337 lines
12 KiB
C
337 lines
12 KiB
C
/* Licensed to the Apache Software Foundation (ASF) under one or more
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* contributor license agreements. See the NOTICE file distributed with
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* this work for additional information regarding copyright ownership.
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* The ASF licenses this file to You under the Apache License, Version 2.0
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* (the "License"); you may not use this file except in compliance with
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* the License. You may obtain a copy of the License at
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*
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* http://www.apache.org/licenses/LICENSE-2.0
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*
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* Unless required by applicable law or agreed to in writing, software
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* distributed under the License is distributed on an "AS IS" BASIS,
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* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
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* See the License for the specific language governing permissions and
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* limitations under the License.
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*/
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/*
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* mod_unique_id.c: generate a unique identifier for each request
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*
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* Original author: Dean Gaudet <dgaudet@arctic.org>
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* UUencoding modified by: Alvaro Martinez Echevarria <alvaro@lander.es>
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*/
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#define APR_WANT_BYTEFUNC /* for htons() et al */
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#include "apr_want.h"
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#include "apr_general.h" /* for APR_OFFSETOF */
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#include "apr_network_io.h"
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#ifdef APR_HAS_THREADS
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#include "apr_atomic.h" /* for apr_atomic_inc32 */
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#include "mpm_common.h" /* for ap_mpm_query */
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#endif
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#include "httpd.h"
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#include "http_config.h"
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#include "http_log.h"
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#include "http_protocol.h" /* for ap_hook_post_read_request */
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#define ROOT_SIZE 10
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typedef struct {
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unsigned int stamp;
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char root[ROOT_SIZE];
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unsigned short counter;
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unsigned int thread_index;
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} unique_id_rec;
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/* We are using thread_index (the index into the scoreboard), because we
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* cannot guarantee the thread_id will be an integer.
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*
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* This code looks like it won't give a unique ID with the new thread logic.
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* It will. The reason is, we don't increment the counter in a thread_safe
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* manner. Because the thread_index is also in the unique ID now, this does
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* not matter. In order for the id to not be unique, the same thread would
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* have to get the same counter twice in the same second.
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*/
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/* Comments:
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*
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* We want an identifier which is unique across all hits, everywhere.
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* "everywhere" includes multiple httpd instances on the same machine, or on
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* multiple machines. Essentially "everywhere" should include all possible
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* httpds across all servers at a particular "site". We make some assumptions
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* that if the site has a cluster of machines then their time is relatively
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* synchronized. We also assume that the first address returned by a
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* gethostbyname (gethostname()) is unique across all the machines at the
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* "site".
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*
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* The root is assumed to absolutely uniquely identify this one child
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* from all other currently running children on all servers (including
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* this physical server if it is running multiple httpds) from each
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* other.
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*
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* The stamp and counter are used to distinguish all hits for a
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* particular root. The stamp is updated using r->request_time,
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* saving cpu cycles. The counter is never reset, and is used to
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* permit up to 64k requests in a single second by a single child.
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*
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* The 144-bits of unique_id_rec are encoded using the alphabet
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* [A-Za-z0-9@-], resulting in 24 bytes of printable characters. That is then
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* stuffed into the environment variable UNIQUE_ID so that it is available to
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* other modules. The alphabet choice differs from normal base64 encoding
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* [A-Za-z0-9+/] because + and / are special characters in URLs and we want to
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* make it easy to use UNIQUE_ID in URLs.
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*
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* Note that UNIQUE_ID should be considered an opaque token by other
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* applications. No attempt should be made to dissect its internal components.
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* It is an abstraction that may change in the future as the needs of this
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* module change.
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*
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* It is highly desirable that identifiers exist for "eternity". But future
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* needs (such as much faster webservers, or moving to a
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* multithreaded server) may dictate a need to change the contents of
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* unique_id_rec. Such a future implementation should ensure that the first
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* field is still a time_t stamp. By doing that, it is possible for a site to
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* have a "flag second" in which they stop all of their old-format servers,
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* wait one entire second, and then start all of their new-servers. This
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* procedure will ensure that the new space of identifiers is completely unique
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* from the old space. (Since the first four unencoded bytes always differ.)
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*
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* Note: previous implementations used 32-bits of IP address plus pid
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* in place of the PRNG output in the "root" field. This was
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* insufficient for IPv6-only hosts, required working DNS to determine
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* a unique IP address (fragile), and needed a [0, 1) second sleep
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* call at startup to avoid pid reuse. Use of the PRNG avoids all
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* these issues.
