flutter_cache_store

A flexible cache manager for Flutter.

This package is highly inspired by flutter_cache_manager. Can be easily switched to each other.

Quick Start

import 'package:flutter_cache_store/flutter_cache_store.dart';

void demo(String url) async {
  final store = await CacheStore.getInstance();
  final file = await store.getFile(url);
  // do something with file...
}

APIs

CacheStore

void api() async {
  // set expiration policy.
  // must be called before `CacheStore.getInstance` or will raise an exception.
  // default: LessRecentlyUsedPolicy(maxCount: 999)
  CacheStore.setPolicy(LessRecentlyUsedPolicy(maxCount: 4096));

  // get a singleton store instance
  CacheStore store = await CacheStore.getInstance(
      clearNow: true // default: false - whether to clean up immediately
      );

  // fetch a file from an URL and cache it
  File file = await store.getFile(
    'url', // GET method
    key: null, // use custom string instead of URL
    headers: {}, // same as http.get
    flushCache: false, // whether to re-download the file
  );

  // flush specific files by keys
  await store.flush([
    'key', // key (default is the URL) passed to `getFile`
  ]);

  // remove all cached files
  await store.clearAll();
}

Cache File Structure

By default, the cached files will be saved under $TEMP/cache_store. $TEMP is generated by path_provider. The default temp filenames are timestamp-based 11 chars.

You can customize your own file structure under $TEMP/cache_store by overriding Policy. There is an example:

Let's suppose your are developing a reader for novels, and your app will cache chapters of books. Your API returns some IDs of books and chapters, and an ID only contains digits.

// Extends a Policy class and override `generateFilename`
class LRUCachePolicy extends LessRecentlyUsedPolicy {
  LRUCachePolicy({int maxCount}) : super(maxCount: maxCount);

  @override
  String generateFilename({final String key, final String url}) =>
      key; // use key as the filename
}

void customizedCacheFileStructure() async {
  // Set it as your Policy
  CacheStore.setPolicy(LRUCachePolicy(maxCount: 4096));

  // get a singleton store instance
  CacheStore store = await CacheStore.getInstance();

  // fetch a file from an URL and cache it
  String bookId = 'book123';
  String chapterId = 'ch42';
  String chapterUrl = 'https://example.com/book123/ch42';
  File file = await store.getFile(
    chapterUrl,
    key: '$bookId/$chapterId', // use IDs as path and filename
  );

  // Your file will be cached as `$TEMP/cache_store/book123/ch42`
}

Cache Policy

  • LessRecentlyUsedPolicy

    LRU policy. Less Recently Used files will be removed when reached maxCount. Each time you access a file will update its used timestamp.

    new LessRecentlyUsedPolicy(
      maxCount: 999,
    );
    
  • LeastFrequentlyUsedPolicy

    LFU policy. Least Frequently Used files will be removed when reached maxCount. Each time you access a file will increase its hit count. After hitAge time the hit will expire. It will fallback to LRU policy if files have same hit count.

    new LeastFrequentlyUsedPolicy(
      maxCount: 999,
      hitAge: Duration(days: 30),
    );
    
  • CacheControlPolicy

    Cache-Control header policy. This policy generally follows max-age=<seconds> or s-maxage=<seconds> rules of http response header Cache-Control. If the max-age-seconds not been set, it will use minAge unless you set it to null. The age will not be longer than maxAge.

    new CacheControlPolicy(
      maxCount: 999,
      minAge: Duration(seconds: 30), // nullable
      maxAge: Duration(days: 30), // nullable
    );
    
  • FifoPolicy

    First-In, First-Out policy, super simple and maybe for example only.

    new LessRecentlyUsedPolicy(
      maxCount: 999, // default: 999
    );
    

Performance Warning:

  • The implementation maintains all key-item in memory to improve the speed. So maxCount must between 1 and 100000 (100k) due to the cost of RAM and file system.

  • Currently, all the policies simply sort all items to expire files. It may hit performance due to O(N*logN) complexity.

    Will switch to priority queue which has O(N*logK) while K usually is a very small number.

How to implement your own policy

The interface is a simple abstract class. You only have to implement a few methods.

abstract class CacheStorePolicy {
  // IT'S THE ONLY METHOD YOU HAVE TO IMPLEMENT.
  // `store` will invoke this method from time to time.
  // Make sure return all expired items at once.
  // then `store` will manage to remove the cached files.
  // you also have to save your data if need to persist some data.
  Future<Iterable<CacheItem>> cleanup(Iterable<CacheItem> allItems);

  // will be invoked when store.clearAll called.
  Future<void> clearAll(Iterable<CacheItem> allItems) async {}

  // will invoke only once when the `store` is created and load saved data.
  // you need to load persistent data and restore items' payload.
  // only returned items will be cached. others will be recycled later.
  Future<Iterable<CacheItem>> restore(List<CacheItem> allItems) async => allItems;

  // event when a new `CacheItem` has been added to the cache.
  // you may need to attach a `CacheItemPayload` instance to it.
  Future<void> onAdded(final CacheItem addedItem) async {}

  // event when an item just been accessed.
  // you may need to attach or update item's payload.
  Future<void> onAccessed(final CacheItem accessedItem, bool flushed) async {}

  // event when a request just finished.
  // the response headers will be passed as well.
  Future<void> onDownloaded(final CacheItem item, final Map<String, String> headers) async {}

  // event when `store.flush` has called
  Future<void> onFlushed(final Iterable<CacheItem> flushedItems) async {}

  // filename (including path) relative to `CacheItem.rootPath`.
  // usually ignore this unless need a better files structure.
  // you must provide valid filenames.
  String generateFilename({final String key, final String url}) =>
      Utils.genName(); // timestamp based random filename
}
  • Tips

    You don't have to implement all of the onAdded, onAccessed and onDownloaded.

Libraries

flutter_cache_store

Dart

dart:ui
Built-in types and core primitives for a Flutter application. [...]

Core

dart:async
Support for asynchronous programming, with classes such as Future and Stream. [...]
dart:collection
Classes and utilities that supplement the collection support in dart:core. [...]
dart:convert
Encoders and decoders for converting between different data representations, including JSON and UTF-8. [...]
dart:core
Built-in types, collections, and other core functionality for every Dart program. [...]
dart:developer
Interact with developer tools such as the debugger and inspector. [...]
dart:math
Mathematical constants and functions, plus a random number generator. [...]
dart:typed_data
Lists that efficiently handle fixed sized data (for example, unsigned 8 byte integers) and SIMD numeric types. [...]

VM

dart:io
File, socket, HTTP, and other I/O support for non-web applications. [...]
dart:isolate
Concurrent programming using isolates: independent workers that are similar to threads but don't share memory, communicating only via messages. [...]