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System.InvalidOperationException: 'The operation is not allowed on non-connected sockets.'

This is my form
https://i.stack.imgur.com/M7fuy.png
This is my code
using System;
using System.Collections.Generic;
using System.ComponentModel;
using System.Data;
using System.Drawing;
using System.Linq;
using System.Text;
using System.Threading.Tasks;
using System.Windows.Forms;
using System.Net.Sockets;
namespace WindowsApplication1
{
public partial class Form1 : Form
{
System.Net.Sockets.TcpClient clientSocket = new
System.Net.Sockets.TcpClient();
//NetworkStream serverStream = default(NetworkStream);
//string readData = null;
public Form1()
{
InitializeComponent();
}
private void Form1_Load(object sender, EventArgs e)
{
msg("Client Started");
clientSocket.Connect("192.168.0.167", 5000);
label1.Text = "Client Socket Program - Server Connected ...";
}
private void button1_Click(object sender, EventArgs e)
{
NetworkStream serverStream = clientSocket.GetStream();
byte[] outStream = System.Text.Encoding.ASCII.GetBytes(textBox2.Text + "$");
serverStream.Write(outStream, 0, outStream.Length);
serverStream.Flush();
byte[] inStream = new byte[10025];
serverStream.Read(inStream, 0, (int)clientSocket.ReceiveBufferSize);
string returndata = System.Text.Encoding.ASCII.GetString(inStream);
msg(returndata);
textBox2.Text = "";
textBox2.Focus();
}
public void msg(string mesg)
{
textBox1.Text = textBox1.Text + Environment.NewLine + " >> " + mesg;
}
}
}
when I click the start button in the code i am getting this error to connect to the server. please guide me how to get rid of this error and connect to the server instead.
https://i.stack.imgur.com/wDSCI.png

