AlexxIT/go2rtc · error

tlv8: can't find T= ,L= ,V= for

Error message

tlv8: can't find T=%d,L=%d,V=%x for: %s

What it means

tlv8.unmarshalTLV encountered a TLV record whose Tag has no corresponding struct field (fields are matched by decimal tag name, e.g. `"1"`). The record's T, L and hex V are printed along with the target struct name. This happens when decoding TLV8 data containing tags the target struct does not model.

Solutions

1. Add a field named after the missing tag (string name of the tag number) to the target struct, or a catch-all map field if supported.
2. Upgrade the tlv8/hap library so its structs cover the new tags.
3. Dump the failing T,L,V from the error and check which HAP spec tag it corresponds to.
4. If the tag is ignorable, pre-filter it from the TLV slice before unmarshalling.

Example fix

// before
type pairVerifyResponse struct {
    "1" []byte
    "3" []byte
}
// after (device also sends tag 2)
type pairVerifyResponse struct {
    "1" []byte
    "2" []byte
    "3" []byte
}

// pre-scan TLV records and drop unknown tags before unmarshalling
func knownOnly(recs []tlv8.Record, known map[byte]bool) []tlv8.Record { ... }

err := tlv8.Unmarshal(data, &msg)
if err != nil {
    var tlvErr error
    if errors.As(err, &tlvErr) && strings.Contains(err.Error(), "can't find T=") {
        log.Printf("unknown TLV tag from device: %v", err)
    }
    return err
}

When it happens

Trigger: Unmarshalling a TLV8 blob (e.g. a HAP pairing message) whose tag set includes values not present as fields in the destination struct — typically a device using newer/extra tags than the struct supports.

Common situations: Accessories implementing newer HAP protocol extensions; mismatched struct definitions after a library upgrade; decoding vendor-specific TLVs into a generic struct.

Understand the failure class

Background: Schema validation failed / invalid input schema: payload rejected because its shape doesn't match the expected schema — this error's family across 28 libraries.

Related errors

• tlv8: value should be pointer:
• tlv8: wrong size:
• tlv8: zero item
• tlv8: unmarshal zero data
• hap: wrong request: %#v

AI-assisted analysis of AlexxIT/go2rtc@c245815e75 (2026-09-07). Data as JSON: /api/errors/b7cc7e32664c655c. Report an issue: GitHub.

Appendix: source

Thrown at pkg/hap/tlv8/tlv8.go:262

			return nil, errors.New("tlv8: wrong size: " + value.Type().Name())
		}

		v = append(v, b[2:2+l]...)
		b = b[2+l:]

		// if size == 255 and same tag - continue read big payload
		if l < 255 || len(b) < 2 || b[0] != t {
			break
		}

		l = int(b[1])
	}

	tag := strconv.Itoa(int(t))

	valueField, ok := getStructField(value, tag)
	if !ok {
		return b, fmt.Errorf("tlv8: can't find T=%d,L=%d,V=%x for: %s", t, l, v, value.Type().Name())
	}

	if err := unmarshalValue(v, valueField); err != nil {
		return nil, err
	}

	return b, nil
}

func unmarshalSlice(b []byte, value reflect.Value) error {
	valueIndex := value.Index(growSlice(value))
	for len(b) > 0 {
		var err error
		if b, err = unmarshalTLV(b, valueIndex); err != nil {
			if b != nil {
				valueIndex = value.Index(growSlice(value))
				continue
			}

View on GitHub (pinned to c245815e75)