imagetools: implement inspect for manifest list

Signed-off-by: Tonis Tiigi <tonistiigi@gmail.com>

util/imagetools/inspect.go

@@ -0,0 +1,92 @@
+package imagetools
+
+import (
+	"bytes"
+	"context"
+	"io"
+	"net/http"
+
+	"github.com/containerd/containerd/remotes"
+	"github.com/containerd/containerd/remotes/docker"
+	clitypes "github.com/docker/cli/cli/config/types"
+	"github.com/docker/distribution/reference"
+	ocispec "github.com/opencontainers/image-spec/specs-go/v1"
+)
+
+type Auth interface {
+	GetAuthConfig(registryHostname string) (clitypes.AuthConfig, error)
+}
+
+type Opt struct {
+	Auth Auth
+}
+
+type Resolver struct {
+	r remotes.Resolver
+}
+
+func New(opt Opt) *Resolver {
+	resolver := docker.NewResolver(docker.ResolverOptions{
+		Client:      http.DefaultClient,
+		Credentials: toCredentialsFunc(opt.Auth),
+	})
+	return &Resolver{
+		r: resolver,
+	}
+}
+
+func (r *Resolver) Get(ctx context.Context, in string) ([]byte, ocispec.Descriptor, error) {
+	ref, err := parseRef(in)
+	if err != nil {
+		return nil, ocispec.Descriptor{}, err
+	}
+
+	in, desc, err := r.r.Resolve(ctx, ref.String())
+	if err != nil {
+		return nil, ocispec.Descriptor{}, err
+	}
+
+	fetcher, err := r.r.Fetcher(ctx, in)
+	if err != nil {
+		return nil, ocispec.Descriptor{}, err
+	}
+
+	rc, err := fetcher.Fetch(ctx, desc)
+	if err != nil {
+		return nil, ocispec.Descriptor{}, err
+	}
+
+	buf := &bytes.Buffer{}
+	_, err = io.Copy(buf, rc)
+	rc.Close()
+	if err != nil {
+		return nil, ocispec.Descriptor{}, err
+	}
+
+	return buf.Bytes(), desc, nil
+}
+
+func parseRef(s string) (reference.Named, error) {
+	ref, err := reference.ParseNormalizedNamed(s)
+	if err != nil {
+		return nil, err
+	}
+	ref = reference.TagNameOnly(ref)
+	return ref, nil
+}
+
+func toCredentialsFunc(a Auth) func(string) (string, string, error) {
+	return func(host string) (string, string, error) {
+		if host == "registry-1.docker.io" {
+			host = "https://index.docker.io/v1/"
+		}
+		ac, err := a.GetAuthConfig(host)
+		if err != nil {
+			return "", "", err
+		}
+		if ac.IdentityToken != "" {
+			return "", ac.IdentityToken, nil
+		}
+		return ac.Username, ac.Password, nil
+	}
+}