/* 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.
*/
/* * mod_unique_id.c: generate a unique identifier for each request * * Original author: Dean Gaudet <dgaudet@arctic.org> * UUencoding modified by: Alvaro Martinez Echevarria <alvaro@lander.es>
*/
#define APR_WANT_BYTEFUNC /* for htons() et al */ #include"apr_want.h" #include"apr_general.h"/* for APR_OFFSETOF */ #include"apr_network_io.h"
#ifdef APR_HAS_THREADS #include"apr_atomic.h"/* for apr_atomic_inc32 */ #include"mpm_common.h"/* for ap_mpm_query */ #endif
#include"httpd.h" #include"http_config.h" #include"http_log.h" #include"http_protocol.h"/* for ap_hook_post_read_request */
/* We are using thread_index (the index into the scoreboard), because we * cannot guarantee the thread_id will be an integer. * * This code looks like it won't give a unique ID with the new thread logic. * It will. The reason is, we don't increment the counter in a thread_safe * manner. Because the thread_index is also in the unique ID now, this does * not matter. In order for the id to not be unique, the same thread would * have to get the same counter twice in the same second.
*/
/* Comments: * * We want an identifier which is unique across all hits, everywhere. * "everywhere" includes multiple httpd instances on the same machine, or on * multiple machines. Essentially "everywhere" should include all possible * httpds across all servers at a particular "site". We make some assumptions * that if the site has a cluster of machines then their time is relatively * synchronized. We also assume that the first address returned by a * gethostbyname (gethostname()) is unique across all the machines at the * "site". * * The root is assumed to absolutely uniquely identify this one child * from all other currently running children on all servers (including * this physical server if it is running multiple httpds) from each * other. * * The stamp and counter are used to distinguish all hits for a * particular root. The stamp is updated using r->request_time, * saving cpu cycles. The counter is never reset, and is used to * permit up to 64k requests in a single second by a single child. * * The 144-bits of unique_id_rec are encoded using the alphabet * [A-Za-z0-9@-], resulting in 24 bytes of printable characters. That is then * stuffed into the environment variable UNIQUE_ID so that it is available to * other modules. The alphabet choice differs from normal base64 encoding * [A-Za-z0-9+/] because + and / are special characters in URLs and we want to * make it easy to use UNIQUE_ID in URLs. * * Note that UNIQUE_ID should be considered an opaque token by other * applications. No attempt should be made to dissect its internal components. * It is an abstraction that may change in the future as the needs of this * module change. * * It is highly desirable that identifiers exist for "eternity". But future * needs (such as much faster webservers, or moving to a * multithreaded server) may dictate a need to change the contents of * unique_id_rec. Such a future implementation should ensure that the first * field is still a time_t stamp. By doing that, it is possible for a site to * have a "flag second" in which they stop all of their old-format servers, * wait one entire second, and then start all of their new-servers. This * procedure will ensure that the new space of identifiers is completely unique * from the old space. (Since the first four unencoded bytes always differ.) * * Note: previous implementations used 32-bits of IP address plus pid * in place of the PRNG output in the "root" field. This was * insufficient for IPv6-only hosts, required working DNS to determine * a unique IP address (fragile), and needed a [0, 1) second sleep * call at startup to avoid pid reuse. Use of the PRNG avoids all * these issues.
*/
/* * Sun Jun 7 05:43:49 CEST 1998 -- Alvaro * More comments: * 1) The UUencoding procedure is now done in a general way, avoiding the problems * with sizes and paddings that can arise depending on the architecture. Now the * offsets and sizes of the elements of the unique_id_rec structure are calculated * in unique_id_global_init; and then used to duplicate the structure without the * paddings that might exist. The multithreaded server fix should be now very easy: * just add a new "tid" field to the unique_id_rec structure, and increase by one * UNIQUE_ID_REC_MAX. * 2) unique_id_rec.stamp has been changed from "time_t" to "unsigned int", because * its size is 64bits on some platforms (linux/alpha), and this caused problems with * htonl/ntohl. Well, this shouldn't be a problem till year 2106.
