Get referrences from OCI Layout

src/main/java/land/oras/Describable.java

@@ -30,4 +30,10 @@ public interface Describable {
      * @return The manifest descriptor
      */
     ManifestDescriptor getDescriptor();
+
+    /**
+     * Get the subject
+     * @return The subject
+     */
+    Subject getSubject();
 }

src/main/java/land/oras/Index.java

@@ -149,10 +149,7 @@ protected Index withJson(String json) {
         return this;
     }
 
-    /**
-     * Get the subject
-     * @return The subject
-     */
+    @Override
     public Subject getSubject() {
         return subject;
     }

src/main/java/land/oras/Manifest.java

@@ -111,10 +111,7 @@ public Config getConfig() {
         return config;
     }
 
-    /**
-     * Get the subject
-     * @return The subject
-     */
+    @Override
     public Subject getSubject() {
         return subject;
     }

src/main/java/land/oras/OCI.java

@@ -358,6 +358,14 @@ public abstract Manifest pushArtifact(
      */
     public abstract Layer pushBlob(T ref, byte[] data);
 
+    /**
+     * Get the referrers of a container
+     * @param ref The ref
+     * @param artifactType The optional artifact type
+     * @return The referrers
+     */
+    public abstract Referrers getReferrers(T ref, @Nullable ArtifactType artifactType);
+
     /**
      * Attach file to an existing manifest
      * @param ref The ref

src/main/java/land/oras/OCILayout.java

@@ -25,6 +25,7 @@
 import java.nio.file.Files;
 import java.nio.file.Path;
 import java.util.HashMap;
+import java.util.LinkedList;
 import java.util.List;
 import java.util.Map;
 import land.oras.exception.OrasException;
@@ -283,6 +284,31 @@
         }
     }
 
+    @Override
+    public Referrers getReferrers(LayoutRef ref, @Nullable ArtifactType artifactType) {
+        Index index = Index.fromPath(getIndexPath());
+        ManifestDescriptor currentDescriptor = findManifestDescriptor(ref);
+        String currentDescriptorDigest = currentDescriptor.getDigest();
+        LOG.info("Looking for referrers of manifest: {}", currentDescriptorDigest);
+        List<ManifestDescriptor> manifestDescriptors = new LinkedList<>();
+        for (ManifestDescriptor manifestDescriptor : index.getManifests()) {
+            String digest = manifestDescriptor.getDigest();
+            Descriptor descriptor = probeDescriptor(ref.withDigest(digest));
+            Describable describable = isIndexMediaType(descriptor.getMediaType())
+                    ? getIndex(ref.withDigest(digest))
+                    : getManifest(ref.withDigest(digest));
+            if (describable.getSubject() != null) {
+                Subject subject = describable.getSubject();
+                String subjectDigest = subject.getDigest();
+                if (subjectDigest.equals(currentDescriptorDigest)) {
+                    LOG.info("Subject with digest {} found for manifest: {}", subjectDigest, digest);
+                    manifestDescriptors.add(manifestDescriptor);
+                }
+            }
+        }
+        return Referrers.from(manifestDescriptors);
+    }
+
     private void setPath(Path path) {
         this.path = path;
     }
@@ -505,12 +531,6 @@
         return getBlobPath().resolve(algorithm.getPrefix()).resolve(SupportedAlgorithm.getDigest(digest));
     }
 
-    private Path getBlobPath(Config config) {
-        String digest = config.getDigest();
-        SupportedAlgorithm algorithm = SupportedAlgorithm.fromDigest(digest);
-        return getBlobPath().resolve(algorithm.getPrefix()).resolve(SupportedAlgorithm.getDigest(digest));
-    }
-
     private Path getBlobPath(Layer layer) {
         String digest = layer.getDigest();
         SupportedAlgorithm algorithm = SupportedAlgorithm.fromDigest(digest);

src/main/java/land/oras/Referrers.java

@@ -21,6 +21,7 @@
 package land.oras;
 
 import java.util.List;
+import land.oras.utils.Const;
 import land.oras.utils.JsonUtils;
 
 /**
@@ -34,7 +35,10 @@ public class Referrers {
     /**
      * Private constructor
      */
-    private Referrers() {}
+    private Referrers(List<ManifestDescriptor> manifests) {
+        this.mediaType = Const.DEFAULT_INDEX_MEDIA_TYPE;
+        this.manifests = manifests;
+    }
 
     /**
      * Get the media type
@@ -68,4 +72,13 @@ public String toJson() {
     public static Referrers fromJson(String json) {
         return JsonUtils.fromJson(json, Referrers.class);
     }
+
+    /**
+     * Create a referrers object from a list of descriptors
+     * @param descriptors The list of descriptors
+     * @return The referrers object
+     */
+    public static Referrers from(List<ManifestDescriptor> descriptors) {
+        return new Referrers(descriptors);
+    }
 }

src/main/java/land/oras/Registry.java

@@ -138,12 +138,7 @@ public List<String> getTags(ContainerRef containerRef) {
         return JsonUtils.fromJson(response.response(), Tags.class).tags();
     }
 
