Re: [PATCH/RFC 4/6] transport: add refspec list parameters to functions

[Stefan Beller <sbeller@google.com>]

On Mon, Apr 25, 2016 at 3:10 PM, Stefan Beller <sbeller@google.com> wrote:
> On Mon, Apr 25, 2016 at 9:44 AM, David Turner <dturner@twopensource.com> wrote:
>> On Wed, 2016-04-20 at 16:57 -0400, Jeff King wrote:
>>> On Wed, Apr 20, 2016 at 04:46:55PM -0400, David Turner wrote:
>>>
>>> > As you note, it appears that git-daemon does sort-of have support
>>> > for
>>> > extra args -- see parse_host_arg.  So it wouldn't be hard to add
>>> > something here. Unfortunately, current versions of git die on
>>> > unknown
>>> > args.  So this change would not be backwards-compatible.  We could
>>> > put
>>> > a decider on it so that clients would only try it when explicitly
>>> > enabled.  Or we could have clients try it with, and in the event of
>>> > an
>>> > error, retry without.  Neither is ideal, but both are possible.
>>>
>>> Right. This ends up being the same difficulty that the v2 protocol
>>> encountered; how do you figure out what you can speak without
>>> resorting
>>> to expensive fallbacks, when do you flip the switch, do you remember
>>> the
>>> protocol you used last time with this server, etc.
>>
>> Right.
>>
>> [moved]
>>> > If I read this code correctly, git-over-ssh will pass through
>>> > arbitrary
>>> > arguments.  So this should be trivial.
>>>
>>> It does if you are ssh-ing to a real shell-level account on the
>>> server,
>>> but if you are using git-shell or some other wrapper to restrict
>>> clients
>>> from running arbitrary commands, it will likely reject it.
>>
>> Oh, I see how I was mis-reading shell.c.  Oops.
>> [/moved]
>>
>>
>>> Which isn't to say it's necessarily a bad thing. Maybe the path
>>> forward
>>> instead of v2 is to shoe-horn this data into the pre-protocol
>>> conversation, and go from there. The protocol accepts that "somehow"
>>> it
>>> got some extra data from the transport layer, and acts on its
>>> uniformly.
>>
>> OK, so it seems like only HTTP (and non-git-shell-git://) allow backwar
>> ds-compatible optional pre-protocol messages.  So we don't have good
>> options; we only have bad ones.  We have to decide which particular
>> kind of badness we're willing to accept, and to what degree we care
>> about extensibility.  As I see it, the badness options are (in no
>> particular order):
>>
>> 1. Nothing changes.
>> 2. HTTP grows more extensions; other protocols stagnate.
>> 3. HTTP grows extensions; other protocols get extensions but:
>>    a. only use them on explicit client configuration or
>>    b. try/fail/remember per-remote
>> 4. A backwards-incompatible protocol v2 is introduced, which
>>    hits alternate endpoints (with the same a/b as above).  This is
>>    different from 3. in that protocol v2 is explicitly designed around
>>    a capabilities negotiation phase rather than unilateral client-side
>>    decisions.
>> 5. Think of another way to make fetch performant with many refs, and
>>     defer the extension decision.
>
> I'd prefer 2,3,4 over 1,5.
>
> Speaking about 2,3,4:
>
> Maybe we can do a mix of 2 and 4:
>
>    1) HTTP grows more extensions; other protocols stagnate for now.
>    2) Come up with a backwards-incompatible protocol v2, foccussed on
>        capabilities negotiation phase, hitting alternative end points
>        (non http only, or rather a subset of protocols only)
>     3) if HTTP sees the benefits of the native protocol v2, we may switch
>         HTTP, too
>
> (in time order of execution. Each point is decoupled from the others and may
> be done by different people at different times.)
>

Today I rebased protocol-v2[1] and it was fewer conflicts than expected.
I am surprised by myself that there is even a test case for v2 already,
so I think it is more progressed that I had in mind. Maybe we can do 1)
for now and hope that the non http catches up eventually?


[1] https://github.com/stefanbeller/git/tree/protocol-v2