Cache: A Swift repository from Antowkos

Description
Key features
Usage
What about images?
Handling JSON response
Installation
Author
Contributing
License

Description

Cache doesn't claim to be unique in this area, but it's not another monster library that gives you a god's power. It does nothing but caching, but it does it well. It offers a good public API with out-of-box implementations and great customization possibilities. Cache utilizes Codable in Swift 4 to perform serialization.

Key features

Work with Swift 4 Codable. Anything conforming to Codable will be saved and loaded easily by Storage.
Disk storage by default. Optionally using memory storage to enable hybrid.
Many options via DiskConfig and MemoryConfig.
Support expiry and clean up of expired objects.
Thread safe. Operations can be accessed from any queue.
Sync by default. Also support Async APIs.
Store images via ImageWrapper.
Extensive unit test coverage and great documentation.
iOS, tvOS and macOS support.

Usage

Storage

Cache is built based on Chain-of-responsibility pattern, in which there are many processing objects, each knows how to do 1 task and delegates to the next one. But that's just implementation detail. All you need to know is Storage, it saves and loads Codable objects.

Storage has disk storage and an optional memory storage. Memory storage should be less time and memory consuming, while disk storage is used for content that outlives the application life-cycle, see it more like a convenient way to store user information that should persist across application launches.

DiskConfig is required to set up disk storage. You can optionally pass MemoryConfig to use memory as front storage.

let diskConfig = DiskConfig(name: "Floppy")
let memoryConfig = MemoryConfig(expiry: .never, countLimit: 10, totalCostLimit: 10)

let storage = try? Storage(diskConfig: diskConfig, memoryConfig: memoryConfig)

Codable types

Storage supports any objects that conform to Codable protocol. You can make your own things conform to Codable so that can be saved and loaded from Storage.

The supported types are

Primitives like Int, Float, String, Bool, ...
Array of primitives like [Int], [Float], [Double], ...
Set of primitives like Set<String>, Set<Int>, ...
Simply dictionary like [String: Int], [String: String], ...
Date
URL
Data

Error handling

Error handling is done via try catch. Storage throws errors in terms of StorageError.

public enum StorageError: Error {
  /// Object can not be found
  case notFound
  /// Object is found, but casting to requested type failed
  case typeNotMatch
  /// The file attributes are malformed
  case malformedFileAttributes
  /// Can't perform Decode
  case decodingFailed
  /// Can't perform Encode
  case encodingFailed
  /// The storage has been deallocated
  case deallocated
}

There can be errors because of disk problem or type mismatch when loading from storage, so if want to handle errors, you need to do try catch

do {
  let storage = try Storage(diskConfig: diskConfig, memoryConfig: memoryConfig)
} catch {
  print(error)
}

Configuration

Here is how you can play with many configuration options

let diskConfig = DiskConfig(
  // The name of disk storage, this will be used as folder name within directory
  name: "Floppy",
  // Expiry date that will be applied by default for every added object
  // if it's not overridden in the `setObject(forKey:expiry:)` method
  expiry: .date(Date().addingTimeInterval(2*3600)),
  // Maximum size of the disk cache storage (in bytes)
  maxSize: 10000,
  // Where to store the disk cache. If nil, it is placed in `cachesDirectory` directory.
  directory: try! FileManager.default.url(for: .documentDirectory, in: .userDomainMask, 
    appropriateFor: nil, create: true).appendingPathComponent("MyPreferences"),
  // Data protection is used to store files in an encrypted format on disk and to decrypt them on demand
  protectionType: .complete
)

let memoryConfig = MemoryConfig(
  // Expiry date that will be applied by default for every added object
  // if it's not overridden in the `setObject(forKey:expiry:)` method
  expiry: .date(Date().addingTimeInterval(2*60)),
  /// The maximum number of objects in memory the cache should hold
  countLimit: 50,
  /// The maximum total cost that the cache can hold before it starts evicting objects
  totalCostLimit: 0
)

On iOS, tvOS we can also specify protectionType on DiskConfig to add a level of security to files stored on disk by your app in the app’s container. For more information, see FileProtectionType

Sync APIs

Storage is sync by default and is thead safe, you can access it from any queues. All Sync functions are constrained by StorageAware protocol.

