Load v2 GroupMetadata attributes

src/main/java/dev/zarr/zarrjava/core/Group.java

@@ -83,4 +83,6 @@ public Node[] listAsArray() {
             return nodeStream.toArray(Node[]::new);
         }
     }
+
+    public abstract GroupMetadata metadata();
 }

src/main/java/dev/zarr/zarrjava/core/GroupMetadata.java

@@ -1,3 +1,11 @@
 package dev.zarr.zarrjava.core;
 
-public abstract class GroupMetadata {}
+import javax.annotation.Nonnull;
+
+import dev.zarr.zarrjava.ZarrException;
+
+public abstract class GroupMetadata {
+
+    public @Nonnull abstract Attributes attributes() throws ZarrException;
+
+}

src/main/java/dev/zarr/zarrjava/v2/Group.java

@@ -24,10 +24,17 @@ protected Group(@Nonnull StoreHandle storeHandle, @Nonnull GroupMetadata groupMe
   }
 
   public static Group open(@Nonnull StoreHandle storeHandle) throws IOException {
-    StoreHandle metadataHandle = storeHandle.resolve(ZGROUP);
-    ByteBuffer metadataBytes = metadataHandle.readNonNull();
-    return new Group(storeHandle, makeObjectMapper()
-        .readValue(Utils.toArray(metadataBytes), GroupMetadata.class));
+    ObjectMapper mapper = makeObjectMapper();
+    GroupMetadata metadata = mapper.readValue(
+        Utils.toArray(storeHandle.resolve(ZGROUP).readNonNull()),
+        GroupMetadata.class
+    );
+    if (storeHandle.resolve(ZATTRS).exists())
+      metadata.attributes = mapper.readValue(
+          Utils.toArray(storeHandle.resolve(ZATTRS).readNonNull()),
+          dev.zarr.zarrjava.core.Attributes.class
+      );
+    return new Group(storeHandle, metadata);
   }
 
   public static Group open(Path path) throws IOException {
@@ -44,6 +51,12 @@ public static Group create(
     ObjectMapper objectMapper = makeObjectMapper();
     ByteBuffer metadataBytes = ByteBuffer.wrap(objectMapper.writeValueAsBytes(groupMetadata));
     storeHandle.resolve(ZGROUP).set(metadataBytes);
+    if (groupMetadata.attributes != null) {
+      StoreHandle attrsHandle = storeHandle.resolve(ZATTRS);
+      ByteBuffer attrsBytes = ByteBuffer.wrap(
+          objectMapper.writeValueAsBytes(groupMetadata.attributes));
+      attrsHandle.set(attrsBytes);
+    }
     return new Group(storeHandle, groupMetadata);
   }
 
@@ -87,4 +100,9 @@ public Array createArray(String key, Function<ArrayMetadataBuilder, ArrayMetadat
   public String toString() {
     return String.format("<v2.Group {%s}>", storeHandle);
   }
+
+  @Override
+  public dev.zarr.zarrjava.core.GroupMetadata metadata() {
+    return metadata;
+  }
 }

src/main/java/dev/zarr/zarrjava/v2/GroupMetadata.java

@@ -1,27 +1,42 @@
 package dev.zarr.zarrjava.v2;
 
+import javax.annotation.Nonnull;
+import javax.annotation.Nullable;
+
 import com.fasterxml.jackson.annotation.JsonCreator;
+import com.fasterxml.jackson.annotation.JsonIgnore;
 import com.fasterxml.jackson.annotation.JsonProperty;
 import dev.zarr.zarrjava.ZarrException;
+import dev.zarr.zarrjava.core.Attributes;
 
 public final class GroupMetadata extends dev.zarr.zarrjava.core.GroupMetadata {
 
   static final int ZARR_FORMAT = 2;
   @JsonProperty("zarr_format")
   public final int zarrFormat = ZARR_FORMAT;
 
+  @Nullable
+  @JsonIgnore
+  public Attributes attributes;
+
   @JsonCreator(mode = JsonCreator.Mode.PROPERTIES)
   public GroupMetadata(
-      @JsonProperty(value = "zarr_format", required = true) int zarrFormat
+      @JsonProperty(value = "zarr_format", required = true) int zarrFormat,
+      @JsonProperty(value = "attributes", required = false) @Nullable Attributes attributes
   ) throws ZarrException {
     if (zarrFormat != this.zarrFormat) {
       throw new ZarrException(
           "Expected zarr format '" + this.zarrFormat + "', got '" + zarrFormat + "'.");
     }
+    this.attributes = attributes;
   }
 
   public GroupMetadata() throws ZarrException {
-    this(ZARR_FORMAT);
+    this(ZARR_FORMAT, null);
   }
 
+  @Override
+  public @Nonnull Attributes attributes() throws ZarrException {
+    return attributes;
+  }
 }

src/main/java/dev/zarr/zarrjava/v3/Group.java

@@ -10,7 +10,6 @@
 import java.nio.ByteBuffer;
 import java.nio.file.Path;
 import java.nio.file.Paths;
-import java.util.Map;
 import java.util.function.Function;
 import javax.annotation.Nonnull;
 import javax.annotation.Nullable;
@@ -136,4 +135,9 @@ public Group updateAttributes(Function<Attributes, Attributes> attributeMapper)
   public String toString() {
     return String.format("<v3.Group {%s}>", storeHandle);
   }
+
+  @Override
+  public GroupMetadata metadata() {
+    return metadata;
+  }
 }

src/main/java/dev/zarr/zarrjava/v3/GroupMetadata.java

@@ -5,6 +5,7 @@
 import dev.zarr.zarrjava.ZarrException;
 import dev.zarr.zarrjava.core.Attributes;
 
+import javax.annotation.Nonnull;
 import javax.annotation.Nullable;
 
 public final class GroupMetadata extends dev.zarr.zarrjava.core.GroupMetadata {
@@ -43,4 +44,12 @@ public GroupMetadata(
   public static GroupMetadata defaultValue() throws ZarrException {
     return new GroupMetadata(ZARR_FORMAT, NODE_TYPE, new Attributes());
   }
+
+  @Override
+  public @Nonnull Attributes attributes() throws ZarrException {
+  if (attributes == null) {
+      throw new ZarrException("Group attributes have not been set.");
+    }
+    return attributes;
+  }
 }