Kotlin BufferedReader from stream is blocking - kotlin

Question

I'm creating an android app with visual studio on clocking, and I'm trying to make the communication between my C++ server (working perfectly) and my android app.
My android socket (client) connect correctly to my serv, i can send message to the server, but when the server is sending message the readText block indefinitly.
here the code for the current fragment :
package com.example.androidapp
import android.app.Activity
import android.os.Bundle
import android.util.Log
import android.view.LayoutInflater
import android.view.View
import android.view.ViewGroup
import androidx.fragment.app.Fragment
import com.example.androidapp.databinding.FragmentServerMainBinding
import androidx.navigation.fragment.findNavController
import java.io.Reader
import java.io.BufferedReader
import java.io.InputStreamReader
import java.util.*
class ServerMainFragment : Fragment() {
//private var _binding: FragmentFirstBinding? = null
private var _binding: FragmentServerMainBinding? = null
// This property is only valid between onCreateView and
// onDestroyView.
private val binding get() = _binding!!
override fun onCreateView(
inflater: LayoutInflater, container: ViewGroup?,
savedInstanceState: Bundle?
): View? {
_binding = FragmentServerMainBinding.inflate(inflater, container, false)
return binding.root
}
override fun onViewCreated(view: View, savedInstanceState: Bundle?) {
super.onViewCreated(view, savedInstanceState)
singleton_ServerInfos.end=false
binding.bBisconnect.setOnClickListener {
singleton_ServerInfos.end=true;
Log.d("ServerMainFragment", "closing socket")
singleton_ServerInfos.clientSocket?.close();
(context as Activity).runOnUiThread(java.lang.Runnable {
Log.d("ServerMain: ", "disconnecting")
findNavController().navigate(R.id.FirstFragment)
})
}
binding.sendmsg.setOnClickListener {
Thread(Runnable {
try {
Log.d(
"ServerMainFragment",
"sendmsg" + singleton_ServerInfos.clientSocket.isConnected
)
singleton_ServerInfos.clientSocket?.outputStream.write("Hello from the client!".toByteArray())
} catch (excep: java.net.SocketException) {
Log.d("SocketException", "catched error")
} catch (e: Exception) {
Log.d("Exception", e.toString() + "---" + e.message)
}
}).start()
}
listenForServerMessage()
Log.d("FirstFragment", "onViewCreated")
}
fun listenForServerMessage() {
//var reader = Scanner(singleton_ServerInfos.clientSocket.getInputStream())
Log.d("ServerMain ", "listenForServerMessage")
Thread(Runnable {
try {
Log.d("ServerMain ","letsgo:"+singleton_ServerInfos.end);
var bufReader = BufferedReader(InputStreamReader (singleton_ServerInfos.clientSocket.getInputStream()))
while (singleton_ServerInfos.end!=true) {
Log.d("ServerMain ", "while")
var nbr = singleton_ServerInfos.clientSocket.getInputStream().available()
if (nbr != 0) {
Log.d("ServerMain read: ", "in:"+nbr+"-"+bufReader.ready());
if (bufReader.ready())
Log.d("ServerMain read: ", "NOOWOWW:"+bufReader.readText());
}
}
}
catch (e: Exception) {
Log.d("ServerMain: ", "exception closing.")
}
}).start()
}
override fun onDestroyView() {
super.onDestroyView()
_binding = null
}
}
The socket is connected on the previous fragment. In the reading function listenForServerMessage , i check if the socket is ready, i check the number of bytes received (non zero) and if the buffer is also ready, both are good but when executing readText i get an infinite loop.
my log look like this :
D/ServerMain: letsgo:false
D/ServerMain: while
I/chatty: uid=10122(com.example.androidapp) Thread-3 identical 73 lines
D/ServerMain: while
D/FirstFragment: onDestroyView
D/ServerMain: while
...same while log until i send a message from the server...
I/chatty: uid=10122(com.example.androidapp) Thread-3 identical 1686 lines
D/ServerMain: while
D/ServerMain read:: in:8-true
I tried many thing but can't figure a solution, and i know my socket correctly receive the message because if i close the C++ server, the android socket finaly read the message.
(i'm planning to send image buffer through the socket in the future)

Answer 1

Ok i found the solution, the only for me to have a non-blocking read is to use a CharArray in the read function, every other function end-up in a infinite loop (even read() without argument)
Here the code that work now:
fun listenForServerMessage() {
//var reader = Scanner(singleton_ServerInfos.clientSocket.getInputStream())
Log.d("ServerMain ", "listenForServerMessage")
Thread(Runnable {
try {
Log.d("ServerMain ","letsgo:"+singleton_ServerInfos.end);
var bufReader = BufferedReader(InputStreamReader (singleton_ServerInfos.clientSocket.getInputStream()))
while (singleton_ServerInfos.end!=true) {
Log.d("ServerMain ", "while")
var nbr = singleton_ServerInfos.clientSocket.getInputStream().available()
if (nbr != 0) {
Log.d("ServerMain read: ", "in:"+nbr+"-"+bufReader.ready());
var mchar : CharArray = CharArray(nbr)
if (bufReader.ready()) {
bufReader.read(mchar)
Log.d("ServerMain read: ", "!!!:" +mchar.concatToString());
}
else
Log.d("ServerMain ", "fail")
}
}
}
catch (e: Exception) {
Log.d("ServerMain: ", "exception closing.")
}
}).start()
}
I will now implement the logic of how i wanted to use my server, if i found a cause of this problem, i will edit my answer.