Network Programming in C# - Part 2

This is the second part of the series of articles about the network programming with C#.


This is the second part of the series of articles about the network programming with C#. The first part is available at NETWORK PROGRAMMING IN C# - PART 1 
Socket Programming: Synchronous Clients 

The steps for creating a simple synchronous client are as follows.

  1. Create a Socket instance.
  2. Connect the above socket instance to an end-point.
  3. Send or Receive information.
  4. Shutdown the socket
  5. Close the socket 

The Socket class provides a constructor for creating a Socket instance. 

public Socket (AddressFamily af, ProtocolType pt, SocketType st)

Where AddressFamily, ProtocolType and SocketTYpe are the enumeration types declared inside the Socket class.

The AddressFamily member specifies the addressing scheme that a socket instance must use to resolve an address. For example AddressFamily.InterNetwork indicates that an IP version 4 addresses is expected when a socket connects to an end point. 

The SocketType parameter specifies the socket type of the current instance. For example SocketType.Stream indicates a connection-oriented stream and SocketType.Dgram indicates a connectionless stream.

The ProtocolType parameter specifies the ptotocol to be used for the communication. For example ProtocolType.Tcp indicates that the protocol used is TCP and ProtocolType.Udp indicates that the protocol using is UDP. 

public Connect (EndPoint ep) 

The Connect() method is used by the local end-point to connect to the remote end-point. This method is used only in the client side. Once the connection has been established the Send() and Receive() methods can be used for sending and receiving the data across the network. 

The Connected property defined inside the class Socket can be used for checking the connection. We can use the Connected property of the Socket class to know whether the current Socket instance is connected or not. A property value of true indicates that the current Socket instance is connected. 

IPHostEntry IPHost = Dns.Resolve(www.c-sharpcorner.com);
Console.WriteLine(IPHost.HostName);
string []aliases = IPHost.Aliases;
IPAddress[] addr = IPHost.AddressList;
Console.WriteLine(addr[0]);
EndPoint ep =
new IPEndPoint(addr[0],80);
Socket sock =
new Socket
(AddressFamily.InterNetwork,SocketType.Stream,ProtocolType.Tcp);
sock.Connect(ep);
if(sock.Connected)
Console.WriteLine("OK");

The Send() method of the socket
class can be used to send data to a connected remote socket.

public int Send (byte[] buffer, int size, SocketFlags flags) 

Where byte[] parameter storing the data to send to the socket, size parameter containing the number of bytes to send across the network. The SocketFlags parameter can be a bitwise combination of any one of the following values defined in the System.Net.Sockets.SocketFlags enumerator.  

SocketFlags.None
SocketFlags.DontRoute
SocketFlags.OutOfBnd

The method Send() returns a System.Int32 containing the number of bytes send.Remember that there are other overloaded versions of Send() method as follows.  

public int Send (byte[] buffer, SocketFlags flags)
public int Send (byte[] buffer)
public int Send (byte[] buffer,int offset, int size, SocketFlags flags)

The Receive() method can be used to receive data from a socket.        

public
int Receive(byte[] buffer, int size, SocketFlags flags)

Where byte[] parameter storing the data to send to the socket, size parameter containing the number of bytes to send across the network. The SocketFlags parameter can be a bitwise combination of any one of the following values defined in the System.Net.Sockets.SocketFlags enumerator explained above. 

The overloaded versions of Receive() methods are shown below.  

public int Receive (byte[] buffer, SocketFlags flags)
public int Receive (byte[] buffer)
public int Receive (byte[] buffer,int offset, int size, SocketFlags flags) 

When the communication across the sockets is over, the connection between the sockets can be terminated by invoking the method ShutDown()  

public void ShutDown(SocketShutdown how)

Where 'how' is one of the values defined in the SocketSHutdown enumeration. The value SoketShutdown.Send means that the socket on the other end of the connection is notified that the current instance would not send any more data. The value SoketShutdown.Receive means that the socket on the other end of the connection is notified that the current instance will not receive any more data and the value SoketShutdown.Both means that both the action are not possible. 

Remember that the ShutDown() method must be called before the Close(0 method to ensure that all pending data is sent or received. 

A socket can be closed by invoking the method Close().  
       
public void Close()

This method closes the current instance and releases all managed and un-managed resources allocated by the current instance. This method internally calls the Dispose() method with an argument of 'true' value, which frees both managed and un-managed resources used by the current instance.  

protected virtual void Dispose(bool)

The above method closes the current instance and releases the un-managed resources allocated by the current instance and exceptionally release the managed resources also. An argument value of 'true' releases both managed and un-managed resources and a value of 'false' releases only un-managed resources. 

The source code for a simple synchronous client by using the sockets is show below. The following program can send an HTTP request to a web server and can read the response from the web server. 

using System;
using System.Net;
using System.Net.Sockets;
using System.Text;
class MyClient
{
public static void Main()
{
IPHostEntry IPHost = Dns.Resolve(www.google.com);
Console.WriteLine(IPHost.HostName);
string []aliases = IPHost.Aliases;
IPAddress[] addr = IPHost.AddressList;
Console.WriteLine(addr[0]);
EndPoint ep =
new IPEndPoint(addr[0],80);
Socket sock =
new Socket(AddressFamily.InterNetwork,SocketType.Stream,ProtocolType.Tcp);
sock.Connect(ep);
if(sock.Connected)
Console.WriteLine("OK");
Encoding ASCII = Encoding.ASCII;
string Get = "GET / HTTP/1.1\r\nHost: " + "www. google.com" +
"\r\nConnection: Close\r\n\r\n";
Byte[] ByteGet = ASCII.GetBytes(Get);
Byte[] RecvBytes =
new Byte[256];
sock.Send(ByteGet, ByteGet.Length, 0);
Int32 bytes = sock.Receive(RecvBytes, RecvBytes.Length, 0);
Console.WriteLine(bytes);
String strRetPage =
null;
strRetPage = strRetPage + ASCII.GetString(RecvBytes, 0, bytes);
while (bytes > 0)
{
bytes = sock.Receive(RecvBytes, RecvBytes.Length, 0);
strRetPage = strRetPage + ASCII.GetString(RecvBytes, 0, bytes);
Console.WriteLine(strRetPage );
}
sock.ShutDown(SocketShutdown.Both);
sock.Close();
}
}