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1#ifndef TEMPFILE_H
2#define TEMPFILE_H
3
4#include "list.h"
5#include "strbuf.h"
6
7/*
8 * Handle temporary files.
9 *
10 * The tempfile API allows temporary files to be created, deleted, and
11 * atomically renamed. Temporary files that are still active when the
12 * program ends are cleaned up automatically. Lockfiles (see
13 * "lockfile.h") are built on top of this API.
14 *
15 *
16 * Calling sequence
17 * ----------------
18 *
19 * The caller:
20 *
21 * * Attempts to create a temporary file by calling
22 * `create_tempfile()`. The resources used for the temporary file are
23 * managed by the tempfile API.
24 *
25 * * Writes new content to the file by either:
26 *
27 * * writing to the `tempfile->fd` file descriptor
28 *
29 * * calling `fdopen_tempfile()` to get a `FILE` pointer for the
30 * open file and writing to the file using stdio.
31 *
32 * Note that the file descriptor created by create_tempfile()
33 * is marked O_CLOEXEC, so the new contents must be written by
34 * the current process, not any spawned one.
35 *
36 * When finished writing, the caller can:
37 *
38 * * Close the file descriptor and remove the temporary file by
39 * calling `delete_tempfile()`.
40 *
41 * * Close the temporary file and rename it atomically to a specified
42 * filename by calling `rename_tempfile()`. This relinquishes
43 * control of the file.
44 *
45 * * Close the file descriptor without removing or renaming the
46 * temporary file by calling `close_tempfile_gently()`, and later call
47 * `delete_tempfile()` or `rename_tempfile()`.
48 *
49 * After the temporary file is renamed or deleted, the `tempfile`
50 * object is no longer valid and should not be reused.
51 *
52 * If the program exits before `rename_tempfile()` or
53 * `delete_tempfile()` is called, an `atexit(3)` handler will close
54 * and remove the temporary file.
55 *
56 * If you need to close the file descriptor yourself, do so by calling
57 * `close_tempfile_gently()`. You should never call `close(2)` or `fclose(3)`
58 * yourself, otherwise the `struct tempfile` structure would still
59 * think that the file descriptor needs to be closed, and a later
60 * cleanup would result in duplicate calls to `close(2)`. Worse yet,
61 * if you close and then later open another file descriptor for a
62 * completely different purpose, then the unrelated file descriptor
63 * might get closed.
64 *
65 *
66 * Error handling
67 * --------------
68 *
69 * `create_tempfile()` returns an allocated tempfile on success or NULL
70 * on failure. On errors, `errno` describes the reason for failure.
71 *
72 * `rename_tempfile()` and `close_tempfile_gently()` return 0 on success.
73 * On failure they set `errno` appropriately and return -1.
74 * `delete_tempfile()` and `rename` (but not `close`) do their best to
75 * delete the temporary file before returning.
76 */
77
78struct tempfile {
79 volatile struct volatile_list_head list;
80 volatile int fd;
81 FILE *volatile fp;
82 volatile pid_t owner;
83 struct strbuf filename;
84 char *directory;
85};
86
87/*
88 * Attempt to create a temporary file at the specified `path`. Return
89 * a tempfile (whose "fd" member can be used for writing to it), or
90 * NULL on error. It is an error if a file already exists at that path.
91 * Note that `mode` will be further modified by the umask, and possibly
92 * `core.sharedRepository`, so it is not guaranteed to have the given
93 * mode.
94 */
95struct tempfile *create_tempfile_mode(const char *path, int mode);
96
97static inline struct tempfile *create_tempfile(const char *path)
98{
99 return create_tempfile_mode(path, 0666);
100}
101
102/*
103 * Register an existing file as a tempfile, meaning that it will be
104 * deleted when the program exits. The tempfile is considered closed,
105 * but it can be worked with like any other closed tempfile (for
106 * example, it can be opened using reopen_tempfile()).
107 */
108struct tempfile *register_tempfile(const char *path);
109
110
111/*
112 * mks_tempfile functions
113 *
114 * The following functions attempt to create and open temporary files
115 * with names derived automatically from a template, in the manner of
116 * mkstemps(), and arrange for them to be deleted if the program ends
117 * before they are deleted explicitly. There is a whole family of such
118 * functions, named according to the following pattern:
119 *
120 * x?mks_tempfile_t?s?m?()
121 *
122 * The optional letters have the following meanings:
123 *
124 * x - die if the temporary file cannot be created.
125 *
126 * t - create the temporary file under $TMPDIR (as opposed to
127 * relative to the current directory). When these variants are
128 * used, template should be the pattern for the filename alone,
129 * without a path.
130 *
131 * s - template includes a suffix that is suffixlen characters long.
132 *
133 * m - the temporary file should be created with the specified mode
134 * (otherwise, the mode is set to 0600).
135 *
136 * None of these functions modify template. If the caller wants to
137 * know the (absolute) path of the file that was created, it can be
138 * read from tempfile->filename.
139 *
140 * On success, the functions return a tempfile whose "fd" member is open
141 * for writing the temporary file. On errors, they return NULL and set
142 * errno appropriately (except for the "x" variants, which die() on
143 * errors).
