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#ifndef TEMPFILE_H
#define TEMPFILE_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:
*
* * Allocates a `struct tempfile` either as a static variable or on
* the heap, initialized to zeros. Once you use the structure to
* call `create_tempfile()`, it belongs to the tempfile subsystem
* and its storage must remain valid throughout the life of the
* program (i.e. you cannot use an on-stack variable to hold this
* structure).
*
* * Attempts to create a temporary file by calling
* `create_tempfile()`.
*
* * Writes new content to the file by either:
*
* * writing to the file descriptor returned by `create_tempfile()`
* (also available via `tempfile->fd`).
*
* * calling `fdopen_tempfile()` to get a `FILE` pointer for the
* open file and writing to the file using stdio.
*
* 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()`, and later call
* `delete_tempfile()` or `rename_tempfile()`.
*
* Even after the temporary file is renamed or deleted, the `tempfile`
* object must not be freed or altered by the caller. However, it may
* be reused; just pass it to another call of `create_tempfile()`.
*
* 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()`. 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 a file descriptor on success or -1 on
* failure. On errors, `errno` describes the reason for failure.
*
* `delete_tempfile()`, `rename_tempfile()`, and `close_tempfile()`
* return 0 on success. On failure they set `errno` appropriately, do
* their best to delete the temporary file, and return -1.
*/
struct tempfile {
struct tempfile *volatile next;
volatile sig_atomic_t active;
volatile int fd;
FILE *volatile fp;
volatile pid_t owner;
char on_list;
struct strbuf filename;
};
/*
* Attempt to create a temporary file at the specified `path`. Return
* a file descriptor for writing to it, or -1 on error. It is an error
* if a file already exists at that path.
*/
extern int create_tempfile(struct tempfile *tempfile, const char *path);
/*
* 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()` is called or
* when the file is deleted or renamed.
*/
extern FILE *fdopen_tempfile(struct tempfile *tempfile, const char *mode);
static inline int is_tempfile_active(struct tempfile *tempfile)
{
return 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.
*/
extern const char *get_tempfile_path(struct tempfile *tempfile);
extern int get_tempfile_fd(struct tempfile *tempfile);
extern 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 and delete the file. Usually
* `delete_tempfile()` or `rename_tempfile()` should eventually be
* called if `close_tempfile()` succeeds.
*/
extern int close_tempfile(struct tempfile *tempfile);
/*
* Re-open a temporary file that has been closed using
* `close_tempfile()` 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()` 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. Make further
* updates to the contents.
*
* * `rename_tempfile()` to move the file to its permanent location.
*/
extern 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.
*/
extern void delete_tempfile(struct tempfile *tempfile);
/*
* 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.
*/
extern int rename_tempfile(struct tempfile *tempfile, const char *path);
#endif /* TEMPFILE_H */
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