feat: make blob storage size threshold configurable (#16806)

### Summary

- Make `BLOB_STORAGE_SIZE_THRESHOLD` configurable through an environment
variable.
  - Preserve the existing 20 MiB default.
  - Add tests for the default and configured values.

  ### Why

Blob storage, Seafile, and WebDAV connectors currently use a hardcoded
20 MiB limit. Self-hosted users
cannot raise this limit without modifying the source code inside the
container.

  ### Testing

  - `test/unit_test/data_source/test_config.py`: 2 passed
- `ruff check common/data_source/config.py
test/unit_test/data_source/test_config.py`

  Fixes #16634

common/data_source/config.py

@@ -114,7 +114,10 @@ _PAGE_EXPANSION_FIELDS = [
 
 
 # Configuration constants
-BLOB_STORAGE_SIZE_THRESHOLD = 20 * 1024 * 1024  # 20MB
+try:
+    BLOB_STORAGE_SIZE_THRESHOLD = int(os.environ.get("BLOB_STORAGE_SIZE_THRESHOLD", 20 * 1024 * 1024))
+except ValueError as error:
+    raise ValueError("BLOB_STORAGE_SIZE_THRESHOLD must be an integer number of bytes") from error
 INDEX_BATCH_SIZE = 2
 SLACK_NUM_THREADS = 4
 ENABLE_EXPENSIVE_EXPERT_CALLS = False

test/unit_test/data_source/test_blob_storage_size_threshold_config.py

@@ -0,0 +1,73 @@
+#
+#  Copyright 2026 The InfiniFlow Authors. All Rights Reserved.
+#
+#  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.
+#
+
+from importlib.util import module_from_spec, spec_from_file_location
+from pathlib import Path
+from types import ModuleType
+import pytest
+
+
+_CONFIG_PATH = Path(__file__).parents[3] / "common" / "data_source" / "config.py"
+
+
+def _load_config_module() -> ModuleType:
+    """Load the config module so each call reads the current environment."""
+    spec = spec_from_file_location("config_under_test", _CONFIG_PATH)
+    assert spec is not None
+    assert spec.loader is not None
+
+    module = module_from_spec(spec)
+    spec.loader.exec_module(module)
+    return module
+
+
+def test_blob_storage_size_threshold_defaults_to_20_mib_when_environment_variable_is_unset(
+    monkeypatch,
+):
+    """Use the 20 MiB default when the environment variable is unset."""
+    monkeypatch.delenv("BLOB_STORAGE_SIZE_THRESHOLD", raising=False)
+
+    config_module = _load_config_module()
+
+    assert config_module.BLOB_STORAGE_SIZE_THRESHOLD == 20 * 1024 * 1024
+
+
+def test_blob_storage_size_threshold_uses_environment_variable_when_set(
+    monkeypatch,
+):
+    """Use the configured threshold when the environment variable is set."""
+    configured_threshold = 50 * 1024 * 1024
+    monkeypatch.setenv(
+        "BLOB_STORAGE_SIZE_THRESHOLD",
+        str(configured_threshold),
+    )
+
+    config_module = _load_config_module()
+
+    assert config_module.BLOB_STORAGE_SIZE_THRESHOLD == configured_threshold
+
+
+def test_blob_storage_size_threshold_raises_clear_error_for_invalid_environment_value(
+    monkeypatch,
+):
+    """Raise an actionable error when the configured threshold is not an integer."""
+    monkeypatch.setenv("BLOB_STORAGE_SIZE_THRESHOLD", "20MB")
+
+    with pytest.raises(
+        ValueError,
+        match="BLOB_STORAGE_SIZE_THRESHOLD must be an integer number of bytes",
+    ):
+        _load_config_module()