Add cache tags checksum-based invalidation

README.md

@@ -16,10 +16,12 @@ installed using Composer:
  composer require wieni/wmpage_cache_redis
 ```
 
-To enable this cache storage, change the `wmpage_cache.storage` container parameter:
+To enable this cache storage, change the following container parameters:
 ```yaml
 parameters:
     wmpage_cache.storage: wmpage_cache.storage.redis
+    wmpage_cache.invalidator: wmpage_cache_redis.checksum
+    wmpage_cache.checksum: wmpage_cache_redis.checksum
 
     wmpage_cache.redis.prefix: 'wmpage_cache:'
 ```

src/RedisCacheTagsChecksum.php

@@ -0,0 +1,78 @@
+<?php
+
+namespace Drupal\wmpage_cache_redis;
+
+use Drupal\Core\Cache\CacheTagsChecksumInterface;
+use Drupal\Core\Cache\CacheTagsInvalidatorInterface;
+use Drupal\wmpage_cache\InvalidatorInterface;
+
+class RedisCacheTagsChecksum implements CacheTagsChecksumInterface, CacheTagsInvalidatorInterface, InvalidatorInterface
+{
+    /** @var RedisClientFactory */
+    protected $redisClientFactory;
+    /** @var CacheTagsChecksumInterface|CacheTagsInvalidatorInterface|null */
+    protected $redisCacheTagsChecksum;
+
+    public function __construct(RedisClientFactory $redisClientFactory)
+    {
+        $this->redisClientFactory = $redisClientFactory;
+    }
+
+    public function getCurrentChecksum(array $tags)
+    {
+        if ($decorated = $this->decorated()) {
+            return $decorated->getCurrentChecksum($tags);
+        }
+
+        return 'noop';
+    }
+
+    public function isValid($checksum, array $tags)
+    {
+        if ($decorated = $this->decorated()) {
+            return $decorated->isValid($checksum, $tags);
+        }
+
+        return false;
+    }
+
+    public function reset()
+    {
+        if ($decorated = $this->decorated()) {
+            $decorated->reset();
+        }
+    }
+
+    public function invalidateCacheTags(array $tags): void
+    {
+        // noop
+        // We use Drupal's cache tag invalidation system to invalidate the cache
+    }
+
+    public function invalidateTags(array $tags)
+    {
+        if ($decorated = $this->decorated()) {
+            $decorated->invalidateTags($tags);
+        }
+    }
+
+    /** @return CacheTagsChecksumInterface|CacheTagsInvalidatorInterface|null */
+    protected function decorated()
+    {
+        if (isset($this->redisCacheTagsChecksum)) {
+            return $this->redisCacheTagsChecksum ?: null;
+        }
+
+        $decorated = false;
+        try {
+            $client = $this->redisClientFactory::getClient();
+            if ($client instanceof \Redis) {
+                $decorated = new RedisCacheTagsChecksum($this->redisClientFactory);
+            }
+        } catch (\Exception $e) {
+            watchdog_exception('wmcontroller.redis', $e);
+        }
+
+        return $this->redisCacheTagsChecksum = $decorated;
+    }
+}

src/RedisCacheTagsChecksumClientFactory.php

@@ -0,0 +1,13 @@
+<?php
+
+namespace Drupal\wmpage_cache_redis;
+
+/**
+ * We extend it because we want a different client
+ * The ClientFactory calls static::$client so we cannot re-use the same
+ * factory. This sucks.
+ */
+class RedisCacheTagsChecksumClientFactory extends RedisClientFactory
+{
+    protected static $client;
+}

src/Storage/RedisStorage.php

@@ -2,6 +2,7 @@
 
 namespace Drupal\wmpage_cache_redis\Storage;
 
+use Drupal\Core\Cache\CacheTagsChecksumInterface;
 use Drupal\wmpage_cache\Cache;
 use Drupal\wmpage_cache\Exception\NoSuchCacheEntryException;
 use Drupal\wmpage_cache\CacheSerializerInterface;
@@ -13,13 +14,16 @@ class RedisStorage implements StorageInterface
 {
     /** @var \Redis */
     protected $redis;
+    /** @var CacheTagsChecksumInterface */
+    protected $checksumProvider;
     /** @var CacheSerializerInterface */
     protected $serializer;
     /** @var string */
     protected $prefix;
 
     public function __construct(
         RedisClientFactory $clientFactory,
+        CacheTagsChecksumInterface $checksumProvider,
         CacheSerializerInterface $serializer,
         $prefix = ''
     ) {
@@ -34,6 +38,7 @@ public function __construct(
             $this->redis = null;
             watchdog_exception('wmpage_cache_redis', $e);
         }
+        $this->checksumProvider = $checksumProvider;
         $this->serializer = $serializer;
         $this->prefix = $prefix;
     }
@@ -60,11 +65,29 @@ public function loadMultiple(array $ids, bool $includeBody = true): \Iterator
             $rows = $this->redis->mget(
                 $this->prefix($chunk, $includeBody ? 'body' : '')
             );
+            $checksums = $this->redis->mget(
+                $this->prefix($chunk, 'checksum')
+            );
 
-            foreach (array_filter($rows) as $rowJson) {
+            foreach ($rows as $i => $rowJson) {
+                if (!$rowJson) {
+                    continue;
+                }
                 $row = json_decode($rowJson, true);
                 $item = $this->serializer->denormalize($row);
-                if ($item->getExpiry() > $time) {
+                $tags = $this->redis->sMembers(
+                    $this->prefix($item->getId(), 'tags')
+                );
+                if (
+                    $item->getExpiry() > $time
+                    && (
+                        !isset($checksums[$i])
+                        || $this->checksumProvider->isValid(
+                            $checksums[$i],
+                            $tags
+                        )
+                    )
+                ) {
                     yield $item;
                 }
             }
@@ -91,6 +114,11 @@ public function set(Cache $item, array $tags): void
             json_encode($this->serializer->normalize($item, true)),
             ($item->getExpiry() - $time)
         );
+        $tx->set(
+            $this->prefix($id, 'checksum'),
+            $this->checksumProvider->getCurrentChecksum($tags),
+            ($item->getExpiry() - $time)
+        );
         $tx->zAdd(
             $this->prefix('expiries'),
             $item->getExpiry(),
@@ -155,6 +183,7 @@ public function remove(array $ids): void
             $tx->del($this->prefix($id));
             $tx->del($this->prefix($id, 'body'));
             $tx->del($this->prefix($id, 'tags'));
+            $tx->del($this->prefix($id, 'checksum'));
             $tx->del($this->prefix($id, 'path'));
             $tx->zRem($this->prefix('expiries'), $id);
 

wmpage_cache_redis.services.yml

@@ -9,5 +9,15 @@ services:
         class: Drupal\wmpage_cache_redis\Storage\RedisStorage
         arguments:
             - '@wmpage_cache.redis.factory'
+            - '@wmpage_cache.checksum'
             - '@wmpage_cache.serializer'
             - '%wmpage_cache.redis.prefix%'
+
+    wmpage_cache_redis.checksum_factory:
+        class: Drupal\wmpage_cache_redis\RedisCacheTagsChecksumClientFactory
+
+    wmpage_cache_redis.checksum:
+        class: Drupal\wmpage_cache_redis\RedisCacheTagsChecksum
+        arguments:
+            - '@wmpage_cache_redis.checksum_factory'
+        tags: [{ name: cache_tags_invalidator }]