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https://github.com/jsumners/abstract-cache


https://github.com/jsumners/abstract-cache

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# abstract-cache



*abstract-cache* is a module that provides a common interface to multiple

caching strategies. It allows for requiring *abstract-cache* everywhere while

defining the strategy via a simple configuration.



*abstract-cache* is heavily inspired by the excellent [Catbox][catbox]. The

decision to create *abstract-cache* was predicated on a desire to require

implementing clients accept previously established connections in addtion to

accepting configuration to create their own connections. It also seeks to

allow using either the callback or async/await style of asynchronous

programming.



[catbox]: https://npm.im/catbox



### Available Clients



+ [abstract-cache-mongo](https://github.com/jsumners/abstract-cache-mongo)

+ [abstract-cache-redis](https://github.com/jsumners/abstract-cache-redis)



## Example



The following example uses *abstract-cache*'s included in-memory cache. Of note,

is that the included in-memory cache is actually callback based.



```js

const cache = require('abstract-cache')({useAwait: true})



async function doSomething () {

  const val = await cache.get('foo')

  console.log(val)

}



cache.set('foo', 'foo', 100)

  .then(doSomething)

  .catch(console.error)

```



This example shows instantiating *abstract-cache* with a specific store that

relies upon a connection to a remote system. In this example we are supplying

an already existing connection to the remote system; all *abstract-cache*

compliant clients **must** support this.



```js

const cache = require('abstract-cache')({

  useAwait: true,

  driver: {

    name: 'abstract-cache-redis',

    options: {

      client: require('redis')({url: 'some.redis.url'})

    }

  }

})



async function doSomething () {

  const val = await cache.get('foo')

  console.log(val)

}



cache.set('foo', 'foo', 100)

  .then(doSomething)

  .catch(console.error)

```



## Options



*abstract-client* accepts an options object with the following properties:



+ `useAwait` (Default: `false`): designate that the resulting cache client

should use `async/await` functions. When `false`, every method accepts a

standard `callback(err, result)`.

+ `client` (Default: `undefined`): an already instantiated strategy client.

In combination with `useAwait` the client can be wrapped accordingly. Specifying

a `client` superceeds the `driver` configuration.

+ `driver`:

    * `name` (Default: `undefined`): specifies the implementing strategy to

    load. The default value results in the buil-in in-memory strategy being

    loaded -- this is **not recommended** for production environments.

    * `options` (Default: `{}`): an options object to pass to the strategy

    while loading. The strategy should describe this object.



### memclient



The included in-memory client is available as:



```js

const memclientFactory = require('abstract-cache').memclient

```



It accepts an options object:



+ `segment` (Default: `abstractMemcache`): the default segment in which to store

items.

+ `maxItems` (Default: `100000`): the maximum number of items to keep in the

cache. The backing is an LRU cache with an upper bound.



## Protocol



All implementing strategies **must** implement the protocol described in this

section.



1. The module should export a factory `function (optionsObject) {}`.

1. Accept an existing connection to data stores via the `optionsObject`.

1. Manage connections created by itself.

1. In all cases where a `key` is required, the `key` may be a simple string,

or it may be an object of the format `{id: 'name', segment: 'name'}`. It is

up to the implementing strategy to decide how to handle these keys.

1. The factory function should return an object (client) that has the following

methods and properties:

    * `await` (boolean property): `true` indicates that the strategy's methods

    are *all* `async` functions. If `false`, all methods **must** have a

    `callback(err, result)` as the last parameter.

    * `delete(key[, callback])`: removes the specified item from the cache.

    * `get(key[, callback])`: retrieves the desired item from the cache. The

    returned item should be a deep copy of the stored value to prevent alterations

    from affecting the cache. The result should be an object with the properties:

        + `item`: the item the user cached.

        + `stored`: a `Date`, in Epoch milliseconds, indicating when the item

        was stored.

        + `ttl`: the *remaining* lifetime of the item in the cache (milliseconds).

    * `has(key[, callback])`: returns a boolean result indicating if the cache

    contains the desired `key`.

    * `set(key, value, ttl[, callback])`: stores the specified `value` in the

    cache under the specified `key` for the time `ttl` in milliseconds.

    * `start([callback])` (optional): clients that require extra initialization,

    e.g. to start a database connection, may export this method. When present,

    this method **must** be invoked by the user before any other method. This

    method may be an `async` function at the discretion of the implementor.

    * `stop([callback])` (optional): required when `start()` is present. This

    should shutdown any connections/processes started via `start()`. It is

    left to the user to invoke this method in their shutdown procedure. This

    method may be an `async` function at the discretion of the implementor.



## License



[MIT License](http://jsumners.mit-license.org/)