Issue with packing a map larger than 15 elements.

[lunarvi]

Hey!

I'm trying to pack a map into a msgpack object and serialize it.

This is the code I'm using:

msgpack::type::variant ObjectNode::toMsgPack() const {
    std::map<msgpack::type::variant, msgpack::type::variant> packed_map;
    for (const auto &pair: children) {
        packed_map.insert({std::move(msgpack::type::variant(pair.first)), std::move(pair.second->toMsgPack())});
    }
    return msgpack::type::variant(std::move(packed_map));
}

At smaller map sizes, everything seems to work fine. However, I've noticed that the moment I try to pack a map larger than 15 elements -> which changes the internal type from fixmap to map16 if I understand correctly -> the output is incorrect.

I tried dissecting the output in hex:

| Fixmap(1el) | 3ch string | "OBJ"  | 16 el fixmap | 0->1, 1->1...                                                                              |
|-------------|------------|--------|--------------|--------------------------------------------------------------------------------------------|
| 81          | a3         | 4f424a | 8f           | a13001a13101a13201a13301a13401a13501a13601a13701a13801a13901a14101a14201a14301a14401a14501 |

(the correct output from a 15 elements long map)

| Fixmap(1el) | 3ch string | "OBJ"  | map16 | map length | 0->1, 1->1...                                                                                    |
|-------------|------------|--------|-------|------------|--------------------------------------------------------------------------------------------------|
| 81          | a3         | 4f424a | de    | 2010       | a13001a13101a13201a13301a13401a13501a13601a13701a13801a13901a14101a14201a14301a14401a14501a14601 |

Output after adding a new key->value pair. (incorrect)

| Fixmap(1el) | 3ch string | "OBJ"  | map16 | map length | 0->1, 1->1...                                                                                    |
|-------------|------------|--------|-------|------------|--------------------------------------------------------------------------------------------------|
| 81          | a3         | 4f424a | de    | 0010       | a13001a13101a13201a13301a13401a13501a13601a13701a13801a13901a14101a14201a14301a14401a14501a14601 |

^The output when I tried using the json->msgpack converter from msgpack's site. (correct)

As you can see, it appears that msgpack::pack() in my case mishandles the length of the map, putting it at 8208(2^13+16?) instead of 16.
I've spent a good while thinking about it & trying to look through the docs, but I've no idea what could cause this.

To be clear, mpgpack-c itself still seems to be able to unpack the map just fine, even if it doesn't seem to conform to the format spec. However I'm slightly worried about whether this would be transferable between various environments, hence - if possible - I'd like to address it.

Would anyone be able to point me in the right direction?
I'd be extremely grateful^^