php: json/array to xml

a.php

<?php
$file = 'https://raw.githubusercontent.com/ZiTAL/flickr-php-cli/master/composer.json';
$file = file_get_contents($file);
$array = json_decode($file, true);

$dom = new DOMDocument('1.0', 'utf-8');
$dom->preserveWhiteSpace = false;
$dom->formatOutput = true;
$root = $dom->createElement('root');
$dom->appendChild($root);

array2xml($array, $root, $dom);

echo $dom->saveXML();

function array2xml($array, $node, &$dom)
{
    foreach($array as $key => $value)
    {
        if(preg_match("/^[0-9]/", $key))
            $key = "node-{$key}";
        $key = preg_replace("/[^a-z0-9_\-]+/i", '', $key);

        if($key==='')
            $key = '_';

        $a = $dom->createElement($key);
        $node->appendChild($a);

        if(!is_array($value))
            $a->appendChild($dom->createTextNode($value));
        else
            array2xml($value, $a, $dom);
    }
}

input.json

{
    "name": "thefox/flickr-cli",
    "description": "Upload and download Flickr photos, photo sets, directories via shell.",
    "license": "GPL-3.0",
    "type": "project",
    "keywords": [
        "Flickr",
        "Upload",
        "Download",
        "Photo",
        "CLI"
    ],
    "homepage": "https://github.com/TheFox/flickr-cli",
    "authors": [
        {
            "name": "Christian Mayer",
            "email": "christian@fox21.at",
            "homepage": "https://fox21.at"
        }
    ],
    "require": {
        "php": "^7.0",
        "rezzza/flickr": "^1.1",
        "symfony/yaml": "^2.3",
        "symfony/console": "^3.1",
        "symfony/filesystem": "^3.1",
        "symfony/finder": "^3.1",
        "monolog/monolog": "^1.21",
        "guzzlehttp/guzzle": "^3.8",
        "lusitanian/oauth": "^0.2",
        "rych/bytesize": "^1.0",
        "doctrine/dbal": "^2.5"
    },
    "require-dev": {
        "phpstan/phpstan": "^0.7",
        "squizlabs/php_codesniffer": "^3.0"
    },
    "autoload": {
        "psr-4": {
            "": "src"
        }
    },
    "bin": [
        "bin/flickr-cli"
    ]
}

output.xml

<?xml version="1.0" encoding="utf-8"?>
<root>
  <name>thefox/flickr-cli</name>
  <description>Upload and download Flickr photos, photo sets, directories via shell.</description>
  <license>GPL-3.0</license>
  <type>project</type>
  <keywords>
    <node-0>Flickr</node-0>
    <node-1>Upload</node-1>
    <node-2>Download</node-2>
    <node-3>Photo</node-3>
    <node-4>CLI</node-4>
  </keywords>
  <homepage>https://github.com/TheFox/flickr-cli</homepage>
  <authors>
    <node-0>
      <name>Christian Mayer</name>
      <email>christian@fox21.at</email>
      <homepage>https://fox21.at</homepage>
    </node-0>
  </authors>
  <require>
    <php>^7.0</php>
    <rezzzaflickr>^1.1</rezzzaflickr>
    <symfonyyaml>^2.3</symfonyyaml>
    <symfonyconsole>^3.1</symfonyconsole>
    <symfonyfilesystem>^3.1</symfonyfilesystem>
    <symfonyfinder>^3.1</symfonyfinder>
    <monologmonolog>^1.21</monologmonolog>
    <guzzlehttpguzzle>^3.8</guzzlehttpguzzle>
    <lusitanianoauth>^0.2</lusitanianoauth>
    <rychbytesize>^1.0</rychbytesize>
    <doctrinedbal>^2.5</doctrinedbal>
  </require>
  <require-dev>
    <phpstanphpstan>^0.7</phpstanphpstan>
    <squizlabsphp_codesniffer>^3.0</squizlabsphp_codesniffer>
  </require-dev>
  <autoload>
    <psr-4>
      <_>src</_>
    </psr-4>
  </autoload>
  <bin>
    <node-0>bin/flickr-cli</node-0>
  </bin>
</root>