TCP Client-Server Connection Example | Unity | C# | Bidirectional communication sample: Client can connect to server; Client can send and receive messages: Server accepts clients; Server reads client messages; Server sends messages to client

TCPTestClient.cs

// This work is licensed under the Creative Commons Attribution-ShareAlike 4.0 International License. 
// To view a copy of this license, visit http://creativecommons.org/licenses/by-sa/4.0/ 
// or send a letter to Creative Commons, PO Box 1866, Mountain View, CA 94042, USA.
using System;
using System.Collections;
using System.Collections.Generic;
using System.Net.Sockets;
using System.Text;
using System.Threading;
using UnityEngine;

public class TCPTestClient : MonoBehaviour {  	
	#region private members 	
	private TcpClient socketConnection; 	
	private Thread clientReceiveThread; 	
	#endregion  	
	// Use this for initialization 	
	void Start () {
		ConnectToTcpServer();     
	}  	
	// Update is called once per frame
	void Update () {         
		if (Input.GetKeyDown(KeyCode.Space)) {             
			SendMessage();         
		}     
	}  	
	/// <summary> 	
	/// Setup socket connection. 	
	/// </summary> 	
	private void ConnectToTcpServer () { 		
		try {  			
			clientReceiveThread = new Thread (new ThreadStart(ListenForData)); 			
			clientReceiveThread.IsBackground = true; 			
			clientReceiveThread.Start();  		
		} 		
		catch (Exception e) { 			
			Debug.Log("On client connect exception " + e); 		
		} 	
	}  	
	/// <summary> 	
	/// Runs in background clientReceiveThread; Listens for incomming data. 	
	/// </summary>     
	private void ListenForData() { 		
		try { 			
			socketConnection = new TcpClient("localhost", 8052);  			
			Byte[] bytes = new Byte[1024];             
			while (true) { 				
				// Get a stream object for reading 				
				using (NetworkStream stream = socketConnection.GetStream()) { 					
					int length; 					
					// Read incomming stream into byte arrary. 					
					while ((length = stream.Read(bytes, 0, bytes.Length)) != 0) { 						
						var incommingData = new byte[length]; 						
						Array.Copy(bytes, 0, incommingData, 0, length); 						
						// Convert byte array to string message. 						
						string serverMessage = Encoding.ASCII.GetString(incommingData); 						
						Debug.Log("server message received as: " + serverMessage); 					
					} 				
				} 			
			}         
		}         
		catch (SocketException socketException) {             
			Debug.Log("Socket exception: " + socketException);         
		}     
	}  	
	/// <summary> 	
	/// Send message to server using socket connection. 	
	/// </summary> 	
	private void SendMessage() {         
		if (socketConnection == null) {             
			return;         
		}  		
		try { 			
			// Get a stream object for writing. 			
			NetworkStream stream = socketConnection.GetStream(); 			
			if (stream.CanWrite) {                 
				string clientMessage = "This is a message from one of your clients."; 				
				// Convert string message to byte array.                 
				byte[] clientMessageAsByteArray = Encoding.ASCII.GetBytes(clientMessage); 				
				// Write byte array to socketConnection stream.                 
				stream.Write(clientMessageAsByteArray, 0, clientMessageAsByteArray.Length);                 
				Debug.Log("Client sent his message - should be received by server");             
			}         
		} 		
		catch (SocketException socketException) {             
			Debug.Log("Socket exception: " + socketException);         
		}     
	} 
}

