Improved version of the Network Layer solution by Tomasz Szulc presented in the article: http://szulctomasz.com/how-do-I-build-a-network-layer/

The idea is to create a modular network layer, 100% testable, that implements NSOperation to manage easily a requests queue, with priority, dependecy, cancel operation etc.

• Request

A struct that implement BackendAPIRequest protocol. It's an object that knows which endpoint to hit, what method to use, should it be GET, POST, PUT or different, how to configure the body of a request and what headers to pass.

public protocol BackendAPIRequest {
    var endpoint: String { get }
    var method: Method { get }
    var query: Query { get }
    var parameters: Parameters? { get }
    var headers: [String: String]? { get }
}

• Mapper

The mapper separates the logic of parsing and mapping JSON to useful items.

There are two type of parsers:

• The first type return just a single object of specific type.

• The second type is a parser that parses array of such items.

• Operation

This is the NSOperation object, ServiceOperation subclass, that instantiates a request, creates the network request and manage the network response.

To test this object we use dependency injection, passing a mock object that implements the BackendService protocol.

public init(uniqueId: String, service: BackendService = MyBackendService(BackendConfiguration.shared)) {
    request = UserShoppingRequest(uniqueId: uniqueId)
    super.init(service: service)
}

• BackendService

It is the class that takes requests (Request objects described above) related to the backend. It uses NetworkService internally.

• NetworkService

It allows you to execute HTTP request, it incorporates NSURLSession internally. Every network service can execute just one request at a time, can cancel the request (big advantage), and has callbacks for success and failure responses.

For the implementation read the original blog post and take a look to Network/Request, Network/Operations and Network/Mappers.

You can find some test examples in NetworkLayerExampleTest/NetworkLayerExampleTest.swift.