Can't parse POSITION_TARGET_GLOBAL_INT messages from ArduPlane 4.6.3

[bringert]

rust-mavlink 0.17.1 async fails to parse POSITION_TARGET_GLOBAL_INT messages from ArduPlane 4.6.3.

When using AsyncMavConnection::recv(), the message is skipped.

When using AsyncMavConnection::recv_raw() + mavlink::read_v2_msg(), this error is produced:

Failed to read message: InvalidFlag {
  flag_type: "PositionTargetTypemask",
  value: 65016,
}

I can build a minimal repro case if needed.

[bringert]

Here's the raw_bytes() output:
[253, 50, 0, 0, 211, 1, 1, 87, 0, 0, 232, 79, 3, 0, 146, 148, 91, 34, 210, 174, 17, 7, 184, 30, 92, 66, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 248, 253, 146, 108]

[onur-ozkan]

The parser currently fails on unknown bits which causes this bug.

Thanks for reporting it.

[pv42]

Relevant ArduPilot code: https://github.com/ArduPilot/ardupilot/blob/2fbb90c8aafe8bd70e7a8b974c25890489464c3f/libraries/GCS_MAVLink/GCS_Common.cpp#L6365

[pv42]

Ardupilot seems to set all bits and then only removes the ones that they dont want to ignore. This has been deliberatly kept in ArduPilot/ardupilot#16925 and was likly there since even longer. In #408 we deceided that we should error on invalid flags but option 1 and 3 there would fix this issue.