                "out of memory");
                        goto done;
                }
                (void) memcpy(reply, (*ans)->reply, (*ans)->reply_len);
                (*ans)->expires += ADVANCE_PER_USE;
        }

        /* notify cache thread of call */
        (void) mutex_lock(&cache_called_lock);
        cache_called = 1;
        (void) cond_signal(&cache_called_cond);
        (void) mutex_unlock(&cache_called_lock);

done:
        (void) mutex_unlock(&cache_lock);
        return (reply);
}

/*
 * Adds 'reply' to the cache under the index 'query'. Both parameters
 * are copied in first, so the caller may free them after the call.
 * 'len' is the length of 'reply' in bytes.
 */
void slp_put_das_cached(const char *query, const char *reply,
                        unsigned int len) {
        cache_entry_t *ce, **ce2;
        time_t now;

        if (!cache_thr_running) {
                if (start_cache_thr() != SLP_OK) {
                        return;
                }
        }

        /* create the cache entry for this reply */
        if (!(ce = malloc(sizeof (*ce)))) {
                slp_err(LOG_CRIT, 0, "slp_put_das_cached", "out of memory");
                return;
        }

        if (!(ce->query = strdup(query))) {
                free(ce);
                slp_err(LOG_CRIT, 0, "slp_put_das_cached", "out of memory");
                return;
        }

        if (!(ce->reply = malloc(len))) {
                free((void *) (ce->query));
                free(ce);
                slp_err(LOG_CRIT, 0, "slp_put_das_cached", "out of memory");
                return;
        }
        (void) memcpy((void *) (ce->reply), reply, len);
        ce->reply_len = len;
        now = time(NULL);
        ce->max_life = now + MAX_LIFETIME;
        ce->expires = now + INIT_LIFETIME;

        /* write to the cache */
        (void) mutex_lock(&cache_lock);
        ce2 = slp_tsearch((void *) ce, &da_cache, compare_entries);
        if (ce != *ce2) {
                /* overwrite existing entry */
                free((void *) ((*ce2)->query));
                free((void *) ((*ce2)->reply));
                free(*ce2);
                *ce2 = ce;
        }

        (void) mutex_unlock(&cache_lock);
}

static int compare_entries(const void *x1, const void *x2) {
        cache_entry_t *e1 = (cache_entry_t *)x1;
        cache_entry_t *e2 = (cache_entry_t *)x2;

        return (strcasecmp(e1->query, e2->query));
}

static void
free_cache_entry(void *node, VISIT order, int arg __unused, void *arg1 __unused)
{
        if (order == endorder || order == leaf) {
                cache_entry_t *ce = *(cache_entry_t **)node;

                free((void *) (ce->query));
                free((void *) (ce->reply));
                free(ce);
                free(node);
        }
}

static SLPError start_cache_thr() {
        int terr;
        SLPError err = SLP_OK;

        (void) mutex_lock(&start_lock);

        if (cache_thr_running) {
                goto start_done;
        }

        (void) cond_init(&cache_called_cond, 0, NULL);

        if ((terr = thr_create(0, 0, cache_thr, NULL, 0, NULL)) != 0) {
                slp_err(LOG_CRIT, 0, "start_cache_thr",
                        "could not start thread: %s", strerror(terr));
                err = SLP_INTERNAL_SYSTEM_ERROR;
                goto start_done;
        }
        cache_thr_running = 1;

start_done:
        (void) mutex_unlock(&start_lock);
        return (err);
}

static void *
cache_thr(void *arg __unused)
{
        timestruc_t timeout;
        timeout.tv_nsec = 0;

        (void) mutex_lock(&cache_called_lock);
        cache_called = 0;

        while (cache_called == 0) {
                int err;

                timeout.tv_sec = IDLE_TIMEOUT;
                err = cond_reltimedwait(&cache_called_cond,
                    &cache_called_lock, &timeout);

                if (err == ETIME) {
                        (void) mutex_lock(&cache_lock);
                        /* free cache */
                        if (da_cache) {
                                slp_twalk(da_cache, free_cache_entry, 0, NULL);
                        }
                        da_cache = NULL;
                        (void) mutex_unlock(&cache_lock);
                        cache_thr_running = 0;
                        (void) mutex_unlock(&cache_called_lock);
                        thr_exit(NULL);
                } else {
                        cache_called = 0;
                }
        }
        return (NULL);
}