/* 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 * UUencoding modified by: Alvaro Martinez Echevarria */ #define APR_WANT_BYTEFUNC /* for htons() et al */ #include "apr_want.h" #include "apr_general.h" /* for APR_OFFSETOF */ #include "apr_network_io.h" #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 prodecure 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; /* * 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) { 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_id.counter, sizeof(cur_unique_id.counter)); } /* NOTE: This is *NOT* the same encoding used by base64encode ... the last two * characters should be + and /. But those two characters have very special * meanings in URLs, and we want to make it easy to use identifiers in * URLs. So we replace them with @ and -. */ 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', '@', '-', }; static const char *gen_unique_id(const request_rec *r) { char *str; /* * Buffer padded with two final bytes, used to copy the unique_id_red * 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; unsigned char *x,*y; unsigned short counter; int i,j,k; memcpy(&new_unique_id.root, &cur_unique_id.root, ROOT_SIZE); new_unique_id.counter = cur_unique_id.counter; new_unique_id.stamp = htonl((unsigned int)apr_time_sec(r->request_time)); new_unique_id.thread_index = htonl((unsigned int)r->connection->id); /* 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'; /* and increment the identifier for the next call */ counter = ntohs(new_unique_id.counter) + 1; cur_unique_id.counter = htons(counter); 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 */ };