to/from_msgpack only works with standard typization

[phyz777]

The to/from_msgpack functions only work for standard typization of nlohmann::basic_json.

Using nlohmann::basic_json<std::map, std::vector, std::string, bool, std::int32_t, std::uint32_t, float> produces the following error:

parse error at 1472: expected a MessagePack string; last byte: 0x68

The error occurs when I put an object into a msgpack, send it over the network, then reconstruct the object using from_msgpack. When I use nlohmann::json instead, everything works fine.

System is linux, compiler is g++, version 7.2.1, nlohmann::json is version 3.1.2.

[nlohmann]

Could you provide a small example that triggers the error?

[phyz777]

I am working on it.
Meanwhile, I came across something similar. I am not even sure whether this is one is a bug:

#include <iostream>
#include "json.hpp"

// using json=nlohmann::json;
using json=nlohmann::basic_json<std::map, std::vector, std::string, bool, std::int32_t, std::uint32_t, float>;

int main()
{
    double Value2 = 1000.0;

    json j;
    j["Key1"] = "Value1";
    j["Key2"] = Value2;

    std::vector<uint8_t> v = json::to_msgpack(j);
    json k = json::from_msgpack(v);

    std::cout << k.dump(4) << std::endl;

    return 0;
}

Is nlohmann::json supposed to safely convert types where necessary? This one throws nlohmann::detail::parse_error

[nlohmann]

The issue is that while the library respects the provided number types in the serialization, it does not add the correct prefixes. For instance, it serializes the float value correctly with 4 bytes, but adds a 0xcb byte (float 64) as type prefix.

To fix this issue, the serialization must derive the MessagePack (and most probably also CBOR and UBJSON) type prefix from the templated type. I am not sure about a nice way, but I think functions like std::is_floating_point would be my friend.

[nlohmann]

I opened branch https://github.com/nlohmann/json/tree/feature/issue1021 which supports float as floating-point type for all binary formats.

@phyz777 Could you check if this fixes your issue?

[nlohmann]

@phyz777 Could you check if this fixes your issue?

[nlohmann]

I merged the fix. If there is still an issue, please let me know.