Re: Weird interaction between Git protocol versions and git:// and https:// URLs (was: Re: Bug with Git shallow clones and submodules)

On Thu, Sep 02, 2021 at 09:49:38AM -0400, Philippe Blain wrote:

quoted

OK, it's running Git 2.20.1. And the list of capabilities above implies that it's responding
with protocol v0, even if my local Git version if 2.29, which defaults to protocol v2. If
it were responding with protocol v2, we would see:

$ GIT_TRACE_PACKET=1 GIT_TRACE_BARE=1 git ls-remote https://github.com/git/git 2>&1 | grep agent
packet:          git< agent=git/github-g78b452413e8b  # server version
packet:          git< agent=git/github-g78b452413e8b
packet:          git> agent=git/2.29.2  # client version
packet:          git< agent=git/2.29.2

And grepping for "version" would confirm it:

$ GIT_TRACE_PACKET=1 GIT_TRACE_BARE=1 git ls-remote https://github.com/git/git 2>&1 | grep version
packet:          git< version 2
packet:          git< version 2

I can't explain why the server refuses to talk with protocol v2. Maybe Jonathan (CC-ed),
who worked on the implementation of protocol v2, would be able to explain that.

I'm sorry to bump this, but I would really like to understand what is going on here.
I'm not familiar at all with the protocol code, but my understanding was that after
Git 2.18, if a client requested protocol v2, the server would answer with v2 (at least
for git:// and http[s]://, and also for ssh:// if AcceptEnv is correctly configured).
Here, Git 2.20.1 at https://dpdk.org/git/dpdk-stable answers with v0 for https://,
but with v2 for git:// !

The server has to be configured correctly at the HTTP level, too. The v2
probe for HTTP is a "Git-Protocol: version=2" header in the HTTP
request. The webserver has to be configured to communicate that to the
rest of Git somehow. In our test setup for Apache, we do:

  SetEnvIf Git-Protocol ".*" GIT_PROTOCOL=$0

If that doesn't happen, then the server doesn't see the header at all,
and just speaks v0 as usual.

I suspect this could be better documented. I have to admit that I have
not actually run a regular HTTP server with Git in a long time (at
GitHub, we have our own custom layer that terminates the HTTP
connections).

-Peff