mod_mem_cache.c

apache服务器源代码（版本号：2.2.2）

        /* CACHE_TYPE_FILE is only valid for local content handled by the
         * default handler. Need a better way to check if the file is
         * local or not.
         */
        if (!r->filename) {
            return DECLINED;
        }
    }

    /* Allocate and initialize cache_object_t */
    obj = calloc(1, sizeof(*obj));
    if (!obj) {
        return DECLINED;
    }
    key_len = strlen(key) + 1;
    obj->key = malloc(key_len);
    if (!obj->key) {
        cleanup_cache_object(obj);
        return DECLINED;
    }
    memcpy((void*)obj->key, key, key_len);

    /* Allocate and init mem_cache_object_t */
    mobj = calloc(1, sizeof(*mobj));
    if (!mobj) {
        cleanup_cache_object(obj);
        return DECLINED;
    }

    /* Finish initing the cache object */
    apr_atomic_set32(&obj->refcount, 1);
    mobj->total_refs = 1;
    obj->complete = 0;
    obj->vobj = mobj;
    /* Safe cast: We tested < sconf->max_cache_object_size above */
    mobj->m_len = (apr_size_t)len;
    mobj->type = type_e;

    /* Place the cache_object_t into the hash table.
     * Note: Perhaps we should wait to put the object in the
     * hash table when the object is complete?  I add the object here to
     * avoid multiple threads attempting to cache the same content only
     * to discover at the very end that only one of them will succeed.
     * Furthermore, adding the cache object to the table at the end could
     * open up a subtle but easy to exploit DoS hole: someone could request
     * a very large file with multiple requests. Better to detect this here
     * rather than after the cache object has been completely built and
     * initialized...
     * XXX Need a way to insert into the cache w/o such coarse grained locking
     */
    if (sconf->lock) {
        apr_thread_mutex_lock(sconf->lock);
    }
    tmp_obj = (cache_object_t *) cache_find(sconf->cache_cache, key);

    if (!tmp_obj) {
        cache_insert(sconf->cache_cache, obj);
        /* Add a refcount to account for the reference by the
         * hashtable in the cache. Refcount should be 2 now, one
         * for this thread, and one for the cache.
         */
        apr_atomic_inc32(&obj->refcount);
    }
    if (sconf->lock) {
        apr_thread_mutex_unlock(sconf->lock);
    }

    if (tmp_obj) {
        /* This thread collided with another thread loading the same object
         * into the cache at the same time. Defer to the other thread which
         * is further along.
         */
        cleanup_cache_object(obj);
        return DECLINED;
    }

    apr_pool_cleanup_register(r->pool, obj, decrement_refcount,
                              apr_pool_cleanup_null);

    /* Populate the cache handle */
    h->cache_obj = obj;

    return OK;
}

static int create_mem_entity(cache_handle_t *h, request_rec *r,
                             const char *key, apr_off_t len)
{
    return create_entity(h, CACHE_TYPE_HEAP, r, key, len);
}

static int create_fd_entity(cache_handle_t *h, request_rec *r,
                            const char *key, apr_off_t len)
{
    return create_entity(h, CACHE_TYPE_FILE, r, key, len);
}

static int open_entity(cache_handle_t *h, request_rec *r, const char *key)
{
    cache_object_t *obj;

    /* Look up entity keyed to 'url' */
    if (sconf->lock) {
        apr_thread_mutex_lock(sconf->lock);
    }
    obj = (cache_object_t *) cache_find(sconf->cache_cache, key);
    if (obj) {
        if (obj->complete) {
            request_rec *rmain=r, *rtmp;
            apr_atomic_inc32(&obj->refcount);
            /* cache is worried about overall counts, not 'open' ones */
            cache_update(sconf->cache_cache, obj);

