ggcr: registry on localhost is defaulted to docker.io - image not known when accessing image

[maximilianbraun]

Hi!

thanks for the great work done here.

Describe the bug

When i.e leveraging podman images are tagged with localhost as default registry [1]. Docker used docker.io.
When calculating an images size [2] based on the locally tagged name, resolution will fail[3] because of defaulting back to docker.io. since localhost is not honnored as a relevant registry name.

I barely remember it, but i think containerd is defaulting to localhost as well (?)

As far as I can see, https://github.com/google/go-containerregistry/blob/main/pkg/name/repository.go#L81 could be the relevant line of code.

With docker the same behaviour works well, since docker uses internally docker.io as a registry name.

To Reproduce

• Use Podman
• Build docker image [1]
• Run Test [2]

Expected behavior

I would expect that a valid hostname, like localhost, is accepted as a registry

Additional context

Add any other context about the problem here.

• Version of the module: github.com/google/go-containerregistry v0.20.2
• Registry used (e.g., GCR, ECR, Quay)

❯ podman --version
podman version 5.3.2

[1]

❯ cat Dockerfile
FROM scratch
❯ docker build . -t testimage:mytag
STEP 1/1: FROM scratch
COMMIT testimage:mytag
--> 379ecbdbbcdc
Successfully tagged localhost/testimage:mytag
379ecbdbbcdcb68e330f76f5928b8aaf37f1a5f13f63d1684a572fa4c7655965

[2]

func Test(t *testing.T) {
	refName := "localhost/testimage:mytag"
	reference, err := name.ParseReference(refName)
	assert.NoError(t, err)
	image, err := daemon.Image(reference)
	assert.NoError(t, err)
	_, err = image.Size()
	assert.NoError(t, err)
}

[3]

=== RUN   Test
    ...test.go:176: 
        	Error Trace:	...test.go:176
        	Error:      	Received unexpected error:
        	            	Error response from daemon: docker.io/library/testimage:mytag: image not known
        	Test:       	Test
--- FAIL: Test (0.01s)

FAIL