Add example using the transfer service

[estesp]

Pulls an image to the containerd content store

[estesp]

Sigh, what's the magic 😅

I ran rustup run nightly rustfmt --edition 2024 --emit stdout container_pull.rs and re-updated with slight changes to import ordering/formatting..still no love with CI checks on cargo fmt

[mxpv]

You can run cargo fmt locally like this:

❯ cargo +nightly fmt --all -- --check

[estesp]

cargo +nightly fmt --all -- --check

Well, I tried that command and it didn't work with a strange error about lack of toolchain directive support in cargo, hence my weird invocation via rustup 😂 Turns out I had a weird path problem with my install, so now cargo +nightly works properly. Thanks!

[aFuerst]

@estesp can auth credentials to a private repository be passed with the OciRegistry.resolver headers hashmap?
I'm trying to replicate ctr images pull --user name:pass

Or a pointer to the containerd could would be helpful

[estesp]

I haven't taken the time to implement it yet, but this feature depends on using a gRPC stream to handle a synchronous callback from containerd's transfer service to ask for credentials.

You pass the stream to the transfer service through the OCI registry type auth_stream entry in the RegistryResolver. Note that the general streaming API is defined here.

The transfer service sends an AuthRequest type on that stream and you would have to respond with an AuthResponse for that host. The headers entry is most likely just to support extra header content you wish to pass for that registry? More details on the auth flow in the transfer service doc: https://github.com/containerd/containerd/blob/main/docs/transfer.md#credentials

[aFuerst]

Thanks for the pointers! I'll see if I can get it working, looks straightforward