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

["lilinchao@oschina.cn" <lilinchao@oschina.cn>]

--------------
lilinchao
>> 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.
> 
These discussions were based on PATCH_v4, which is quiet immature then,
In the latest PATCH_v5, for the case of native protocols(ssh, git, file://), they
will eventually call do_fetch_pack_v2() if it's protocol v2,  and then will call
receive_shallow_info() for the case FETCH_GET_PACK, so this is the place
I made the change.
As for HTTPs protocl, as long as it's still smart protocol, which means do not
fallback to dumb protocol, it will also call do_fetch_pack_v2(), and go to 
"check shallow info" trigger in receive_shallow_info().

So, base on PATCH_V5, I have tested protocol v2, which goes like this:

First, I created a shallow repo on gitlab and gitee respectively.

Then tried to clone them in my terminal, (in order not to look too verbose,
I ommited the result when GIT_TRACE_PACKET is on).

$ ./git-clone --reject-shallow https://gitlab.com/Cactusinhand/rugged.git
Cloning into 'rugged'...
fatal: source repository is shallow, reject to clone.

$ ./git-clone --reject-shallow ssh://gitlab.com/Cactusinhand/rugged.git
Cloning into 'rugged'...
fatal: source repository is shallow, reject to clone.

$ ./git-clone --reject-shallow git@gitlab.com:Cactusinhand/rugged.git
Cloning into 'rugged'...
fatal: source repository is shallow, reject to clone.

$ ./git-clone --reject-shallow https://gitee.com/cactusinhand/rugged.git
Cloning into 'rugged'...
fatal: source repository is shallow, reject to clone.

$ ./git-clone --reject-shallow ssh://gitee.com/cactusinhand/rugged.git
Cloning into 'rugged'...
fatal: source repository is shallow, reject to clone.

$ ./git-clone --reject-shallow git@gitee.com:cactusinhand/rugged.git
Cloning into 'rugged'...
fatal: source repository is shallow, reject to clone.

I haven't tested protocol v1, but I've made the change in do_fetch_pack(),
which is for protocol version 0 and version 1.

I hope you can review the latest patch, and give me some suggestions.

Thanks!

>> [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.
>