about summary refs log tree commit diff
path: root/third_party/git/tempfile.h
blob: cddda0a33c3e1ef39c6d294221fc9f7ae5205217 (plain) (blame)
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
159
160
161
162
163
164
165
166
167
168
169
170
171
172
173
174
175
176
177
178
179
180
181
182
183
184
185
186
187
188
189
190
191
192
193
194
195
196
197
198
199
200
201
202
203
204
205
206
207
208
209
210
211
212
213
214
215
216
217
218
219
220
221
222
223
224
225
226
227
228
229
230
231
232
233
234
235
236
237
238
239
240
241
242
243
244
245
246
247
248
249
250
251
252
253
254
255
256
257
258
259
260
261
262
263
264
265
#ifndef TEMPFILE_H
#define TEMPFILE_H

#include "list.h"
#include "strbuf.h"

/*
 * Handle temporary files.
 *
 * The tempfile API allows temporary files to be created, deleted, and
 * atomically renamed. Temporary files that are still active when the
 * program ends are cleaned up automatically. Lockfiles (see
 * "lockfile.h") are built on top of this API.
 *
 *
 * Calling sequence
 * ----------------
 *
 * The caller:
 *
 * * Attempts to create a temporary file by calling
 *   `create_tempfile()`. The resources used for the temporary file are
 *   managed by the tempfile API.
 *
 * * Writes new content to the file by either:
 *
 *   * writing to the `tempfile->fd` file descriptor
 *
 *   * calling `fdopen_tempfile()` to get a `FILE` pointer for the
 *     open file and writing to the file using stdio.
 *
 *   Note that the file descriptor created by create_tempfile()
 *   is marked O_CLOEXEC, so the new contents must be written by
 *   the current process, not any spawned one.
 *
 * When finished writing, the caller can:
 *
 * * Close the file descriptor and remove the temporary file by
 *   calling `delete_tempfile()`.
 *
 * * Close the temporary file and rename it atomically to a specified
 *   filename by calling `rename_tempfile()`. This relinquishes
 *   control of the file.
 *
 * * Close the file descriptor without removing or renaming the
 *   temporary file by calling `close_tempfile_gently()`, and later call
 *   `delete_tempfile()` or `rename_tempfile()`.
 *
 * After the temporary file is renamed or deleted, the `tempfile`
 * object is no longer valid and should not be reused.
 *
 * If the program exits before `rename_tempfile()` or
 * `delete_tempfile()` is called, an `atexit(3)` handler will close
 * and remove the temporary file.
 *
 * If you need to close the file descriptor yourself, do so by calling
 * `close_tempfile_gently()`. You should never call `close(2)` or `fclose(3)`
 * yourself, otherwise the `struct tempfile` structure would still
 * think that the file descriptor needs to be closed, and a later
 * cleanup would result in duplicate calls to `close(2)`. Worse yet,
 * if you close and then later open another file descriptor for a
 * completely different purpose, then the unrelated file descriptor
 * might get closed.
 *
 *
 * Error handling
 * --------------
 *
 * `create_tempfile()` returns an allocated tempfile on success or NULL
 * on failure. On errors, `errno` describes the reason for failure.
 *
 * `rename_tempfile()` and `close_tempfile_gently()` return 0 on success.
 * On failure they set `errno` appropriately and return -1.
 * `delete_tempfile()` and `rename` (but not `close`) do their best to
 * delete the temporary file before returning.
 */

struct tempfile {
	volatile struct volatile_list_head list;
	volatile sig_atomic_t active;
	volatile int fd;
	FILE *volatile fp;
	volatile pid_t owner;
	struct strbuf filename;
};

/*
 * Attempt to create a temporary file at the specified `path`. Return
 * a tempfile (whose "fd" member can be used for writing to it), or
 * NULL on error. It is an error if a file already exists at that path.
 */
struct tempfile *create_tempfile(const char *path);

/*
 * Register an existing file as a tempfile, meaning that it will be
 * deleted when the program exits. The tempfile is considered closed,
 * but it can be worked with like any other closed tempfile (for
 * example, it can be opened using reopen_tempfile()).
 */
struct tempfile *register_tempfile(const char *path);


/*
 * mks_tempfile functions
 *
 * The following functions attempt to create and open temporary files
 * with names derived automatically from a template, in the manner of
 * mkstemps(), and arrange for them to be deleted if the program ends
 * before they are deleted explicitly. There is a whole family of such
 * functions, named according to the following pattern:
 *
 *     x?mks_tempfile_t?s?m?()
 *
 * The optional letters have the following meanings:
 *
 *   x - die if the temporary file cannot be created.
 *
 *   t - create the temporary file under $TMPDIR (as opposed to
 *       relative to the current directory). When these variants are
 *       used, template should be the pattern for the filename alone,
 *       without a path.
 *
 *   s - template includes a suffix that is suffixlen characters long.
 *
 *   m - the temporary file should be created with the specified mode
 *       (otherwise, the mode is set to 0600).
 *
 * None of these functions modify template. If the caller wants to
 * know the (absolute) path of the file that was created, it can be
 * read from tempfile->filename.
 *
 * On success, the functions return a tempfile whose "fd" member is open
 * for writing the temporary file. On errors, they return NULL and set
 * errno appropriately (except for the "x" variants, which die() on
 * errors).
 */

