Unknown M17 packet

[GM7KBK]

Using WPSD. I get unknown m17 packet in logs. Resulting in nothing being passed through urfd. Works fine connecting via my mrefd server.

This results in one way audio. A complaint made by other admins.

[dbehnke]

Audit Findings: M17 Protocol Compliance

I have completed a deep-dive audit of urfd against the M17 Specification.

Verdict: urfd is currently non-compliant, utilizing a 54-byte packet structure instead of the mandated 56-byte structure.

• The LICH (Link Information Channel) is missing its internal 2-byte CRC.
• The Packet CRC is displaced by 2 bytes (offset 52 instead of 54).
• Validation logic (IsValidDvPacket) strictly checks Buffer[19] bits, which works for DroidStar's current output but is technically brittle.

Relation to DroidStar Issues:
This non-compliance mirrors the implementation in DroidStar (see issue created there). Because both projects share this "legacy" 54-byte definition, they interoperate with each other but likely will not work with official M17 clients/reflectors.

Next Steps:
We should proceed with updating urfd to support the spec-compliant 56-byte format. Ideally, we should implement a dual-mode or version-detection logic if backward compatibility with legacy DroidStar is defined, otherwise we should move forward to the standard.