happyr/message-serializer

Serialize classes the good way.

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Nyholm

0.5.1 2020-12-02 14:47 UTC

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Last update: 2020-12-02 14:48:15 UTC


README

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This package contains some interfaces and classes to help you serialize and deserialize a PHP class to an array. The package does not do any magic for you but rather help you to define your serialization rules yourself.

Install

composer require happyr/message-serializer

See integration with Symfony Messenger.

The Problem

When you serialize a PHP class to show the output for a different user or application there is one thing you should really keep in mind. That output is part of a public contract that you cannot change without possibly breaking other applications.

Consider this example:

class Foo {
    private $bar;

    public function getBar()
    {
        return $this->bar;
    }

    public function setBar($bar)
    {
        $this->bar = $bar;
    }
}

$x = new Foo();
$x->setBar('test string');

$output = serialize($x);
echo $output;

This will output:

O:3:"Foo":1:{s:8:"Foobar";s:11:"test string";}

Even if you doing something smart with json_encode you will get:

{"bar":"test string"}

This might seem fine at first. But if you change the Foo class slightly, say, rename the private property or add another property, then your output will differ and you have broken your contract with your users.

The solution

To avoid this problem we need to separate the class from the plain representation. The way we do that is to use a Transformer to take a class and produce an array.

use Happyr\MessageSerializer\Transformer\TransformerInterface;

class FooTransformer implements TransformerInterface
{
    public function getVersion(): int
    {
        return 1;
    }

    public function getIdentifier(): string
    {
        return 'foo';
    }

    public function getPayload($message): array
    {
        return [
            'bar' => $message->getBar(),
        ];
    }

    public function supportsTransform($message): bool
    {
        return $message instanceof Foo;
    }
}

This transformer is only responsible to convert a Foo class to an array. The reverse operation is handled by a Hydrator:

use Happyr\MessageSerializer\Hydrator\HydratorInterface;

class FooHydrator implements HydratorInterface
{
    public function toMessage(array $payload, int $version)
    {
        $object = new Foo();
        $object->setBar($payload['bar']);

        return $object;
    }

    public function supportsHydrate(string $identifier, int $version): bool
    {
        return $identifier === 'foo' && $version === 1;
    }
}

With transformers and hydrators you are sure to never accidentally change the output to the user.

The text representation of Foo when using the Transformer above will look like:

{
    "version": 1,
    "identifier": "foo",
    "timestamp": 1566491957,
    "payload": {
        "bar": "test string"
    },
    "_meta": []
}

Manage versions

If you need to change the output you may do so with help of the version property. As an example, say you want to rename the key bar to something differently. Then you create a new Hydrator like:

use Happyr\MessageSerializer\Hydrator\HydratorInterface;

class FooHydrator2 implements HydratorInterface
{
   public function toMessage(array $payload, int $version)
   {
       $object = new Foo();
       $object->setBar($payload['new_bar']);

       return $object;
   }

   public function supportsHydrate(string $identifier, int $version): bool
   {
       return $identifier === 'foo' && $version === 2;
   }
}

Now you simply update the transformer to your new contract:

use Happyr\MessageSerializer\Transformer\TransformerInterface;

class FooTransformer implements TransformerInterface
{
    public function getVersion(): int
    {
        return 2;
    }

    public function getIdentifier(): string
    {
        return 'foo';
    }

    public function getPayload($message): array
    {
        return [
            'new_bar' => $message->getBar(),
        ];
    }

    public function supportsTransform($message): bool
    {
        return $message instanceof Foo;
    }
}

Differentiate between "I cant hydrate message" and "Wrong version"

Sometimes it is important to know the difference between "I dont not want this message" and "I want this message, but not this version". An example scenario would be when you have multiple applications that communicate with each other and you are using a retry mechanism when a message failed to be delivered/handled. You do not want to retry a message if the application is not interested but you do want to retry if the message has wrong version (like it would be when you updated the sender app but not the receiver app).

So lets update FooHydrator2 from previous example:

use Happyr\MessageSerializer\Hydrator\Exception\VersionNotSupportedException;
use Happyr\MessageSerializer\Hydrator\HydratorInterface;

class FooHydrator2 implements HydratorInterface
{
   // ...

   public function supportsHydrate(string $identifier, int $version): bool
   {
       if ('foo' !== $identifier) {
           return false;
       }
       
       if (2 === $version) {
           return true;
       }
       
       // We do support the message, but not the version
       throw new VersionNotSupportedException();
   }
}

SerializerRouter

If you dispatch/consume messages serialized with Happyr\MessageSerializer\Serializer and default Symfony messenger to same transport you might wanna use Happyr\MessageSerializer\SerializerRouter. This serializer will decide whether it will use Happyr\MessageSerializer\Serializer to decode/encode your message or the default one from Symfony messenger.

