Add ManifestList support

registry/manifest.go

@@ -2,15 +2,19 @@ package registry
 
 import (
 	"bytes"
+	"encoding/json"
+	"fmt"
 	"io/ioutil"
 	"net/http"
 
 	"github.com/docker/distribution"
+	"github.com/docker/distribution/manifest/manifestlist"
 	"github.com/docker/distribution/manifest/schema1"
 	"github.com/docker/distribution/manifest/schema2"
 	digest "github.com/opencontainers/go-digest"
 )
 
+// Manifest returns with the schema1 manifest addressed by repository/reference
 func (registry *Registry) Manifest(repository, reference string) (*schema1.SignedManifest, error) {
 	url := registry.url("/v2/%s/manifests/%s", repository, reference)
 	registry.Logf("registry.manifest.get url=%s repository=%s reference=%s", url, repository, reference)
@@ -41,6 +45,40 @@ func (registry *Registry) Manifest(repository, reference string) (*schema1.Signe
 	return signedManifest, nil
 }
 
+// ManifestList returns with the ManifestList addressed by repository/reference
+func (registry *Registry) ManifestList(repository, reference string) (*manifestlist.DeserializedManifestList, error) {
+	url := registry.url("/v2/%s/manifests/%s", repository, reference)
+	registry.Logf("registry.manifestlist.get url=%s repository=%s reference=%s", url, repository, reference)
+
+	req, err := http.NewRequest("GET", url, nil)
+	if err != nil {
+		return nil, err
+	}
+	req.Header.Set("Accept", manifestlist.MediaTypeManifestList)
+	resp, err := registry.Client.Do(req)
+	if err != nil {
+		return nil, err
+	}
+	defer resp.Body.Close()
+	ml := new(manifestlist.DeserializedManifestList)
+	err = json.NewDecoder(resp.Body).Decode(ml)
+	if err != nil {
+		return nil, err
+	}
+
+	if ml.MediaType != manifestlist.MediaTypeManifestList {
+		err = fmt.Errorf("mediaType in manifest list should be '%s' not '%s'",
+			manifestlist.MediaTypeManifestList, ml.MediaType)
+		return nil, err
+	}
+	return ml, nil
+}
+
+// ManifestV2 returns with the schema2 manifest addressed by repository/reference
+// If reference is an image digest (sha256:...) that is the hash of a manifestlist,
+// not a manifest, then the method will return the first manifest with amd64 architecture,
+// or in the absence thereof, the first manifest in the list. (Rationale: the Docker
+// Image Digests returned by `docker images --digests` often refer to manifestlists)
 func (registry *Registry) ManifestV2(repository, reference string) (*schema2.DeserializedManifest, error) {
 	url := registry.url("/v2/%s/manifests/%s", repository, reference)
 	registry.Logf("registry.manifest.get url=%s repository=%s reference=%s", url, repository, reference)
@@ -55,19 +93,56 @@ func (registry *Registry) ManifestV2(repository, reference string) (*schema2.Des
 	if err != nil {
 		return nil, err
 	}
-
 	defer resp.Body.Close()
 	body, err := ioutil.ReadAll(resp.Body)
 	if err != nil {
 		return nil, err
 	}
 
-	deserialized := &schema2.DeserializedManifest{}
-	err = deserialized.UnmarshalJSON(body)
-	if err != nil {
-		return nil, err
+	actualMediaType := resp.Header.Get("Content-Type")
+	switch actualMediaType {
+	case schema2.MediaTypeManifest:
+		deserialized := &schema2.DeserializedManifest{}
+		err = deserialized.UnmarshalJSON(body)
+		if err != nil {
+			return nil, err
+		}
+		return deserialized, nil
+
+	case manifestlist.MediaTypeManifestList:
+		// if `reference` is an image digest, a manifest list may be received even though a schema2 manifest was requested
+		// (since the image digest is the hash of the manifest list, not the manifest)
+		// unwrap the referred manifest in this case
+		ml := new(manifestlist.DeserializedManifestList)
+		err := ml.UnmarshalJSON(body)
+		if err != nil {
+			return nil, err
+		}
+
+		if ml.MediaType != manifestlist.MediaTypeManifestList {
+			err = fmt.Errorf("mediaType in manifest list should be '%s' not '%s'",
+				manifestlist.MediaTypeManifestList, ml.MediaType)
+			return nil, err
+		}
+		if len(ml.Manifests) == 0 {
+			return nil, fmt.Errorf("empty manifest list was receceived: repository=%s reference=%s", repository, reference)
+		}
+
+		// use the amd64 manifest by default
+		// TODO: query current platform architecture, OS and Variant and use those as selection criteria
+		for _, m := range ml.Manifests {
+			if m.Platform.Architecture == "amd64" {
+				// address the manifest explicitly with its digest
+				return registry.ManifestV2(repository, m.Digest.String())
+			}
+		}
+		// fallback: use the first manifest in the list
+		// NOTE: emptiness of the list was checked above
+		return registry.ManifestV2(repository, ml.Manifests[0].Digest.String())
+
+	default:
+		return nil, fmt.Errorf("unexpected manifest schema was received from registry: mediatype should be %s, not %s (registry may not support schema2 manifests)", schema2.MediaTypeManifest, actualMediaType)
 	}
-	return deserialized, nil
 }
 
 func (registry *Registry) ManifestDigest(repository, reference string) (digest.Digest, error) {