Client.swift

// The MIT License (MIT)
//
// Copyright (c) 2017 Alexander Grebenyuk (github.com/kean).

import Foundation
import Alamofire
import RxSwift
import RxCocoa


protocol ClientProtocol {
    func request<Response>(_ endpoint: Endpoint<Response>) -> Single<Response>
}

final class Client: ClientProtocol {
    private let manager: Alamofire.SessionManager
    private let baseURL = URL(string: "<your_server_base_url>")!
    private let queue = DispatchQueue(label: "<your_queue_label>")

    init(accessToken: String) {
        var defaultHeaders = Alamofire.SessionManager.defaultHTTPHeaders
        defaultHeaders["Authorization"] = "Bearer \(accessToken)"

        let configuration = URLSessionConfiguration.default

        // Add `Auth` header to the default HTTP headers set by `Alamofire`
        configuration.httpAdditionalHeaders = defaultHeaders

        self.manager = Alamofire.SessionManager(configuration: configuration)
        self.manager.retrier = OAuth2Retrier()
    }

    func request<Response>(_ endpoint: Endpoint<Response>) -> Single<Response> {
        return Single<Response>.create { observer in
            let request = self.manager.request(
                self.url(path: endpoint.path),
                method: httpMethod(from: endpoint.method),
                parameters: endpoint.parameters
            )
            request
                .validate()
                .responseData(queue: self.queue) { response in
                    let result = response.result.flatMap(endpoint.decode)
                    switch result {
                    case let .success(val): observer(.success(val))
                    case let .failure(err): observer(.error(err))
                    }
            }
            return Disposables.create {
                request.cancel()
            }
        }
    }

    private func url(path: Path) -> URL {
        return baseURL.appendingPathComponent(path)
    }
}

private func httpMethod(from method: Method) -> Alamofire.HTTPMethod {
    switch method {
    case .get: return .get
    case .post: return .post
    case .put: return .put
    case .patch: return .patch
    case .delete: return .delete
    }
}


private class OAuth2Retrier: Alamofire.RequestRetrier {
    func should(_ manager: SessionManager, retry request: Request, with error: Error, completion: @escaping RequestRetryCompletion) {
        if (error as? AFError)?.responseCode == 401 {
            // TODO: implement your Auth2 refresh flow
            // See https://github.com/Alamofire/Alamofire#adapting-and-retrying-requests
        }
        completion(false, 0)
    }
}

Endpoint.swift

// The MIT License (MIT)
//
// Copyright (c) 2017 Alexander Grebenyuk (github.com/kean).

import Foundation


// MARK: Defines

typealias Parameters = [String: Any]
typealias Path = String

enum Method {
    case get, post, put, patch, delete
}


// MARK: Endpoint

final class Endpoint<Response> {
    let method: Method
    let path: Path
    let parameters: Parameters?
    let decode: (Data) throws -> Response

    init(method: Method = .get,
         path: Path,
         parameters: Parameters? = nil,
         decode: @escaping (Data) throws -> Response) {
        self.method = method
        self.path = path
        self.parameters = parameters
        self.decode = decode
    }
}


// MARK: Convenience

extension Endpoint where Response: Swift.Decodable {
    convenience init(method: Method = .get,
                     path: Path,
                     parameters: Parameters? = nil) {
        self.init(method: method, path: path, parameters: parameters) {
            try JSONDecoder().decode(Response.self, from: $0)
        }
    }
}

extension Endpoint where Response == Void {
    convenience init(method: Method = .get,
                     path: Path,
                     parameters: Parameters? = nil) {
        self.init(
            method: method,
            path: path,
            parameters: parameters,
            decode: { _ in () }
        )
    }
}

Usage.swift

// The MIT License (MIT)
//
// Copyright (c) 2017 Alexander Grebenyuk (github.com/kean).

import Foundation


// MARK: Defining Endpoints

enum API {}

extension API {
    static func getCustomer() -> Endpoint<Customer> {
        return Endpoint(path: "customer/profile")
    }

    static func patchCustomer(name: String) -> Endpoint<Customer> {
        return Endpoint(
            method: .patch,
            path: "customer/profile",
            parameters: ["name" : name]
        )
    }
}

final class Customer: Decodable {
    let name: String
}


// MARK: Using Endpoints

func test() {
    let client = Client(accessToken: "<access_token>")
    _ = client.request(API.getCustomer())
    _ = client.request(API.patchCustomer(name: "Alex"))
}

how do you get the results from the client.request(API.getCustomers())

@eli007s "Each of the requests return cold observables. So nothing is going to happen until someone subscribes to the observable. "

Could you create a sample project, It will much better to understand with a project.

This is perfect, but... how to unit test your requests using mock responses? 👍

what about API error handling? i'm pretty new to decodable and i'd like to decode errors after validation.
Any help would be much appreciated.

I really like this abstracion. I thought I'd share an enhancement that can be really useful:

Implement map on Endpoint (make it a functor) like this:

    func map<N>(_ f: @escaping ((Response) throws -> N)) -> Endpoint<N> {
        let newDecodingFuntion: (Data) throws -> N = { data in
            return try f(self.decode(data))
        }
        return Endpoint<N>(method: self.method, path: self.path, parameters: self.parameters, decode: newDecodingFuntion)
    }

This enables transforming the initial expectation of the Endpoint (its Response generic parameter), in some cases you could reuse an endpoint already created.

I am getting errors like

load failed with error Error Domain=NSURLErrorDomain Code=-999 "cancelled" UserInfo={NSErrorFailingURLStringKey=

How would go about adding support for Encodable Parameters?