Ok, cool
I got a bit further now.
I'm not using handles anymore (they seem to break indeed for ptys).
Just using executePseudoTerminalFd now (from the original blogpost)
and fdRead/fdWrite.
Now I can communicate with the process and all goes well.
If I really want lazy-like behaviour, I can just forkIo and talk
through a Chan, but for now this is enough.
Also sending "\^C" and "\^D" work as expected, although I just saw the
reply mentioning I should ask stty for the current EOF character.
The only thing I'm still looking for is a way to stop echoing input.
Right now, fdRead gives me back the output of the process, mixed with
the input I supplied.
I'm pretty sure this can be turned off.
Any suggestions?
On Mon, Mar 8, 2010 at 11:11 PM, Nick Bowler
On 20:38 Mon 08 Mar , Mathijs Kwik wrote:
Hi all,
I found this blogpost from Bryan O'Sullivan http://www.serpentine.com/blog/2008/09/30/unix-hacking-in-haskell-better-pse... and I wanted to try it out.
Before moving to an interactive command (which needs pty), I just did a small test for "ls -l /" to see if it worked. I got it to compile, but when running, it throws an exception when reaching the end of the output (in this case because I evaluate the length to force reading all). Main: /dev/ptmx: hGetContents: hardware fault (Input/output error)
You have just stumbled into the wonderful world of pseudo-terminals, where their behaviour is subtly different on every bloody platform. It appears that on your platform, after the last user closes the slave port (i.e. after your child process terminates), subsequent reads from the master port return EIO.
One would normally detect this condition with the poll system call, by looking for POLLHUP on the master port.
On some platforms (but evidently not yours), the last close of the slave port causes the behaviour you seem to have expected, where a subsequent read returns 0.
What's wrong? :)
Presumably the problem is that handle-based I/O is not suitable for pseudo-terminal masters. Definitely not lazy I/O.
And further... If I do want to use an interactive program which needs input, how do I send ctrl-d or ctrl-c? tail -f needs ctrl-c (or I need to kill the process)
These so-called "control characters" are normally configured by termios. If suitably configured, the appropriate action will be performed when the control characters are written to the master port.
-- Nick Bowler, Elliptic Technologies (http://www.elliptictech.com/)