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

[Copilot]

Related command
az storage fs file download

Description
az storage fs file download can fail on ADLS Gen2 files when the response carries Content-Encoding: deflate; upload/list/show paths succeed, but download trips the SDK readall() decode path.

• Download path
  • Switch ADLS file download from buffered readall() to streamed readinto(stream).
  • Aligns storage fs file download with the existing stream-to-file pattern used elsewhere in storage download flows.
• Effect
  • Avoids client-side content-decoding failures during download.
  • Preserves destination path resolution and overwrite behavior.

with open(destination_path, 'wb') as stream:
    download = client.download_file(timeout=timeout)
    download.readinto(stream)

• Regression coverage
  • Add a focused storage unit test that verifies the ADLS helper writes via readinto() and does not depend on readall().

Testing Guide
Example reproduction path:

az storage fs file download \
  --file-system <fs> \
  --path 'testdata/special_character_test/ファイル_japanese_日本語.txt' \
  --destination <local-path> \
  --account-name <account>

Expected: file is written successfully even when the service response includes Content-Encoding.

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

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[azure-client-tools-agent]

Live test results — azdev test --live --series (changed test files only)

✅ PASS

Selectors: test_storage_fs_file_operations (module)
PR head ref: copilot/fix-deflate-decompression-error
PR head sha: c76ba1f5d9a2138dacba78f3a094fa91078d2d5f
PR base ref: dev
New test files in PR: true

Changed test files run

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

New test files

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

Workflow run: https://github.com/Azure/issue-sentinel/actions/runs/29383646373

Last 80 lines of azdev output

=============
| Run Tests |
=============


=====================
| Discovering Tests |
=====================

/home/runner/work/issue-sentinel/issue-sentinel/azure-cli/src/azure-cli/azure/cli/command_modules/identity/tests/latest/test_identity.py:18: SyntaxWarning: invalid escape sequence '\{'
  'resource_restriction_compute': '\{"providers":\["Microsoft.Compute"\]\}',
/home/runner/work/issue-sentinel/issue-sentinel/azure-cli/src/azure-cli/azure/cli/command_modules/identity/tests/latest/test_identity.py:19: SyntaxWarning: invalid escape sequence '\{'
  'resource_restriction_empty': '\{"providers":\[\]\}'
/home/runner/work/issue-sentinel/issue-sentinel/azure-cli/src/azure-cli/azure/cli/command_modules/vm/tests/latest/test_vm_commands.py:13533: SyntaxWarning: invalid escape sequence '\]'
  self.cmd('vmss application set -g {rg} -n {vmss} --app-version-ids {vid1} {vid2} --enable-automatic-upgrade True\]', checks=[

test index updated: /home/runner/.azdev/env_config/home/runner/work/issue-sentinel/issue-sentinel/.venv/test_index/latest.json

Test on modules: test_storage_fs_file_operations

WARNING: RUNNING TESTS LIVE
The tests are set to run against current profile "latest"
============================= test session starts ==============================
platform linux -- Python 3.12.13, pytest-9.1.1, pluggy-1.6.0 -- /home/runner/work/issue-sentinel/issue-sentinel/.venv/bin/python
cachedir: .pytest_cache
rootdir: /home/runner/work/issue-sentinel/issue-sentinel/azure-cli/src/azure-cli
plugins: forked-1.6.0, xdist-3.8.0
collecting ... collected 1 item

azure-cli/src/azure-cli/azure/cli/command_modules/storage/tests/latest/test_storage_fs_file_operations.py::TestStorageFsFileOperations::test_download_file_streams_content_to_destination PASSED [100%]

- generated xml file: /home/runner/work/issue-sentinel/issue-sentinel/test-output/results.xml -
============================== 1 passed in 0.13s ===============================

Posted by agent-assist live-test workflow.

[azure-client-tools-agent]

✅ Review: All checks passed

Live test: Run #29383646373 — success
CI checks: 1 passed, 0 failed, 0 pending

Summary

PR #33730 fixes az storage fs file download failures on ADLS Gen2 files with Content-Encoding: deflate by switching from buffered readall() to streamed readinto(stream). This aligns with the existing stream-to-file pattern used elsewhere in storage downloads.

All checks are green and the live test completed successfully. This PR is ready for maintainer review and merge.

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Posted by agent-assist (autonomous bug-fix pipeline).

[yonzhan]

Storage