Multithreaded TCP server and client

I just search around before asking this problem, looking for example of TCP Server and Client in C#.
I found this link, I just used the given code by the link but unfortunately there's a problem and I'm stuck!
The following code is the complete code for server (console):
using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Net.Sockets;
namespace TCP_Server_Console
{
class Program
{
static void Main(string[] args)
{
TcpListener serverSocket = new TcpListener(8888);
int requestCount = 0;
TcpClient clientSocket = default(TcpClient);
serverSocket.Start();
Console.WriteLine(" >> Server Started");
clientSocket = serverSocket.AcceptTcpClient();
Console.WriteLine(" >> Accept connection from client");
requestCount = 0;
while ((true))
{
try
{
requestCount = requestCount + 1;
NetworkStream networkStream = clientSocket.GetStream();
byte[] bytesFrom = new byte[10025];
networkStream.Read(bytesFrom, 0, (int)clientSocket.ReceiveBufferSize);
string dataFromClient = System.Text.Encoding.ASCII.GetString(bytesFrom);
dataFromClient = dataFromClient.Substring(0, dataFromClient.IndexOf("$"));
Console.WriteLine(" >> Data from client - " + dataFromClient);
string serverResponse = "Last Message from client" + dataFromClient;
Byte[] sendBytes = Encoding.ASCII.GetBytes(serverResponse);
networkStream.Write(sendBytes, 0, sendBytes.Length);
networkStream.Flush();
Console.WriteLine(" >> " + serverResponse);
}
catch (Exception ex)
{
Console.WriteLine(ex.ToString());
}
}
clientSocket.Close();
serverSocket.Stop();
Console.WriteLine(" >> exit");
Console.ReadLine();
}
}
}
/*HandleClient Class */
using System;
using System.Collections.Generic;
using System.Linq;
using System.Net.Sockets;
using System.Text;
using System.Threading;
using System.Threading.Tasks;
namespace TCP_Server_Console
{
public class HandleClient
{
TcpClient clientSocket;
string clNo;
public void startClient(TcpClient inClientSocket, string clineNo)
{
this.clientSocket = inClientSocket;
this.clNo = clineNo;
Thread ctThread = new Thread(doChat);
ctThread.Start();
}
private void doChat()
{
int requestCount = 0;
byte[] bytesFrom = new byte[10025];
string dataFromClient = null;
Byte[] sendBytes = null;
string serverResponse = null;
string rCount = null;
requestCount = 0;
while ((true))
{
try
{
requestCount = requestCount + 1;
NetworkStream networkStream = clientSocket.GetStream();
networkStream.Read(bytesFrom, 0, (int)clientSocket.ReceiveBufferSize);
dataFromClient = System.Text.Encoding.ASCII.GetString(bytesFrom);
dataFromClient = dataFromClient.Substring(0, dataFromClient.IndexOf("$"));
Console.WriteLine(" >> " + "From client-" + clNo + dataFromClient);
rCount = Convert.ToString(requestCount);
serverResponse = "Server to clinet(" + clNo + ") " + rCount;
sendBytes = Encoding.ASCII.GetBytes(serverResponse);
networkStream.Write(sendBytes, 0, sendBytes.Length);
networkStream.Flush();
Console.WriteLine(" >> " + serverResponse);
}
catch (Exception ex)
{
Console.WriteLine(" >> " + ex.ToString());
}
}
}
}
}
The following code is the complete code for client (Windows Forms):
using System;
using System.Collections.Generic;
using System.ComponentModel;
using System.Data;
using System.Drawing;
using System.Linq;
using System.Net.Sockets;
using System.Text;
using System.Threading.Tasks;
using System.Windows.Forms;
namespace TCP_Client_Sample
{
public partial class Form1 : Form
{
System.Net.Sockets.TcpClient clientSocket = new System.Net.Sockets.TcpClient();
NetworkStream serverStream;
public Form1()
{
InitializeComponent();
}
private void Form1_Load(object sender, EventArgs e)
{
label_status.Text = "Client Started, Connecting...";
try
{
clientSocket.Connect("127.0.0.1", 8888);
if (clientSocket.Connected)
{
label_status.Text = "Connected";
label_status.ForeColor = Color.Green;
}
}
catch (Exception xe)
{
MessageBox.Show("OOPS!!! SERVER MUST BE STARTED FIRST! \n\n" + xe.ToString());
}
}
//Function to Send Message to Server (On Button Click)
private void btn_send_Click(object sender, EventArgs e)
{
try
{
NetworkStream serverStream = clientSocket.GetStream();
byte[] outStream = System.Text.Encoding.ASCII.GetBytes("Message From Client$");
serverStream.Write(outStream, 0, outStream.Length);
serverStream.Flush();
byte[] inStream = new byte[10025];
serverStream.Read(inStream, 0, (int)clientSocket.ReceiveBufferSize);
string returnData = System.Text.Encoding.ASCII.GetString(inStream);
chatBox.AppendText(">> Server: " + returnData);
}
catch (Exception ex)
{
MessageBox.Show("Unable to Send Data: " + ex);
}
}
}
}
Every time I execute the code of server it works and started. But when I execute the client, the server throws an error
Specified Argument was out of the range
Here is the complete error:
System.ArgumentOutOfRangeException: Specified argument was out of the range of valid values.
Parameter name: size
at System.Net.Sockets.NetworkStream.Read(Byte[] buffer, Int32 offset, Int32 size)
at TCP_Server_Console.Program.Main(String[] args) in C:\Users\user\Documents\Visual Studio 2015\Projects\TCP_Server_Console\TCP_Server_Console\Program.cs:line 50
I'm also getting the same error every time I click the btn_send from client form.
I am stuck here and I don't know what's the problem since this is the first time I'm work with TCP Socket.
Can anynone help me?

The problem lies in that your code used two different sizes
byte[] inStream = new byte[10025];
serverStream.Read(inStream, 0, (int)clientSocket.ReceiveBufferSize);
In this. Youve reserved space for 10025 bytes, but RecieveBufferSize maybe another size, bigger or smaller, but if bigger, it will error.
If you make the read call call the same length as your byte array you wont have your problem.

byte[] inStream = new byte[10025];
byte[] tStream = new byte[(int)clientSocket.ReceiveBufferSize];
serverStream.Read(tStream, 0, (int)clientSocket.ReceiveBufferSize);
Would be the quick easy fix to ensure that the byte buffer its reading into will always be the correct size needed.

