Cache Control for Laravel Response

helpers.php

<?php

function addResponseHeaders($request, $response, $ext, $modifiedTimestamp, $downloadFileName = null)
{
    $mime = ExtToMIME::convert($ext);
    $headers = &$response->headers;
    $headers->set('Content-Type', $mime, true);
    $headers->set('Cache-Control', 'public', true); // TODO max-age=xxx
    $headers->set('Last-Modified', gmdate("D, d M Y H:i:s", $modifiedTimestamp) . " GMT", true);
    if ($downloadFileName != null) {
        $headers->set('Content-Disposition', 'filename="' . $downloadFileName . '"', true);
    }
    // note that it should be STRING
    $eTag = (string) $modifiedTimestamp;
    addRespETag($request, $response, $eTag);
}

function addRespETag($request, $response, string $eTag)
{
    $requestEtag = str_replace('"', '', $request->getETags());
    // Check to see if Etag has changed
    // strpos -> in case the browser gets `{etag}-gzip`
    if ($requestEtag && strpos($requestEtag[0], $eTag) === 0) {
        $response->setNotModified();
    }
    // Set Etag
    $response->setEtag($eTag);
}