Config processors

The ConfigAggregator can apply processors to the configuration by aggregating "config processors" passed to its constructor. Each processor should be a PHP callable which consumes either the list of providers (pre-processors) or the merged configuration (post-processors) as its sole argument, and which then returns the processed array.

$providers = [
    function () {
        return ['foo' => 'bar'];
    },
    new PhpFileProvider('*.global.php'),
];

$preProcessors = [
    function (iterable $providers) {
        return [...$providers, new ArrayProvider(['pre-processed' => true])];
    }
];

$postProcessors = [
    function (array $config) {
        return $config + ['post-processed' => true];
    },
];

$aggregator = new ConfigAggregator($providers, null, $postProcessors, $preProcessors);
var_dump($aggregator->getMergedConfig());

Output from the example:

array(2) {
  'foo' =>
  string(3) "bar"
  'pre-processed' =>
  bool(true)
  'post-processed' =>
  bool(true)
}

If the processor is a class name, the aggregator automatically instantiates it before invoking it; as such, any class name you use as a config provider must also define __invoke(), and that method must return an array and may consume either the list of providers (pre-processors) or merged configuration (post-processors) as a parameter.

Pre-processor examples

Pre-processors can be used to modify the list of providers prior to their configuration being retrieved. This could be used to provide a list of providers for use in development, or to allow providers to have their own dependencies as just a couple of examples.

Post-processor examples

Post-processors can be used to mimic tools such as the Symfony configuration parameter system. As an example, you can specify a config processor which consumes the merged configuration and resolves templated parameters to other parameters within your configuration.

Symfony ParameterBag Post Processor

The following example resolves templated parameters to either other parameters within your configuration, or a static set of substitutions. Templated parameters have the format %<config_key>%; . characters indicate an additional level of nesting. If you want to provide configuration parameters with % in the value, you must escape any occurences of % by using another %; as examples, %%bar or %%foo%%.

In the following example, we define a provider that returns a nested array of configuration. We then define additional parameters and pass them to a Symfony DI ParameterBag, which we develop a closure over. This closure checks for parameters in the passed configuration itself, and then attempts to resolve all configuration values based on the parameters in the ParameterBag.

$provider = [
    function () {
        return [
            'session' => [
                'cookie_domain' => '%cookie_domain%',
            ],
            'tracking' => [
                'cookie_domain' => '%cookie_domain%',
            ],
            // Will be converted to %foo% after resolving
            'config_parameter_with_percent' => '%%foo%%',
        ];
    },
];

$parameters = [
    'cookie_domain' => 'example.com',
];

$bag = new \Symfony\Component\DependencyInjection\ParameterBag\ParameterBag($parameters);
$resolver = function (array $config) use ($bag) {
    $parametersFromConfiguration = isset($config['parameters']) ? $config['parameters'] : [];
    $bag->add($parametersFromConfiguration);

    // Resolve parameters which probably base on parameters
    $bag->resolve();
    
    // Replace all parameters within the configuration
    $resolved = $bag->resolveValue($config);
    $resolved['parameters'] = $bag->all();
    
    return $bag->unescapeValue($resolved);
};

$aggregator = new ConfigAggregator($provider, null, [
    $resolver,
]);

var_dump($aggregator->getMergedConfig());

The above would result in the following when complete:

array(2) {
  'session' =>
  array(1) {
    'cookie_domain' =>
    string(11) "example.com"
  }
  'tracking' =>
  array(1) {
    'cookie_domain' =>
    string(11) "example.com"
  }
  'config_parameter_with_percent' =>
    string(7) "%foo%"
  }
  'parameters' =>
  array(1) {
    'cookie_domain' =>
    string(11) "example.com"
  }
}

There is an extension for this feature available via the package laminas/laminas-config-aggregator-parameters:

$ composer require laminas/laminas-config-aggregator-parameters