On Sat, Jan 21, 2023 at 07:25:33PM +0100, S??ren Tempel wrote:
> Hello,
>
> Section 11.1.9 of POSIX.1-2008 mandates the following behavior regarding
> the handling of the special EOF character:
>
> EOF Special character on input, which is recognized if the
> ICANON flag is set. When received, all the bytes waiting to be
> read are immediately passed to the process without waiting for a
> <newline>, and the EOF is discarded. [...] If ICANON is set, the
> EOF character shall be discarded when processed.
>
> The "Special Characters" section of the OpenBSD termios(4) man page also
> emphasizes that EOF is discarded if there is pending input. However, it
> seems that this is not correctly implemented on -stable presently.
> Consider the following C program:
>
> #include <unistd.h>
> #include <stdio.h>
>
> int main(void) {
> for (;;) {
> char c;
>
> int r = read(1, &c, sizeof(c));
> if (r == 0) break; /* EOF */
> printf("c: %c\n", c);
> }
> }
>
> After compiling and executing this program (in canonical mode input
> processing), enter "foo<ctrl-d>". According to the text referenced
> above, this should cause the characters 'f', 'o', and 'o' to be printed.
> The EOF should be discarded and hence the program should prompt for more
> input. Over in Linux-land this is exactly what happens, however, on
> OpenBSD 7.2 the EOF is **not** discarded and hence the program
> terminates after printing the aforementioned characters. If my
> understanding of the POSIX standard and the termios(4) man page is
> correct, then OpenBSD's handling of the EOF character is not conforming
> to the specification, and hence I would consider this a bug.
>
> I ran into this while using GNU ed(1) on OpenBSD where partially entered
> text in input and command mode is not handled correctly on EOF because
> of this bug.
>
> Greetings,
> S??ren
>
Some observations:
- You are reading from stdout.
- Since you are reading one char at the time, the moment the EOF is
processed the buffer is empty, so no pending chars. I'll take that as
a valid interpretation of Posix.
- If you modify your program to read 4 chars at the time (see below),
you will see your expected behaviour.
-Otto
#include <unistd.h>
#include <stdio.h>
int main(void)
{
for (;;) {
char c[4];
ssize_t r = read(0, c, sizeof(c));
if (r == 0)
break; /* EOF */
printf("read: %zd chars\n", r);
}
}
