fix: guard UNC namespace client exports

python/python/lancedb/namespace.py

@@ -919,17 +919,7 @@ class LanceNamespaceDBConnection(DBConnection):
             The namespace client for this connection.
         """
         if self._namespace_client is None:
-            if (
-                self._namespace_client_impl is None
-                or self._namespace_client_properties is None
-            ):
-                raise ValueError(
-                    "Cannot construct a Python namespace client without "
-                    "namespace implementation properties"
-                )
-            self._namespace_client = namespace_connect(
-                self._namespace_client_impl, self._namespace_client_properties
-            )
+            self._namespace_client = LOOP.run(self._inner.namespace_client())
         return self._namespace_client
 
 
@@ -1370,17 +1360,7 @@ class AsyncLanceNamespaceDBConnection:
             The namespace client for this connection.
         """
         if self._namespace_client is None:
-            if (
-                self._namespace_client_impl is None
-                or self._namespace_client_properties is None
-            ):
-                raise ValueError(
-                    "Cannot construct a Python namespace client without "
-                    "namespace implementation properties"
-                )
-            self._namespace_client = namespace_connect(
-                self._namespace_client_impl, self._namespace_client_properties
-            )
+            self._namespace_client = await self._inner.namespace_client()
         return self._namespace_client
 
 

python/python/tests/test_db.py

@@ -1230,6 +1230,40 @@ def test_clone_table_deep_clone_fails(tmp_path):
         db.clone_table("cloned", source_uri, is_shallow=False)
 
 
+class _UnsupportedNamespaceConfig:
+    async def namespace_client_config(self):
+        raise RuntimeError("UNC namespace client export is not supported")
+
+
+def test_sync_namespace_client_propagates_export_guard(monkeypatch):
+    from lancedb.db import AsyncConnection, LanceDBConnection
+
+    monkeypatch.setattr(
+        "lancedb.db.namespace_connect",
+        lambda *_args, **_kwargs: pytest.fail("guarded config was reconstructed"),
+    )
+    db = LanceDBConnection.__new__(LanceDBConnection)
+    db._conn = AsyncConnection(_UnsupportedNamespaceConfig())
+    db._cached_namespace_client = None
+
+    with pytest.raises(RuntimeError, match="UNC namespace client export"):
+        db.namespace_client()
+
+
+@pytest.mark.asyncio
+async def test_async_namespace_client_propagates_export_guard(monkeypatch):
+    from lancedb.db import AsyncConnection
+
+    monkeypatch.setattr(
+        "lancedb.db.namespace_connect",
+        lambda *_args, **_kwargs: pytest.fail("guarded config was reconstructed"),
+    )
+    db = AsyncConnection(_UnsupportedNamespaceConfig())
+
+    with pytest.raises(RuntimeError, match="UNC namespace client export"):
+        await db.namespace_client()
+
+
 @pytest.mark.skipif(sys.platform == "win32", reason="Namespace client issues")
 def test_namespace_client_native_storage(tmp_path):
     """Test namespace_client() returns DirectoryNamespace for native storage."""

python/python/tests/test_namespace.py

@@ -60,6 +60,11 @@ class _NamespaceClient:
         return _ipc_file()
 
 
+class _UnsupportedNamespaceConfig:
+    async def namespace_client_config(self):
+        raise RuntimeError("UNC namespace client export is not supported")
+
+
 def _namespace_lance_table(namespace_client: _NamespaceClient) -> LanceTable:
     table = LanceTable.__new__(LanceTable)
     table._table = _FailingSyncInner()
@@ -138,6 +143,24 @@ class TestNamespaceConnection:
         db.drop_namespace(["test_ns"])
         assert "test_ns" not in db.list_namespaces().namespaces
 
+    def test_sync_namespace_client_propagates_export_guard(self, monkeypatch):
+        from lancedb.db import AsyncConnection
+
+        monkeypatch.setattr(
+            "lancedb.namespace.namespace_connect",
+            lambda *_args, **_kwargs: pytest.fail("guarded config was reconstructed"),
+        )
+        db = lancedb.LanceNamespaceDBConnection.__new__(
+            lancedb.LanceNamespaceDBConnection
+        )
+        db._namespace_client = None
+        db._namespace_client_impl = "dir"
+        db._namespace_client_properties = {"root": "file://server/share/database"}
+        db._inner = AsyncConnection(_UnsupportedNamespaceConfig())
+
+        with pytest.raises(RuntimeError, match="UNC namespace client export"):
+            db.namespace_client()
+
     def test_create_table_through_namespace(self):
         """Test creating a table through namespace."""
         db = lancedb.connect_namespace("dir", {"root": self.temp_dir})
@@ -639,6 +662,24 @@ class TestAsyncNamespaceConnection:
         await db.drop_namespace(["test_ns"])
         assert "test_ns" not in (await db.list_namespaces()).namespaces
 
+    async def test_async_namespace_client_propagates_export_guard(self, monkeypatch):
+        from lancedb.db import AsyncConnection
+
+        monkeypatch.setattr(
+            "lancedb.namespace.namespace_connect",
+            lambda *_args, **_kwargs: pytest.fail("guarded config was reconstructed"),
+        )
+        db = lancedb.AsyncLanceNamespaceDBConnection.__new__(
+            lancedb.AsyncLanceNamespaceDBConnection
+        )
+        db._namespace_client = None
+        db._namespace_client_impl = "dir"
+        db._namespace_client_properties = {"root": "file://server/share/database"}
+        db._inner = AsyncConnection(_UnsupportedNamespaceConfig())
+
+        with pytest.raises(RuntimeError, match="UNC namespace client export"):
+            await db.namespace_client()
+
     async def test_async_namespace_client_is_lazy(self):
         """namespace_client() should still return the backing client on demand."""
         pytest.importorskip("lance")

rust/lancedb/src/database/namespace.rs

@@ -697,6 +697,7 @@ impl Database for LanceNamespaceDatabase {
     }
 
     async fn namespace_client_config(&self) -> Result<(String, HashMap<String, String>)> {
+        self.ensure_storage_supported()?;
         Ok((self.ns_impl.clone(), self.ns_properties.clone()))
     }
 }
@@ -769,6 +770,10 @@ mod tests {
             .unwrap_err();
         assert!(matches!(error, Error::NotSupported { .. }));
         assert!(error.to_string().contains("UNC roots"));
+
+        let error = db.namespace_client_config().await.unwrap_err();
+        assert!(matches!(error, Error::NotSupported { .. }));
+        assert!(error.to_string().contains("UNC roots"));
     }
 
     #[tokio::test]