php curl上传文件$_FILES为空问题

php使用curl上传文件，代码如下：

发送的代码(完全是官方的示例)

<?php

/* http://localhost/upload.php:
print_r($_POST);
print_r($_FILES);
*/

$ch = curl_init();

$data = array('name' => 'Foo', 'file' => '@/home/vagrant/test.png');

curl_setopt($ch, CURLOPT_URL, 'http://localhost/test/curl/load_file.php');
curl_setopt($ch, CURLOPT_POST, 1);
curl_setopt($ch, CURLOPT_POSTFIELDS, $data);

curl_exec($ch);
?>

接收代码(也是官方的)

<?php
print_r($_POST);
print_r($_FILES);
运行结果

php -f demo.php
Array
(
[name] => Foo
[file] => @/home/vagrant/test.png
)
Array
(
)

解决方法1：
<?php

/* http://localhost/upload.php:
print_r($_POST);
print_r($_FILES);
*/

$ch = curl_init();

$data = array('name' => 'Foo', 'file' => '@/home/vagrant/test.png');