Re: Can I fetch an arbitrary commit by sha1?

From: Jeff King <peff@peff.net>
Date: Oct 2, 2014, 16:10 UTC
Message-ID: <20141002161006.GB2505@peff.net>
In-Reply-To: <CAPBPrnsA4KxNximtKXcC37kuwBHK0Esytdm4nsgLHkrJSg3Ufw@mail.gmail.com>

On Thu, Oct 02, 2014 at 10:22:50AM -0400, Dan Johnson wrote:

Show 19 quoted lines

> >> git show af00f4c39bcc8dc29ed8f59a47066d5993c279e4
> > fatal: bad object af00f4c39bcc8dc29ed8f59a47066d5993c279e4
> >> git fetch origin af00f4c39bcc8dc29ed8f59a47066d5993c279e4
> > error: no such remote ref af00f4c39bcc8dc29ed8f59a47066d5993c279e4
> >> git fetch origin refs/foo/b1
> > remote: Counting objects: 3, done.
> > remote: Compressing objects: 100% (2/2), done.
> > remote: Total 3 (delta 0), reused 0 (delta 0)
> > Unpacking objects: 100% (3/3), done.
> > From https://github.com/chalstrick/dondalfi
> >  * branch            refs/foo/b1 -> FETCH_HEAD
> >> git fetch origin af00f4c39bcc8dc29ed8f59a47066d5993c279e4
> > From https://github.com/chalstrick/dondalfi
> >  * branch            af00f4c39bcc8dc29ed8f59a47066d5993c279e4 -> FETCH_HEAD
> 
> 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.

-Peff