script input redirection / eof handling

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I came across an old bug filed in debian about script being redirected from a file misbehaving. It seems that when the master ( input ) process hits eof, it exits immediately, orphaning the child ( output ) and user processes.

I believe the correct thing to do is signal the eof to the user process and wait for the children to exit, but I'm not sure how to make a pty signal eof.

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Do you mean something like:

echo "ps uf" | script

.. if yes, then it's pretty unexpected usage. The code expects that stdin is terminal. (For example it copy the current terminal attributes the new pseudo-terminal.)

Unfortunately it does not check tcgetatt() return code so the problem is not visible. I'll fix it.

Yep, I think it would be enough to add

       kill(0, SIGTERM);

before done() in doinput() to avoid orphans.

Karel

 Karel Zak  <[email protected]>
 http://karelzak.blogspot.com

Note, that if you want to support this scenario (stdin is not a terminal) then send a patch ;-)

I guess you have to initialize the terminal (see inlude/ttyutils.h, reset_virtual_console()) and use this dummy struct termios instead of the current 'tt'.

This is probably not the best solution (because shell will print "Terminated" etc.), but it's definitely better than orphans.

Karel

 Karel Zak  <[email protected]>
 http://karelzak.blogspot.com

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It seems to work fine up until it hits eof, which can also happen on a tty and you'll get the same bad behavior, so I think refusing to run on a non tty isn't a proper fix.

You don't want to just make sure the children die, you want to make sure that the child sees the eof and capture any final output it may have.

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well, it's nasty that the code ignores return codes and it call's tty ioctls/functions for non-tty file descriptors.

never ending orphans suck...

The possible solution (hack) to emulate end-of-file is by write "exit\n" to the master tty. For example patch below works for me (it also make it more robust for non-ttys).

Karel

index c18274c..8437ec8 100644
@@ -107,6 +107,7 @@ int	fflg = 0;
 int	qflg = 0;
 int	tflg = 0;
 int	forceflg = 0;
+int	isterm;
 
 int die;
 int resized;

@@ -230,9 +231,6 @@ main(int argc, char **argv) {
 		die_if_link(fname);
 	}
 
-	if (!isatty(STDIN_FILENO))
-		errx(EXIT_FAILURE, _("The stdin is not a terminal."));
-
 	if ((fscript = fopen(fname, aflg ? "a" : "w")) == NULL) {
 		warn(_("cannot open %s"), fname);
 		fail();

@@ -314,11 +312,21 @@ doinput(void) {
 		else if (cc < 0 && errno == EINTR && resized)
 		{
 			/* transmit window change information to the child */
-			ioctl(STDIN_FILENO, TIOCGWINSZ, (char *)&win);
-			ioctl(slave, TIOCSWINSZ, (char *)&win);
+			if (isterm) {
+				ioctl(STDIN_FILENO, TIOCGWINSZ, (char *)&win);
+				ioctl(slave, TIOCSWINSZ, (char *)&win);
+			}
 			resized = 0;
-		}
-		else
+		} else if (cc == 0 && errno == 0) {
+			/* end-of-file, probably "foo | script" */
+			strcpy(ibuf, "exit\n");
+			if (write(master, ibuf, 5) < 0) {
+				warn (_("write failed"));
+				fail();
+			}
+			pause();		/* wait for SIGCHLD */
+			break;
+		} else
 			break;
 	}
 

@@ -473,6 +481,9 @@ void
 fixtty(void) {
 	struct termios rtt;
 
+	if (!isterm)
+		return;
+
 	rtt = tt;
 	cfmakeraw(&rtt);
 	rtt.c_lflag &= ~ECHO;

@@ -503,7 +514,8 @@ done(void) {
 
 		master = -1;
 	} else {
-		tcsetattr(STDIN_FILENO, TCSADRAIN, &tt);
+		if (isterm)
+			tcsetattr(STDIN_FILENO, TCSADRAIN, &tt);
 		if (!qflg)
 			printf(_("Script done, file is %s\n"), fname);
 #ifdef HAVE_LIBUTEMPTER

@@ -524,9 +536,19 @@ done(void) {
 void
 getmaster(void) {
 #if defined(HAVE_LIBUTIL) && defined(HAVE_PTY_H)
-	tcgetattr(STDIN_FILENO, &tt);
-	ioctl(STDIN_FILENO, TIOCGWINSZ, (char *)&win);
-	if (openpty(&master, &slave, NULL, &tt, &win) < 0) {
+	int rc;
+
+	isterm = isatty(STDIN_FILENO);
+
+	if (isterm) {
+		if (tcgetattr(STDIN_FILENO, &tt) != 0)
+			err(EXIT_FAILURE, _("failed to get terminal attributes"));
+		ioctl(STDIN_FILENO, TIOCGWINSZ, (char *) &win);
+		rc = openpty(&master, &slave, NULL, &tt, &win);
+	} else
+		rc = openpty(&master, &slave, NULL, NULL, NULL);
+
+	if (rc < 0) {
 		warn(_("openpty failed"));
 		fail();
 	}

@@ -534,6 +556,8 @@ getmaster(void) {
 	char *pty, *bank, *cp;
 	struct stat stb;
 
+	isterm = isatty(STDIN_FILENO);
+
 	pty = &line[strlen("/dev/ptyp")];
 	for (bank = "pqrs"; *bank; bank++) {
 		line[strlen("/dev/pty")] = *bank;

@@ -552,9 +576,11 @@ getmaster(void) {
 				ok = access(line, R_OK|W_OK) == 0;
 				*tp = 'p';
 				if (ok) {
-					tcgetattr(STDIN_FILENO, &tt);
-					ioctl(STDIN_FILENO, TIOCGWINSZ,
-						(char *)&win);
+					if (isterm) {
+						tcgetattr(STDIN_FILENO, &tt);
+						ioctl(STDIN_FILENO, TIOCGWINSZ,
+								(char *)&win);
+					}
 					return;
 				}
 				close(master);

@@ -577,8 +603,10 @@ getslave(void) {
 		warn(_("cannot open %s"), line);
 		fail();
 	}
-	tcsetattr(slave, TCSANOW, &tt);
-	ioctl(slave, TIOCSWINSZ, (char *)&win);
+	if (isterm) {
+		tcsetattr(slave, TCSANOW, &tt);
+		ioctl(slave, TIOCSWINSZ, (char *)&win);
+	}
 #endif
 	setsid();
 	ioctl(slave, TIOCSCTTY, 0);

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Yes, but the idea is not to orphan them in the first place and wait for them to terminate instead.

That only works if the program on the other end knows what "exit" means, which is basically only true if it's a shell. Surely there must be a proper way to signal EOF over a pty? Can you use shutdown() on a pty?

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yep, fingers have been faster than brain.. (I forgot we have --command).

I'm going to play with that tomorrow.

Karel

 Karel Zak  <[email protected]>
 http://karelzak.blogspot.com

Oh, now it reminds me... in include/ttyutils.h we have macros to generate tty control chars, for example ^C

			char eof = DEF_EOF;

			if (write(master, &eof, 1) < 0) {
				warn (_("write failed"));
				fail();
			}
            pause();

is what we need.

Karel

 Karel Zak  <[email protected]>
 http://karelzak.blogspot.com

It was more tricky than I have originally expected, but it seems it works. (It seems that it is not enough to send EOF, you have to be sure that someone already listens on slave side.)

Karel

 Karel Zak  <[email protected]>
 http://karelzak.blogspot.com