RestLikeKit is my personal Swift API for building clients for REST-like APIs. The goal of RestLikeKit is to remove the need to copy-pasta this code from project to project, or have to re-invent the wheel for each new app.

RestLikeKit supports iOS, macOS, and tvOS.

• Swift 5.1 or greater
• iOS/tvOS 13 or greater OR macOS 10.15 or greater

Currently, RestLikeKit is only available as a Swift Package.

Open the Package.swift file and edit it:

1. Add RestLikeKit repo to the dependencies array.
2. Add RestLikeKit as a dependency of the target that will use it

// swift-tools-version:5.1

import PackageDescription

let package = Package(
  // ...snip...
  dependencies: [
    .package(url: "https://github.com/andyfinnell/RestLikeKit.git", from: "0.0.1")
  ],
  targets: [
    .target(name: "MyTarget", dependencies: ["RestLikeKit"])
  ]
)

Then build to pull down the dependencies:

$ swift build

Use the Swift Packages tab on the project to add RestLikeKit:

1. Open the Xcode workspace or project that you want to add RestLikeKit to
2. In the file browser, select the project to show the list of projects/targets on the right
3. In the list of projects/targets on the right, select the project
4. Select the "Swift Packages" tab
5. Click on the "+" button to add a package
6. In the "Choose Package Repository" sheet, search for "https://github.com/andyfinnell/RestLikeKit.git"
7. Click "Next"
8. Choose the version rule you want
9. Click "Next"
10. Choose the target you want to add RestLikeKit to
11. Click "Finish"

To create a new type of resource request, create a new type that implements the ResourceRequest.

For example:

struct User: Decodable, Equatable {} // API model

struct ShowUserRequest: ResourceRequest {
    typealias ResourceType = User
    
    let verb = ResourceVerb.show
    let path: String
    let parameters = Empty()
    
    init(userId: String) {
        path = "/users/\(userId)/"
    }
}

The ResourceType defines the response payload. It has to be Equatable and Decodable, and by default is assumed to be encoded as JSON. verb is a required property that has to be show, index, create, update, or delete. path is also required, and is a relative path for the resource. parameters describe the parameters sent out on the HTTP request. They are are required to be Encodable and Equatable, and for .show verb requests will be encoded as query parameters. In this example a special value called Empty is used to indicate there are no parameters.

Update requests are similar to show requests, but typically have different values. For example:

struct UpdateUserRequest: ResourceRequest {
    typealias ResourceType = Empty
    struct ParameterType: Encodable, Equatable {
        let firstName: String?
        let lastName: String?
    }
    let verb = ResourceVerb.update
    let path: String
    let parameters: ParameterType
    
    init(userId: String, firstName: String? = nil, lastName: String? = nil) {
        path = "/users/\(userId)/"
        parameters = ParameterType(firstName: firstName, lastName: lastName)
    }
}

In this case, the update operation doesn't return anything, so it's modeled with the special value Empty. However, update does take parameters, so they are created as an Encodable, Equatable struct nested inside the request type. Since the update verb is used, they'll be encoded as JSON in the body of the request.

All requests are made through an API instance, which allows common API configuration like headers, base URL, and authentication. These are injected to the API through the init method.

First, we need to create the APIConfig value that we'll use in the dependencies:

extension APIConfig {
    static let `default` = APIConfig(baseURL: URL(string: "https://myservice.example.com/api/")!,
                                     baseHeaders: [.apiKey: "super-secret-api-key"])
}

The API config defines the static parts of the API, namely the base URL and any common headers that should be set on all HTTP requests.

Next, we need to implement an authentication header storage. This will dynamically provide a value to put in the HTTP Authentication header. It conforms to the AuthenticationStorageType protocol. If not value is ever needed, it can just return nil:

struct AuthenticationStorage: AuthenticationStorageType {
    func authenticationHeader(for service: String) -> String? {
        nil
    }
}

RestLikeKit also provides Keychain bindings, so pulling a value from the Keychain can be done like so:

struct AuthenticationStorage: AuthenticationStorageType {
    private let keychain = Keychain()
    private let userId: String
    
    func authenticationHeader(for service: String) -> String? {
        keychain.password(service: service, account: userId).map { "Bearer \($0)" }
    }
}

With our API config and authentication storage created, we can now create our API:

let httpClient = HTTPClient(logger: Logger(),
                            urlSession: URLSession.shared,
                            httpRequestEncoder: HTTPRequestEncoder(),
                            httpResponseDecoder: HTTPResponseDecoder())

let api = API(httpClient: httpClient, apiConfig: .default, authenticationStorage: AuthenticationStorage())

The httpClient is the only other dependency required by API that we haven't already created. There's no reason not to use the HTTPClient provided by RestLikeKit, however we may want to swap out a different logger, or more rarely a different encoder or decoder.

Typically the api instance is created once and put in the dependency injection system for anyone code that needs it.

After create the request type and instantiating an API, we can make request with the call method:

func fetchUser(with id: String) -> AnyPublisher<User, Error> {
    api.call(ShowUserRequest(userId: id))
}

The result is a Combine AnyPublisher that will have at most one value. It also operates as a "cold" observable, meaning the request won't be made until someone is listening on the publisher.

RestLikeKit provides a rudimentary logging system via the Logger type. It wraps OSLog, and the LogTag type gets mapped into the OSLog category. Logging is on in the DEBUG builds and off otherwise.

By default the API type will log requests and responses. Individual ResourceRequests can opt-out of being logging by providing values for the shouldRedactRequestBody or shouldRedactResponseBody properties. This is useful for requests that contain sensitive information, like login tokens or passwords.

As mentioned earlier, RestLikeKit provides basic Keychain functionality through the Keychain type. It can fetch, update, or delete Keychain entries.