            /* If this is a subrequest, register the cleanup against
             * the main request. This will prevent the cache object
             * from being cleaned up from under the request after the
             * subrequest is destroyed.
             */
            rtmp = r;
            while (rtmp) {
                rmain = rtmp;
                rtmp = rmain->main;
            }
            apr_pool_cleanup_register(rmain->pool, obj, decrement_refcount,
                                      apr_pool_cleanup_null);
        }
        else {
            obj = NULL;
        }
    }

    if (sconf->lock) {
        apr_thread_mutex_unlock(sconf->lock);
    }

    if (!obj) {
        return DECLINED;
    }

    /* Initialize the cache_handle */
    h->cache_obj = obj;
    h->req_hdrs = NULL;  /* Pick these up in recall_headers() */
    return OK;
}

/* remove_entity()
 * Notes:
 *   refcount should be at least 1 upon entry to this function to account
 *   for this thread's reference to the object. If the refcount is 1, then
 *   object has been removed from the cache by another thread and this thread
 *   is the last thread accessing the object.
 */
static int remove_entity(cache_handle_t *h)
{
    cache_object_t *obj = h->cache_obj;
    cache_object_t *tobj = NULL;

    if (sconf->lock) {
        apr_thread_mutex_lock(sconf->lock);
    }

    /* If the entity is still in the cache, remove it and decrement the
     * refcount. If the entity is not in the cache, do nothing. In both cases
     * decrement_refcount called by the last thread referencing the object will
     * trigger the cleanup.
     */
    tobj = cache_find(sconf->cache_cache, obj->key);
    if (tobj == obj) {
        cache_remove(sconf->cache_cache, obj);
        apr_atomic_dec32(&obj->refcount);
    }

    if (sconf->lock) {
        apr_thread_mutex_unlock(sconf->lock);
    }

    return OK;
}
static apr_status_t serialize_table(cache_header_tbl_t **obj,
                                    apr_ssize_t *nelts,
                                    apr_table_t *table)
{
    const apr_array_header_t *elts_arr = apr_table_elts(table);
    apr_table_entry_t *elts = (apr_table_entry_t *) elts_arr->elts;
    apr_ssize_t i;
    apr_size_t len = 0;
    apr_size_t idx = 0;
    char *buf;

    *nelts = elts_arr->nelts;
    if (*nelts == 0 ) {
        *obj=NULL;
        return APR_SUCCESS;
    }
    *obj = malloc(sizeof(cache_header_tbl_t) * elts_arr->nelts);
    if (NULL == *obj) {
        return APR_ENOMEM;
    }
    for (i = 0; i < elts_arr->nelts; ++i) {
        len += strlen(elts[i].key);
        len += strlen(elts[i].val);
        len += 2;  /* Extra space for NULL string terminator for key and val */
    }

    /* Transfer the headers into a contiguous memory block */
    buf = malloc(len);
    if (!buf) {
        *obj = NULL;
        return APR_ENOMEM;
    }

    for (i = 0; i < *nelts; ++i) {
        (*obj)[i].hdr = &buf[idx];
        len = strlen(elts[i].key) + 1;              /* Include NULL terminator */
        memcpy(&buf[idx], elts[i].key, len);
        idx+=len;

        (*obj)[i].val = &buf[idx];
        len = strlen(elts[i].val) + 1;
        memcpy(&buf[idx], elts[i].val, len);
        idx+=len;
    }
    return APR_SUCCESS;
}
static int unserialize_table( cache_header_tbl_t *ctbl,
                              int num_headers,
                              apr_table_t *t )
{
    int i;

    for (i = 0; i < num_headers; ++i) {
        apr_table_addn(t, ctbl[i].hdr, ctbl[i].val);
    }

    return APR_SUCCESS;
}
/* Define request processing hook handlers */
/* remove_url()
 * Notes:
 */
static int remove_url(cache_handle_t *h, apr_pool_t *p)
{
    cache_object_t *obj;
    int cleanup = 0;

