Re: [RFC PATCH 02/22] hex: add functions to parse hex object IDs in any algorithm

From: Junio C Hamano <gitster@pobox.com>
Date: Jan 15, 2020, 21:40 UTC
Message-ID: <xmqqv9pciejd.fsf@gitster-ct.c.googlers.com>
In-Reply-To: <20200113124729.3684846-3-sandals@crustytoothpaste.net>

"brian m. carlson" <sandals@crustytoothpaste.net> writes:

Show 13 quoted lines

> +/*
> + * NOTE: This function relies on hash algorithms being in order from shortest
> + * length to longest length.
> + */
> +int get_oid_hex_any(const char *hex, struct object_id *oid)
> +{
> +	int i;
> +	for (i = GIT_HASH_NALGOS - 1; i > 0; i--) {
> +		if (!get_hash_hex_algop(hex, oid->hash, &hash_algos[i]))
> +			return i;
> +	}
> +	return GIT_HASH_UNKNOWN;
> +}

Two rather obvious questions are

 - what if we have more than one algos that produce hashes of the
   same length?

 - it feels that GIT_HASH_UNKNOWN being 0 wastes the first/zeroth
   element in the hash_algos[] array.

In the future, I would imagine that we would want to be able to say "here I have a dozen hexdigits that is an abbreviated SHA2 hash", and we would use some syntax (e.g. "sha2:123456123456") for that. Would this function be at the layer that would be extended later to support such a syntax, or would we have a layer higher than this to do so?

Show 18 quoted lines

>  int get_oid_hex(const char *hex, struct object_id *oid)
>  {
>  	return get_oid_hex_algop(hex, oid, the_hash_algo);
> @@ -87,6 +101,14 @@ int parse_oid_hex_algop(const char *hex, struct object_id *oid,
>  	return ret;
>  }
>  
> +int parse_oid_hex_any(const char *hex, struct object_id *oid, const char **end)
> +{
> +	int ret = get_oid_hex_any(hex, oid);
> +	if (ret)
> +		*end = hex + hash_algos[ret].hexsz;
> +	return ret;
> +}
> +
>  int parse_oid_hex(const char *hex, struct object_id *oid, const char **end)
>  {
>  	return parse_oid_hex_algop(hex, oid, end, the_hash_algo);