protected function getSourceHeaders()
    {
        $headers = [];

        if (!$this->user_agent_header || !$this->source_header) {
            $version = trim(file_get_contents(__DIR__ . '/../../VERSION'));

            if (!$this->user_agent_header) {
                $this->user_agent_header = sprintf('filestack-php-%s',
                    $version);
            }

            if (!$this->source_header) {
                $this->source_header = sprintf('PHP-%s',
                    $version);
            }
        }

        $headers['user-agent'] = $this->user_agent_header;
        $headers['filestack-source'] = $this->source_header;

        //user_agent_header
        return $headers;
    }