How to deal with lost connection?

[davidemannone]

I cannot find any way to catch connection loss (remote disconnection or cable disconnection, etc).
The c library should do it (i used it in c), and even log reports it: Connection closed by remote.
Even the is_open property did not change its state to False if polled while disconnected.

[chrisbeardy]

The is_open property just tells you a connection to the local router is open or not, not the PLC, the only way to tell if a connection is lost is by trying to read a variable. I normally set up a "heartbeat" to read a variable on a set time basis. When you say the C library does it, what function is this? It may be able to be added.

[davidemannone]

I had right a closer look to the code I wrote in c++ much time ago linking the same c library. And I apologize, I misremembered! My implementation upon the library did it, but without support of the library because it is maybe UDP communication. Having also a closer look in the library the assertion ("communication closed by remote") is reported simply when closing connection and no reply response is received.
What I used for? 2 mechanism:

1. I use poll the AdsSyncReadStateReqEx to request the PLC status so getting also the internal behavior let's say: RUNNING MODE, CONFIG MODE, and all others. These function doesn't requires any symbol handling, nor index research and return only 2 ushorts: I suppose it could execute slightly faster, and knowing about PLC status is important too. No answer -> no connection! When connection is established, and will be lost and if restored, it returns operating without any issue.
2. I also use not just an "haertbeat" but more a cyclic keepalive (pc->byte increment)-watchdog (plc->same byte reply, within a certain time) after success for the step 1, that will execute without waiting for timeout and tells me not only that's fine, but also that PLC is executing the expected program.

So, again, sorry for my request, and hope at least that these thread could help others to implement such important feature.