Change return type of remote.Referrers

Actually using this was cumbersome because it just returns a struct.
This is a breaking change, but I don't think it's a huge deal because
not too many people should be using this yet (and we're < 1.0.0).

pkg/v1/empty/index.go

@@ -60,5 +60,6 @@ func base() *v1.IndexManifest {
 	return &v1.IndexManifest{
 		SchemaVersion: 2,
 		MediaType:     types.OCIImageIndex,
+		Manifests:     []v1.Descriptor{},
 	}
 }

pkg/v1/mutate/mutate_test.go

@@ -289,7 +289,7 @@ func TestAnnotations(t *testing.T) {
 	}, {
 		desc: "index",
 		in:   empty.Index,
-		want: `{"schemaVersion":2,"mediaType":"application/vnd.oci.image.index.v1+json","manifests":null,"annotations":{"foo":"bar"}}`,
+		want: `{"schemaVersion":2,"mediaType":"application/vnd.oci.image.index.v1+json","manifests":[],"annotations":{"foo":"bar"}}`,
 	}, {
 		desc: "arbitrary",
 		in:   arbitrary{},

pkg/v1/remote/descriptor.go

@@ -17,7 +17,6 @@ package remote
 import (
 	"bytes"
 	"context"
-	"encoding/json"
 	"errors"
 	"fmt"
 	"io"
@@ -31,6 +30,8 @@ import (
 	"github.com/google/go-containerregistry/pkg/logs"
 	"github.com/google/go-containerregistry/pkg/name"
 	v1 "github.com/google/go-containerregistry/pkg/v1"
+	"github.com/google/go-containerregistry/pkg/v1/empty"
+	"github.com/google/go-containerregistry/pkg/v1/mutate"
 	"github.com/google/go-containerregistry/pkg/v1/partial"
 	"github.com/google/go-containerregistry/pkg/v1/remote/transport"
 	"github.com/google/go-containerregistry/pkg/v1/types"
@@ -301,7 +302,7 @@ func fallbackTag(d name.Digest) name.Tag {
 	return d.Context().Tag(strings.Replace(d.DigestStr(), ":", "-", 1))
 }
 
-func (f *fetcher) fetchReferrers(ctx context.Context, filter map[string]string, d name.Digest) (*v1.IndexManifest, error) {
+func (f *fetcher) fetchReferrers(ctx context.Context, filter map[string]string, d name.Digest) (v1.ImageIndex, error) {
 	// Check the Referrers API endpoint first.
 	u := f.url("referrers", d.DigestStr())
 	req, err := http.NewRequestWithContext(ctx, http.MethodGet, u.String(), nil)
@@ -319,32 +320,40 @@ func (f *fetcher) fetchReferrers(ctx context.Context, filter map[string]string,
 	if err := transport.CheckError(resp, http.StatusOK, http.StatusNotFound, http.StatusBadRequest); err != nil {
 		return nil, err
 	}
+
+	var b []byte
 	if resp.StatusCode == http.StatusOK {
-		var im v1.IndexManifest
-		if err := json.NewDecoder(resp.Body).Decode(&im); err != nil {
+		b, err = io.ReadAll(resp.Body)
+		if err != nil {
 			return nil, err
 		}
-		return filterReferrersResponse(filter, &im), nil
-	}
-
-	// The registry doesn't support the Referrers API endpoint, so we'll use the fallback tag scheme.
-	b, _, err := f.fetchManifest(ctx, fallbackTag(d), []types.MediaType{types.OCIImageIndex})
-	if err != nil {
+	} else {
+		// The registry doesn't support the Referrers API endpoint, so we'll use the fallback tag scheme.
+		b, _, err = f.fetchManifest(ctx, fallbackTag(d), []types.MediaType{types.OCIImageIndex})
 		var terr *transport.Error
-		if ok := errors.As(err, &terr); ok && terr.StatusCode == http.StatusNotFound {
+		if errors.As(err, &terr) && terr.StatusCode == http.StatusNotFound {
 			// Not found just means there are no attachments yet. Start with an empty manifest.
-			return &v1.IndexManifest{MediaType: types.OCIImageIndex}, nil
+			return empty.Index, nil
+		} else if err != nil {
+			return nil, err
 		}
-
-		return nil, err
 	}
 
-	var im v1.IndexManifest
-	if err := json.Unmarshal(b, &im); err != nil {
+	h, sz, err := v1.SHA256(bytes.NewReader(b))
+	if err != nil {
 		return nil, err
 	}
-
-	return filterReferrersResponse(filter, &im), nil
+	idx := &remoteIndex{
+		fetcher:   *f,
+		manifest:  b,
+		mediaType: types.OCIImageIndex,
+		descriptor: &v1.Descriptor{
+			Digest:    h,
+			MediaType: types.OCIImageIndex,
+			Size:      sz,
+		},
+	}
+	return filterReferrersResponse(filter, idx), nil
 }
 
 func (f *fetcher) fetchManifest(ctx context.Context, ref name.Reference, acceptable []types.MediaType) ([]byte, *v1.Descriptor, error) {
@@ -551,19 +560,15 @@ func (f *fetcher) blobExists(h v1.Hash) (bool, error) {
 
