test client response.close() closes input stream

[davidism]

When passing a large amount of data (> 500 KiB) with the test client, it uses a temporary file to store the encoded multipart form data. The test client has no way to close the file, and if it's left open after a test finishes Python may show a ResourceWarning. It's not entirely clear when Python decides to do this, pytest doesn't show it but unittest does, but neither show it with the latest Werkzeug code unless -Walways is used.

Now, the input stream is closed automatically when following redirects (except for 307 and 308, which preserve the body), and the final request's stream.close method is added to the response's close callbacks. So calling response.close() will close the input stream in addition to the response stream.

I couldn't figure out a reliable way to make a test for this, given how inconsistent the warning is in the first place, but all current tests pass.

• fixes Sending >=500 KB file with test client causes warning #1785

Checklist:

• Add tests that demonstrate the correct behavior of the change. Tests should fail without the change.
• Add or update relevant docs, in the docs folder and in code.
• Add an entry in CHANGES.rst summarizing the change and linking to the issue.
• Add .. versionchanged:: entries in any relevant code docs.
• Run pre-commit hooks and fix any issues.
• Run pytest and tox, no tests failed.

[davidism]

And in the first interesting win for type annotations, mypy caught that environ_property for request.input_stream was being used incorrectly, treating the doc string as the default value.