sending big file with socket to server c#

I'm trying to send a file about 250 kb to server but i have a corruption and it seemd that tottaly transfered some bytes only. The flow of command is
Write to stream: Send\r\n
Write to stream: FileName\r\n
Write to stream: FileData \r\n
Close the connection
Here is the code:
TcpClient sendClient = new TcpClient(serverName, port);
SslStream sendStream = new SslStream(sendClient.GetStream(), false, new RemoteCertificateValidationCallback(ValidateServerCertificate), null);
try
{
sendStream.AuthenticateAsClient(serverName, null, SslProtocols.Ssl2, true);
sendStream.Write(Encoding.UTF8.GetBytes("Login\r\n" + username + "\r\n" + password + "\r\n"));
sendStream.Flush();
int bytesResp = -1;
byte[] buffer = new byte[1026];
bytesResp = sendStream.Read(buffer, 0, buffer.Length);
string response = Encoding.UTF8.GetString(buffer, 0, bytesResp);
if (response.Trim() == "OK")
{
byte[] fileNameByte = Encoding.UTF8.GetBytes(fileName + "\r\n");
byte[] fileData = File.ReadAllBytes(filePath);
byte[] newLine = Encoding.ASCII.GetBytes("\r\n");
byte[] clientData = new byte[4 + Encoding.ASCII.GetBytes("Send\r\n").Length + fileNameByte.Length + fileData.Length+newLine.Length];
byte[] fileNameLen = BitConverter.GetBytes(fileNameByte.Length);
byte[] send = Encoding.ASCII.GetBytes("Send\r\n");
send.CopyTo(clientData, 0);
fileNameLen.CopyTo(clientData, 4 + send.Length);
fileNameByte.CopyTo(clientData, send.Length);
fileData.CopyTo(clientData, 4 + fileNameByte.Length + send.Length);
newLine.CopyTo(clientData, 4+ fileNameByte.Length + send.Length + fileData.Length);
MessageBox.Show(clientData.Length.ToString());
sendStream.Write(clientData, 0, clientData.Length);
sendStream.Flush();
sendStream.Write(Encoding.UTF8.GetBytes("Quit\r\n"));
sendClient.Close();
}
}
catch (Exception ex)
{
MessageBox.Show(ex.ToString());
}
Does anybody have an idea please?

You haven't told us about the other end of the connection, so this answer is partially speculative...
BitConverter.GetBytes(fileNameByte.Length); is likely to be a little-endian conversion.
Almost all network encoding will be big-endian, so this is a strong candidate for the failure.
I suggest you use the EndianBitConverter.Big converter from Jon Skeet's miscutil to get the proper encoding order.

