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/**
* A simple lease-based cache in javascript used for node.js
*
* This cache allows to insert key-value pairs that will be automatically removed after a distinct lease time.
* A cache object has a capacity. If the capacity limit is hit, it will automatically remove the oldest entries.
* Entries can't be removed from the cache. However, they can be overwritten.
*
* Note that this is not exactly the same than a LRU cache, although it works similar. It has been used for caching
* authentication data. Only after lookups fail, the data will be caught from the database. The additional time-out
* prevents the usage of too old entries and allows some efficient caching between distributed nodes sharing
* authentication data.
*
* @author Benjamin Erb | http://www.benjamin-erb.de
*
*/
/**
* Creates a new Cache object.
*
* @param capacity The
* @param expireTime
* @return
*/
var Cache = exports.Cache = function(capacity, expireTime)
{
this.items = 0;
this.internalCache = {};
this.expireTime = expireTime;
this.capacity = capacity;
};
/**
* Inserts a new key/value pair.
* @param k
* @param v
* @return
*/
Cache.prototype.put = function(k, v)
{
if (k != null && v != null)
{
if (this.internalCache[k])
{
this._remove(k);
}
var value = new ValueWrapper(k, v);
this.internalCache[k] = value;
var cache = this;
var timer = this.expireTime;
var timeoutId = setTimeout(function()
{
cache._remove(k);
}, this.expireTime);
value.setTimeoutId(timeoutId);
if (++this.items > this.capacity)
{
this._purge();
}
}
};
/**
* Checks if the given key is present in the cache.
* @param k
* @return
*/
Cache.prototype.contains = function(k)
{
return !!(this.internalCache[k]);
};
/**
* Internal method for removing an entry.
* @param k
* @return
*/
Cache.prototype._remove = function(k)
{
if (this.internalCache[k])
{
this.internalCache[k].unregisterTimeout();
delete this.internalCache[k];
this.items--;
}
};
/**
* Returns the value of a given key in the cache.
* @param k
* @return
*/
Cache.prototype.get = function(k)
{
if (k != null && this.internalCache[k])
{
return this.internalCache[k].getValue();
}
};
/**
* Removes all entries from this cache.
* @return
*/
Cache.prototype.clear = function()
{
for ( var k in this.internalCache)
{
this._remove(k);
}
};
/**
* Returns the number of elements that are currently in the cache.
* @return
*/
Cache.prototype.size = function()
{
return this.items;
};
/**
* Purges the cache by removing the oldest entries if the cache is full.
* @return
*/
Cache.prototype._purge = function()
{
var keylist = [];
for ( var k in this.internalCache)
{
keylist.push(this.internalCache[k]);
}
keylist.sort(function(k1, k2)
{
return k2.getTimeCreated() - k1.getTimeCreated();
});
while (this.items > this.capacity)
{
var k = keylist.pop();
this._remove(k.getKey());
}
};
/**
* Returns a list of all key items.
* @return
*/
Cache.prototype.keySet = function()
{
var keylist = [];
for ( var k in this.internalCache)
{
keylist.push(k);
}
return keylist;
};
/**
* Creates a wrapper object for a key/value pair, that internally handles the time created.
* @param k
* @param v
* @return
*/
ValueWrapper = function ValueWrapper(k, v)
{
this.key = k;
this.value = v;
this.time = new Date().getTime();
this.timeoutId = null;
};
/**
* Returns the value of this wrapper object.
* @return
*/
ValueWrapper.prototype.getValue = function()
{
return this.value;
};
/**
* Returns the key of this wrapper object.
* @return
*/
ValueWrapper.prototype.getKey = function()
{
return this.key;
};
/**
* Sets the timeout id associated with this wrapper object.
* @param id
* @return
*/
ValueWrapper.prototype.setTimeoutId = function(id)
{
this.timeoutId = id;
};
/**
* Unregisters the timeout of this entry.
* @return
*/
ValueWrapper.prototype.unregisterTimeout = function()
{
clearTimeout(this.timeoutId);
};
/**
* Returns the time this wrapper object has been created.
* @return
*/
ValueWrapper.prototype.getTimeCreated = function()
{
return this.time;
};
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