src/Viserio/Component/Http/Response/BinaryFileResponse.php
protected function setAutoLastModified(): void
    {
        $date = DateTime::createFromFormat('U', (string) $this->file->getMTime());
        $date = DateTimeImmutable::createFromMutable($date);
        $date = $date->setTimezone(new \DateTimeZone('UTC'));

        $this->headers['Last-Modified']     = [$date->format('D, d M Y H:i:s') . ' GMT'];
        $this->headerNames['last-modified'] = 'Last-Modified';
    }
protected function setAutoLastModified(): void
    {
        $date = DateTime::createFromFormat('U', (string) $this->file->getMTime());
        $date = DateTimeImmutable::createFromMutable($date);
        $date = $date->setTimezone(new \DateTimeZone('UTC'));

        $this->headers['Last-Modified']     = [$date->format('D, d M Y H:i:s') . ' GMT'];
        $this->headerNames['last-modified'] = 'Last-Modified';
    }
Automatically sets the Last-Modified header according the file modification date.

@return void