Re: Enforcing clone/fetch to use references.

On Tue, Sep 21, 2010 at 01:44:56PM -0700, David Brown wrote:

Suppose I want to publish some changes to a tree.  I have a server
available where I can run a git daemon, but for one reason or another
I want to force people to use the another git repo as a reference.
The reason could be one of bandwidth, or someone who isn't comfortable
making all of the other source available.  Ideally, someone who
already has the other git repo cloned, and just adds mine as a remote
wouldn't notice the difference.

I think the gentoo people were talking about doing something like this.
They wanted you to use some faster and/or restartable protocol to clone
initially, and so they wanted to reject initial clones. I'm not sure if
they are doing that, and how (from the thread below, I suspect they run
a patched git).

The simplest thing would be a pre-upload-pack hook. There was some
discussion of that in this thread:

  http://article.gmane.org/gmane.comp.version-control.git/137007

but there are some security implications. For a remote site, where the
user running upload-pack trusts the hook, it should be fine.

Once you have that hook, then you basically need to just check whether
they are requesting objects in your "you should have this in your
reference repository" set (probably by using merge-base to see if it is
contained in some "everything our alternate has" ref), and then just

  echo >&2 Sorry, here's how to clone properly...
  exit 1

which should go to the user over the sideband.

And that would cover both the "clone --reference" and "git remote add"
cases, as it is not looking at what the user invoked, but which objects
they're requesting.

-Peff