How to apply the PSR-15 middleware pattern to any PHP library component, as an alternative to the Decorator pattern.

Maxime Gosselin

PSR-15's middleware pattern can be applied beyond HTTP to any PHP library component as a more flexible alternative to the Decorator pattern. The approach involves creating a middleware interface that mirrors the component interface with an added `$next` parameter, a delegator class to bridge the two, and using `array_reduce` to build the chain. This enables runtime composition, input/output modification, and short-circuiting — capabilities the Decorator pattern cannot cleanly express. A concrete HtmlRenderer example with caching and page title middlewares illustrates all three execution models: before, after, and both.

Using the Middleware Pattern to Extend PHP Libraries