harden DbAsset less publishing:

- make cacheComponent configurable to be able to use a persistent cache component to store less checksum
- if not exists, create empty sourcePath dir to prevent race condition with next req
- convert less before replacing content of sourcePath to prevent multiple converter runs while publishing
- use tmp folders and rename() while replacing sourcePath to get atomic operations in the filesystem
- if something went wrong the previous state (prev. checksum in cache) is restored

Author: handcode

src/assets/DbAsset.php

@@ -17,6 +17,26 @@
 use yii\helpers\Json;
 use yii\web\AssetBundle;
 
+/**
+ * Class DbAsset
+ * @package extensions\dmstr\prototype\assets
+ *
+ * This class implements an AssetBundle for Less "files" stored in DB as prototype\models\Less models
+ * In init() we get the less models from DB, build an overall checksum that will be compared with a cached value
+ * previous run.
+ *
+ * If nothing has changed (checksum match, and db less was yet exported to disc) nothing will be done here
+ * If "something" changed (or in the first run):
+ * - if not exists, create empty sourcePath dir to prevent race condition with next req which will try to init
+ *   this bundle again...
+ * - write contents of less models as *.less files in a tmp dir
+ * - To prevent multiple converter runs while asset publishing the main less will be converted in this tmp dir
+ * - To prevent multiple publishing runs we use another tmp file and simple renames while changing the sourcePath contents
+ * - To prevent unnecessary publishing you should configure a persistent cacheComponent to store the checksum
+ *   which survive a restart (eg. do not use a memory cache which is part of a docker-compose stack)
+ * - if something went wrong the previous state (prev. checksum in cache) is restored
+ *
+ */
 class DbAsset extends AssetBundle
 {
     const CACHE_ID = 'app\assets\SettingsAsset';
@@ -26,6 +46,15 @@ class DbAsset extends AssetBundle
 
     public $sourcePath = '@runtime/settings-asset';
     public $tmpPath = '@runtime/settings-asset-tmp';
+    /**
+     *
+     * name of the cache component that should be used for the less checksum cache
+     * for high volume sites this should be set to a persistent cache which survive a
+     * restart
+     *
+     * @var string
+     */
+    public $cacheComponent = 'cache';
 
     public $settingsKey = 'registerPrototypeAssetKey';
 
@@ -34,9 +63,18 @@ class DbAsset extends AssetBundle
         // if a full BootstrapAsset (CSS) is compiled, it's recommended to disable it in assetManager configuration
         'yii\bootstrap\BootstrapPluginAsset', // (JS)
     ];
+    /**
+     * internal cache property
+     *
+     * @var
+     */
+    protected $cache;
 
     public function init()
     {
+        // init configured cache component
+        $this->cache = Yii::$app->{$this->cacheComponent};
+
         $this->css[] = Yii::$app->settings->get($this->settingsKey, self::SETTINGS_SECTION).'-'.self::MAIN_LESS_FILE;
 
         parent::init();
@@ -49,21 +87,56 @@ public function init()
 
             $models = Less::find()->all();
             $hash = sha1(Json::encode($models));
-            if (!is_dir($sourcePath) || ($hash !== Yii::$app->cache->get(self::CACHE_ID))) {
+            $prevHash = $this->cache->get(self::CACHE_ID);
+            $sourcePathExists = is_dir($sourcePath);
+            if (($hash !== $prevHash) || ! $sourcePathExists) {
+
+                // create empty sourcePath dir to prevent race condition with next req which will init again...
+                if ( ! $sourcePathExists) {
+                    FileHelper::createDirectory($sourcePath);
+                }
+                $dependency = new FileDependency();
+                $dependency->fileName = __FILE__;
+                $this->cache->set(self::CACHE_ID, $hash, 0, $dependency);
+
                 $tmpPath = uniqid($sourcePath.'-');
                 FileHelper::createDirectory($tmpPath);
-
                 foreach ($models as $model) {
                     file_put_contents("$tmpPath/{$model->key}.less", $model->value);
                 }
 
-                $dependency = new FileDependency();
-                $dependency->fileName = __FILE__;
-                Yii::$app->cache->set(self::CACHE_ID, $hash, 0, $dependency);
+                // convert less with new files in tmp folder before replacing bundle sourcePath
+                // to prevent multiple conversions while republishing on high-traffic sites
+                $converter = Yii::$app->assetManager->getConverter();
+                try {
+                    foreach ($this->css as $cssFile) {
+                        $result = $converter->convert($cssFile, $tmpPath);
+                    }
+                } catch (\Exception $exception) {
+                    $this->cache->set(self::CACHE_ID, $prevHash, 0, $dependency);
+                    Yii::error($exception->getMessage(), __METHOD__);
+                    return false;
+                }
 
                 // force republishing of asset files by Yii Framework
-                FileHelper::removeDirectory($sourcePath);
-                rename($tmpPath, $sourcePath);
+                // to prevent race conditions, use 2 rename cmds to switch dir and remove prev. dir afterwards
+                $sourcePathToDelete = uniqid($sourcePath.'-to-delete-');
+                $sourcePathRenamed = false;
+                if ($sourcePathExists) {
+                    if (rename($sourcePath, $sourcePathToDelete)) {
+                        $sourcePathRenamed = true;
+                    } else {
+                        $this->cache->set(self::CACHE_ID, $prevHash, 0, $dependency);
+                        return false;
+                    }
+                }
+                if ( ! rename($tmpPath, $sourcePath)) {
+                    $this->cache->set(self::CACHE_ID, $prevHash, 0, $dependency);
+                    return false;
+                }
+                if ($sourcePathRenamed) {
+                    FileHelper::removeDirectory($sourcePathToDelete);
+                }
             }
         }
     }