tempfile.hon commit Merge branch 'master' of git://github.com/git-l10n/git-po (7398243)
   1#ifndef TEMPFILE_H
   2#define TEMPFILE_H
   3
   4#include "list.h"
   5
   6/*
   7 * Handle temporary files.
   8 *
   9 * The tempfile API allows temporary files to be created, deleted, and
  10 * atomically renamed. Temporary files that are still active when the
  11 * program ends are cleaned up automatically. Lockfiles (see
  12 * "lockfile.h") are built on top of this API.
  13 *
  14 *
  15 * Calling sequence
  16 * ----------------
  17 *
  18 * The caller:
  19 *
  20 * * Attempts to create a temporary file by calling
  21 *   `create_tempfile()`. The resources used for the temporary file are
  22 *   managed by the tempfile API.
  23 *
  24 * * Writes new content to the file by either:
  25 *
  26 *   * writing to the `tempfile->fd` file descriptor
  27 *
  28 *   * calling `fdopen_tempfile()` to get a `FILE` pointer for the
  29 *     open file and writing to the file using stdio.
  30 *
  31 *   Note that the file descriptor created by create_tempfile()
  32 *   is marked O_CLOEXEC, so the new contents must be written by
  33 *   the current process, not any spawned one.
  34 *
  35 * When finished writing, the caller can:
  36 *
  37 * * Close the file descriptor and remove the temporary file by
  38 *   calling `delete_tempfile()`.
  39 *
  40 * * Close the temporary file and rename it atomically to a specified
  41 *   filename by calling `rename_tempfile()`. This relinquishes
  42 *   control of the file.
  43 *
  44 * * Close the file descriptor without removing or renaming the
  45 *   temporary file by calling `close_tempfile_gently()`, and later call
  46 *   `delete_tempfile()` or `rename_tempfile()`.
  47 *
  48 * After the temporary file is renamed or deleted, the `tempfile`
  49 * object is no longer valid and should not be reused.
  50 *
  51 * If the program exits before `rename_tempfile()` or
  52 * `delete_tempfile()` is called, an `atexit(3)` handler will close
  53 * and remove the temporary file.
  54 *
  55 * If you need to close the file descriptor yourself, do so by calling
  56 * `close_tempfile_gently()`. You should never call `close(2)` or `fclose(3)`
  57 * yourself, otherwise the `struct tempfile` structure would still
  58 * think that the file descriptor needs to be closed, and a later
  59 * cleanup would result in duplicate calls to `close(2)`. Worse yet,
  60 * if you close and then later open another file descriptor for a
  61 * completely different purpose, then the unrelated file descriptor
  62 * might get closed.
  63 *
  64 *
  65 * Error handling
  66 * --------------
  67 *
  68 * `create_tempfile()` returns an allocated tempfile on success or NULL
  69 * on failure. On errors, `errno` describes the reason for failure.
  70 *
  71 * `rename_tempfile()` and `close_tempfile_gently()` return 0 on success.
  72 * On failure they set `errno` appropriately and return -1.
  73 * `delete_tempfile()` and `rename` (but not `close`) do their best to
  74 * delete the temporary file before returning.
  75 */
  76
  77struct tempfile {
  78        volatile struct volatile_list_head list;
  79        volatile sig_atomic_t active;
  80        volatile int fd;
  81        FILE *volatile fp;
  82        volatile pid_t owner;
  83        struct strbuf filename;
  84};
  85
  86/*
  87 * Attempt to create a temporary file at the specified `path`. Return
  88 * a tempfile (whose "fd" member can be used for writing to it), or
  89 * NULL on error. It is an error if a file already exists at that path.
  90 */
  91extern struct tempfile *create_tempfile(const char *path);
  92
  93/*
  94 * Register an existing file as a tempfile, meaning that it will be
  95 * deleted when the program exits. The tempfile is considered closed,
  96 * but it can be worked with like any other closed tempfile (for
  97 * example, it can be opened using reopen_tempfile()).
  98 */
  99extern struct tempfile *register_tempfile(const char *path);
 100
 101
 102/*
 103 * mks_tempfile functions
 104 *
 105 * The following functions attempt to create and open temporary files
 106 * with names derived automatically from a template, in the manner of
 107 * mkstemps(), and arrange for them to be deleted if the program ends
 108 * before they are deleted explicitly. There is a whole family of such
 109 * functions, named according to the following pattern:
 110 *
 111 *     x?mks_tempfile_t?s?m?()
 112 *
 113 * The optional letters have the following meanings:
 114 *
 115 *   x - die if the temporary file cannot be created.
 116 *
 117 *   t - create the temporary file under $TMPDIR (as opposed to
 118 *       relative to the current directory). When these variants are
 119 *       used, template should be the pattern for the filename alone,
 120 *       without a path.
 121 *
 122 *   s - template includes a suffix that is suffixlen characters long.
 123 *
 124 *   m - the temporary file should be created with the specified mode
 125 *       (otherwise, the mode is set to 0600).
 126 *
 127 * None of these functions modify template. If the caller wants to
 128 * know the (absolute) path of the file that was created, it can be
 129 * read from tempfile->filename.
 130 *
 131 * On success, the functions return a tempfile whose "fd" member is open
 132 * for writing the temporary file. On errors, they return NULL and set
 133 * errno appropriately (except for the "x" variants, which die() on
 134 * errors).