144 */
145
146/* See "mks_tempfile functions" above. */
147struct tempfile *mks_tempfile_sm(const char *filename_template,
148 int suffixlen, int mode);
149
150/* See "mks_tempfile functions" above. */
151static inline struct tempfile *mks_tempfile_s(const char *filename_template,
152 int suffixlen)
153{
154 return mks_tempfile_sm(filename_template, suffixlen, 0600);
155}
156
157/* See "mks_tempfile functions" above. */
158static inline struct tempfile *mks_tempfile_m(const char *filename_template, int mode)
159{
160 return mks_tempfile_sm(filename_template, 0, mode);
161}
162
163/* See "mks_tempfile functions" above. */
164static inline struct tempfile *mks_tempfile(const char *filename_template)
165{
166 return mks_tempfile_sm(filename_template, 0, 0600);
167}
168
169/* See "mks_tempfile functions" above. */
170struct tempfile *mks_tempfile_tsm(const char *filename_template,
171 int suffixlen, int mode);
172
173/* See "mks_tempfile functions" above. */
174static inline struct tempfile *mks_tempfile_ts(const char *filename_template,
175 int suffixlen)
176{
177 return mks_tempfile_tsm(filename_template, suffixlen, 0600);
178}
179
180/* See "mks_tempfile functions" above. */
181static inline struct tempfile *mks_tempfile_tm(const char *filename_template, int mode)
182{
183 return mks_tempfile_tsm(filename_template, 0, mode);
184}
185
186/* See "mks_tempfile functions" above. */
187static inline struct tempfile *mks_tempfile_t(const char *filename_template)
188{
189 return mks_tempfile_tsm(filename_template, 0, 0600);
190}
191
192/* See "mks_tempfile functions" above. */
193struct tempfile *xmks_tempfile_m(const char *filename_template, int mode);
194
195/* See "mks_tempfile functions" above. */
196static inline struct tempfile *xmks_tempfile(const char *filename_template)
197{
198 return xmks_tempfile_m(filename_template, 0600);
199}
200
201/*
202 * Attempt to create a temporary directory in $TMPDIR and to create and
203 * open a file in that new directory. Derive the directory name from the
204 * template in the manner of mkdtemp(). Arrange for directory and file
205 * to be deleted if the program exits before they are deleted
206 * explicitly. On success return a tempfile whose "filename" member
207 * contains the full path of the file and its "fd" member is open for
208 * writing the file. On error return NULL and set errno appropriately.
209 */
210struct tempfile *mks_tempfile_dt(const char *directory_template,
211 const char *filename);
212
213/*
214 * Associate a stdio stream with the temporary file (which must still
215 * be open). Return `NULL` (*without* deleting the file) on error. The
216 * stream is closed automatically when `close_tempfile_gently()` is called or
217 * when the file is deleted or renamed.
218 */
219FILE *fdopen_tempfile(struct tempfile *tempfile, const char *mode);
220
221static inline int is_tempfile_active(struct tempfile *tempfile)
222{
223 return !!tempfile;
224}
225
226/*
227 * Return the path of the lockfile. The return value is a pointer to a
228 * field within the lock_file object and should not be freed.
229 */
230const char *get_tempfile_path(struct tempfile *tempfile);
231
232int get_tempfile_fd(struct tempfile *tempfile);
233FILE *get_tempfile_fp(struct tempfile *tempfile);
234
235/*
236 * If the temporary file is still open, close it (and the file pointer
237 * too, if it has been opened using `fdopen_tempfile()`) without
238 * deleting the file. Return 0 upon success. On failure to `close(2)`,
239 * return a negative value. Usually `delete_tempfile()` or `rename_tempfile()`
240 * should eventually be called regardless of whether `close_tempfile_gently()`
241 * succeeds.
242 */
243int close_tempfile_gently(struct tempfile *tempfile);
244
245/*
246 * Re-open a temporary file that has been closed using
247 * `close_tempfile_gently()` but not yet deleted or renamed. This can be used
248 * to implement a sequence of operations like the following:
249 *
250 * * Create temporary file.
251 *
252 * * Write new contents to file, then `close_tempfile_gently()` to cause the
253 * contents to be written to disk.
254 *
255 * * Pass the name of the temporary file to another program to allow
256 * it (and nobody else) to inspect or even modify the file's
257 * contents.
258 *
259 * * `reopen_tempfile()` to reopen the temporary file, truncating the existing
260 * contents. Write out the new contents.
261 *
262 * * `rename_tempfile()` to move the file to its permanent location.
263 */
264int reopen_tempfile(struct tempfile *tempfile);
265
266/*
267 * Close the file descriptor and/or file pointer and remove the
268 * temporary file associated with `tempfile`. It is a NOOP to call
269 * `delete_tempfile()` for a `tempfile` object that has already been
270 * deleted or renamed.
271 */
272int delete_tempfile(struct tempfile **tempfile_p);
273
274/*
275 * Close the file descriptor and/or file pointer if they are still
276 * open, and atomically rename the temporary file to `path`. `path`
277 * must be on the same filesystem as the lock file. Return 0 on
278 * success. On failure, delete the temporary file and return -1, with
279 * `errno` set to the value from the failing call to `close(2)` or
280 * `rename(2)`. It is a bug to call `rename_tempfile()` for a
281 * `tempfile` object that is not currently active.
282 */
283int rename_tempfile(struct tempfile **tempfile_p, const char *path);
284
285#endif /* TEMPFILE_H */