Fix race conditions and improve robustness during socket I/O #779

julianz- · 2025-10-05T18:43:42Z

Fixed race conditions to make socket I/O more resilient during connection teardown.

BufferedWriter's write(): Added error handling to ignore common socket errors (e.g., ECONNRESET, EPIPE, ENOTCONN, EBADF) that occur when the underlying connection has been unexpectedly closed by the client or OS. This prevents a crash when attempting to write to a defunct socket.
BufferedWriters's close(): Made idempotent, allowing safe repeated calls without raising exceptions.
Needed to add explicit handling of WINDOWS environments as these are seen to throw Windows specific WSAENOTSOCK errors.

Includes new unit tests to cover the idempotency and graceful handling of already closed underlying buffers.

This change is

codecov · 2025-10-05T19:08:12Z

Codecov Report

❌ Patch coverage is 64.28571% with 25 lines in your changes missing coverage. Please review.
✅ Project coverage is 78.99%. Comparing base (e9b4361) to head (1c7c0c0).
✅ All tests successful. No failed tests found.

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #779      +/-   ##
==========================================
- Coverage   79.24%   78.99%   -0.26%     
==========================================
  Files          29       29              
  Lines        4197     4261      +64     
  Branches      538      549      +11     
==========================================
+ Hits         3326     3366      +40     
- Misses        727      750      +23     
- Partials      144      145       +1

cheroot/makefile.py

cheroot/errors.py

cheroot/makefile.py

webknjaz · 2025-10-06T15:17:02Z

cheroot/makefile.py

+
+        try:
+            super().close()
+        except (OSError, SysCallError) as e:


Should this be in a var?

i can reuse acceptable_sock_shutdown_error_codes?

cheroot/server.py

cheroot/test/test_conn.py

webknjaz · 2025-10-06T15:20:16Z

cheroot/test/test_conn.py

    assert faux_get_map.conn_closed
+
+
+class TestBufferedWriter:


Drop the class. This should go into test_makefile.py.

webknjaz · 2025-10-06T15:20:46Z

docs/changelog-fragments.d/779.bugfix.rst

@@ -0,0 +1,2 @@
+Fixed race conditions to make socket I/O more resilient during connection teardown.
+-- by :user:`julianz-`


Suggested change

-- by :user:`julianz-`

-- by :user:`julianz-`

docs/spelling_wordlist.txt

cheroot/server.py

webknjaz · 2025-10-06T15:23:08Z

cheroot/server.py

+            else:
+                self.conn.wfile.write(chunk)
+        except (SysCallError, ConnectionError, OSError) as e:
+            error_code = e.errno if isinstance(e, OSError) else e.args[0]


There's a number of places where this is repeated. It's worth having a helper function, I think.

cheroot/server.py

cheroot/makefile.py

cheroot/errors.py

Fixes to make socket I/O more resilient during connection teardown. 1. BufferedWriter's write(): Added error handling to ignore common socket errors (e.g., ECONNRESET, EPIPE, ENOTCONN, EBADF) that occur when the underlying connection has been unexpectedly closed by the client or OS. This prevents a crash when attempting to write to a defunct socket. 2. BufferedWriters's close(): Made idempotent, allowing safe repeated calls without raising exceptions. 3. Needed to add explicit handling of WINDOWS environments as these are seen to throw Windows specific WSAENOTSOCK errors. Includes new unit tests to cover the idempotency and graceful handling of already closed underlying buffers.

julianz- closed this Oct 5, 2025

julianz- reopened this Oct 5, 2025

julianz- changed the title ~~Fix race condition and improve robustness during socket I/O~~ [DRAFT] Fix race condition and improve robustness during socket I/O Oct 5, 2025

julianz- force-pushed the fix-socket-teardown branch 2 times, most recently from 887399d to 4f1662e Compare October 5, 2025 19:04

julianz- force-pushed the fix-socket-teardown branch from 4f1662e to 4833dac Compare October 5, 2025 19:09

psf-chronographer bot added the bot:chronographer:provided label Oct 5, 2025

julianz- marked this pull request as draft October 5, 2025 19:09

julianz- changed the title ~~[DRAFT] Fix race condition and improve robustness during socket I/O~~ Fix race condition and improve robustness during socket I/O Oct 5, 2025

julianz- changed the title ~~Fix race condition and improve robustness during socket I/O~~ Fix race conditions and improve robustness during socket I/O Oct 5, 2025

julianz- marked this pull request as ready for review October 5, 2025 19:26