tempfile: add several functions for creating temporary files

Add several functions for creating temporary files with
automatically-generated names, analogous to mkstemps(), but also
arranging for the files to be deleted on program exit.

The functions are named according to a pattern depending how they
operate. They will be used to replace many places in the code where
temporary files are created and cleaned up ad-hoc.

Signed-off-by: Michael Haggerty <mhagger@alum.mit.edu>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

tempfile.h

@@ -92,6 +92,102 @@ struct tempfile {
  */
 extern int create_tempfile(struct tempfile *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 file descriptor that is open for
+ * writing the temporary file. On errors, they return -1 and set errno
+ * appropriately (except for the "x" variants, which die() on errors).
+ */
+
+/* See "mks_tempfile functions" above. */
+extern int mks_tempfile_sm(struct tempfile *tempfile,
+			   const char *template, int suffixlen, int mode);
+
+/* See "mks_tempfile functions" above. */
+static inline int mks_tempfile_s(struct tempfile *tempfile,
+				 const char *template, int suffixlen)
+{
+	return mks_tempfile_sm(tempfile, template, suffixlen, 0600);
+}
+
+/* See "mks_tempfile functions" above. */
+static inline int mks_tempfile_m(struct tempfile *tempfile,
+				 const char *template, int mode)
+{
+	return mks_tempfile_sm(tempfile, template, 0, mode);
+}
+
+/* See "mks_tempfile functions" above. */
+static inline int mks_tempfile(struct tempfile *tempfile,
+			       const char *template)
+{
+	return mks_tempfile_sm(tempfile, template, 0, 0600);
+}
+
+/* See "mks_tempfile functions" above. */
+extern int mks_tempfile_tsm(struct tempfile *tempfile,
+			    const char *template, int suffixlen, int mode);
+
+/* See "mks_tempfile functions" above. */
+static inline int mks_tempfile_ts(struct tempfile *tempfile,
+				  const char *template, int suffixlen)
+{
+	return mks_tempfile_tsm(tempfile, template, suffixlen, 0600);
+}
+
+/* See "mks_tempfile functions" above. */
+static inline int mks_tempfile_tm(struct tempfile *tempfile,
+				  const char *template, int mode)
+{
+	return mks_tempfile_tsm(tempfile, template, 0, mode);
+}
+
+/* See "mks_tempfile functions" above. */
+static inline int mks_tempfile_t(struct tempfile *tempfile,
+				 const char *template)
+{
+	return mks_tempfile_tsm(tempfile, template, 0, 0600);
+}
+
+/* See "mks_tempfile functions" above. */
+extern int xmks_tempfile_m(struct tempfile *tempfile,
+			   const char *template, int mode);
+
+/* See "mks_tempfile functions" above. */
+static inline int xmks_tempfile(struct tempfile *tempfile,
+				const char *template)
+{
+	return xmks_tempfile_m(tempfile, template, 0600);
+}
+
 /*
  * Associate a stdio stream with the temporary file (which must still
  * be open). Return `NULL` (*without* deleting the file) on error. The