feat: use db cache for caching across autoscaling instances

Author: tractorcow

_config/assets.yml

@@ -6,22 +6,15 @@ After:
   - '#assetsflysystem'
 ---
 SilverStripe\Core\Injector\Injector:
-  League\Flysystem\Adapter\Local.cache:
-    class: League\Flysystem\Adapter\Local
-    constructor:
-      root: '`TEMP_PATH`'
   FullscreenInteractive\SilverStripe\AzureStorage\Adapter\PublicAdapter:
     constructor:
       connectionUrl: '`AZURE_CONNECTION_URL`'
       containerName: '`AZURE_CONTAINER_NAME`'
       assetDomain: '`AZURE_PUBLIC_BLOB_DOMAIN`'
-  League\Flysystem\Cached\Storage\Memory.public:
-    class: League\Flysystem\Cached\Storage\Memory
   League\Flysystem\Cached\Storage\Adapter.public:
-    class: League\Flysystem\Cached\Storage\Adapter
+    class: FullscreenInteractive\SilverStripe\AzureStorage\Adapter\DBCache
     constructor:
-      adapter: '%$League\Flysystem\Adapter\Local.cache'
-      file: 'azuremetadata/public'
+      key: 'azuremetadata/public'
       expire: 259200
   SilverStripe\Assets\Flysystem\PublicAdapter:
     class: FullscreenInteractive\SilverStripe\AzureStorage\Adapter\PublicCachedAdapter
@@ -33,10 +26,9 @@ SilverStripe\Core\Injector\Injector:
       connectionUrl: '`AZURE_CONNECTION_URL`'
       containerName: '`AZURE_PROTECTED_CONTAINER_NAME`'
   League\Flysystem\Cached\Storage\Adapter.protected:
-    class: League\Flysystem\Cached\Storage\Adapter
+    class: FullscreenInteractive\SilverStripe\AzureStorage\Adapter\DBCache
     constructor:
-      adapter: '%$League\Flysystem\Adapter\Local.cache'
-      file: 'azuremetadata/protected'
+      key: 'azuremetadata/protected'
       expire: 259200
   SilverStripe\Assets\Flysystem\ProtectedAdapter:
     class: FullscreenInteractive\SilverStripe\AzureStorage\Adapter\ProtectedCachedAdapter

src/Adapter/DBCache.php

@@ -0,0 +1,69 @@
+<?php
+
+namespace FullscreenInteractive\SilverStripe\AzureStorage\Adapter;
+
+use Exception;
+use FullscreenInteractive\SilverStripe\AzureStorage\Model\BlobCache;
+use League\Flysystem\Cached\Storage\AbstractCache;
+
+class DBCache extends AbstractCache
+{
+    /**
+     * Cache key
+     *
+     * @var string|null
+     */
+    protected $key = null;
+
+    /**
+     * @var int|null seconds until cache expiration
+     */
+    protected $expire = null;
+
+    protected $ready = false;
+
+    /**
+     * Constructor.
+     *
+     * @param string $key storage key
+     * @param int|null $expire
+     */
+    public function __construct(string $key = 'flysystem', int $expire = null)
+    {
+        $this->key = $key;
+        $this->expire = $expire;
+        $this->ready = BlobCache::ready();
+    }
+
+    /**
+     * @throws Exception
+     */
+    public function load()
+    {
+        if (!$this->ready) {
+            return;
+        }
+
+        $cache = BlobCache::instance($this->key, $this->expire);
+        $contents = $cache->Contents;
+
+        if ($contents) {
+            $this->setFromStorage($contents);
+        }
+    }
+
+    /**
+     * @throws Exception
+     */
+    public function save()
+    {
+        if (!$this->ready) {
+            return;
+        }
+
+        $contents = $this->getForStorage();
+        $blobCache = BlobCache::instance($this->key, $this->expire);
+        $blobCache->Contents = $contents;
+        $blobCache->write();
+    }
+}

src/Model/BlobCache.php

@@ -0,0 +1,84 @@
+<?php
+
+namespace FullscreenInteractive\SilverStripe\AzureStorage\Model;
+
+use DateTimeImmutable;
+use Exception;
+use SilverStripe\Core\ClassInfo;
+use SilverStripe\ORM\DataObject;
+use SilverStripe\Security\Security;
+
+/**
+ * @property string $Key
+ * @property string $Contents JSON cache
+ */
+class BlobCache extends DataObject
+{
+    private static $table_name = 'Azure_BlobCache';
+
+    /**
+     * @var array
+     */
+    protected static $instances = [];
+
+    private static $db = [
+        'Key'      => 'Varchar(255)',
+        'Contents' => 'Text',
+    ];
+
+    private static $indexes = [
+        'UniqueKey' => [
+            'type'    => 'unique',
+            'columns' => ['Key'],
+        ],
+    ];
+
+    /**
+     * Get cache for key
+     *
+     * @param string $key
+     * @param int $maxAge Max age
+     * @return static
+     * @throws Exception
+     */
+    public static function instance(string $key, int $maxAge): self
+    {
+        if (isset(static::$instances[$key])) {
+            return static::$instances[$key];
+        }
+
+        // Query from DB, respecting max age
+        /** @var self $cache */
+        $cache = static::get()->filter('Key', $key)->first();
+        if (!$cache) {
+            // Create blank record
+            $cache = new self();
+            $cache->Key = $key;
+            $cache->write();
+        } elseif ($maxAge) {
+            // Expire contents if older than maxAge
+            $modified = new DateTimeImmutable($cache->LastEdited);
+            $expires = (new DateTimeImmutable())
+                ->sub(new \DateInterval("PT{$maxAge}S"));
+
+            // Flush expired contents
+            if ($modified < $expires) {
+                $cache->Contents = null;
+                $cache->write();
+            }
+        }
+
+        // Return
+        static::$instances[$key] = $cache;
+        return $cache;
+    }
+
+    /**
+     * Safely disable db cache if not built yet
+     * @return bool
+     */
+    public static function ready(): bool
+    {
+        return Security::database_is_ready() && ClassInfo::hasTable('Azure_BlobCache');
+    }
+}