Merge r1501827 from trunk:

                                                         -*- coding: utf-8 -*-

Changes with Apache 2.4.29

  *) mod_unique_id: Use output of the PRNG rather than IP address and

     pid, avoiding sleep() call and possible DNS issues at startup,

     plus improving randomness for IPv6-only hosts.  [Jan Kaluza]

  *) mod_rewrite, core: Avoid the 'Vary: Host' response header when HTTP_HOST

     is used in a condition that evaluates to true. PR 58231 [Luca Toscano]

#include "http_log.h"

#include "http_protocol.h"  /* for ap_hook_post_read_request */

#if APR_HAVE_UNISTD_H

#include <unistd.h>         /* for getpid() */

#endif

#define ROOT_SIZE 10

typedef struct {

    unsigned int stamp;

    unsigned int in_addr;

    unsigned int pid;

    char root[ROOT_SIZE];

    unsigned short counter;

    unsigned int thread_index;

} unique_id_rec;

 * 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

 * 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

 * (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 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

 * 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

 * 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

 * 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:

 * htonl/ntohl. Well, this shouldn't be a problem till year 2106.

 */

static unsigned global_in_addr;

/*

 * 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

/*

 * Number of elements in the structure unique_id_rec.

 */

#define UNIQUE_ID_REC_MAX 5

#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],

static int unique_id_global_init(apr_pool_t *p, apr_pool_t *plog, apr_pool_t *ptemp, server_rec *main_server)

{

    char str[APRMAXHOSTLEN + 1];

    apr_status_t rv;

    char *ipaddrstr;

    apr_sockaddr_t *sockaddr;

    /*

     * 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, in_addr);

    unique_id_rec_size[1] = sizeof(cur_unique_id.in_addr);

    unique_id_rec_offset[2] = APR_OFFSETOF(unique_id_rec, pid);

    unique_id_rec_size[2] = sizeof(cur_unique_id.pid);

    unique_id_rec_offset[3] = APR_OFFSETOF(unique_id_rec, counter);

    unique_id_rec_size[3] = sizeof(cur_unique_id.counter);

    unique_id_rec_offset[4] = APR_OFFSETOF(unique_id_rec, thread_index);

    unique_id_rec_size[4] = sizeof(cur_unique_id.thread_index);

    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] +

                               unique_id_rec_size[4];

                               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 ((rv = apr_gethostname(str, sizeof(str) - 1, p)) != APR_SUCCESS) {

        ap_log_error(APLOG_MARK, APLOG_ALERT, rv, main_server, APLOGNO(01563)

          "unable to find hostname of the server");

        return HTTP_INTERNAL_SERVER_ERROR;

    }

    if ((rv = apr_sockaddr_info_get(&sockaddr, str, AF_INET, 0, 0, p)) == APR_SUCCESS) {

        global_in_addr = sockaddr->sa.sin.sin_addr.s_addr;

    }

    else {

        ap_log_error(APLOG_MARK, APLOG_ALERT, rv, main_server, APLOGNO(01564)

                    "unable to find IPv4 address of \"%s\"", str);

#if APR_HAVE_IPV6

        if ((rv = apr_sockaddr_info_get(&sockaddr, str, AF_INET6, 0, 0, p)) == APR_SUCCESS) {

            memcpy(&global_in_addr,

                   (char *)sockaddr->ipaddr_ptr + sockaddr->ipaddr_len - sizeof(global_in_addr),

                   sizeof(global_in_addr));

            ap_log_error(APLOG_MARK, APLOG_ALERT, rv, main_server, APLOGNO(01565)

                         "using low-order bits of IPv6 address "

                         "as if they were unique");

        }

        else

#endif

        return HTTP_INTERNAL_SERVER_ERROR;

    }

    apr_sockaddr_ip_get(&ipaddrstr, sockaddr);

    ap_log_error(APLOG_MARK, APLOG_INFO, 0, main_server, APLOGNO(01566) "using ip addr %s",

                 ipaddrstr);

    /*

     * 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.

     */

    apr_sleep(apr_time_from_sec(1) - apr_time_usec(apr_time_now()));

    return OK;

}

static void unique_id_child_init(apr_pool_t *p, server_rec *s)

{

    pid_t pid;

    /*

     * 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 ((pid_t)cur_unique_id.pid != pid) {

        ap_log_error(APLOG_MARK, APLOG_CRIT, 0, s, APLOGNO(01567)

                    "oh no! pids are greater than 32-bits!  I'm broken!");

    }

    cur_unique_id.in_addr = global_in_addr;

    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

     */

    ap_random_insecure_bytes(&cur_unique_id.counter,

                             sizeof(cur_unique_id.counter));

    /*

     * 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);

}

/* NOTE: This is *NOT* the same encoding used by base64encode ... the last two

    unsigned short counter;

    int i,j,k;

    new_unique_id.in_addr = cur_unique_id.in_addr;

    new_unique_id.pid = cur_unique_id.pid;

    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);