Re: [RFC PATCH 5/6] object-name: use hexval

[Junio C Hamano <gitster@pobox.com>]

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

> We've open-coded a different implementation of parsing hex values here
> when we already have a perfectly good one in hexval.  This
> implementation will almost certainly be slower because it isn't
> table-driven, unlike the other one, and since it's not constant time it
> has no other advantages either.  To tidy things up and prepare for
> future work, switch to hexval in this case.
>
> Signed-off-by: brian m. carlson <sandals@crustytoothpaste.net>
> ---
>  object-name.c | 13 +++----------
>  1 file changed, 3 insertions(+), 10 deletions(-)
>
> diff --git a/object-name.c b/object-name.c
> index 83efba0ba6..d2d81b3511 100644
> --- a/object-name.c
> +++ b/object-name.c
> @@ -236,17 +236,10 @@ static int parse_oid_prefix(const char *name, int len,
>  {
>  	for (int i = 0; i < len; i++) {
>  		unsigned char c = name[i];
> -		unsigned char val;
> -		if (c >= '0' && c <= '9') {
> -			val = c - '0';
> -		} else if (c >= 'a' && c <= 'f') {
> -			val = c - 'a' + 10;
> -		} else if (c >= 'A' && c <='F') {
> -			val = c - 'A' + 10;
> -			c -= 'A' - 'a';
> -		} else {
> +		int val = hexval(c, HEX_KIND_OID);
> +
> +		if (val < 0)
>  			return -1;
> -		}
>  
>  		if (hex_out)
>  			hex_out[i] = c;

When hex_out[] is given by the caller, they used to get a downcased
version of object name.  After your planned transition to forbid
uppercase hex, they will get an error, which is exactly as you
intend.

However, during transition, they will *not* get an error (as
KIND_OID is still KIND_MIXED before the transition), and they will
see the hex_out[] filled with object names in the original case,
without canonicalization that the original code gave them.

While seemingly harmless, because repo_for_each_abbrev() doesn't
seem to malfunction on uppercase string metadata for
disambiguation), we may want to mention that this changes API
contract (until we forbid uppercase input altogether).