How is Ctrl+C key behaves in a TCP connection

Question

I'm studying network and specifically tcp connection and i wondering in a situation that you connect remotely to a server using tcp connection and sending command line to execute some actions, How they handle sending a ctrl+c signals?
Is it sends a normal tcp package that in data section describes ctrl+c hits?
or is it sends a package that have RST flag turned on or FIN flag to cut or close the connection?

Answer 1

There's no such thing as sending a signal over TCP.

Ctrl+C is a terminal generated signal. Assuming you (or the running process) didn't change the terminal's settings, this means that the terminal driver transforms the Ctrl+C key combination into a kill(x, SIGINT), where x is the process group ID of the foreground process group (and as such, SIGINT is delivered to every process in the foreground process group, which, in your case, is probably just one process).

What the process does when the signal is delivered is not the terminal driver's business. The process may have ignored the signal, so nothing happens. Or it may have installed a signal handler, and do some work inside the signal handler (like writing something to the socket that when read by the receiver will cause it to send SIGINT to itself - this emulates a "remote signal delivery"). Or it may have blocked the signal - in that case, the signal is delivered when the process unblocks it, or it is canceled if the process ignores it in the meantime.

If, on the other hand, you (or the running process) changed the terminal settings such that Ctrl+C is not interpreted as a signal-generating key combination, then the process will read Ctrl+C from input. Of course, what happens depends on what the process does with the input that it reads.

In short, if you didn't change the default behavior for SIGINT and you didn't change your terminal's settings, Ctrl+C raises SIGINT; the default action is to terminate the process, and so the socket will be closed and the connection terminated.