[FEATURE] Refinery: Add Decode group and Json transformation

components/ILIAS/Refinery/README.md

@@ -20,6 +20,8 @@ processed by the ILIAS project.
         * [htmlAttributeValue](#htmlAttributeValue)
         * [json](#json)
         * [url](#url)
+      - [decode](#decode)
+        * [json](#json-1)
   * [Custom Transformation](#custom-transformation)
     + [DeriveApplyToFromTransform](#deriveapplytofromtransform)
       - [Error Handling](#error-handling)
@@ -329,6 +331,31 @@ The transformation prevents a value to change other URL parameters & values or t
 $link = $ctrl->setParameterByClass(FooGUI::class, 'bar', $refinery->encode()->url()->transform($foobar));
 ```
 
+##### decode
+
+The `decode` group is the counterpart of the [encode](#encode) group and turns encoded strings back
+into native PHP values.
+
+###### json
+
+This transformation is a wrapper around `json_decode`. In contrast to `json_decode` it never returns
+`null` to signal a problem, because `null` cannot be told apart from the successfully decoded JSON
+literal `null`. Undecodable input raises an `InvalidArgumentException` instead, as announced by the
+`Transformation` interface, so `applyTo` can be used to reify the problem into a `Result`.
+
+JSON objects are decoded into associative arrays rather than `stdClass`, so the result can be
+processed further with the `container`, `to` and `kindlyTo` groups.
+
+```php
+$settings = $refinery->decode()->json()->transform('{"limit":10,"tags":["a","b"]}');
+// $settings => ['limit' => 10, 'tags' => ['a', 'b']]
+
+$refinery->decode()->json()->transform('{'); // throws an InvalidArgumentException
+
+$result = $refinery->decode()->json()->applyTo(new ILIAS\Data\Result\Ok('{'));
+// $result->isError() => true
+```
+
 ##### Custom
 
 The `Custom` group contains `Transformations` and `Constraints`

components/ILIAS/Refinery/src/Decode/Group.php

@@ -0,0 +1,39 @@
+<?php
+
+/**
+ * This file is part of ILIAS, a powerful learning management system
+ * published by ILIAS open source e-Learning e.V.
+ *
+ * ILIAS is licensed with the GPL-3.0,
+ * see https://www.gnu.org/licenses/gpl-3.0.en.html
+ * You should have received a copy of said license along with the
+ * source code, too.
+ *
+ * If this is not the case or you just want to try ILIAS, you'll find
+ * us at:
+ * https://www.ilias.de
+ * https://github.com/ILIAS-eLearning
+ *
+ *********************************************************************/
+
+declare(strict_types=1);
+
+namespace ILIAS\Refinery\Decode;
+
+use ILIAS\Refinery\Decode\Transformation\Json;
+use ILIAS\Refinery\Transformation;
+
+final class Group
+{
+    /**
+     * Decodes a JSON string into native PHP values, JSON objects become associative arrays.
+     *
+     * @param int $max_depth Maximum nesting depth of the structure being decoded, counting the
+     *                       scalars at the very bottom as one level. Defaults to the depth PHP
+     *                       itself uses for `json_decode`.
+     */
+    public function json(int $max_depth = Json::DEFAULT_MAX_DEPTH): Transformation
+    {
+        return new Json($max_depth);
+    }
+}

components/ILIAS/Refinery/src/Decode/Transformation/Json.php

@@ -0,0 +1,86 @@
+<?php
+
+/**
+ * This file is part of ILIAS, a powerful learning management system
+ * published by ILIAS open source e-Learning e.V.
+ *
+ * ILIAS is licensed with the GPL-3.0,
+ * see https://www.gnu.org/licenses/gpl-3.0.en.html
+ * You should have received a copy of said license along with the
+ * source code, too.
