Re: Git Push Always uses Protocol Version 0

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Hi. Thanks for your response. Yes, I saw those switch statements, but probably misunderstood the intent behind them.

Checking `determine_protocol_version_server` the in-code documentation says:

* Used by a server to determine which protocol version should be used based on
* a client's request, communicated via the 'GIT_PROTOCOL' environment variable

I explicitly set the `GIT_PROTOCOL` environment variable to `version=2`. (Will share more at the end of this email why, as you asked anyways)

The client-side calls `discover_version` to check the version supported by the server. Which ultimately ends up being done as:


enum protocol_version determine_protocol_version_client(const char *server_response)
{
enum protocol_version version = protocol_v0;

if (skip_prefix(server_response, "version ", &server_response)) {
version = parse_protocol_version(server_response);

if (version == protocol_unknown_version)
die("server is speaking an unknown protocol");
if (version == protocol_v0)
die("protocol error: server explicitly said version 0");
}

return version;
}

The server, according to my understanding of the documentations so far, will not return a version identifier if the client is not talking the version 2 (or maybe even version 1) of the protocol. 
The git clone I mentioned in my previous email was clearly using protocol version 2 and it set the appropriate header to indicate this when discovering capabilities. See full request headers below.

POST /testing.git/git-upload-pack HTTP/1.1
Host: 127.0.0.1:9000
Accept: application/x-git-upload-pack-result
Accept-Encoding: deflate, gzip
Accept-Language: en-GB, *;q=0.9
Content-Length: 122
Content-Type: application/x-git-upload-pack-request
Git-Protocol: version=2
User-Agent: git/2.43.0

The server, in this case did not return a version identifier as the first PKT-LINE either, but responded otherwise according to the V2 protocol. Everything was working well.

Then, the above request was followed by by a proper fetch command in which the client again specified the use of V2 protocol:

POST /testing.git/git-upload-pack HTTP/1.1
Host: 127.0.0.1:9000
Accept: application/x-git-upload-pack-result
Accept-Encoding: deflate, gzip
Accept-Language: en-GB, *;q=0.9
Content-Length: 160
Content-Type: application/x-git-upload-pack-request
Git-Protocol: version=2
User-Agent: git/2.43.0

Accordingly, the cloning worked perfectly fine.

But then, when I want to push to the repo, the client does not do any capabilities or version discovery, just goes with V0 of the protocol to get the refs:

GET /testing.git/info/refs?service=git-receive-pack HTTP/1.1
Host: 127.0.0.1:9000
Accept: */*
Accept-Encoding: deflate, gzip
Accept-Language: en-GB, *;q=0.9
Cache-Control: no-cache
Pragma: no-cache
User-Agent: git/2.43.0

What I was expecting, given things are going stateless, that on push the client first discovers the protocol supported by the server and picks the most recent - in this case, that would be version 2.

And to answer your question of what I cannot do with the "current versions" of the protocol: I could do everything, of course. But, if there's protocol 0, 1 and 2 and I wanted to implement only version 2, I thought I should be able to. If protocol V2 was complete, I would not have to worry about implementing V0 and V1 (saving some time and headache), especially because I do not care about supporting old clients. I may have misunderstood the word "version" and version 2 is more of an "extension" to V1?


> On 22 Jan 2024, at 18:52, Junio C Hamano <gitster@xxxxxxxxx> wrote:
> 
> Zsolt Imre <imrexzsolt@xxxxxxxxx> writes:
> 
>> I'm not entirely sure if this is a bug or I am missing something,
>> but I thought I would share in the hope someone can help out. I'm
>> playing around with Git and trying to implement a git server that
>> communicates over HTTP and supports Git protocol version 2 *only*.
>> 
>> When I `clone` a repository, the Git client (version 2.43.0),
>> after fetching the capabilities using protocol version 2, it
>> proceeds to fetch the refs, again, via protocol version 2 using
>> the `ls-refs` command.  However, when I try to `push` my changes
>> to the repo, the Git client refuses to use protocol version 2 and
>> tries to obtain the ref list using protocol version 0, even if I
>> pass in the `-c protocol.version=2` command line argument.
> 
> Given that v0 and v1 in the push direction behave exactly the same,
> and there has been no need to add features that were not supportable
> in v1 in the push direction, it is not surprising to see this code
> 
>        int cmd_send_pack(int argc, const char **argv, const char *prefix)
>        {
> ...
>                switch (discover_version(&reader)) {
>                case protocol_v2:
>                        die("support for protocol v2 not implemented yet");
>                        break;
> 
> in https://github.com/git/git/blob/master/builtin/send-pack.c#L282
> and also
> 
>        int cmd_receive_pack(int argc, const char **argv, const char *prefix)
>        {
> ...
>                switch (determine_protocol_version_server()) {
>                case protocol_v2:
>                        /*
>                         * push support for protocol v2 has not been implemented yet,
>                         * so ignore the request to use v2 and fallback to using v0.
>                         */
>                        break;
> 
> in https://github.com/git/git/blob/master/builtin/receive-pack.c#L2538
> 
> that tells the receiving end to demote "v2" request down to "v0",
> and have the pushing end honor that choice.
> 
> What specifically did you want to gain by using protocol version 2
> in the "push" direction that you cannot do with the current
> versions?
> 
> 






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