访问
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; // 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.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) {// 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 paulnicitiz.net(paulnicitiz.net)。
