@chriscdn/file-cache

FileCache is a node utility for caching generated and remote files. Common use cases include:

• Caching files stored in Amazon S3: Keep a local cache of frequently accessed files to avoid repeatedly fetching them.
• Thumbnail caching: Store generated thumbnails locally for quick access instead of regenerating them every time.

FileCache does not store state in memory, meaning your cache remains unaffected by application restarts. Cached files are automatically expired using a time-to-live (TTL) policy and the file's modified date. The file's modified date is updated each time the file is accessed.

Installing

Using npm:

npm install @chriscdn/file-cache

Using yarn:

yarn add @chriscdn/file-cache

Usage

The general approach is this:

• Create a callback — Write an async function that takes a file path and your custom input (like a URL), then generates or downloads the file and saves it to the path.
• Set up the cache — Initialize a FileCache with your callback and some options (like where to store files and how long to keep them).
• Get a file — Call the cache with your input. It will:
  • Hash the input to create a unique file name.
  • If the file is already cached and still valid, return its path.
  • If not, run your callback to create it, then cache and return the path.

Here's an example of an image cache:

import { FileCache, type FileCacheOptions } from "@chriscdn/file-cache";

// not required, but helps with duration calculations
import { Duration } from "@chriscdn/duration";

const downloadAndConvertToJPG = async (url: string, filePath: string) => {
  // ...
};

type MyCallbackArgs = {
  url: string;
};

const options: FileCacheOptions<MyCallbackArgs> = {
  // The path to the cache directory. The directory must exist. Do not store
  // anything else in this directory.
  cachePath: "/some/path/on/your/filesystem/",

  // optional, automatically create cachePath if it doesn't exist
  autoCreateCachePath: false,

  // An asynchronous callback function, which is executed if no matching cached
  // file is found. It is the responsibility of this function to use `args`
  // to write a file to `filePath`.
  cb: async (filePath: string, args: MyCallbackArgs) => {
    const { url } = args;
    await downloadAndConvertToJPG(url, filePath);
  },

  // Specifies the file extension for the cached file. Can be synchronous or asynchronous.
  ext: (args: MyCallbackArgs) => ".jpg",

  // Determines the time-to-live (TTL) of a cached file, in milliseconds,
  // based on when it was last accessed.
  ttl: Duration.toMilliseconds({ days: 7 }),

  // How often the cleanup task should run to purge expired cached files, in milliseconds.
  cleanupInterval: Duration.toMilliseconds({ hours: 4 }),
};

// create an instance
const imageCache = new FileCache(options);

const imageFilePath = await imageCache({
  url: "https://example.com/some/file/path.jpg",
});

Cleanup

FileCache instances are intended to be instantiated as singletons, persisting throughout the lifecycle of your app. If you need to deallocate an instance, be sure to call the destroy() method to prevent a memory leak. This does not cleanup the cache directory.

Tests

Run the tests using:

yarn test

License

MIT