remotes/docker: add scope (registry:foo/bar:pull)

Signed-off-by: Akihiro Suda <suda.akihiro@lab.ntt.co.jp>

remotes/docker/scope.go

@@ -0,0 +1,60 @@
+package docker
+
+import (
+	"context"
+	"net/url"
+	"sort"
+	"strings"
+
+	"github.com/containerd/containerd/reference"
+)
+
+// repositoryScope returns a repository scope string such as "repository:foo/bar:pull"
+// for "host/foo/bar:baz".
+// When push is true, both pull and push are added to the scope.
+func repositoryScope(refspec reference.Spec, push bool) (string, error) {
+	u, err := url.Parse("dummy://" + refspec.Locator)
+	if err != nil {
+		return "", err
+	}
+	s := "repository:" + strings.TrimPrefix(u.Path, "/") + ":pull"
+	if push {
+		s += ",push"
+	}
+	return s, nil
+}
+
+// tokenScopesKey is used for the key for context.WithValue().
+// value: []string (e.g. {"registry:foo/bar:pull"})
+type tokenScopesKey struct{}
+
+// contextWithRepositoryScope returns a context with tokenScopesKey{} and the repository scope value.
+func contextWithRepositoryScope(ctx context.Context, refspec reference.Spec, push bool) (context.Context, error) {
+	s, err := repositoryScope(refspec, push)
+	if err != nil {
+		return nil, err
+	}
+	return context.WithValue(ctx, tokenScopesKey{}, []string{s}), nil
+}
+
+// getTokenScopes returns deduplicated and sorted scopes from ctx.Value(tokenScopesKey{}) and params["scope"].
+func getTokenScopes(ctx context.Context, params map[string]string) []string {
+	var scopes []string
+	if x := ctx.Value(tokenScopesKey{}); x != nil {
+		scopes = append(scopes, x.([]string)...)
+	}
+	if scope, ok := params["scope"]; ok {
+		for _, s := range scopes {
+			// Note: this comparison is unaware of the scope grammar (https://docs.docker.com/registry/spec/auth/scope/)
+			// So, "repository:foo/bar:pull,push" != "repository:foo/bar:push,pull", although semantically they are equal.
+			if s == scope {
+				// already appended
+				goto Sort
+			}
+		}
+		scopes = append(scopes, scope)
+	}
+Sort:
+	sort.Strings(scopes)
+	return scopes
+}