mod_unique_id.c

apache简化版

                    "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 uuencode ... 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 */
};