"brian m. carlson" <[email protected]> writes:
> I'm currently working on getting Git to support multiple hash algorithms
> in the same binary (SHA-1 and SHA-256). In order to have a fully
> functional binary, we'll need to have some way of indicating to certain
> commands (such as init and show-index) that they should assume a certain
> hash algorithm.
>
> There are basically two approaches I can take. The first is to provide
> each command that needs to learn about this with its own --hash
> argument. So we'd have:
>
> git init --hash=sha256
> git show-index --hash=sha256 <some-file
>
> The other alternative is that we provide a global option to git, which
> is parsed by all programs, like so:
>
> git --hash=sha256 init
> git --hash=sha256 show-index <some-file
I am assuming that "show-index" above is a typo for something like
"hash-object"?
It is hard to answer the question without knowing what exactly does
"(to) support multiple hash algorithms" mean. For example, inside
today's repository, what should this command do?
git --hash=sha256 cat-file commit HEAD
It can work this way:
- read HEAD, discover that I am on 'master' branch, read refs/heads/master
to learn the object name in 40-hex, realize that it cannot be
sha256 and report "corrupt ref".
Or it can work this way:
- read repository format, realize it is a good old sha1 repository.
- do the usual thing to get to read_object() to read the commit
object data for the commit at HEAD, doing all of it in sha1.
- in the commit object data, locate references to other objects
that use sha1 name.
- replace these sha1 references with their sha256 counterparts and
show the result.
I am guessing that you are doing the former as a good first step, in
which case, as an option that changes/affects the behaviour of git
globally, I think "git --hash=sha256" would make sense, like other
global options like --literal-pathspecs and --no-replace-objects.
Thanks.
