[skissane]

There should be an IOCTL to trigger an EOF condition on a PTY (even if it is in raw mode). So (once the input buffer is empty), read() calls on the client side will just return 0 instead of blocking.

That requires code changes to the Linux (or whatever other OS you are using) kernel. An approach without any kernel code changes, for Linux, would be to use CUSE to implement a user-space character device. (FreeBSD has a CUSE too, although apparently its implementation is not very compatible with the Linux one). Note you can't actually create a custom tty using CUSE – it doesn't support registering its devices with the tty subsystem – but you can create a device which implements (yourself) enough of the TTY IOCTLs to trick other programs into thinking it is a TTY. (isatty() calls tcgetattr() which calls ioctl(TCGETS), so implementing that IOCTL is enough to convince most programs you are a TTY.)