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Leash

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Introduction

Do you use Alamofire? Are you used to create some network layer called APIManager or Alamofire+NameOfProject in every new project? Are you used to spend time deintegrating and taking what you need from previous implementations? Or even coding what you have previously done? What if there is a solution and you should not deal with this anymore?

Now, instead of creating a network layer, you create Interceptors, which are responsible for intercepting the requests at different moments of its life cycle (depending on the requirements). Go to Interceptors for more information.

Moreover, Leash also includes some processes that are common on the network layers, such as encoding, decoding, authentication and more. And, just to clarify, it also uses Alamofire.

Example

To run the example project there are two possibilities:

  • Run pod try Leash.
  • Clone the repo and run pod install from the Example directory first.

Requirements

  • Xcode 9.0+
  • Swift 3.2+

Installation

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

pod 'Leash', '~> 2.1'

# or

pod 'Leash/RxSwift', '~> 2.1'

Usage

Setup

First, we need to configure a Manager. You can see here all the options available. Here is an example:

let manager = Manager.Builder()
    .scheme("http")
    .host("localhost")
    .port(8080)
    .path("api")
    .build()

Then, we need a Client to create and execute the requests:

let client = Client(manager: manager)

Now, assuming that we have already created an APIEndpoint with all the reachable endpoints, we can execute requests. For example:

client.execute(APIEndpoint.readAllUsers) { (response: Response<[User]>) in
    // Do whatever you have to do with the response here.
}

Ok, that is good. But, what if we just want to call it like this?

usersClient.readAll { response in
    // Do whatever you have to do with the response here.
}

Much simpler, huh? To keep your project as simple and clean as possible, follow the architecture of the example project.

Encoding

Now that you know how to execute the requests you may be asking how to configure the parameters (because Any is accepted). There are different options depending if the endpoint is query or body encodable:

  • Query types: QueryEncodable or [String: CustomStringConvertible].
  • Body types: Encodable or [String: Any].

Here is an example with all the possibilities:

enum APIEndpoint {
    case first(QueryEncodable)
    case second([String: CustomStringConvertible])
    case third(Encodable)
    case fourth([String: Any])
}

extension APIEndpoint: Endpoint {

    var path: String {
        return "/it/does/not/matter/"
    }

    var method: HTTPMethod {
        switch self {
        case .first: return .get
        case .second: return .get
        case .third: return .post
        case .fourth: return .post
        }
    }

    var parameters: Any? {
        switch self {
        case .first(let request): return request // This is `QueryEncodable`.
        case .second(let request): return request // This is `[String: CustomStringConvertible]`.
        case .third(let request): return request // This is `Encodable`.
        case .fourth(let request): return request // This is `[String: Any]`.
        }
    }
    
}

Three different classes are being used to encode the parameters:

In case you want to encode the parameters in a different way, you have to override the method Client.urlRequest(for:).

Decoding

When you execute a request you have to specify the type of the response. Also, this type must conform to Decodable. After executing the request, in case of a successful response, you will have the response with a value of the specified type. So, a simple example could be:

client.execute(APIEndpoint.readAllUsers) { (response: Response<[User]>) in
    // Here, in case of a successful response, the `response.value` is of the type `[User]`.
}

The only available option to serialize the response is through the JSONDecoder. In case you need to do it in a different way, you should implement your own response serializer. Yes, it uses the DataResponseSerializer provided by Alamofire!

For example, here is how a JSON response handler might be implemented:

extension DataRequest {

    @discardableResult
    func responseJSON(client: Client,
                      endpoint: Endpoint,
                      completion: @escaping (Response<Any>) -> ()) -> Self {
        return response(client: client,
                        endpoint: endpoint,
                        serializer: DataRequest.jsonResponseSerializer(),
                        completion: completion)
    }

}

To facilitate the process of executing requests, you should add a method like this to the Client:

extension Client {

    @discardableResult
    func execute(_ endpoint: Endpoint, completion: @escaping (Response<Any>) -> ()) -> DataRequest? {
        do {
            let request = try self.request(for: endpoint)
            return request.responseJSON(client: self, endpoint: endpoint, completion: completion)
        } catch {
            completion(.failure(Error.encoding(error)))
            return nil
        }
    }

}

An example of the result of these extensions could be:

client.execute(APIEndpoint.readAllUsers) { (response: Response<Any>) in
    // Here, in case of a successful response, the `response.value` is of the type `Any`.
}

Now, you are able to create your own DataResponseSerializer and use all the features of Leash!