-    /**
-     * Get the referrers of a container
-     * @param containerRef The container
-     * @param artifactType The optional artifact type
-     * @return The referrers
-     */
+    @Override
     public Referrers getReferrers(ContainerRef containerRef, @Nullable ArtifactType artifactType) {
         if (containerRef.getDigest() == null) {
             throw new OrasException("Digest is required to get referrers");

src/test/java/land/oras/OCILayoutTest.java

@@ -491,6 +491,30 @@ void shouldPullViaTagFromOciLayout() throws IOException {
                 Files.readString(extractDir1.resolve("manifest.json")));
     }
 
+    @Test
+    void shouldGetReferrers() throws IOException {
+
+        Path extractDir1 = extractDir.resolve("shouldGetReferrers");
+        Files.createDirectory(extractDir1);
+
+        LayoutRef layoutRef = LayoutRef.parse("src/test/resources/oci/subject:latest");
+        OCILayout ociLayout =
+                OCILayout.Builder.builder().defaults(layoutRef.getFolder()).build();
+
+        Referrers referrers = ociLayout.getReferrers(layoutRef, null);
+        assertEquals(1, referrers.getManifests().size());
+
+        ManifestDescriptor manifestDescriptor = referrers.getManifests().get(0);
+        assertEquals(
+                "sha256:ccec2a2be7ce7c6aadc8ed0dc03df8f91cbd3534272dd1f8284226a8d3516dd6",
+                manifestDescriptor.getDigest());
+        assertEquals(746, manifestDescriptor.getSize());
+        assertEquals("application/vnd.oci.image.manifest.v1+json", manifestDescriptor.getMediaType());
+        assertNotNull(manifestDescriptor.getAnnotations());
+        assertEquals(1, manifestDescriptor.getAnnotations().size());
+        assertEquals("2025-04-07T14:54:25Z", manifestDescriptor.getAnnotations().get(Const.ANNOTATION_CREATED));
+    }
+
     @Test
     void shouldPullIndex() throws IOException {
 

src/test/resources/oci/subject/blobs/sha256/44136fa355b3678a1146ad16f7e8649e94fb4fc21fe77e8310c060f61caaff8a

@@ -0,0 +1 @@
+{}

src/test/resources/oci/subject/blobs/sha256/98ea6e4f216f2fb4b69fff9b3a44842c38686ca685f3f55dc48c5d3fb1107be4

@@ -0,0 +1 @@
+hi

src/test/resources/oci/subject/blobs/sha256/bb329f103a5fd68e96771f7dcfaa7722e9ec727bb9ab83c2beee96d6f25b08d6

@@ -0,0 +1 @@
+{"schemaVersion":2,"mediaType":"application/vnd.oci.image.manifest.v1+json","artifactType":"application/vnd.text.file.v1+json","config":{"mediaType":"application/vnd.oci.empty.v1+json","digest":"sha256:44136fa355b3678a1146ad16f7e8649e94fb4fc21fe77e8310c060f61caaff8a","size":2,"data":"e30="},"layers":[{"mediaType":"plain/text","digest":"sha256:98ea6e4f216f2fb4b69fff9b3a44842c38686ca685f3f55dc48c5d3fb1107be4","size":3,"annotations":{"org.opencontainers.image.title":"hi.txt"}}],"annotations":{"org.opencontainers.image.created":"2025-04-07T14:54:19Z"}}

src/test/resources/oci/subject/blobs/sha256/ccec2a2be7ce7c6aadc8ed0dc03df8f91cbd3534272dd1f8284226a8d3516dd6

@@ -0,0 +1 @@
+{"schemaVersion":2,"mediaType":"application/vnd.oci.image.manifest.v1+json","artifactType":"application/vnd.text.file.v1+json","config":{"mediaType":"application/vnd.oci.empty.v1+json","digest":"sha256:44136fa355b3678a1146ad16f7e8649e94fb4fc21fe77e8310c060f61caaff8a","size":2,"data":"e30="},"layers":[{"mediaType":"application/vnd.oci.image.layer.v1.tar","digest":"sha256:e094bc809626f0a401a40d75c56df478e546902ff812772c4594265203b23980","size":4,"annotations":{"org.opencontainers.image.title":"hi2.txt"}}],"subject":{"mediaType":"application/vnd.oci.image.manifest.v1+json","digest":"sha256:bb329f103a5fd68e96771f7dcfaa7722e9ec727bb9ab83c2beee96d6f25b08d6","size":554},"annotations":{"org.opencontainers.image.created":"2025-04-07T14:54:25Z"}}

src/test/resources/oci/subject/blobs/sha256/e094bc809626f0a401a40d75c56df478e546902ff812772c4594265203b23980

@@ -0,0 +1 @@
+hi2

src/test/resources/oci/subject/index.json

@@ -0,0 +1 @@
+{"schemaVersion":2,"manifests":[{"mediaType":"application/vnd.oci.image.manifest.v1+json","digest":"sha256:bb329f103a5fd68e96771f7dcfaa7722e9ec727bb9ab83c2beee96d6f25b08d6","size":554,"annotations":{"org.opencontainers.image.ref.name":"latest"}},{"mediaType":"application/vnd.oci.image.manifest.v1+json","digest":"sha256:ccec2a2be7ce7c6aadc8ed0dc03df8f91cbd3534272dd1f8284226a8d3516dd6","size":746,"annotations":{"org.opencontainers.image.created":"2025-04-07T14:54:25Z"},"artifactType":"application/vnd.text.file.v1+json"}]}

src/test/resources/oci/subject/oci-layout

@@ -0,0 +1 @@
+{"imageLayoutVersion":"1.0.0"}