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[BZ 1190] Make EOF sticky in stdio.
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.
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17
ChangeLog
17
ChangeLog
@ -1,3 +1,20 @@
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2018-03-12 Zack Weinberg <zackw@panix.com>
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[BZ #1190]
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[BZ #19476]
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* libio/fileops.c (_IO_new_file_underflow): Return EOF immediately
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if the _IO_EOF_SEEN bit is already set; update commentary.
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* libio/oldfileops.c (_IO_old_file_underflow): Likewise.
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* libio/wfileops.c (_IO_wfile_underflow): Likewise.
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* support/support_openpty.c, support/tty.h: New files.
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* support/Makefile (libsupport-routines): Add support_openpty.
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* libio/tst-fgetc-after-eof.c, wcsmbs/test-fgetwc-after-eof.c:
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New test cases.
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* libio/Makefile (tests): Add tst-fgetc-after-eof.
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* wcsmbs/Makefile (tests): Add tst-fgetwc-after-eof.
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2018-03-12 Dmitry V. Levin <ldv@altlinux.org>
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* po/pt_BR.po: Update translations.
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8
NEWS
8
NEWS
@ -28,6 +28,14 @@ Deprecated and removed features, and other changes affecting compatibility:
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investigate using (f)getc_unlocked and (f)putc_unlocked, and, if
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necessary, flockfile and funlockfile.
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* All stdio functions now treat end-of-file as a sticky condition. If you
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read from a file until EOF, and then the file is enlarged by another
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process, you must call clearerr or another function with the same effect
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(e.g. fseek, rewind) before you can read the additional data. This
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corrects a longstanding C99 conformance bug. It is most likely to affect
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programs that use stdio to read interactive input from a terminal.
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(Bug #1190.)
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* The macros 'major', 'minor', and 'makedev' are now only available from
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the header <sys/sysmacros.h>; not from <sys/types.h> or various other
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headers that happen to include <sys/types.h>. These macros are rarely
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@ -64,7 +64,8 @@ tests = tst_swprintf tst_wprintf tst_swscanf tst_wscanf tst_getwc tst_putwc \
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bug-memstream1 bug-wmemstream1 \
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tst-setvbuf1 tst-popen1 tst-fgetwc bug-wsetpos tst-fseek \
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tst-fwrite-error tst-ftell-partial-wide tst-ftell-active-handler \
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tst-ftell-append tst-fputws tst-bz22415
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tst-ftell-append tst-fputws tst-bz22415 tst-fgetc-after-eof
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ifeq (yes,$(build-shared))
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# Add test-fopenloc only if shared library is enabled since it depends on
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# shared localedata objects.
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@ -468,11 +468,10 @@ int
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_IO_new_file_underflow (FILE *fp)
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{
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ssize_t count;
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#if 0
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/* SysV does not make this test; take it out for compatibility */
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/* C99 requires EOF to be "sticky". */
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if (fp->_flags & _IO_EOF_SEEN)
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return (EOF);
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#endif
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return EOF;
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if (fp->_flags & _IO_NO_READS)
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{
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@ -294,11 +294,10 @@ attribute_compat_text_section
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_IO_old_file_underflow (FILE *fp)
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{
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ssize_t count;
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#if 0
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/* SysV does not make this test; take it out for compatibility */
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/* C99 requires EOF to be "sticky". */
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if (fp->_flags & _IO_EOF_SEEN)
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return (EOF);
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#endif
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return EOF;
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if (fp->_flags & _IO_NO_READS)
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{
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109
libio/tst-fgetc-after-eof.c
Normal file
109
libio/tst-fgetc-after-eof.c
Normal file
@ -0,0 +1,109 @@
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/* Bug 1190: EOF conditions are supposed to be sticky.
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Copyright (C) 2018 Free Software Foundation.
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Copying and distribution of this file, with or without modification,
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are permitted in any medium without royalty provided the copyright
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notice and this notice are preserved. This file is offered as-is,
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without any warranty. */
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/* ISO C1999 specification of fgetc:
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#include <stdio.h>
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int fgetc (FILE *stream);
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Description
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If the end-of-file indicator for the input stream pointed to by
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stream is not set and a next character is present, the fgetc
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function obtains that character as an unsigned char converted to
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an int and advances the associated file position indicator for
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the stream (if defined).
