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For more * information on the Apache Software Foundation, please see * . * * Portions of this software are based upon public domain software * originally written at the National Center for Supercomputing Applications, * University of Illinois, Urbana-Champaign. */ /* * mod_unique_id.c: generate a unique identifier for each request * * Original author: Dean Gaudet * UUencoding modified by: Alvaro Martinez Echevarria */ #include "apr_general.h" /* for XtOffsetOf */ #include "httpd.h" #include "http_config.h" #include "http_log.h" #include "http_protocol.h" /* for ap_hook_post_read_request */ #if APR_HAVE_NETDB_H #include #endif #if APR_HAVE_ARPA_INET_H #include #endif #if APR_HAVE_UNISTD_H #include #endif typedef struct { unsigned int stamp; unsigned int in_addr; unsigned int pid; unsigned short counter; unsigned int thread_index; } unique_id_rec; /* We are using thread_index (the index into the scoreboard), because we * cannont garauntee 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". * * We also further assume that pids fit in 32-bits. If something uses more * than 32-bits, the fix is trivial, but it requires the unrolled uuencoding * loop to be extended. * A similar fix is needed to support multithreaded * servers, using a pid/tid combo. * * Together, the in_addr and pid are 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 * (in_addr,pid) pair. 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 112-bits of unique_id_rec are encoded using the alphabet * [A-Za-z0-9@-], resulting in 19 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, moving to 64-bit pids, 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.) */ /* * 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. */ static unsigned global_in_addr; static unique_id_rec cur_unique_id; /* * Number of elements in the structure unique_id_rec. */ #define UNIQUE_ID_REC_MAX 5 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 void unique_id_global_init(apr_pool_t *p, apr_pool_t *plog, apr_pool_t *ptemp, server_rec *main_server) { #ifndef MAXHOSTNAMELEN #define MAXHOSTNAMELEN 256 #endif char str[MAXHOSTNAMELEN + 1]; struct hostent *hent; apr_short_interval_time_t pause; /* * Calculate the sizes and offsets in cur_unique_id. */ unique_id_rec_offset[0] = XtOffsetOf(unique_id_rec, stamp); unique_id_rec_size[0] = sizeof(cur_unique_id.stamp); unique_id_rec_offset[1] = XtOffsetOf(unique_id_rec, in_addr); unique_id_rec_size[1] = sizeof(cur_unique_id.in_addr); unique_id_rec_offset[2] = XtOffsetOf(unique_id_rec, pid); unique_id_rec_size[2] = sizeof(cur_unique_id.pid); unique_id_rec_offset[3] = XtOffsetOf(unique_id_rec, counter); unique_id_rec_size[3] = sizeof(cur_unique_id.counter); unique_id_rec_offset[4] = XtOffsetOf(unique_id_rec, thread_index); unique_id_rec_size[4] = 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] + unique_id_rec_size[4]; /* * Calculate the size of the structure when encoded. */ unique_id_rec_size_uu = (unique_id_rec_total_size*8+5)/6; /* * Now get the global in_addr. Note that it is not sufficient to use one * of the addresses from the main_server, since those aren't as likely to * be unique as the physical address of the machine */ if (gethostname(str, sizeof(str) - 1) != 0) { ap_log_error(APLOG_MARK, APLOG_NOERRNO|APLOG_ALERT, errno, main_server, "gethostname: mod_unique_id requires the hostname of the server"); exit(1); } str[sizeof(str) - 1] = '\0'; if ((hent = gethostbyname(str)) == NULL) { ap_log_error(APLOG_MARK, APLOG_NOERRNO|APLOG_ALERT, h_errno, main_server, "mod_unique_id: unable to gethostbyname(\"%s\")", str); exit(1); } global_in_addr = ((struct in_addr *) hent->h_addr_list[0])->s_addr; ap_log_error(APLOG_MARK, APLOG_NOERRNO|APLOG_INFO, 0, main_server, "mod_unique_id: using ip addr %s", inet_ntoa(*(struct in_addr *) hent->h_addr_list[0])); /* * If the server is pummelled with restart requests we could possibly end * up in a situation where we're starting again during the same second * that has been used in previous identifiers. Avoid that situation. * * In truth, for this to actually happen not only would it have to restart * in the same second, but it would have to somehow get the same pids as * one of the other servers that was running in that second. Which would * mean a 64k wraparound on pids ... not very likely at all. * * But protecting against it is relatively cheap. We just sleep into the * next second. */ pause = (apr_short_interval_time_t)(1000000 - (apr_time_now() % APR_USEC_PER_SEC)); apr_sleep(pause); } static void unique_id_child_init(apr_pool_t *p, server_rec *s) { pid_t pid; apr_time_t tv; /* * Note that we use the pid because it's possible that on the same * physical machine there are multiple servers (i.e. using Listen). But * it's guaranteed that none of them will share the same pids between * children. * * XXX: for multithread this needs to use a pid/tid combo and probably * needs to be expanded to 32 bits */ pid = getpid(); cur_unique_id.pid = pid; /* * Test our assumption that the pid is 32-bits. It's possible that * 64-bit machines will declare pid_t to be 64 bits but only use 32 * of them. It would have been really nice to test this during * global_init ... but oh well. */ if (cur_unique_id.pid != pid) { ap_log_error(APLOG_MARK, APLOG_NOERRNO|APLOG_CRIT, 0, s, "oh no! pids are greater than 32-bits! I'm broken!"); } cur_unique_id.in_addr = global_in_addr; /* * 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. */ tv = apr_time_now(); /* Some systems have very low variance on the low end of their system * counter, defend against that. */ cur_unique_id.counter = tv % APR_USEC_PER_SEC / 10; /* * We must always use network ordering for these bytes, so that * identifiers are comparable between machines of different byte * orderings. Note in_addr is already in network order. */ cur_unique_id.pid = htonl(cur_unique_id.pid); cur_unique_id.counter = htons(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 int gen_unique_id(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; const char *e; int i,j,k; /* 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 && (e = apr_table_get(r->subprocess_env, "REDIRECT_UNIQUE_ID"))) { apr_table_setn(r->subprocess_env, "UNIQUE_ID", e); return DECLINED; } new_unique_id.in_addr = cur_unique_id.in_addr; new_unique_id.pid = cur_unique_id.pid; new_unique_id.counter = cur_unique_id.counter; new_unique_id.stamp = htonl((unsigned int)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; y = (unsigned char *) &new_unique_id; 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'; /* set the environment variable */ apr_table_setn(r->subprocess_env, "UNIQUE_ID", str); /* and increment the identifier for the next call */ counter = ntohs(new_unique_id.counter) + 1; cur_unique_id.counter = htons(counter); 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(gen_unique_id, NULL, NULL, APR_HOOK_MIDDLE); } module AP_MODULE_DECLARE_DATA unique_id_module = { 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 */ };