swift echo server

extension.swift

//
//  main.swift
//  Echo
//
//  Created by juchen3 on 1/29/21.
//
// http://www.alwaysrightinstitute.com/network-framework/
// https://www.appcoda.com.tw/network-framework-http/

import Foundation
import Network

extension NWListener {
    fileprivate func startListeningToIncomingConnections(newConnectionHandler: @escaping(NWConnection) -> Void){
        
        self.stateUpdateHandler = { state in
           switch state {
           case .setup:
               print("Listener: setup")
           case .ready:
               print("Listener: receiving new connection")
           case .waiting(let error):
               print("Listener: waiting (\(error))")
           case .failed(let error):
               print("Listener: failed (\(error))")
           case .cancelled:
               print("Listener: cancelled")
           @unknown default:
               fatalError()
           }
        }
        
        self.newConnectionHandler = { connection in
            print("Listener: new connection received:", connection)

            newConnectionHandler(connection)
        }
        
        start(queue: .global())
    }
}

extension NWConnection {
    fileprivate func receiveRequest()
    {
        func readData()
        {
            receive(minimumIncompleteLength: 1, maximumLength: 1024)
            {
                data, context, isComplete, error in
                
                error.map { print("Connection: receiving request error: \($0)") }
                guard error == nil, let data = data else {
                    return self.cancel()
                }
                
                print("Received:", data)
                self.send(content : data,
                          completion: .idempotent)

                readData()
            }
        }
        
        start(queue: .global())
        readData()
    }
}

func startServer()
{
    let listener = try! NWListener(using: .tcp, on: 8000)
    listener.startListeningToIncomingConnections()
    {
        connection in
        print("Someone tries to talk to us!:", connection)
        connection.receiveRequest()
    }
}

startServer()
dispatchMain() // keep the tool running

main.swift

//
//  main.swift
//  Echo
//
//  Created by juchen3 on 1/29/21.
//
// http://www.alwaysrightinstitute.com/network-framework/

import Foundation
import Network

let listener = try NWListener(using: .tcp, on: 8000)
listener.newConnectionHandler = {
    connection in
    print("Someone tries to talk to us!:", connection)

    func readData() {
        connection.receive(minimumIncompleteLength: 1, maximumLength: 1024)
        {
            data, context, isComplete, error in
            guard error == nil, let data = data else {
                return connection.cancel()
            }
            
            print("Received:", data)
            connection.send(content : data,
                            completion: .idempotent)
            
            readData() // continue reading
        }
    }
    
    connection.start(queue: .main)
    
    readData()
}

listener.start(queue: .main)
dispatchMain() // keep the tool running