Respond to a client using a socket?

Question

I have two basic console apps that communicate "over the network" even though all of the communication takes place on my local machine.

Client code:

public static void Main()
{
    while (true)
    {
        try
        {
            TcpClient client = new TcpClient();

            client.Connect("127.0.0.1", 500);

            Console.WriteLine("Connected.");

            byte[] data = ASCIIEncoding.ASCII.GetBytes(new FeederRequest("test", TableType.Event).GetXmlRequest().ToString());

            Console.WriteLine("Sending data.....");

            using (var stream = client.GetStream())
            {
                stream.Write(data, 0, data.Length);
                stream.Flush();

                Console.WriteLine("Data sent.");
            }

            client.Close();

            Console.ReadLine();
        }
        catch (Exception e)
        {
            Console.WriteLine("Error: " + e.StackTrace);

            Console.ReadLine();
        }
    }
}

Server code:

public static void Main()
{
    try
    {
        IPAddress ipAddress = IPAddress.Parse("127.0.0.1");

        Console.WriteLine("Starting TCP listener...");

        TcpListener listener = new TcpListener(ipAddress, 500);

        listener.Start();

        Console.WriteLine("Server is listening on " + listener.LocalEndpoint);

        while (true)
        {
            Socket client = listener.AcceptSocket();

            Console.WriteLine("\nConnection accepted.");

            var childSocketThread = new Thread(() =>
                {
                    Console.WriteLine("Reading data...\n");

                    byte[] data = new byte[100];
                    int size = client.Receive(data);
                    Console.WriteLine("Recieved data: ");
                    for (int i = 0; i < size; i++)
                        Console.Write(Convert.ToChar(data[i]));

                    //respond to client


                    Console.WriteLine("\n");

                    client.Close();

                    Console.WriteLine("Waiting for a connection...");
                });

            childSocketThread.Start();
        }
    }
    catch (Exception e)
    {
        Console.WriteLine("Error: " + e.StackTrace);
        Console.ReadLine();
    }
}

How can I alter both of these applications so that when the Server has received the data, it responds to the Client with some kind of confirmation?

Thanks in advance!

Answer 1

Here a short example how I would do it:

Server:

class Server
    {
        static void Main(string[] args)
        {
            TcpListener listener = new TcpListener(IPAddress.Any, 1500);
            listener.Start();

            TcpClient client = listener.AcceptTcpClient();

            NetworkStream stream = client.GetStream();

            // Create BinaryWriter for writing to stream
            BinaryWriter binaryWriter = new BinaryWriter(stream);

            // Creating BinaryReader for reading the stream
            BinaryReader binaryReader = new BinaryReader(stream);

            while (true) 
            {
                // Read incoming information
                byte[] data = new byte[16];
                int receivedDataLength = binaryReader.Read(data, 0, data.Length);
                string stringData = Encoding.ASCII.GetString(data, 0, receivedDataLength);

                // Write incoming information to console
                Console.WriteLine("Client: " + stringData);

                // Respond to client
                byte[] respondData = Encoding.ASCII.GetBytes("respond");
                Array.Resize(ref respondData, 16); // Resizing to 16 byte, because in this example all messages have 16 byte to make it easier to understand.
                binaryWriter.Write(respondData, 0, 16);
            }

        }
    }

Client:

class Client
    {
        private static void Main(string[] args)
        {
            Console.WriteLine("Press any key to start Client");
            while (! Console.KeyAvailable)
            {
            }


            TcpClient client = new TcpClient();
            client.Connect("127.0.0.1", 1500);

            NetworkStream networkStream = client.GetStream();

            // Create BinaryWriter for writing to stream
            BinaryWriter binaryWriter = new BinaryWriter(networkStream);

            // Creating BinaryReader for reading the stream
            BinaryReader binaryReader = new BinaryReader(networkStream);

