Re: Regarding the depreciation of ssh+git/git+ssh protocols

From: Jonathan Nieder <jrnieder@gmail.com>
To: Drew DeVault <sir@cmpwn.com>
Cc: git@vger.kernel.org
Subject: Re: Regarding the depreciation of ssh+git/git+ssh protocols
Date: Mon, 15 Mar 2021 10:56:05 -0700	[thread overview]
Message-ID: <YE+ftT2WaKDzc+45@google.com> (raw)
In-Reply-To: <C9Y2DPYH4XO1.3KFD8LT770P2@taiga>

Hi,

Drew DeVault wrote:

> c05186cc38ca4605bff1f275619d7d0faeaf2fa5 introduced ssh+git, and
> 07c7782cc8e1f37c7255dfc69c5d0e3f4d4d728c admitted this was a mistake. I
> argue that it was not a mistake.
>
> The main use-case for the git-specific protocol is to disambiguate with
> other version control systems which also use SSH (or HTTPS), such as
> Mercurial, or simply downloading a tarball over HTTP.

Following the trail of links, I reach
https://public-inbox.org/git/CA+55aFyWqK0bu2V1SYagrYCBGpj0=2orobK2vT-KRkqpq=kgtw@mail.gmail.com/,
but that email mostly just makes assertions rather than explaining the
rationale.  So it's probably worth talking it through now.

> Some things that are affected by this include package manager source
> lists and configurations for CI tooling (the latter being my main
> interest in this).

The original idea of URI schemes like svn+https is that we can treat
these version control URLs as part of the general category of uniform
resource identifiers --- in other words, you might be able to type
them in a browser's URL bar, browse the content of a repository, use
an <img> tag to point to a file within a version control repository,
and so on.

_That_ idea, at least, does not work all that well.  There's not an
equivalent to a fragment identifier to refer to a particular file
within a repository.  Further, if I have an https URL referring to a
Git repository, I'm better off viewing it without a "git+" prefix
because then I can see the content of the repository using a web based
repository browser.

In other words, a "Git URL" is not a URI at all; it's simply the
identifier that Git uses to clone a repository.  A package manager or
CI tool is perfectly within its rights to provide its own naming
scheme for sources, such as "git::https://example.com/path/to/repo" or
even the same with "git+" prefix; or it can use an https URL and infer
from the content it gets there what version control system it uses.

The missing piece is an HTTP header to unambiguously mark that URL as
being usable by Git.  I'm not aware of a standard way to do that; e.g.
golang's "go get" tool[*] uses a custom 'meta name="go-import"' HTML
element.

Thanks and hope that helps,
Jonathan

[*] https://golang.org/cmd/go/#hdr-Remote_import_paths