Fix remote GPIO hang on macOS

[ralphweng2023]

Description

Fixes the issue where remote_raspi_init hangs indefinitely on macOS when trying to connect to a remote Raspberry Pi.

Root Cause: SDLNet_TCP_Open is a blocking function with no timeout. On macOS, when the host is unreachable, it hangs indefinitely (potentially for minutes due to OS-level TCP timeout settings).

Solution: Implement a non-blocking TCP connection with a 5-second timeout using native socket calls:

1. Create a non-blocking socket using fcntl()/ioctlsocket()
2. Initiate connection (returns immediately with EINPROGRESS)
3. Use select() with timeout to wait for connection
4. Check connection result with getsockopt(SO_ERROR)
5. If successful, close the test socket and use SDLNet_TCP_Open (which now succeeds immediately)

Changes to network_driver.cpp:

• Added platform-specific includes for socket operations (fcntl.h, winsock2.h, etc.)
• Added SK_CONNECTION_TIMEOUT_SECONDS constant (5 seconds)
• Added _connect_with_timeout() helper function
• Modified sk_open_tcp_connection() to use timeout for client connections
• Server socket creation (host=null) still uses the original blocking method

Type of change

• Bug fix (non-breaking change which fixes an issue)

How Has This Been Tested?

Built and tested on macOS using CMake:

cd projects/cmake
cmake --preset macOS
cmake --build build/

cd ../../bin
./skunit_tests --order rand
# Result: All tests passed (1263 assertions in 79 test cases)

./skunit_tests "[networking]"
# Result: All tests passed (31 assertions in 2 test cases)

Testing Checklist

• Code compiles without errors on macOS
• All existing unit tests pass (79 test cases)
• All networking tests pass (31 assertions)
• Connection timeout works correctly (5 second limit)
• Tested on Linux/WSL (not available on this machine)
• Tested on Windows/MSYS2 (not available on this machine)

Checklist

• My code follows the style guidelines of this project
• I have performed a self-review of my own code
• I have commented my code in hard-to-understand areas
• My changes generate no new warnings
• Existing tests continue to pass
• The fix is backward compatible with existing code

[222448082Ashen]

Detailed Feedback

• Architecture & Simplicity:

  • The "double connect" strategy (connect with raw socket -> close -> connect with SDL_net) is a pragmatic solution. While it does involve two TCP handshakes, it ensures compatibility with the existing SDL_net architecture without rewriting the entire networking stack.
  • Note: Be aware that some strict server-side firewalls or rate limiters might flag two rapid connections from the same IP as suspicious, but for the intended use case (Raspberry Pi connection), this is unlikely to be an issue.

• Code Quality & Readability:

  • The extraction of _connect_with_timeout into a static helper function is excellent. It keeps sk_open_tcp_connection clean and readable.
  • Platform-specific includes and socket flags are correctly guarded with #ifdef _WIN32 / #else, maintaining cross-platform compatibility.

• Maintainability:

  • Restoring the socket to blocking mode at the end of _connect_with_timeout (lines 190-196) is good practice for function reusability, even though the socket is closed immediately in the current usage. This prevents future bugs if the helper is used elsewhere.

• Performance:

  • The inet_pton check (lines 117-120) is a good optimization to avoid unnecessary DNS lookups for IP addresses.
  • There is a minor redundancy where SDLNet_ResolveHost might be called twice (once in the helper, once in the main function) for hostnames, but the performance impact is negligible compared to the network latency.

• Testing:

  • The PR description indicates thorough testing on macOS. Since this code involves platform-specific socket calls (fcntl vs ioctlsocket), reliance on the manual verification described is high. The logic appears correct for both POSIX and Windows sockets.

Checklist Verification

• Code Quality: Clean and modular.
• Functionality: Addresses the root cause (blocking connect).
• Edge Cases: Handles timeouts and immediate failures correctly.
• Backward Compatibility: Server creation (host == nullptr) path is untouched.