feat: add "ThreeLevelNamespaceAdapter" for enforcing 3-level table identifiers

java/lance-namespace-impls-core/src/main/java/org/lance/namespace/util/ThreeLevelNamespaceAdapter.java

@@ -0,0 +1,183 @@
+/*
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+package org.lance.namespace.util;
+
+import org.lance.namespace.LanceNamespace;
+import org.lance.namespace.errors.InvalidInputException;
+import org.lance.namespace.model.CreateNamespaceRequest;
+import org.lance.namespace.model.CreateNamespaceResponse;
+import org.lance.namespace.model.DeclareTableRequest;
+import org.lance.namespace.model.DeclareTableResponse;
+import org.lance.namespace.model.DeregisterTableRequest;
+import org.lance.namespace.model.DeregisterTableResponse;
+import org.lance.namespace.model.DescribeNamespaceRequest;
+import org.lance.namespace.model.DescribeNamespaceResponse;
+import org.lance.namespace.model.DescribeTableRequest;
+import org.lance.namespace.model.DescribeTableResponse;
+import org.lance.namespace.model.DropNamespaceRequest;
+import org.lance.namespace.model.DropNamespaceResponse;
+import org.lance.namespace.model.ListNamespacesRequest;
+import org.lance.namespace.model.ListNamespacesResponse;
+import org.lance.namespace.model.ListTablesRequest;
+import org.lance.namespace.model.ListTablesResponse;
+
+import org.apache.arrow.memory.BufferAllocator;
+
+import java.util.List;
+import java.util.Map;
+
+/**
+ * Adapter that enforces exactly 3 levels for table identifiers and 2 levels for namespace
+ * identifiers.
+ *
+ * <p>This adapter wraps any {@link LanceNamespace} implementation and validates that:
+ *
+ * <ul>
+ *   <li>Table identifiers have exactly 3 levels: [catalog, database, table]
+ *   <li>Namespace identifiers have at most 2 levels: [catalog] or [catalog, database]
+ *   <li>Operations on non-conforming identifiers are rejected with {@link InvalidInputException}
+ * </ul>
+ *
+ * <p>This is useful for namespace implementations that need to enforce a strict 3-level hierarchy
+ * (e.g., Unity Catalog, Gravitino) while allowing the underlying implementation to be more
+ * flexible.
+ *
+ * <p>Example usage:
+ *
+ * <pre>{@code
+ * LanceNamespace underlying = new SomeNamespace();
+ * LanceNamespace enforced = new ThreeLevelNamespaceAdapter(underlying);
+ * enforced.initialize(properties, allocator);
+ * }</pre>
+ */
+public class ThreeLevelNamespaceAdapter implements LanceNamespace {
+
+  private final LanceNamespace delegate;
+
+  public ThreeLevelNamespaceAdapter(LanceNamespace delegate) {
+    this.delegate = delegate;
+  }
+
+  @Override
+  public void initialize(Map<String, String> configProperties, BufferAllocator allocator) {
+    delegate.initialize(configProperties, allocator);
+  }
+
+  @Override
+  public String namespaceId() {
+    return "ThreeLevelNamespaceAdapter { delegate: " + delegate.namespaceId() + " }";
+  }
+
+  @Override
+  public ListNamespacesResponse listNamespaces(ListNamespacesRequest request) {
+    validateNamespaceId(request.getId(), "list");
+    return delegate.listNamespaces(request);
+  }
+
+  @Override
+  public CreateNamespaceResponse createNamespace(CreateNamespaceRequest request) {
+    validateNamespaceId(request.getId(), "create");
+    return delegate.createNamespace(request);
+  }
+
+  @Override
+  public DescribeNamespaceResponse describeNamespace(DescribeNamespaceRequest request) {
+    validateNamespaceId(request.getId(), "describe");
+    return delegate.describeNamespace(request);
+  }
+
+  @Override
+  public DropNamespaceResponse dropNamespace(DropNamespaceRequest request) {
+    validateNamespaceId(request.getId(), "drop");
+    return delegate.dropNamespace(request);
+  }
+
+  @Override
+  public ListTablesResponse listTables(ListTablesRequest request) {
+    validateNamespaceId(request.getId(), "list tables in");
+    return delegate.listTables(request);
+  }
+
+  @Override
+  public DeclareTableResponse declareTable(DeclareTableRequest request) {
+    validateTableId(request.getId());
+    return delegate.declareTable(request);
+  }
+
+  @Override
+  public DescribeTableResponse describeTable(DescribeTableRequest request) {
+    validateTableId(request.getId());
+    return delegate.describeTable(request);
+  }
+
+  @Override
+  public DeregisterTableResponse deregisterTable(DeregisterTableRequest request) {
+    validateTableId(request.getId());
+    return delegate.deregisterTable(request);
+  }
+
+  /**
+   * Validates that a namespace identifier has at most 2 levels.
+   *
+   * @param id the namespace identifier to validate
+   * @param operation the operation being performed (for error messages)
+   * @throws InvalidInputException if the identifier has more than 2 levels
+   */
+  private void validateNamespaceId(List<String> id, String operation) {
+    if (id == null) {
+      return; // Root namespace is allowed
+    }
+
+    int levels = id.size();
+    if (levels > 2) {
+      throw new InvalidInputException(
+          String.format(
+              "Cannot %s namespace with %d levels. Expected at most 2 levels (catalog.database), but got: %s",
+              operation, levels, String.join(".", id)),
+          "INVALID_NAMESPACE_LEVELS",
+          String.join(".", id));
+    }
+  }
+
+  /**
+   * Validates that a table identifier has exactly 3 levels.
+   *
+   * @param id the table identifier to validate
+   * @throws InvalidInputException if the identifier does not have exactly 3 levels
+   */
+  private void validateTableId(List<String> id) {
+    if (id == null || id.size() != 3) {
+      String idStr = id != null ? String.join(".", id) : "null";
+      int levels = id != null ? id.size() : 0;
+      throw new InvalidInputException(
+          String.format(
+              "Table identifier must have exactly 3 levels (catalog.database.table), but got %d levels: %s",
+              levels, idStr),
+          "INVALID_TABLE_LEVELS",
+          idStr);
+    }
+
+    // Validate that no level is null or empty
+    for (int i = 0; i < id.size(); i++) {
+      String level = id.get(i);
+      if (level == null || level.isEmpty()) {
+        throw new InvalidInputException(
+            String.format(
+                "Table identifier level %d cannot be null or empty: %s", i, String.join(".", id)),
+            "INVALID_TABLE_IDENTIFIER",
+            String.join(".", id));
+      }
+    }
+  }
+}