*/
/* * XXX: We should have a per-thread counter and not use cur_unique_id.counter * XXX: in all threads, because this is bad for performance on multi-processor * XXX: systems: Writing to the same address from several CPUs causes cache * XXX: thrashing.
*/ static unique_id_rec cur_unique_id; static apr_uint32_t cur_unique_counter; #ifdef APR_HAS_THREADS staticint is_threaded_mpm; #endif
/* * Number of elements in the structure unique_id_rec.
*/ #define UNIQUE_ID_REC_MAX 4
/* * If we use 0 as the initial counter we have a little less protection * against restart problems, and a little less protection against a clock * going backwards in time.
*/
ap_random_insecure_bytes(&cur_unique_counter, sizeof(cur_unique_counter));
}
staticconstchar *gen_unique_id(const request_rec *r)
{ char *str; /* * Buffer padded with two final bytes, used to copy the unique_id_rec * structure without the internal paddings that it could have.
*/
unique_id_rec new_unique_id; struct {
unique_id_rec foo; unsignedchar pad[2];
} paddedbuf;
apr_uint32_t counter; unsignedchar *x,*y; int i,j,k;
/* The counter is two bytes for the uuencoded unique id, in network * byte order.
*/
new_unique_id.counter = htons(counter % APR_UINT16_MAX);
/* we'll use a temporal buffer to avoid uuencoding the possible internal
* paddings of the original structure */
x = (unsignedchar *) &paddedbuf;
k = 0; for (i = 0; i < UNIQUE_ID_REC_MAX; i++) {
y = ((unsignedchar *) &new_unique_id) + unique_id_rec_offset[i]; for (j = 0; j < unique_id_rec_size[i]; j++, k++) {
x[k] = y[j];
}
} /* * We reset two more bytes just in case padding is needed for the uuencoding.
*/
x[k++] = '\0';
x[k++] = '\0';
/* alloc str and do the uuencoding */
str = (char *)apr_palloc(r->pool, unique_id_rec_size_uu + 1);
k = 0; for (i = 0; i < unique_id_rec_total_size; i += 3) {
y = x + i;
str[k++] = uuencoder[y[0] >> 2];
str[k++] = uuencoder[((y[0] & 0x03) << 4) | ((y[1] & 0xf0) >> 4)]; if (k == unique_id_rec_size_uu) break;
str[k++] = uuencoder[((y[1] & 0x0f) << 2) | ((y[2] & 0xc0) >> 6)]; if (k == unique_id_rec_size_uu) break;
str[k++] = uuencoder[y[2] & 0x3f];
}
str[k++] = '\0';
return str;
}
/* * There are two ways the generation of a unique id can be triggered: * * - from the post_read_request hook which calls set_unique_id() * - from error logging via the generate_log_id hook which calls * generate_log_id(). This may happen before or after set_unique_id() * has been called, or not at all.
*/
staticint generate_log_id(const conn_rec *c, const request_rec *r, constchar **id)
{ /* we do not care about connection ids */ if (r == NULL) return DECLINED;
/* XXX: do we need special handling for internal redirects? */
/* if set_unique_id() has been called for this request, use it */
*id = apr_table_get(r->subprocess_env, "UNIQUE_ID");
if (!*id)
*id = gen_unique_id(r); return OK;
}
staticint set_unique_id(request_rec *r)
{ constchar *id = NULL; /* copy the unique_id if this is an internal redirect (we're never * actually called for sub requests, so we don't need to test for
* them) */ if (r->prev) {
id = apr_table_get(r->subprocess_env, "REDIRECT_UNIQUE_ID");
}
if (!id) { /* if we have a log id, it was set by our generate_log_id() function * and we should reuse the same id
*/
id = r->log_id;
}
if (!id) {
id = gen_unique_id(r);
}
/* set the environment variable */
apr_table_setn(r->subprocess_env, "UNIQUE_ID", id);
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