diff: generate pretty filenames in prep_temp_blob()

Naturally, prep_temp_blob() did not care about filenames.
As a result, GIT_EXTERNAL_DIFF and textconv generated
filenames such as ".diff_XXXXXX".

This modifies prep_temp_blob() to generate user-friendly
filenames when creating temporary files.

Diffing "name.ext" now generates "XXXXXX_name.ext".

Signed-off-by: David Aguilar <davvid@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

1 files changed, 16 insertions, 0 deletions

diff --git a/path.c b/path.c
index 8a0a6741f..047fdb0a1 100644
--- a/path.c
+++ b/path.c
@@ -139,6 +139,22 @@ int git_mkstemp(char *path, size_t len, const char *template)
 	return mkstemp(path);
 }
 
+/* git_mkstemps() - create tmp file with suffix honoring TMPDIR variable. */
+int git_mkstemps(char *path, size_t len, const char *template, int suffix_len)
+{
+	const char *tmp;
+	size_t n;
+
+	tmp = getenv("TMPDIR");
+	if (!tmp)
+		tmp = "/tmp";
+	n = snprintf(path, len, "%s/%s", tmp, template);
+	if (len <= n) {
+		errno = ENAMETOOLONG;
+		return -1;
+	}
+	return mkstemps(path, suffix_len);
+}
 
 int validate_headref(const char *path)
 {