QTcpSocket利用setsockopt实现连接保活

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QTcpSocket利用setsockopt实现连接保活

保活机制

socket保活有三种机制：

  • SO_KEEPALIVE
  • SIO_KEEPALIVE_VALS
  • Heart-Beat

Linux的keepalive机制

Linux内置支持keepalive机制，涉及三个变量：

  • tcp_keepalive_time：失连时间（秒）
  • tcp_keepalive_intvl：重连间隔（秒）
  • tcp_keepalive_probes：重连次数（次）

查看方式：

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cat /proc/sys/net/ipv4/tcp_keepalive_time
cat /proc/sys/net/ipv4/tcp_keepalive_intvl
cat /proc/sys/net/ipv4/tcp_keepalive_probes

默认情况下为：

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7200
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9

手动设置方式（重启失效）：

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echo 100 > /proc/sys/net/ipv4/tcp_keepalive_time
echo 10 > /proc/sys/net/ipv4/tcp_keepalive_intvl
echo 1 > /proc/sys/net/ipv4/tcp_keepalive_probes

QTcpSocket中设置keepalive

Qt提供了开启keepalive的接口，但是没有提供上述三个变量的配置接口：

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QTcpSocket::setSocketOption(QAbstractSocket::KeepAliveOption, 1);

设置方式需要使用中提供的：

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/* Set socket FD's option OPTNAME at protocol level LEVEL
   to *OPTVAL (which is OPTLEN bytes long).
   Returns 0 on success, -1 for errors.  */
extern int setsockopt (int __fd, int __level, int __optname, const void *__optval, socklen_t __optlen) __THROW;

其中：

  • fd: socket句柄
  • level: 协议层（SOL_SOCKET、SOL_TCP）
  • optname: 变量名（SO_KEEPALIVE、TCP_KEEPIDLE、TCP_KEEPINTVL、TCP_KEEPCNT）
  • optval: 变量指针
  • optlen: 变量长度

如使用了SO_KEEPALIVE可不设置qt自带的QAbstractSocket::KeepAliveOption

代码示例

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#include <sys/types.h>
#include <sys/socket.h>
#include <fcntl.h>
#include <netinet/tcp.h>

QTcpSocket *client = new QTcpSocket(this);
client->connectToHost(ip,8888);
if(client->waitForConnected(1000))
{
    if(client->socketDescriptor() == -1)
    {
        S_WARN("fail to get socketDescriptor");
    }
    else
    {
        Log("socketDescriptor {}", client->socketDescriptor());
    }

    //开启保活
    int enable = 1;
    if(setsockopt(client->socketDescriptor(), SOL_SOCKET, SO_KEEPALIVE, &enable, sizeof(enable)) != 0)
    {
        Log("fail to enable SO_KEEPALIVE");
    }
    //失连时间>0
    int lost_time = 1;
    if(setsockopt(client->socketDescriptor(), SOL_TCP, TCP_KEEPIDLE, &lost_time, sizeof(lost_time)) != 0)
    {
        Log("fail to enable TCP_KEEPIDLE");
    }
    //重连时间>0
    int retry_time = 1;
    if(setsockopt(client->socketDescriptor(), SOL_TCP, TCP_KEEPINTVL, &retry_time, sizeof(retry_time)) != 0)
    {
        Log("fail to enable TCP_KEEPINTVL");
    }
    //重连次数>0
    int retry_num = 1;
    if(setsockopt(client->socketDescriptor(), SOL_TCP, TCP_KEEPCNT, &retry_num, sizeof(retry_num)) != 0)
    {
        Log("fail to enable TCP_KEEPCNT");
    }
}

参考