Networking with the Compact Framework

When developing applications that communicate over a network using .NET, most of the classes that you will need to familiarize yourself with are part of the System.Net namespace. It contains classes for handling Internet communications with objects that support proxy servers, IP addresses, DNS name resolution, network data streams, and specific classes for handling pluggable protocols such as the Hypertext Transfer Protocol (HTTP).

Table 12.1 describes the objects contained in the System.Net namespace.

Table 12.1. The System.Net Namespace

Name	Object Type	Description
AuthenticationManager	Class	Manages authentication models
Authorization	Class	Handles authorization messages to a sever
Dns	Class	Handles domain name resolution
EndPoint	Class	Abstract class for identifying a network address
GlobalProxySelection	Class	Handles the default proxy for HTTP requests
HttpContinueDelegate	Delegate	Callback used for HTTP requests
HttpStatusCode	Enumeration	Status codes used for HTTP requests
HttpVersion	Class	Handles version numbers supported by HTTP requests
HttpWebRequest	Class	Handles an HTTP request
HttpWebResponse	Class	Handles the response of an HTTP request
IAuthenticationModule	Interface	Interface used for Web authentication
ICertificatePolicy	Interface	Interface that validates a server's certificate
ICredentials	Interface	Interface for handling Web client authentication
IPAddress	Class	Handles IP addressing
IPEndPoint	Class	Handles an IP address and port number
IPHostEntry	Class	Handles Internet host address information
IrDAEndPoint	Class	Handles an infrared connection to another device
IWebProxy	Interface	Interface to handle a proxy request
IWebRequestCreate	Interface	Interface to handle new WebRequest instances
NetworkCredential	Class	Handles network usernames and passwords
ProtocolViolationException	Class	Exception used when a network protocol error occurs
ServicePoint	Class	Handles connection management for HTTP
ServicePointManager	Class	Handles a collection of ServicePoint classes
SocketAddress	Class	Stores information from EndPoint classes
WebException	Class	Exception used when an error occurs accessing the network
WebExceptionStatus	Enumeration	Status codes used with the WebException class
WebHeaderCollection	Class	Handles protocol headers for a network request or response
WebProxy	Class	Handles HTTP proxy settings
WebRequest	Class	Handles a request to a URI
WebResponse	Class	Handles a response to a URI

TCP/IP Addresses

In Chapter 1, you learned about the Internet Protocol version 4 (or IPv4) address scheme on Pocket PC. You may remember that an IPv4 address is used by a device to specify its unique host and subnet address, which it uses to communicate over a TCP/IP network. All of the methods and properties that are needed to manage an Internet address within the Compact Framework are handled by the System.Net.IPAddress class.

The IPAddress constructor is defined as follows:

 public IPAddress(long newAddress); 

The only parameter needed is the 32-bit value of the IP address. The class also contains the methods and properties described in Table 12.2.

Table 12.2. IPAddress Class Methods and Properties

Method	Description
HostToNetworkOrder()	Converts from host byte order to network byte order
IsLoopback()	Returns TRUE if the network address is the loopback adapter
NetworkToHostOrder()	Converts from network byte order to host byte order
Parse()	Converts a string to an IPAddress class
Property	Get/Set/Read-Only	Description
Address	Get/set	Value of the IP address
Any	Read-only field	Indicates that the IP address is used for all network adapters
Broadcast	Read-only field	Returns the IP broadcast address
Loopback	Read-only field	Returns the IP loopback address
None	Read-only field	Indicates that the IP address is not used for any network adapter

One of the most useful methods in the IPAddress class is the Parse() method. You can use this to easily construct a new IPAddress object using the standard dotted-notation Internet address, as shown in the following example:

 System.Net.IPAddress localIPAddress =    System.Net.IPAddress.Parse("127.0.0.1"); 

Although the IPAddress class by itself is useful for managing an Internet address, most of the networking functions in the Compact Framework use the System.Net.IPEndPoint class to specify another machine on the network. An IPEndPoint not only specifies the IP address of the remote connection, but also contains information about the port that will be used to connect with the service running on the remote device (for more information about Internet ports, see Chapter 1).

There are two ways to construct a new IPEndPoint class. The first method takes the 32-bit value of the IP address and a port:

 public IPEndPoint(long address, int port); 

You can also create a new IPEndPoint by passing in a previously created IPAddress object:

 public IPEndPoint(IPAddress address, int port); 

The following code shows how you can create an IPEndPoint that represents a connection to the local machine on port 80:

 System.Net.IPAddress localIPAddress = System.Net.IPAddress.Parse("127.0.0.1"); System.Net.IPEndPoint localIPEndpoint = new    System.Net.IPEndPoint(localIPAddress, 80); 

The IPEndPoint class consists of the methods and properties described in Table 12.3.

Table 12.3. IPEndPoint Class Methods and Properties

Method	Description
Create()	Creates an IPEndPoint based on an IP address and port
Serialize()	Serializes IPEndPoint information into a SocketAddress instance
Property	Get/Set/Read-Only	Description
Address	Get/set	Value of the IP address
AddressFamily	Get	Gets the address family for the IP address
Port	Get/set	Value of the port
MaxPort	Read-only field	Specifies the maximum value for the port
MinPort	Read-only field	Specifies the minimum value for the port

Name Resolution

The resolution of a domain name (such as www.furrygoat.com) or IP address is handled by the System.Net.Dns class. It contains the methods described in Table 12.4.

Table 12.4. Dns Class Methods

Method	Description
BeginGetHostByName()	Starts an asynchronous GetHostByName() request
BeginResolve()	Starts an asynchronous Resolve() request
EndGetHostByName()	Ends an asynchronous GetHostByName() request
EndResolve()	Ends an asynchronous Resolve() request
GetHostByAddress()	Gets host information based on the IP address
GetHostByName()	Gets host information based on the name
Resolve()	Resolves a host name or IP address to an IPHostEntry() class

After the DNS resolution process has completed, information about the domain is stored in a new instance of the System.Net.IPHostEntry class. The class has the properties described in Table 12.5.

Table 12.5. IPHostEntry Class Properties

Property	Get/Set/Read-Only	Description
AddressList	Get/set	Gets or sets a list of IPAddress objects associated with the host
Aliases	Get/set	Gets or sets a list of aliases associated with the host
HostName	Get/set	Gets or sets the DNS host name

The following code shows how you can create an IPEndPoint that is associated with the Microsoft Web Server by using the System.Net.Dns class to first resolve the IP address:

 // Resolve the MS Web Server IP address System.Net.IPHostEntry microsoftHost =    System.Net.Dns.GetHostByName("www.microsoft.com"); // Copy the resolved IP address to a string String msIP = microsoftHost.AddressList[0].ToString(); // Create the endpoint System.Net.IPEndPoint microsoftEndPoint = new    System.Net.IPEndPoint(microsoftHost.AddressList[0], 80);