Multi-Client Chat and file transfer in linux - server

Question

\I want to make a socket application that will run on Linux and provide multiple messaging and file transfer. Can you share sample code? Can you help me i am a second year computer engineering student?
I found a similar code in my research, but I cannot connect to my linux server from different computers.I learned this code from github #HondaPL.
This is client codes
using System;
using System.Net;
using System.Net.Sockets;
using System.Text;
using System.Threading;
using System.Collections.Generic;
using MessengerLogic;
using System.IO;
namespace Messenger
{
public class Connection
{
public static int BufferSize = 1024;
public static string nick;
public static IPAddress ip = IPAddress.Parse("-.-.-.-");
public static int port = 1234;
public static TcpClient client = new TcpClient();
public static List<string> users = new List<string>();
public static bool isEnd = false;
public static string[] fromServer = new string[30];
public void Connect(string nickname)
{
nick = nickname;
client.Connect(ip, port);
nickname += "$Welcome$";
byte[] buffer = Encoding.ASCII.GetBytes(nickname);
NetworkStream ns = client.GetStream();
Console.WriteLine(nickname);
ns.Write(buffer, 0, buffer.Length);
Thread thread = new Thread(o => ReceiveData((TcpClient)o));
thread.Start(client);
}
static void ReceiveData(TcpClient client)
{
NetworkStream ns = client.GetStream();
byte[] receivedBytes = new byte[1024];
int byte_count;
StringParser parser = new StringParser();
while ((byte_count = ns.Read(receivedBytes, 0, receivedBytes.Length)) > 0)
{
fromServer = new string[30];
users.Clear();
string message = Encoding.ASCII.GetString(receivedBytes, 0, byte_count);
fromServer = parser.Parser(message);
if (fromServer[0] == "List")
{
for (int i = 1; i < fromServer.Length; i++)
{
users.Add(fromServer[i]);
}
isEnd = true;
}
else
{
Console.WriteLine(message);
Console.WriteLine(fromServer[0]);
Console.WriteLine(fromServer[1]);
FrmOnlineUsers.frm.AssignValues(fromServer[0], fromServer[1]);
FrmOnlineUsers.frm.MessageFromClient();
}
}
}
public List<string> Refresh()
{
NetworkStream ns = client.GetStream();
string temp = nick;
temp += "$List$";
byte[] buffer = ASCIIEncoding.ASCII.GetBytes(temp);
ns.Write(buffer, 0, buffer.Length);
while (!isEnd)
{
}
isEnd = false;
return users;
}
public void SendMessage(string who, string msg)
{
NetworkStream ns = client.GetStream();
string temp = $"{who}$Message${msg}$";
byte[] buffer = ASCIIEncoding.ASCII.GetBytes(temp);
ns.Write(buffer, 0, buffer.Length);
}
public void FileSend(string filepath, string nick, string fileName)
{
NetworkStream ns = client.GetStream();
FileStream fs = new FileStream(filepath, FileMode.Open, FileAccess.Read);
byte[] bytesToSend = new byte[fs.Length];
int numBytesRead = fs.Read(bytesToSend, 0, bytesToSend.Length);
int totalBytes = 0;
//Tutaj trzeba dodać, aby pobierał nazwę pliku
string temp = $"{nick}$File${fileName}${fs.Length}";
byte[] buffer = ASCIIEncoding.ASCII.GetBytes(temp);
ns.Write(buffer, 0, buffer.Length);
Thread.Sleep(1000);
for (int i = 0; i <= fs.Length / BufferSize; i++)
{
if (fs.Length - (i * BufferSize) > BufferSize)
{
ns.Write(bytesToSend, i * BufferSize,
BufferSize);
totalBytes += BufferSize;
}
else
{
ns.Write(bytesToSend, i * BufferSize,
(int)fs.Length - (i * BufferSize));
totalBytes += (int)fs.Length - (i * BufferSize);
}
}
fs.Close();
}
}
}