Comment by doorman2 | Hacker News Reader

Comment by doorman2 | Hacker News Reader

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Thanks, that's is interesting background. From my pty experience, though, the answer is a bit unsatisfying. One reason is that I thought ^D generated an EOF in the terminal. For instance, if I use `wc` in the terminal, it reads from STDIN until I use ^D and then I get the output. Another reason is that it seems like a bug in the program to not respond to EOF. At the very least, unbuffer could offer an option? Anyway, I digress...

The PTY interface in general feels a bit lacking. Normally, if you use a pipe, you can close to write end of the pipe to generate an EOF. With pseudo-terminals, you only have one file descriptor for writing input and reading output so you can't have the system generate an EOF without disabling your ability to read the output.

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.)

^D only does that in cooked input mode. In raw mode ^D send ^D, and it's up to the program to interpret that, or not. This is essential in, eg, telnet, since it wants to be able to open a session on a remote host that behaves exactly like a session on a local host, including its behaviour in response to ^D.

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