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Returns
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If the end-of-file indicator for the stream is set, or if the
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stream is at end-of-file, the end-of-file indicator for the
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stream is set and the fgetc function returns EOF. Otherwise, the
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fgetc function returns the next character from the input stream
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pointed to by stream. If a read error occurs, the error indicator
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for the stream is set and the fgetc function returns EOF.
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The requirement to return EOF "if the end-of-file indicator for the
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stream is set" was new in C99; the language in the 1989 edition of
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the standard was ambiguous. Historically, BSD-derived Unix always
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had the C99 behavior, whereas in System V fgetc would attempt to
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call read() again before returning EOF again. Prior to version 2.28,
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glibc followed the System V behavior even though this does not
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comply with C99.
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See
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<https://sourceware.org/bugzilla/show_bug.cgi?id=1190>,
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<https://sourceware.org/bugzilla/show_bug.cgi?id=19476>,
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and the thread at
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<https://sourceware.org/ml/libc-alpha/2012-09/msg00343.html>
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for more detail. */
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#include <support/tty.h>
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#include <support/check.h>
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#include <fcntl.h>
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#include <stdio.h>
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#include <stdlib.h>
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#include <string.h>
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#include <unistd.h>
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#define XWRITE(fd, s, msg) do { \
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if (write (fd, s, sizeof s - 1) != sizeof s - 1) \
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{ \
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perror ("write " msg); \
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return 1; \
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} \
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} while (0)
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int
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do_test (void)
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{
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/* The easiest way to set up the conditions under which you can
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notice whether the end-of-file indicator is sticky, is with a
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pseudo-tty. This is also the case which applications are most
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likely to care about. And it avoids any question of whether and
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how it is legitimate to access the same physical file with two
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independent FILE objects. */
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int outer_fd, inner_fd;
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FILE *fp;
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support_openpty (&outer_fd, &inner_fd, 0, 0, 0);
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fp = fdopen (inner_fd, "r+");
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if (!fp)
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{
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perror ("fdopen");
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return 1;
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}
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XWRITE (outer_fd, "abc\n\004", "first line + EOF");
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TEST_COMPARE (fgetc (fp), 'a');
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TEST_COMPARE (fgetc (fp), 'b');
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TEST_COMPARE (fgetc (fp), 'c');
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TEST_COMPARE (fgetc (fp), '\n');
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TEST_COMPARE (fgetc (fp), EOF);
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TEST_VERIFY_EXIT (feof (fp));
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TEST_VERIFY_EXIT (!ferror (fp));
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XWRITE (outer_fd, "d\n", "second line");
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/* At this point, there is a new full line of input waiting in the
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kernelside input buffer, but we should still observe EOF from
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stdio, because the end-of-file indicator has not been cleared. */
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TEST_COMPARE (fgetc (fp), EOF);
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/* Clearing EOF should reveal the next line of input. */
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clearerr (fp);
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TEST_COMPARE (fgetc (fp), 'd');
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TEST_COMPARE (fgetc (fp), '\n');
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fclose (fp);
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close (outer_fd);
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return 0;
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}
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#include <support/test-driver.c>
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@ -116,6 +116,10 @@ _IO_wfile_underflow (FILE *fp)
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enum __codecvt_result status;
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ssize_t count;
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/* C99 requires EOF to be "sticky". */
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if (fp->_flags & _IO_EOF_SEEN)
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return WEOF;
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if (__glibc_unlikely (fp->_flags & _IO_NO_READS))
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{
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fp->_flags |= _IO_ERR_SEEN;
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@ -52,6 +52,7 @@ libsupport-routines = \
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support_format_hostent \
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support_format_netent \
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support_isolate_in_subprocess \
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support_openpty \
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support_record_failure \
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support_run_diff \
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support_shared_allocate \
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109
support/support_openpty.c
Normal file
109
support/support_openpty.c
Normal file
@ -0,0 +1,109 @@
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/* Open a pseudoterminal.
