/* Licensed to the Apache Software Foundation (ASF) under one or more

 * contributor license agreements.  See the NOTICE file distributed with

 * this work for additional information regarding copyright ownership.

 * The ASF licenses this file to You under the Apache License, Version 2.0

 * (the "License"); you may not use this file except in compliance with

 * the License.  You may obtain a copy of the License at

 *

 *     http://www.apache.org/licenses/LICENSE-2.0

 *

 * Unless required by applicable law or agreed to in writing, software

 * distributed under the License is distributed on an "AS IS" BASIS,

 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.

 * See the License for the specific language governing permissions and

 * limitations under the License.

 */

#include "util_time.h"

/* Number of characters needed to format the microsecond part of a timestamp.

 * Microseconds have 6 digits plus one separator character makes 7.

 *   */

#define AP_CTIME_USEC_LENGTH      7

/* Length of ISO 8601 date/time */

#define AP_CTIME_COMPACT_LEN      20

/* Cache for exploded values of recent timestamps

 */

struct exploded_time_cache_element {

    apr_int64_t t;

    apr_time_exp_t xt;

    apr_int64_t t_validate; /* please see comments in cached_explode() */

};

/* the "+ 1" is for the current second: */

#define TIME_CACHE_SIZE (AP_TIME_RECENT_THRESHOLD + 1)

/* Note that AP_TIME_RECENT_THRESHOLD is defined to

 * be a power of two minus one in util_time.h, so that

 * we can replace a modulo operation with a bitwise AND

 * when hashing items into a cache of size

 * AP_TIME_RECENT_THRESHOLD+1

 */

#define TIME_CACHE_MASK (AP_TIME_RECENT_THRESHOLD)

static struct exploded_time_cache_element exploded_cache_localtime[TIME_CACHE_SIZE];

static struct exploded_time_cache_element exploded_cache_gmt[TIME_CACHE_SIZE];

static apr_status_t cached_explode(apr_time_exp_t *xt, apr_time_t t,

                                   struct exploded_time_cache_element *cache,

                                   int use_gmt)

{

    apr_int64_t seconds = apr_time_sec(t);

    struct exploded_time_cache_element *cache_element =

        &(cache[seconds & TIME_CACHE_MASK]);

    struct exploded_time_cache_element cache_element_snapshot;

    /* The cache is implemented as a ring buffer.  Each second,

     * it uses a different element in the buffer.  The timestamp

     * in the element indicates whether the element contains the

     * exploded time for the current second (vs the time

     * 'now - AP_TIME_RECENT_THRESHOLD' seconds ago).  If the

     * cached value is for the current time, we use it.  Otherwise,

     * we compute the apr_time_exp_t and store it in this

     * cache element. Note that the timestamp in the cache

     * element is updated only after the exploded time.  Thus

     * if two threads hit this cache element simultaneously

     * at the start of a new second, they'll both explode the

     * time and store it.  I.e., the writers will collide, but

     * they'll be writing the same value.

     */

    if (cache_element->t >= seconds) {

        /* There is an intentional race condition in this design:

         * in a multithreaded app, one thread might be reading

         * from this cache_element to resolve a timestamp from

         * TIME_CACHE_SIZE seconds ago at the same time that

         * another thread is copying the exploded form of the

         * current time into the same cache_element.  (I.e., the

         * first thread might hit this element of the ring buffer

         * just as the element is being recycled.)  This can

         * also happen at the start of a new second, if a

         * reader accesses the cache_element after a writer

         * has updated cache_element.t but before the writer

         * has finished updating the whole cache_element.

         *

         * Rather than trying to prevent this race condition

         * with locks, we allow it to happen and then detect

         * and correct it.  The detection works like this:

         *   Step 1: Take a "snapshot" of the cache element by

         *           copying it into a temporary buffer.

         *   Step 2: Check whether the snapshot contains consistent

         *           data: the timestamps at the start and end of

         *           the cache_element should both match the 'seconds'

         *           value that we computed from the input time.

         *           If these three don't match, then the snapshot

         *           shows the cache_element in the middle of an

         *           update, and its contents are invalid.

         *   Step 3: If the snapshot is valid, use it.  Otherwise,

         *           just give up on the cache and explode the

         *           input time.

         */

        memcpy(&cache_element_snapshot, cache_element,

               sizeof(struct exploded_time_cache_element));

        if ((seconds != cache_element_snapshot.t) ||

            (seconds != cache_element_snapshot.t_validate)) {

            /* Invalid snapshot */

            if (use_gmt) {

                return apr_time_exp_gmt(xt, t);

            }

            else {

                return apr_time_exp_lt(xt, t);

            }

        }

        else {

            /* Valid snapshot */

            memcpy(xt, &(cache_element_snapshot.xt),

                   sizeof(apr_time_exp_t));

        }

    }

    else {

        apr_status_t r;

        if (use_gmt) {

            r = apr_time_exp_gmt(xt, t);

        }

        else {

            r = apr_time_exp_lt(xt, t);

        }

        if (r != APR_SUCCESS) {

            return r;

        }

        cache_element->t = seconds;

        memcpy(&(cache_element->xt), xt, sizeof(apr_time_exp_t));

        cache_element->t_validate = seconds;

    }

    xt->tm_usec = (int)apr_time_usec(t);

    return APR_SUCCESS;

}

AP_DECLARE(apr_status_t) ap_explode_recent_localtime(apr_time_exp_t * tm,

                                                     apr_time_t t)

{

    return cached_explode(tm, t, exploded_cache_localtime, 0);

}

AP_DECLARE(apr_status_t) ap_explode_recent_gmt(apr_time_exp_t * tm,

                                               apr_time_t t)

{

    return cached_explode(tm, t, exploded_cache_gmt, 1);

}

AP_DECLARE(apr_status_t) ap_recent_ctime(char *date_str, apr_time_t t)

{

    int len = APR_CTIME_LEN;

    return ap_recent_ctime_ex(date_str, t, AP_CTIME_OPTION_NONE, &len;;

}

AP_DECLARE(apr_status_t) ap_recent_ctime_ex(char *date_str, apr_time_t t,

                                            int option, int *len)

{

    /* ### This code is a clone of apr_ctime(), except that it

     * uses ap_explode_recent_localtime() instead of apr_time_exp_lt().

