PYTHON-5867 - Close sockets on interruption or cancellation during async connection creation

[NoahStapp]

PYTHON-5867

Changes in this PR

Close sockets opened as part of async connection creation when an interruption or cancellation occurs.

Test Plan

Fix existing PyPy test failure.

Checklist

Checklist for Author

• Did you update the changelog (if necessary)?
• Is there test coverage?
• Is any followup work tracked in a JIRA ticket? If so, add link(s).

Checklist for Reviewer

• Does the title of the PR reference a JIRA Ticket?
• Do you fully understand the implementation? (Would you be comfortable explaining how this code works to someone else?)
• Is all relevant documentation (README or docstring) updated?

[Copilot]

Pull request overview

This PR addresses a resource-leak scenario in PyMongo’s async connection setup by ensuring sockets/transports are closed when connection creation is interrupted (e.g., task cancellation), which is especially important for event-loop reliability and preventing leaked file descriptors.

Changes:

• Add cancellation/interruption-safe cleanup (except BaseException: close(); raise) in async socket creation and TLS configuration paths.
• Ensure transports are aborted / sockets are closed when failures occur during async protocol interface setup.
• Add a destructor (__del__) to AsyncNetworkingInterface to synchronously close the underlying raw socket if the connection is orphaned (e.g., loop already closed).

Reviewed changes

Copilot reviewed 2 out of 2 changed files in this pull request and generated 2 comments.

File	Description
pymongo/pool_shared.py	Adds broad-exception cleanup to prevent socket leaks during async connection creation/configuration and protocol setup.
pymongo/network_layer.py	Adds AsyncNetworkingInterface.__del__ to defensively close raw sockets when async connections are orphaned.

[codecov-commenter]

Codecov Report

❌ Patch coverage is 73.07692% with 7 lines in your changes missing coverage. Please review.

Files with missing lines	Patch %	Lines
pymongo/pool_shared.py	73.07%	5 Missing and 2 partials ⚠️

📢 Thoughts on this report? Let us know!

[Copilot]

Pull request overview

Copilot reviewed 2 out of 2 changed files in this pull request and generated 1 comment.

[Copilot]

Pull request overview

Copilot reviewed 2 out of 2 changed files in this pull request and generated 2 comments.

[Copilot]

Pull request overview

Copilot reviewed 2 out of 2 changed files in this pull request and generated no new comments.

[sophiayangDB]

LGTM!

[aclark4life]

Do _socket and _ssl need to be private here ?

[NoahStapp]

Good catch, vestigial import naming from an earlier version that overrode them.

[Copilot]

Pull request overview

Copilot reviewed 2 out of 2 changed files in this pull request and generated no new comments.

[aclark4life]

How about a context manager to avoid repeated BaseException handling ?

E.g. add something like:

@contextmanager
def _close_on_error(closer):
    try:
        yield
    except BaseException:
        closer()
        raise

So then:

try:
    ...
    return sock
except BaseException:
    sock.close()
    raise

would become something like:

with _close_on_error(sock.close):
    ...
    return sock

[NoahStapp]

How about a context manager to avoid repeated BaseException handling ?

E.g. add something like:

@contextmanager
def _close_on_error(closer):
    try:
        yield
    except BaseException:
        closer()
        raise

So then:

try:
    ...
    return sock
except BaseException:
    sock.close()
    raise

would become something like:

with _close_on_error(sock.close):
    ...
    return sock

I like it, good cleanup!

[aclark4life]

Hmmm, the exhaustive code review 🤖 found a "cross-thread fd-reuse hazard":

_async_configured_socket hands sock to a worker thread via run_in_executor(wrap_socket, sock) and asyncio can't stop that thread on cancel and wrap_socket calls sock.detach() before the slow handshake

It suggests replacing the above with _clean_on_error block with

ssl_sock = await asyncio.shield(future)

and then after the except (OSError, *SSLErrors) as exc add another except BaseException:

except BaseException:
    future.add_done_callback(_close_executor_socket)
    raise

and add the proposed corresponding _close_executor_socket helper:

def _close_executor_socket(future):
    try:
        ssl_sock = future.result()
    except BaseException:
        pass
    else:
        ssl_sock.close()