SWE 344
Internet Protocols & Client Server
Programming
Network Layer Programing
Connection-Oriented Sockets
A Simple TCP Server
 We have four tasks to perform before a server can
transfer data with a client connection:
 Create a socket
 Bind the socket to a local IPEndPoint
 Place the socket in listen mode
 Accept an incoming connection on the socket
The IPEndPoint class contains the host and local or remote port
information needed by an application to connect to a service on a
host. By combining the host's IP address and port number of a
service, the IPEndPoint class forms a connection point to a service.
Creating the Server
 The first step to constructing a TCP server is to
create an instance of a Socket object. The other
three functions necessary for successful server
operations are then accomplished by using
methods of the Socket object.
IPEndPoint ipep = new IPEndPoint(IPAddress.Any, 9050);
Socket newsock = Socket(AddressFamily.InterNetwork,
SocketType.Stream, ProtocolType.Tcp);
newsock.Bind(ipep);
newsock.Listen(10);
Socket client = newsock.Accept();
 The Socket object created by the Accept() method
can now be used to transmit data in either
direction between the server and the remote
client.
//SimpleTcpSrvr.cs program
using System;
using System.Net;
using System.Net.Sockets;
using System.Text;
class SimpleTcpSrvr
{
public static void Main()
{
int recv;
byte[] data = new byte[1024];
IPEndPoint ipep = new IPEndPoint(IPAddress.Any, 9050);
Socket newsock = new Socket(AddressFamily.InterNetwork,
SocketType.Stream, ProtocolType.Tcp);
newsock.Bind(ipep);
newsock.Listen(10);
Console.WriteLine("Waiting for a client...");
Socket client = newsock.Accept();
IPEndPoint clientep =
(IPEndPoint)client.RemoteEndPoint;
Console.WriteLine("Connected with {0} at port {1}",
clientep.Address, clientep.Port);
string welcome = "Welcome to my test server";
data = Encoding.ASCII.GetBytes(welcome);
client.Send(data, data.Length,
SocketFlags.None);
while(true)
{
data = new byte[1024];
recv = client.Receive(data);
if (recv == 0)
break;
}
Console.WriteLine(
Encoding.ASCII.GetString(data, 0, recv));
client.Send(data, recv, SocketFlags.None);
Console.WriteLine("Disconnected from {0}",
clientep.Address);
client.Close();
newsock.Close();
}
}
Testing the Server
To start the sample TCP server, open a command prompt window and
type SimpleTcpSrvr. The server will display the opening greeting and
wait for an incoming client:
C:\>SimpleTcpSrvr
Waiting for a client...
Once the server is running, open another command prompt window
(either on the same system or another system on the network) and start
the Telnet program. Connect to the address of the server and the 9050
port used:
C:\>telnet 127.0.0.1 9050
The connection should start, and the server welcome screen should
appear.
At this point, the server is waiting for a message from the client. Using the Telnet
program, a strange thing happens. If you try to type a message, each individual
character is sent to the server and immediately echoed back. If you try to type in
a phrase, each character is sent individually and returned by the server
individually.
Creating the Client
the first step of creating the client program is to create a
Socket object. The Socket object is used by the Socket
Connect() method to connect the socket to a remote host:
IPEndPoint ipep = new
IPEndPoint(Ipaddress.Parse("192.168.1.6"), 9050);
Socket server = new Socket(AddressFamily.InterNetwork,
SocketType.Stream, ProtocolType.Tcp);
server.Connect(ipep);
This example attempts to connect the socket to the server
located at address 192.168.1.6.
//SimpleTcpClient.cs program
using System;
using System.Net;
using System.Net.Sockets;
using System.Text;
class SimpleTcpClient
{
public static void Main()
{
byte[] data = new byte[1024];
string input, stringData;
IPEndPoint ipep = new IPEndPoint(
IPAddress.Parse("127.0.0.1"), 9050);
Socket server = new Socket(AddressFamily.InterNetwork,
SocketType.Stream, ProtocolType.Tcp);
try
{
server.Connect(ipep);
} catch (SocketException e) {
Console.WriteLine("Unable to connect to server.");
Console.WriteLine(e.ToString());
return;
}
int recv = server.Receive(data);
stringData = Encoding.ASCII.GetString(data, 0, recv);
Console.WriteLine(stringData);
while(true)
{
input = Console.ReadLine();
if (input == "exit")
break;
server.Send(Encoding.ASCII.GetBytes(input));
data = new byte[1024];
recv = server.Receive(data);
stringData = Encoding.ASCII.GetString(data, 0, recv);
Console.WriteLine(stringData);
}
Console.WriteLine("Disconnecting from server...");
server.Shutdown(SocketShutdown.Both);
server.Close();
}
}
Testing the Client
The first thing to test is the Exception code used for the situation
where the server is unavailable. This is an easy thing to do: just
don’t start the server program and do run the SimpleTcpClient
program. This should produce the warning message you created in
the Exception code:
C:\>SimpleTcpClient
Unable to connect to server.
System.Net.Sockets.SocketException: Unknown error (0x274d)
at System.Net.Sockets.Socket.Connect(EndPoint remoteEP)
at SimpleTcpClient.Main()
C:\>
First, start the SimpleTcpSrvr program on the designated server
machine. Once it has indicated it is waiting for clients, start the
SimpleTcpClient program either in a separate command prompt
window on the same machine, or on another machine on the network.
When the client establishes the TCP connection, it should display the
greeting banner from the server. At this point, it is ready to accept
data from the console, so you can start entering data.
END