Add support for Memcached/Improve database cache

- Create Cache Driver interface
- Update cache table fields
- Add CacheSessionHandler

src/Core/Session/CacheSessionHandler.php

@@ -0,0 +1,81 @@
+<?php
+
+namespace Friendica\Core\Session;
+
+use Friendica\BaseObject;
+use Friendica\Core\Cache;
+use Friendica\Core\Session;
+use SessionHandlerInterface;
+
+require_once 'boot.php';
+require_once 'include/text.php';
+
+/**
+ * SessionHandler using Friendica Cache
+ *
+ * @author Hypolite Petovan <mrpetovan@gmail.com>
+ */
+class CacheSessionHandler extends BaseObject implements SessionHandlerInterface
+{
+	public function open($save_path, $session_name)
+	{
+		return true;
+	}
+
+	public function read($session_id)
+	{
+		if (!x($session_id)) {
+			return '';
+		}
+
+		$data = Cache::get('session:' . $session_id);
+		if (!empty($data)) {
+			Session::$exists = true;
+			return $data;
+		}
+		logger("no data for session $session_id", LOGGER_TRACE);
+		return '';
+	}
+
+	/**
+	 * @brief Standard PHP session write callback
+	 *
+	 * This callback updates the stored session data and/or the expiration depending
+	 * on the case. Uses the Session::expire for existing session, 5 minutes
+	 * for newly created session.
+	 *
+	 * @param  string $session_id   Session ID with format: [a-z0-9]{26}
+	 * @param  string $session_data Serialized session data
+	 * @return boolean Returns false if parameters are missing, true otherwise
+	 */
+	public function write($session_id, $session_data)
+	{
+		if (!$session_id) {
+			return false;
+		}
+
+		if (!$session_data) {
+			return true;
+		}
+
+		Cache::set('session:' . $session_id, $session_data, Session::$expire);
+
+		return true;
+	}
+
+	public function close()
+	{
+		return true;
+	}
+
+	public function destroy($id)
+	{
+		Cache::delete('session:' . $id);
+		return true;
+	}
+
+	public function gc($maxlifetime)
+	{
+		return true;
+	}
+}