 // If filter applied, filter out by artifactType.
 // See https://github.com/opencontainers/distribution-spec/blob/main/spec.md#listing-referrers
-func filterReferrersResponse(filter map[string]string, origIndex *v1.IndexManifest) *v1.IndexManifest {
-	newIndex := origIndex
+func filterReferrersResponse(filter map[string]string, in v1.ImageIndex) v1.ImageIndex {
 	if filter == nil {
-		return newIndex
-	}
-	if v, ok := filter["artifactType"]; ok {
-		tmp := []v1.Descriptor{}
-		for _, desc := range newIndex.Manifests {
-			if desc.ArtifactType == v {
-				tmp = append(tmp, desc)
-			}
-		}
-		newIndex.Manifests = tmp
+		return in
+	}
+	v, ok := filter["artifactType"]
+	if !ok {
+		return in
 	}
-	return newIndex
+	return mutate.RemoveManifests(in, func(desc v1.Descriptor) bool {
+		return desc.ArtifactType != v
+	})
 }

pkg/v1/remote/referrers.go

@@ -22,7 +22,7 @@ import (
 // Referrers returns a list of descriptors that refer to the given manifest digest.
 //
 // The subject manifest doesn't have to exist in the registry for there to be descriptors that refer to it.
-func Referrers(d name.Digest, options ...Option) (*v1.IndexManifest, error) {
+func Referrers(d name.Digest, options ...Option) (v1.ImageIndex, error) {
 	o, err := makeOptions(options...)
 	if err != nil {
 		return nil, err

pkg/v1/remote/referrers_test.go

@@ -100,7 +100,11 @@ func TestReferrers(t *testing.T) {
 		if err != nil {
 			t.Fatal(err)
 		}
-		if numManifests := len(index.Manifests); numManifests != 0 {
+		m, err := index.IndexManifest()
+		if err != nil {
+			t.Fatal(err)
+		}
+		if numManifests := len(m.Manifests); numManifests != 0 {
 			t.Fatalf("expected index to contain 0 manifests, but had %d", numManifests)
 		}
 
@@ -126,7 +130,12 @@ func TestReferrers(t *testing.T) {
 		if err != nil {
 			t.Fatal(err)
 		}
-		if d := cmp.Diff([]v1.Descriptor{leafDesc}, index.Manifests); d != "" {
+		m2, err := index.IndexManifest()
+		if err != nil {
+			t.Fatal(err)
+		}
+		if d := cmp.Diff([]v1.Descriptor{leafDesc}, m2.Manifests); d != "" {
+			t.Logf("m2.Manifests: %v", m2.Manifests)
 			t.Fatalf("referrers diff (-want,+got): %s", d)
 		}
 
@@ -144,7 +153,11 @@ func TestReferrers(t *testing.T) {
 			if err != nil {
 				t.Fatal(err)
 			}
-			if d := cmp.Diff(index.Manifests, mf.Manifests); d != "" {
+			m2, err := index.IndexManifest()
+			if err != nil {
+				t.Fatal(err)
+			}
+			if d := cmp.Diff(m2.Manifests, mf.Manifests); d != "" {
 				t.Fatalf("fallback tag diff (-want,+got): %s", d)
 			}
 		}
@@ -166,7 +179,11 @@ func TestReferrers(t *testing.T) {
 		if err != nil {
 			t.Fatal(err)
 		}
-		if d := cmp.Diff([]v1.Descriptor{leafDesc}, index.Manifests); d != "" {
+		m3, err := index.IndexManifest()
+		if err != nil {
+			t.Fatal(err)
+		}
+		if d := cmp.Diff([]v1.Descriptor{leafDesc}, m3.Manifests); d != "" {
 			t.Fatalf("referrers diff after second push (-want,+got): %s", d)
 		}
 
@@ -176,7 +193,11 @@ func TestReferrers(t *testing.T) {
 		if err != nil {
 			t.Fatal(err)
 		}
-		if numManifests := len(index.Manifests); numManifests == 0 {
+		m4, err := index.IndexManifest()
+		if err != nil {
+			t.Fatal(err)
+		}
+		if numManifests := len(m4.Manifests); numManifests == 0 {
 			t.Fatal("index contained 0 manifests")
 		}
 
@@ -185,7 +206,11 @@ func TestReferrers(t *testing.T) {
 		if err != nil {
 			t.Fatal(err)
 		}
-		if numManifests := len(index.Manifests); numManifests != 0 {
+		m5, err := index.IndexManifest()
+		if err != nil {
+			t.Fatal(err)
+		}
+		if numManifests := len(m5.Manifests); numManifests != 0 {
 			t.Fatalf("expected index to contain 0 manifests, but had %d", numManifests)
 		}
 	}