I send file up to 1GB with this code
Server Code
using System;
using System.Linq;
using System.Text;
using System.Windows.Forms;
using System.Threading;
using System.Net.Sockets;
using System.Net;
using System.IO;
namespace Server_FileSend
{
public partial class Form1 : Form
{
Socket Server = null;
Socket Client = null;
Thread trStart;
Thread trRecive;
const int sizeByte = 1024;
public Form1()
{
InitializeComponent();
}
private void ReciveFile()
{
while (true)
{
try
{
byte[] b = new byte[sizeByte];
int rec = 1;
int vp = 0;
rec = Client.Receive(b);
int index;
for (index = 0; index < b.Length; index++)
if (b[index] == 63)
break;
string[] fInfo = Encoding.UTF8.GetString(b.Take(index).ToArray()).Split(':');
this.Invoke((MethodInvoker)delegate
{
progressBar1.Maximum = int.Parse(fInfo[0]);
});
string path = Application.StartupPath + "\\Downloads\\";
if (!Directory.Exists(path))
Directory.CreateDirectory(path);
FileStream fs = new FileStream(path + fInfo[1], FileMode.Append, FileAccess.Write);
string strEnd;
while (true)
{
rec = Client.Receive(b);
vp = vp + rec;
strEnd = ((char)b[0]).ToString() + ((char)b[1]).ToString() + ((char)b[2]).ToString() + ((char)b[3]).ToString() + ((char)b[4]).ToString() + ((char)b[5]).ToString();
if (strEnd == "!endf!")
{
fs.Flush();
fs.Close();
MessageBox.Show("Receive File " + ((float)(float.Parse(fInfo[0]) / 1024)).ToString() + " KB");
break;
}
fs.Write(b, 0, rec);
this.Invoke((MethodInvoker)delegate
{
progressBar1.Value = vp;
});
}
}
catch (Exception ex)
{
MessageBox.Show(ex.Message);
Form1_FormClosing(null, null);
}
}
}
private void StartSocket()
{
Server.Listen(1);
Client = Server.Accept();
trRecive = new Thread(new ThreadStart(ReciveFile));
trRecive.Start();
}
private void Form1_Load(object sender, EventArgs e)
{
Server = new Socket(AddressFamily.InterNetwork, SocketType.Stream, ProtocolType.IP);
IPEndPoint IP = new IPEndPoint(IPAddress.Any, 5050);
Server.Bind(IP);
trStart = new Thread(new ThreadStart(StartSocket));
trStart.Start();
}
private void Form1_FormClosing(object sender, FormClosingEventArgs e)
{
try
{
trRecive.Abort();
trStart.Abort();
Environment.Exit(Environment.ExitCode);
}
catch (Exception)
{
Environment.Exit(Environment.ExitCode);
}
}
}
}
Client Code
using System;
using System.IO;
using System.Net;
using System.Net.Sockets;
using System.Text;
using System.Threading;
using System.Windows.Forms;
namespace Clienf_fileSend
{
public partial class Form1 : Form
{
Socket Client = null;
Thread trRecive;
const int sizeByte = 1024;
public Form1()
{
InitializeComponent();
}
private void button1_Click(object sender, EventArgs e)
{
try
{
Client = new Socket(AddressFamily.InterNetwork, SocketType.Stream, ProtocolType.IP);
IPEndPoint IP = new IPEndPoint(IPAddress.Parse(textBox1.Text), 5050);
Client.Connect(IP);
button1.Enabled = false;
button2.Enabled = true;
}
catch (Exception ex)
{
MessageBox.Show(ex.Message);
}
}
private void SendFile(object FName)
{
try
{
FileInfo inf = new FileInfo((string)FName);
progressBar1.Invoke((MethodInvoker)delegate
{
progressBar1.Maximum = (int)inf.Length;
progressBar1.Value = 0;
});
FileStream f = new FileStream((string)FName, FileMode.Open);
byte[] fsize = Encoding.UTF8.GetBytes(inf.Length.ToString() + ":");
byte[] fname = Encoding.UTF8.GetBytes(inf.Name + "?");
byte[] fInfo = new byte[sizeByte];
fsize.CopyTo(fInfo, 0);
fname.CopyTo(fInfo, fsize.Length);
Client.Send(fInfo);
if (sizeByte> f.Length)
{
byte[] b = new byte[f.Length];
f.Seek(0, SeekOrigin.Begin);
f.Read(b, 0, (int)f.Length);
Client.Send(b);
}
else
{
for (int i = 0; i < (f.Length - sizeByte); i = i + sizeByte)
{
byte[] b = new byte[sizeByte];
f.Seek(i, SeekOrigin.Begin);
f.Read(b, 0, b.Length);
Client.Send(b);
progressBar1.Invoke((MethodInvoker)delegate
{
progressBar1.Value = i;
});
if (i + sizeByte >= f.Length - sizeByte)
{
progressBar1.Invoke((MethodInvoker)delegate
{
progressBar1.Value = (int)f.Length;
});
int ind = (int)f.Length - (i + sizeByte);
byte[] ed = new byte[ind];
f.Seek(i + sizeByte, SeekOrigin.Begin);
f.Read(ed, 0, ed.Length);
Client.Send(ed);
}
}
}
f.Close();
Thread.Sleep(1000);
Client.Send(Encoding.UTF8.GetBytes("!endf!"));
Thread.Sleep(1000);
MessageBox.Show("Send File " + ((float)inf.Length / 1024).ToString() + " KB");
}
catch (Exception ex)
{
MessageBox.Show(ex.Message);
}
}
private void button2_Click(object sender, EventArgs e)
{
OpenFileDialog fdl = new OpenFileDialog();
if (fdl.ShowDialog() == DialogResult.OK)
{
trRecive = new Thread(new ParameterizedThreadStart(SendFile));
trRecive.Start(fdl.FileName);
}
fdl = null;
}
private void Form1_FormClosing(object sender, FormClosingEventArgs e)
{
try
{
trRecive.Abort();
Environment.Exit(Environment.ExitCode);
}
catch (Exception)
{
Environment.Exit(Environment.ExitCode);
}
}
}
}

How can I encrypt my message when sending to the server?

