MDL-66428 cachestore_redis: add Zstd compression support

cache/stores/redis/lang/en/cachestore_redis.php

@@ -26,6 +26,7 @@
 
 $string['compressor_none'] = 'No compression.';
 $string['compressor_php_gzip'] = 'Use gzip compression.';
+$string['compressor_php_zstd'] = 'Use Zstandard compression.';
 $string['pluginname'] = 'Redis';
 $string['prefix'] = 'Key prefix';
 $string['prefix_help'] = 'This prefix is used for all key names on the Redis server.

cache/stores/redis/lib.php

@@ -48,6 +48,11 @@ class cachestore_redis extends cache_store implements cache_is_key_aware, cache_
      */
     const COMPRESSOR_PHP_GZIP = 1;
 
+    /**
+     * Compressor: PHP Zstandard.
+     */
+    const COMPRESSOR_PHP_ZSTD = 2;
+
     /**
      * Name of this store.
      *
@@ -597,10 +602,17 @@ public static function config_get_serializer_options() {
      * @return array
      */
     public static function config_get_compressor_options() {
-        return [
+        $arr = [
             self::COMPRESSOR_NONE     => get_string('compressor_none', 'cachestore_redis'),
             self::COMPRESSOR_PHP_GZIP => get_string('compressor_php_gzip', 'cachestore_redis'),
         ];
+
+        // Check if the Zstandard PHP extension is installed.
+        if (extension_loaded('zstd')) {
+            $arr[self::COMPRESSOR_PHP_ZSTD] = get_string('compressor_php_zstd', 'cachestore_redis');
+        }
+
+        return $arr;
     }
 
     /**
@@ -619,6 +631,9 @@ private function compress($value) {
             case self::COMPRESSOR_PHP_GZIP:
                 return gzencode($value);
 
+            case self::COMPRESSOR_PHP_ZSTD:
+                return zstd_compress($value);
+
             default:
                 debugging("Invalid compressor: {$this->compressor}");
                 return $value;
@@ -642,6 +657,9 @@ private function uncompress($value) {
             case self::COMPRESSOR_PHP_GZIP:
                 $value = gzdecode($value);
                 break;
+            case self::COMPRESSOR_PHP_ZSTD:
+                $value = zstd_uncompress($value);
+                break;
             default:
                 debugging("Invalid compressor: {$this->compressor}");
         }

cache/stores/redis/tests/compressor_test.php

@@ -166,11 +166,11 @@ public function test_it_works_with_different_types_for_many() {
     }
 
     /**
-     * Provider for serializer tests.
+     * Provider for set/get combination tests.
      *
      * @return array
      */
-    public function provider_for_test_it_can_use_serializers() {
+    public function provider_for_tests_setget() {
         $data = [
             ['none, none',
                 Redis::SERIALIZER_NONE, cachestore_redis::COMPRESSOR_NONE,
@@ -199,20 +199,41 @@ public function provider_for_test_it_can_use_serializers() {
             ];
         }
 
+        if (extension_loaded('zstd')) {
+            $data[] = [
+                'none, zstd',
+                Redis::SERIALIZER_NONE, cachestore_redis::COMPRESSOR_PHP_ZSTD,
+                zstd_compress('value1'), zstd_compress('value2'),
+            ];
+            $data[] = [
+                'php, zstd',
+                Redis::SERIALIZER_PHP, cachestore_redis::COMPRESSOR_PHP_ZSTD,
+                zstd_compress(serialize('value1')), zstd_compress(serialize('value2')),
+            ];
+
+            if (defined('Redis::SERIALIZER_IGBINARY')) {
+                $data[] = [
+                    'igbinary, zstd',
+                    Redis::SERIALIZER_IGBINARY, cachestore_redis::COMPRESSOR_PHP_ZSTD,
+                    zstd_compress(igbinary_serialize('value1')), zstd_compress(igbinary_serialize('value2')),
+                ];
+            }
+        }
+
         return $data;
     }
 
     /**
-     * Test it can use  serializers with get and set.
+     * Test we can use get and set with all combinations.
      *
-     * @dataProvider provider_for_test_it_can_use_serializers
+     * @dataProvider provider_for_tests_setget
      * @param string $name
      * @param int $serializer
      * @param int $compressor
      * @param string $rawexpected1
      * @param string $rawexpected2
      */
-    public function test_it_can_use_serializers_getset($name, $serializer, $compressor, $rawexpected1, $rawexpected2) {
+    public function test_it_can_use_getset($name, $serializer, $compressor, $rawexpected1, $rawexpected2) {
         // Create a connection with the desired serialisation.
         $store = $this->create_store($compressor, $serializer);
         $store->set('key', 'value1');
@@ -227,16 +248,16 @@ public function test_it_can_use_serializers_getset($name, $serializer, $compress
     }
 
     /**
-     * Test it can use  serializers with get and set many.
+     * Test we can use get and set many with all combinations.
      *
-     * @dataProvider provider_for_test_it_can_use_serializers
+     * @dataProvider provider_for_tests_setget
      * @param string $name
      * @param int $serializer
      * @param int $compressor
      * @param string $rawexpected1
      * @param string $rawexpected2
      */
-    public function test_it_can_use_serializers_getsetmany($name, $serializer, $compressor, $rawexpected1, $rawexpected2) {
+    public function test_it_can_use_getsetmany($name, $serializer, $compressor, $rawexpected1, $rawexpected2) {
         $many = [
             ['key' => 'key1', 'value' => 'value1'],
             ['key' => 'key2', 'value' => 'value2'],

cache/upgrade.txt

@@ -1,6 +1,9 @@
 This files describes API changes in /cache/stores/* - cache store plugins.
 Information provided here is intended especially for developers.
 
+=== 3.8 ===
+* The Redis cache store can now make use of the Zstandard compression algorithm (see MDL-66428).
+
 === 3.7 ===
 * Upgraded MongoDB cache store to use the new lower level PHP-driver and MongoDB PHP Library.
 * The mongodb extension has replaced the old mongo extension. The mongodb pecl extension >= 1.5 must be installed to use MongoDB