Raise DB-API errors for transport failures and empty access tokens

- ThriftDatabricksClient.make_request re-raised urllib3 HTTP errors of
  every request except GetOperationStatus unchanged, so an unreachable
  workspace (refused connection, proxy/tunnel failure) surfaced from
  connect() and execute() as a raw urllib3 MaxRetryError instead of a
  DB-API error. Report it through the normal non-retryable path as a
  RequestError (OperationalError).
- connect(access_token="") dropped the empty token and fell back to the
  interactive browser OAuth flow, blocking on a local callback server.
  An explicitly empty token now raises 'No valid authentication
  settings!' at once.

Signed-off-by: Amin Ghadersohi <amin.ghadersohi@gmail.com>

Author: aminghadersohi

src/databricks/sql/auth/auth.py

@@ -43,6 +43,10 @@ def get_auth_provider(cfg: ClientContext, http_client):
             cfg.auth_type,
         )
     elif cfg.access_token is not None:
+        if not cfg.access_token:
+            # An explicitly empty token is a missing credential; never fall
+            # back to an interactive browser login for it.
+            raise RuntimeError("No valid authentication settings! access_token is empty")
         base_provider = AccessTokenAuthProvider(cfg.access_token)
     elif cfg.use_cert_as_auth and cfg.tls_client_cert_file:
         # no op authenticator. authentication is performed using ssl certificate outside of headers

src/databricks/sql/backend/thrift_backend.py

@@ -459,7 +459,11 @@ def attempt_request(attempt):
                         f"GetOperationStatus failed with HTTP error and will be retried: {str(err)}"
                     )
                 else:
-                    raise err
+                    # Not retried here (urllib3 already applied the retry policy),
+                    # but surfaced as a DB-API RequestError rather than a raw
+                    # urllib3 exception.
+                    error = err
+                    error_message = str(err)
             except OSError as err:
                 error = err
                 error_message = str(err)

src/databricks/sql/client.py

@@ -372,7 +372,7 @@ def read(self) -> Optional[OAuthToken]:
             http_path,
         )
 
-        if access_token:
+        if access_token is not None:
             access_token_kv = {"access_token": access_token}
             kwargs = {**kwargs, **access_token_kv}
 

tests/unit/test_auth.py

@@ -152,6 +152,13 @@ def test_get_python_sql_connector_auth_provider_access_token(self):
         auth_provider.add_headers(headers)
         self.assertEqual(headers["Authorization"], "Bearer dpi123")
 
+    def test_get_python_sql_connector_auth_provider_empty_access_token(self):
+        """An explicitly empty token must not start an interactive OAuth login."""
+        with self.assertRaisesRegex(RuntimeError, "No valid authentication settings!"):
+            get_python_sql_connector_auth_provider(
+                "moderakh-test.cloud.databricks.com", MagicMock(), access_token=""
+            )
+
     def test_get_python_sql_connector_auth_provider_external(self):
         class MyProvider(CredentialsProvider):
             def auth_type(self) -> str:

tests/unit/test_thrift_backend.py

@@ -1927,7 +1927,7 @@ def test_make_request_will_retry_GetOperationStatus(
 
         import thrift, errno
         from databricks.sql.thrift_api.TCLIService.TCLIService import Client
-        from databricks.sql.exc import RequestError
+        from databricks.sql.exc import RequestError, RequestError
         from databricks.sql.utils import NoRetryReason
 
         this_gos_name = "GetOperationStatus"
@@ -2047,6 +2047,36 @@ def test_make_request_will_retry_GetOperationStatus_for_http_error(
             f"{EXPECTED_RETRIES}/{EXPECTED_RETRIES}", cm.exception.context["attempt"]
         )
 
+    @patch("thrift.transport.THttpClient.THttpClient")
+    def test_make_request_wraps_urllib3_http_error_as_request_error(
+        self, t_transport_class
+    ):
+        import urllib3
+
+        t_transport_instance = t_transport_class.return_value
+        t_transport_instance.code = None
+        t_transport_instance.headers = {}
+        mock_method = Mock()
+        mock_method.__name__ = "OpenSession"
+        mock_method.side_effect = urllib3.exceptions.MaxRetryError(
+            None, "/", "Tunnel connection failed: 503"
+        )
+
+        thrift_backend = ThriftDatabricksClient(
+            "foobar",
+            443,
+            "path",
+            [],
+            auth_provider=AuthProvider(),
+            ssl_options=SSLOptions(),
+            http_client=MagicMock(),
+        )
+
+        with self.assertRaises(RequestError) as cm:
+            thrift_backend.make_request(mock_method, Mock())
+
+        self.assertIn("Tunnel connection failed", str(cm.exception.message_with_context()))
+
     @patch("thrift.transport.THttpClient.THttpClient")
     def test_make_request_wont_retry_if_error_code_not_429_or_503(
         self, t_transport_class