VictoriaMetrics/VictoriaMetrics · error

cannot read KeyValueList

Error message

cannot read KeyValueList

What it means

In decodeAnyValueToJSON, field 6 of AnyValue is kvlist_value (an embedded KeyValueList message). If fc.MessageData() cannot extract a length-delimited message for that field, the decoder returns 'cannot read KeyValueList'. Like the ArrayValue case, this indicates the on-the-wire encoding does not match the AnyValue schema.

Source

Thrown at lib/protoparser/opentelemetry/pb/pb_json.go:112

			doubleValue, ok := fc.Double()
			if !ok {
				return nil, fmt.Errorf("cannot read DoubleValue")
			}
			return a.NewNumberFloat64(doubleValue), nil
		case 5:
			data, ok := fc.MessageData()
			if !ok {
				return nil, fmt.Errorf("cannot read ArrayValue")
			}
			arr, err := decodeArrayValueToJSON(data, a, fb)
			if err != nil {
				return nil, fmt.Errorf("cannot decode ArrayValue: %w", err)
			}
			return arr, nil
		case 6:
			data, ok := fc.MessageData()
			if !ok {
				return nil, fmt.Errorf("cannot read KeyValueList")
			}
			obj, err := decodeKeyValueListToJSON(data, a, fb)
			if err != nil {
				return nil, fmt.Errorf("cannot decode KeyValueList: %w", err)
			}
			return obj, nil
		case 7:
			bytesValue, ok := fc.Bytes()
			if !ok {
				return nil, fmt.Errorf("cannot read BytesValue")
			}
			v := fb.formatBase64(bytesValue)
			return a.NewString(v), nil
		}
	}
	return a.NewNull(), nil
}

View on GitHub (pinned to 5079fb58f1)

Solutions

1. Verify with protoc --decode_raw that kvlist_value is wire type 2 length-delimited.
2. Correct the producer's encoding or regenerate it with an up-to-date OTLP proto.
3. Check transport layers for truncation (Content-Length mismatches, proxy buffering limits).
4. Isolate the failure to the single attribute instead of rejecting the entire request.

// Ensure kvlist field is length-delimited before decoding
num, typ, n := protowire.ConsumeTag(src)
if n < 0 || typ != protowire.BytesType {
    return errors.New("kvlist_value is not a length-delimited message")
}

func isMessageField(src []byte) bool {
    _, typ, n := protowire.ConsumeTag(src)
    return n >= 0 && typ == protowire.BytesType
}

When it happens

Trigger: An AnyValue contains field 6 encoded with a non-length-delimited wire type (varint/fixed instead of wire type 2), or the message length prefix extends beyond the buffer.

Common situations: Hand-written protobuf in a custom exporter, corrupted or truncated spans/logs in transit, or replaying captured traffic whose buffers were sliced incorrectly.

Related errors

• cannot read DoubleValue
• cannot read ArrayValue
• cannot unmarshal ResourceMetrics: %w
• cannot read ScopeMetrics data
• cannot unmarshal ScopeMetrics: %w

AI-assisted analysis of VictoriaMetrics/VictoriaMetrics@5079fb58f1 (2026-09-03). Data as JSON: /api/errors/70d51d50c2bca673. Report an issue: GitHub.