I would like to encrypt my message when sending to the server from client, how can I do it?
Client
using System;
using System.Collections.Generic;
using System.ComponentModel;
using System.Data;
using System.Drawing;
using System.Linq;
using System.Text;
using System.Windows.Forms;
using System.Net.Sockets;
using System.Threading;
namespace SocketClient
{
public partial class SocketClient : Form
{
System.Net.Sockets.TcpClient clientSocket = new System.Net.Sockets.TcpClient();
NetworkStream serverStream = default(NetworkStream);
string readData = null;
public SocketClient()
{
InitializeComponent();
}
private void getMessage()
{
while (true)
{
serverStream = clientSocket.GetStream();
int buffSize = 0;
byte[] inStream = new byte[10025];
buffSize = clientSocket.ReceiveBufferSize;
serverStream.Read(inStream, 0, buffSize);
string returndata = System.Text.Encoding.ASCII.GetString(inStream);
readData = "" + returndata;
msg();
}
}
private void msg()
{
if (this.InvokeRequired)
this.Invoke(new MethodInvoker(msg));
else
textDisplay.Text = textDisplay.Text + Environment.NewLine + " >> " + readData;
}
private void buttonConnect_Click(object sender, EventArgs e)
{
readData = "Connected to NYP Chat Server ...";
msg();
//clientSocket.Connect("127.0.0.1", 8888);
clientSocket.Connect(textIP.Text, Convert.ToInt32(textPort.Text));
serverStream = clientSocket.GetStream();
byte[] outStream = System.Text.Encoding.ASCII.GetBytes(textName.Text + "$");
serverStream.Write(outStream, 0, outStream.Length);
serverStream.Flush();
Thread ctThread = new Thread(getMessage);
ctThread.Start();
}
private void buttonSend_Click(object sender, EventArgs e)
{
// Show msg box if no server is connected
if (serverStream == null)
{
MessageBox.Show("Please connect to a server first!");
return;
}
// Send text
byte[] outStream = System.Text.Encoding.ASCII.GetBytes(textSend.Text + "$");
serverStream.Write(outStream, 0, outStream.Length);
serverStream.Flush();
// Clear text
textSend.Text = "";
}
private void textDisplay_TextChanged(object sender, EventArgs e)
{
textDisplay.SelectionStart = textDisplay.Text.Length;
textDisplay.ScrollToCaret();
textDisplay.Refresh();
}
private void textSend_TextChanged(object sender, EventArgs e)
{
buttonSend.Enabled = !string.IsNullOrEmpty(textSend.Text);
}
}
}
server
using System;
using System.Threading;
using System.Net.Sockets;
using System.Text;
using System.Collections;
namespace ConsoleApplication1
{
class Program
{
public static Hashtable clientsList = new Hashtable();
static void Main(string[] args)
{
//TcpListener serverSocket = new TcpListener(portFromAppConfig);
TcpListener serverSocket = new TcpListener(9999);
TcpClient clientSocket = default(TcpClient);
int counter = 0;
serverSocket.Start();
Console.WriteLine("Welcome to NYP Chat Server ");
counter = 0;
while ((true))
{
counter += 1;
clientSocket = serverSocket.AcceptTcpClient();
byte[] bytesFrom = new byte[10025];
string dataFromClient = null;
NetworkStream networkStream = clientSocket.GetStream();
networkStream.Read(bytesFrom, 0, (int)clientSocket.ReceiveBufferSize);
dataFromClient = System.Text.Encoding.ASCII.GetString(bytesFrom);
dataFromClient = dataFromClient.Substring(0, dataFromClient.IndexOf("$"));
clientsList.Add(dataFromClient, clientSocket);
broadcast(dataFromClient + " Connected ", dataFromClient, false);
Console.WriteLine(dataFromClient + " has join the chat room ");
handleClient client = new handleClient();
client.startClient(clientSocket, dataFromClient, clientsList);
}
clientSocket.Close();
serverSocket.Stop();
Console.WriteLine("exit");
Console.ReadLine();
}
public static void broadcast(string msg, string uName, bool flag)
{
foreach (DictionaryEntry Item in clientsList)
{
TcpClient broadcastSocket;
broadcastSocket = (TcpClient)Item.Value;
NetworkStream broadcastStream = broadcastSocket.GetStream();
Byte[] broadcastBytes = null;
if (flag == true)
{
broadcastBytes = Encoding.ASCII.GetBytes(uName + " says : " + msg);
}
else
{
broadcastBytes = Encoding.ASCII.GetBytes(msg);
}
broadcastStream.Write(broadcastBytes, 0, broadcastBytes.Length);
broadcastStream.Flush();
}
} //end broadcast function
}//end Main class
public class handleClient
{
TcpClient clientSocket;
string clNo;
Hashtable clientsList;
public void startClient(TcpClient inClientSocket, string clineNo, Hashtable cList)
{
this.clientSocket = inClientSocket;
this.clNo = clineNo;
this.clientsList = cList;
Thread ctThread = new Thread(doChat);
ctThread.Start();
}
private void doChat()
{
int requestCount = 0;
byte[] bytesFrom = new byte[10025];
string dataFromClient = null;
Byte[] sendBytes = null;
string serverResponse = null;
string rCount = null;
requestCount = 0;
while ((true))
{
try
{
requestCount = requestCount + 1;
NetworkStream networkStream = clientSocket.GetStream();
networkStream.Read(bytesFrom, 0, (int)clientSocket.ReceiveBufferSize);
dataFromClient = System.Text.Encoding.ASCII.GetString(bytesFrom);
dataFromClient = dataFromClient.Substring(0, dataFromClient.IndexOf("$"));
Console.WriteLine("From client - " + clNo + " : " + dataFromClient);
rCount = Convert.ToString(requestCount);
Program.broadcast(dataFromClient, clNo, true);
}
catch (Exception ex)
{
Console.WriteLine(ex.ToString());
}
}//end while
}//end doChat
} //end class handleClient
}//end namespace

