threema-ios/Threema/VoIPIceServerSource.swift

//  _____ _
// |_   _| |_  _ _ ___ ___ _ __  __ _
//   | | | ' \| '_/ -_) -_) '  \/ _` |_
//   |_| |_||_|_| \___\___|_|_|_\__,_(_)
//
// Threema iOS Client
// Copyright (c) 2020 Threema GmbH
//
// This program is free software: you can redistribute it and/or modify
// it under the terms of the GNU Affero General Public License, version 3,
// as published by the Free Software Foundation.
//
// This program is distributed in the hope that it will be useful,
// but WITHOUT ANY WARRANTY; without even the implied warranty of
// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
// GNU Affero General Public License for more details.
//
// You should have received a copy of the GNU Affero General Public License
// along with this program. If not, see <https://www.gnu.org/licenses/>.

import Foundation
import ThreemaFramework

let MIN_SPARE_VALIDITY: TimeInterval = 3600

struct TurnServerInfo {
    var turnUrls: Array<String>
    var turnUrlsDualStack: Array<String>
    var turnUsername: String
    var turnPassword: String
    var expirationDate: Date
}

enum TurnServerError: Error {
    case badServerData
}

class VoIPIceServerSource {
    private static var cachedTurnServers: TurnServerInfo?
    
    public static func prefetchIceServers() {
        obtainIceServers(dualStack: false) { (result) in
            // ignored
        }
    }
    
    public static func obtainIceServers(dualStack: Bool, completion: @escaping (Result<RTCIceServer, Error>) -> Void) {
        if cachedTurnServers != nil {
            let minExpiration = Date().addingTimeInterval(MIN_SPARE_VALIDITY)
            if cachedTurnServers!.expirationDate > minExpiration {
                completion(.success(makeIceServers(dualStack: dualStack, turnServerInfo: cachedTurnServers!)))
                return
            }
        }
        
        // No unexpired TURN server info in cache; must fetch
        ServerAPIConnector().obtainTurnServers(with: MyIdentityStore.shared()) { (response: [AnyHashable : Any]?) in            
            guard let expiration = response?["expiration"] as? TimeInterval,
                  let turnUrls = response?["turnUrls"] as? Array<String>,
                  let turnUrlsDualStack = response?["turnUrlsDualStack"] as? Array<String>,
                  let turnUsername = response?["turnUsername"] as? String,
                  let turnPassword = response?["turnPassword"] as? String else {
                completion(.failure(TurnServerError.badServerData))
                return
            }
            
            let expirationDate = Date().addingTimeInterval(expiration)
            cachedTurnServers = TurnServerInfo(
                turnUrls: turnUrls,
                turnUrlsDualStack: turnUrlsDualStack,
                turnUsername: turnUsername,
                turnPassword: turnPassword,
                expirationDate: expirationDate
            )
            completion(.success(makeIceServers(dualStack: dualStack, turnServerInfo: cachedTurnServers!)))
        } onError: { (e: Error?) in
            completion(.failure(e!))
        }
    }
    
    private static func makeIceServers(dualStack: Bool, turnServerInfo: TurnServerInfo) -> RTCIceServer {
        let urls = dualStack ? turnServerInfo.turnUrlsDualStack : turnServerInfo.turnUrls
        return RTCIceServer.init(urlStrings: urls, username: turnServerInfo.turnUsername, credential: turnServerInfo.turnPassword, tlsCertPolicy: .secure)
    }
}