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*/
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/*
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* Sun Jun 7 05:43:49 CEST 1998 -- Alvaro
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* More comments:
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* 1) The UUencoding procedure is now done in a general way, avoiding the problems
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* with sizes and paddings that can arise depending on the architecture. Now the
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* offsets and sizes of the elements of the unique_id_rec structure are calculated
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* in unique_id_global_init; and then used to duplicate the structure without the
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* paddings that might exist. The multithreaded server fix should be now very easy:
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* just add a new "tid" field to the unique_id_rec structure, and increase by one
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* UNIQUE_ID_REC_MAX.
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* 2) unique_id_rec.stamp has been changed from "time_t" to "unsigned int", because
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* its size is 64bits on some platforms (linux/alpha), and this caused problems with
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* htonl/ntohl. Well, this shouldn't be a problem till year 2106.
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*/
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/*
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* XXX: We should have a per-thread counter and not use cur_unique_id.counter
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* XXX: in all threads, because this is bad for performance on multi-processor
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* XXX: systems: Writing to the same address from several CPUs causes cache
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* XXX: thrashing.
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*/
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static unique_id_rec cur_unique_id;
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static apr_uint32_t cur_unique_counter;
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#ifdef APR_HAS_THREADS
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static int is_threaded_mpm;
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#endif
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/*
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* Number of elements in the structure unique_id_rec.
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*/
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#define UNIQUE_ID_REC_MAX 4
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static unsigned short unique_id_rec_offset[UNIQUE_ID_REC_MAX],
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unique_id_rec_size[UNIQUE_ID_REC_MAX],
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unique_id_rec_total_size,
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unique_id_rec_size_uu;
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static int unique_id_global_init(apr_pool_t *p, apr_pool_t *plog, apr_pool_t *ptemp, server_rec *main_server)
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{
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/*
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* Calculate the sizes and offsets in cur_unique_id.
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*/
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unique_id_rec_offset[0] = APR_OFFSETOF(unique_id_rec, stamp);
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unique_id_rec_size[0] = sizeof(cur_unique_id.stamp);
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unique_id_rec_offset[1] = APR_OFFSETOF(unique_id_rec, root);
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unique_id_rec_size[1] = sizeof(cur_unique_id.root);
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unique_id_rec_offset[2] = APR_OFFSETOF(unique_id_rec, counter);
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unique_id_rec_size[2] = sizeof(cur_unique_id.counter);
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unique_id_rec_offset[3] = APR_OFFSETOF(unique_id_rec, thread_index);
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unique_id_rec_size[3] = sizeof(cur_unique_id.thread_index);
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unique_id_rec_total_size = unique_id_rec_size[0] + unique_id_rec_size[1] +
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unique_id_rec_size[2] + unique_id_rec_size[3];
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/*
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* Calculate the size of the structure when encoded.
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*/
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unique_id_rec_size_uu = (unique_id_rec_total_size*8+5)/6;
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return OK;
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}
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static void unique_id_child_init(apr_pool_t *p, server_rec *s)
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{
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#ifdef APR_HAS_THREADS
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is_threaded_mpm = 0;
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ap_mpm_query(AP_MPMQ_IS_THREADED, &is_threaded_mpm);
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#endif
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ap_random_insecure_bytes(&cur_unique_id.root,
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sizeof(cur_unique_id.root));
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/*
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* If we use 0 as the initial counter we have a little less protection
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* against restart problems, and a little less protection against a clock
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* going backwards in time.
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*/
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ap_random_insecure_bytes(&cur_unique_counter,
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sizeof(cur_unique_counter));
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}
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/* Use the base64url encoding per RFC 4648, avoiding characters which
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* are not safe in URLs. ### TODO: can switch to apr_encode_*. */
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static const char uuencoder[64] = {
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'A', 'B', 'C', 'D', 'E', 'F', 'G', 'H', 'I', 'J', 'K', 'L', 'M',
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'N', 'O', 'P', 'Q', 'R', 'S', 'T', 'U', 'V', 'W', 'X', 'Y', 'Z',
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'a', 'b', 'c', 'd', 'e', 'f', 'g', 'h', 'i', 'j', 'k', 'l', 'm',
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'n', 'o', 'p', 'q', 'r', 's', 't', 'u', 'v', 'w', 'x', 'y', 'z',
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'0', '1', '2', '3', '4', '5', '6', '7', '8', '9', '-', '_',
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};
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#ifndef APR_UINT16_MAX
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#define APR_UINT16_MAX 0xffffu
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#endif
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static const char *gen_unique_id(const request_rec *r)
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{
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char *str;
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/*
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* Buffer padded with two final bytes, used to copy the unique_id_rec
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* structure without the internal paddings that it could have.
