From: Jeff King <firstname.lastname@example.org> To: Josh Triplett <email@example.com> Cc: firstname.lastname@example.org Subject: Re: upload-pack/ls-remote: showing non-HEAD symbolic refs? Date: Tue, 16 Aug 2016 12:31:45 -0400 [thread overview] Message-ID: <email@example.com> (raw) In-Reply-To: <20160816161838.klvjhhoxsftvkfmd@x> 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 <ref>" packets. Probably <ref> 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 <from> <to>" packets, followed by a flush packet. That should Just Work over the existing http protocol without requiring an extra request. -Peff
next prev parent reply other threads:[~2016-08-16 16:38 UTC|newest] Thread overview: 12+ messages / expand[flat|nested] mbox.gz Atom feed top 2016-08-16 16:18 Josh Triplett 2016-08-16 16:31 ` Jeff King [this message] 2016-08-16 17:34 ` Josh Triplett 2016-08-16 18:28 ` Jeff King 2016-08-16 18:50 ` Stefan Beller 2016-08-16 20:34 ` Josh Triplett 2016-08-16 20:31 ` Josh Triplett 2016-08-16 20:54 ` Jeff King 2016-08-16 21:11 ` Josh Triplett 2016-08-16 21:15 ` Jeff King 2016-08-16 22:24 ` Josh Triplett 2016-08-19 13:47 ` Jeff King
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