对于已经上传的文件，如何通过api修改http头的Content-Disposition

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修改文件元信息(Object Meta)

可以通过拷贝操作来实现修改已有文件元信息。如果拷贝操作的源文件地址和目标文件地址相同，都会直接替换源文件的文件元信息。
PHP实现

https://help.aliyun.com/document_detail/oss/sdk/php-sdk/manage_object.html

/**
* 修改文件元信息
* 利用copyObject接口的特性：当目的object和源object完全相同时，表示修改object的文件元信息
*
* @param OssClient $ossClient OSSClient实例
* @param string $bucket 存储空间名称
* @return null
*/
function modifyMetaForObject($ossClient, $bucket)
{
    $fromBucket = $bucket;
    $fromObject = "oss-php-sdk-test/upload-test-object-name.txt";
    $toBucket = $bucket;
    $toObject = $fromObject;
    $copyOptions = array(
        OssClient::OSS_HEADERS => array(
            'Expires' => '2012-10-01 08:00:00',
            'Content-Disposition' => 'attachment; filename="xxxxxx"',
        ),
    );
    try{
        $ossClient->copyObject($fromBucket, $fromObject, $toBucket, $toObject, $copyOptions);
    } catch(OssException $e) {
        printf(__FUNCTION__ . ": FAILED\n");
        printf($e->getMessage() . "\n");
        return;
    }
    print(__FUNCTION__ . ": OK" . "\n");
}