ratchetphp/Ratchet · error · InvalidArgumentException

Handler must be instance of SessionHandlerInterface

Error message

Handler must be instance of SessionHandlerInterface

What it means

VirtualSessionStorage::setSaveHandler validates that the session save handler passed in implements \SessionHandlerInterface and throws InvalidArgumentException when it does not. The constructor calls setSaveHandler, so this error fires as soon as a VirtualSessionStorage is built (or the method is called directly) with a handler that does not implement the interface. Ratchet requires the interface so it can transparently wrap any handler in VirtualProxy for its virtual (non-PHP-native) sessions.

Solutions

Pass an object implementing \SessionHandlerInterface (e.g. new \SessionHandler(), or Ratchet's SessionServiceProvider) to VirtualSessionStorage.
If you have a legacy handler, make it implement \SessionHandlerInterface (add open/close/read/write/destroy/gc methods with interface-compatible signatures).
Wrap or adapt third-party handlers in your own class that implements \SessionHandlerInterface before passing it in.

Example fix

// before
$storage = new \Ratchet\Session\Storage\VirtualSessionStorage('MYSESSION');
$storage->setSaveHandler(new LegacyArrayHandler());
// after
$storage = new \Ratchet\Session\Storage\VirtualSessionStorage('MYSESSION');
$storage->setSaveHandler(new \SessionHandler()); // or any \SessionHandlerInterface implementation

Defensive patterns

Strategy: type-guard

Validate before calling

if (!$handler instanceof \SessionHandlerInterface) {
    throw new \InvalidArgumentException('setSaveHandler requires a \SessionHandlerInterface instance');
}
$storage->setSaveHandler($handler);

Type guard

function isValidSessionHandler($h): bool { return $h instanceof \SessionHandlerInterface; }

Try / catch

try {
    $storage = new \Ratchet\Session\Storage\VirtualSessionStorage('sid', $handler);
} catch (\InvalidArgumentException $e) {
    // fall back to a default handler
    $storage = new \Ratchet\Session\Storage\VirtualSessionStorage('sid', new \SessionHandler());
}

Prevention

Always instantiate the handler class before passing it — never pass a class-name string or null.
Assert instanceof \SessionHandlerInterface in your DI/factory configuration.
Keep custom session handlers updated to implement \SessionHandlerInterface after PHP upgrades.

When it happens

Trigger: Passing null (the default) or an object not implementing \SessionHandlerInterface to VirtualSessionStorage::__construct / setSaveHandler; e.g. a legacy custom session handler class missing the interface, or passing a fully-qualified class name string instead of an instance.

Common situations: Upgrading PHP where old session handler classes were written before SessionHandlerInterface existed; wiring a non-standard handler object; forgetting to instantiate the handler class (passing a string) inside a Symfony session factory integration.

Understand the failure class

Background: "Must be a positive integer", "Invalid value", "Unsupported": the invalid-argument-value error family, when a library rejects the value you pass — this error's family across 35 libraries.

Related errors

AI-assisted analysis of ratchetphp/Ratchet@e621c6c40b (2026-09-16). Data as JSON: /api/errors/1314e6202e584e4d. Report an issue: GitHub.

Appendix: source

Thrown at src/Ratchet/Session/Storage/VirtualSessionStorage.php:89

    public function save() {
        // get the data from the bags?
        // serialize the data
        // save the data using the saveHandler
//        $this->saveHandler->write($this->saveHandler->getId(),

        if (!$this->saveHandler->isWrapper() && !$this->getSaveHandler()->isSessionHandlerInterface()) {
            $this->saveHandler->setActive(false);
        }

        $this->closed = true;
    }

    /**
     * {@inheritdoc}
     */
    public function setSaveHandler($saveHandler = null) {
        if (!($saveHandler instanceof \SessionHandlerInterface)) {
            throw new \InvalidArgumentException('Handler must be instance of SessionHandlerInterface');
        }

        if (!($saveHandler instanceof VirtualProxy)) {
            $saveHandler = new VirtualProxy($saveHandler);
        }

        $this->saveHandler = $saveHandler;
    }
}

}

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