tchigher / netable

A Swift library for encapsulating network APIs using Codable in a type-oriented way.

Modern apps interact with a lot of different APIs. Netable makes that easier by providing a simple interface for using those APIs to drive high quality iOS and MacOS apps, built on Swift Codable, while still supporting non-standard and unusual APIs when need be.

• Features
• Usage
• Example
• Requirements
• Installation
• License

Features

Netable is built on a number of core principles we believe a networking library should follow:

• Handle the simplest REST API calls with minimal code, while still having the extensibility to decode the gnarliest responses
• Leverage Swift’s Codabale protocols for automatic decoding and encoding
• Avoid monolithic networking files and avoid wrappers
• Straightforward global and local error handling
• Add a little bit of magic, but only where it goes a long way

Usage

Standard Usage

Make a new instance of Netable, and pass in your base URL:

let netable = Netable(baseURL: URL(string: "https://api.thecatapi.com/v1/")!)

Extend Request

struct CatImage: Decodable {
    let id: String
    let url: String
}

struct GetCatImages: Request {
    typealias Parameters = [String: String]
    typealias RawResource = [CatImage]

    public var method: HTTPMethod { return .get }

    public var path: String {
        return "images/search"
    }

    public var parameters: [String: String] {
        return ["mime_type": "jpg,png", "limit": "2"]
    }
}

Make your request and handle the result:

netable.request(GetCatImages()) { result in
    switch result {
    case .success(let catImages):
        if let firstCat = catImages.first,
           let url = URL(string: firstCat.url),
           let imageData = try? Data(contentsOf: url) {
            self.catsImageView1.image = UIImage(data: imageData)
        }

        if let lastCat = catImages.last,
           let url = URL(string: lastCat.url),
           let imageData = try? Data(contentsOf: url) {
            self.catsImageView2.image = UIImage(data: imageData)
        }
    case .failure(let error):
        let alert = UIAlertController(
            title: "Uh oh!",
            message: "Get cats request failed with error: \(error)",
            preferredStyle: .alert
        )

        alert.addAction(UIAlertAction(title: "OK", style: .cancel))
        self.present(alert, animated: true, completion: nil)
    }
}

Resource Extraction

Have your request object handle extracting a usable object from the raw resource

struct CatImage: Decodable {
    let id: String
    let url: String
}

struct GetCatImageURL: Request {
    typealias Parameters = [String: String]
    typealias RawResource = [CatImage]
    typealias FinalResource = URL

     // ...

    func finalize(raw: RawResource) -> Result<FinalResource, NetableError> {
        guard let catImage = raw.first else {
            return .failure(NetableError.resourceExtractionError("The CatImage array is empty"))
        }

        guard let url = URL(string: catImage.url) else {
            return .failure(NetableError.resourceExtractionError("Could not build URL from CatImage url string"))
        }

        return .success(url)
    }
}

Leave your network code to deal with the important stuff

netable.request(GetCatImageURL()) { result in
    switch result {
    case .success(let catUrl):
        guard let imageData = try? Data(contentsOf: catUrl) else {
            return
        }

        self.imageView.image = UIImage(data: imageData)
    case .failure(let error):
        // ...
    }
}

Smart Unwrapping Objects

Sometimes APIs like to return the object you actually care about inside of a single level wrapper, which Finalize is great at dealing with, but requires a little more boilerplate code than we'd like. This is where SmartUnwrap<> comes in!

Create your request as normal, but set your RawResource = SmartUnwrap<ObjectYouCareAbout> and FinalResource = ObjectYourCareAbout. You can also specify Request.smartUnwrapKey to avoid ambiguity when unwrapping objects from your response.

Before:

struct UserResponse {
    let user: User
}

struct User {
    let name: String
    let email: String
}

struct GetUserRequest: Request {
    typealias Parameters: GetUserParams
    typealias RawResource: UserResponse
    typealias FinalResource: User
    
    // ...
    
    func finalize(raw: RawResource) -> Result<FinalResource, NetableError> {
        return .success(raw.user)
    }
}

After:

struct User: {
    let name: String
    let email: String
}

struct GetUserRequest: Request {
    typealias Parameters: GetUserParams
    typealias RawResource: SmartUnwrap<User>
    typealias FinalResource: User
}

Handling Errors

In addition to handling errors locally through the completion callback provided by request(), we provide two ways to handle errors globally. These can be useful for doing things like presenting errors in the UI for common error cases across multiple requests, or catching things like failed authentication requests to clear a stored user.

Using requestFailureDelegate

See GlobalRequestFailureDelegate in the Example project for a more detailed example.

extension GlobalRequestFailureDelegateExample: RequestFailureDelegate {
    func requestDidFail<T>(_ request: T, error: NetableError) where T : Request {
        let alert = UIAlertController(title: "Uh oh!", message: error.errorDescription, preferredStyle: .alert)
        present(alert, animated: true)
    }
}

Using requestFailurePublisher

If you prefer Combine, you can subscribe to this publisher to recieve NetableErrors from elsewhere in your app.

See GlobalRequestFailurePublisher in the Example project for a more detailed example.

netable.requestFailurePublisher.sink { error in
    let alert = UIAlertController(title: "Uh oh!", message: error.errorDescription, preferredStyle: .alert)
    self.present(alert, animated: true)
}.store(in: &cancellables)

Using FallbackResource

Sometimes, you may want to specify a backup type to try and decode your response to if the initial decoding fails, for example:

• You want to provide a fallback option for an important request that may have changed due to protocol versioning
• An API may send back different types of responses for different types of success

Request allows you to optionally declare a FallbackResource: Decodable associated type when creating your request. If you do and your request fails to decode the RawResource, it will try to decode your fallback resource, and if successful, throw a NetableError.fallbackDecode with your successful decoding.

See FallbackDecoderViewController in the Example project for a more detailed example.

Full Documentation

In-depth documentation is provided through Jazzy and GitHub Pages.

Example

To run the example project, clone the repo, and run pod install from inside the Example directory first.

Requirements

• iOS 13.0+
• MacOS 10.15+
• Xcode 11.0+

Installation

Netable is available through Swift Package Manager. To install it, follow these steps:

1. In Xcode, click File, then Swift Package Manager, then Add Package Dependency
2. Choose your project
3. Enter this URL in the search bar https://github.com/steamclock/netable.git

License

Netable is available under the MIT license. See the License.md for more info.