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Diffstat (limited to 'src/temp-stream.c')
| -rw-r--r-- | src/temp-stream.c | 165 |
1 files changed, 165 insertions, 0 deletions
diff --git a/src/temp-stream.c b/src/temp-stream.c new file mode 100644 index 0000000..9150304 --- /dev/null +++ b/src/temp-stream.c @@ -0,0 +1,165 @@ +/* temp-stream.c -- provide a stream to a per process temp file + + Copyright (C) 2023 Free Software Foundation, Inc. + + This program is free software: you can redistribute it and/or modify + it under the terms of the GNU General Public License as published by + the Free Software Foundation, either version 3 of the License, or + (at your option) any later version. + + This program 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 General Public License for more details. + + You should have received a copy of the GNU General Public License + along with this program. If not, see <https://www.gnu.org/licenses/>. */ + +#include <config.h> + +#include <stdbool.h> +#include <stdio.h> + +#include "stdlib--.h" /* For mkstemp that returns safer FDs. */ +#include "system.h" +#include "tmpdir.h" + +#include "temp-stream.h" + + +#if defined __MSDOS__ || defined _WIN32 +/* Define this to non-zero on systems for which the regular mechanism + (of unlinking an open file and expecting to be able to write, seek + back to the beginning, then reread it) doesn't work. E.g., on Windows + and DOS systems. */ +# define DONT_UNLINK_WHILE_OPEN 1 +#endif + +#if DONT_UNLINK_WHILE_OPEN + +/* FIXME-someday: remove all of this DONT_UNLINK_WHILE_OPEN junk. + Using atexit like this is wrong, since it can fail + when called e.g. 32 or more times. + But this isn't a big deal, since the code is used only on WOE/DOS + systems, and few people invoke tac on that many nonseekable files. */ + +static char const *file_to_remove; +static FILE *fp_to_close; + +static void +unlink_tempfile (void) +{ + fclose (fp_to_close); + unlink (file_to_remove); +} + +static void +record_or_unlink_tempfile (char const *fn, FILE *fp) +{ + if (!file_to_remove) + { + file_to_remove = fn; + fp_to_close = fp; + atexit (unlink_tempfile); + } +} + +#else + +static void +record_or_unlink_tempfile (char const *fn, MAYBE_UNUSED FILE *fp) +{ + unlink (fn); +} + +#endif + +/* A wrapper around mkstemp that gives us both an open stream pointer, + FP, and the corresponding FILE_NAME. Always return the same FP/name + pair, rewinding/truncating it upon each reuse. + + Note this honors $TMPDIR, unlike the standard defined tmpfile(). + + Returns TRUE on success. */ +bool +temp_stream (FILE **fp, char **file_name) +{ + static char *tempfile = nullptr; + static FILE *tmp_fp; + if (tempfile == nullptr) + { + char *tempbuf = nullptr; + size_t tempbuf_len = 128; + + while (true) + { + if (! (tempbuf = realloc (tempbuf, tempbuf_len))) + { + error (0, errno, _("failed to make temporary file name")); + return false; + } + + if (path_search (tempbuf, tempbuf_len, nullptr, "cutmp", true) == 0) + break; + + if (errno != EINVAL || PATH_MAX / 2 < tempbuf_len) + { + error (0, errno == EINVAL ? ENAMETOOLONG : errno, + _("failed to make temporary file name")); + return false; + } + + tempbuf_len *= 2; + } + + tempfile = tempbuf; + + /* FIXME: there's a small window between a successful mkstemp call + and the unlink that's performed by record_or_unlink_tempfile. + If we're interrupted in that interval, this code fails to remove + the temporary file. On systems that define DONT_UNLINK_WHILE_OPEN, + the window is much larger -- it extends to the atexit-called + unlink_tempfile. + FIXME: clean up upon fatal signal. Don't block them, in case + $TMPDIR is a remote file system. */ + + int fd = mkstemp (tempfile); + if (fd < 0) + { + error (0, errno, _("failed to create temporary file %s"), + quoteaf (tempfile)); + goto Reset; + } + + tmp_fp = fdopen (fd, (O_BINARY ? "w+b" : "w+")); + if (! tmp_fp) + { + error (0, errno, _("failed to open %s for writing"), + quoteaf (tempfile)); + close (fd); + unlink (tempfile); + Reset: + free (tempfile); + tempfile = nullptr; + return false; + } + + record_or_unlink_tempfile (tempfile, tmp_fp); + } + else + { + clearerr (tmp_fp); + if (fseeko (tmp_fp, 0, SEEK_SET) < 0 + || ftruncate (fileno (tmp_fp), 0) < 0) + { + error (0, errno, _("failed to rewind stream for %s"), + quoteaf (tempfile)); + return false; + } + } + + *fp = tmp_fp; + if (file_name) + *file_name = tempfile; + return true; +} |