How to detect which type to unpack / deserialize?

[cnf]

Hi, if you get msgpack messages in, and they can be one of say 4 different formats, based on custom classes, how would you go about detecting which one to unpack?

I am trying to figure something out with unpackable, but that doesn't like custom classes, and I soft of have something working by just trying deserialize, and rewinding the index if it returns false, but that seems like a lot of overhead every time you get a message, especially if you have many types.

Is it not the point of msgpack compared to cpnproto or something that you are more flexible in your messages? Maybe I am misunderstanding something, but I'm afraid I can't quite figure it out.

Thanks

[cnf]

To add a bit more info, I am working with some example data

struct IntTopic : public Printable {
  MsgPack::str_t topic;
  int int_data;
  MSGPACK_DEFINE_MAP(topic, int_data);
  size_t printTo(Print &p) const { return p.printf("{ %s : %i }", topic.c_str(), int_data); }
};

struct StringTopic : public Printable {
  MsgPack::str_t topic;
  MsgPack::str_t string_data;
  MSGPACK_DEFINE_MAP(topic, string_data);
  size_t printTo(Print &p) const { return p.printf("{ %s : %s }", topic.c_str(), string_data.c_str()); }
};

and then I try do do

void Receive(char *data, uint16_t length) {
StringTopic string_payload;
  IntTopic int_payload;
  LOG_DEBUG("Received msg");
  hexdump((const unsigned char *)data, length);

  unpacker.feed((uint8_t *)data, length);
  int i = unpacker.index();

  if (unpacker.deserialize(int_payload)) {
    LOG_DEBUG("INT Message:", int_payload);
    unpacker.clear();
    return;
  }
  unpacker.index(i);
  if (unpacker.deserialize(string_payload)) {
    LOG_DEBUG("STR Message:", string_payload);
    unpacker.clear();
    return;
  }
  unpacker.index(i);
  /// etc for different message types
  unpacker.clear();
}

[hideakitai]

Your usage is almost OK based on your example. However, your understanding of the index is not correct.

• index 0: map size (== 2)
• index 1: topic

• index 2: int or string

  I will use this library as follows with multiple formats:

1. Use different endpoints for different types of message
2. Use an index outside of msgpack (like MsgPacketizer)
3. Use topic/type (as you did) and two-step deserialization