symfony/http-foundation · error · InvalidArgumentException

Unsupported Redis or Memcached DSN. Try running "composer…

Error message

Unsupported Redis or Memcached DSN. Try running "composer require symfony/cache".

What it means

An InvalidArgumentException thrown by SessionHandlerFactory::createHandler() when the DSN string starts with redis:, rediss:, valkey:, valkeys: or memcached: but symfony/cache (which provides AbstractAdapter used to build the client) is not installed. Like the other LogicException-style dependency guards, it reports a missing package, not a malformed DSN.

Solutions

1. Run composer require symfony/cache so Redis/Memcached DSNs can be converted into connections
2. Create the Redis/Memcached client manually (\Redis, Predis, \Memcached) and pass the object to the factory instead of a DSN
3. Choose a different session save handler (e.g. file:// or a PDO DSN) that needs no extra package

When it happens

Trigger: Thrown at Session/Storage/Handler/SessionHandlerFactory.php:64 when the library encounters an invalid state.

Common situations: See trigger scenarios.

AI-assisted analysis of symfony/http-foundation@5aea19cd67 (2026-09-13). Data as JSON: /api/errors/e24e72a0adc5ae3a. Report an issue: GitHub.

Appendix: source

Thrown at Session/Storage/Handler/SessionHandlerFactory.php:64

            case str_starts_with($connection, 'redis:'):
            case str_starts_with($connection, 'rediss:'):
            case str_starts_with($connection, 'valkey:'):
            case str_starts_with($connection, 'valkeys:'):
            case str_starts_with($connection, 'memcached:'):
                if (!class_exists(AbstractAdapter::class)) {
                    throw new \InvalidArgumentException('Unsupported Redis or Memcached DSN. Try running "composer require symfony/cache".');
                }
                $handlerClass = str_starts_with($connection, 'memcached:') ? MemcachedSessionHandler::class : RedisSessionHandler::class;
                $connection = preg_replace('/([?&])prefix=[^&]*+&?/', '\1', $connection);
                $connection = AbstractAdapter::createConnection($connection, ['lazy' => true]);

                return new $handlerClass($connection, array_intersect_key($options, ['prefix' => 1, 'ttl' => 1]));

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