Re: Can I fetch an arbitrary commit by sha1?

From: Patrick Donnelly <batrick@batbytes.com>
Date: Oct 6, 2014, 18:25 UTC
Message-ID: <CACh33FpWPuyJRryf6hzbAkqWJMwzz1mLLDDRxEQ0niT2CznTRg@mail.gmail.com>
In-Reply-To: <20141002161006.GB2505@peff.net>

On Thu, Oct 2, 2014 at 12:10 PM, Jeff King <peff@peff.net> wrote:

Show 18 quoted lines

> On Thu, Oct 02, 2014 at 10:22:50AM -0400, Dan Johnson wrote:
>> My understanding is that you are allowed to ask for a SHA1, but most
>> git servers refuse the request. But if you already have the SHA
>> locally, then git doesn't neet to bother asking the server for it, so
>> there's no request to be refused.
>
> That's right. It is the server which enforces the "you cannot fetch an
> arbitrary sha1" rule.
>
> But I think Christian is arguing that the client side should complain
> that $sha1 is not a remote ref, and therefore not something we can
> fetch.  This used to be the behavior until 6e7b66e (fetch: fetch objects
> by their exact SHA-1 object names, 2013-01-29). The idea there is that
> some refs may be kept "hidden" from the ref advertisement, but clients
> who learn about the sha1 out-of-band may fetch the tips of hidden refs.
>
> I'm not sure it is a feature that has been particularly well-used to
> date, though.

There are efforts in the scientific communities at preserving experimental software and results. One of the things we'd like to do is shallow clone a specific sha1 commit from e.g. GitHub. [I think GitHub has this disabled though? I haven't been able to get it to work.] I guess this feature was a step in the right direction but it's not usable AFAIK. Tags are not really suitable as they could change and there are possible namespace issues.

-- 
Patrick Donnelly