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Copyright (C) 2018 Free Software Foundation, Inc.
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This file is part of the GNU C Library.
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The GNU C Library is free software; you can redistribute it and/or
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modify it under the terms of the GNU Lesser General Public
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License as published by the Free Software Foundation; either
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version 2.1 of the License, or (at your option) any later version.
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The GNU C Library is distributed in the hope that it will be useful,
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but WITHOUT ANY WARRANTY; without even the implied warranty of
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MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
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Lesser General Public License for more details.
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You should have received a copy of the GNU Lesser General Public
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License along with the GNU C Library; if not, see
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<http://www.gnu.org/licenses/>. */
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#include <support/tty.h>
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#include <support/check.h>
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#include <support/support.h>
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#include <errno.h>
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#include <stdlib.h>
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#include <string.h>
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#include <fcntl.h>
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#include <termios.h>
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#include <sys/ioctl.h>
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#include <unistd.h>
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/* As ptsname, but allocates space for an appropriately-sized string
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using malloc. */
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static char *
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xptsname (int fd)
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{
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int rv;
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size_t buf_len = 128;
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char *buf = xmalloc (buf_len);
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for (;;)
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{
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rv = ptsname_r (fd, buf, buf_len);
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if (rv)
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FAIL_EXIT1 ("ptsname_r: %s", strerror (errno));
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if (memchr (buf, '\0', buf_len))
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return buf; /* ptsname succeeded and the buffer was not truncated */
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buf_len *= 2;
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buf = xrealloc (buf, buf_len);
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}
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}
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void
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support_openpty (int *a_outer, int *a_inner, char **a_name,
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const struct termios *termp,
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const struct winsize *winp)
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{
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int outer = -1, inner = -1;
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char *namebuf = 0;
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outer = posix_openpt (O_RDWR | O_NOCTTY);
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if (outer == -1)
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FAIL_EXIT1 ("posix_openpt: %s", strerror (errno));
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if (grantpt (outer))
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FAIL_EXIT1 ("grantpt: %s", strerror (errno));
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if (unlockpt (outer))
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FAIL_EXIT1 ("unlockpt: %s", strerror (errno));
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#ifdef TIOCGPTPEER
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inner = ioctl (outer, TIOCGPTPEER, O_RDWR | O_NOCTTY);
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#endif
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if (inner == -1)
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{
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/* The kernel might not support TIOCGPTPEER, fall back to open
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by name. */
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namebuf = xptsname (outer);
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inner = open (namebuf, O_RDWR | O_NOCTTY);
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if (inner == -1)
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FAIL_EXIT1 ("%s: %s", namebuf, strerror (errno));
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}
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if (termp)
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{
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if (tcsetattr (inner, TCSAFLUSH, termp))
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FAIL_EXIT1 ("tcsetattr: %s", strerror (errno));
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}
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#ifdef TIOCSWINSZ
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if (winp)
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{
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if (ioctl (inner, TIOCSWINSZ, winp))
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FAIL_EXIT1 ("TIOCSWINSZ: %s", strerror (errno));
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}
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#endif
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if (a_name)
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{
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if (!namebuf)
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namebuf = xptsname (outer);
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*a_name = namebuf;
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}
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else
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free (namebuf);
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*a_outer = outer;
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*a_inner = inner;
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}
|
45
support/tty.h
Normal file
45
support/tty.h
Normal file
@ -0,0 +1,45 @@
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/* Support functions related to (pseudo)terminals.
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Copyright (C) 2018 Free Software Foundation, Inc.
|
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This file is part of the GNU C Library.
|
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|
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The GNU C Library is free software; you can redistribute it and/or
|
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modify it under the terms of the GNU Lesser General Public
|
||||
License as published by the Free Software Foundation; either
|
||||
version 2.1 of the License, or (at your option) any later version.
|
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|
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The GNU C Library is distributed in the hope that it will be useful,
|
||||
but WITHOUT ANY WARRANTY; without even the implied warranty of
|
||||
MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
|
||||
Lesser General Public License for more details.
|
||||
|
||||
You should have received a copy of the GNU Lesser General Public
|
||||
License along with the GNU C Library; if not, see
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<http://www.gnu.org/licenses/>. */
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#ifndef _SUPPORT_TTY_H
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#define _SUPPORT_TTY_H 1
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struct termios;
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struct winsize;
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/** Open a pseudoterminal pair. The outer fd is written to the address
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A_OUTER and the inner fd to A_INNER.