TCPTestServer.cs

// This work is licensed under the Creative Commons Attribution-ShareAlike 4.0 International License. 
// To view a copy of this license, visit http://creativecommons.org/licenses/by-sa/4.0/ 
// or send a letter to Creative Commons, PO Box 1866, Mountain View, CA 94042, USA.
using System;
using System.Collections; 
using System.Collections.Generic; 
using System.Net; 
using System.Net.Sockets; 
using System.Text; 
using System.Threading; 
using UnityEngine;  

public class TCPTestServer : MonoBehaviour {  	
	#region private members 	
	/// <summary> 	
	/// TCPListener to listen for incomming TCP connection 	
	/// requests. 	
	/// </summary> 	
	private TcpListener tcpListener; 
	/// <summary> 
	/// Background thread for TcpServer workload. 	
	/// </summary> 	
	private Thread tcpListenerThread;  	
	/// <summary> 	
	/// Create handle to connected tcp client. 	
	/// </summary> 	
	private TcpClient connectedTcpClient; 	
	#endregion 	
		
	// Use this for initialization
	void Start () { 		
		// Start TcpServer background thread 		
		tcpListenerThread = new Thread (new ThreadStart(ListenForIncommingRequests)); 		
		tcpListenerThread.IsBackground = true; 		
		tcpListenerThread.Start(); 	
	}  	
	
	// Update is called once per frame
	void Update () { 		
		if (Input.GetKeyDown(KeyCode.Space)) {             
			SendMessage();         
		} 	
	}  	
	
	/// <summary> 	
	/// Runs in background TcpServerThread; Handles incomming TcpClient requests 	
	/// </summary> 	
	private void ListenForIncommingRequests () { 		
		try { 			
			// Create listener on localhost port 8052. 			
			tcpListener = new TcpListener(IPAddress.Parse("127.0.0.1"), 8052); 			
			tcpListener.Start();              
			Debug.Log("Server is listening");              
			Byte[] bytes = new Byte[1024];  			
			while (true) { 				
				using (connectedTcpClient = tcpListener.AcceptTcpClient()) { 					
					// Get a stream object for reading 					
					using (NetworkStream stream = connectedTcpClient.GetStream()) { 						
						int length; 						
						// Read incomming stream into byte arrary. 						
						while ((length = stream.Read(bytes, 0, bytes.Length)) != 0) { 							
							var incommingData = new byte[length]; 							
							Array.Copy(bytes, 0, incommingData, 0, length);  							
							// Convert byte array to string message. 							
							string clientMessage = Encoding.ASCII.GetString(incommingData); 							
							Debug.Log("client message received as: " + clientMessage); 						
						} 					
					} 				
				} 			
			} 		
		} 		
		catch (SocketException socketException) { 			
			Debug.Log("SocketException " + socketException.ToString()); 		
		}     
	}  	
	/// <summary> 	
	/// Send message to client using socket connection. 	
	/// </summary> 	
	private void SendMessage() { 		
		if (connectedTcpClient == null) {             
			return;         
		}  		
		
		try { 			
			// Get a stream object for writing. 			
			NetworkStream stream = connectedTcpClient.GetStream(); 			
			if (stream.CanWrite) {                 
				string serverMessage = "This is a message from your server."; 			
				// Convert string message to byte array.                 
				byte[] serverMessageAsByteArray = Encoding.ASCII.GetBytes(serverMessage); 				
				// Write byte array to socketConnection stream.               
				stream.Write(serverMessageAsByteArray, 0, serverMessageAsByteArray.Length);               
				Debug.Log("Server sent his message - should be received by client");           
			}       
		} 		
		catch (SocketException socketException) {             
			Debug.Log("Socket exception: " + socketException);         
		} 	
	} 
}

The tcp port connection is not being freed since the client and server are running a background thread that only gets finished after closing or reloading the Editor (not totally sure about the last one), not after exiting play mode. So in order to reset the connection properly, call Close() on the server and the client, and make sure the threads can finish, adding a different condition inside the while(true) loops

Is while true loop necessary? I found that disposable getstream usage closes that socket, so next iteration of while loop throws exception dur to closed socket.

@ Send message to server
Servers expect an end of line after the text message. In my case a CR. Therefore, the code for the TCP client private void SendMessage() looks like this:
byte[] clientMessageAsByteArray = Encoding.ASCII.GetBytes(clientMessage + “\r”);