Simple TCP/IP Echo Server & Client Application in C#

1. TCP Server

The server’s job is to set up an endpoint for clients to connect to and passively wait for connections.

The typical TCP server goes through two steps:

1. Construct a TcpListener instance, specifying the local address and port, and call the Start() method.

This socket listens for incoming connections on the specified port.

2. Repeatedly:
■ Call the AcceptTcpClient() method of TcpListener to get the next incoming
   client connection. Upon establishment of a new client connection, an instance of
   TcpClient for the new connection is created and returned by the AcceptTcp-
   Client() call.
■ Communicate with the client using the Read() and Write() methods of TcpClient’s
   NetworkStream.
■ Close the new client socket connection and stream using the Close() methods of
   NetworkStream and TcpClient.

TcpEchoServer.cs

using System; // For Console, Int32, ArgumentException, Environment

using System.Net; // For IPAddress

using System.Net.Sockets; // For TcpListener, TcpClient

class TcpEchoServer

{

    private const int BUFSIZE = ; // Size of receive buffer

    static void Main(string[] args)

    {

        if (args.Length > ) // Test for correct # of args

            throw new ArgumentException("Parameters: [<Port>]");

        int servPort = (args.Length == ) ? Int32.Parse(args[]): ;

        TcpListener listener = null;

        try

        {

            // Create a TCPListener to accept client connections

            listener = new TcpListener(IPAddress.Any, servPort);

            listener.Start();

        }

        catch (SocketException se)

        {

            Console.WriteLine(se.ErrorCode + ": " + se.Message);

            Environment.Exit(se.ErrorCode);

        }

        byte[] rcvBuffer = new byte[BUFSIZE]; // Receive buffer

        int bytesRcvd; // Received byte count

        for (;;)

        {

            // Run forever, accepting and servicing connections

            TcpClient client = null;

            NetworkStream netStream = null;

            try

            {

                client = listener.AcceptTcpClient(); // Get client connection

                netStream = client.GetStream();

                Console.Write("Handling client - ");

                // Receive until client closes connection, indicated by 0 return value

                int totalBytesEchoed = ;

                while ((bytesRcvd = netStream.Read(rcvBuffer, , rcvBuffer.Length)) > )

                {

                    netStream.Write(rcvBuffer, , bytesRcvd);

                    totalBytesEchoed += bytesRcvd;

                }

                Console.WriteLine("echoed {0} bytes.", totalBytesEchoed);

                // Close the stream and socket. We are done with this client!

                netStream.Close();

                client.Close();

            }

            catch (Exception e)

            {

                Console.WriteLine(e.Message);

                netStream.Close();

            }

        }

    }

}

The TcpListener listens for client connection requests on the port specified in the constructor.

Be careful to use a port that is not in use by another application, or a SocketException will be thrown.

Loop forever, iteratively handling incoming connections.

Receive and repeat data until the client closes.

Close the client stream and socket.

TcpEchoClient.cs

using System; // For String, Int32, Console, ArgumentException

using System.Text; // For Encoding

using System.IO; // For IOException

using System.Net.Sockets; // For TcpClient, NetworkStream, SocketException

class TcpEchoClient

{

    static void Main(string[] args)

    {

        if ((args.Length < ) || (args.Length > ))

        {

            // Test for correct # of args

            throw new ArgumentException("Parameters: <Server> <Word> [<Port>]");

        }

        String server = args[]; // Server name or IP address

        // Convert input String to bytes

        byte[] byteBuffer = Encoding.ASCII.GetBytes(args[]);

        // Use port argument if supplied, otherwise default to 7

        int servPort = (args.Length == ) ? Int32.Parse(args[]) : ;

        TcpClient client = null;

        NetworkStream netStream = null;

        try

        {

            // Create socket that is connected to server on specified port

            client = new TcpClient(server, servPort);

            Console.WriteLine("Connected to server... sending echo string");

            netStream = client.GetStream();

            // Send the encoded string to the server

            netStream.Write(byteBuffer, , byteBuffer.Length);

            Console.WriteLine("Sent {0} bytes to server...", byteBuffer.Length);

            int totalBytesRcvd = ; // Total bytes received so far

            int bytesRcvd = ; // Bytes received in last read

            // Receive the same string back from the server

            while (totalBytesRcvd < byteBuffer.Length)

            {

                if ((bytesRcvd = netStream.Read(byteBuffer, totalBytesRcvd, byteBuffer.Length - totalBytesRcvd)) == )

                {

                    Console.WriteLine("Connection closed prematurely.");

                    break;

                }

                totalBytesRcvd += bytesRcvd;

            }

            Console.WriteLine("Received {0} bytes from server: {1}", totalBytesRcvd,

            Encoding.ASCII.GetString(byteBuffer, , totalBytesRcvd));

        }

        catch (Exception e)

        {

            Console.WriteLine(e.Message);

        }

        finally

        {

            netStream.Close();

            client.Close();

        }

    }

}

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Simple TCP/IP Echo Server & Client Application in C#

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