异步服务器套接字示例

下面的示例程序创建一个接收来自客户端的连接请求的服务器。该服务器是用异步套接字生成的，因此在等待来自客户端的连接时不挂起服务器应用程序的执行。该应用程序接收来自客户端的字符串，在控制台显示该字符串，然后将该字符串回显到客户端。来自客户端的字符串必须包含字符串“<EOF>”，以发出表示消息结尾的信号。

 [C#]

using System;

using System.Net;

using System.Net.Sockets;

using System.Text;

using System.Threading;

// State object for reading client data asynchronously

public class StateObject {

 public Socket workSocket = null; // Clientsocket.

 public const int BufferSize = 1024; // Size of receive buffer.

 public byte[] buffer = new byte[BufferSize]; // Receive buffer.

 public StringBuilder sb = new StringBuilder();// Received data string.

}

public class AsynchronousSocketListener {

 // Incoming data from client.

 public static string data = null;

 // Thread signal.

 public static ManualResetEvent allDone = new ManualResetEvent(false);

 public AsynchronousSocketListener() {

 }

 public static void StartListening() {

// Data buffer for incoming data.

byte[] bytes = new Byte[1024];

// Establish the local endpoint for thesocket.

// The DNS name of the computer

//running the listener is "host.contoso.com".

IPHostEntry ipHostInfo = Dns.Resolve(Dns.GetHostName());

IPAddress ipAddress = ipHostInfo.AddressList[0];

IPEndPoint localEndPoint = new IPEndPoint(ipAddress, 11000);

// Create a TCP/IPsocket.

Socket listener = new Socket(AddressFamily.InterNetwork,

 SocketType.Stream, ProtocolType.Tcp );

// Bind thesocket to the local endpoint and listen for incoming connections.

try {

 listener.Bind(localEndPoint);

 listener.Listen(100);

 while (true) {

// Set the event tononsignaled state.

allDone.Reset();

// Startan asynchronous socket to listen for connections.

Console.WriteLine("Waiting for a connection...");

listener.BeginAccept( 

 new AsyncCallback(AcceptCallback),

 listener );

// Wait until a connection is made before continuing.

allDone.WaitOne();

 }

} catch (Exception e) {

 Console.WriteLine(e.ToString());

}

Console.WriteLine("\nHit enter to continue...");

Console.Read();

 }

 public static void AcceptCallback(IAsyncResult ar) {

// Signal the main thread to continue.

allDone.Set();

// Get the socket that handles the client request.

Socket listener = (Socket) ar.AsyncState;

Socket handler = listener.EndAccept(ar);

// Create the state object.

StateObject state = new StateObject();

state.workSocket = handler;

handler.BeginReceive( state.buffer, 0, StateObject.BufferSize, 0,

 new AsyncCallback(ReadCallback), state);

 }

 public static void ReadCallback(IAsyncResult ar) {

String content = String.Empty;

// Retrieve the state object and the handler socket

// from the async state object.

StateObject state = (StateObject) ar.AsyncState;

Socket handler = state.workSocket;

// Read data from the client socket. 

int bytesRead = handler.EndReceive(ar);

if (bytesRead > 0) {

 // Theremight be more data, so storethe data received so far.

 state.sb.Append(Encoding.ASCII.GetString(

state.buffer,0,bytesRead));

 // Check for end-of-file tag. Ifit is not there, read 

 // more data.

 content = state.sb.ToString();

 if (content.IndexOf("<EOF>") > -1) {

// All the data has been read from the 

// client. Display it on the console.

Console.WriteLine("Read {0} bytes from socket. \n Data : {1}",

 content.Length, content );

// Echo the data back to the client.

Send(handler, content);

 } else {

// Not all data received. Get more.

handler.BeginReceive(state.buffer, 0, StateObject.BufferSize, 0,

new AsyncCallback(ReadCallback), state);

 }

}

 }

 private static void Send(Socket handler, String data) {

// Convert the string data to byte data using ASCII encoding.

byte[] byteData = Encoding.ASCII.GetBytes(data);

// Begin sending the data to the remote device.

handler.BeginSend(byteData, 0, byteData.Length, 0,

 new AsyncCallback(SendCallback), handler);

 }

 private static void SendCallback(IAsyncResult ar) {

try {

 // Retrieve the socket from the state object.

 Socket handler = (Socket) ar.AsyncState;

 // Complete sending the data to the remote device.

 int bytesSent = handler.EndSend(ar);

 Console.WriteLine("Sent {0} bytes to client.", bytesSent);

 handler.Shutdown(SocketShutdown.Both);

 handler.Close();

} catch (Exception e) {

 Console.WriteLine(e.ToString());

}

 }

 public static int Main(String[] args) {

StartListening();

return 0;

 }

}

使用 Net 类的最佳做法

下列建议将帮助您最有效地使用 System.Net 中包含的类：

• 尽可能使用 WebRequest 和 WebResponse 而不是类型转换为子代类。使用 WebRequest 和 WebResponse 的应用程序可以利用新的 Internet 协议，而不需要进行大范围的代码更改。
• 当使用 System.Net 类编写运行在服务器上的 ASP.NET 应用程序时，从性能的角度来看，使用 GetResponse 和 GetResponseStream 的异步方法通常更好。
• 对 Internet 资源打开的连接数可能对网络性能和吞吐量有显著的影响。默认情况下，System.Net 对每个主机的每个应用程序使用两个连接。设置应用程序的 ServicePoint 中的 ConnectionLimit 属性可为特定主机增加此数目。设置 ServicePointManager.DefaultPersistentConnectionLimit 属性可为所有主机增加此默认值。
• 当编写套接字级别的协议时，请尽可能尝试使用 TCPClient 或 UDPClient，而不是直接向 Socket 中写。这两个客户端类封装 TCP 和 UDP 套接字的创建，而不需要您处理连接的细节。
• 当访问要求凭据的站点时，请使用 CredentialCache 类创建凭据的缓存而不要对每个请求都提供它们。CredentialCache 类搜索缓存以查找要提供给请求的适当凭据，从而使您不必根据统一资源定位器来创建和提供凭据。

总结

上面是VS.NET中.NET访问Internet的一些基本概念和代码示例（包括访问Internet的各种方法和步骤），给大家参考一下。有任何建议请MAIL我 paulni@citiz.net(paulni@citiz