未设置 PHP cURL 内容类型

我有一个简单的 Web 服务，我想与之连接。为了发布一些，这将在Web服务端正确进行，我需要准备一个适当的请求。我用这个像这样：XMLcURL

try {
    $ch = curl_init();

    if (FALSE === $ch)
        throw new Exception('failed to initialize');
    
    curl_setopt($ch, CURLOPT_URL,"192.168.1.37");
    curl_setopt($ch, CURLOPT_HTTPHEADER, array(
        'Content-Type: application/xml',
        'Connection: Keep-Alive'
    ));
    curl_setopt($ch, CURLOPT_HEADER, 1);
    curl_setopt($ch, CURLOPT_USERPWD, $username . ":" . $password);
    curl_setopt($ch, CURLOPT_PROXY, '');
    curl_setopt($ch, CURLOPT_POST, 1);
    curl_setopt($ch, CURLOPT_FRESH_CONNECT, TRUE);
    curl_setopt($ch, CURLOPT_HTTPHEADER,array("Expect:  "));
    curl_setopt($ch, CURLOPT_SSL_VERIFYPEER, false);
    curl_setopt($ch, CURLOPT_POSTFIELDS,$xml);

    $request=  curl_getinfo($ch);
    var_dump($request);

    $content = curl_exec($ch);

    if (false === $content) {
        throw new Exception(curl_error($ch), curl_errno($ch));
    }
} catch(Exception $e) {
    trigger_error(sprintf(
        'Curl failed with error #%d: %s',
        $e->getCode(), $e->getMessage()),E_USER_ERROR);
}

一切都应该没问题。首先，我显示来自的请求正文，然后显示来自变量的响应。curl_getinfo($ch);$content

将请求发送到服务器的唯一限制是标头 - 它必须是，否则服务器将响应错误（这不是我的想法，我对此无能为力）Content-Typeapplication/xml

下面是输出请求：

array(21) { ["url"]=> string(68) "192.168.1.37" ["content_type"]=> NULL ["http_code"]=> int(0) ["header_size"]=> int(0) ["request_size"]=> int(0) ["filetime"]=> int(0) ["ssl_verify_result"]=> int(0) ["redirect_count"]=> int(0) ["total_time"]=> float(0) ["namelookup_time"]=> float(0) ["connect_time"]=> float(0) ["pretransfer_time"]=> float(0) ["size_upload"]=> float(0) ["size_download"]=> float(0) ["speed_download"]=> float(0) ["speed_upload"]=> float(0) ["download_content_length"]=> float(-1) ["upload_content_length"]=> float(-1) ["starttransfer_time"]=> float(0) ["redirect_time"]=> float(0) ["certinfo"]=> array(0) { } }

并且响应为HTTP 400 Bad Request

我从中可以看出，但我在PHP代码中设置了这个变量......["content_type"]=> NULL

谁能告诉我我错过了什么？