套接字Keepalive无法正常工作

Question

我有一个客户端connect（）连接到服务器，闲置时它会在几个小时后超时。 我加了 setsockopt（socket，SOL_SOCKET，SO_KEEPALIVE ...）1秒 但它没有什么区别。 为什么Keepalive不会工作的任何线索？ 如果我使用SOL_TCP而不是SOL_SOCKET，它会有所作为吗？ 这是在Linux上。

Answer 1

int val = 1; 
setsockopt(socket, SOL_SOCKET, SO_KEEPALIVE, &val, sizeof val) 

只是启用keepalives。你会得到默认的定时器的存活探测，您可以用命令查看：

sysctl net.ipv4.tcp_keepalive_time 

通常默认值是几个小时。

如果要更改默认的定时器，你可以这样做：

struct KeepConfig cfg = { 60, 5, 5}; 
set_tcp_keepalive_cfg(fd, &cfg); 

随着辅助功能在这里：

struct KeepConfig { 
    /** The time (in seconds) the connection needs to remain 
    * idle before TCP starts sending keepalive probes (TCP_KEEPIDLE socket option) 
    */ 
    int keepidle; 
    /** The maximum number of keepalive probes TCP should 
    * send before dropping the connection. (TCP_KEEPCNT socket option) 
    */ 
    int keepcnt; 

    /** The time (in seconds) between individual keepalive probes. 
    * (TCP_KEEPINTVL socket option) 
    */ 
    int keepintvl; 
}; 

/** 
* enable TCP keepalive on the socket 
* @param fd file descriptor 
* @return 0 on success -1 on failure 
*/ 
int set_tcp_keepalive(int sockfd) 
{ 
    int optval = 1; 

    return setsockopt(sockfd, SOL_SOCKET, SO_KEEPALIVE, &optval, sizeof(optval)); 
} 

/** Set the keepalive options on the socket 
* This also enables TCP keepalive on the socket 
* 
* @param fd file descriptor 
* @param fd file descriptor 
* @return 0 on success -1 on failure 
*/ 
int set_tcp_keepalive_cfg(int sockfd, const struct KeepConfig *cfg) 
{ 
    int rc; 

    //first turn on keepalive 
    rc = set_tcp_keepalive(sockfd); 
    if (rc != 0) { 
     return rc; 
    } 

    //set the keepalive options 
    rc = setsockopt(sockfd, IPPROTO_TCP, TCP_KEEPCNT, &cfg->keepcnt, sizeof cfg->keepcnt); 
    if (rc != 0) { 
     return rc; 
    } 

    rc = setsockopt(sockfd, IPPROTO_TCP, TCP_KEEPIDLE, &cfg->keepidle, sizeof cfg->keepidle); 
    if (rc != 0) { 
     return rc; 
    } 

    rc = setsockopt(sockfd, IPPROTO_TCP, TCP_KEEPINTVL, &cfg->keepintvl, sizeof cfg->keepintvl); 
    if (rc != 0) { 
     return rc; 
    } 

    return 0; 
} 

Answer 2

尽管它的名字，保活是不是保持连接活着，它是关于定期交换数据包以确保对等体之间存在网络路径。它会导致在闲置时延长网络中断的连接。

由于这种行为，除非有充分的理由，如telnet或SSH连接，当客户端失去联系时可以合理地终止会话，否则不应使用保持活动状态。

由于某些连接处理策略，很可能是服务器在n小时后关闭连接，无论存活使用情况如何。