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Set Keep-Alive Values---C到C#代码的转换

news 来源：原创 2024/5/8 3:15:38

一、什么是Keep-Alive模式？

我们知道HTTP协议采用“请求-应答”模式，当使用普通模式，即非KeepAlive模式时，每个请求/应答客户和服务器都要新建一个连接，完成之后立即断开连接（HTTP协议为无连接的协议）；当使用Keep-Alive模式（又称持久连接、连接重用）时，Keep-Alive功能使客户端到服务器端的连接持续有效，当出现对服务器的后继请求时，Keep-Alive功能避免了建立或者重新建立连接。
http 1.0中默认是关闭的，需要在http头加入"Connection: Keep-Alive"，才能启用Keep-Alive；http 1.1中默认启用Keep-Alive，如果加入"Connection: close "，才关闭。目前大部分浏览器都是用http1.1协议，也就是说默认都会发起Keep-Alive的连接请求了，所以是否能完成一个完整的Keep- Alive连接就看服务器设置情况。

二、代码使用

SetKeepAliveValues 方法启用或禁用 TCP 保持选项指定的 TCP 保持超时和间隔用于保持 TCP 数据包的每个连接设置。保持选项的详细信息，请参阅 4.2.3.6 节要求的互联网 HostsCommunication 图层在 IETF 网站上可用的 RFC 1122 中指定。

optionInValue 参数，传递给 Socket.IOControl 应指向 Mstcpip.h 头文件中定义的 tcp_keepalive 结构。这种结构的定义如下：

1 /* Argument structure for SIO_KEEPALIVE_VALS */
2 struct tcp_keepalive {
3 u_long onoff;
4 u_long keepalivetime;
5 u_long keepaliveinterval;
6 };

将 tcp_keepalive C 转换为 C# struct结构

 1 // Convert tcp_keepalive C struct To C# struct
 2 [
 3        System.Runtime.InteropServices.StructLayout
 4        (
 5            System.Runtime.InteropServices.LayoutKind.Explicit
 6        )
 7 ]
 8 unsafe struct TcpKeepAlive
 9 {
10     [System.Runtime.InteropServices.FieldOffset(0)]
11     [
12           System.Runtime.InteropServices.MarshalAs
13            (
14                System.Runtime.InteropServices.UnmanagedType.ByValArray,
15                SizeConst = 12
16            )
17     ]
18     public fixed byte Bytes[12];
19 
20     [System.Runtime.InteropServices.FieldOffset(0)]
21     public uint On_Off;
22         
23     [System.Runtime.InteropServices.FieldOffset(4)]
24     public uint KeepaLiveTime;
25         
26     [System.Runtime.InteropServices.FieldOffset(8)]
27     public uint KeepaLiveInterval;
28 }
29 
30 public int SetKeepAliveValues
31       (
32            System.Net.Sockets.Socket Socket,
33            bool On_Off,
34            uint KeepaLiveTime,
35            uint KeepaLiveInterval
36        )
37 {       
38     int Result = -1;
39 
40     unsafe
41     {
42         TcpKeepAlive KeepAliveValues = new TcpKeepAlive();
43 
44         KeepAliveValues.On_Off = Convert.ToUInt32(On_Off);
45         KeepAliveValues.KeepaLiveTime = KeepaLiveTime;
46         KeepAliveValues.KeepaLiveInterval = KeepaLiveInterval;
47 
48         byte[] InValue = new byte[12];
49 
50         for (int I = 0; I < 12; I++)
51             InValue[I] = KeepAliveValues.Bytes[I];
52 
53         Result = Socket.IOControl(IOControlCode.KeepAliveValues, InValue, null);
54     }
55 
56     return Result;
57 }

调用方法：

1 System.Net.Sockets.Socket Socket = new System.Net.Sockets.Socket
2     (
3         System.Net.Sockets.AddressFamily.InterNetwork,
4         System.Net.Sockets.SocketType.Stream,
5         System.Net.Sockets.ProtocolType.Tcp
6     );
7     
8 // Set 10 Hours: 10 * 60 * 60 * 1000 = 36,000,000 every 1 Second 1000
9 SetKeepAliveValues(Socket, true, 36000000, 1000);