TCP level communication with C# .NET

.NET has the necessary objects to enable TCP-level messaging in the System.Net.Sockets namespace. The key objects to build an extremely simple TCP server are TcpListener and Socket. The TCP client and server can communicate in a stream-like fashion over the network using the NetworkStream object.

Here’s an example of how a TCP server can ingest the message of a single client:

static void Main(string[] args)
	IPAddress localhost = IPAddress.Parse("");
	TcpListener tcpListener = new TcpListener(localhost, 42000);

	Socket tcpClient = tcpListener.AcceptSocket();
	int bytesRead = 0;
	StringBuilder messageBuilder = new StringBuilder();
	using (NetworkStream ns = new NetworkStream(tcpClient))
		int messageChunkSize = 10;				
			byte[] chunks = new byte[messageChunkSize];
			bytesRead = ns.Read(chunks, 0, chunks.Length);
		while (bytesRead != 0);


	Console.WriteLine("Main done...");

We declare a TCP listener on port 42000 on localhost. You might need to adjust the port number of it’s in use on your machine. We then start the listener and call the AcceptSocket method which will block code execution until a client joins. Then as soon as the client joins we read their message in chunks of 10 bytes and append each chunk to a string builder. We repeat this loop until the size of the received byte array is 0, i.e. there’s nothing else to read from the network stream.

You can put the above code in a C# console application. We’ll see in the post on the client side how a client can send a message to this listener.

The client code is even simpler:

static void Main(string[] args)
	TcpClient tcpClient = new TcpClient("localHost", 42000);
	using (NetworkStream ns = tcpClient.GetStream())
		using (BufferedStream bs = new BufferedStream(ns))
			byte[] messageBytesToSend = Encoding.UTF8.GetBytes("This is a very serious message from the client over TCP.");
			bs.Write(messageBytesToSend, 0, messageBytesToSend.Length);

	Console.WriteLine("Main done...");

We connect to localhost port number 42000, i.e. the address we set up in the post on the server side of the communication. We then use a NetworkStream object wrapped within a buffered stream to send a message to the TCP listener. We convert the string into a byte array and send it over the network.

Put the above code into another C# console application. Start the TCP listener console app first and then run the client. The listener should be able to read the message from the client:

TCP communication basics

View the list of posts on Messaging here.


About Andras Nemes
I'm a .NET/Java developer living and working in Stockholm, Sweden.

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