refactor(kernel): forward metadata filters unchanged

Author: vuanhphung

CHANGELOG.md

@@ -1,7 +1,7 @@
 # Release History
 
 # Unreleased
-- Kernel metadata filters now preserve empty strings, matching no catalogs, schemas, tables, or columns. Only `None` leaves a filter unset; other values retain their exact-identifier or pattern semantics (PECOBLR-4221).
+- Kernel metadata filters are now forwarded unchanged instead of collapsing empty strings to `None`. Only `None` leaves a filter unset; empty pattern filters match nothing (PECOBLR-4221).
 - Kernel backend (`use_kernel=True`): OAuth **M2M with a JWT private-key client assertion** (RFC 7523) is now supported. Pass `oauth_client_id` + `oauth_jwt_key_file` + `oauth_jwt_kid` (with optional `oauth_jwt_passphrase` for an encrypted PKCS#8 key, `oauth_jwt_algorithm` defaulting to `RS256`, `oauth_scopes`, and `token_url` for the IdP token endpoint) and the connector routes them to the kernel's `auth_type="oauth-m2m-jwt"`, which signs a short-lived assertion with the private key instead of sending a client secret. The kernel owns the token lifecycle. A private-key file is treated as unambiguous JWT M2M intent and is mutually exclusive with `oauth_client_secret` / `credentials_provider` (both raise `NotSupportedError`). Verified end-to-end against an Azure Databricks workspace with the service principal's public certificate registered on its Entra ID app registration. Requires `databricks-sql-kernel >= 0.2.0` with JWT support.
 - Kernel backend (`use_kernel=True`): OAuth U2M with `auth_type="databricks-oauth"` now forwards the connector's `databricks-sql-python` OAuth-app bundle (`client_id` + `sql offline_access` scopes + redirect port) into the kernel, so a bare U2M connection authenticates as `databricks-sql-python` — parity with the Thrift path — instead of inheriting the kernel's own `databricks-sql-connector` default. A caller-supplied `oauth_client_id` (with its coupled `oauth_redirect_port`) is honored, as is a caller-supplied `oauth_scopes`; absent one, the connector default (`sql offline_access`) is forwarded. Note: the kernel binds a single U2M redirect port, so unlike the Thrift path (which tries the full `8020..8024` range) the kernel path uses only one port and does not fall back to the next port if it is already bound — pass `oauth_redirect_port` (with `oauth_client_id`) to pick a free one on a port collision (PECOBLR-4040)
 - Kernel backend (`use_kernel=True`): **Azure Entra (Azure AD) service-principal M2M is now supported.** `auth_type="azure-sp-m2m"` forwards `azure_client_id` / `azure_client_secret`; the kernel is the Azure-aware auth core — it builds the Entra v2.0 token endpoint and the `{app_id}/.default` scope, and **auto-discovers the tenant** from the workspace's `/aad/auth` redirect when `azure_tenant_id` is omitted (matching Thrift). The `Authorization` bearer is the Databricks-audience data token, which alone authenticates a workspace-member SP. Set `azure_workspace_resource_id` and the kernel also sends the Azure SP management token (`X-Databricks-Azure-SP-Management-Token`) + `X-Databricks-Azure-Workspace-Resource-Id` header (matching the JDBC driver), so a service principal with an Azure RBAC role but no workspace membership can authenticate; omit it and no ARM management-scope token is fetched. Azure AD **U2M** (`auth_type="azure-oauth"`) now routes to the kernel's OAuth U2M flow, identically to `auth_type="databricks-oauth"`: the kernel runs the in-house workspace-federated browser flow, which Azure workspaces support (the workspace federates login to Entra). It forwards the connector's `databricks-sql-python` OAuth app, not the Thrift Azure app (`96eecda7` / port 8030), which is registered for Thrift's direct-Entra flow the kernel does not perform (PECOBLR-4141; PECOBLR-4120)

src/databricks/sql/backend/databricks_client.py

@@ -248,8 +248,8 @@ def get_schemas(
             max_rows: Maximum number of rows to fetch in a single batch
             max_bytes: Maximum number of bytes to fetch in a single batch
             cursor: The cursor object that will handle the results
-            catalog_name: Optional exact catalog name to filter by. ``None``
-                leaves the filter unset; an empty string matches nothing.
+            catalog_name: Optional exact catalog name to filter by, forwarded
+                unchanged. ``None`` leaves the filter unset.
             schema_name: Optional schema name pattern to filter by. ``None``
                 leaves the filter unset; an empty string matches nothing.
 
@@ -327,8 +327,8 @@ def get_columns(
             max_rows: Maximum number of rows to fetch in a single batch
             max_bytes: Maximum number of bytes to fetch in a single batch
             cursor: The cursor object that will handle the results
-            catalog_name: Optional exact catalog name to filter by. ``None``
-                leaves the filter unset; an empty string matches nothing.
+            catalog_name: Optional exact catalog name to filter by, forwarded
+                unchanged. ``None`` leaves the filter unset.
             schema_name: Optional schema name pattern to filter by. ``None``
                 leaves the filter unset; an empty string matches nothing.
             table_name: Optional table name pattern to filter by

src/databricks/sql/backend/kernel/client.py

@@ -25,7 +25,7 @@
 import logging
 import threading
 import uuid
-from typing import Any, Dict, List, Optional, Set, Tuple, TYPE_CHECKING, Union
+from typing import Any, Dict, List, Optional, Set, TYPE_CHECKING, Union
 
 from databricks.sql.backend.databricks_client import DatabricksClient
 from databricks.sql.backend.kernel._errors import (
@@ -117,15 +117,6 @@ def _is_not_found(exc: BaseException) -> bool:
     )
 
