Re: [PATCH v4] builtin/clone.c: add --reject-shallow option

[Junio C Hamano <gitster@pobox.com>]

Jonathan Tan <jonathantanmy@google.com> writes:

>> This may reject to clone from a shallow repository, but at this
>> point the bulk of the tranfer from the origin repository has already
>> happened, no?  Rejecting after transferring many megabytes feels a
>> bit too late.  That is one of the reasons why I kept hinting that
>> the transport layer needs to be taught an option to reject talking
>> to a shallow counterpart if we want to add this feature [*1*].
>
> Extending the transport layer in this way might not be too difficult in
> the case of native (SSH, git://) protocols and using protocol v0, since
> handshake() in transport.c (called indirectly from
> transport_get_remote_refs()) writes shallow information to a data
> structure that we could potentially expose for the caller to use (before
> it calls transport_fetch_refs(). I couldn't see how remote-using
> protocols (e.g. HTTP) communicate shallow information, though
> (remote-curl.c seems to just keep it for itself), so that will be a more
> difficult task. And of course there's the matter of protocol v2, which I
> discuss below.
>
>> [Footnote]
>> 
>> *1* Looking at Documentation/technical/pack-protocol.txt, "git
>>     fetch" seem to learn if the repository is shallow immediately
>>     upon contacting "upload-pack" during the Reference Discovery
>>     phase (we'd see 'shallow' packets if they are shallow). I
>>     suspect that the right solution would be to teach the codepath
>>     on the "git fetch" side that accepts, parses, and acts on this
>>     packet to optionally stop communication and error out when the
>>     caller asks not to talk with a shallow repository.
>
> This is true with protocol v0, but protocol v2 bundles all shallow
> information (whether coming from the fact that the remote is shallow or
> the fact that the fetcher specified --depth etc.) and sends them
> together with the packfile. It may be possible to stop packfile download
> (saving bandwidth on the client side, at least) once such information is
> returned, though.

So in short, the "we do not want to clone from a shallow upstream"
would not be possible to implement sensibly without significantly
cleaning up the protocol layers first, which makes the whole thing
pretty much moot.

Thanks for a review and insight.