Add element registry

composer.json

@@ -1,7 +1,7 @@
 {
     "name": "simplesamlphp/xml-common",
     "description": "A library with classes and utilities for handling XML structures.",
-    "type": "project",
+    "type": "simplesamlphp-xmlprovider",
     "keywords": ["saml", "xml"],
     "homepage": "http://simplesamlphp.org",
     "license": "LGPL-2.1-or-later",
@@ -34,7 +34,8 @@
         "ext-spl": "*",
         "ext-xmlreader": "*",
 
-        "simplesamlphp/assert": "^1.2"
+        "simplesamlphp/assert": "^1.2",
+        "symfony/finder": "^6.4"
     },
     "require-dev": {
         "simplesamlphp/simplesamlphp-test-framework": "^1.7"
@@ -47,7 +48,8 @@
         "allow-plugins": {
             "composer/package-versions-deprecated": true,
             "dealerdirect/phpcodesniffer-composer-installer": true,
-            "phpstan/extension-installer": true
+            "phpstan/extension-installer": true,
+            "simplesamlphp/composer-xmlprovider-installer": true
         }
     }
 }

src/Registry/AbstractElementRegistry.php

@@ -0,0 +1,89 @@
+<?php
+
+declare(strict_types=1);
+
+namespace SimpleSAML\XML\Registry;
+
+use SimpleSAML\Assert\Assert;
+use SimpleSAML\XML\AbstractElement;
+use SimpleSAML\XML\Exception\InvalidDOMElementException;
+use Symfony\Component\Finder\Finder;
+
+use function array_key_exists;
+use function array_merge;
+use function dirname;
+use function implode;
+
+abstract class AbstractElementRegistry
+{
+    /** @var \SimpleSAML\XML\Registry\AbstractElementRegistry|null $instance */
+    protected static ?AbstractElementRegistry $instance = null;
+
+
+    /** @var array<string, string> */
+    protected array $registry = [];
+
+    final private function __construct()
+    {
+        // Initialize the registry with all the elements we know
+        $classesDir = dirname(__FILE__, 3) . '/vendor/simplesamlphp/composer-xmlprovider-installer/classes';
+
+        $finder = Finder::create()->files()->name('element.registry.*.php')->in($classesDir);
+        if ($finder->hasResults()) {
+            foreach ($finder as $file) {
+                $elements = include($file);
+                $this->registry = array_merge($this->registry, $elements);
+            }
+        }
+    }
+
+
+    public static function getInstance(): AbstractElementRegistry
+    {
+        if (self::$instance === null) {
+            self::$instance = new static();
+        }
+
+        return self::$instance;
+    }
+
+
+    /**
+     * Register a class that can process a certain XML-element.
+     *
+     * @param string $class The class name of a class extending AbstractElement.
+     */
+    public function registerElementHandler(string $class): void
+    {
+        Assert::subclassOf($class, AbstractElement::class);
+        $className = AbstractElement::getClassName($class);
+        $key = ($class::NS === null) ? $className : implode(':', [$class::NS, $className]);
+        $this->registry[$key] = $class;
+    }
+
+
+    /**
+     * Search for a class that implements an $element in the given $namespace.
+     *
+     * Such classes must have been registered previously by calling registerElementHandler(), and they must
+     * extend \SimpleSAML\XML\AbstractElement.
+     *
+     * @param string|null $namespace The namespace URI for the given element.
+     * @param string $element The local name of the element.
+     *
+     * @return string|null The fully-qualified name of a class extending \SimpleSAML\XML\AbstractElement and
+     * implementing support for the given element, or null if no such class has been registered before.
+     */
+    public function getElementHandler(?string $namespace, string $element): ?string
+    {
+        Assert::nullOrValidURI($namespace, InvalidDOMElementException::class);
+        Assert::validNCName($element, InvalidDOMElementException::class);
+
+        $key = ($namespace === null) ? $element : implode(':', [$namespace, $element]);
+        if (array_key_exists($key, $this->registry) === true) {
+            return $this->registry[$key];
+        }
+
+        return null;
+    }
+}