eZ\Publish\Core\Search\Elasticsearch\Content\Gateway\HttpClient\Stream::getRequestHeaders PHP Method

    protected function getRequestHeaders(array $headers)
    {
        $requestHeaders = '';
        foreach ($this->headers as $name => $value) {
            if (!isset($headers[$name])) {
                $requestHeaders .= "{$name}: {$value}\r\n";
            }
        }
        foreach ($headers as $name => $value) {
            if (is_numeric($name)) {
                throw new RuntimeException("Invalid HTTP header name {$name}");
            }
            $requestHeaders .= "{$name}: {$value}\r\n";
        }
        return $requestHeaders;
    }