[PATCH] type_from_string_gently: make sure length matches

When commit fe8e3b7 refactored type_from_string to allow
input that was not NUL-terminated, it switched to using
strncmp instead of strcmp. But this means we check only the
first "len" bytes of the strings, and ignore any remaining
bytes in the object_type_string. We should make sure that it
is also "len" bytes, or else we would accept "comm" as
"commit", and so forth.

Signed-off-by: Jeff King <redacted>
---
Since the strings we are matching are literals, we could also record
their sizes in the object_type_strings array and check the length first
before even calling strncmp. I doubt this is a performance hot-spot,
though.

You could also potentially just use strlen(object_type_strings[i]), but
I'm not sure if compilers will optimize out the strlen in this case,
since it is in a loop.

 object.c               | 3 ++-
 t/t1007-hash-object.sh | 8 ++++++++
 2 files changed, 10 insertions(+), 1 deletion(-)

diff --git a/object.c b/object.c
index 23d6c96..980ac5f 100644
--- a/object.c
+++ b/object.c

@@ -41,7 +41,8 @@ int type_from_string_gently(const char *str, ssize_t len, int gentle)
 		len = strlen(str);
 
 	for (i = 1; i < ARRAY_SIZE(object_type_strings); i++)
-		if (!strncmp(str, object_type_strings[i], len))
+		if (!strncmp(str, object_type_strings[i], len) &&
+		    object_type_strings[i][len] == '\0')
 			return i;
 
 	if (gentle)

diff --git a/t/t1007-hash-object.sh b/t/t1007-hash-object.sh
index f83df8e..ebb3a69 100755
--- a/t/t1007-hash-object.sh
+++ b/t/t1007-hash-object.sh

@@ -201,4 +201,12 @@ test_expect_success 'corrupt tag' '
 	test_must_fail git hash-object -t tag --stdin </dev/null
 '
 
+test_expect_success 'hash-object complains about bogus type name' '
+	test_must_fail git hash-object -t bogus --stdin </dev/null
+'
+
+test_expect_success 'hash-object complains about truncated type name' '
+	test_must_fail git hash-object -t bl --stdin </dev/null
+'
+
 test_done

-- 
2.4.0.rc2.384.g7297a4a