Sparse registry support

[Shnatsel]

Cargo is currently testing a sparse registry served over HTTPS, instead of downloading the entire git repo: https://blog.rust-lang.org/2022/06/22/sparse-registry-testing.html

Are there any plans to support it in this crate?

I'm looking to use it in cargo audit for two reasons:

1. Shorter CI times without having to download the entire registry
2. Removing the dependency on OpenSSL via libgit2 and replacing it with rustls. (Although Replace git2 with gitoxide #82 would also solve this)

[Byron]

Shorter CI times without having to download the entire registry

Note that I am actively working on supporting shallow clones in cargo by the end of the year, and with it being available in gitoxide it should be possible to support it here as well.

[Shnatsel]

I understand that the Cargo sparse registry is distinct from Git sparse checkouts, and doesn't use Git at all - just plain HTTP. Am I mistaken?

[Byron]

No, you are not mistaken and maybe my comment is out of place or confusing.

I was referring to the shorter CI times specifically and that these will also be reduced once shallow clones are supported by gitoxide. My feeling is that gitoxide will land here before sparse-index support is ready to be used outside of cargo, unless the Cargo Team is making sure the sparse registry is accessible via some API crate which may well be the case.

[kornelski]

Yes, I think this crate could support a sparse registry. You could DIY a solution already, because for fetching a single crate that's a matter of making an HTTP request, and this crate exposes Crate::parse_from_slice already.