tempfile: add mks_tempfile_dt()

Add a function to create a temporary file with a certain name in a
temporary directory created using mkdtemp(3).  Its result is more
sightly than the paths created by mks_tempfile_ts(), which include
a random prefix.  That's useful for files passed to a program that
displays their name, e.g. an external diff tool.

Signed-off-by: René Scharfe <l.s.r@web.de>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

tempfile.c

@@ -56,6 +56,20 @@
 
 static VOLATILE_LIST_HEAD(tempfile_list);
 
+static void remove_template_directory(struct tempfile *tempfile,
+				      int in_signal_handler)
+{
+	if (tempfile->directorylen > 0 &&
+	    tempfile->directorylen < tempfile->filename.len &&
+	    tempfile->filename.buf[tempfile->directorylen] == '/') {
+		strbuf_setlen(&tempfile->filename, tempfile->directorylen);
+		if (in_signal_handler)
+			rmdir(tempfile->filename.buf);
+		else
+			rmdir_or_warn(tempfile->filename.buf);
+	}
+}
+
 static void remove_tempfiles(int in_signal_handler)
 {
 	pid_t me = getpid();
@@ -74,6 +88,7 @@ static void remove_tempfiles(int in_signal_handler)
 			unlink(p->filename.buf);
 		else
 			unlink_or_warn(p->filename.buf);
+		remove_template_directory(p, in_signal_handler);
 
 		p->active = 0;
 	}
@@ -100,6 +115,7 @@ static struct tempfile *new_tempfile(void)
 	tempfile->owner = 0;
 	INIT_LIST_HEAD(&tempfile->list);
 	strbuf_init(&tempfile->filename, 0);
+	tempfile->directorylen = 0;
 	return tempfile;
 }
 
@@ -198,6 +214,52 @@ struct tempfile *mks_tempfile_tsm(const char *filename_template, int suffixlen,
 	return tempfile;
 }
 
+struct tempfile *mks_tempfile_dt(const char *directory_template,
+				 const char *filename)
+{
+	struct tempfile *tempfile;
+	const char *tmpdir;
+	struct strbuf sb = STRBUF_INIT;
+	int fd;
+	size_t directorylen;
+
+	if (!ends_with(directory_template, "XXXXXX")) {
+		errno = EINVAL;
+		return NULL;
+	}
+
+	tmpdir = getenv("TMPDIR");
+	if (!tmpdir)
+		tmpdir = "/tmp";
+
+	strbuf_addf(&sb, "%s/%s", tmpdir, directory_template);
+	directorylen = sb.len;
+	if (!mkdtemp(sb.buf)) {
+		int orig_errno = errno;
+		strbuf_release(&sb);
+		errno = orig_errno;
+		return NULL;
+	}
+
+	strbuf_addf(&sb, "/%s", filename);
+	fd = open(sb.buf, O_CREAT | O_EXCL | O_RDWR, 0600);
+	if (fd < 0) {
+		int orig_errno = errno;
+		strbuf_setlen(&sb, directorylen);
+		rmdir(sb.buf);
+		strbuf_release(&sb);
+		errno = orig_errno;
+		return NULL;
+	}
+
+	tempfile = new_tempfile();
+	strbuf_swap(&tempfile->filename, &sb);
+	tempfile->directorylen = directorylen;
+	tempfile->fd = fd;
+	activate_tempfile(tempfile);
+	return tempfile;
+}
+
 struct tempfile *xmks_tempfile_m(const char *filename_template, int mode)
 {
 	struct tempfile *tempfile;
@@ -316,6 +378,7 @@ void delete_tempfile(struct tempfile **tempfile_p)
 
 	close_tempfile_gently(tempfile);
 	unlink_or_warn(tempfile->filename.buf);
+	remove_template_directory(tempfile, 0);
 	deactivate_tempfile(tempfile);
 	*tempfile_p = NULL;
 }

tempfile.h

@@ -82,6 +82,7 @@ struct tempfile {
 	FILE *volatile fp;
 	volatile pid_t owner;
 	struct strbuf filename;
+	size_t directorylen;
 };
 
 /*
@@ -198,6 +199,18 @@ static inline struct tempfile *xmks_tempfile(const char *filename_template)
 	return xmks_tempfile_m(filename_template, 0600);
 }
 
+/*
+ * Attempt to create a temporary directory in $TMPDIR and to create and
+ * open a file in that new directory. Derive the directory name from the
+ * template in the manner of mkdtemp(). Arrange for directory and file
+ * to be deleted if the program exits before they are deleted
+ * explicitly. On success return a tempfile whose "filename" member
+ * contains the full path of the file and its "fd" member is open for
+ * writing the file. On error return NULL and set errno appropriately.
+ */
+struct tempfile *mks_tempfile_dt(const char *directory_template,
+				 const char *filename);
+
 /*
  * Associate a stdio stream with the temporary file (which must still
  * be open). Return `NULL` (*without* deleting the file) on error. The