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system/Format/XMLFormatter.php

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+<?php
+
+/**
+ * This file is part of CodeIgniter 4 framework.
+ *
+ * (c) CodeIgniter Foundation <admin@codeigniter.com>
+ *
+ * For the full copyright and license information, please view
+ * the LICENSE file that was distributed with this source code.
+ */
+
+namespace CodeIgniter\Format;
+
+use CodeIgniter\Format\Exceptions\FormatException;
+use Config\Format;
+use SimpleXMLElement;
+
+/**
+ * XML data formatter
+ */
+class XMLFormatter implements FormatterInterface
+{
+    /**
+     * Takes the given data and formats it.
+     *
+     * @param mixed $data
+     *
+     * @return bool|string (XML string | false)
+     */
+    public function format($data)
+    {
+        $config = new Format();
+
+        // SimpleXML is installed but default
+        // but best to check, and then provide a fallback.
+        if (! extension_loaded('simplexml')) {
+            // never thrown in travis-ci
+            // @codeCoverageIgnoreStart
+            throw FormatException::forMissingExtension();
+            // @codeCoverageIgnoreEnd
+        }
+
+        $options = $config->formatterOptions['application/xml'] ?? 0;
+        $output  = new SimpleXMLElement('<?xml version="1.0"?><response></response>', $options);
+
+        $this->arrayToXML((array) $data, $output);
+
+        return $output->asXML();
+    }
+
+    /**
+     * A recursive method to convert an array into a valid XML string.
+     *
+     * Written by CodexWorld. Received permission by email on Nov 24, 2016 to use this code.
+     *
+     * @see http://www.codexworld.com/convert-array-to-xml-in-php/
+     *
+     * @param SimpleXMLElement $output
+     */
+    protected function arrayToXML(array $data, &$output)
+    {
+        foreach ($data as $key => $value) {
+            $key = $this->normalizeXMLTag($key);
+
+            if (is_array($value)) {
+                $subnode = $output->addChild("{$key}");
+                $this->arrayToXML($value, $subnode);
+            } else {
+                $output->addChild("{$key}", htmlspecialchars("{$value}"));
+            }
+        }
+    }
+
+    /**
+     * Normalizes tags into the allowed by W3C.
+     * Regex adopted from this StackOverflow answer.
+     *
+     * @param int|string $key
+     *
+     * @return string
+     *
+     * @see https://stackoverflow.com/questions/60001029/invalid-characters-in-xml-tag-name
+     */
+    protected function normalizeXMLTag($key)
+    {
+        $startChar = 'A-Z_a-z' .
+            '\\x{C0}-\\x{D6}\\x{D8}-\\x{F6}\\x{F8}-\\x{2FF}\\x{370}-\\x{37D}' .
+            '\\x{37F}-\\x{1FFF}\\x{200C}-\\x{200D}\\x{2070}-\\x{218F}' .
+            '\\x{2C00}-\\x{2FEF}\\x{3001}-\\x{D7FF}\\x{F900}-\\x{FDCF}' .
+            '\\x{FDF0}-\\x{FFFD}\\x{10000}-\\x{EFFFF}';
+        $validName = $startChar . '\\.\\d\\x{B7}\\x{300}-\\x{36F}\\x{203F}-\\x{2040}';
+
+        $key = trim($key);
+        $key = preg_replace("/[^{$validName}-]+/u", '', $key);
+        $key = preg_replace("/^[^{$startChar}]+/u", 'item$0', $key);
+
+        return preg_replace('/^(xml).*/iu', 'item$0', $key); // XML is a reserved starting word
+    }
+}