How to use socket in Android with Kotlin

Question

I want to achieve something in Android using Kotlin to do:

If I click a button on the app, the app sends a word to a TCP server (which I wrote with python). The server will send back another word, and the app will show a toast message.

Here is what I have done so far, I can figure out the sending part but I can't manage to make it keep listening to the socket to hear from the server.

I am trying to use coroutine but after finding all the resources online, this is as best as I can get.

Also, I am not sure if I am setting the IP address in the correct manner.

Thank you in advance for your help!

'''

class MainActivity : AppCompatActivity() {
override fun onCreate(savedInstanceState: Bundle?) {
    super.onCreate(savedInstanceState)
    setContentView(R.layout.activity_main)

    val sendBtn = findViewById<Button>(R.id.sendBtn )
    val ipBtn = findViewById<Button>(R.id.ipBtn)
    val ipInput = findViewById<TextView>(R.id.ipInput)

    var ipAddress: String = "192.168.0.101"

    // Below is my attempt to keep listening to the socket, if commented, the sending would work. 
    // My guess is the IO thread is caught in the while loop so the other coroutines cannot use 
    // IO thread to send to the server.
    CoroutineScope(IO).launch{
        val socket = Socket(ipAddress, 9999)
        var text = ""
        while (true) {
            text = BufferedReader(InputStreamReader(socket.inputStream)).readLine()
            // if text is not null
            // Toast.makeText(this@MainActivity, "Set IP", Toast.LENGTH_SHORT).show()
        }
    }

    suspend fun sendMessage(message:String){
        val socket = Socket(ipAddress, 9999)
        socket.outputStream.write(message.toByteArray())
        socket.close()
    }

    ipBtn.setOnClickListener {
        Toast.makeText(this@MainActivity, "Set IP", Toast.LENGTH_SHORT).show()
        ipAddress = ipInput.text.toString()
    }

    sendBtn .setOnClickListener {
        CoroutineScope(IO).launch {
            Log.d("TAG", "message")
            sendMessage("record")
        }
    }

'''

Answer 1

To send a Data from P2P Fist we required a Server and Client . Here the Socket act as end point for sending and receiving data across the network .

1. Create a Server Class like this

 class ServerClass() :Thread(){
       
        lateinit var serverSocket:ServerSocket
        lateinit var inputStream: InputStream
        lateinit var  outputStream: OutputStream
        lateinit var socket: Socket



        override fun run() {
            try {
                serverSocket = ServerSocket(8888)
                socket = serverSocket.accept()
                inputStream =socket.getInputStream()
                outputStream = socket.getOutputStream()
            }catch (ex:IOException){
                ex.printStackTrace()
            }

            val executors = Executors.newSingleThreadExecutor()
            val handler = Handler(Looper.getMainLooper())
            executors.execute(Runnable{
                kotlin.run {
                    val buffer = ByteArray(1024)
                    var byte:Int
                    while (true){
                        try {
                            byte =  inputStream.read(buffer)
                            if(byte > 0){
                                var finalByte = byte
                                handler.post(Runnable{
                                    kotlin.run {
                                        var tmpMeassage = String(buffer,0,finalByte)
                                      
                                        Log.i("Server class","$tmpMeassage")
                                    }
                                })

                            }
                        }catch (ex:IOException){
                            ex.printStackTrace()
                        }
                    }
                }
            })
        }

        fun write(byteArray: ByteArray){
            try {
                Log.i("Server write","$byteArray sending")
                outputStream.write(byteArray)
            }catch (ex:IOException){
                ex.printStackTrace()
            }
        }
    }

2. Create a client Class where we need to pass hostaddress

class ClientClass(hostAddress: InetAddress): Thread() {
        
         var hostAddress: String = hostAddress.hostAddress
         lateinit var inputStream: InputStream
         lateinit var outputStream: OutputStream
         lateinit var socket: Socket

          fun write(byteArray: ByteArray){
              try {
                  outputStream.write(byteArray)
              }catch (ex:IOException){
                  ex.printStackTrace()
              }
          }

         override fun run() {
             try {
                 socket = Socket()
                 socket.connect(InetSocketAddress(hostAddress,8888),500)
                 inputStream = socket.getInputStream()
                 outputStream = socket.getOutputStream()
             }catch (ex:IOException){
                 ex.printStackTrace()
             }
             val executor = Executors.newSingleThreadExecutor()
             var handler =Handler(Looper.getMainLooper())

             executor.execute(kotlinx.coroutines.Runnable {
                 kotlin.run {
                     val buffer =ByteArray(1024)
                     var byte:Int
                     while (true){
                         try{
                             byte = inputStream.read(buffer)
                             if(byte>0){
                                 val finalBytes = byte
                        handler.post(Runnable{
                                     kotlin.run {
                                         val tmpMeassage = String(buffer,0,finalBytes)
                                        
                                         Log.i("client class", tmpMeassage)
                                     }
                                 })
                             }
                         }catch (ex:IOException){
                             ex.printStackTrace()
                         }
                     }
                 }
             })
         }

     }

make sure server and client port should be same , this is two way communication where we can transfer data in both sides .