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/* -*- Mode: IDL; tab-width: 4; indent-tabs-mode: nil; c-basic-offset: 4 -*-
 *
 * This Source Code Form is subject to the terms of the Mozilla Public
 * License, v. 2.0. If a copy of the MPL was not distributed with this
 * file, You can obtain one at http://mozilla.org/MPL/2.0/. */

#include "nsISupports.idl"

typedef long nsCacheStoragePolicy;
typedef long nsCacheAccessMode;

/**
 * nsICache is a namespace for various cache constants.  It does not represent
 * an actual object.
 */
[builtinclass, uuid(d6c67f38-b39a-4582-8a48-4c4f8a56dfd0)]
interface nsICache : nsISupports
{
    /**
     * Access Modes
     *
     *
     * Mode Requested | Not Cached          | Cached
     * ------------------------------------------------------------------------
     * READ           | KEY_NOT_FOUND       | NS_OK
     *                | Mode = NONE         | Mode = READ
     *                | No Descriptor       | Descriptor
     * ------------------------------------------------------------------------
     * WRITE          | NS_OK               | NS_OK            (Cache service
     *                | Mode = WRITE        | Mode = WRITE      dooms existing
     *                | Descriptor          | Descriptor        cache entry)
     * ------------------------------------------------------------------------
     * READ_WRITE     | NS_OK               | NS_OK
     * (1st req.)     | Mode = WRITE        | Mode = READ_WRITE
     *                | Descriptor          | Descriptor
     * ------------------------------------------------------------------------
     * READ_WRITE     | N/A                 | NS_OK
     * (Nth req.)     |                     | Mode = READ
     *                |                     | Descriptor
     * ------------------------------------------------------------------------
     *
     *
     * Access Requested:
     *
     * READ	       - I only want to READ, if there isn't an entry just fail
     * WRITE       - I have something new I want to write into the cache, make
     *               me a new entry and doom the old one, if any.
     * READ_WRITE  - I want to READ, but I'm willing to update an existing
     *               entry if necessary, or create a new one if none exists.
     *
     *
     * Access Granted:
     *
     * NONE        - No descriptor is provided. You get zilch. Nada. Nothing.
     * READ		   - You can READ from this descriptor.
     * WRITE	   - You must WRITE to this descriptor because the cache entry
     *               was just created for you.
     * READ_WRITE  - You can READ the descriptor to determine if it's valid,
     *               you may WRITE if it needs updating.
     *
     *
     * Comments:
     *
     * If you think that you might need to modify cached data or meta data,
     * then you must open a cache entry requesting WRITE access.  Only one
     * cache entry descriptor, per cache entry, will be granted WRITE access.
     * 
     * Usually, you will request READ_WRITE access in order to first test the
     * meta data and informational fields to determine if a write (ie. going
     * to the net) may actually be necessary.  If you determine that it is 
     * not, then you would mark the cache entry as valid (using MarkValid) and
     * then simply read the data from the cache.
     *
     * A descriptor granted WRITE access has exclusive access to the cache
     * entry up to the point at which it marks it as valid.  Once the cache
     * entry has been "validated", other descriptors with READ access may be
     * opened to the cache entry.
     *
     * If you make a request for READ_WRITE access to a cache entry, the cache
     * service will downgrade your access to READ if there is already a
     * cache entry descriptor open with WRITE access.
     *
     * If you make a request for only WRITE access to a cache entry and another
     * descriptor with WRITE access is currently open, then the existing cache
     * entry will be 'doomed', and you will be given a descriptor (with WRITE
     * access only) to a new cache entry.
     *
     */
    const nsCacheAccessMode ACCESS_NONE       = 0;
    const nsCacheAccessMode ACCESS_READ       = 1;
    const nsCacheAccessMode ACCESS_WRITE      = 2;
    const nsCacheAccessMode ACCESS_READ_WRITE = 3;

    /**
     * Storage Policy
     *
     * The storage policy of a cache entry determines the device(s) to which
     * it belongs.  See nsICacheSession and nsICacheEntryDescriptor for more
     * details.
     *
     * STORE_ANYWHERE        - Allows the cache entry to be stored in any device.
     *                         The cache service decides which cache device to use
     *                         based on "some resource management calculation."
     * STORE_IN_MEMORY       - Requires the cache entry to reside in non-persistent
     *                         storage (ie. typically in system RAM).
     * STORE_ON_DISK         - Requires the cache entry to reside in persistent
     *                         storage (ie. typically on a system's hard disk).
     * STORE_OFFLINE         - Requires the cache entry to reside in persistent,
     *                         reliable storage for offline use.
     */
    const nsCacheStoragePolicy STORE_ANYWHERE        = 0;
    const nsCacheStoragePolicy STORE_IN_MEMORY       = 1;
    const nsCacheStoragePolicy STORE_ON_DISK         = 2;
    // value 3 was used by STORE_ON_DISK_AS_FILE which was removed
    const nsCacheStoragePolicy STORE_OFFLINE         = 4;

    /**
     * All entries for a cache session are stored as streams of data or
     * as objects.  These constant my be used to specify the type of entries
     * when calling nsICacheService::CreateSession().
     */
    const long NOT_STREAM_BASED = 0;
    const long STREAM_BASED     = 1;
    
    /**
     * The synchronous OpenCacheEntry() may be blocking or non-blocking.  If a cache entry is
     * waiting to be validated by another cache descriptor (so no new cache descriptors for that
     * key can be created, OpenCacheEntry() will return NS_ERROR_CACHE_WAIT_FOR_VALIDATION in
     * non-blocking mode.  In blocking mode, it will wait until the cache entry for the key has
     * been validated or doomed.  If the cache entry is validated, then a descriptor for that
     * entry will be created and returned.  If the cache entry was doomed, then a descriptor
     * will be created for a new cache entry for the key. 
     */
    const long NON_BLOCKING = 0;
    const long BLOCKING     = 1;

    /**
     * Constant meaning no expiration time.
     */
    const unsigned long NO_EXPIRATION_TIME = 0xFFFFFFFF;
};