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/*
* mod_unique_id.c: generate a unique identifier for each request
*
* Original author: Dean Gaudet
* UUencoding modified by: Alvaro Martinez Echevarria
*/
#include "httpd.h"
#include "http_config.h"
#include "http_log.h"
#include "multithread.h"
#ifdef MULTITHREAD
#error sorry this module does not support multithreaded servers yet
#endif
typedef struct {
unsigned int stamp;
unsigned int in_addr;
unsigned int pid;
unsigned short counter;
} unique_id_rec;
/* 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 APACHE_TLS 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 void unique_id_global_init(server_rec *s, pool *p)
{
#ifndef MAXHOSTNAMELEN
#define MAXHOSTNAMELEN 256
#endif
char str[MAXHOSTNAMELEN + 1];
struct hostent *hent;
#ifndef NO_GETTIMEOFDAY
struct timeval tv;
#endif
/*
* 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_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;
/*
* 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, s,
"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, s,
"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, s,
"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.
*/
#ifdef NO_GETTIMEOFDAY
sleep(1);
#else
if (gettimeofday(&tv, NULL) == -1) {
sleep(1);
}
else if (tv.tv_usec) {
tv.tv_sec = 0;
tv.tv_usec = 1000000 - tv.tv_usec;
select(0, NULL, NULL, NULL, &tv);
}
#endif
}
static void unique_id_child_init(server_rec *s, pool *p)
{
pid_t pid;
#ifndef NO_GETTIMEOFDAY
struct timeval tv;
#endif
/*
* 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, 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.
*/
#ifndef NO_GETTIMEOFDAY
if (gettimeofday(&tv, NULL) == -1) {
cur_unique_id.counter = 0;
}
else {
/* Some systems have very low variance on the low end of their
* system counter, defend against that.
*/
cur_unique_id.counter = tv.tv_usec / 10;
}
#else
cur_unique_id.counter = 0;
#endif
/*
* 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.
*/
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 = ap_table_get(r->subprocess_env, "REDIRECT_UNIQUE_ID"))) {
ap_table_setn(r->subprocess_env, "UNIQUE_ID", e);
return DECLINED;
}
cur_unique_id.stamp = htonl((unsigned int)r->request_time);
/* we'll use a temporal buffer to avoid uuencoding the possible internal
* paddings of the original structure */
x = (unsigned char *) &paddedbuf;
y = (unsigned char *) &cur_unique_id;
k = 0;
for (i = 0; i < UNIQUE_ID_REC_MAX; i++) {
y = ((unsigned char *) &cur_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 *)ap_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 */
ap_table_setn(r->subprocess_env, "UNIQUE_ID", str);
/* and increment the identifier for the next call */
counter = ntohs(cur_unique_id.counter) + 1;
cur_unique_id.counter = htons(counter);
return DECLINED;
}
module MODULE_VAR_EXPORT unique_id_module = {
STANDARD_MODULE_STUFF,
unique_id_global_init, /* initializer */
NULL, /* dir config creater */
NULL, /* dir merger --- default is to override */
NULL, /* server config */
NULL, /* merge server configs */
NULL, /* command table */
NULL, /* handlers */
NULL, /* filename translation */
NULL, /* check_user_id */
NULL, /* check auth */
NULL, /* check access */
NULL, /* type_checker */
NULL, /* fixups */
NULL, /* logger */
NULL, /* header parser */
unique_id_child_init, /* child_init */
NULL, /* child_exit */
gen_unique_id /* post_read_request */
};