Symfony BadMethodCallException: Cannot serialize FilesystemAdapter When Using AWS Presigned URLs (DynamoDB Issue)

Question

I'm working in Symfony 6.0 and PHP 8.1, and the following error appeared in my logs when injecting my custom AWSService into a custom object:

Uncaught PHP Exception BadMethodCallException: "Cannot serialize Symfony\Component\Cache\Adapter\FilesystemAdapter" at /app/vendor/symfony/cache/Traits/FilesystemCommonTrait.php line 176
Channel: request
Context: exception: 
{
    "class": "BadMethodCallException",
    "message": "Cannot serialize Symfony\\Component\\Cache\\Adapter\\FilesystemAdapter",
    "code": 0,
    "file": "/app/vendor/symfony/cache/Traits/FilesystemCommonTrait.php:176",
    "trace": [
        "/app/vendor/symfony/http-foundation/Session/Storage/NativeSessionStorage.php:241",
        "/app/vendor/symfony/http-foundation/Session/Session.php:195",
        "/app/vendor/symfony/http-kernel/EventListener/AbstractSessionListener.php:132",
        "/app/vendor/symfony/event-dispatcher/EventDispatcher.php:270",
        "/app/vendor/symfony/event-dispatcher/EventDispatcher.php:230",
        "/app/vendor/symfony/event-dispatcher/EventDispatcher.php:59",
        "/app/vendor/symfony/http-kernel/HttpKernel.php:185",
        "/app/vendor/symfony/http-kernel/HttpKernel.php:173",
        "/app/vendor/symfony/http-kernel/HttpKernel.php:74",
        "/app/vendor/symfony/http-kernel/Kernel.php:202",
        "/app/public/index.php:25"
    ]
}

I've added other logging throughout the code, and it appears that this happens AFTER my controller exits and returns successfully. I am not clear on how to further debug this issue, since after the controller exits it goes into Symfony-land.

My AWSService handles things like storage to and retrieval from AWS services, such as S3 or DynamoDB. I'm injecting it into an object that keeps the caller's info in the session for easy access, and for the call that throws this error, I'm using it to create a Presigned URL for one of the object's attributes.

The thing that seems strange to me is that the AWSService isn't accessing the filesystem explicitly... it's taking an object and creating a string from it using AWS' $s3->createPresignedRequest() call. Even the AWS docs for createPresignedRequest() imply that the function just spits out an answer based on the settings it was provided:

Important

The URL returned by this method is not validated to ensure that the bucket or key exists, nor does this method ensure that the object allows unauthenticated access.

Further, as stated above, the function call completes with out error, and the Controller that called it also completes without error, before this exception is thrown. So it's hard to believe that the AWSService itself is causing this problem.

Clearly this has something to do with how objects are serialized, but I'm not sure exactly what as this error is pretty vague, and I'm creating a string (not a resource). Any thoughts would be appreciated!

jetsetter jetsetter · Accepted Answer · 2022-07-28T17:43:00

After banging my head against this for a few hours, I finally figured it out... and since I couldn't find anything here at StackOverflow that addresses the issue specifically, here are my notes.

It turns out that Symfony appears to serialize all of the objects in session so that they can be de/re-hydrated after the main processing is complete, and before listeners, post processors, etc. are called.

I got a hint from this StackOverflow post, which told me that resources are not supported in serialized data. But I didn't think that getting a Presigned URL would cause an issue... and as it turned out, that was correct.

I finally created a helper class for the object, and just set the attributes externally instead of internally when the object was constructed. Only at that point did I get a better error:

request.CRITICAL: Uncaught PHP Exception RuntimeException: "Instances of Aws\DynamoDb\DynamoDbClient cannot be serialized" at /app/vendor/aws/aws-sdk-php/src/AwsClient.php line 276

So... because the AWSService included an instance of DynamoDbClient, and because I was putting the AWSService into an object, which was then being stored in the session, Symfony was crashing when the object hit the internal serializer.

I'm not sure why that exception isn't bubbled up better, but... at least now it's documented here. Hope it helps someone else!

Symfony BadMethodCallException: Cannot serialize FilesystemAdapter When Using AWS Presigned URLs (DynamoDB Issue)

1 Answers