Protocol Oriented Request

Requests.swift

import Foundation
import RxSwift

// Requests 
enum HTTPMethod: String {
    case POST, GET
}

// Define what a request is
protocol Request {
    var path: String { get }
    var method: HTTPMethod { get }
    var param: [String: Any] { get }

    associatedtype ResponseObject: Decodable
}

// Define what shoud have to send a request
protocol RequestSender {
    var base: String { get }
    func send<T: Request>(_ r: T) -> Observable<T.ResponseObject?>
}

// An object who can send out Request
struct URLSessionRequestSender: RequestSender {
    var base = "http://www.dummy.api"
    func send<T: Request>(_ r: T) -> Observable<T.ResponseObject?> {
        let url = URL(string: base.appending(r.path))!
        var request = URLRequest(url: url)
        request.httpMethod = r.method.rawValue

        if let body = try? JSONSerialization.data(withJSONObject: r.param, options: .prettyPrinted) {
            request.httpBody = body
        }

        return Observable.create { subscriber in
            let task =  URLSession.shared.dataTask(with: request) { data, res, error in
                if let data = data, let object = try? JSONDecoder().decode(T.ResponseObject.self, from: data) {
                    subscriber.onNext(object)
                } else {
                    subscriber.onError(error!)
                }
            }
            task.resume()
            return Disposables.create()
        }
    }
}

// An object
struct User: Decodable {
    let id: String
    let name: String
    let gender: String
}

// A real request
struct GetUserRequest: Request {
    typealias ResponseObject = User
    let id: String
    var path: String {
        return "/users/\(id)"
    
    var param: [String : Any]
    let method: HTTPMethod = .GET

    init(id: String, param: [String: Any] = [:]) {
        self.id = id
        self.param = param
    }
}

// usage example
func example() {
    let request = GetUserRequest(id: "a12345", param: ["foo": "bar"])
    _ = URLSessionRequestSender().send(request)
        .subscribe(onNext: { user in
            if let user = user {
                print("user is : \(user.name)")
            } else {
                print("got nothing")
            }
        })
}