Add GET /internal/files. (#4295)

* Create internal route table.

* List files.

* Add GET /internal/files.

Retrieves list of files in models, output, and user directories.

* Refactor file names.

* Use typing_extensions for Python 3.8

* Fix tests.

* Remove print statements.

* Update README.

* Add output and user to valid directory test.

* Add missing type hints.

tests-unit/server/services/file_service_test.py

@@ -0,0 +1,54 @@
+import pytest
+from unittest.mock import MagicMock
+from api_server.services.file_service import FileService
+
+@pytest.fixture
+def mock_file_system_ops():
+    return MagicMock()
+
+@pytest.fixture
+def file_service(mock_file_system_ops):
+    allowed_directories = {
+        "models": "/path/to/models",
+        "user": "/path/to/user",
+        "output": "/path/to/output"
+    }
+    return FileService(allowed_directories, file_system_ops=mock_file_system_ops)
+
+def test_list_files_valid_directory(file_service, mock_file_system_ops):
+    mock_file_system_ops.walk_directory.return_value = [
+        {"name": "file1.txt", "path": "file1.txt", "type": "file", "size": 100},
+        {"name": "dir1", "path": "dir1", "type": "directory"}
+    ]
+    
+    result = file_service.list_files("models")
+    
+    assert len(result) == 2
+    assert result[0]["name"] == "file1.txt"
+    assert result[1]["name"] == "dir1"
+    mock_file_system_ops.walk_directory.assert_called_once_with("/path/to/models")
+
+def test_list_files_invalid_directory(file_service):
+    # Does not support walking directories outside of the allowed directories
+    with pytest.raises(ValueError, match="Invalid directory key"):
+        file_service.list_files("invalid_key")
+
+def test_list_files_empty_directory(file_service, mock_file_system_ops):
+    mock_file_system_ops.walk_directory.return_value = []
+    
+    result = file_service.list_files("models")
+    
+    assert len(result) == 0
+    mock_file_system_ops.walk_directory.assert_called_once_with("/path/to/models")
+
+@pytest.mark.parametrize("directory_key", ["models", "user", "output"])
+def test_list_files_all_allowed_directories(file_service, mock_file_system_ops, directory_key):
+    mock_file_system_ops.walk_directory.return_value = [
+        {"name": f"file_{directory_key}.txt", "path": f"file_{directory_key}.txt", "type": "file", "size": 100}
+    ]
+    
+    result = file_service.list_files(directory_key)
+    
+    assert len(result) == 1
+    assert result[0]["name"] == f"file_{directory_key}.txt"
+    mock_file_system_ops.walk_directory.assert_called_once_with(f"/path/to/{directory_key}")