Authenticator

Do you need to authenticate your requests? That's something really simple, lets do it!

class APIAuthenticator {

    var accessToken: String?

}

extension APIAuthenticator: Authenticator {

    static var header: String = "Authorization"

    var authentication: String? {
        guard let accessToken = accessToken else { return nil }
        return "Bearer \(accessToken)"
    }

}

Then, you just need to register the authenticator:

let authenticator = APIAuthenticator()
let manager = Manager.Builder()
    { ... }
    .authenticator(authenticator)
    .build()

Now, you have all your requests authenticated. But, are you wondering about token expiration? Here is the solution!

Interceptors

Now, it is the moment of the most powerful tool of this framework. The Interceptors gives you the capability to intercept the requests in different moments of its life cycle. There are five different moments to be explicit:

  • Execution: called before a request is executed.
  • Failure: called when there is a problem executing a request.
  • Success: called when there is no problem executing a request.
  • Completion: called before the completion handler.
  • Serialization: called after a serialization operation.

Three types of Interceptors are called in every request (Execution, Failure or Success, Completion). Also, there is one more type that is called depending if you are serializing the response or not (Serialization).

The Manager can store as many Interceptors as you need. And, at the moment of being called, it is done one per time, asynchronously, in a queue order (the same order in which they were added). In case that one of any type is completed requesting to finish the operation, no more Interceptors of that type are called.

One of the best advantages is that the Interceptors does not depend between them to work. So, any of them is a piece that can be taken out of your project at any moment (without having to deal with compilation issues). Moreover, you can take any of these pieces and reuse them in any other project without having to make changes at all!

Below I will show you how to interact with the different types with some examples. There are a lot more use cases, it is up to you and your requirements!

Just as a reminder, do not forget to add the Interceptors to the Manager, like this:

let manager = Manager.Builder()
    { ... }
    .add(interceptor: Interceptor())
    .build()

Execution

The purpose of this Interceptor is to intercept before a request is executed. Let me show you two examples:

First, the simplest one, we need to log every request that is executed:

class LoggerInterceptor: ExecutionInterceptor {

    func intercept(chain: InterceptorChain<Data>) {
        defer { chain.proceed() }
        guard let request = chain.request.request,
            let method = request.httpMethod,
            let url = request.url?.absoluteString else { return }

        Logger.shared.logDebug("👉👉👉 \(method) \(url)")
    }
    
}

Now, one more complex, but not more difficult to implement:

class CacheInterceptor: ExecutionInterceptor {

    func intercept(chain: InterceptorChain<Data>) {
        // On that case, the cache controller may need to finish the operation or not (depending on the policies).
        // So, we can easily tell the chain wether the operation should be finished or not.
        defer { chain.proceed() }
        guard let cachedResponse = try? CacheController().cachedResponse(for: chain.endpoint) else { return }
        chain.complete(with: cachedResponse.data, finish: cachedResponse.finish)
    }

}

Failure

Basically, the purpose of this Interceptor is to intercept when Alamofire retrieves an error. A simple example could be:

class ErrorValidator: FailureInterceptor {

    func intercept(chain: InterceptorChain<Data>, error: Swift.Error) {
        defer { chain.proceed() }
        guard case Error.some = error else { return }
        chain.complete(with: Error.another)
    }

}

Success

Basically, the purpose of this Interceptor is to intercept when Alamofire retrieves a response. Let me show you two examples:

We know that, sometimes, the API could retrieve a custom error with more information:

class BodyValidator: SuccessInterceptor {

    func intercept(chain: InterceptorChain<Data>, response: HTTPURLResponse, data: Data) {
        defer { chain.proceed() }

        if let error = try? chain.client.manager.jsonDecoder.decode(APIError.self, from: data) {
            chain.complete(with: Error.server(error))
        }
    }

}

Maybe, there is no custom error, but we still need to validate the status code of the response:

class ResponseValidator: SuccessInterceptor {

    func intercept(chain: InterceptorChain<Data>, response: HTTPURLResponse, data: Data) {
        defer { chain.proceed() }

        let error: Error

        switch response.statusCode {
            // You should match your errors here.
            case 200...299: return
            case 401, 403: error = .unauthorized
            default: error = .unknown
        }

        chain.complete(with: error)
    }

}

Completion

The purpose of this Interceptor is to intercept before the completion handler is called. Let me show you two examples:

Again, the simplest one, we need to log every response:

class LoggerInterceptor: CompletionInterceptor {

    func intercept(chain: InterceptorChain<Data>, response: Response<Data>) {
        defer { chain.proceed() }
        guard let request = chain.request.request,
            let method = request.httpMethod,
            let url = request.url?.absoluteString else { return }

        switch response {
        case .success(_):
            Logger.shared.logDebug("✔✔✔ \(method) \(url)")
        case .failure(let error):
            Logger.shared.logDebug("✖✖✖ \(method) \(url)")
            Logger.shared.logError(error)
        }
    }

}

Now, one more complex, we have to update the authentication when expired. There are two options here:

  • Use the Adapter and Retrier provided by Alamofire.
  • Use the Authenticator and an Interceptor! Let me show you how it should look like:
class AuthenticationValidator: CompletionInterceptor {

    func intercept(chain: InterceptorChain<Data>, response: Response<Data>) {
        guard let error = response.error, case Error.unauthorized = error else {
            chain.proceed()
            return
        }

        RefreshTokenManager.shared.refreshTokenIfNeeded { authenticated in
            guard authenticated else {
                chain.complete(with: Error.unableToAuthenticate)
                return
            }

            do {
                try chain.retry()
            } catch {
                // In almost every case, no error is thrown.
                // But, because we prefer the safest way, we use the do-catch.
                chain.complete(with: Error.unableToRetry)
            }
        }
    }

}

Serialization

This is the last Interceptor in being called. Also, it is optional. It depends if you are serializing your response or you only need the Data. In most cases, you probably do it.

The serialization process is built on top of the process of getting the Data from the request. This is why it is called after all the previous Interceptors. Let me show you an example:

We started before with the CacheController, right? Well, now we need to update the cache in case that the response was serialized successfully:

class CacheInterceptor: SerializationInterceptor {

    func intercept<T: DataResponseSerializerProtocol>(chain: InterceptorChain<T.SerializedObject>,
                                                      response: Response<Data>,
                                                      result: Result<T.SerializedObject>,
                                                      serializer: T) {
        defer { chain.proceed() }
        guard let value = response.value, result.isSuccess else { return }
        CacheController().updateCacheIfNeeded(for: chain.endpoint, value: value)
    }

}

RxSwift

Do you use RxSwift? There is an extension for that! Let me show you how to use it:

client.rx.execute(APIEndpoint.readAllUsers, type: [User].self).subscribe { event in
    // Do whatever you have to do with the response here.
}

Ok, that is good. But, what if we just want to call it like this?

usersClient.rx.readAll().subscribe { event in
    // Do whatever you have to do with the response here.
}

Much simpler, again, huh? As mentioned before, to keep your project as simple and clean as possible, follow the architecture of the example project.

Communication

  • If you need help, open an issue.
  • If you found a bug, open an issue.
  • If you have a feature request, open an issue.
  • If you want to contribute, submit a pull request.

Author

Luciano Polit, lucianopolit@gmail.com

License

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

Github

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