mod_unique_id.c revision ce9621257ef9e54c1bbe5ad8a5f445a1f211c2dc
/* Copyright 2000-2004 Apache Software Foundation
*
* Licensed 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
*
*
* 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"
#include "httpd.h"
#include "http_config.h"
#include "http_log.h"
#include "http_protocol.h" /* for ap_hook_post_read_request */
#include <unistd.h> /* for getpid() */
#endif
typedef struct {
unsigned int stamp;
unsigned int in_addr;
unsigned int pid;
unsigned short counter;
unsigned int thread_index;
/* 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".
*
* 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
*
* 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
*/
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],
static int unique_id_global_init(apr_pool_t *p, apr_pool_t *plog, apr_pool_t *ptemp, server_rec *main_server)
{
char *ipaddrstr;
/*
* Calculate the sizes and offsets in cur_unique_id.
*/
/*
* Calculate the size of the structure when encoded.
*/
/*
* 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
*/
"mod_unique_id: unable to find hostname of the server");
return HTTP_INTERNAL_SERVER_ERROR;
}
}
else {
"mod_unique_id: unable to find IPv4 address of \"%s\"", str);
#if APR_HAVE_IPV6
sizeof(global_in_addr));
"mod_unique_id: using low-order bits of IPv6 address "
"as if they were unique");
}
else
#endif
return HTTP_INTERNAL_SERVER_ERROR;
}
"mod_unique_id: using ip addr %s",
/*
* 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.
*/
return OK;
}
{
/*
* 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.
*
* needs to be expanded to 32 bits
*/
/*
* 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.
*/
"oh no! pids are greater than 32-bits! I'm broken!");
}
/*
* 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.
*/
/*
* 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.
*/
}
/* 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 {
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) */
return DECLINED;
}
/* 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 */
k = 0;
for (i = 0; i < unique_id_rec_total_size; i += 3) {
y = x + i;
if (k == unique_id_rec_size_uu) break;
if (k == unique_id_rec_size_uu) break;
}
str[k++] = '\0';
/* set the environment variable */
/* and increment the identifier for the next call */
return DECLINED;
}
static void register_hooks(apr_pool_t *p)
{
}
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 */
};