Laravel/Lumen Etag Middleware

EtagMiddleware.php

<?php

namespace App\Http\Middleware;

use Closure;
use Illuminate\Http\Request;

class EtagMiddleware
{
    public function handle(Request $request, Closure $next)
    {
        $response = $next($request);

        if (!$request->isMethod('get') && !$request->isMethod('head')) {
            return $response;
        }

        $etag = hash('fnv1a32', $response->getContent());
        $requestETag = str_replace('W/"', '', $request->getETags());
        $requestETag = str_replace('"', '', $requestETag);
        if ($requestETag && $requestETag[0] === $etag) {
            $response->setNotModified();
        }
        $response->setETag($etag, true);

        return $response;
    }
}