CacheResolver.php

<?php

use Liip\ImagineBundle\Binary\BinaryInterface;
use Liip\ImagineBundle\Imagine\Cache\Resolver\ResolverInterface;
use Predis\Client;
use Symfony\Component\Messenger\MessageBusInterface;

class CacheResolver implements ResolverInterface
{
    protected $redis;
    protected $redisImageServer;
    protected $messengerBus;

    public function __construct(Client $imageCacheRedisClient,
                                MessageBusInterface $bus,
                                RedisImageServer $redisImageServer
    ){
        $this->redis = $imageCacheRedisClient;
        $this->redisImageServer = $redisImageServer;
        $this->messengerBus = $bus;
        $this->cachePrefix = "image_cache";
    }

    private function getKey($path, $filter){
        $pathKey = $path? md5($path) : "";
        return "image_cache_$filter-$pathKey";
    }

    public function isStored($path, $filter)
    {
        $key = $this->getKey($path, $filter);

        # If we don't have any entries for this image in Redis yet, then no filter was generated
        list($isStored, $content) = $this->redis->mget([$key."_stored", $key."_content"]);
        if( ($isStored && $isStored !== "false") || $content != null) return true;
        return false;
    }

    public function resolve($path, $filter)
    {
        $key = $this->getKey($path, $filter);

        # If this function was called, there should always be a redis entry (as isStored won't return true unless there is)
        $isStored = $this->redis->get($key."_stored");

        # if the result was already stored in permanent storage, return the image path from there
        # replace following piece of code with something that retuns a deterministic path to your image/filter in your permanent storage (cloud storage)
        if($isStored && $isStored !== "false") return $this->mountManager->getWebUrl($this->getFileUrl($path, $filter));
        # otherwise, serve it from redis.
        # $redisImageServer is just a symfony-service that would return a url to the nodejs service we'll cleate. You can replace this directly 
        # with something like localhost:8008/get/$key, if you wanted to run the nodejs image service on port 8008
        else return $this->redisImageServer->getUrlForImage($key);
    }


    public function store(BinaryInterface $binary, $path, $filter)
    {
        $key = $this->getKey($path, $filter);

        $values = [
            $key."_stored"  => false,
            $key.'_content' => base64_encode($binary->getContent())
        ];

        $this->redis->mset($values);
        $this->redis->expire($key."_content", 60*60);

        try {
            # this part is to send a message to symfony-messenger that an image filter got applied. You need to configure Messenger correctly
            $this->messengerBus->dispatch(new ImageFilterAppliedMessage($key, $this->getFileUrl($path, $filter)));
        } catch (\AMQPConnectionException $ee){
            error_log("AMQP: could not send ImageFilterAppliedMessage");
        }

    }

    public function remove(array $paths, array $filters)
    {
       # you'll find a way to implement this ;) it does not matter for this demo
    }

    protected function getFileUrl($path, $filter)
    {
        // crude way of sanitizing URL scheme ("protocol") part
        $path = str_replace('://', '---', $path);
        return $this->cachePrefix.'/'.$filter.'/'.ltrim($path, '/');
    }

}