Laravel - Simple file extension validator

ValidatorServiceProvider.php

<?php 

namespace App\Providers;

use Illuminate\Support\ServiceProvider;

use Symfony\Component\HttpFoundation\File\UploadedFile;

class ValidatorServiceProvider extends ServiceProvider
{
    /**
	 * Bootstrap any application services.
	 *
	 * @return void
	 */
	public function boot() {
		$this->app['validator']->extend('ext', function ($attribute, $value, $params) {
			if (!($value instanceof UploadedFile && $value->isValid())) {
				return false;
			}

			$ext = $value->getClientOriginalExtension();

			return in_array($ext, $params);
		});
	}

	/**
	 * Register any application services.
	 *
	 * @return void
	 */
	public function register() {

	}
}

Usage

$rules => [
    "field" => 'ext:pdf,docx,png'
]