<?php
namespace Aws\DynamoDb;
/**
* Provides an interface for using Amazon DynamoDB as a session store by hooking
* into PHP's session handler hooks. Once registered, You may use the native
* `$_SESSION` superglobal and session functions, and the sessions will be
* stored automatically in DynamoDB. DynamoDB is a great session storage
* solution due to its speed, scalability, and fault tolerance.
*
* For maximum performance, we recommend that you keep the size of your sessions
* small. Locking is disabled by default, since it can drive up latencies and
* costs under high traffic. Only turn it on if you need it.
*
* By far, the most expensive operation is garbage collection. Therefore, we
* encourage you to carefully consider your session garbage collection strategy.
* Note: the DynamoDB Session Handler does not allow garbage collection to be
* triggered randomly. You must run garbage collection manually or through other
* automated means using a cron job or similar scheduling technique.
*/
class SessionHandler implements \SessionHandlerInterface
{
/** @var SessionConnectionInterface Session save logic.*/
private $connection;
/** @var string Session save path. */
private $savePath;
/** @var string Session name. */
private $sessionName;
/** @var string The last known session ID */
private $openSessionId = '';
/** @var string Stores serialized data for tracking changes. */
private $dataRead = '';
/** @var bool Keeps track of whether the session has been written. */
private $sessionWritten = false;
/**
* Creates a new DynamoDB Session Handler.
*
* The configuration array accepts the following array keys and values:
* - table_name: Name of table to store the sessions.
* - hash_key: Name of hash key in table. Default: "id".
* - session_lifetime: Lifetime of inactive sessions expiration.
* - consistent_read: Whether or not to use consistent reads.
* - batch_config: Batch options used for garbage collection.
* - locking: Whether or not to use session locking.
* - max_lock_wait_time: Max time (s) to wait for lock acquisition.
* - min_lock_retry_microtime: Min time (µs) to wait between lock attempts.
* - max_lock_retry_microtime: Max time (µs) to wait between lock attempts.
*
* @param DynamoDbClient $client Client for doing DynamoDB operations
* @param array $config Configuration for the Session Handler
*
* @return SessionHandler
*/
public static function fromClient(DynamoDbClient $client, array $config = [])
{
$config += ['locking' => false];
if ($config['locking']) {
$connection = new LockingSessionConnection($client, $config);
} else {
$connection = new StandardSessionConnection($client, $config);
}
return new static($connection);
}
/**
* @param SessionConnectionInterface $connection
*/
public function __construct(SessionConnectionInterface $connection)
{
$this->connection = $connection;
}
/**
* Register the DynamoDB session handler.
*
* @return bool Whether or not the handler was registered.
* @codeCoverageIgnore
*/
public function register()
{
return session_set_save_handler($this, true);
}
/**
* Open a session for writing. Triggered by session_start().
*
* @param string $savePath Session save path.
* @param string $sessionName Session name.
*
* @return bool Whether or not the operation succeeded.
*/
public function open($savePath, $sessionName)
{
$this->savePath = $savePath;
$this->sessionName = $sessionName;
return true;
}
/**
* Close a session from writing.
*
* @return bool Success
*/
public function close()
{
$id = session_id();
// Make sure the session is unlocked and the expiration time is updated,
// even if the write did not occur
if ($this->openSessionId !== $id || !$this->sessionWritten) {
$result = $this->connection->write($this->formatId($id), '', false);
$this->sessionWritten = (bool) $result;
}
return $this->sessionWritten;
}
/**
* Read a session stored in DynamoDB.
*
* @param string $id Session ID.
*
* @return string Session data.
*/
public function read($id)
{
$this->openSessionId = $id;
// PHP expects an empty string to be returned from this method if no
// data is retrieved
$this->dataRead = '';
// Get session data using the selected locking strategy
$item = $this->connection->read($this->formatId($id));
// Return the data if it is not expired. If it is expired, remove it
if (isset($item['expires']) && isset($item['data'])) {
$this->dataRead = $item['data'];
if ($item['expires'] <= time()) {
$this->dataRead = '';
$this->destroy($id);
}
}
return $this->dataRead;
}
/**
* Write a session to DynamoDB.
*
* @param string $id Session ID.
* @param string $data Serialized session data to write.
*
* @return bool Whether or not the operation succeeded.
*/
public function write($id, $data)
{
$changed = $id !== $this->openSessionId
|| $data !== $this->dataRead;
$this->openSessionId = $id;
// Write the session data using the selected locking strategy
$this->sessionWritten = $this->connection
->write($this->formatId($id), $data, $changed);
return $this->sessionWritten;
}
/**
* Delete a session stored in DynamoDB.
*
* @param string $id Session ID.
*
* @return bool Whether or not the operation succeeded.
*/
public function destroy($id)
{
$this->openSessionId = $id;
// Delete the session data using the selected locking strategy
$this->sessionWritten
= $this->connection->delete($this->formatId($id));
return $this->sessionWritten;
}
/**
* Satisfies the session handler interface, but does nothing. To do garbage
* collection, you must manually call the garbageCollect() method.
*
* @param int $maxLifetime Ignored.
*
* @return bool Whether or not the operation succeeded.
* @codeCoverageIgnore
*/
public function gc($maxLifetime)
{
// Garbage collection for a DynamoDB table must be triggered manually.
return true;
}
/**
* Triggers garbage collection on expired sessions.
* @codeCoverageIgnore
*/
public function garbageCollect()
{
$this->connection->deleteExpired();
}
/**
* Prepend the session ID with the session name.
*
* @param string $id The session ID.
*
* @return string Prepared session ID.
*/
private function formatId($id)
{
return trim($this->sessionName . '_' . $id, '_');
}
}
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