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Chapter 6 Part 3:

Introduction to System.Net

 

 

What do we have in this chapter 6 Part 3?

11. Using the Socket-Level Classes

12. Socket Classes

13. Reading and Writing with NetworkStream

14. Using the Socket-Level Helper Classes

15. C++ Socket Program Example

 

Using the Socket-Level Classes   The socket-level classes in System.Net enable fine-grained control over the way data is read from and written to the network. These classes include access to sockets, a stream pattern for network I/O, and some helper classes that simplify a number of the most common tasks that are desirable when working with this level of the network. Figure 6-3 displays the groups of classes that make up the socket-level APIs for System.Net.     Figure 6-3: Socket-level classes in System.Net   Socket Classes   The System.Net.Sockets namespace contains a class-based representation of the Windows Sockets model commonly known as Winsock. These classes are particularly focused on a subset of the Winsock model that deals with IP-based protocols such as User Datagram Protocol (UDP) and Transmission Control Protocol (TCP). These classes can be extended to enable other protocols such as NetBIOS and Infrared. The key classes to be aware of at this level are Socket, SocketPermission, and SocketException. The Socket class provides the vast majority of the functionality needed to access the network and acts as the gatekeeper for the transition from managed .NET Framework code to the underlying native Win32 APIs. SocketException is used to represent most exceptions that occur within the Socket class. The SocketPermission class is used to control access to socket-level resources through code access security. These classes are described in more detail in Chapters 8 and 9. The following example demonstrates how to download a Web page using the socket-level classes.

 

C#

 

static void Main(string[ ] args)

{

    // Validate the input values

    if(args.Length < 2)

    {

        Console.WriteLine("Expected executable_file_name serverName path");

        Console.WriteLine("Example: DownloadWebPage contoso.com /");

        return;

    }

 

    string server = args[0];

    string path = args[1];

    int port = 80;

 

    IPHostEntry host = null;

    IPEndPoint remoteEndPoint = null;

    Socket client = null;

 

    // Resolve the server name

    try

    {

        host = Dns.GetHostByName(server);

    }

    catch(Exception ex)

    {

        Console.WriteLine(ex.ToString());

        return;

    }

 

    // Attempt to connect on each address returned from DNS.

    // Break out once successfully connected

    foreach(IPAddress address in host.AddressList)

    {

        try

        {

            client = new Socket(address.AddressFamily, SocketType.Stream, ProtocolType.Tcp);

 

            remoteEndPoint = new IPEndPoint(address, port);

            client.Connect(remoteEndPoint);

            break;

        }

        catch(SocketException ex)

        {

            Console.WriteLine(ex.ToString());

        }

    }

 

    // MakeRequest will issue the HTTP download request and write the server response to the console

    MakeRequest(client, path, server);

    client.Close();

}

 

public static void MakeRequest(Socket client, string path, string server)

{

    // Format the HTTP GET request string

    string Get = "GET " + path + " HTTP/1.0\r\nHost: " + server  + "\r\nConnection: Close\r\n\r\n";

 

    Byte[ ] ByteGet = Encoding.ASCII.GetBytes(Get);

 

    // Send the GET request to the connected server

    client.Send(ByteGet);

 

    // Create a buffer that is used to read the response

    byte[ ] responseData = new byte[1024];

 

    // read the response and save the ASCII data in a string

    int bytesRead = client.Receive(responseData);

    StringBuilder responseString = new StringBuilder();

    while (bytesRead != 0)

    {

        responseString.Append(Encoding.ASCII.GetChars(responseData), 0, bytesRead);

        bytesRead = client.Receive(responseData);

    }

 

    // Display the response to the console

    Console.WriteLine(responseString.ToString());

}

 

 

 

 

Visual Basic .NET

 

Sub Main(ByVal args As String())

 

    ' Validate the input values

    If args.Length < 2 Then

        Console.WriteLine("Expected executable_file_name serverName path")

        Console.WriteLine("Example: DownloadWebPage contoso.com /")

        Return

    End If

 

    Dim server As String = args(0)

    Dim path As String = args(1)

    Dim port As Integer = 80

 

    Dim host As IPHostEntry

    Dim remoteEndPoint As IPEndPoint

    Dim client As Socket

 

    ' Resolve the server name

    Try

        host = Dns.GetHostByName(server)

    Catch ex As Exception

        Console.WriteLine(ex.ToString())

        Return

    End Try

 

    ' Attempt to connect on each address returned from DNS.

    ' Exit out once successfully connected

    For Each address As IPAddress In host.AddressList

        Try

            client = New Socket(address.AddressFamily, SocketType.Stream, ProtocolType.Tcp)

            remoteEndPoint = New IPEndPoint(address, port)

            client.Connect(remoteEndPoint)

            Exit For

        Catch ex As Exception

            Console.WriteLine(ex.ToString())

        End Try

    Next

 

    ' MakeRequest will issue the HTTP download request and write the server response to the console

    MakeRequest(client, path, server)

    client.Close()

End Sub

 

Sub MakeRequest(ByVal client As Socket, ByVal path As String,

ByVal server As String)

 

    ' Format the HTTP GET request string

    Dim getString As String = "GET " + path + " HTTP/1.0" + ControlChars.CrLf

    getString += "Host: " + server + ControlChars.CrLf + "Connection: Close"

    getString += ControlChars.CrLf + ControlChars.CrLf

 

    Dim ByteGet As Byte() = Encoding.ASCII.GetBytes(getString)

 

    ' Send the GET request to the connected server

    client.Send(ByteGet)

 

    ' Create a buffer that is used to read the response

    Dim responseData() As Byte = New Byte(1024) { }

 

    ' Read the response and save the ASCII data in a string

    Dim bytesRead As Integer = client.Receive(responseData)

    Dim responseString As StringBuilder = New StringBuilder

 

    While bytesRead > 0

        responseString.Append(Encoding.ASCII.GetChars(responseData), 0, bytesRead)

        bytesRead = client.Receive(responseData)

    End While

 

    ' Display the response to the console

    Console.WriteLine(responseString.ToString())

End Sub

 

You’ll notice that the sample for downloading a Web page using sockets is much longer than the code it would take to do the same thing using a higher layer in System.Net, such as WebRequest or WebClient. This additional code is the tradeoff that’s often made when you decide to program at the socket level. Your application will have much greater control over the protocol that’s emitted, but it does so at the cost of additional code.

 

Reading and Writing with NetworkStream

 

Although NetworkStream isn’t a large class, it’s extremely useful because it provides a stream-based model for reading and writing data over a network. NetworkStream implements the standard methods and properties that you’ll find on the base System.IO.Stream pattern, as discussed in Chapter 2. You should consider a couple of interesting elements that are specific to this implementation when working with NetworkStream. First, a NetworkStream instance can be obtained either by constructing one from a socket or by getting one from another class such as one of the socket-level helper classes described in the next section. Second, because NetworkStream is based on a TCP connection and does not buffer data, it’s not seekable.

You can’t set the Position property to seek a particular point in the stream. You should be aware of this limitation if you rely on other classes that use the Stream type and expect this functionality from the stream.

 

 

C++ Socket Program Example

 

Create a new CLR console application and you can use SocketChap6CP as the project and solution names if you want.

 

 

Add the following code.

 

 

Build and run the project. The following are the output samples.

 

 

 

 

 

 

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