 135 */
 136
 137/* See "mks_tempfile functions" above. */
 138extern struct tempfile *mks_tempfile_sm(const char *template,
 139                                        int suffixlen, int mode);
 140
 141/* See "mks_tempfile functions" above. */
 142static inline struct tempfile *mks_tempfile_s(const char *template,
 143                                              int suffixlen)
 144{
 145        return mks_tempfile_sm(template, suffixlen, 0600);
 146}
 147
 148/* See "mks_tempfile functions" above. */
 149static inline struct tempfile *mks_tempfile_m(const char *template, int mode)
 150{
 151        return mks_tempfile_sm(template, 0, mode);
 152}
 153
 154/* See "mks_tempfile functions" above. */
 155static inline struct tempfile *mks_tempfile(const char *template)
 156{
 157        return mks_tempfile_sm(template, 0, 0600);
 158}
 159
 160/* See "mks_tempfile functions" above. */
 161extern struct tempfile *mks_tempfile_tsm(const char *template,
 162                                         int suffixlen, int mode);
 163
 164/* See "mks_tempfile functions" above. */
 165static inline struct tempfile *mks_tempfile_ts(const char *template,
 166                                               int suffixlen)
 167{
 168        return mks_tempfile_tsm(template, suffixlen, 0600);
 169}
 170
 171/* See "mks_tempfile functions" above. */
 172static inline struct tempfile *mks_tempfile_tm(const char *template, int mode)
 173{
 174        return mks_tempfile_tsm(template, 0, mode);
 175}
 176
 177/* See "mks_tempfile functions" above. */
 178static inline struct tempfile *mks_tempfile_t(const char *template)
 179{
 180        return mks_tempfile_tsm(template, 0, 0600);
 181}
 182
 183/* See "mks_tempfile functions" above. */
 184extern struct tempfile *xmks_tempfile_m(const char *template, int mode);
 185
 186/* See "mks_tempfile functions" above. */
 187static inline struct tempfile *xmks_tempfile(const char *template)
 188{
 189        return xmks_tempfile_m(template, 0600);
 190}
 191
 192/*
 193 * Associate a stdio stream with the temporary file (which must still
 194 * be open). Return `NULL` (*without* deleting the file) on error. The
 195 * stream is closed automatically when `close_tempfile_gently()` is called or
 196 * when the file is deleted or renamed.
 197 */
 198extern FILE *fdopen_tempfile(struct tempfile *tempfile, const char *mode);
 199
 200static inline int is_tempfile_active(struct tempfile *tempfile)
 201{
 202        return tempfile && tempfile->active;
 203}
 204
 205/*
 206 * Return the path of the lockfile. The return value is a pointer to a
 207 * field within the lock_file object and should not be freed.
 208 */
 209extern const char *get_tempfile_path(struct tempfile *tempfile);
 210
 211extern int get_tempfile_fd(struct tempfile *tempfile);
 212extern FILE *get_tempfile_fp(struct tempfile *tempfile);
 213
 214/*
 215 * If the temporary file is still open, close it (and the file pointer
 216 * too, if it has been opened using `fdopen_tempfile()`) without
 217 * deleting the file. Return 0 upon success. On failure to `close(2)`,
 218 * return a negative value. Usually `delete_tempfile()` or `rename_tempfile()`
 219 * should eventually be called regardless of whether `close_tempfile_gently()`
 220 * succeeds.
 221 */
 222extern int close_tempfile_gently(struct tempfile *tempfile);
 223
 224/*
 225 * Re-open a temporary file that has been closed using
 226 * `close_tempfile_gently()` but not yet deleted or renamed. This can be used
 227 * to implement a sequence of operations like the following:
 228 *
 229 * * Create temporary file.
 230 *
 231 * * Write new contents to file, then `close_tempfile_gently()` to cause the
 232 *   contents to be written to disk.
 233 *
 234 * * Pass the name of the temporary file to another program to allow
 235 *   it (and nobody else) to inspect or even modify the file's
 236 *   contents.
 237 *
 238 * * `reopen_tempfile()` to reopen the temporary file. Make further
 239 *   updates to the contents.
 240 *
 241 * * `rename_tempfile()` to move the file to its permanent location.
 242 */
 243extern int reopen_tempfile(struct tempfile *tempfile);
 244
 245/*
 246 * Close the file descriptor and/or file pointer and remove the
 247 * temporary file associated with `tempfile`. It is a NOOP to call
 248 * `delete_tempfile()` for a `tempfile` object that has already been
 249 * deleted or renamed.
 250 */
 251extern void delete_tempfile(struct tempfile **tempfile_p);
 252
 253/*
 254 * Close the file descriptor and/or file pointer if they are still
 255 * open, and atomically rename the temporary file to `path`. `path`
 256 * must be on the same filesystem as the lock file. Return 0 on
 257 * success. On failure, delete the temporary file and return -1, with
 258 * `errno` set to the value from the failing call to `close(2)` or
 259 * `rename(2)`. It is a bug to call `rename_tempfile()` for a
 260 * `tempfile` object that is not currently active.
 261 */
 262extern int rename_tempfile(struct tempfile **tempfile_p, const char *path);
 263
 264#endif /* TEMPFILE_H */