// Save to storage
try? storage.setObject(10, forKey: "score")
try? storage.setObject("Oslo", forKey: "my favorite city", expiry: .never)
try? storage.setObject(["alert", "sounds", "badge"], forKey: "notifications")
try? storage.setObject(data, forKey: "a bunch of bytes")
try? storage.setObject(authorizeURL, forKey: "authorization URL")

// Load from storage
let score = try? storage.object(ofType: Int.self, forKey: "score")
let favoriteCharacter = try? storage.object(ofType: String.self, forKey: "my favorite city")

// Check if an object exists
let hasFavoriteCharacter = try? storage.existsObject(ofType: String.self, forKey: "my favorite city")

// Remove an object in storage
try? storage.removeObject(forKey: "my favorite city")

// Remove all objects
try? storage.removeAll()

// Remove expired objects
try? storage.removeExpiredObjects()

Entry

There is time you want to get object together with its expiry information and meta data. You can use Entry

let entry = try? storage.entry(ofType: String.self, forKey: "my favorite city")
print(entry?.object)
print(entry?.expiry)
print(entry?.meta)

meta may contain file information if the object was fetched from disk storage.

Custom Codable

Codable works for simple dictionary like [String: Int], [String: String], ... It does not work for [String: Any] as Any is not Codable conformance, it will raise fatal error at runtime. So when you get json from backend responses, you need to convert that to your custom Codable objects and save to Storage instead.

struct User: Codable {
  let firstName: String
  let lastName: String
}

let user = User(fistName: "John", lastName: "Snow")
try? storage.setObject(user, forKey: "character")

Async APIs

In async fashion, you deal with Result instead of try catch because the result is delivered at a later time, in order to not block the current calling queue. In the completion block, you either have value or error.

You access Async APIs via storage.async, it is also thread safe, and you can use Sync and Async APIs in any order you want. All Async functions are constrained by AsyncStorageAware protocol.

storage.async.setObject("Oslo", forKey: "my favorite city") { result in
  switch result {
    case .value:
      print("saved successfully")
    case .error:
      print(error)
    }
  }
}

storage.async.object(ofType: String.self, forKey: "my favorite city") { result in
  switch result {
    case .value(let city):
      print("my favorite city is \(city)")
    case .error:
      print(error)
    }
  }
}

storage.async.existsObject(ofType: String.self, forKey: "my favorite city") { result in
  if case .value(let exists) = result, exists {
    print("I have a favorite city")
  }
}

storage.async.removeAll() { result in
  print("removal completes")
}

storage.async.removeExpiredObjects() { result in
  print("removal completes")
}

Expiry date

By default, all saved objects have the same expiry as the expiry you specify in DiskConfig or MemoryConfig. You can overwrite this for a specific object by specifying expiry for setObject

// Default cexpiry date from configuration will be applied to the item
try? storage.setObject("This is a string", forKey: "string")

// A given expiry date will be applied to the item
try? storage.setObject(
  "This is a string",
  forKey: "string"
  expiry: .date(Date().addingTimeInterval(2 * 3600))
)

// Clear expired objects
storage.removeExpiredObjects()

What about images?

As you may know, NSImage and UIImage don't conform to Codable by default. To make it play well with Codable, we introduce ImageWrapper, so you can save and load images like

let wrapper = ImageWrapper(image: starIconImage)
try? storage.setObject(wrapper, forKey: "star")

let icon = try? storage.object(ofType: ImageWrapper.self, forKey: "star").image

If you want to load image into UIImageView or NSImageView, then we also have a nice gift for you. It's called Imaginary and uses Cache under the hood to make you life easier when it comes to working with remote images.

Handling JSON response

Most of the time, our use case is to fetch some json from backend, display it while saving the json to storage for future uses. If you're using libraries like Alamofire or Malibu, you mostly get json in the form of dictionary, string, or data.

Storage can persist String or Data. You can even save json to Storage using JSONArrayWrapper and JSONDictionaryWrapper, but we prefer persisting the strong typed objects, since those are the objects that you will use to display in UI. Furthermore, if the json data can't be converted to strongly typed objects, what's the point of saving it ? 😉

You can use these extensions on JSONDecoder to decode json dictionary, string or data to objects.

let user = JSONDecoder.decode(jsonString, to: User.self)
let cities = JSONDecoder.decode(jsonDictionary, to: [City].self)
let dragons = JSONDecoder.decode(jsonData, to: [Dragon].self)

This is how you perform object converting and saving with Alamofire

Alamofire.request("https://gameofthrones.org/mostFavoriteCharacter").responseString { response in
  do {
    let user = try JSONDecoder.decode(response.result.value, to: User.self)
    try storage.setObject(user, forKey: "most favorite character")
  } catch {
    print(error)
  }
}

Installation

Cocoapods

Cache is available through CocoaPods. To install it, simply add the following line to your Podfile:

pod 'Cache'

Carthage

Cache is also available through Carthage. To install just write into your Cartfile:

github "hyperoslo/Cache"

You also need to add SwiftHash.framework in your copy-frameworks script.

Author

Hyper made this with ❤️
Inline MD5 implementation from SwiftHash

Contributing

We would love you to contribute to Cache, check the CONTRIBUTING file for more info.

License

Cache is available under the MIT license. See the LICENSE file for more info.

Antowkos/Cache

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