From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on dcvr.yhbt.net X-Spam-Level: X-Spam-ASN: AS31976 209.132.180.0/23 X-Spam-Status: No, score=-3.7 required=3.0 tests=AWL,BAYES_00, HEADER_FROM_DIFFERENT_DOMAINS,RCVD_IN_DNSWL_HI,RP_MATCHES_RCVD shortcircuit=no autolearn=ham autolearn_force=no version=3.4.0 Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by dcvr.yhbt.net (Postfix) with ESMTP id C91B21F859 for ; Tue, 16 Aug 2016 16:38:32 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1752534AbcHPQia (ORCPT ); Tue, 16 Aug 2016 12:38:30 -0400 Received: from cloud.peff.net ([104.130.231.41]:56340 "HELO cloud.peff.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with SMTP id S1752466AbcHPQia (ORCPT ); Tue, 16 Aug 2016 12:38:30 -0400 Received: (qmail 17871 invoked by uid 109); 16 Aug 2016 16:31:48 -0000 Received: from Unknown (HELO peff.net) (10.0.1.2) by cloud.peff.net (qpsmtpd/0.84) with SMTP; Tue, 16 Aug 2016 16:31:48 +0000 Received: (qmail 27748 invoked by uid 111); 16 Aug 2016 16:31:49 -0000 Received: from sigill.intra.peff.net (HELO sigill.intra.peff.net) (10.0.0.7) by peff.net (qpsmtpd/0.84) with SMTP; Tue, 16 Aug 2016 12:31:49 -0400 Received: by sigill.intra.peff.net (sSMTP sendmail emulation); Tue, 16 Aug 2016 12:31:45 -0400 Date: Tue, 16 Aug 2016 12:31:45 -0400 From: Jeff King To: Josh Triplett Cc: git@vger.kernel.org Subject: Re: upload-pack/ls-remote: showing non-HEAD symbolic refs? Message-ID: <20160816163145.mjc726til2daxl3d@sigill.intra.peff.net> References: <20160816161838.klvjhhoxsftvkfmd@x> MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Disposition: inline In-Reply-To: <20160816161838.klvjhhoxsftvkfmd@x> Sender: git-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: git@vger.kernel.org On Tue, Aug 16, 2016 at 09:18:39AM -0700, Josh Triplett wrote: > Commit 5e7dcad771cb873e278a0571b46910d7c32e2f6c in September 2013 added > support to upload-pack to show the symbolic target of non-HEAD symbolic > refs. However, commit d007dbf7d6d647dbcf0f357545f43f36dec46f3b in > November 2013 reverted that, because it used a capability to transmit > the information, and capabilities have a limited size (limited by the > pkt-line format which can't send lines longer than 64k) and can't > transmit an arbitrary number of symrefs. > > (Incidentally, couldn't the same problem occur if the HEAD points to a > long enough path to exceed 64k? Yes. But it's a lot easier to say "your 64k symref is ridiculous; don't do that" than it is to say "oh, you happened to have a lot of symrefs in your repository, so we overflowed and failed". Besides which, the whole protocol cannot handle refnames larger than 64k, so it's not a new problem. > I'd like to be able to see the targets of non-HEAD symbolic refs for a > repository (symbolic refs under refs/). I'm interested in extending > upload-pack to expose those somehow. What seems like a sensible format > to do so? > > Would it make sense to advertise a new capability for symbolic ref > targets, which would allow the client to send back a dedicated request > for the targets of all symrefs? It will definitely require a new capability. You cannot just send a "\0symref=..." trailer after each ref, because older clients treat multiple "\0" trailers as overwriting one another (so it essentially overwrites the old capabilities). 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). So you are stuck introducing a new phase into the protocol, which is probably rather tricky (especially with the http protocol, which is very sensitive to extra round-trips). I guess the least-invasive way would be to communicate the desires in the "want" phase, and then have the server dump it out with the packfile. Like: - server claims "I support symref-wants" in the capability phase - during the negotiation phase, in addition to "want" and "have", the client may send "symref " packets. Probably should be a wildcard to avoid having to ask about each ref individually. - before outputting the packfile in the final phase, if any "symref" wants were sent by the client, the server dumps a list of "symref " packets, followed by a flush packet. That should Just Work over the existing http protocol without requiring an extra request. -Peff