[PATCH v3 2/3] diff: Let "git diff -O" read orderfile from any file, failing when appropriate

[Samuel Bronson <naesten@gmail.com>]

The -O flag really shouldn't silently fail to do anything when given a
path that it can't read from.

However, it should be able to read from un-mappable files, such as
pipes/fifos, /dev/null (as we document in the next patch), or in fact
*any* empty file (since Linux 2.6.12).  (Especially since we will be
documenting "-O/dev/null" to override "diff.orderfile" when we add that.)

(Note: "-O/dev/null" did have the right effect, since the existing error
handling essentially worked out to "silently ignore the orderfile".)

So lets toss all of that logic to get the file mmapped and just use
strbuf_read_file() instead, which gives us decent error handling
practically for free.

Signed-off-by: Samuel Bronson <naesten@gmail.com>
---
 diffcore-order.c      | 23 ++++++++---------------
 t/t4056-diff-order.sh | 23 +++++++++++++++++++++++
 2 files changed, 31 insertions(+), 15 deletions(-)

diff --git a/diffcore-order.c b/diffcore-order.c
index 23e9385..a63f332 100644
--- a/diffcore-order.c
+++ b/diffcore-order.c
@@ -10,28 +10,21 @@ static int order_cnt;
 
 static void prepare_order(const char *orderfile)
 {
-	int fd, cnt, pass;
+	int cnt, pass;
+	struct strbuf sb = STRBUF_INIT;
 	void *map;
 	char *cp, *endp;
-	struct stat st;
-	size_t sz;
+	ssize_t sz;
 
 	if (order)
 		return;
 
-	fd = open(orderfile, O_RDONLY);
-	if (fd < 0)
-		return;
-	if (fstat(fd, &st)) {
-		close(fd);
-		return;
-	}
-	sz = xsize_t(st.st_size);
-	map = mmap(NULL, sz, PROT_READ|PROT_WRITE, MAP_PRIVATE, fd, 0);
-	close(fd);
-	if (map == MAP_FAILED)
-		return;
+	sz = strbuf_read_file(&sb, orderfile, 0);
+	if (sz < 0)
+		die_errno(_("failed to read orderfile '%s'"), orderfile);
+	map = strbuf_detach(&sb, NULL);
 	endp = (char *) map + sz;
+
 	for (pass = 0; pass < 2; pass++) {
 		cnt = 0;
 		cp = map;
diff --git a/t/t4056-diff-order.sh b/t/t4056-diff-order.sh
index 398b3f6..eb471e7 100755
--- a/t/t4056-diff-order.sh
+++ b/t/t4056-diff-order.sh
@@ -61,12 +61,35 @@ test_expect_success "no order (=tree object order)" '
 	test_cmp expect_none actual
 '
 
+test_expect_success 'missing orderfile' '
+	rm -f bogus_file &&
+	test_must_fail git diff -Obogus_file --name-only HEAD^..HEAD
+'
+
+test_expect_success 'unreadable orderfile' '
+	touch unreadable_file &&
+	chmod -r unreadable_file &&
+	test_must_fail git diff -Ounreadable_file --name-only HEAD^..HEAD
+'
+
+test_expect_success 'orderfile is a directory' '
+	test_must_fail git diff -O/ --name-only HEAD^..HEAD
+'
+
 for i in 1 2
 do
 	test_expect_success "orderfile using option ($i)" '
 	git diff -Oorder_file_$i --name-only HEAD^..HEAD >actual &&
 	test_cmp expect_$i actual
 '
+
+	test_expect_success PIPE "orderfile is fifo ($i)" '
+	rm -f order_fifo &&
+	mkfifo order_fifo &&
+	cat order_file_$i >order_fifo &
+	git diff -O order_fifo --name-only HEAD^..HEAD >actual &&
+	test_cmp expect_$i actual
+'
 done
 
 test_done
-- 
1.8.4.3