diff options
Diffstat (limited to 'lib/fflush.c')
| -rw-r--r-- | lib/fflush.c | 233 |
1 files changed, 233 insertions, 0 deletions
diff --git a/lib/fflush.c b/lib/fflush.c new file mode 100644 index 0000000..69511cd --- /dev/null +++ b/lib/fflush.c @@ -0,0 +1,233 @@ +/* fflush.c -- allow flushing input streams + Copyright (C) 2007-2022 Free Software Foundation, Inc. + + This file is free software: you can redistribute it and/or 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. + + This file 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 this program. If not, see <https://www.gnu.org/licenses/>. */ + +/* Written by Eric Blake. */ + +#include <config.h> + +/* Specification. */ +#include <stdio.h> + +#include <errno.h> +#include <unistd.h> + +#include "freading.h" + +#include "stdio-impl.h" + +#undef fflush + + +#if defined _IO_EOF_SEEN || defined _IO_ftrylockfile || __GNU_LIBRARY__ == 1 +/* GNU libc, BeOS, Haiku, Linux libc5 */ + +/* Clear the stream's ungetc buffer, preserving the value of ftello (fp). */ +static void +clear_ungetc_buffer_preserving_position (FILE *fp) +{ + if (fp->_flags & _IO_IN_BACKUP) + /* _IO_free_backup_area is a bit complicated. Simply call fseek. */ + fseeko (fp, 0, SEEK_CUR); +} + +#else + +/* Clear the stream's ungetc buffer. May modify the value of ftello (fp). */ +static void +clear_ungetc_buffer (FILE *fp) +{ +# if defined __sferror || defined __DragonFly__ || defined __ANDROID__ + /* FreeBSD, NetBSD, OpenBSD, DragonFly, Mac OS X, Cygwin, Minix 3, Android */ + if (HASUB (fp)) + { + fp_->_p += fp_->_r; + fp_->_r = 0; + } +# elif defined __EMX__ /* emx+gcc */ + if (fp->_ungetc_count > 0) + { + fp->_ungetc_count = 0; + fp->_rcount = - fp->_rcount; + } +# elif defined _IOERR /* Minix, AIX, HP-UX, IRIX, OSF/1, Solaris, OpenServer, UnixWare, mingw, MSVC, NonStop Kernel, OpenVMS */ + /* Nothing to do. */ +# else /* other implementations */ + fseeko (fp, 0, SEEK_CUR); +# endif +} + +#endif + +#if ! (defined _IO_EOF_SEEN || defined _IO_ftrylockfile || __GNU_LIBRARY__ == 1) +/* GNU libc, BeOS, Haiku, Linux libc5 */ + +# if (defined __sferror || defined __DragonFly__ || defined __ANDROID__) && defined __SNPT +/* FreeBSD, NetBSD, OpenBSD, DragonFly, Mac OS X, Cygwin, Minix 3, Android */ + +static int +disable_seek_optimization (FILE *fp) +{ + int saved_flags = fp_->_flags & (__SOPT | __SNPT); + fp_->_flags = (fp_->_flags & ~__SOPT) | __SNPT; + return saved_flags; +} + +static void +restore_seek_optimization (FILE *fp, int saved_flags) +{ + fp_->_flags = (fp_->_flags & ~(__SOPT | __SNPT)) | saved_flags; +} + +# else + +static void +update_fpos_cache (_GL_ATTRIBUTE_MAYBE_UNUSED FILE *fp, + _GL_ATTRIBUTE_MAYBE_UNUSED off_t pos) +{ +# if defined __sferror || defined __DragonFly__ || defined __ANDROID__ + /* FreeBSD, NetBSD, OpenBSD, DragonFly, Mac OS X, Cygwin, Minix 3, Android */ +# if defined __CYGWIN__ + /* fp_->_offset is typed as an integer. */ + fp_->_offset = pos; +# else + /* fp_->_offset is an fpos_t. */ + /* Use a union, since on NetBSD, the compilation flags determine + whether fpos_t is typedef'd to off_t or a struct containing a + single off_t member. */ + union + { + fpos_t f; + off_t o; + } u; + u.o = pos; + fp_->_offset = u.f; +# endif + fp_->_flags |= __SOFF; +# endif +} +# endif +#endif + +/* Flush all pending data on STREAM according to POSIX rules. Both + output and seekable input streams are supported. */ +int +rpl_fflush (FILE *stream) +{ + /* When stream is NULL, POSIX and C99 only require flushing of "output + streams and update streams in which the most recent operation was not + input", and all implementations do this. + + When stream is "an output stream or an update stream in which the most + recent operation was not input", POSIX and C99 requires that fflush + writes out any buffered data, and all implementations do this. + + When stream is, however, an input stream or an update stream in + which the most recent operation was input, C99 specifies nothing, + and POSIX only specifies behavior if the stream is seekable. + mingw, in particular, drops the input buffer, leaving the file + descriptor positioned at the end of the input buffer. I.e. ftell + (stream) is lost. We don't want to call the implementation's + fflush in this case. + + We test ! freading (stream) here, rather than fwriting (stream), because + what we need to know is whether the stream holds a "read buffer", and on + mingw this is indicated by _IOREAD, regardless of _IOWRT. */ + if (stream == NULL || ! freading (stream)) + return fflush (stream); + +#if defined _IO_EOF_SEEN || defined _IO_ftrylockfile || __GNU_LIBRARY__ == 1 + /* GNU libc, BeOS, Haiku, Linux libc5 */ + + clear_ungetc_buffer_preserving_position (stream); + + return fflush (stream); + +#else + { + /* What POSIX says: + 1) About the file-position indicator (-> fseeko, ftello): + The file position indicator is incremented by fgetc() and decremented + by ungetc(): + <https://pubs.opengroup.org/onlinepubs/9699919799/functions/fgetc.html> + "... the fgetc() function shall ... advance the associated file + position indicator for the stream ..." + <https://pubs.opengroup.org/onlinepubs/9699919799/functions/ungetc.html> + "The file-position indicator is decremented by each successful + call to ungetc()..." + 2) fflush discards bytes pushed back by ungetc: + <https://pubs.opengroup.org/onlinepubs/9699919799/functions/fflush.html> + "...any characters pushed back onto the stream by ungetc() + or ungetwc() that have not subsequently been read from the + stream shall be discarded..." + This implies implicitly: fflush does not change the file position + indicator. + 3) Effects on the file descriptor, if the file descriptor is capable of + seeking: + <https://pubs.opengroup.org/onlinepubs/9699919799/functions/fflush.html> + "...the file offset of the underlying open file description shall + be set to the file position of the stream..." */ + + /* POSIX does not specify fflush behavior for non-seekable input + streams. Some implementations purge unread data, some return + EBADF, some do nothing. */ + off_t pos = ftello (stream); + if (pos == -1) + { + errno = EBADF; + return EOF; + } + + /* Clear the ungetc buffer. */ + clear_ungetc_buffer (stream); + + /* To get here, we must be flushing a seekable input stream, so the + semantics of fpurge are now appropriate to clear the buffer. To + avoid losing data, the lseek is also necessary. */ + { + int result = fpurge (stream); + if (result != 0) + return result; + } + +# if (defined __sferror || defined __DragonFly__ || defined __ANDROID__) && defined __SNPT + /* FreeBSD, NetBSD, OpenBSD, DragonFly, Mac OS X, Cygwin, Minix 3, Android */ + + { + /* Disable seek optimization for the next fseeko call. This tells the + following fseeko call to seek to the desired position directly, rather + than to seek to a block-aligned boundary. */ + int saved_flags = disable_seek_optimization (stream); + int result = fseeko (stream, pos, SEEK_SET); + + restore_seek_optimization (stream, saved_flags); + return result; + } + +# else + + pos = lseek (fileno (stream), pos, SEEK_SET); + if (pos == -1) + return EOF; + /* After a successful lseek, update the file descriptor's position cache + in the stream. */ + update_fpos_cache (stream, pos); + + return 0; + +# endif + } +#endif +} |