Absolute simplest way is to rip all the code you wrote and just use WCF.
Next simplest way is to use a secure stream instead of the raw Network Stream, like SslStream or NegotiateStream. There a full blown sample at Secure Streams Sample that shows both the client and the server for NTLM/Kerberos and SChannel protocols (aka SSL/TLS).
One thing you should absolutely not do is write your own encryption. Encrypting messages is trivial and you'll find a myriad samples on the web. But creating a key exchange protocol so you actually have something to encrypt with is one of the hardest tasks in crypto. Use one of the industry acknowledged key exchange schemes like Kerberos or SSL/TLS, and these are already implemented in the two stream classes I linked.

C# provides a namespace for cryptography System.Security.Cryptography... for start you could check that out... Or try to implement a cryptography algorithm like Vernamm which is the simplest and easiest to implement. Or if you want to be fully secured you should use both the System.Security.Cryptography namespace the System.Security.Cryptography.X509Certificates namespace.

I would like the send button to be inactive until the user key in something in the textbox. How can I do this?

using System;
using System.Collections.Generic;
using System.ComponentModel;
using System.Data;
using System.Drawing;
using System.Linq;
using System.Text;
using System.Windows.Forms;
using System.Net.Sockets;
using System.Threading;
namespace SocketClient
{
public partial class SocketClient : Form
{
System.Net.Sockets.TcpClient clientSocket = new System.Net.Sockets.TcpClient();
NetworkStream serverStream = default(NetworkStream);
string readData = null;
public SocketClient()
{
InitializeComponent();
}
private void getMessage()
{
while (true)
{
serverStream = clientSocket.GetStream();
int buffSize = 0;
byte[] inStream = new byte[10025];
buffSize = clientSocket.ReceiveBufferSize;
serverStream.Read(inStream, 0, buffSize);
string returndata = System.Text.Encoding.ASCII.GetString(inStream);
readData = "" + returndata;
msg();
}
}
private void msg()
{
if (this.InvokeRequired)
this.Invoke(new MethodInvoker(msg));
else
textDisplay.Text = textDisplay.Text + Environment.NewLine + " >> " + readData;
}
private void buttonConnect_Click(object sender, EventArgs e)
{
readData = "Conected to NYP Chat Server ...";
msg();
clientSocket.Connect("127.0.0.1", 8888);
serverStream = clientSocket.GetStream();
byte[] outStream = System.Text.Encoding.ASCII.GetBytes(textName.Text + "$");
serverStream.Write(outStream, 0, outStream.Length);
serverStream.Flush();
Thread ctThread = new Thread(getMessage);
ctThread.Start();
}
private void buttonSend_Click(object sender, EventArgs e)
{
// send text
byte[] outStream = System.Text.Encoding.ASCII.GetBytes(textSend.Text + "$");
serverStream.Write(outStream, 0, outStream.Length);
serverStream.Flush();
//clear textsend textbox
textSend.Text = "";
}
private void textDisplay_TextChanged(object sender, EventArgs e)
{
textDisplay.SelectionStart = textDisplay.Text.Length;
textDisplay.ScrollToCaret();
textDisplay.Refresh();
}
}
}

Assign this event handler to the TextChanged event of the textbox and set the Enabled property of the button initially to false.
private void textSend_TextChanged(object sender, EventArgs e)
{
buttonSend.Enabled = !string.IsNullOrEmpty(textSend.Text);
}