raise ServerOperationError for no 0th chunk

Signed-off-by: varun-edachali-dbx <varun.edachali@databricks.com>

Author: varun-edachali-dbx

src/databricks/sql/backend/sea/backend.py

@@ -653,7 +653,7 @@ def get_chunk_link(self, statement_id: str, chunk_index: int) -> ExternalLink:
         )
         response = GetChunksResponse.from_dict(response_data)
 
-        links = response.external_links
+        links = response.external_links or []
         link = next((l for l in links if l.chunk_index == chunk_index), None)
         if not link:
             raise ServerOperationError(

src/databricks/sql/backend/sea/queue.py

@@ -147,7 +147,13 @@ def __init__(
         initial_links = result_data.external_links or []
         first_link = next((l for l in initial_links if l.chunk_index == 0), None)
         if not first_link:
-            return
+            raise ServerOperationError(
+                "No initial link found for chunk 0",
+                {
+                    "operation-id": statement_id,
+                    "diagnostic-info": None,
+                },
+            )
 
         # Track the current chunk we're processing
         self._current_chunk_link = first_link

tests/unit/test_sea_queue.py

@@ -378,33 +378,19 @@ def test_init_no_initial_links(
     ):
         """Test initialization with no initial links."""
         # Create a queue with empty initial links
-        queue = SeaCloudFetchQueue(
-            result_data=ResultData(external_links=[]),
-            max_download_threads=5,
-            ssl_options=ssl_options,
-            sea_client=mock_sea_client,
-            statement_id="test-statement-123",
-            total_chunk_count=0,
-            lz4_compressed=False,
-            description=description,
-        )
-
-        # Verify debug message was logged
-        mock_logger.debug.assert_called_with(
-            "SeaCloudFetchQueue: Initialize CloudFetch loader for statement {}, total chunks: {}".format(
-                "test-statement-123", 0
+        with pytest.raises(
+            ServerOperationError, match="No initial link found for chunk 0"
+        ):
+            queue = SeaCloudFetchQueue(
+                result_data=ResultData(external_links=[]),
+                max_download_threads=5,
+                ssl_options=ssl_options,
+                sea_client=mock_sea_client,
+                statement_id="test-statement-123",
+                total_chunk_count=0,
+                lz4_compressed=False,
+                description=description,
             )
-        )
-
-        # Verify download manager wasn't created
-        mock_download_manager_class.assert_not_called()
-
-        # Verify attributes
-        assert queue._statement_id == "test-statement-123"
-        assert (
-            not hasattr(queue, "_current_chunk_link")
-            or queue._current_chunk_link is None
-        )
 
     @patch("databricks.sql.backend.sea.queue.logger")
     def test_progress_chunk_link_no_current_link(self, mock_logger):