feat: add context manager to mrd

[chandra-siri]

feat: add context manager to mrd

[gemini-code-assist]

Summary of Changes

Hello @chandra-siri, I'm Gemini Code Assist¹! I'm currently reviewing this pull request and will post my feedback shortly. In the meantime, here's a summary to help you and other reviewers quickly get up to speed!

This pull request introduces an asynchronous context manager for the AsyncMultiRangeDownloader class, enhancing its usability and ensuring proper resource management in asynchronous operations. By enabling the use of async with statements, the PR simplifies the lifecycle of download operations, automatically handling the opening and closing of the underlying gRPC connection, which leads to more robust and readable code.

Highlights

• Asynchronous Context Manager Implementation: The AsyncMultiRangeDownloader class now implements the asynchronous context manager protocol by adding __aenter__ and __aexit__ methods. This allows the class to be used with async with statements, automatically handling the opening and closing of the underlying bidi-gRPC connection.
• Simplified Resource Management in Tests: System tests have been updated to utilize the new async with syntax for AsyncMultiRangeDownloader, replacing explicit open() and close() calls. This demonstrates the intended usage and simplifies resource lifecycle management.
• Unit Test Coverage for Context Manager: A new unit test, test_async_context_manager_calls_open_and_close, has been added to verify that the __aenter__ method correctly calls open() and __aexit__ correctly calls close() when the AsyncMultiRangeDownloader is used as an asynchronous context manager.

Using Gemini Code Assist

The full guide for Gemini Code Assist can be found on our documentation page, here are some quick tips.

Invoking Gemini

You can request assistance from Gemini at any point by creating a comment using either /gemini <command> or @gemini-code-assist <command>. Below is a summary of the supported commands on the current page.

Feature	Command	Description
Code Review	/gemini review	Performs a code review for the current pull request in its current state.
Pull Request Summary	/gemini summary	Provides a summary of the current pull request in its current state.
Comment	@gemini-code-assist	Responds in comments when explicitly tagged, both in pull request comments and review comments.
Help	/gemini help	Displays a list of available commands.

Customization

To customize Gemini Code Assist for GitHub experience, repository maintainers can create a configuration file and/or provide a custom code review style guide (such as PEP-8 for Python) by creating and adding files to a .gemini/ folder in the base of the repository. Detailed instructions can be found here.

Limitations & Feedback

Gemini Code Assist may make mistakes. Please leave feedback on any instances where its feedback is incorrect or counter productive. You can react with 👍 and 👎 on @gemini-code-assist comments. If you're interested in giving your feedback about your experience with Gemini Code Assist for Github and other Google products, sign up here.

You can also get AI-powered code generation, chat, as well as code reviews directly in the IDE at no cost with the Gemini Code Assist IDE Extension.

Footnotes

1. Review the Privacy Notices, Generative AI Prohibited Use Policy, Terms of Service, and learn how to configure Gemini Code Assist in GitHub here. Gemini can make mistakes, so double check it and use code with caution. ↩

[gemini-code-assist]

Code Review

This pull request introduces a convenient async context manager for AsyncMultiRangeDownloader, which is a great improvement for ensuring resources are properly managed. The implementation is correct and is accompanied by a new unit test and an update to a system test.

One suggestion for further improvement is to refactor the other system tests in tests/system/test_zonal.py that use AsyncMultiRangeDownloader to also adopt the new async with syntax. This would improve consistency and readability across the test suite.

I've also added a comment with suggestions to enhance the unit tests for the new context manager by covering some important edge cases.

[gemini-code-assist]

This is a good test for the happy path of the async context manager. To make it more robust, it would be beneficial to also test the behavior in edge cases.

Specifically, consider adding tests for:

1. When open() fails (e.g., raises an exception). In this scenario, close() should not be called.
2. When an exception is raised from within the async with block. In this case, close() should still be called to ensure cleanup.

Here are some examples of how you could structure these tests:

Test for open() failure:

@mock.patch("...")
@pytest.mark.asyncio
async def test_context_manager_no_close_on_open_failure(self, mock_grpc_client, mock_close, mock_open):
    mock_open.side_effect = ValueError("Failed to open")
    mrd = AsyncMultiRangeDownloader(
        mock_grpc_client, _TEST_BUCKET_NAME, _TEST_OBJECT_NAME
    )
    
    with pytest.raises(ValueError, match="Failed to open"):
        async with mrd:
            pytest.fail("This block should not be executed.")

    mock_open.assert_called_once()
    mock_close.assert_not_called()

Test for exception within the block:

@mock.patch("...")
@pytest.mark.asyncio
async def test_context_manager_closes_on_exception(self, mock_grpc_client, mock_close, mock_open):
    mrd = AsyncMultiRangeDownloader(
        mock_grpc_client, _TEST_BUCKET_NAME, _TEST_OBJECT_NAME
    )
    # set up side effects for open/close as in the existing test
    async def open_side_effect():
        mrd._is_stream_open = True
    mock_open.side_effect = open_side_effect
    
    with pytest.raises(RuntimeError, match="Oops"):
        async with mrd:
            raise RuntimeError("Oops")

    mock_open.assert_called_once()
    mock_close.assert_called_once()