AdvancesInNetworkingPart1.md

Advancd in Networking, Part 1

@ WWDC 19

Low Data Mode

설정에서 low data mode를 설정할 수 있다. 이 옵션을 켰을 때 앱이 어떻게 작동할 지 개발하면서 설정해 줄 수 있다.

• User preference to minimize data usage
  • Explicit signal to reduce network data use
  • Peer Wi-Fi and Cellular network
• System plicy
  • Discretionary tasks deferred
  • Background App Refresh disabled

Application Adoption

내 앱에 적용할 때!, 이 옵션이 켜져 있다면

• Reduce image quality
• Reduce pre-fetching
• Synchronize less often
• Mark tasks discretionary
• Disble auto-play
• Do not block user-initiated work

Low Data Mode APIs

• URLSession
  • Try large/prefetch with allowsConstrainedNetworkAccess = false
  • On failure with error.networkUnavailableReason == .constrained try Low Data Mode alternative
• Network framework
  • Set prohibitConstrainedPaths on NWParameteers
  • Handle path updatees

Constrained and Expensive

• Constrained - Low Data Mode
• Expensive - Cellular and Personal Hotspot
• URLSession
  • allowsExpensiveNetworkAccess
• Network.framework
  • Set prohibitExpensivePaths on NWParameters
  • Check isExpensive on NWPath

Combine in URLSession

13부터 나온 Combine을 어떻게 URLSession과 함께 쓰는지 데모와 함께 설명. Combine에 대해 좀 알고 봐야 이해가 가능하지만 대강 Rx 살짝 맛봤던 정도로 이해 가능

• Streamline networking code with Combine
• Support retry
  • Use low retry count
  • Only idempotent request
• Best practices for Low Data Mode

// Generalized Publisher for Adaptive URL Loading
func adaptiveLoader(regularURL: URL, lowDataURL: URL) -> AnyPPublisher<Data, Error> {
  var request = URLRequest(url: regularURL)
  request.allowsConstrainedNetworkAccess = false
  return URLSession.shared.dataTaskPublisher(for: request)
  	.tryCatch { error -> URLSession.DataTaskPublisher in
			guard error.networkUnavailableReason == .constrained else {
        throw error
      }
			return URLSession.shared.dataTaskPublisher(for: lowDataURL)
    }
  	
  	.tryMap { data, response -> Data in
			guard let httpResponse = response as? HTTPURLResponse,
				httpResponse.statusCode == 200 else {
          throw MyNetworkingError.invalidServerResponse
        }
				return data
		}
  	.eraseToAnyPublisher()
}

WebSocket

웹소켓 이용하면 양방향 통신이 가능하다.

• Two-way communication over TLS/TCP connection
• Works with Firewalls and CDNs
• Proxy support

이번에 URLSessioon과 Network.framework에서 웹 소켓을 이용 가능하게 만들었다!

URLSessionWebSocketTask

• Foundation API for WebSocket
• Works with existing URLSession

// Create with URL
let task = URLSession.shared.webSocketTask(with: URL(string: "wss://websocket.example")!)
task.resume()

// Send a message
task.send(.string("Hello")) { error in /* Handle error */ }

// Receive a message
task.receive { result in /* Handle result */ }

Network.framework

• Both client and server support
• Receive partial or complete WebSocket messages

// Create parameters for WebSocket over TLS
let parameters = NWParameters.tls
let websocketOptions = NWProtocolWebSocket.Options()
parameters.defaultProtoocolStack.applicationProtocols.insert(websocketOptions, at: 0)

// Create a connection with those parameters
let websocketConnection = NWConnection(to: endppoint, using: parameters)

// Create a listener with those parameters
let websocketListener = try NWListener(using: parameters)

WebSocket APIs

• WebKit
  • JavaScript WebSocket
• URLSession
  • URLSessionWebSocketTask
• Network.framework
  • WebSocket Connection
  • WebSocket Listener

Mobilty Improvements

네트워크를 이야기할 때, mobility 중요! Wi-Fi Assist, Multipath Transport가 강한 iOS 13 소개

Wi-Fi Assist in iOS 13

Cross-layer Mobility Detection, Improved Flow Recovery

• Use high-level APIs like URLSession or Network.framework
• Rethink SCNetworkReachability usage
• Control access with allowsExpensiveNetworkAccess = false

Multipath Transports

Responsiveness for Maps, Fewer streaming stalls in Music

• Multipath Transports for your App
  • multipathServiceType URLSessionConfiguration and Network.framework
• Server-side configuration
  • Linux Kernel at https://multipath-tcp.org

Mobility Improvements

• Mobility should not impair your Apps
• Use high-level APIs
• Rethink interface management
• Prepare your servers and use multipathServiceType