allow unknown record structures in sFlow (#153)

decoders/sflow/packet.go

@@ -60,7 +60,15 @@ type RecordHeader struct {
 
 type FlowRecord struct {
 	Header RecordHeader
-	Data   interface{}
+	Data   interface{} // replace by FlowRecordData
+}
+
+type FlowRecordRaw struct {
+	Data []byte
+}
+
+type FlowRecordData interface {
+	GetBytes(offset int, length int, dst []byte) error
 }
 
 type CounterRecord struct {

decoders/sflow/sflow.go

@@ -247,7 +247,10 @@ func DecodeFlowRecord(header *RecordHeader, payload *bytes.Buffer) (FlowRecord,
 
 		flowRecord.Data = extendedGateway
 	default:
-		return flowRecord, errors.New(fmt.Sprintf("Unknown data format %v.", (*header).DataFormat))
+		//return flowRecord, errors.New(fmt.Sprintf("Unknown data format %v.", (*header).DataFormat))
+		flowRecord.Data = &FlowRecordRaw{
+			Data: payload.Next(int(header.Length)),
+		}
 	}
 	return flowRecord, nil
 }