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If A_NAME is not NULL, it will be set to point to a string naming
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the /dev/pts/NNN device corresponding to the inner fd; space for
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this string is allocated with malloc and should be freed by the
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caller when no longer needed. (This is different from the libutil
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function 'openpty'.)
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If TERMP is not NULL, the terminal parameters will be initialized
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according to the termios structure it points to.
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If WINP is not NULL, the terminal window size will be set
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accordingly.
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|
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Terminates the process on failure (like xmalloc). */
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extern void support_openpty (int *a_outer, int *a_inner, char **a_name,
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const struct termios *termp,
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const struct winsize *winp);
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|
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#endif
|
@ -50,7 +50,7 @@ strop-tests := wcscmp wcsncmp wmemcmp wcslen wcschr wcsrchr wcscpy wcsnlen \
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tests := tst-wcstof wcsmbs-tst1 tst-wcsnlen tst-btowc tst-mbrtowc \
|
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tst-wcrtomb tst-wcpncpy tst-mbsrtowcs tst-wchar-h tst-mbrtowc2 \
|
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tst-c16c32-1 wcsatcliff tst-wcstol-locale tst-wcstod-nan-locale \
|
||||
tst-wcstod-round test-char-types \
|
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tst-wcstod-round test-char-types tst-fgetwc-after-eof \
|
||||
$(addprefix test-,$(strop-tests))
|
||||
|
||||
include ../Rules
|
||||
|
114
wcsmbs/tst-fgetwc-after-eof.c
Normal file
114
wcsmbs/tst-fgetwc-after-eof.c
Normal file
@ -0,0 +1,114 @@
|
||||
/* 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 fgetwc:
|
||||
|
||||
#include <stdio.h>
|
||||
#include <wchar.h>
|
||||
wint_t fgetwc (FILE *stream);
|
||||
|
||||
Description
|
||||
|
||||
If the end-of-file indicator for the input stream pointed to by
|
||||
stream is not set and a next wide character is present, the
|
||||
fgetwc function obtains that wide character as a wchar_t
|
||||
converted to a wint_t 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 fgetwc function returns WEOF. Otherwise,
|
||||
the fgetwc function returns the next wide character from the
|
||||
input stream pointed to by stream. If a read error occurs, the
|
||||
error indicator for the stream is set and the fgetwc function
|
||||
returns WEOF. If an encoding error occurs (including too few
|
||||
bytes), the value of the macro EILSEQ is stored in errno and the
|
||||
fgetwc function returns WEOF.
|
||||
|
||||
The requirement to return WEOF "if the end-of-file indicator for the
|
||||
stream is set" was new in C99; the language in the 1995 edition of
|
||||
the standard was ambiguous. Historically, BSD-derived Unix always
|
||||
had the C99 behavior, whereas in System V fgetwc 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>
|
||||
#include <wchar.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 (fgetwc (fp), L'a');
|
||||
TEST_COMPARE (fgetwc (fp), L'b');
|
||||
TEST_COMPARE (fgetwc (fp), L'c');
|
||||
TEST_COMPARE (fgetwc (fp), L'\n');
|
||||
TEST_COMPARE (fgetwc (fp), WEOF);
|
||||
|
||||
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 (fgetwc (fp), WEOF);
|
||||
|
||||
/* Clearing EOF should reveal the next line of input. */
|
||||
clearerr (fp);
|
||||
TEST_COMPARE (fgetwc (fp), L'd');
|
||||
TEST_COMPARE (fgetwc (fp), L'\n');
|
||||
|
||||
fclose (fp);
|
||||
close (outer_fd);
|
||||
return 0;
|
||||
}
|
||||
|
||||
#include <support/test-driver.c>
|
Loading…
Reference in New Issue
Block a user