Subject: Re: Request for detailed documentation of git pack protocol

From: Jakub Narebski <[email-masked]>
Date: Sat, 6 Jun 2009 19:41:15 +0200

On Sat, 6 Jan 2009, Scott Chacon wrote:
> On Wed, Jun 3, 2009 at 9:56 AM, Shawn O. Pearce <[email-masked]> wrote:
>> Jakub Narebski <[email-masked]> wrote:
>>> On Wed, 3 Jun 2009, Shawn O. Pearce wrote:
>>>>
>>>> Oh, and send-pack/receive-pack protocol now has ".have" refs [...]
>>>
>>> What are those ".have" refs? They are not described in current version
>>> of "Transfer Protocols" (sub)section in "The Community Book". I remember
>>> that they were discussed on git mailing list, but I don't remember what
>>> they were about...
>>
>> If the remote receiving repository has alternates, the ".have" refs are
>> the refs of the alternate repositories.  This signals to the client that
>> the server has these objects reachable, but the client isn't permitted
>> to send commands to alter these refs.
> 
> Can someone help me out with the '.have' refs?  What do they look
> like?  Is this the same as the '.keep' ref Jakub mentioned earlier in
> one of the example server responses?

This was my mistake, and even more that was double mistake. It is 
'.have', not '.keep', and (as Shawn said) it can be found in response
during _push_ as a reply from git-receive-pack, not during fetch / clone
as reply from git-upload-pack.

If a repository you want to push to uses alternates (e.g. was cloned
using --shared option, or using --reference=<repository path> option),
then refs from repository which serves as source of alternate 
(additional) object database are shown as '.have' refs.

Create some repository, add some objects to it that it is not empty,
then clone it (locally) using e.g. "git clone --mirror --shared",
do some work on clone (for example delete one of branches), then try to
push.
 
I used "ssh localhost git-receive-pack /path/to/clone.git" as a dummy
client to see what response from git-receive-pack would be:

  0059c0a92eb6f58c25a4c00e5e754e6de83e103231a1 .have report-status delete-refs ofs-delta\n 
  0033efd990cb1a5f35b2b3e8b0ef0a85f43b118b8688 .have\n
  0033c0a92eb6f58c25a4c00e5e754e6de83e103231a1 .have\n
  003fefd990cb1a5f35b2b3e8b0ef0a85f43b118b8688 refs/heads/master\n
  0000

'.have' are references in repository which given repository borrows
object from, i.e. which object database is in $GIT_DIR/objects/info/alternates
file.

Sidenote: here as far as I can see we do not use "\0" trick... 
which is a bit strange (at least for me).

> 
> I'm trying to take this whole thread and actually write an RFC style
> document for all of this stuff, but I'm still unclear on the .have
> portion of the conversation.  Pointing me to an earlier relevant
> thread in the Git mailing list would be fine, too - it's difficult to
> search for '.have' usefully.

Well, "Transfer Protocols" section in "Git Community Book" is a good
start. I think that it would be better to have pack protocol described
first there, not necessary with the amount of detail required for 
technical reference documentation (format) like RFC.

Currently the "Pushing Data" subsection in "Transfer Protocols" consist
currently of two short paragraphs... and that is the section where 
description of fake '.have' refs should go to. They do not matter and
are not used for fetching.

P.S. I'll try to send, as a summary of this thread (and my experiments),
second round of my comments about smart protocols section of "Transfer
Protocols" section soon, and most probably third round would be in the
form of a patch to Markdown sources for this section (chapter).

-- 
Jakub Narebski
Poland