relates to;

• registry: don't call "/info" API endpoint to get default registry cli#2819
• moby/moby@7bfb804 / Move remaining image packages to daemon moby/moby#50446

Rewrite to remove the github.com/docker/docker/registry dependency, which will not be included in the upcoming "api" and "client" modules, and will not be a public package in the module used for the daemon itself.

1. don't call "/info" API endpoint to get default registry

The IndexServerAddress in the /info endpoint was added as part of the initial Windows implementation of the engine. For legal reasons, Microsoft Windows (and thus Docker images based on Windows) were not allowed to be distributed through non-Microsoft infrastructure. As a temporary solution, a dedicated "registry-win-tp3.docker.io" registry was created to serve Windows images.

Using separate registries was not an ideal solution, and a more permanent solution was created by introducing "foreign image layers" in the distribution spec, after which the "registry-win-tp3.docker.io" ceased to exist, and removed from the engine through docker/docker PR 21100.

However, the ElectAuthServer was left in place, quoting from that PR;

make the client check which default registry the daemon uses is still
more correct than leaving it up to the client, even if it won't technically
matter after this PR. There may be some backward compatibility scenarios
where ElectAuthServer [sic] is still helpful.

That comment was 10 Years ago, and the CLI stopped using this information, as the default registry is not configurable, so in practice was a static value. (see docker/cli@b4ca1c7).

2. replace ParseRepositoryInfo and GetAuthConfigKey with local implementation

The ParseRepositoryInfo function was originally implemented for use by the daemon itself. It returns a RepositoryInfo struct that holds information about the repository and the registry the repository can be found in.

As it was written for use by the daemon, it also was designed to be used in combination with the daemon's configuration (such as mirrors, and insecure registries). If no daemon configuration is present, which would be the case when used in a CLI, it uses fallback logic as used in the daemon to detect if the registry is running on a localhost / loopback address, because such addresses are allowed to be "insecure" by default; this includes resolving the IP-address of the host (if it's not an IP-address).

Unfortunately, these functions (and related types) were reused in the CLI and many other places, which resulted in those types to be deeply ingrained in interfaces and (external) code.

For compose; it was only used to get the "auth-config key" to use for looking up auth information from the credentials store, which still needs special handling for the "default" (docker hub) domain, which unlike other image references doesn't use the hostname included in the image reference for the actual registry (and key for storing auth).

For those that want to follow along;

First, note that GetAuthConfig only requires a registry.IndexInfo, so not the whole RepositoryInfo struct;
https://github.com/moby/moby/blob/v28.3.3/registry/types.go#L8-L24

From the registry.IndexInfo it only uses the IsOfficial and Name fields; https://github.com/moby/moby/blob/v28.3.3/registry/config.go#L390-L395

But to get the IndexInfo, ParseRepositoryInfo is needed, which first takes the image reference's "domain name" (e.g. docker.io); https://github.com/moby/moby/blob/v28.3.3/registry/config.go#L421

This gets "normalized" for some cases where the info.IndexServerAddress was incorrectly assumed to be the canonical domain for Docker Hub registry, and which does happen to also be accessible as a "v2" registry. https://github.com/moby/moby/blob/v28.3.3/registry/config.go#L334-L341

After normalizing, it checks if it's a docker hub address ("docker.io" after normalizing); Docker Hub is always required to use a secure connection, so no detection happens, and the Official field is set to indicate it's Docker Hub (this code path was already simplified as historically it would try to find daemon configuration (or otherwise use a default) for Mirror configuration;
https://github.com/moby/moby/blob/v28.3.3/registry/config.go#L420-L443

For non-Docker Hub registries, it also sets the name, and attempts to detect if the registry is allowed to be "insecure"; https://github.com/moby/moby/blob/v28.3.3/registry/config.go#L435-L442

Which (as mentioned) involves parsing the address and, if needed, resolving the hostname
https://github.com/moby/moby/blob/v28.3.3/registry/config.go#L445-L481

As Insecure is not used for looking up the auth-config key, all of the above can be reduced to;

• Is the hostname obtained from the image reference "docker.io" (after normalizing)?
• If so, use the special https://index.docker.io/v1/ as auth-config key (another horrible remnant)
• Otherwise use the hostname obtained from the image reference as-is

What I did

Related issue

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