$requestCallback
$requestCallback : callable
Determines if a request can be cached using a callback
canCacheRequest(\Guzzle\Http\Message\RequestInterface  $request) : boolean
                Determine if a request can be cached
| \Guzzle\Http\Message\RequestInterface | $request | Request to determine | 
canCacheResponse(\Guzzle\Http\Message\Response  $response) : boolean
                Determine if a response can be cached
| \Guzzle\Http\Message\Response | $response | Response to determine | 
__construct(\Closure|array|mixed $requestCallback = null, \Closure|array|mixed $responseCallback = null)
| \Closure|array|mixed | $requestCallback | Callable method to invoke for requests | 
| \Closure|array|mixed | $responseCallback | Callable method to invoke for responses |