Symfony News

New in Symfony 5.1: Stack decorators

Contributed by
Nicolas Grekas
in #36373.

Middleware is computer software that separates two or more APIs and provides services such as rate-limiting, authentication, and logging. In Symfony you can achieve something like that using service decoration.

However, when decorating multiple services, the config is verbose and it's cumbersome to change the decoration order:

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services:
    App\Mailer\Mailer: ~

    App\Mailer\RateLimitedMailer:
        decorates: App\Mailer\Mailer
        arguments: [20] # mails per second

    App\Mailer\LoggingMailer:
        decorates: App\Mailer\RateLimitedMailer

That's why in Symfony 5.1 we've introduced a new syntax to chain several decorators using a new concept called "stack". This is the equivalent config of the previous example:

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services:
    mailer:
        stack:
            - App\Mailer\Mailer: ~
            - App\Mailer\RateLimitedMailer:
                arguments: [20]
            - App\Mailer\LoggingMailer: ~

This new syntax (which is also available when using XML and PHP formats) makes it trivial to add/remove/reorder the decorated services. The main advantage of "stacks" over classic middleware is that middleware defines a domain-specific interface that each processing step must implement to be stackable.