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*/
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unique_id_rec new_unique_id;
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struct {
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unique_id_rec foo;
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unsigned char pad[2];
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} paddedbuf;
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apr_uint32_t counter;
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unsigned char *x,*y;
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int i,j,k;
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memcpy(&new_unique_id.root, &cur_unique_id.root, ROOT_SIZE);
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new_unique_id.stamp = htonl((unsigned int)apr_time_sec(r->request_time));
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new_unique_id.thread_index = htonl((unsigned int)r->connection->id);
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#ifdef APR_HAS_THREADS
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if (is_threaded_mpm)
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counter = apr_atomic_inc32(&cur_unique_counter);
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else
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#endif
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counter = cur_unique_counter++;
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/* The counter is two bytes for the uuencoded unique id, in network
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* byte order.
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*/
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new_unique_id.counter = htons(counter % APR_UINT16_MAX);
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/* we'll use a temporal buffer to avoid uuencoding the possible internal
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* paddings of the original structure */
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x = (unsigned char *) &paddedbuf;
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k = 0;
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for (i = 0; i < UNIQUE_ID_REC_MAX; i++) {
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y = ((unsigned char *) &new_unique_id) + unique_id_rec_offset[i];
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for (j = 0; j < unique_id_rec_size[i]; j++, k++) {
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x[k] = y[j];
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}
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}
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/*
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* We reset two more bytes just in case padding is needed for the uuencoding.
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*/
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x[k++] = '\0';
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x[k++] = '\0';
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/* alloc str and do the uuencoding */
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str = (char *)apr_palloc(r->pool, unique_id_rec_size_uu + 1);
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k = 0;
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for (i = 0; i < unique_id_rec_total_size; i += 3) {
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y = x + i;
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str[k++] = uuencoder[y[0] >> 2];
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str[k++] = uuencoder[((y[0] & 0x03) << 4) | ((y[1] & 0xf0) >> 4)];
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if (k == unique_id_rec_size_uu) break;
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str[k++] = uuencoder[((y[1] & 0x0f) << 2) | ((y[2] & 0xc0) >> 6)];
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if (k == unique_id_rec_size_uu) break;
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str[k++] = uuencoder[y[2] & 0x3f];
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}
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str[k++] = '\0';
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return str;
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}
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/*
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* There are two ways the generation of a unique id can be triggered:
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*
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* - from the post_read_request hook which calls set_unique_id()
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* - from error logging via the generate_log_id hook which calls
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* generate_log_id(). This may happen before or after set_unique_id()
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* has been called, or not at all.
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*/
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static int generate_log_id(const conn_rec *c, const request_rec *r,
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const char **id)
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{
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/* we do not care about connection ids */
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if (r == NULL)
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return DECLINED;
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/* XXX: do we need special handling for internal redirects? */
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/* if set_unique_id() has been called for this request, use it */
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*id = apr_table_get(r->subprocess_env, "UNIQUE_ID");
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if (!*id)
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*id = gen_unique_id(r);
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return OK;
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}
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static int set_unique_id(request_rec *r)
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{
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const char *id = NULL;
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/* copy the unique_id if this is an internal redirect (we're never
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* actually called for sub requests, so we don't need to test for
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* them) */
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if (r->prev) {
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id = apr_table_get(r->subprocess_env, "REDIRECT_UNIQUE_ID");
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}
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if (!id) {
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/* if we have a log id, it was set by our generate_log_id() function
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* and we should reuse the same id
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*/
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id = r->log_id;
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}
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if (!id) {
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id = gen_unique_id(r);
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}
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/* set the environment variable */
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apr_table_setn(r->subprocess_env, "UNIQUE_ID", id);
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return DECLINED;
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}
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static void register_hooks(apr_pool_t *p)
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{
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ap_hook_post_config(unique_id_global_init, NULL, NULL, APR_HOOK_MIDDLE);
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ap_hook_child_init(unique_id_child_init, NULL, NULL, APR_HOOK_MIDDLE);
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ap_hook_post_read_request(set_unique_id, NULL, NULL, APR_HOOK_MIDDLE);
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ap_hook_generate_log_id(generate_log_id, NULL, NULL, APR_HOOK_MIDDLE);
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}
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AP_DECLARE_MODULE(unique_id) = {
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STANDARD20_MODULE_STUFF,
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NULL, /* dir config creater */
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NULL, /* dir merger --- default is to override */
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NULL, /* server config */
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NULL, /* merge server configs */
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NULL, /* command apr_table_t */
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register_hooks /* register hooks */
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};
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