feat: Add a file system cache class

README.md

@@ -300,6 +300,24 @@ $memoryCache = new MemoryCacheItemPool;
 $middleware = ApplicationDefaultCredentials::getCredentials($scope, cache: $memoryCache);
 ```
 
+### FileSystemCacheItemPool Cache
+The `FileSystemCacheItemPool` class is a `PSR-6` compliant cache that stores its
+ serialized objects on disk eliminating for caching data between processes making it possible to use data between different requests.
+
+```php
+use Google\Auth\Cache\FileSystemCacheItemPool;
+use Google\Auth\ApplicationDefaultCredentials;
+
+// Create a Cache pool instance
+$cache = new FileSystemCacheItemPool(__DIR__ . '/cache');
+
+// Pass your Cache to the Auth Library
+$credentials = ApplicationDefaultCredentials::getCredentials($scope, cache: $cache);
+
+// This token will be cached and be able to be used for the next request
+$token = $credentials->fetchAuthToken();
+```
+
 ### Integrating with a third party cache
 You can use a third party that follows the `PSR-6` interface of your choice.
 

src/Cache/FileSystemCacheItemPool.php

@@ -0,0 +1,230 @@
+<?php
+/**
+ * Copyright 2024 Google Inc. All Rights Reserved.
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *      http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+namespace Google\Auth\Cache;
+
+use ErrorException;
+use Psr\Cache\CacheItemInterface;
+use Psr\Cache\CacheItemPoolInterface;
+
+class FileSystemCacheItemPool implements CacheItemPoolInterface
+{
+    /**
+     * @var string
+     */
+    private string $cachePath;
+
+    /**
+     * @var array<CacheItemInterface>
+     */
+    private array $buffer = [];
+
+    /**
+     * Creates a FileSystemCacheItemPool cache that stores values in local storage
+     *
+     * @param string $path The string representation of the path where the cache will store the serialized objects.
+     */
+    public function __construct(string $path)
+    {
+        $this->cachePath = $path;
+
+        if (is_dir($this->cachePath)) {
+            return;
+        }
+
+        if (!mkdir($this->cachePath)) {
+            throw new ErrorException("Cache folder couldn't be created.");
+        }
+    }
+
+    /**
+     * {@inheritdoc}
+     */
+    public function getItem(string $key): CacheItemInterface
+    {
+        if (!$this->validKey($key)) {
+            throw new InvalidArgumentException("The key '$key' is not valid. The key should follow the pattern |^[a-zA-Z0-9_\.! ]+$|");
+        }
+
+        $item = new TypedItem($key);
+
+        $itemPath = $this->cacheFilePath($key);
+
+        if (!file_exists($itemPath)) {
+            return $item;
+        }
+
+        $serializedItem = file_get_contents($itemPath);
+
+        if ($serializedItem === false) {
+            return $item;
+        }
+
+        $item->set(unserialize($serializedItem));
+
+        return $item;
+    }
+
+    /**
+     * {@inheritdoc}
+     *
+     * @return iterable<CacheItemInterface> An iterable object containing all the
+     *   A traversable collection of Cache Items keyed by the cache keys of
+     *   each item. A Cache item will be returned for each key, even if that
+     *   key is not found. However, if no keys are specified then an empty
+     *   traversable MUST be returned instead.
+     */
+    public function getItems(array $keys = []): iterable
+    {
+        $result = [];
+
+        foreach ($keys as $key) {
+            $result[$key] = $this->getItem($key);
+        }
+
+        return $result;
+    }
+
+    /**
+     * {@inheritdoc}
+     */
+    public function save(CacheItemInterface $item): bool
+    {
+        if (!$this->validKey($item->getKey())) {
+            return false;
+        }
+
+        $itemPath = $this->cacheFilePath($item->getKey());
+        $serializedItem = serialize($item->get());
+
+        $result = file_put_contents($itemPath, $serializedItem);
+
+        // 0 bytes write is considered a successful operation
+        if ($result === false) {
+            return false;
+        }
+
+        return true;
+    }
+
+    /**
+     * {@inheritdoc}
+     */
+    public function hasItem(string $key): bool
+    {
+        return $this->getItem($key)->isHit();
+    }
+
+    /**
+     * {@inheritdoc}
+     */
+    public function clear(): bool
+    {
+        $this->buffer = [];
+
+        if (!is_dir($this->cachePath)) {
+            return false;
+        }
+
+        $files = scandir($this->cachePath);
+        if (!$files) {
+            return false;
+        }
+
+        foreach ($files as $fileName) {
+            if ($fileName === '.' || $fileName === '..') {
+                continue;
+            }
+
+            if (!unlink($this->cachePath . '/' . $fileName)) {
+                return false;
+            }
+        }
+
+        return true;
+    }
+
+    /**
+     * {@inheritdoc}
+     */
+    public function deleteItem(string $key): bool
+    {
+        if (!$this->validKey($key)) {
+            throw new InvalidArgumentException("The key '$key' is not valid. The key should follow the pattern |^[a-zA-Z0-9_\.! ]+$|");
+        }
+
+        $itemPath = $this->cacheFilePath($key);
+
+        if (!file_exists($itemPath)) {
+            return true;
+        }
+
+        return unlink($itemPath);
+    }
+
+    /**
+     * {@inheritdoc}
+     */
+    public function deleteItems(array $keys): bool
+    {
+        $result = true;
+
+        foreach ($keys as $key) {
+            if (!$this->deleteItem($key)) {
+                $result = false;
+            }
+        }
+
+        return $result;
+    }
+
+    /**
+     * {@inheritdoc}
+     */
+    public function saveDeferred(CacheItemInterface $item): bool
+    {
+        array_push($this->buffer, $item);
+
+        return true;
+    }
+
+    /**
+     * {@inheritdoc}
+     */
+    public function commit(): bool
+    {
+        $result = true;
+
+        foreach ($this->buffer as $item) {
+            if (!$this->save($item)) {
+                $result = false;
+            }
+        }
+
+        return $result;
+    }
+
+    private function cacheFilePath(string $key): string
+    {
+        return $this->cachePath . '/' . $key;
+    }
+
+    private function validKey(string $key): bool
+    {
+        return (bool) preg_match('|^[a-zA-Z0-9_\.]+$|', $key);
+    }
+}