text: #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   * object is no longer valid and should not be reused.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 */
  