msgpack.md

msgpack extension

The msgpack extension implements encode to and decode from the MessagePack data format. You can either parse into or serialize from a variant-like data structure, basic_json, or your own data structures, using json_type_traits.

decode_msgpack, try_decode_msgpack

basic_msgpack_cursor

encode_msgpack

basic_msgpack_encoder

msgpack_options

Mappings between MessagePack and jsoncons data items

MessagePack data item	ext type	jsoncons data item	jsoncons tag
nil		null
true, false		bool
negative fixnum, int 8, int 16, int 32, int 64		int64
positive fixnum, uint 8, uint 16, uint 32, uint 64		uint64
float32, float64		double
fixstr, str 8, str 16, str 32		string
bin 8, bin 16, bin 32		byte_string
fixext1, fixext2, fixext4, fixext8, fixext16, ext8, ext16, ext32	0-127	byte_string
4 byte length	-1 (timestamp 32)	uint64	seconds
8 byte length	-1 (timestamp 64)	string	epoch_nanosecond
12 byte length	-1 (timestamp 96)	string	epoch_nanosecond
array		array
map		object

Examples

ext format code example

#include <jsoncons/json.hpp>
#include <jsoncons_ext/msgpack/msgpack.hpp>
#include <cassert>

using namespace jsoncons;

int main()
{
    std::vector<uint8_t> input = {

        0x82, // map, length 2
          0xa5, // string, length 5
            'H','e','l','l','o',
          0xa5, // string, length 5
            'W','o','r','l','d',
          0xa4, // string, length 4
             'D','a','t','a',
          0xc7, // ext8 format code
            0x06, // length 6
            0x07, // type
              'f','o','o','b','a','r'
    };

    ojson j = msgpack::decode_msgpack<ojson>(input);

    std::cout << "(1)\n" << pretty_print(j) << "\n\n";
    std::cout << "(2) " << j["Data"].tag() << "("  << j["Data"].ext_tag() << ")\n\n";
    
    // Get ext value as a std::vector<uint8_t>
    auto v = j["Data"].as<std::vector<uint8_t>>(); 

    std::cout << "(3)\n";
    std::cout << byte_string_view(v) << "\n\n";

    std::vector<uint8_t> output;
    msgpack::encode_msgpack(j,output);
    assert(output == input);
}

Output:

(1)
{
    "Hello": "World",
    "Data": "Zm9vYmFy"
}

(2) ext(7)

(3)
66,6f,6f,62,61,72

JSON to message pack

Input JSON file book.json

[
    {
        "category": "reference",
        "author": "Nigel Rees",
        "title": "Sayings of the Century",
        "price": 8.95
    },
    {
        "category": "fiction",
        "author": "Evelyn Waugh",
        "title": "Sword of Honour",
        "price": 12.99
    }
]

#include <jsoncons/json.hpp>
#include <jsoncons_ext/msgpack/msgpack.hpp>

using namespace jsoncons;

int main()
{
    std::ifstream is("input/book.json");
    ojson j1;
    is >> j1;

    // Encode ojson to MessagePack
    std::vector<uint8_t> v;
    msgpack::encode_msgpack(j1, v);

    // Decode MessagePack to ojson 
    ojson j2 = msgpack::decode_msgpack<ojson>(v);

    std::cout << pretty_print(j2) << '\n';

    // or to json (now alphabetically sorted)
    json j3 = msgpack::decode_msgpack<json>(v);

    // or to wjson (converts from utf8 to wide characters)
    wjson j4 = msgpack::decode_msgpack<wjson>(v);
}

Output:

[
    {
        "category": "reference",
        "author": "Nigel Rees",
        "title": "Sayings of the Century",
        "price": 8.95
    },
    {
        "category": "fiction",
        "author": "Evelyn Waugh",
        "title": "Sword of Honour",
        "price": 12.99
    }
]