+ *
+ * If this is not the case or you just want to try ILIAS, you'll find
+ * us at:
+ * https://www.ilias.de
+ * https://github.com/ILIAS-eLearning
+ *
+ *********************************************************************/
+
+declare(strict_types=1);
+
+namespace ILIAS\Refinery\Decode\Transformation;
+
+use ILIAS\Refinery\DeriveApplyToFromTransform;
+use ILIAS\Refinery\DeriveInvokeFromTransform;
+use ILIAS\Refinery\Transformation;
+use InvalidArgumentException;
+use JsonException;
+
+/**
+ * This class is a wrapper around `json_decode` which rejects undecodable input with an
+ * `InvalidArgumentException` instead of returning `null`, which cannot be told apart from the
+ * successfully decoded JSON literal `null`.
+ *
+ * JSON objects are decoded into associative arrays instead of `stdClass`, so that results can be
+ * processed further with the `container`, `to` and `kindlyTo` groups and round-trip with the
+ * `encode` group.
+ *
+ * Please see https://www.php.net/manual/en/function.json-decode.php for more information.
+ */
+final class Json implements Transformation
+{
+    use DeriveInvokeFromTransform;
+    use DeriveApplyToFromTransform;
+
+    /**
+     * PHP does not expose the default of its JSON parser (PHP_JSON_PARSER_DEFAULT_DEPTH) to userland.
+     */
+    public const int DEFAULT_MAX_DEPTH = 512;
+    public const int MAX_DEPTH_LOWER_BOUND = 1;
+    public const int MAX_DEPTH_UPPER_BOUND = 2147483647;
+
+    public function __construct(private readonly int $max_depth = self::DEFAULT_MAX_DEPTH)
+    {
+        if ($max_depth < self::MAX_DEPTH_LOWER_BOUND || $max_depth > self::MAX_DEPTH_UPPER_BOUND) {
+            throw new InvalidArgumentException(
+                \sprintf(
+                    'Maximum depth must be between %d and %d, got %d.',
+                    self::MAX_DEPTH_LOWER_BOUND,
+                    self::MAX_DEPTH_UPPER_BOUND,
+                    $max_depth
+                )
+            );
+        }
+    }
+
+    public function transform($from): mixed
+    {
+        if (!\is_string($from)) {
+            throw new InvalidArgumentException(
+                \sprintf(
+                    'The value of type "%s" is not a string and cannot be decoded as JSON.',
+                    get_debug_type($from)
+                )
+            );
+        }
+
+        try {
+            return json_decode($from, true, $this->max_depth, JSON_THROW_ON_ERROR);
+        } catch (JsonException $exception) {
+            // The value itself is left out of the message, it may be large and carry sensitive data.
+            throw new InvalidArgumentException(
+                \sprintf('The value cannot be decoded as JSON: %s.', $exception->getMessage())
+            );
+        }
+    }
+}

components/ILIAS/Refinery/src/Factory.php

@@ -161,6 +161,11 @@ public function encode(): Encode\Group
         return new Encode\Group();
     }
 
+    public function decode(): Decode\Group
+    {
+        return new Decode\Group();
+    }
+
     /**
      * Accepts Transformations and uses first successful one.
      * @param Transformation[] $transformations

components/ILIAS/Refinery/tests/Decode/GroupTest.php

@@ -0,0 +1,40 @@
+<?php
+
+/**
+ * This file is part of ILIAS, a powerful learning management system
+ * published by ILIAS open source e-Learning e.V.
+ *
+ * ILIAS is licensed with the GPL-3.0,
+ * see https://www.gnu.org/licenses/gpl-3.0.en.html
+ * You should have received a copy of said license along with the
+ * source code, too.
+ *
+ * If this is not the case or you just want to try ILIAS, you'll find
+ * us at:
+ * https://www.ilias.de
+ * https://github.com/ILIAS-eLearning
+ *
+ *********************************************************************/
+
+declare(strict_types=1);
+
+namespace ILIAS\Tests\Refinery\Decode;
+
+use ILIAS\Refinery\Decode\Group;
+use ILIAS\Refinery\Decode\Transformation\Json;
+use PHPUnit\Framework\TestCase;
+
+class GroupTest extends TestCase
+{
+    public function testConstruct(): void
+    {
+        self::assertInstanceOf(Group::class, new Group());
+    }
+
+    public function testJson(): void
+    {
+        $group = new Group();
+
+        self::assertInstanceOf(Json::class, $group->json());
+    }
+}