[fpc-pascal] How to detect connection status of a socket

[Marco van de Voort]

In our previous episode, Xiangrong Fang said:
> I am writing a redis client in fpc and found that even when the connection
> is closed by server (via redis CLIENT KILL),

I don't know the redis protocol is, but "CLIENT KILL" sounds like redis
protocol, while you are trying to detect disconnect at socket level. And is
your socket layer really connection oriented ?

IOW does the remote server really actively close the socket?

Maybe stracing the application during a disconnect event might yield some
more information.

> How do I tell if a socket is still connected or not?

Limit the timeout time (some socketoption or ioctl iirc, search the web),
send something, and wait the timeout time.  Then read something.