 
-def _exact_catalog_and_pattern(
-    catalog: Optional[str], pattern: Optional[str]
-) -> Tuple[Optional[str], Optional[str]]:
-    """Avoid constructing the kernel's invalid empty ``Identifier``."""
-    if catalog == "":
-        return None, ""
-    return catalog, pattern
-
-
 def _is_staging_statement(operation: str) -> bool:
     """True iff ``operation`` is a volume/staging statement (PUT / GET /
     REMOVE).
@@ -912,12 +903,9 @@ def get_schemas(
         if self._kernel_session is None:
             raise InterfaceError("get_schemas requires an open session.")
         try:
-            catalog, schema_pattern = _exact_catalog_and_pattern(
-                catalog_name, schema_name
-            )
             stream = self._kernel_session.metadata().list_schemas(
-                catalog=catalog,
-                schema_pattern=schema_pattern,
+                catalog=catalog_name,
+                schema_pattern=schema_name,
             )
             return self._make_result_set(stream, cursor, self._synthetic_command_id())
         except Exception as exc:
@@ -972,12 +960,9 @@ def get_columns(
             # row's `TABLE_CAT` is correctly attributed. Matches the
             # Thrift backend's `getColumns(null, …)` behaviour from
             # the user's perspective.
-            catalog, schema_pattern = _exact_catalog_and_pattern(
-                catalog_name, schema_name
-            )
             stream = self._kernel_session.metadata().list_columns(
-                catalog=catalog,
-                schema_pattern=schema_pattern,
+                catalog=catalog_name,
+                schema_pattern=schema_name,
                 table_pattern=table_name,
                 column_pattern=column_name,
             )

src/databricks/sql/client.py

@@ -1577,8 +1577,9 @@ def schemas(
         """
         Get schemas corresponding to the catalog_name and schema_name.
 
-        ``None`` leaves a filter unset and an empty string matches nothing.
-        ``catalog_name`` is exact; ``schema_name`` can contain % wildcards.
+        Filters are forwarded unchanged; only ``None`` leaves one unset.
+        ``catalog_name`` is exact. ``schema_name`` is a pattern, can contain
+        % wildcards, and an empty pattern matches nothing.
         :returns self
         """
         self._check_not_closed()
@@ -1604,8 +1605,9 @@ def tables(
         """
         Get tables corresponding to the catalog_name, schema_name and table_name.
 
-        ``None`` leaves a filter unset and an empty string matches nothing.
-        Names can contain % wildcards.
+        Filters are forwarded unchanged; only ``None`` leaves one unset.
+        Names are patterns, can contain % wildcards, and empty patterns match
+        nothing.
         :returns self
         """
         self._check_not_closed()
@@ -1634,8 +1636,9 @@ def columns(
         """
         Get columns corresponding to the catalog_name, schema_name, table_name and column_name.
 
-        ``None`` leaves a filter unset and an empty string matches nothing.
-        ``catalog_name`` is exact; other names can contain % wildcards.
+        Filters are forwarded unchanged; only ``None`` leaves one unset.
+        ``catalog_name`` is exact. Other names are patterns, can contain
+        % wildcards, and empty patterns match nothing.
 
         ``catalog_name=None`` is accepted on all backends and matches
         columns across every catalog (the kernel issues ``SHOW COLUMNS``

tests/e2e/test_kernel_backend.py

@@ -367,7 +367,7 @@ def test_schemas_with_empty_string_filter_matches_nothing(conn):
 
 
 @pytest.mark.parametrize(
-    "empty_filter", ["catalog_name", "schema_name", "table_name", "column_name"]
+    "empty_filter", ["schema_name", "table_name", "column_name"]
 )
 def test_columns_with_empty_string_filter_matches_nothing(conn, empty_filter):
     filters = {

tests/unit/test_kernel_client.py

@@ -1615,8 +1615,7 @@ def test_get_schemas_preserves_empty_pattern():
     list_schemas.assert_called_once_with(catalog="main", schema_pattern="")
 
 
-def test_get_schemas_empty_catalog_uses_empty_pattern():
-    """Avoid passing an empty exact ``Identifier`` to the kernel."""
+def test_get_schemas_preserves_empty_catalog():
     c = _make_client()
     c._kernel_session = MagicMock()
     list_schemas = c._kernel_session.metadata.return_value.list_schemas
@@ -1634,7 +1633,7 @@ def test_get_schemas_empty_catalog_uses_empty_pattern():
         schema_name="ignored",
     )
 
-    list_schemas.assert_called_once_with(catalog=None, schema_pattern="")
+    list_schemas.assert_called_once_with(catalog="", schema_pattern="ignored")
 
 
 def test_get_tables_preserves_empty_patterns():
@@ -1692,8 +1691,7 @@ def test_get_columns_preserves_empty_patterns():
     )
 
 
-def test_get_columns_empty_catalog_uses_empty_pattern():
-    """An empty catalog matches nothing without constructing ``Identifier("")``."""
+def test_get_columns_preserves_empty_catalog():
     c = _make_client()
     c._kernel_session = MagicMock()
     list_columns = c._kernel_session.metadata.return_value.list_columns
@@ -1714,8 +1712,8 @@ def test_get_columns_empty_catalog_uses_empty_pattern():
     )
 
     list_columns.assert_called_once_with(
-        catalog=None,
-        schema_pattern="",
+        catalog="",
+        schema_pattern="ignored",
         table_pattern="table",
         column_pattern="column",
     )