Fix _sock_recv infinite loop when StatusDB TCP connection drops

[TKeji]

Problem

When using --reruns with pytest-xdist, every test makes two blocking TCP calls to the StatusDB server (get_test_failures and set_test_reruns in pytest_runtest_protocol). If the server-side connection drops, _sock_recv enters an infinite loop:

def _sock_recv(self, conn) -> str:
    buf = b""
    while True:
        b = conn.recv(1)
        if b == self.delim:  # b"" != b"\n" → never breaks
            break
        buf += b
    return buf.decode()

recv(1) returns b"" (empty bytes) on a closed socket, but the code only checks for the newline delimiter. Since b"" != b"\n" is always True, the loop never exits.

This causes xdist workers to hang indefinitely at ~90% CPU, appearing stuck on a test that never completes ([pytest-xdist running] ...). The hang persists until the process is manually killed.

Fix

Add a check for empty bytes from recv(1) and raise ConnectionError:

b = conn.recv(1)
if not b:
    raise ConnectionError("StatusDB connection closed unexpectedly")

The ConnectionError propagates as an INTERNALERROR that xdist handles by replacing the worker — much better than hanging forever.

Reproduction

Minimal reproduction (proves the infinite loop on the unpatched version):

import socket
from pytest_rerunfailures import SocketDB

s1, s2 = socket.socketpair()
s2.close()  # recv on s1 will now return b""

db = SocketDB()
db._sock_recv(s1)  # hangs forever on unpatched, raises ConnectionError on patched

Full reproduction in a test run: monkey-patch ServerStatusDB.run_connection to close the server-side connection after a few requests, then run pytest --reruns=1 -n 1 --dist=loadgroup. The worker hangs on the next test's db.get_test_failures() call in _sock_recv.

Impact

Affects any xdist run with --reruns enabled. Without --reruns, the TCP protocol is never exercised (pytest_runtest_protocol returns early), so the bug doesn't manifest.

Checklist

• Changelog entry in CHANGES.rst
• Test added
• Pre-commit hooks pass

[Copilot]

Pull request overview

This PR fixes a hang in the StatusDB socket protocol used during pytest-xdist runs with --reruns by making _sock_recv detect closed TCP connections and fail fast instead of looping forever.

Changes:

• Update SocketDB._sock_recv to raise ConnectionError when recv(1) returns empty bytes (closed connection).
• Add a regression test covering the closed-connection behavior.
• Document the fix in the changelog.

Reviewed changes

Copilot reviewed 3 out of 3 changed files in this pull request and generated 3 comments.

File	Description
src/pytest_rerunfailures.py	Adds an EOF (b"") check in _sock_recv and raises ConnectionError to avoid infinite loops on dropped connections.
tests/test_pytest_rerunfailures.py	Adds a unit test using socket.socketpair() to ensure _sock_recv raises on closed connections.
CHANGES.rst	Adds a 16.2 (unreleased) changelog entry describing the fix and impact in xdist runs.

---

💡 Add Copilot custom instructions for smarter, more guided reviews. Learn how to get started.

[icemac]

Hi @TKeji, thank you for your PR. It looks legit to me. I let copliot review it. Could you please check its comments?
The broken tests against main are fixed in #324.