use Happyr\MessageSerializer\SerializerRouter;

$serializerRouter = new SerializerRouter($happyrSerializer, $symfonySerializer);

Integration with Symfony Messenger

To make it work with Symfony Messenger, add the following service definition:

# config/packages/happyr_message_serializer.yaml

services:
  Happyr\MessageSerializer\Serializer:
    autowire: true

  Happyr\MessageSerializer\Transformer\MessageToArrayInterface: '@happyr.message_serializer.transformer'
  happyr.message_serializer.transformer:
    class: Happyr\MessageSerializer\Transformer\Transformer
    arguments: [!tagged happyr.message_serializer.transformer]


  Happyr\MessageSerializer\Hydrator\ArrayToMessageInterface: '@happyr.message_serializer.hydrator'
  happyr.message_serializer.hydrator:
    class: Happyr\MessageSerializer\Hydrator\Hydrator
    arguments: [!tagged happyr.message_serializer.hydrator]

  # If you want to use SerializerRouter
  Happyr\MessageSerializer\SerializerRouter:
    arguments:
      - '@Happyr\MessageSerializer\Serializer'
      - '@Symfony\Component\Messenger\Transport\Serialization\SerializerInterface'

If you automatically want to tag all your Transformers and Hydrators, add this to your main service file:

# config/services.yaml
services:
    # ...

    _instanceof:
        Happyr\MessageSerializer\Transformer\TransformerInterface:
            tags:
                - 'happyr.message_serializer.transformer'

        Happyr\MessageSerializer\Hydrator\HydratorInterface:
            tags:
                - 'happyr.message_serializer.hydrator'

Then finally, make sure you configure your transport to use this serializer:

# config/packages/messenger.yaml

framework:
    messenger:
        transports:
            amqp: '%env(MESSENGER_TRANSPORT_DSN)%'
            
            to_foobar_application:
              dsn: '%env(MESSENGER_TRANSPORT_FOOBAR)%'
              serializer: 'Happyr\MessageSerializer\Serializer'

            # If you use SerializerRouter
            from_foobaz_application:
              dsn: '%env(MESSENGER_TRANSPORT_FOOBAZ)%'
              serializer: 'Happyr\MessageSerializer\SerializerRouter'

Note about Envelopes

When using Symfony Messenger you will get an Envelope passed to TransformerInterface::getPayload(). You need to handle this like:

use Happyr\MessageSerializer\Transformer\TransformerInterface;

class FooTransformer implements TransformerInterface
{
    // ...

    public function getPayload($message): array
    {
        if ($message instanceof Envelope) {
            $message = $message->getMessage();
        }
            
        return [
            'bar' => $message->getBar(),
        ];
    }

    public function supportsTransform($message): bool
    {
        if ($message instanceof Envelope) {
            $message = $message->getMessage();
        }
            
        return $message instanceof Foo;
    }
}

Pro tip

You can let your messages implement both HydratorInterface and TransformerInterface:

use Happyr\MessageSerializer\Hydrator\HydratorInterface;
use Happyr\MessageSerializer\Transformer\TransformerInterface;
use Ramsey\Uuid\Uuid;
use Ramsey\Uuid\UuidInterface;
use Symfony\Component\Messenger\Envelope;

class CreateUser implements HydratorInterface, TransformerInterface
{
    private $uuid;
    private $username;

    /** Constructor must be public and empty. */
    public function __construct() {}

    public static function create(UuidInterface $uuid, string $username): self
    {
        $message = new self();
        $message->uuid = $uuid;
        $message->username = $username;
        
        return $message;
    }

    public function getUuid(): UuidInterface
    {
        return $this->uuid;
    }
    
    public function getUsername(): string
    {
        return $this->username;
    }

    public function toMessage(array $payload, int $version): self
    {
        return self::create(Uuid::fromString($payload['id']), $payload['username']);
    }

    public function supportsHydrate(string $identifier, int $version): bool
    {
        return $identifier === 'create-user' && $version === 1;
    }

    public function getVersion(): int
    {
        return 1;
    }

    public function getIdentifier(): string
    {
        return 'create-user';
    }

    public function getPayload($message): array
    {
        if ($message instanceof Envelope) {
            $message = $message->getMessage();
        }

        return [
            'id' => $message->getUuid()->toString(),
            'username' => $message->getUsername(),
        ];
    }

    public function supportsTransform($message): bool
    {
        if ($message instanceof Envelope) {
            $message = $message->getMessage();
        }

        return $message instanceof self;
    }
}

Just note that we cannot use a constructor to this class since it will work both as a value object and a service.