php使用curl提交xml数据

$xml_data ='<xml> 
  <return_code><![CDATA[SUCCESS]]></return_code>
  <return_msg><![CDATA[OK]]></return_msg>
</xml> 
';
 
            $URL = "http://localhost/aa.php";
            $ch = curl_init($URL);
            curl_setopt($ch, CURLOPT_SSL_VERIFYHOST, 0);
            curl_setopt($ch, CURLOPT_SSL_VERIFYPEER, 0); //禁用后cURL将终止从服务端进行验证
            curl_setopt($ch, CURLOPT_HTTPHEADER, array('Content-Type: text/xml'));   //设置header
            curl_setopt($ch, CURLOPT_POST, 1);                                       //post提交方式
            curl_setopt($ch, CURLOPT_POSTFIELDS, "$xml_data");         
            curl_setopt($ch, CURLOPT_RETURNTRANSFER, 1);  //将curl_exec()获取的信息以文件流的形式返回，而不是直接输出
            $data = curl_exec($ch);  
            if($data){
                curl_close($ch);
                echo($data);
             }
             else{
                $error = curl_errno($ch);
                curl_close($ch);
                echo("curl出错，错误码:$error");
             }

<?php
echo "<pre>";
var_dump($_POST);
$data = file_get_contents('php://input');   //都要解下码
var_dump(($data));
echo "<br>";
var_dump(($GLOBALS['HTTP_RAW_POST_DATA']));
?>