network audit fixes

[bretth18]

Description

This PR introduces several improvements and fixes to the peer-to-peer connection and file transfer logic, focusing on race condition prevention, robust timeout handling, and more reliable data buffering. The changes ensure that connection attempts are properly tracked, timeouts reliably cancel pending operations, and file transfer buffers are used consistently to avoid data loss or duplication.

Connection attempt tracking and race condition prevention:

• Added a generation counter (connectAttemptGeneration) to uniquely identify each connection attempt, ensuring that only the latest attempt can update state or resume continuations, preventing race conditions when multiple attempts overlap. (PeerConnection.swift) [1] [2] [3] [4] [5] [6]

Timeout and cancellation handling:

• Improved timeout handling by ensuring that a timed-out receive operation cancels the underlying NWConnection, preventing orphaned continuations and guaranteeing that timeouts are honored. (PeerConnection.swift, FileConnectionAttempt.swift) [1] [2] [3]
• Refactored the connect logic to use a shared claimResume closure and a mutex-protected timeout task, ensuring only one outcome is processed and resources are cleaned up correctly. (FileConnectionAttempt.swift)

File transfer buffer and receive logic:

• Refactored file transfer receive logic to always drain the buffer before issuing new receives, and to wait for any in-flight message loop receives to finish before proceeding, ensuring data is read in order and without loss. (PeerConnection.swift) [1] [2] [3]
• Added helper methods and state to track when the message loop has an in-flight receive, and to allow raw readers to wait until it completes before issuing their own receives. (PeerConnection.swift)

Thread safety and state tracking:

• Changed lastActivityAt to be mutex-protected and accessible from nonisolated contexts, improving thread safety for activity tracking. (PeerConnection.swift)

Robustness and cleanup:

• Ensured that connections are always cancelled on failure to prevent resource leaks, and that event streams are properly finished if a connection cannot be established. (PeerConnection.swift, FileConnectionAttempt.swift) [1] [2]

These changes collectively make connection management and file transfers more robust, race-free, and reliable under concurrent and error conditions.

How to test

• Ensure all checks pass

Author checklist

This PR:

• Satisfies a goal that is specific & clearly motivated
• Adds value in isolation (whether user-facing or sustainability-related)
• Contains a concise & easy-to-understand title + description
• Adheres to SRP by default
• Presents the best possible implementation to meet its goal, given constraints at hand