golang判断tcp是否断开的方法

golang判断tcp是否断开的方法：

keepalive检测，对于设置了keepalive来说，当tcp检测到对端socket不再可用时(不能发出探测包,或探测包没有收到ACK的响应包),select会返回socket可读,并且在recv时返回-1,同时置上errno为ETIMEDOUT。此时TCP的状态是断开的。

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struct TCP_KEEPALIVE {  
    unsigned long onoff;  
    unsigned long keepalivetime;  
    unsigned long keepaliveinterval;  
} ;  
  
#define SIO_KEEPALIVE_VALS _WSAIOW(IOC_VENDOR,4)  
  
/* KeepAlive实现 */  
void set_keepalive (SOCKET s)  
{  
    BOOL bKeepAlive = TRUE;  
    int nRet = ::setsockopt(s, SOL_SOCKET, SO_KEEPALIVE, (char*)&bKeepAlive, sizeof(bKeepAlive));  
    if (nRet == SOCKET_ERROR)  
    {  
        return ;  
    }  
    /* 输入参数 */  
    struct TCP_KEEPALIVE inKeepAlive = {0};   
    unsigned long ulInLen = sizeof(struct TCP_KEEPALIVE);  
  
    /* 输出参数 */  
    struct TCP_KEEPALIVE outKeepAlive = {0};   
    unsigned long ulOutLen = sizeof(struct TCP_KEEPALIVE);  
    unsigned long ulBytesReturn = 0;  
    int ret = 0;  
  
    /* 设置keepalive 为5秒，并且发送次数为3次 */  
    inKeepAlive.onoff             = 1;  
    /* 2次keepalive探测间隔时间 */  
    inKeepAlive.keepaliveinterval = 5000;   
    /* 开始首次keepalive探测前的tcp空闲时间 */  
    inKeepAlive.keepalivetime     = 5000;   
  
    ret = WSAIoctl((unsigned int)s,  
            SIO_KEEPALIVE_VALS,  
            (LPVOID)&inKeepAlive,   
            ulInLen,  
            (LPVOID)&outKeepAlive,   
            ulOutLen,  
            &ulBytesReturn,   
            NULL,   
            NULL);  
    if (ret == SOCKET_ERROR)  
    {  
        printf ("error: %d\n", WSAGetLastError());  
    }  
}

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