[PATCH v2 12/13] hex: default to the_hash_algo on zero algorithm value

From: brian m. carlson <sandals@crustytoothpaste.net>
Date: Apr 26, 2021, 01:03 UTC
Message-ID: <20210426010301.1093562-13-sandals@crustytoothpaste.net>
In-Reply-To: <20210426010301.1093562-1-sandals@crustytoothpaste.net>

There are numerous places in the codebase where we assume we can initialize data by zeroing all its bytes. However, when we do that with a struct object_id, it leaves the structure with a zero value for the algorithm, which is invalid.

We could forbid this pattern and require that all struct object_id instances be initialized using oidclr, but this seems burdensome and it's unnatural to most C programmers. Instead, if the algorithm is zero, assume we wanted to use the default hash algorithm instead.

Signed-off-by: brian m. carlson <sandals@crustytoothpaste.net>
---
 hex.c | 7 +++++++
 1 file changed, 7 insertions(+)

diff --git a/hex.c b/hex.c
index e7af18fe55..74d256f239 100644
--- a/hex.c
+++ b/hex.c
@@ -124,6 +124,13 @@ char *hash_to_hex_algop_r(char *buffer, const unsigned char *hash,
 	char *buf = buffer;
 	int i;
 
+	/*
+	 * Our struct object_id has been memset to 0, so default to printing
+	 * using the default hash.
+	 */
+	if (algop == &hash_algos[0])
+		algop = the_hash_algo;
+
 	for (i = 0; i < algop->rawsz; i++) {
 		unsigned int val = *hash++;
 		*buf++ = hex[val >> 4];