SimpleTimeServerusingSocketsinC#

Simple Time Server using Sockets in C#

Here is a basic implementation of a socket client and server

You should include the System.Net and System.Net.Sockets and System.Text assemblies

using System;
using System.Net;
using System.Net.Sockets;
using System.Text;

class Server 
{

Declare the main entry point for the server assembly:

    public static void Main() 
    {

Create a listening socket:

        try
        {

            // listen on port 14
           // Dns.Resolve() can return multiple addresses for the given IP. Lets go with the first one (index 0)

            TcpListener tcpl = new TcpListener(Dns.Resolve("localhost").AddressList[0], 14); 

            //start the listener
            tcpl.Start();
        
            Console.WriteLine("Waiting for clients to connect");
            Console.WriteLine("Press Ctrl+c to Quit...");

Wait for incoming connections:

            while (true)
            {
                // Accept will block until someone connects
                Socket s = tcpl.AcceptSocket();

We have a connection! Now pass the current date and time to the client. First thing is we need to get the current time:

                // Get the current date and time then concatenate it
                // into a string
                DateTime now = DateTime.Now;
                String strDateLine = now.ToShortDateString() + " " + now.ToLongTimeString();

Convert the time into ASCII bytes to send thru the socket (.NET stores all strings as UNICODE)

                // Convert the string to a Byte Array and send it
                Byte[] byteDateLine = Encoding.ASCII.GetBytes(strDateLine.ToCharArray());

Send the time over the socket to the client:

                s.Send(byteDateLine, byteDateLine.Length, 0);

Close the socket.

                s.Close();

We can use Console.WriteLine to show what time the server sent to the client:

                Console.WriteLine("Sent {0}", strDateLine);
            }
        }

You should catch exceptions of type SocketException to see if there was an error while sending to the client:

        catch (SocketException socketError)
        {

This can be a common problem when you forget to close your socket before starting the socket server up again :)

            if (socketError.ErrorCode == 10048)
            {
                Console.WriteLine("Connection to this port failed.  There is another server is listening on this port.");
            }
        }
    }
}

Thats it for the time server! Lets take a look at the time client:

#region SocketClient
using System;
using System.Net;
using System.Net.Sockets;
using System.IO;
using System.Text;

class Client 
{

declare the Main entry point for the time client program:

    public static void Main(String[] args) 
    {

Create a socket to connect to the server with:

        TcpClient tcpc = new TcpClient();

Allocate a buffer to retrieve the time from the server:

        tcpc.ReceiveBufferSize = 32;

We are using a command line option that contains the server ip to connect to:

        if (args.Length != 1) 
        {
            Console.WriteLine("Please specify a server name in the command line");
            return;
        }

Get the server ip or name from the command line argument:

        String server = args[0];

Verify that the server that was passed in as the command line parameter is a valid server:

        // Verify that the server exists
        try 
        {
            IPHostEntry ipInfo = Dns.GetHostByName(server);
        }

If this is not a valid server, and exception will be thrown.

        catch (SocketException socketExcep) 
        {

Display an appropriate message to the user and exit the application:

            Console.WriteLine("Cannot find server: " + server + "\nException:\n" + socketExcep.ToString());
            return;
        }

Attempt to connect to the time server:

        // Try to connect to the server
        try
        {
            tcpc.Connect(server, 14);
        }
        catch(Exception e)
        {
            Console.WriteLine("Could not connect to server {0}\n" + e.Message,server);
        }

We use a Stream object to stream data from the server's socket:

        // Get the stream
        Stream s;
        try
        {
            s = tcpc.GetStream();
        }
        catch (InvalidOperationException)
        {
            Console.WriteLine("Cannot connect to server {0}", server);
            return;
        }

Read the ASCII data sent from the server:

        Byte[] read = new Byte[32];

        // Read the stream and convert it to ASII
        int bytes = s.Read(read, 0, read.Length);
        String Time = Encoding.ASCII.GetString(read);

Display the result to the user:

        Console.WriteLine("Received " + bytes + " bytes");
        Console.WriteLine("Current date and time is: " + Time);

Don't forget to close the client socket:

        tcpc.Close();

By calling Console.Read() we can make the window stay open when executing the program in debug mode:

        // Wait for user response to exit
        Console.WriteLine("Press Enter to exit");
        Console.Read();
    }
}