QTcpSocket state always connected

JonB

@puzzled_giraffe , @KroMignon
I will just throw in an observation based on my tests years ago. Please take what I say with a pinch of salt, I might be wrong, @KroMignon may know more than I do, but....

When I tried this out (under Windows) on a product we developed I actually found that the keep-alive stuff made the situation worse. Because it's testing all the time, I found that it actually noticed missing connections and dropped/closed them more than if I had nothing and left TCP to its own devices.

So do you really need to be heartbeat pinging?

puzzled_giraffe

@KroMignon said in QTcpSocket state always connected:

result = setsockopt(fd, SOL_SOCKET, SO_KEEPALIVE, &enableKeepAlive, sizeof(enableKeepAlive));
result = setsockopt(fd, IPPROTO_TCP, TCP_KEEPIDLE, &maxIdle, sizeof(maxIdle));
result = setsockopt(fd, IPPROTO_TCP, TCP_KEEPCNT, &count, sizeof(count));
result = setsockopt(fd, IPPROTO_TCP, TCP_KEEPINTVL, &interval, sizeof(interval));

TCP_KEEPIDLE / TCP_KEEPCNT / TCP_KEEPINTVL - linux options, aren't they?

So for windows I found next solution:
add this lib to your project *.pro file

LIBS += -lws2_32

Next after socket connection you should use:

#include <Ws2tcpip.h>
//------
// socket is QTcpSocket*
if (socket->state() == QAbstractSocket::ConnectedState) {
    int fd = socket->socketDescriptor();    
    DWORD  dwBytesRet = 0;
    
    struct tcp_keepalive   alive;    // your options for "keepalive" mode    
    alive.onoff = TRUE;              // turn it on    
    alive.keepalivetime = 30000;     // delay (ms) between requests, here is 30s, default is 2h (7200000)    
    alive.keepaliveinterval = 5000;  // delay between "emergency" ping requests, their number (6) is not configurable
    /* So with this config  socket will send keepalive requests every 30 seconds after last data transaction when everything is ok.
       If there is no reply (wire plugged out) it'll send 6 requests with 5s delay  between them and then close. 
       As a result we will get disconnect after approximately 1 min timeout.
    */
    if (WSAIoctl(fd, SIO_KEEPALIVE_VALS, &alive, sizeof(alive), NULL, 0, &dwBytesRet, NULL, NULL) == SOCKET_ERROR) {    
        QDebug() << "WSAIotcl(SIO_KEEPALIVE_VALS) failed with err#" <<  WSAGetLastError();    
        return;    
    }
}

Pangolin

@puzzled_giraffe
QTcpsocket have not got "connectState" setup? I think qt use long tcp connection by default.