[Storage] az storage fs file download: Stream ADLS Gen2 downloads to avoid content-encoding decode failures

src/azure-cli/azure/cli/command_modules/storage/operations/fs_file.py

@@ -43,8 +43,7 @@ def download_file(client, destination_path=None, overwrite=True, timeout=None):
 
     with open(destination_path, 'wb') as stream:
         download = client.download_file(timeout=timeout)
-        download_content = download.readall()
-        stream.write(download_content)
+        download.readinto(stream)
 
 
 def exists(cmd, client, timeout=None):

src/azure-cli/azure/cli/command_modules/storage/tests/latest/test_storage_fs_file_operations.py

@@ -0,0 +1,36 @@
+# --------------------------------------------------------------------------------------------
+# Copyright (c) Microsoft Corporation. All rights reserved.
+# Licensed under the MIT License. See License.txt in the project root for license information.
+# --------------------------------------------------------------------------------------------
+
+import os
+import tempfile
+import unittest
+from types import SimpleNamespace
+from unittest import mock
+
+from azure.cli.command_modules.storage.operations.fs_file import download_file
+
+
+class TestStorageFsFileOperations(unittest.TestCase):
+
+    def test_download_file_streams_content_to_destination(self):
+        download = mock.Mock()
+
+        def _write_to_stream(target_stream):
+            return target_stream.write(b'hello world')
+
+        download.readinto.side_effect = _write_to_stream
+
+        client = mock.Mock()
+        client.get_file_properties.return_value = SimpleNamespace(name='dir/test.txt')
+        client.download_file.return_value = download
+
+        with tempfile.TemporaryDirectory() as temp_dir:
+            download_file(client, destination_path=temp_dir)
+
+            with open(os.path.join(temp_dir, 'test.txt'), 'rb') as downloaded_file:
+                self.assertEqual(downloaded_file.read(), b'hello world')
+
+        download.readinto.assert_called_once()
+        download.readall.assert_not_called()