PHP
Middleware chain
Learn to chain multiple middlewares with arrays and callables.
The middleware chain
Instead of one middleware, you often run a list of middlewares in sequence. Each hands off to the next with $next; the real handler at the end produces the response.
This structure is a pipeline. With array_reduce you can fold the middleware array into a single callable. Each step produces a new closure that wraps the $next it received.
Order matters: the first middleware becomes the outer layer, so its before runs first and its after runs last. That is why you reverse the array with array_reverse before folding.
Pipeline with array_reduce
buildPipeline works like this: array_reduce walks the reversed middleware array. The initial value is the innermost handler. At each step a new closure is returned that wraps $mw and $next.
The wrapper closure: function ($request) use ($mw, $next) { return $mw($request, $next); }. So from outside in, each middleware wraps the call after it.
The reversal is needed because array_reduce goes left to right; the first middleware must be the outer layer. Without reversal the order would be inverted.
Exercise Write the buildPipeline function
Define a buildPipeline(array $middlewares, callable $handler): callable function. Use array_reduce to walk array_reverse($middlewares); at each step return a closure that wraps $mw and $next. $finalHandler and $middlewares are already defined. Build the pipeline, call it with "istek" and print the result.
Show example solution
callable { return array_reduce(array_reverse($middlewares), function ($next, $mw) { return function ($request) use ($mw, $next) { return $mw($request, $next); }; }, $handler); }. Then $pipeline = buildPipeline($middlewares, $finalHandler); echo $pipeline("istek") . "\n";.
Example solution:
<?php
function buildPipeline(array $middlewares, callable $handler): callable {
return array_reduce(array_reverse($middlewares), function ($next, $mw) {
return function ($request) use ($mw, $next) {
return $mw($request, $next);
};
}, $handler);
}
$finalHandler = function ($request) {
return "TAMAM";
};
$middlewares = [
function ($request, $next) {
echo "A-before\n";
$r = $next($request);
echo "A-after\n";
return $r;
},
function ($request, $next) {
echo "B-before\n";
$r = $next($request);
echo "B-after\n";
return $r;
},
];
$pipeline = buildPipeline($middlewares, $finalHandler);
echo $pipeline("istek") . "\n";
Test yourself
-
The pipeline builder call
$pipeline = ____($middlewares, $handler);
Show answer
$pipeline = buildPipeline($middlewares, $handler);
-
Why is the array reversed when building a pipeline with array_reduce?
- To sort the array alphabetically
- To make it run faster
- So the first middleware becomes the outer layer
- To save memory
Show answer
So the first middleware becomes the outer layer — Correct. array_reduce goes left to right; reversing puts the first middleware outermost.
-
Match the pipeline tools
- array_reduce
- Folds the array into one value
- array_reverse
- Reverses the array order
- callable
- Invocable function
- Closure
- Anonymous function
Next lesson: Auth middleware
