使用.NET访问Internet(5) Paul_Ni（原作）(补充)

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 asynchronouslypublic class StateObject {   public Socket workSocket = null;       // Client  socket.   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 the  socket.      //   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/IP  socket.      Socket listener = new Socket(AddressFamily.InterNetwork,         SocketType.Stream, ProtocolType.Tcp );       // Bind the  socket to the local endpoint and listen for incoming connections.      try {         listener.Bind(localEndPoint);         listener.Listen(100);          while (true) {            // Set the event to  nonsignaled state.            allDone.Reset();             // Start  an asynchronous socket to listen for connections.            Console.WriteLine("Waiting for a connection...");            listener.BeginAclearcase/" target="_blank" >ccept(                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) {         // There  might be more data, so store  the data received so far.         state.sb.Append(Encoding.ASCII.GetString(            state.buffer,0,bytesRead));          // Check for end-of-file tag. If  it 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()。

原文转自：http://www.ltesting.net