fix(meta): guard GetReferrersInfo against a missing referrer entry (#4213)

Signed-off-by: Artem Muterko <artem@sopho.tech>

Author: archy-rock3t-cloud

pkg/meta/boltdb/boltdb.go

@@ -1250,7 +1250,7 @@ func (bdw *BoltDB) GetReferrersInfo(repo string, referredDigest godigest.Digest,
 			return err
 		}
 
-		referrersInfo := protoRepoMeta.Referrers[referredDigest.String()].List
+		referrersInfo := protoRepoMeta.Referrers[referredDigest.String()].GetList()
 		seenDigests := make(map[string]struct{})
 
 		for i := range referrersInfo {

pkg/meta/boltdb/boltdb_test.go

@@ -306,6 +306,15 @@ func TestWrapperErrors(t *testing.T) {
 				_, err = boltdbWrapper.GetReferrersInfo("repo", "refDig", []string{})
 				So(err, ShouldNotBeNil)
 			})
+
+			Convey("digest with no referrers entry returns empty list without panic", func() {
+				err := boltdbWrapper.SetRepoReference(ctx, "repo", "tag", imageMeta)
+				So(err, ShouldBeNil)
+
+				referrers, err := boltdbWrapper.GetReferrersInfo("repo", godigest.FromString("no-referrers"), []string{})
+				So(err, ShouldBeNil)
+				So(referrers, ShouldBeEmpty)
+			})
 		})
 
 		Convey("ResetRepoReferences", func() {

pkg/meta/redis/redis.go

@@ -1732,7 +1732,7 @@ func (rc *RedisDB) GetReferrersInfo(repo string, referredDigest godigest.Digest,
 		return referrersInfoResult, err
 	}
 
-	referrersInfo := protoRepoMeta.Referrers[referredDigest.String()].List
+	referrersInfo := protoRepoMeta.Referrers[referredDigest.String()].GetList()
 	seenDigests := make(map[string]struct{})
 
 	for i := range referrersInfo {

pkg/meta/redis/redis_test.go

@@ -822,6 +822,15 @@ func TestWrapperErrors(t *testing.T) {
 				_, err = metaDB.GetReferrersInfo("repo", "refDig", []string{})
 				So(err, ShouldNotBeNil)
 			})
+
+			Convey("digest with no referrers entry returns empty list without panic", func() {
+				err := metaDB.SetRepoReference(ctx, "repo", "tag", imageMeta)
+				So(err, ShouldBeNil)
+
+				referrers, err := metaDB.GetReferrersInfo("repo", godigest.FromString("no-referrers"), []string{})
+				So(err, ShouldBeNil)
+				So(referrers, ShouldBeEmpty)
+			})
 		})
 
 		Convey("ResetRepoReferences", func() {