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| -rw-r--r-- | modules/metadata/mod_unique_id.c | 336 |
1 files changed, 336 insertions, 0 deletions
diff --git a/modules/metadata/mod_unique_id.c b/modules/metadata/mod_unique_id.c new file mode 100644 index 0000000..2555749 --- /dev/null +++ b/modules/metadata/mod_unique_id.c @@ -0,0 +1,336 @@ +/* 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 */ + +#define ROOT_SIZE 10 + +typedef struct { + unsigned int stamp; + char root[ROOT_SIZE]; + unsigned short counter; + unsigned int thread_index; +} unique_id_rec; + +/* 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 +static int is_threaded_mpm; +#endif + +/* + * Number of elements in the structure unique_id_rec. + */ +#define UNIQUE_ID_REC_MAX 4 + +static unsigned short unique_id_rec_offset[UNIQUE_ID_REC_MAX], + unique_id_rec_size[UNIQUE_ID_REC_MAX], + unique_id_rec_total_size, + unique_id_rec_size_uu; + +static int unique_id_global_init(apr_pool_t *p, apr_pool_t *plog, apr_pool_t *ptemp, server_rec *main_server) +{ + /* + * Calculate the sizes and offsets in cur_unique_id. + */ + unique_id_rec_offset[0] = APR_OFFSETOF(unique_id_rec, stamp); + unique_id_rec_size[0] = sizeof(cur_unique_id.stamp); + unique_id_rec_offset[1] = APR_OFFSETOF(unique_id_rec, root); + unique_id_rec_size[1] = sizeof(cur_unique_id.root); + unique_id_rec_offset[2] = APR_OFFSETOF(unique_id_rec, counter); + unique_id_rec_size[2] = sizeof(cur_unique_id.counter); + unique_id_rec_offset[3] = APR_OFFSETOF(unique_id_rec, thread_index); + unique_id_rec_size[3] = sizeof(cur_unique_id.thread_index); + unique_id_rec_total_size = unique_id_rec_size[0] + unique_id_rec_size[1] + + unique_id_rec_size[2] + unique_id_rec_size[3]; + + /* + * Calculate the size of the structure when encoded. + */ + unique_id_rec_size_uu = (unique_id_rec_total_size*8+5)/6; + + return OK; +} + +static void unique_id_child_init(apr_pool_t *p, server_rec *s) +{ +#ifdef APR_HAS_THREADS + is_threaded_mpm = 0; + ap_mpm_query(AP_MPMQ_IS_THREADED, &is_threaded_mpm); +#endif + + ap_random_insecure_bytes(&cur_unique_id.root, + sizeof(cur_unique_id.root)); + + /* + * 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)); +} + +/* Use the base64url encoding per RFC 4648, avoiding characters which + * are not safe in URLs. ### TODO: can switch to apr_encode_*. */ +static const char uuencoder[64] = { + 'A', 'B', 'C', 'D', 'E', 'F', 'G', 'H', 'I', 'J', 'K', 'L', 'M', + 'N', 'O', 'P', 'Q', 'R', 'S', 'T', 'U', 'V', 'W', 'X', 'Y', 'Z', + 'a', 'b', 'c', 'd', 'e', 'f', 'g', 'h', 'i', 'j', 'k', 'l', 'm', + 'n', 'o', 'p', 'q', 'r', 's', 't', 'u', 'v', 'w', 'x', 'y', 'z', + '0', '1', '2', '3', '4', '5', '6', '7', '8', '9', '-', '_', +}; + +#ifndef APR_UINT16_MAX +#define APR_UINT16_MAX 0xffffu +#endif + +static const char *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; + unsigned char pad[2]; + } paddedbuf; + apr_uint32_t counter; + unsigned char *x,*y; + int i,j,k; + + memcpy(&new_unique_id.root, &cur_unique_id.root, ROOT_SIZE); + new_unique_id.stamp = htonl((unsigned int)apr_time_sec(r->request_time)); + new_unique_id.thread_index = htonl((unsigned int)r->connection->id); +#ifdef APR_HAS_THREADS + if (is_threaded_mpm) + counter = apr_atomic_inc32(&cur_unique_counter); + else +#endif + counter = cur_unique_counter++; + + /* 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 = (unsigned char *) &paddedbuf; + k = 0; + for (i = 0; i < UNIQUE_ID_REC_MAX; i++) { + y = ((unsigned char *) &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. + */ + +static int generate_log_id(const conn_rec *c, const request_rec *r, + const char **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; +} + +static int set_unique_id(request_rec *r) +{ + const char *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); + + return DECLINED; +} + +static void register_hooks(apr_pool_t *p) +{ + ap_hook_post_config(unique_id_global_init, NULL, NULL, APR_HOOK_MIDDLE); + ap_hook_child_init(unique_id_child_init, NULL, NULL, APR_HOOK_MIDDLE); + ap_hook_post_read_request(set_unique_id, NULL, NULL, APR_HOOK_MIDDLE); + ap_hook_generate_log_id(generate_log_id, NULL, NULL, APR_HOOK_MIDDLE); +} + +AP_DECLARE_MODULE(unique_id) = { + STANDARD20_MODULE_STUFF, + NULL, /* dir config creater */ + NULL, /* dir merger --- default is to override */ + NULL, /* server config */ + NULL, /* merge server configs */ + NULL, /* command apr_table_t */ + register_hooks /* register hooks */ +}; |