Re: Git Push Always uses Protocol Version 0
- From
- Zsolt Imre <imrexzsolt@gmail.com>
- Date
- Jan 22, 2024, 19:24 UTC
- Message-ID
- <E121C312-5771-47EF-9099-BEC8EFC2B9BD@gmail.com>
- In-Reply-To
- <xmqqa5oxurnj.fsf@gitster.g>
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?
Show 53 quoted lines
> On 22 Jan 2024, at 18:52, Junio C Hamano <gitster@pobox.com> wrote:
>
> Zsolt Imre <imrexzsolt@gmail.com> 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?
>
>