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Networking in C#

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C# is a language designed for the modern computing

environment, of which the Internet is, obviously, an important

part.

A main design criteria for C# was, therefore, to include those

features necessary for accessing the Internet.

Using standard features of C# and the .NET Framework, it is

easy to Internet-enable your applications and write other

types of Internet-based code.

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Primary namespace for networking isSystem.Net. It defines alarge number of highlevel, easy-to-use classes that support

the various types of operations common to the Internet.

Several namespaces nested under System.Net are alsoprovided. For example, low-levelnetworking control throughsockets is found inSystem.Net.Sockets.

Mail support is found in System.Net.Mail. Support forsecure network streams is found inSystem.Net.Security.

Another important networking-related namespace isSystem.Web. It supports ASP.NET-based networkapplications.

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System.Net

Although System.Netdefines many members, only a few areneeded to accomplish mostcommon Internet programming tasks.

At the core of networking are the abstract classes WebRequest

andWebResponse.

These classes are inherited by classes that support a specificnetwork protocol.

For example, the derived classes that support the standard HTTP

protocol areHttpWebRequestandHttpWebResponse.

Even thoughWebRequestandWebResponseare easy to use, forsome tasks, you canemploy an even simpler approach based on

WebClient.

For example, if you only need toupload or download a file, then

WebClientis often the best way to accomplish it.

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Uniform Resource Identifiers

Fundamental to Internet programming is the Uniform Resource

Identifier(URI).

A URI describes the location of some resource on the network. A

URI has the following simplified general form:

Protocol://HostName/FilePath?Query

Protocolspecifies the protocol being used, such as HTTP.

HostName identifies a specific server, such as or

www.HerbSchildt.com. FilePathspecifies the path to a specific file.

Queryspecifies information that will be sent to the server. Query

is optional.

In C#, URIs are encapsulated by theUri class.

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Since WebRequest and WebResponse are main classes of

System.Net, they are discussed as:

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WebRequest

TheWebRequest class manages a network request. It is abstract

because it does not implement a specific protocol. It does, however,

define those methods and properties common to all requests.

WebRequestdefines no public constructors.

To send a request to a URI, you must first create an object of a class

derived fromWebRequestthat implements the desired protocol.

This can be done by callingCreate( ), which is a static methoddefined byWebRequest. Create( ) returns an object of a class that

inheritsWebRequestand implements a specific protocol.

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Methods of WebRequest class

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WebResponse

WebResponseencapsulates a response that is obtained as theresult of a request.

WebResponse is an abstract class. Inheriting classes create

specific, concrete versions of it that support a protocol.

AWebResponseobject is normally obtained by calling theGetResponse( )methoddefined byWebRequest.

This object will be an instance of a concrete class derivedfromWebResponsethat implements a specific protocol.

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Methods of WebResponse class

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HttpWebRequest and HttpWebResponse

The classes HttpWebRequest and HttpWebResponse

inherit the WebRequest and WebResponse classes and

implement theHTTP protocol.

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using System;

using System.Net;

using System.IO;

class NetDemo {

static void Main() {

int ch;

// First, create a WebRequest to a URI.HttpWebRequest req = (HttpWebRequest)

WebRequest.Create("http://www.McGraw-Hill.com");

// Next, send that request and return the response.

HttpWebResponse resp = (HttpWebResponse)

req.GetResponse();

// From the response, obtain an input stream.

Stream istrm = resp.GetResponseStream();

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/*Now, read and display the html present at the specified URI. So you

can see what is being displayed, the data is shown 400 characters at a

time. After each 400 characters are displayed, you must press ENTERto get the next 400. */

for(int i=1; ; i++) {

ch = istrm.ReadByte();

if(ch == -1) break;Console.Write((char) ch);

if((i%400)==0) {

Console.Write("\nPress Enter.");

Console.ReadLine();

}}

resp.Close();

}}

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The Uri Class

WebRequest.Create( ) has two different versions.

1. One accepts the URI as a string. This is the version used by

the preceding programs.

2. The other takes the URI as an instance of the Uri class,which is defined in the System namespace.

The Uri class

encapsulates a URI. Using Uri, you can construct a URI thatcan be passed to Create()

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class UriDemo {static void Main() {

Uri sample = new Uri("http://HerbSchildt.com/somefile.txt ");

Console.WriteLine("Host: " + sample.Host);

Console.WriteLine("Port: " + sample.Port);

Console.WriteLine("Scheme: " + sample.Scheme);

}

}

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The output is shown here:

Host: HerbSchildt.com

Port: 80

Scheme: httpLocal Path: /somefile.txt

Query: ?SomeQuery

Path and query: /somefile.txt?SomeQuery

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Using WebClient

If your application only needs to upload or download data to

or from the Internet, then you can use WebClient.

