获得'；Multipart必须具有Atom和媒体部件'；尝试将带有元数据的照片上载到Picasa时出错

我有下面的代码，它试图将带有元数据的图像上传到Picasa网络相册。

如果我取出元数据，直接执行内容类型：image/jpegPOST请求，下面的代码就可以上传图像。

$albumUrl = "https://picasaweb.google.com/data/feed/api/user/$userId/albumid/$albumId";
$imgName = $_SERVER['DOCUMENT_ROOT'] . '/picasa/cute_baby_kitten.jpg';
$rawImgXml = '<entry xmlns="http://www.w3.org/2005/Atom">
              <title>plz-to-love-realcat.jpg</title>
              <summary>Real cat wants attention too.</summary>
              <category scheme="http://schemas.google.com/g/2005#kind"
                term="http://schemas.google.com/photos/2007#photo"/>
            </entry>';
$fileSize = filesize($imgName);
$fh = fopen($imgName, 'rb');
$imgData = fread($fh, $fileSize);
fclose($fh);
$dataLength = strlen($rawImgXml) + $fileSize;
$data = "";
$data .= "'nMedia multipart posting'n";
$data .= "--P4CpLdIHZpYqNn7'n";
$data .= "Content-Type: application/atom+xml'n'n";
$data .= $rawImgXml . "'n";
$data .= "--P4CpLdIHZpYqNn7'n";
$data .= "Content-Type: image/jpeg'n'n";
$data .= $imgData . "'n";
$data .= "--P4CpLdIHZpYqNn7--";
$header = array('GData-Version:  2', $authHeader, 'Content-Type: multipart/related;boundary=P4CpLdIHZpYqNn7', 'Content-Length: ' . $dataLength, 'MIME-version: 1.0');
$ret = "";
$ch  = curl_init($albumUrl);
$options = array(
        CURLOPT_SSL_VERIFYPEER=> false,
        CURLOPT_POST=> true,
        CURLOPT_RETURNTRANSFER=> true,
        CURLOPT_HEADER=> true,
        CURLOPT_FOLLOWLOCATION=> true,
        CURLOPT_POSTFIELDS=> $data,
        CURLOPT_HTTPHEADER=> $header
    );
curl_setopt_array($ch, $options);
$ret = curl_exec($ch);
curl_close($ch);

问题是我一直收到一条400 Bad Request: Multipart must have Atom and media part错误消息。

以下是我发送的标题：

Array
(
    [0] => GData-Version:  2
    [1] => Authorization:  GoogleLogin auth="THISISAVALIDAUTHCODE"
    [2] => Content-Type: multipart/related;boundary=P4CpLdIHZpYqNn7
    [3] => Content-Length: 179951
    [4] => MIME-version: 1.0
)

以下是POST请求主体的样子：

Media multipart posting
--P4CpLdIHZpYqNn7
Content-Type: application/atom+xml
<entry xmlns="http://www.w3.org/2005/Atom">
              <title>plz-to-love-realcat.jpg</title>
              <summary>Real cat wants attention too.</summary>
              <category scheme="http://schemas.google.com/g/2005#kind"
                term="http://schemas.google.com/photos/2007#photo"/>
            </entry>
--P4CpLdIHZpYqNn7
Content-Type: image/jpeg
IMAGE DATA GOES HERE
--P4CpLdIHZpYqNn7--

我想我在POST正文中正确地放置了换行符，但我不能100%确定。我还想知道我是否正确计算了Content-Length。

我在这里做错了什么？