Fix: Handle UnicodeDecodeError and suppress exceptions for Motive 3 compatibility

[hello-bharadwaj]

NatNet 0.2.0 Compatibility Patch for Motive 3.X (NatNet 4.2)

Problem Description

The natnet python library (v0.2.0) crashes when connecting to newer Motive servers (e.g., Motive 3.3.0 which uses NatNet Protocol 4.2).

The crashes occur in two places:

1. UnicodeDecodeError: When parsing strings in MODELDEF packets using PacketBuffer.read_string. The newer protocol seems to send bytes that are not strictly valid utf-8 in the expected context or the parsing offset is misaligned.
2. struct.error: When parsing DataDescriptions. Because the library does not support Protocol 4.X, it fails to account for new fields or size changes in the packet structure, leading to invalid pointer offsets.

Proposed Fix

1. Robust String Decoding: Patches PacketBuffer.read_string to use errors="replace" when decoding utf-8. This prevents the immediate crash on invalid strings.
2. Exception Swallowing in Message Processing: Patches NatNetClient.__process_message to catch and log exceptions instead of letting them propagate and kill the client thread.
   • Rationale: Since the MODELDEF packet parsing is fundamentally incompatible, we simply want to ignore it (or partial failures) so that the client can continue to process FRAMEOFDATA packets, which are backward compatible enough to extract rigid body poses.

[TimSchneider42]

Looks good to me. Thanks for fixing these issues!

[Copilot]

Pull request overview

Compatibility patch to keep the natnet Python client running against newer Motive 3.x / NatNet 4.2 servers by avoiding crashes during packet parsing, especially for MODELDEF parsing failures.

Changes:

• Decode NatNet strings with UTF-8 errors="replace" to avoid UnicodeDecodeError crashes.
• Suppress exceptions during packet processing so the client thread continues running even when parsing fails.

Reviewed changes

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

File	Description
natnet/packet_buffer.py	Makes string decoding tolerant of invalid UTF-8 bytes.
natnet/nat_net_client.py	Wraps message processing in a try/except to prevent receiver loop termination on parse errors.

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[TimSchneider42]

@hello-bharadwaj, maybe Copilot has a fair point here; we could be a bit more specific about which errors we are catching. Which exception are you getting when a MODELDEF package is being processed? Or maybe we should just implement parsing of the new MODELDEF packages.

[TimSchneider42]

Actually, let me try to vibe-code support for 4.2 right now. I suspect that the Unicode error is also because we are parsing the modeldef wrong.

[hello-bharadwaj]

@TimSchneider42 Copilot definitely had a fair point. I didnt do a lot of digging and patched it right away with the easiest answer i could think of. The actual issue was the rigid body description has quat added to it in Natnet 4.2. Thanks for catching that and fixing it. This whole conversation has been fruitful for sure.