Example

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IPAddress Class

AnIPAddressobject is used to represent a single IP address.

This value can then be used in the various socket methods to

represent the IP address.

The default constructor for IPAddress is as follows:public IPAddress(longaddress)

Some of the methods associated with IPAddress class are as

follows:

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The Parse() method is most often used to create IPAddress

instances:

IPAddressnewaddress = IPAddress.Parse("192.168.1.1");

This format allows you to use a standard dotted quad IPaddress in string format and convert it to an IPAddress object.

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The IPAddress class also provides four read-only fields that

represent special IP addresses for use in programs:

Any

Used to represent any IP address available on the local

system

Broadcast

Used to represent the IP broadcast address for the local

network

Loopback

Used to represent the loopback address of the system

None

Used to represent no network interface on the system

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IPHostEntry hostDnsEntry = Dns.GetHostEntry("localhost");

foreach(IPAddress address in hostDnsEntry.AddressList)

{

Console.WriteLine("Type: {0}, Address: {1}",

address.AddressFamily, address);}

//example console application 17

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the method used to obtain the local IP address:

IPHostEntry i =

Dns.GetHostByName(Dns.GetHostName());

IPAddress myself = i.AddressList[0];

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using System;

using System.Net;

class AddressSample{

public static void Main ()

{

IPAddress test1 = IPAddress.Parse("192.168.1.1");IPAddress test2 = IPAddress.Loopback;

IPAddress test3 = IPAddress.Broadcast;

IPAddress test4 = IPAddress.Any;

IPAddress test5 = IPAddress.None;

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IPHostEntry ihe =

Dns.GetHostByName(Dns.GetHostName());

IPAddress myself = ihe.AddressList[0];if (IPAddress.IsLoopback(test2))

Console.WriteLine("The Loopback address is: {0}",

test2.ToString());

else

Console.WriteLine("Error obtaining the loopback address");

Console.WriteLine("The Local IP address is: {0}\n",

myself.ToString());}

}

} /// window application 18

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Socket

A socketis one endpoint of a two-way communication link

between two programs running on the network. A socket is

bound to a port number so that the TCP layer can identify the

application that data is destined to be sent.

An endpoint is a combination of an IP address and a port

number. Every TCP connection can be uniquely identified by

its two endpoints. That way you can have multiple connections

between your host and the server.

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Sockets are the fundamental technology for programming

software to communicate on TCP/IP networks. A socket

provides a bidirectional communication endpoint for sending

and receiving data with another socket. Socket connections

normally run between two different computers on a LAN oracross the Internet, but they can also be used for inter-process

communication on a single computer.

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The socket defines the following:

A specific communication domain, such as a network

connection

A specific communication type, such as stream or datagram

A specific protocol, such as TCP or UDP

After the socket is created, it must be bound to either a specific

network address and port on the system, or to a remote network

address and port. Once the socket is bound, it can be used to

send and receive data from the network.

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The following example creates a Socket that can be used to

communicate on a TCP/IP-based network, such as the Internet.

Socket s = new Socket(AddressF amily.I nterN etwork,

SocketType.Str eam, Pr otocolType.Tcp);

the AddressFamily.InterNetwork member specifies the IP

version 4 address family).

ProtocolType.Tcp indicates that the socket uses

TCP;ProtocolType.Udpindicates that the socket uses UDP).

SocketType.Stream member indicates a standard socket forsending and receiving data with flow control).

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in .NET, there is a class underSystem.Netnamespace

called IPEndPoint, which represents a networkcomputer as an IP address and a port number.

public IPEndPoint(System.Net.IPAddress address,int port);

you can send data to the other side using

theSendmethod of theSocket class.

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Try

{

String s= "I am here";

byte[] byData = System.Text.Encoding.ASCII.GetBytes(s);

m_socClient.Send(byData);

}

catch (SocketException se)

{

MessageBox.Show ( se.Message );

}

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Similar to Send, there is a Receive method on

the Socket class. You can receive data using the

following call:

byte [] buffer = new byte[1024];int i = m_socClient.Receive (buffer);

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Listen causes a connection-oriented Socket to listen for

incoming connection attempts. Thebacklogparameter specifies

the number of incoming connections that can be queued for

acceptance. To determine the maximum number ofconnections you can specify, retrieve theMaxConnections

value.

Socket listenSocket = new

Socket(AddressFamily.InterNetwork, SocketType.Stream,ProtocolType.Tcp);

IPEndPoint ep = new IPEndPoint(hostIP, port);

listenSocket.Bind(ep);

listenSocket.Listen(backlog);

http://msdn.microsoft.com/en-us/library/system.net.sockets.socketoptionname.aspxhttp://msdn.microsoft.com/en-us/library/system.net.sockets.socketoptionname.aspx

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