On Thu, Aug 02 2018, Jeff King wrote:
> On Thu, Aug 02, 2018 at 12:58:52PM -0500, Liam Decker wrote: > >> I've been working on a git hook in golang recently. However, the library I >> was using did not support a possible quarantine directory, which I would >> use for my hook. >> >> I have been trying to find out how git finds this incoming directory in the >> objects folder, as their code simply assumed it resided in >> .git/objects/<1st byte>/<last 19 bytes> > > When you're running a hook inside the quarantine environment, then > $GIT_OBJECT_DIRECTORY in the environment will be set to the quarantine > directory, and $GIT_ALTERNATE_OBJECT_DIRECTORIES will point to the main > repository object directory (possibly alongside other alternates, if > there were any already set). > > Any Git commands you run should therefore find objects from either > location, but any writes would go to the quarantine (most notably, Git's > own index-pack/unpack-objects processes, which is the point of the > quarantine in the first place). To add to this, one interesting thing that you can do with hooks because of this quarantine is to answer certain questions about the push that were prohibitively expensive before it existed, but there's no explicit documentation for this. E.g. for a hook that wants to ban big blobs in the repo, but wants to allow all existing blobs (you don't want to block e.g. a revert of a commit that removed it from the checkout), you can juggle these two env variables and hide the "main" object dir from the hook for some operations, so e.g. if a blob lookup succeeds in the alternate quarantine dir, but not the main object dir, you know it's new. >> The solution that I implemented was to check the objects directory for the >> object, and if it was not there, to look for a quarantine directory and try >> there. However, that feels fairly inefficient. > > That's more or less what Git will do under the hood (though in the > opposite order). > >> For the curious, the library and solution I attempted are both here [5] > > Just skimming, but it sounds like go-git does not support the > GIT_OBJECT_DIRECTORY environment variable. > > -Peff
