Here is php 5.2 code which will convert array of any depth to xml document:

Array
(
    ['total_stud']=> 500
    [0] => Array
        (
            [student] => Array
                (
                    [id] => 1
                    [name] => abc
                    [address] => Array
                        (
                            [city]=>Pune
                            [zip]=>411006
                        )                       
                )
        )
    [1] => Array
        (
            [student] => Array
                (
                    [id] => 2
                    [name] => xyz
                    [address] => Array
                        (
                            [city]=>Mumbai
                            [zip]=>400906
                        )   
                )

        )
)

generated XML would be as:

<?xml version="1.0"?>
<student_info>
    <total_stud>500</total_stud>
    <student>
        <id>1</id>
        <name>abc</name>
        <address>
            <city>Pune</city>
            <zip>411006</zip>
        </address>
    </student>
    <student>
        <id>1</id>
        <name>abc</name>
        <address>
            <city>Mumbai</city>
            <zip>400906</zip>
        </address>
    </student>
</student_info>

PHP snippet

<?php
// function defination to convert array to xml
function array_to_xml( $data, &$xml_data ) {
    foreach( $data as value ) {
        if( is_array($value) ) {
            if( is_numeric($key) ){
                $key = 'item'.$key; //dealing with <0/>..<n/> issues
            }
            $subnode = $xml_data->addChild($key);
            array_to_xml($value, $subnode);
        } else {
            $xml_data->addChild("$key",htmlspecialchars("$value"));
        }
     }
}

// initializing or creating array
$data = array('total_stud' => 500);

// creating object of SimpleXMLElement
$xml_data = new SimpleXMLElement('<?xml version="1.0"?><data></data>');

// function call to convert array to xml
array_to_xml($data,$xml_data);

//saving generated xml file; 
$result = $xml_data->asXML('/file/path/name.xml');

?>

Documentation on SimpleXMLElement::asXML used in this snippet

Its easy with the below package, Just install the package via composer :

https://github.com/spatie/array-to-xml

The implementation will be :

$array= 'invoice' => [
    'date' => date('Y-m-d H:i:s'),
    'due_date' => date('Y-m-d H:i:s'),
    'client' => ['name' => 'John', 'code' => ''],
    'items' => [
        'item' => [
            'name' => 'reg1',
            'description' => 'reg1 on evt',
            'unit_price' => '10',
            'quantity' => '1.0'
        ],
        'item' => [
            'name' => 'reg1',
            'description' => 'reg1 on evt',
            'unit_price' => '10',
            'quantity' => '1.0'
        ]
    ]
]

And then :

$result = ArrayToXml::convert($array);

Don't forget to include use Spatie\ArrayToXml\ArrayToXml; at the top of the class/Controller.

Assuming that the content of xml is in $xml variable, you can use one of the followings:

return response($xml, 200)->header('Content-Type', 'application/xml');

OR

return response($xml, 200, ['Content-Type' => 'application/xml']);

easy!

$xml = simplexml_load_string($xmlstring, "SimpleXMLElement", LIBXML_NOCDATA);
$json = json_encode($xml);
$array = json_decode($json,TRUE);