     */

    apr_time_exp_t xt;

    const char *s;

    int real_year;

    int needed;

    /* Calculate the needed buffer length */

    if (option & AP_CTIME_OPTION_COMPACT)

        needed = AP_CTIME_COMPACT_LEN;

    else

        needed = APR_CTIME_LEN;

    if (option & AP_CTIME_OPTION_USEC) {

        needed += AP_CTIME_USEC_LENGTH;

    }

    /* Check the provided buffer length */

    if (len && *len >= needed) {

        *len = needed;

    }

    else {

        if (len != NULL) {

            *len = 0;

        }

        return APR_ENOMEM;

    }

    /* example without options: "Wed Jun 30 21:49:08 1993" */

    /*                           123456789012345678901234  */

    /* example for compact format: "1993-06-30 21:49:08" */

    /*                              1234567890123456789  */

    ap_explode_recent_localtime(&xt, t);

    real_year = 1900 + xt.tm_year;

    if (option & AP_CTIME_OPTION_COMPACT) {

        int real_month = xt.tm_mon + 1;

        *date_str++ = real_year / 1000 + '0';

        *date_str++ = real_year % 1000 / 100 + '0';

        *date_str++ = real_year % 100 / 10 + '0';

        *date_str++ = real_year % 10 + '0';

        *date_str++ = '-';

        *date_str++ = real_month / 10 + '0';

        *date_str++ = real_month % 10 + '0';

        *date_str++ = '-';

    }

    else {

        s = &apr_day_snames[xt.tm_wday][0];

        *date_str++ = *s++;

        *date_str++ = *s++;

        *date_str++ = *s++;

        *date_str++ = ' ';

        s = &apr_month_snames[xt.tm_mon][0];

        *date_str++ = *s++;

        *date_str++ = *s++;

        *date_str++ = *s++;

        *date_str++ = ' ';

    }

    *date_str++ = xt.tm_mday / 10 + '0';

    *date_str++ = xt.tm_mday % 10 + '0';

    *date_str++ = ' ';

    *date_str++ = xt.tm_hour / 10 + '0';

    *date_str++ = xt.tm_hour % 10 + '0';

    *date_str++ = ':';

    *date_str++ = xt.tm_min / 10 + '0';

    *date_str++ = xt.tm_min % 10 + '0';

    *date_str++ = ':';

    *date_str++ = xt.tm_sec / 10 + '0';

    *date_str++ = xt.tm_sec % 10 + '0';

    if (option & AP_CTIME_OPTION_USEC) {

        int div;

        int usec = (int)xt.tm_usec;

        *date_str++ = '.';

        for (div=100000; div>0; div=div/10) {

            *date_str++ = usec / div + '0';

            usec = usec % div;

        }

    }

    if (!(option & AP_CTIME_OPTION_COMPACT)) {

        *date_str++ = ' ';

        *date_str++ = real_year / 1000 + '0';

        *date_str++ = real_year % 1000 / 100 + '0';

        *date_str++ = real_year % 100 / 10 + '0';

        *date_str++ = real_year % 10 + '0';

    }

    *date_str++ = 0;

    return APR_SUCCESS;

}

AP_DECLARE(apr_status_t) ap_recent_rfc822_date(char *date_str, apr_time_t t)

{

    /* ### This code is a clone of apr_rfc822_date(), except that it

     * uses ap_explode_recent_gmt() instead of apr_time_exp_gmt().

     */

    apr_time_exp_t xt;

    const char *s;

    int real_year;

    ap_explode_recent_gmt(&xt, t);

    /* example: "Sat, 08 Jan 2000 18:31:41 GMT" */

    /*           12345678901234567890123456789  */

    s = &apr_day_snames[xt.tm_wday][0];

    *date_str++ = *s++;

    *date_str++ = *s++;

    *date_str++ = *s++;

    *date_str++ = ',';

    *date_str++ = ' ';

    *date_str++ = xt.tm_mday / 10 + '0';

    *date_str++ = xt.tm_mday % 10 + '0';

    *date_str++ = ' ';

    s = &apr_month_snames[xt.tm_mon][0];

    *date_str++ = *s++;

    *date_str++ = *s++;

    *date_str++ = *s++;

    *date_str++ = ' ';

    real_year = 1900 + xt.tm_year;

    /* This routine isn't y10k ready. */

    *date_str++ = real_year / 1000 + '0';

    *date_str++ = real_year % 1000 / 100 + '0';

    *date_str++ = real_year % 100 / 10 + '0';

    *date_str++ = real_year % 10 + '0';

    *date_str++ = ' ';

    *date_str++ = xt.tm_hour / 10 + '0';

    *date_str++ = xt.tm_hour % 10 + '0';

    *date_str++ = ':';

    *date_str++ = xt.tm_min / 10 + '0';

    *date_str++ = xt.tm_min % 10 + '0';

    *date_str++ = ':';

    *date_str++ = xt.tm_sec / 10 + '0';

    *date_str++ = xt.tm_sec % 10 + '0';

    *date_str++ = ' ';

    *date_str++ = 'G';

    *date_str++ = 'M';

    *date_str++ = 'T';

    *date_str++ = 0;

    return APR_SUCCESS;

}