Handle read() returning None on a non-blocking socket

[afonsojanu]

Fixes #278.

When cheroot serves with a non-blocking socket (timeout=0), io.BufferedReader.read() can legitimately return None instead of b'' when there's nothing to read yet - that's the documented contract for io.RawIOBase in non-blocking mode, not an error condition. StreamReader.read() overrides read() to track bytes_read but didn't account for this, so it crashed with TypeError: object of type 'NoneType' has no len() any time a non-blocking read came back with nothing available.

I confirmed this is still live on current main, not just a Python 2 quirk as the original report speculated - reproduced it with a real non-blocking socket pair (no data sent yet, read() blows up immediately).

The fix just skips the byte count update when val is None and returns it unchanged, so the rest of the io stack still sees the documented would-block signal it already knows how to handle.

Added a regression test using the existing MockSocket pattern (its recv_into now raises BlockingIOError to simulate the non-blocking-no-data case) - fails on unmodified makefile.py with the exact same TypeError from the issue, passes with the fix. Ran the full test_makefile.py, test_conn.py, and test_wsgi.py suites before and after, all green.

[read-the-docs-community]

Documentation build overview

📚 cheroot | 🛠️ Build #34429390 | 📁 Comparing 758d609 against latest (edef8ff)

  🔍 Preview build  

7 files changed · ± 7 modified

± Modified

• genindex/index.html
• history/index.html
• pkg/cheroot/index.html
• pkg/cheroot.server/index.html
• pkg/cheroot.ssl.pyopenssl/index.html
• pkg/cheroot.test/index.html
• pkg/cheroot.test.test_makefile/index.html

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 78.21%. Comparing base (edef8ff) to head (758d609).
✅ All tests successful. No failed tests found.

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #839      +/-   ##
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- Coverage   78.37%   78.21%   -0.16%     
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  Files          41       41              
  Lines        4791     4802      +11     
  Branches      548      550       +2     
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+ Hits         3755     3756       +1     
- Misses        899      906       +7     
- Partials      137      140       +3