/* See "mks_tempfile functions" above. */
struct tempfile *mks_tempfile_sm(const char *filename_template,
				 int suffixlen, int mode);

/* See "mks_tempfile functions" above. */
static inline struct tempfile *mks_tempfile_s(const char *filename_template,
					      int suffixlen)
{
	return mks_tempfile_sm(filename_template, suffixlen, 0600);
}

/* See "mks_tempfile functions" above. */
static inline struct tempfile *mks_tempfile_m(const char *filename_template, int mode)
{
	return mks_tempfile_sm(filename_template, 0, mode);
}

/* See "mks_tempfile functions" above. */
static inline struct tempfile *mks_tempfile(const char *filename_template)
{
	return mks_tempfile_sm(filename_template, 0, 0600);
}

/* See "mks_tempfile functions" above. */
struct tempfile *mks_tempfile_tsm(const char *filename_template,
				  int suffixlen, int mode);

/* See "mks_tempfile functions" above. */
static inline struct tempfile *mks_tempfile_ts(const char *filename_template,
					       int suffixlen)
{
	return mks_tempfile_tsm(filename_template, suffixlen, 0600);
}

/* See "mks_tempfile functions" above. */
static inline struct tempfile *mks_tempfile_tm(const char *filename_template, int mode)
{
	return mks_tempfile_tsm(filename_template, 0, mode);
}

/* See "mks_tempfile functions" above. */
static inline struct tempfile *mks_tempfile_t(const char *filename_template)
{
	return mks_tempfile_tsm(filename_template, 0, 0600);
}

/* See "mks_tempfile functions" above. */
struct tempfile *xmks_tempfile_m(const char *filename_template, int mode);

/* See "mks_tempfile functions" above. */
static inline struct tempfile *xmks_tempfile(const char *filename_template)
{
	return xmks_tempfile_m(filename_template, 0600);
}

/*
 * Associate a stdio stream with the temporary file (which must still
 * be open). Return `NULL` (*without* deleting the file) on error. The
 * stream is closed automatically when `close_tempfile_gently()` is called or
 * when the file is deleted or renamed.
 */
FILE *fdopen_tempfile(struct tempfile *tempfile, const char *mode);

static inline int is_tempfile_active(struct tempfile *tempfile)
{
	return tempfile && tempfile->active;
}

/*
 * Return the path of the lockfile. The return value is a pointer to a
 * field within the lock_file object and should not be freed.
 */
const char *get_tempfile_path(struct tempfile *tempfile);

int get_tempfile_fd(struct tempfile *tempfile);
FILE *get_tempfile_fp(struct tempfile *tempfile);

/*
 * If the temporary file is still open, close it (and the file pointer
 * too, if it has been opened using `fdopen_tempfile()`) without
 * deleting the file. Return 0 upon success. On failure to `close(2)`,
 * return a negative value. Usually `delete_tempfile()` or `rename_tempfile()`
 * should eventually be called regardless of whether `close_tempfile_gently()`
 * succeeds.
 */
int close_tempfile_gently(struct tempfile *tempfile);

/*
 * Re-open a temporary file that has been closed using
 * `close_tempfile_gently()` but not yet deleted or renamed. This can be used
 * to implement a sequence of operations like the following:
 *
 * * Create temporary file.
 *
 * * Write new contents to file, then `close_tempfile_gently()` to cause the
 *   contents to be written to disk.
 *
 * * Pass the name of the temporary file to another program to allow
 *   it (and nobody else) to inspect or even modify the file's
 *   contents.
 *
 * * `reopen_tempfile()` to reopen the temporary file, truncating the existing
 *   contents. Write out the new contents.
 *
 * * `rename_tempfile()` to move the file to its permanent location.
 */
int reopen_tempfile(struct tempfile *tempfile);

/*
 * Close the file descriptor and/or file pointer and remove the
 * temporary file associated with `tempfile`. It is a NOOP to call
 * `delete_tempfile()` for a `tempfile` object that has already been
 * deleted or renamed.
 */
void delete_tempfile(struct tempfile **tempfile_p);

/*
 * Close the file descriptor and/or file pointer if they are still
 * open, and atomically rename the temporary file to `path`. `path`
 * must be on the same filesystem as the lock file. Return 0 on
 * success. On failure, delete the temporary file and return -1, with
 * `errno` set to the value from the failing call to `close(2)` or
 * `rename(2)`. It is a bug to call `rename_tempfile()` for a
 * `tempfile` object that is not currently active.
 */
int rename_tempfile(struct tempfile **tempfile_p, const char *path);

#endif /* TEMPFILE_H */