Proof on concept WebSocket application comparing the built in NSURLSessionWebSocketTask and the Starscream WebSocket library on Github

ViewController+Starscream.swift

//
//  ViewController.swift
//  WebSocket Echo
//
//  Created by Kyle Howells on 02/08/2020.
//  Copyright © 2020 Kyle Howells. All rights reserved.
//

import UIKit
import Starscream

class ViewController: UIViewController, UITextFieldDelegate, WebSocketDelegate {

	// MARK: View Setup
	
	let textView:UITextView = {
		let tv = UITextView()
		tv.font = UIFont.systemFont(ofSize: 16)
		tv.isEditable = false
		tv.backgroundColor = UIColor(white: 0.95, alpha: 1)
		return tv
	}()
	
	let textfield:UITextField = {
		let tf = UITextField()
		tf.backgroundColor = UIColor(white: 0.9, alpha: 1)
		
		return tf
	}()
	
	override func viewDidLoad() {
		super.viewDidLoad()
		// Do any additional setup after loading the view.
		
		self.view.addSubview(textView)
		self.view.addSubview(textfield)
		
		self.textfield.delegate = self
		self.textfield.becomeFirstResponder()
		
		textView.text = ""
		
		self.connect()
	}
	
	// MARK: Layout
	
	override func viewDidLayoutSubviews() {
		super.viewDidLayoutSubviews()
		let size = self.view.bounds.size
		
		self.textfield.frame = {
			var f = CGRect.zero
			f.size.width = size.width - 20
			f.size.height = 30
			f.origin.y = size.height - (f.size.height + self.view.safeAreaInsets.bottom + 10)
			f.origin.x = 10
			return f
		}()
		
		self.textView.frame = {
			var f = CGRect.zero
			f.size.width = size.width
			f.size.height = self.textfield.frame.minY - (self.view.safeAreaInsets.top + 8)
			f.origin.y = self.view.safeAreaInsets.top
			return f
		}()
	}
	
	
	// MARK: UITextField
	
	@objc func textFieldShouldReturn(_ textField: UITextField) -> Bool {
		if true {
			let text = textfield.text ?? ""
			self.sendMessage(text)
		}
		
		textfield.text = ""
		return false
	}

	
	func log(_ text:String) {
		print(text)
		DispatchQueue.main.async {
			var existingText = (self.textView.text ?? "")
			if existingText.count > 0 {
				existingText += "\n"
			}
			
			self.textView.text = existingText + text
			
			if self.textView.text.count > 2 {
				let range = NSRange(location: (self.textView.text as NSString).length - 2, length: 1)
				self.textView.scrollRangeToVisible(range)
			}
		}
	}
	
	
	// MARK: - Web Sockets
	
	let urlString = "ws://echo.websocket.org"
	
	lazy var socket:WebSocket = {
		var request = URLRequest(url: URL(string: urlString)!)
		request.setValue("superchat", forHTTPHeaderField: "Sec-WebSocket-Protocol")
		request.timeoutInterval = 5
		let socket = WebSocket(request: request)
		socket.delegate = self
		return socket
	}()
	
	var isConnected:Bool = false
	
	
	func connect() {
		self.log("Connect to: \(urlString)")
		self.socket.connect()
	}
	
	func disconnect() {
		self.socket.disconnect()
		self.log("Disconnect")
	}
	
	
	func sendMessage(_ text:String) {
		self.log("Send message: \"\(text)\"")
		
		self.socket.write(string: text)
	}
	
	
	// MARK: WebSocketDelegate
	
	func didReceive(event: WebSocketEvent, client: WebSocket) {
		switch event {
		case .connected(let headers):
			isConnected = true
			self.log("Websocket is connected: \(headers)")
		
		case .disconnected(let reason, let code):
			isConnected = false
			self.log("websocket is disconnected: \(reason) with code: \(code)")
		
		case .text(let string):
			self.log("Received text: \(string)")
		
		case .binary(let data):
			self.log("Received data: \(data.count)")
		
		case .ping(let data):
			self.log("Ping: \(data)")
		
		case .pong(let data):
			self.log("Pong: \(data)")
		
		case .viabilityChanged(let connected):
			self.log("Viability Changed: \(connected)")
			if connected {
				self.socket.write(ping: Data())
			}
		
		case .reconnectSuggested(let connect):
			self.log("Reconnect Suggested: \(connect)")
		
		case .cancelled:
			isConnected = false
			self.log("Connection Cancelled")
		
		case .error(let error):
			isConnected = false
			self.log("Connection error: \(error)")
		}
	}
}

