[PATCH v2 3/3] commit: refuse commit messages that contain NULs

Current implementation sees NUL as terminator. If users give a
NUL-included message (e.g. editor accidentally set to save as UTF-16),
the new commit message will have NULs. However following operations
(displaying or amending a commit for example) will not show anything
after the first NUL.

Stop user right when they do this. If NUL is added by mistake, they
have their chance to fix. If they know that they are doing,
commit-tree will gladly commit whatever is given.

Signed-off-by: Nguyễn Thái Ngọc Duy <redacted>
---
 Advice stuff dropped. I realized quite late that commit_tree() is
 also used for plumbing commands (also thanks to Junio's comments),
 while I wanted to check at porcelain level only. So I moved the check
 up to builtin/commit.c. If we need the same check for other commands,
 which I doubt, similar checks can be added.

 builtin/commit.c       |    7 +++++++
 t/t3900-i18n-commit.sh |    6 ++++++
 2 files changed, 13 insertions(+), 0 deletions(-)

diff --git a/builtin/commit.c b/builtin/commit.c
index 849151e..5db7673 100644
--- a/builtin/commit.c
+++ b/builtin/commit.c

@@ -1483,6 +1483,13 @@ int cmd_commit(int argc, const char **argv, const char *prefix)
 		exit(1);
 	}
 
+	if (memchr(sb.buf, '\0', sb.len)) {
+		rollback_index_files();
+		die(_("your commit message contains NUL characters.\n"
+		      "hint: This is often caused by using wide encodings such as\n"
+		      "hint: UTF-16. Please check your editor settings."));
+	}
+
 	if (commit_tree(&sb, active_cache_tree->sha1, parents, sha1,
 			author_ident.buf)) {
 		rollback_index_files();

diff --git a/t/t3900-i18n-commit.sh b/t/t3900-i18n-commit.sh
index 1f62c15..d48a7c0 100755
--- a/t/t3900-i18n-commit.sh
+++ b/t/t3900-i18n-commit.sh

@@ -34,6 +34,12 @@ test_expect_success 'no encoding header for base case' '
 	test z = "z$E"
 '
 
+test_expect_failure 'UTF-16 refused because of NULs' '
+	echo UTF-16 >F &&
+	git commit -a -F "$TEST_DIRECTORY"/t3900/UTF-16.txt
+'
+
+
 for H in ISO8859-1 eucJP ISO-2022-JP
 do
 	test_expect_success "$H setup" '

-- 
1.7.8.36.g69ee2