Re: upload-pack/ls-remote: showing non-HEAD symbolic refs?

From: Stefan Beller <sbeller@google.com>
Date: Aug 16, 2016, 18:50 UTC
Message-ID: <CAGZ79kZ7dzh6AhQRQZsEFdWB4MQxW431yfDuEXao=k_meNE8Nw@mail.gmail.com>
In-Reply-To: <20160816182852.inyqzplee5m3wzt6@sigill.intra.peff.net>

On Tue, Aug 16, 2016 at 11:28 AM, Jeff King <peff@peff.net> wrote:

Show 25 quoted lines

> On Tue, Aug 16, 2016 at 10:34:44AM -0700, Josh Triplett wrote:
>
>> > Sadly you cannot use a capability to fix that, because all of this
>> > happens before the client agrees to any capabilities (you can find
>> > discussion of a "v2" protocol on the list which solves this, but it's
>> > sort of languishing in the design phase).
>>
>> As a potential 1.1 version, which could work in a backward-compatible
>> way with existing servers and no additional round-trip: what if, in the
>> smart HTTP protocol, the client advertised client capabilities with an
>> additional HTTP header (e.g.  "Git-Client-Caps: symrefs othershiny
>> featurenames"?  git-http-backend could then pass those capabilities to
>> git-upload-pack (--client-caps='...'), which could take them into
>> account in the initial response?
>>
>> That wouldn't work as a single-pass approach for SSH, since the client
>> can't know if the server's upload-pack supports --client-caps, but it
>> would work for the smart HTTP protocol.
>
> You can dig up the discussion on the list under the name "protocol v2",
> but basically yes, that approach has been considered. It's a little
> gross just because it leaves other protocols behind http (and it is not
> necessarily a good idea to push people into http, because it has some
> fundamental drawbacks over the other protocols because of its
> half-duplex nature).

Some more thoughts on protocol v2 (the good parts to be attributed to jrnieder@gmail.com):

* In case of http we can use the http header and know information
  about the client, i.e. if it may support the following ideas:

* Instead of introducing a new protocol we introduce a capability\
  "resend-ref-advertisement" and only advertise very few refs (e.g.
  only the branches, not the pending changes in case of Gerrit)

* The client can then ignore the refs advertisement and ask for a resend
  of the refs with more specification,
  e.g. "want refs/heads/*", so allowing more than just sha1s in the
  want line but complex things like branch patterns.

Show 15 quoted lines

>
>> > That should Just Work over the existing http protocol without requiring
>> > an extra request.
>>
>> It'd require one extra request for git ls-remote, which normally doesn't
>> need the second round-trip, but that still seems reasonable.
>
> Good point. I don't think there's an easy way around that short of v2 or
> v1.1 that you mention above. I agree it's probably reasonable, though.
>
> -Peff
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