c#网络编程之------------DNS编程

System.Net 名称空间包含了 DNS 类,它可以提供了编写 DNS 所需要的函数。下面讲解 DNS 类的一些方法以及在 C# 中如何利用该类编写程序。

** 一、 ** ** 同步方法 ** ** **

在 DNS 类中定义了四个同步方法: GetHostName() 、 GetHostByName() 、 GetHostByAddress() 、 Resolve() 。下面分别讲解。

** 1 ** ** 、 ** ** public static string GetHostName(); **

功能: 获取本地计算机的主机名。

返回值:字符串,包含本地计算机的 DNS 主机名。

**2、** **public static IPHostEntry GetHostByName(string hostName)** ****

功能:获取指定 DNS 主机名的 DNS 信息。

参数:包含主机的 DNS 名的字符串

using System;

using System.Net;

class GetDNSHostInfo

{

public static void Main(string[] argv)

{

if (argv.Length != 1)

{

Console.WriteLine("Usage: GetDNSHostInfo hostname");

return;

}

IPHostEntry results = Dns.GetHostByName(argv[0]);

Console.WriteLine("Host name: {0}",results.HostName);

foreach(string alias in results.Aliases)

{

Console.WriteLine("Alias: {0}", alias);

}

foreach(IPAddress address in results.AddressList)

{

Console.WriteLine("Address: {0}", address.ToString());

}

}

}

** 注: IPHostEntry(为 Internet 主机地址信息提供容器类)属性介绍: **

AddressList:获取或设置与主机关联的 IP 地址列表。

Aliases:获取或设置与主机关联的别名列表。

HostName:获取或设置主机的 DNS 名称。 ** **

** 3 ** ** 、 ** ** GetHostByAddress() **

功能:获取 IP 地址的 DNS 主机信息。

public static IPHostEntry GetHostByAddress(IPAddress);

public static IPHostEntry GetHostByAddress(string);

using System;

using System.Net;

class GetDNSAddressInfo

{

public static void Main(string)[] argv)

{

if (argv.Length != 1)

{

Console.WriteLine("Usage: GetDNSAddressInfo address");

return;

}

IPAddress test = IPAddress.Parse(argv[0]);

IPHostEntry iphe = Dns.GetHostByAddress(test);

Console.WriteLine("Information for {0}", test.ToString());

Console.WriteLine("Host name: {0}", iphe.HostName);

foreach(string alias in iphe.Aliases)

{

Console.WriteLine("Alias: {0}", alias);

}

foreach(IPAddress address in iphe.AddressList)

{

Console.WriteLine("Address: {0}", address.ToString());

}

}

}

** 注: IPAddress,提供网际协议 (IP) 地址。 **


**4** **、** **public static IPHostEntry Resolve(string hostName)** ****

功能:将 DNS 主机名或 IP 地址解析为 IPHostEntry 实例。

参数: DNS 样式的主机名或 IP 地址。

备注: Resolve 方法在 DNS 服务器中查询与主机名或 IP 地址相关联的 IP 地址。当 hostName 是 DNS 样式的主机名并且与多个 IP 地址关联时,仅返回解析为该主机名的第一个 IP 地址。

using System;

using System.Net;

class GetResolveInfo

{

public static void Main(string[] argv)

{

if (argv.Length != 1)

{

Console.WriteLine("Usage: GetResolveInfo address");

return;

}

IPHostEntry iphe = Dns.Resolve(argv[0]);

Console.WriteLine("Information for {0}", argv[0]);

Console.WriteLine("Host name: {0}", iphe.HostName);

foreach(string alias in iphe.Aliases)

{

Console.WriteLine("Alias: {0}", alias);

}

foreach(IPAddress address in iphe.AddressList)

{

Console.WriteLine("Address: {0}",address.ToString());

}

}

}

二、 异步方法

在 DNS 中定义了四个异步方法 : BeginGetHostByName() 、 BeginResolve() 、 EndGetHostByName() 、 EndResolve()

使用范例:

using System;

using System.Drawing;

using System.Net;

using System.Text;

using System.Windows.Forms;

class AsyncResolve Form:

{

TextBox address;

ListBox results;

private AsyncCallback OnResolved ;

public AsyncResolve()

{

Text = "DNS Address Resolver";

Size = new Size(400,380);

OnResolved = new AsyncCallback(Resolved);

Label label1 = new Label();

label1.Parent = this;

label1.Text = "Enter address to resolve:";

label1.AutoSize = true;

label1.Location = new Point(10, 10);

address = new TextBox();

address.Parent = this;

address.Size = new Size(200, 2 * Font.Height);

address.Location = new Point(10, 35);

results = new ListBox();

results.Parent = this;

results.Location = new Point(10, 65);

results.Size = new Size(350, 20 * Font.Height);

Button checkit = new Button();

checkit.Parent = this;

checkit.Text = "Resolve";

checkit.Location = new Point(235,32);

checkit.Size = new Size(7 * Font.Height, 2 * Font.Height);

checkit.Click += new EventHandler(ButtonResolveOnClick);

}

void ButtonResolveOnClick(object obj, EventArgs ea)

{

results.Items.Clear();

string addr = address.Text;

Object state = new Object();

Dns. BeginResolve (addr, OnResolved , state);

}

private void Resolved (IAsyncResult ar)

{

string buffer;

IPHostEntry iphe = Dns. EndResolve (ar);

buffer = "Host name: " + iphe.HostName;

results.Items.Add(buffer);

foreach(string alias in iphe.Aliases)

{

buffer = "Alias: " + alias;

results.Items.Add(buffer);

}

foreach(IPAddress addrs in iphe.AddressList)

{

buffer = "Address: " + addrs.ToString();

results.Items.Add(buffer);

}

}

public static void Main()

{

Application.Run(new AsyncResolve());

}

}

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