/* 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 (including trailing '\0') */ #define AP_CTIME_COMPACT_LEN 20
/* Length of timezone offset from GMT ([+-]hhmm) plus leading space */ #define AP_CTIME_GMTOFF_LEN 6
/* 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)
/* 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_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; constchar *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;
}
if (option & AP_CTIME_OPTION_GMTOFF) {
needed += AP_CTIME_GMTOFF_LEN;
}
/* Check the provided buffer length (note: above AP_CTIME_COMPACT_LEN * and APR_CTIME_LEN include the trailing '\0'; so does 'needed' then).
*/ 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" */ /* example for compact format: "1993-06-30 21:49:08" */ /* example for compact+usec+gmtoff format: * "1993-06-30 22:49:08.123456 +0100"
*/
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; constchar *s; int real_year;
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