            // Writing "test" to stream
            byte[] writeData = Encoding.ASCII.GetBytes("test");
            Array.Resize(ref writeData, 16); // Resizing to 16 byte, because in this example all messages have 16 byte to make it easier to understand.
            binaryWriter.Write(writeData, 0, 16);

            // Reading response and writing it to console
            byte[] responeBytes = new byte[16];
            binaryReader.Read(responeBytes, 0, 16);
            string response = Encoding.ASCII.GetString(responeBytes);
            Console.WriteLine("Server: " + response);


            while (true)
            {
            }
        }
    }

I hope this helps! ;)

Answer 2

Here's an example of what (I think) you want to do:

    static void Main(string[] args) {
        var server = new Task(Server);
        server.Start();
        System.Threading.Thread.Sleep(10); // give server thread a chance to setup
        try {
            TcpClient client = new TcpClient();
            client.Connect("127.0.0.1", 1500);
            Console.WriteLine("Connected.");
            var data = new byte[100];
            var hello = ASCIIEncoding.ASCII.GetBytes("Hello");
            Console.WriteLine("Sending data.....");
            using (var stream = client.GetStream()) {
                stream.Write(hello, 0, hello.Length);
                stream.Flush();
                Console.WriteLine("Data sent.");
                // You could then read data from server here:
                var returned = stream.Read(data, 0, data.Length);
                var rec = new String(ASCIIEncoding.ASCII.GetChars(data, 0, data.Length));
                rec = rec.TrimEnd('\0');
                if (rec == "How are you?") {
                    var fine  = ASCIIEncoding.ASCII.GetBytes("fine and you?");
                    stream.Write(fine, 0, fine.Length);
                    }
                }
            client.Close();
            Console.ReadLine();
            }
        catch (Exception e) {
            Console.WriteLine("Error: " + e.StackTrace);
            Console.ReadLine();
            }
        }

    public static void Server() {
        try {
            IPAddress ipAddress = IPAddress.Parse("127.0.0.1");
            Console.WriteLine("*Starting TCP listener...");
            TcpListener listener = new TcpListener(ipAddress, 1500); // generally use ports > 1024
            listener.Start();
            Console.WriteLine("*Server is listening on " + listener.LocalEndpoint);
            Console.WriteLine("*Waiting for a connection...");
            while (true) {
                Socket client = listener.AcceptSocket();
                while (client.Connected) {
                    Console.WriteLine("*Connection accepted.");
                    Console.WriteLine("*Reading data...");
                    byte[] data = new byte[100];
                    int size = client.Receive(data);
                    Console.WriteLine("*Recieved data: ");
                    var rec = new String(ASCIIEncoding.ASCII.GetChars(data, 0, size));
                    rec = rec.TrimEnd('\0');
                    Console.WriteLine(rec);
                    if (client.Connected == false) {
                        client.Close();
                        break;
                        }
                    // you would write something back to the client here
                    if (rec == "Hello") {
                        client.Send(ASCIIEncoding.ASCII.GetBytes("How are you?"));
                        }
                    if (rec == "fine and you?") {
                        client.Disconnect(false);
                        }
                    }
                }
            listener.Stop();
            }
        catch (Exception e) {
            Console.WriteLine("Error: " + e.StackTrace);
            Console.ReadLine();
            }
        }
    }

Keep in mind that data sent via sockets can arrive fragmented (in different packets). This doesn't usually happen with the packets are small.

Answer 3

You can perform both Read and Write on the same stream. After you send all the data over, just call stream.Read as in

        using (var stream = client.GetStream())
        {
            stream.Write(data, 0, data.Length);
            stream.Flush();

            Console.WriteLine("Data sent.");

            stream.Read(....); //added sync read here                
        }

MSDN documentation on TcpClient has an example as well http://msdn.microsoft.com/en-us/library/system.net.sockets.tcpclient.aspx

If you want feed back such as reporting # of bytes received so far, you'll have to use async methods.