Mounting doesn't work when specifying a domain for dockerhub

[jonjohnsonjr]

# broken 
crane cp hello-world index.docker.io/jonjohnson/hello-world

# broken
crane cp hello-world docker.io/jonjohnson/hello-world

# works
crane cp hello-world jonjohnson/hello-world

I'm suspicious of these bits of code:

go-containerregistry/pkg/v1/remote/write.go

Lines 444 to 467 in fcc8ea8

	func scopesForUploadingImage(repo name.Repository, layers []v1.Layer) []string {
	// use a map as set to remove duplicates scope strings
	scopeSet := map[string]struct{}{}
	for _, l := range layers {
	if ml, ok := l.(*MountableLayer); ok {
	// we will add push scope for ref.Context() after the loop.
	// for now we ask pull scope for references of the same registry
	if ml.Reference.Context() != repo && ml.Reference.Context().Registry == repo.Registry {
	scopeSet[ml.Reference.Scope(transport.PullScope)] = struct{}{}
	}
	}
	}
	scopes := make([]string, 0)
	// Push scope should be the first element because a few registries just look at the first scope to determine access.
	scopes = append(scopes, repo.Scope(transport.PushScope))
	for scope := range scopeSet {
	scopes = append(scopes, scope)
	}
	return scopes
	}

go-containerregistry/pkg/v1/remote/transport/bearer.go

Lines 58 to 66 in fcc8ea8

	// http.Client handles redirects at a layer above the http.RoundTripper
	// abstraction, so to avoid forwarding Authorization headers to places
	// we are redirected, only set it when the authorization header matches
	// the registry with which we are interacting.
	// In case of redirect http.Client can use an empty Host, check URL too.
	if matchesHost(bt.registry, in, bt.scheme) {
	hdr := fmt.Sprintf("Bearer %s", bt.bearer.RegistryToken)
	in.Header.Set("Authorization", hdr)
	}

Looking at the token I get back from dockerhub, it looks like we're missing pull scopes for the source repo:

"access":[{"type":"repository","name":"jonjohnson/hello-world","actions":["pull","push"]}]

[jonjohnsonjr]

So this fixes things:

diff --git a/pkg/v1/remote/write.go b/pkg/v1/remote/write.go
index 7b431c0..13f6873 100644
--- a/pkg/v1/remote/write.go
+++ b/pkg/v1/remote/write.go
@@ -449,7 +449,7 @@ func scopesForUploadingImage(repo name.Repository, layers []v1.Layer) []string {
                if ml, ok := l.(*MountableLayer); ok {
                        // we will add push scope for ref.Context() after the loop.
                        // for now we ask pull scope for references of the same registry
-                       if ml.Reference.Context() != repo && ml.Reference.Context().Registry == repo.Registry {
+                       if ml.Reference.Context().String() != repo.String() && ml.Reference.Context().Registry.String() == repo.Registry.String() {
                                scopeSet[ml.Reference.Scope(transport.PullScope)] = struct{}{}
                        }
                }

but I'm not actually sure how we're getting to this state.

Printing some nonsense out...

diff --git a/pkg/v1/remote/write.go b/pkg/v1/remote/write.go
index 7b431c0..089449c 100644
--- a/pkg/v1/remote/write.go
+++ b/pkg/v1/remote/write.go
@@ -449,6 +449,8 @@ func scopesForUploadingImage(repo name.Repository, layers []v1.Layer) []string {
                if ml, ok := l.(*MountableLayer); ok {
                        // we will add push scope for ref.Context() after the loop.
                        // for now we ask pull scope for references of the same registry
+                       logs.Debug.Printf("MOUNTABLE LAYER: %#v", ml.Reference.Context().Registry)
+                       logs.Debug.Printf("TARGET REPO: %#v", repo.Registry)
                        if ml.Reference.Context() != repo && ml.Reference.Context().Registry == repo.Registry {
                                scopeSet[ml.Reference.Scope(transport.PullScope)] = struct{}{}
                        }

I see:

2020/03/09 17:16:19 MOUNTABLE LAYER: name.Registry{insecure:false, registry:""}
2020/03/09 17:16:19 TARGET REPO: name.Registry{insecure:false, registry:"index.docker.io"}                                                                                                                                                         

So for some reason, the layer registry is an empty string, but the target repo gets the default registry.

Looks like this defaulting is deferred to an accessor, so comparing the struct values doesn't work:

go-containerregistry/pkg/name/registry.go

Lines 44 to 51 in fcc8ea8

	// RegistryStr returns the registry component of the Registry.
	func (r Registry) RegistryStr() string {
	if r.registry != "" {
	return r.registry
	}
	return DefaultRegistry
	}

I think we should clean that up but let's just do string comparisons first?