ViewController+URLSessionWebSocketTask.swift

//
//  ViewController.swift
//  WebSocket Client
//
//  Created by Kyle Howells on 01/08/2020.
//  Copyright © 2020 Kyle Howells. All rights reserved.
//

import UIKit

class ViewController: UIViewController, UITextFieldDelegate, URLSessionDelegate, URLSessionWebSocketDelegate {

	// MARK: View Setup
	
	let textView:UITextView = {
		let tv = UITextView()
		tv.font = UIFont.systemFont(ofSize: 16)
		tv.isEditable = false
		tv.backgroundColor = UIColor(white: 0.95, alpha: 1)
		return tv
	}()
	
	let textfield:UITextField = {
		let tf = UITextField()
		tf.backgroundColor = UIColor(white: 0.9, alpha: 1)
		
		return tf
	}()
	
	override func viewDidLoad() {
		super.viewDidLoad()
		// Do any additional setup after loading the view.
		
		self.view.addSubview(textView)
		self.view.addSubview(textfield)
		
		self.textfield.delegate = self
		self.textfield.becomeFirstResponder()
		
		textView.text = ""
		
		self.connect()
	}
	
	// MARK: Layout
	
	override func viewDidLayoutSubviews() {
		super.viewDidLayoutSubviews()
		let size = self.view.bounds.size
		
		self.textfield.frame = {
			var f = CGRect.zero
			f.size.width = size.width - 20
			f.size.height = 30
			f.origin.y = size.height - (f.size.height + self.view.safeAreaInsets.bottom + 10)
			f.origin.x = 10
			return f
		}()
		
		self.textView.frame = {
			var f = CGRect.zero
			f.size.width = size.width
			f.size.height = self.textfield.frame.minY - (self.view.safeAreaInsets.top + 8)
			f.origin.y = self.view.safeAreaInsets.top
			return f
		}()
	}
	
	
	// MARK: UITextField
	
	@objc func textFieldShouldReturn(_ textField: UITextField) -> Bool {
		if true {
			let text = textfield.text ?? ""
			self.sendMessage(text)
		}
		
		textfield.text = ""
		return false
	}

	
	func log(_ text:String) {
		print(text)
		DispatchQueue.main.async {
			var existingText = (self.textView.text ?? "")
			if existingText.count > 0 {
				existingText += "\n"
			}
			self.textView.text = existingText + text
		}
	}
	
	
	// MARK: - Web Sockets
	
	lazy var urlSession: URLSession = {
		print(self)
		let session = URLSession(configuration: .default, delegate: self, delegateQueue: self.delegateQueue)
		print(session)
		return session
	}()
    let delegateQueue = OperationQueue()
	
	let urlString = "ws://echo.websocket.org"
	lazy var webSocketTask: URLSessionWebSocketTask = {
		return self.urlSession.webSocketTask(with: URL(string: urlString)!) //, protocols: ["protocolOne"])
	}()
	
	
	func connect() {
		self.webSocketTask.resume()
		self.listen()
	}
	
	func disconnect() {
        webSocketTask.cancel(with: .goingAway, reason: nil)
	}
	
	func listen() {
        webSocketTask.receive { result in
            switch result {
            case .failure(let error):
				self.log("Connection error: \(error)")
			
            case .success(let message):
                switch message {
                case .string(let text):
					self.log("Received text message: \"\(text)\"")
                case .data(let data):
					self.log("Received data message: \"\(data)\"")
                @unknown default:
                    fatalError()
                }
                
                self.listen()
            }
        }
    }
	
	
	func sendMessage(_ text:String) {
		self.log("Send message: \"\(text)\"")
		
		webSocketTask.send(URLSessionWebSocketTask.Message.string(text)) { error in
            if let error = error {
				self.log("Connection error: \(error)")
            }
        }
	}
	
	
	// MARK: URLSessionDelegate
	
	func urlSession(_ session: URLSession, webSocketTask: URLSessionWebSocketTask, didOpenWithProtocol _protocol: String?) {
		self.log("Connected to: \(urlString), protocol: \(_protocol ?? "(null)")")
    }
    
    func urlSession(_ session: URLSession, webSocketTask: URLSessionWebSocketTask, didCloseWith closeCode: URLSessionWebSocketTask.CloseCode, reason: Data?) {
		self.log("Disconnected from: \(urlString)")
    }
	
	func urlSession(_ session: URLSession, task: URLSessionTask, didCompleteWithError error: Error?) {
		self.log("Encountered error: \(error)")
	}
	
}