I have a Swift app that uses a web socket to download stock price information from a public API. I send a message through the socket to subscribe to various stock price changes then wait for a continuous stream of messages to be received but when I turn off wifi the call to the message receive function, webSocketTask.receive, never returns. How can I force abort of the message receive function so that I alert the user that the network connection has been lost.
Here is my NetworkServices class;
import UIKit
import Network
protocol NetworkServicesDelegate: AnyObject {
func sendStockInfo(stocksInfo: [String: StockInfo])
}
final class NetworkServices: NSObject {
static let sharedInstance = NetworkServices()
var urlSession: URLSession?
var webSocketTask: URLSessionWebSocketTask?
var stocksInfo: [String: StockInfo] = [:]
var socketResults: [String: [StockInfo]] = [:]
weak var delegate: NetworkServicesDelegate?
var timer: Timer?
var stockSymbols: [String] = []
private let queue = DispatchQueue.global(qos: .background)
private let monitor = NWPathMonitor()
public private(set) var isConnected: Bool = false
public private(set) var connectionType: ConnectionType = .unknown
enum ConnectionType {
case wifi
case cellular
case wiredEthernet
case unknown
}
public func startMonitoring() {
monitor.start(queue: queue)
monitor.pathUpdateHandler = { path in
self.isConnected = path.status == .satisfied
self.getConnectionType(path)
print("DEBUG: isConnected = \(self.isConnected); connectionType = \(self.connectionType)")
if self.isConnected == false {
}
}
}
public func stopMonitoring() {
monitor.cancel()
}
private func getConnectionType(_ path: NWPath) {
if path.usesInterfaceType(.wifi) {
connectionType = .wifi
} else if path.usesInterfaceType(.cellular) {
connectionType = .cellular
} else if path.usesInterfaceType(.wiredEthernet) {
connectionType = .wiredEthernet
} else {
connectionType = .unknown
}
}
func fetchStockInfo(symbols: [String], delegate: CompanyPriceListVC) {
stockSymbols = symbols
self.delegate = delegate
let configuration = URLSessionConfiguration.default
configuration.waitsForConnectivity = false
urlSession = URLSession(configuration: configuration, delegate: self, delegateQueue: OperationQueue.main)
webSocketTask = urlSession?.webSocketTask(with: FINNHUB_SOCKET_STOCK_INFO_URL!)
webSocketTask?.delegate = self
webSocketTask!.resume()
for symbol in symbols {
let string = FINNHUB_SOCKET_MESSAGE_STRING + symbol + "\"}"
let message = URLSessionWebSocketTask.Message.string(string)
if isConnected {
webSocketTask!.send(message) { error in
if let error = error {
print("DEBUG: Error sending message: \(error)")
}
self.receiveMessage()
}
} else {
// Post notification to view controllers that connection has been lost
let name = Notification.Name(rawValue: isNotConnectedNotificationKey)
NotificationCenter.default.post(name: name, object: nil)
// try to re-connect
// successful re-connect?
// No, keep trying. Yes, call send message method again
}
}
}
private func receiveMessage() {
if isConnected {
self.webSocketTask?.receive { result in
print("DEBUG: Inside closure.")
switch result {
case .failure(let error):
print("DEBUG: Error receiving message: \(error.localizedDescription)")
case .success(.string(let jsonData)):
guard let stockData = jsonData.data(using: .utf8) else { return }
self.socketResults = [:]
self.stocksInfo = [:]
let decoder = JSONDecoder()
do {
let socketData = try decoder.decode(SocketData.self, from: stockData)
guard let stockInfoData = socketData.data else { return }
for stockInfo in stockInfoData {
let symbol = stockInfo.symbol
if self.socketResults[symbol] == nil {
self.socketResults[symbol] = [StockInfo]()
}
self.socketResults[symbol]?.append(stockInfo)
}
for (symbol, stocks) in self.socketResults {
for item in stocks {
if self.stocksInfo[symbol] == nil {
self.stocksInfo[symbol] = item
} else if item.timestamp > self.stocksInfo[symbol]!.timestamp {
self.stocksInfo[symbol] = item
}
}
}
self.delegate?.sendStockInfo(stocksInfo: self.stocksInfo)
self.receiveMessage()
} catch {
print("DEBUG: Error converting JSON: \(error)")
}
default:
print("DEBUG: default")
}
}
print("DEBUG: Got here 1")
} else {
print("DEBUG: Got here 2")
// Post notification to view controllers that connection has been lost
let name = Notification.Name(rawValue: isNotConnectedNotificationKey)
NotificationCenter.default.post(name: name, object: nil)
// try to re-connect.
// successful reconnect?
// No, keep trying. Yes, call receive message method again.
}
}
func closeWebSocketConnection() {
webSocketTask?.cancel(with: .goingAway, reason: nil)
}
func urlSession(_ session: URLSession, task: URLSessionTask, didCompleteWithError error: Error?) {
if let error = error {
print("DEBUG: didCompleteWithError called: error = \(error)")
}
}
func fetchCompanyInfo(symbol: String, completion: @escaping (CompanyInfo?, UIImage?)->()) {
let urlString = FINNHUB_HTTP_COMPANY_INFO_URL_STRING + symbol + "&token=" + FINNHUB_API_TOKEN
guard let url = URL(string: urlString) else { return }
let task = URLSession.shared.dataTask(with: url) { data, response, error in
if let error = error {
print("Error fetching company info: \(error)")
}
guard let data = data else { return }
let decoder = JSONDecoder()
do {
let companyInfo = try decoder.decode(CompanyInfo.self, from: data)
guard let logoURL = URL(string: companyInfo.logo) else { return }
let task = URLSession.shared.dataTask(with: logoURL) { data, response, error in
if let error = error {
print("Error fetching logo image: \(error)")
}
guard let data = data else { return }
guard let logoImage = UIImage(data: data) else { return }
completion(companyInfo, logoImage)
}
task.resume()
} catch {
print("Error decoding JSON: \(error)")
completion(nil, nil)
}
}
task.resume()
}
}
extension NetworkServices: URLSessionTaskDelegate, URLSessionWebSocketDelegate, URLSessionDelegate {
func urlSession(_ session: URLSession, taskIsWaitingForConnectivity task: URLSessionTask) {
print("DEBUG: inside taskIsWaitingForConnectivity")
}
func urlSession(_ session: URLSession, didBecomeInvalidWithError error: Error?) {
print("DEBUG: didBecomeInvalidWithError: error = \(String(describing: error?.localizedDescription))")
}
func urlSession(_ session: URLSession, webSocketTask: URLSessionWebSocketTask, didCloseWith closeCode: URLSessionWebSocketTask.CloseCode, reason: Data?) {
let reasonString: String
if let reason = reason, let string = String(data: reason, encoding: .utf8) {
reasonString = string
} else {
reasonString = ""
}
print("DEBUG: didCloseWith called: close code is \(closeCode), reason is \(String(describing: reasonString))")
}
func urlSessionDidFinishEvents(forBackgroundURLSession session: URLSession) {
print("DEBUG: urlSessionDidFinishEvents called")
}
}
I have tried placing code in the pathUpdateHandler closure to cancel the task on the task object and finish current tasks and cancel on the URLSession object but neither works.
I needed to post a notification when path.status == .satisfied. The notification goes to the custom UIViewController class which then calls the FetchStockInfo(symbols:delegate) method.