parshikovpavel/array-cache

Non-persistent PSR-6/PSR-16 compatible cache using an array. Useful for mocking the original cache in tests

0.0.1 2019-10-10 12:56 UTC

Requires

• php: ^7.1
• parshikovpavel/psr-cache-adapter: *
• psr/cache: ^1.0
• psr/simple-cache: ^1.0

Requires (Dev)

• phpunit/phpunit: 7

MIT

• Pavel Parshikov

• cache
• mock
• array
• mocking
• psr-6
• psr6
• psr16
• psr-16

README

The package for caching data in memory using a PHP array.

As cached data is only available in the current request the package should be used for mocking the original cache in tests.

The cache implementation is compatible with PSR-6/PSR-16. In addition, CounterInterface (excluded from PSR-16) is included in the library and used for implementation.

The table below shows the correspondence between the library classes and the implemented interfaces.

PSR	Class	Implements
PSR-6	CacheItemPool	CacheItemPoolInterface
PSR-6	CacheItem	CacheItemInterface
PSR-16	Cache	CacheInterface
PSR-16 + excluded CounterInterface	CountingCache	CacheInterface + CounterInterface

Installation

The recommended method of installing is via Composer.

Run the following command from the project root:

composer require parshikovpavel/array-cache --dev

Usage

A detailed description of the interfaces implemented in the library can be found in PSR-6 and PSR-16.

Here are some common usage patterns of the library for testing your application using PHPUnit.

PSR-6

According to PSR-6, the package provides \ppCache\CacheItemPool class (implementing the \PSR\Cache\CacheItemPoolInterface interface) and \ppCache\CacheItem class (implementing the \PSR\Cache\CacheItemInterface interface).

Cache fixture

Use \ppCache\CacheItemPool instance as a fixture. Put the creating of the cache fixture into the setUp() method.

final class CacheTest extends TestCase
{
    private $itemPool;

    protected function setUp(): void
    {
        $this->itemPool = new \ppCache\CacheItemPool();
    }
    
    /* ... */
}

Dependency injection

If your application based on the dependency inversion principle and the dependency injection technique, it's very easy to replace a real cache with a mock cache.

Consider the case of constructor injection. Let's assume Client class provide a parameter in a constructor to inject a cache instance.

final class CacheTest extends TestCase
{
    /* ... */
    
    public function testFeature(): void
    {
        $client = new Client($this->itemPool);
        
        /* ... */
    }
}

Get value from cache

The most common cache use case is a getting value and computing in case of cache miss.

A cache client must first try to get value from cache by $key.

• If trying is successful, return $value

• otherwise compute $value by calling the time-consuming compute() function and cache the value for a while

final class Client {

    private $itemPool;

    public function __construct(\Psr\Cache\CacheItemPoolInterface $itemPool)
    {
        $this->itemPool = $itemPool;
    }

    private function getValue(string $key, int $ttl = 3600)
    {
        $item = $this->itemPool->getItem($key);
        if (!$item->isHit()) {
            $value = $this->compute();
            $item->set($value);
            $item->expiresAfter($ttl);
            $this->itemPool->save($item);
        }
        return $item->get();
    }

    /* ... */
}

PSR-16

According to PSR-16, the package provides \ppCache\Cache class (implementing the \Psr\SimpleCache\CacheInterface interface).

Cache fixture

Use \ppCache\Cache instance as a fixture. Put the creating of the cache fixture into the setUp() method.

final class CacheTest extends TestCase
{
    private $cache;

    protected function setUp(): void
    {
        $this->cache = new \ppCache\Cache();
    }
    
    /* ... */
}

Dependency injection

Similarly, inject a cache instance into the client constructor:

final class CacheTest extends TestCase
{
    /* ... */
    
    public function testFeature(): void
    {
        $client = new Client($this->cache);
        
        /* ... */
    }
}

Get value from cache

The algorithm is the same as the one for \ppCache\CacheItemPool but the implementation is a bit simpler.

final class Client
{
    private $cache;

    public function __construct(\Psr\SimpleCache\CacheInterface $cache)
    {
        $this->cache = $cache;
    }

    private function getValue(string $key, int $ttl = 3600)
    {
        if (null === ($value = $this->cache->get($key))) {
            $value = $this->compute();
            $this->cache->set($key, $value, $ttl);
        }

        return $value;
    }

    /* ... */
}

PSR-16 + CounterInterface

The package provides the \ppCache\CountingCache class which implements both the \Psr\SimpleCache\CacheInterface (introduced PSR-16) and the CounterInterface (excluded from PSR-16). CounterInterface definition is taken from PGP-FIG repository and is in this package.

The \ppCache\CountingCache implementation decorates a \ppCache\Cache instance and supplements its implementation with atomic increment-decrement methods.

Cache fixture

final class CacheTest extends TestCase
{
    private $countingCache;

    protected function setUp(): void
    {
        $this->countingCache = new \ppCache\CountingCache();
    }
    
    /* ... */
}

Dependency injection

final class CacheTest extends TestCase
{
    /* ... */
    
    public function testFeature(): void
    {
        $client = new Client($this->countingCache);
        
        /* ... */
    }
}

Value increment and decrement

final class Client
{
    private $countingCache;

    public function __construct(\ppCache\CountingCache $countingCache)
    {
        $this->countingCache = $countingCache;
    }

    private function changeValue(string $key): void
    {
        /* ... */ 
        
        $newValue = $this->countingCache->increment($key);
        
        /* ... */
        
        $newValue = $this->countingCache->decrement($key);
        
        /* ... */
    }

    /* ... */
}

Unit testing

There are unit tests in the ./tests directory. You can run all tests with the following command:

$ ./vendor/bin/phpunit tests/ --testdox

ppCache\CacheItemPool
 ✔ Throws exception for invalid key
 ✔ Detects missing item
 ✔ Saves detects retrieves an eternal item
 ✔ Detects an expired item

ppCache\Cache
 ✔ Throws exception for invalid key
 ✔ Detects missing item
 ✔ Saves detects retrieves an eternal item
 ✔ Detects an expired item
 ✔ Gets items with a specified expiration time
 ✔ Supports multiple functions
 ✔ Performs deletion and clearing

ppCache\CountingCache
 ✔ Increments a value
 ✔ Decrements a value