ayourtch / arrgap

a workaround against my serial tty not being able to use SIGWINCH

This is a small convenience utility for a more convenient working in a secured environment where your VPN blocks all of the connections to local network, but nonetheless you would like to retain the terminal shell access to the devices on it.

For this, one can configure a raspberry pi zero w to act as a USB gadget with the login shell on the serial port - thus, for your main laptop it will appear as a serial port dongle connected to "some" linux computer.

Since the serial communication is uninhibited, you can get the simultaneous control over the device on the local network (from raspberry), as well as in the secured environment (directly over VPN).

However, there is a catch: the serial interface assumes a fixed window size. This makes it supremely inconvenient to use it in a window - the moment you resize the window away from the default 80x24, all your output goes very corrupt.

Quite obviously - because SIGWINCH, which is sent to your local terminal when you resize the window, is not sent over the serial interface. This small program is there to take care of that: first, on your main/secured host launch "ARRGAP_LOCAL=y ./arrgap". This will give you a shell.

In this shell, connect to the serial port, raspberry pi, etc. On the raspberry pi, start ./arrgap - this will give you another shell. If you now start a full screen terminal app (like vi or tmux), and resize your terminal, you will see that the target application has resized as well!

This is achieved by emitting from the host machine an escape sequence each time it gets a SIGWINCH, and the target machine intercepts this escape sequence and sends the appropriate ioctl() locally, setting the terminal window size. The local apps notice that and adapt accordingly.