mirror of
https://sourceware.org/git/glibc.git
synced 2024-11-08 14:20:07 +00:00
2cc7bad0ae
C99 specifies that the EOF condition on a file is "sticky": once EOF has been encountered, all subsequent reads should continue to return EOF until the file is closed or something clears the "end-of-file indicator" (e.g. fseek, clearerr). This is arguably a change from C89, where the wording was ambiguous; the BSDs always had sticky EOF, but the System V lineage would attempt to read from the underlying fd again. GNU libc has followed System V for as long as we've been using libio, but nowadays C99 conformance and BSD compatibility are more important than System V compatibility. You might wonder if changing the _underflow impls is sufficient to apply the C99 semantics to all of the many stdio functions that perform input. It should be enough to cover all paths to _IO_SYSREAD, and the only other functions that call _IO_SYSREAD are the _seekoff impls, which is OK because seeking clears EOF, and the _xsgetn impls, which, as far as I can tell, are unused within glibc. The test programs in this patch use a pseudoterminal to set up the necessary conditions. To facilitate this I added a new test-support function that sets up a pair of pty file descriptors for you; it's almost the same as BSD openpty, the only differences are that it allocates the optionally-returned tty pathname with malloc, and that it crashes if anything goes wrong. [BZ #1190] [BZ #19476] * libio/fileops.c (_IO_new_file_underflow): Return EOF immediately if the _IO_EOF_SEEN bit is already set; update commentary. * libio/oldfileops.c (_IO_old_file_underflow): Likewise. * libio/wfileops.c (_IO_wfile_underflow): Likewise. * support/support_openpty.c, support/tty.h: New files. * support/Makefile (libsupport-routines): Add support_openpty. * libio/tst-fgetc-after-eof.c, wcsmbs/test-fgetwc-after-eof.c: New test cases. * libio/Makefile (tests): Add tst-fgetc-after-eof. * wcsmbs/Makefile (tests): Add tst-fgetwc-after-eof.
110 lines
3.7 KiB
C
110 lines
3.7 KiB
C
/* Bug 1190: EOF conditions are supposed to be sticky.
|
|
Copyright (C) 2018 Free Software Foundation.
|
|
Copying and distribution of this file, with or without modification,
|
|
are permitted in any medium without royalty provided the copyright
|
|
notice and this notice are preserved. This file is offered as-is,
|
|
without any warranty. */
|
|
|
|
/* ISO C1999 specification of fgetc:
|
|
|
|
#include <stdio.h>
|
|
int fgetc (FILE *stream);
|
|
|
|
Description
|
|
|
|
If the end-of-file indicator for the input stream pointed to by
|
|
stream is not set and a next character is present, the fgetc
|
|
function obtains that character as an unsigned char converted to
|
|
an int and advances the associated file position indicator for
|
|
the stream (if defined).
|
|
|
|
Returns
|
|
|
|
If the end-of-file indicator for the stream is set, or if the
|
|
stream is at end-of-file, the end-of-file indicator for the
|
|
stream is set and the fgetc function returns EOF. Otherwise, the
|
|
fgetc function returns the next character from the input stream
|
|
pointed to by stream. If a read error occurs, the error indicator
|
|
for the stream is set and the fgetc function returns EOF.
|
|
|
|
The requirement to return EOF "if the end-of-file indicator for the
|
|
stream is set" was new in C99; the language in the 1989 edition of
|
|
the standard was ambiguous. Historically, BSD-derived Unix always
|
|
had the C99 behavior, whereas in System V fgetc would attempt to
|
|
call read() again before returning EOF again. Prior to version 2.28,
|
|
glibc followed the System V behavior even though this does not
|
|
comply with C99.
|
|
|
|
See
|
|
<https://sourceware.org/bugzilla/show_bug.cgi?id=1190>,
|
|
<https://sourceware.org/bugzilla/show_bug.cgi?id=19476>,
|
|
and the thread at
|
|
<https://sourceware.org/ml/libc-alpha/2012-09/msg00343.html>
|
|
for more detail. */
|
|
|
|
#include <support/tty.h>
|
|
#include <support/check.h>
|
|
|
|
#include <fcntl.h>
|
|
#include <stdio.h>
|
|
#include <stdlib.h>
|
|
#include <string.h>
|
|
#include <unistd.h>
|
|
|
|
#define XWRITE(fd, s, msg) do { \
|
|
if (write (fd, s, sizeof s - 1) != sizeof s - 1) \
|
|
{ \
|
|
perror ("write " msg); \
|
|
return 1; \
|
|
} \
|
|
} while (0)
|
|
|
|
int
|
|
do_test (void)
|
|
{
|
|
/* The easiest way to set up the conditions under which you can
|
|
notice whether the end-of-file indicator is sticky, is with a
|
|
pseudo-tty. This is also the case which applications are most
|
|
likely to care about. And it avoids any question of whether and
|
|
how it is legitimate to access the same physical file with two
|
|
independent FILE objects. */
|
|
int outer_fd, inner_fd;
|
|
FILE *fp;
|
|
|
|
support_openpty (&outer_fd, &inner_fd, 0, 0, 0);
|
|
fp = fdopen (inner_fd, "r+");
|
|
if (!fp)
|
|
{
|
|
perror ("fdopen");
|
|
return 1;
|
|
}
|
|
|
|
XWRITE (outer_fd, "abc\n\004", "first line + EOF");
|
|
TEST_COMPARE (fgetc (fp), 'a');
|
|
TEST_COMPARE (fgetc (fp), 'b');
|
|
TEST_COMPARE (fgetc (fp), 'c');
|
|
TEST_COMPARE (fgetc (fp), '\n');
|
|
TEST_COMPARE (fgetc (fp), EOF);
|
|
|
|
TEST_VERIFY_EXIT (feof (fp));
|
|
TEST_VERIFY_EXIT (!ferror (fp));
|
|
|
|
XWRITE (outer_fd, "d\n", "second line");
|
|
|
|
/* At this point, there is a new full line of input waiting in the
|
|
kernelside input buffer, but we should still observe EOF from
|
|
stdio, because the end-of-file indicator has not been cleared. */
|
|
TEST_COMPARE (fgetc (fp), EOF);
|
|
|
|
/* Clearing EOF should reveal the next line of input. */
|
|
clearerr (fp);
|
|
TEST_COMPARE (fgetc (fp), 'd');
|
|
TEST_COMPARE (fgetc (fp), '\n');
|
|
|
|
fclose (fp);
|
|
close (outer_fd);
|
|
return 0;
|
|
}
|
|
|
|
#include <support/test-driver.c>
|