亚马逊s3 api putObject内容标题

I'm trying to upload a file to my s3 using the php sdk and for each file I'm setting the ConentDisposition and ContentType just as the documentation says (http://docs.aws.amazon.com/aws-sdk-php/latest/class-Aws.S3.S3Client.html#_putObject), but after uploading I look at the http header for the file and the only thing set is Content-Type and that's set to the default 'octet-stream':

$result = $client->putObject(array(
    'Bucket'     => $bucket,
    'Key'        => $file_name,
    'SourceFile' => $tmp_file,
    'ACL' => 'public-read',
    'ContentDisposition' => 'inline; filename=',
    'ContentType' => 'application/pdf'
));