    if (sconf->lock) {
        apr_thread_mutex_lock(sconf->lock);
    }

    obj = h->cache_obj;
    if (obj) {
        cache_remove(sconf->cache_cache, obj);
        /* For performance, cleanup cache object after releasing the lock */
        cleanup = !apr_atomic_dec32(&obj->refcount);
    }
    if (sconf->lock) {
        apr_thread_mutex_unlock(sconf->lock);
    }

    if (cleanup) {
        cleanup_cache_object(obj);
    }

    return OK;
}

static apr_status_t recall_headers(cache_handle_t *h, request_rec *r)
{
    int rc;
    mem_cache_object_t *mobj = (mem_cache_object_t*) h->cache_obj->vobj;

    h->req_hdrs = apr_table_make(r->pool, mobj->num_req_hdrs);
    h->resp_hdrs = apr_table_make(r->pool, mobj->num_header_out);

    rc = unserialize_table(mobj->req_hdrs, mobj->num_req_hdrs, h->req_hdrs);
    rc = unserialize_table(mobj->header_out, mobj->num_header_out,
                           h->resp_hdrs);

    return rc;
}

static apr_status_t recall_body(cache_handle_t *h, apr_pool_t *p, apr_bucket_brigade *bb)
{
    apr_bucket *b;
    mem_cache_object_t *mobj = (mem_cache_object_t*) h->cache_obj->vobj;

    if (mobj->type == CACHE_TYPE_FILE) {
        /* CACHE_TYPE_FILE */
        apr_file_t *file;
        apr_os_file_put(&file, &mobj->fd, mobj->flags, p);
        b = apr_bucket_file_create(file, 0, mobj->m_len, p, bb->bucket_alloc);
    }
    else {
        /* CACHE_TYPE_HEAP */
        b = apr_bucket_immortal_create(mobj->m, mobj->m_len, bb->bucket_alloc);
    }
    APR_BRIGADE_INSERT_TAIL(bb, b);
    b = apr_bucket_eos_create(bb->bucket_alloc);
    APR_BRIGADE_INSERT_TAIL(bb, b);

    return APR_SUCCESS;
}


static apr_status_t store_headers(cache_handle_t *h, request_rec *r, cache_info *info)
{
    cache_object_t *obj = h->cache_obj;
    mem_cache_object_t *mobj = (mem_cache_object_t*) obj->vobj;
    int rc;
    apr_table_t *headers_out;

    /*
     * The cache needs to keep track of the following information:
     * - Date, LastMod, Version, ReqTime, RespTime, ContentLength
     * - The original request headers (for Vary)
     * - The original response headers (for returning with a cached response)
     * - The body of the message
     */
    rc = serialize_table(&mobj->req_hdrs,
                         &mobj->num_req_hdrs,
                         r->headers_in);
    if (rc != APR_SUCCESS) {
        return rc;
    }

    /* Precompute how much storage we need to hold the headers */
    headers_out = ap_cache_cacheable_hdrs_out(r->pool, r->headers_out,
                                              r->server);
    headers_out = apr_table_overlay(r->pool, headers_out, r->err_headers_out);

    rc = serialize_table(&mobj->header_out, &mobj->num_header_out,
                         headers_out);
    if (rc != APR_SUCCESS) {
        return rc;
    }

    /* Init the info struct */
    obj->info.status = info->status;
    if (info->date) {
        obj->info.date = info->date;
    }
    if (info->response_time) {
        obj->info.response_time = info->response_time;
    }
    if (info->request_time) {
        obj->info.request_time = info->request_time;
    }
    if (info->expire) {
        obj->info.expire = info->expire;
    }

    return APR_SUCCESS;
}

static apr_status_t store_body(cache_handle_t *h, request_rec *r, apr_bucket_brigade *b)
{
    apr_status_t rv;
    cache_object_t *obj = h->cache_obj;
    cache_object_t *tobj = NULL;
    mem_cache_object_t *mobj = (mem_cache_object_t*) obj->vobj;
    apr_read_type_e eblock = APR_BLOCK_READ;
    apr_bucket *e;
    char *cur;