SpecialistPreflightLegacyHandler.php

<?php declare(strict_types=1);

namespace AppBundle\EventListener;

use Symfony\Component\EventDispatcher\EventSubscriberInterface;
use Symfony\Component\HttpKernel\Event\{GetResponseEvent, FilterResponseEvent};
use Symfony\Component\HttpKernel\KernelEvents;
use Symfony\Component\HttpFoundation\HeaderBag;

class SpecialistPreflightLegacyHandler implements EventSubscriberInterface
{
    // Try to run as soon as possible.
    const HIGH_PRIORITY_REQUEST = 999999;

    /**
     * {@inheritDoc}
     */
    public static function getSubscribedEvents(): array
    {
        return [
            KernelEvents::REQUEST => [
                ['recordRequestedHeaders', self::HIGH_PRIORITY_REQUEST],
                ['parseSpecialistFlags',   self::HIGH_PRIORITY_REQUEST-1]
            ],
            KernelEvents::RESPONSE => 'varyOnRequestedSpecialistHeaders'
        ];
    }

    /**
     * Replace the HeaderBag with one that keeps track of which Headers are read.
     *
     * @param GetResponseEvent $event
     *
     * @return void
     */
    public function recordRequestedHeaders(GetResponseEvent $event)
    {
        $request = $event->getRequest();
        $request->originalHeaderBag = $request->headers;

        /**
         * Wrap the Request object with a shim that records all property accesses..
         */
        $request->headers = new class($request->originalHeaderBag->all()) extends HeaderBag {

            /**
             * @var string[]
             */
            protected $varyHeaders = [];

            /**
             * {@inheritDoc}
             */
            public function all()
            {
                $this->varyHeaders += parent::keys();
                return parent::all();
            }

            /**
             * {@inheritDoc}
             */
            public function keys()
            {
                $keys = parent::keys();
                $this->varyHeaders += $keys;
                return $keys;
            }

            /**
             * {@inheritDoc}
             */
            public function get($key, $default = null, $first = true)
            {
                $this->varyHeaders[] = $key;
                return parent::get($key, $default, $first);
            }

            /**
             * {@inheritDoc}
             */
            public function has($key)
            {
                $this->varyHeaders[] = $key;
                return parent::has($key);
            }

            /**
             * {@inheritDoc}
             */
            public function contains($key, $value)
            {
                $this->varyHeaders[] = $key;
                return parent::contains($key, $value);
            }

            /**
             * @return string[] An array of headers we may Vary on.
             */
            public function getVaryHeaders()
            {
                return array_unique($this->varyHeaders);
            }
        };
    }
    
    /**
     * Interpret KV flag data of format "KEY=VALUE,KEY=VALUE" passed in 'Specialist-Flags' header
     *
     * @param GetResponseEvent $event
     * @return void
     */
    public function parseSpecialistFlags(GetResponseEvent $event)
    {
        $request = $event->getRequest();
        $request->flags = new HeaderBag();
        if ($flags = $request->headers->get('Specialist-Flags')) {
            parse_str(str_replace(',', '&', $flags), $parsedFlags);
            foreach ($parsedFlags as $key => $value){
                $sanitizeFlagValue = filter_var($value, FILTER_VALIDATE_BOOLEAN);
                $request->flags->set($key, $sanitizeFlagValue);
            }
        }
    }

    /**
     * Automatically tags a FilterResponseEvent with the correct Vary based on what we have read during a request.
     *
     * @param FilterResponseEvent $event
     *
     * @return void
     */
    public function varyOnRequestedSpecialistHeaders(FilterResponseEvent $event): void
    {
        $request = $event->getRequest();
        $response = $event->getResponse();
        foreach ($request->headers->getVaryHeaders() as $header) {
            if (0 === strpos($header, 'Specialist')) {
                $response->setVary($header, false);
            }
        }
    }
}