Return value from index.php

Benny Andersen 0
Viewed 58

I have installed a symfony app skeleton using 2 composer commands as advised from symfony.com/doc

file: index.php

<?php

use App\Kernel;

require_once dirname(__DIR__).'/vendor/autoload_runtime.php';

return function (array $context) {
    return new Kernel($context['APP_ENV'], (bool) $context['APP_DEBUG']);
};

snippets from file: autoload_runtime.php

<?php
if (true === (require_once __DIR__.'/autoload.php') || empty($_SERVER['SCRIPT_FILENAME'])) {
    return;
}

...

[$app, $args]= ...

...

exit(
    $runtime
        ->getRunner($app)
        ->run()
);

So the return statement in index.php gets thread of execution dependt on some condition.

What handles something returned from the main script. It looks like a callback that some runtime (in mod_php?) not only calls but also can do something with, with the returned object.

symfony php
1 Answers

I don't know if this will help you in anyway, but here's a general breakdown of what's going on.

But before that, return, include and their _once versions are strange language constructs, and not really functions, and what they really do is sometimes weird and unexpected. You kind of have to read through the man page on it to get a full understanding, and even then there's some surprises I think.

In autoload_runtime.php, the following code's job is to guard against accidentally booting things twice (or possibly a missing server variable) because the require_once function will return true if the called file has already be included already.

if (true === (require_once __DIR__.'/autoload.php') || empty($_SERVER['SCRIPT_FILENAME'])) {
    return;
}

Then the following line re-loads the index.php (or whatever the file is called) which is the clever part:

$app = require $_SERVER['SCRIPT_FILENAME'];

Because autoload_runtime.php was brought in using require_once it is skipped and just the function is returned which is set to the $app variable. The function, when invoked actually boots the kernel, however that happens a little bit later.

(One clever aspect of returning a closure that boots the kernel is that Kernel isn't event type-checked until the closure is invoked. You can see that here where nothing is thrown for a class that doesn't exist.)

If you var_dump($app) at that point you'd see a normal closure.

Then finally a runtime which depends on how you installed the Symfony is instantiated, the $app closure is actually invoked returning a Kernel, the runtime "runs" and the final result is past to exit which is universally used for all PHP SAPIs to give a status code.

The "runtime runs" might involve looking at $_SERVER variables to determine the route, etc.

Chris Haas0
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