Decoder fails on unknown TLV tags in port 151 payloads #180
Description
Describe the bug
The TLV parser in pkg/common/helpers.go returns a hard error when it encounters a tag that isn't defined in the decoder's config:
return nil, fmt.Errorf("unknown tag %x", tag)
This means if the device firmware adds new config settings to port 151, the entire decode fails — even though the known fields are perfectly valid and the TLV format is inherently forward-compatible (each tag carries its own length).
Port 151 on the Tag XL is currently the only port using TLV-based parsing, but the bug is in the shared Decode function and would affect any future TLV-based ports as well.
To Reproduce
Steps to reproduce the behavior:
- Send a port 151 payload containing a tag not defined in the decoder (e.g. 4c0501ff020000 which contains an unknown tag 0xff)
- See error: unknown tag f
Expected behavior
Unknown tags should be skipped gracefully (advancing the index past their value using the length field) instead of causing the entire decode to fail. A warning log should be emitted so new tags are visible.
Screenshots
N/A
Desktop (please complete the following information):
- OS: any
- Version any
Additional context
The fix is straightforward: Replace the hard error with a skip + warning:
if found { index += length } else { slog.Warn("skipping unknown tag", "tag", fmt.Sprintf("%x", tag), "length", length) index += length }