json/example/cbor.cpp at develop · boostorg/json · GitHub

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// Distributed under the Boost Software License, Version 1.0. (See accompanying

// file LICENSE_1_0.txt or copy at http://www.boost.org/LICENSE_1_0.txt)

// Official repository: https://github.com/boostorg/json

// tag::example_cbor[]

This example implements simple parsing and serialization of a

subset of CBOR types that are directly supported by JSON.

#include <boost/json.hpp>

#include <boost/endian.hpp>

#include <stdexcept>

#include <fstream>

#include <iostream>

using namespace boost::json;

void serialize_cbor_number(

unsigned char mt, std::uint64_t n, std::vector<unsigned char> & out )

{

mt <<= 5;

if( n < 24 )

{

out.push_back( static_cast<unsigned char>( mt + n ) );

}

else if( n < 256 )

{

unsigned char data[] = { static_cast<unsigned char>( mt + 24 ), static_cast<unsigned char>( n ) };

out.insert( out.end(), std::begin( data ), std::end( data ) );

}

else if( n < 65536 )

{

unsigned char data[] = { static_cast<unsigned char>( mt + 25 ), static_cast<unsigned char>( n >> 8 ), static_cast<unsigned char>( n ) };

out.insert( out.end(), std::begin( data ), std::end( data ) );

}

else if( n < 0x1000000ull )

{

unsigned char data[ 5 ];

data[ 0 ] = static_cast<unsigned char>( mt + 26 );

boost::endian::endian_store<std::uint32_t, 4, boost::endian::order::big>( data + 1, static_cast<std::uint32_t>( n ) );

out.insert( out.end(), std::begin( data ), std::end( data ) );

}

else

{

unsigned char data[ 9 ];

data[ 0 ] = static_cast<unsigned char>( mt + 27 );

boost::endian::endian_store<std::uint64_t, 8, boost::endian::order::big>( data + 1, n );

out.insert( out.end(), std::begin( data ), std::end( data ) );

}

void

serialize_cbor_string( string_view sv, std::vector<unsigned char>& out )

{

std::size_t n = sv.size();

serialize_cbor_number( 3, n, out );

out.insert( out.end(), sv.data(), sv.data() + n );

}

void

serialize_cbor_value( const value& jv, std::vector<unsigned char>& out )

{

switch( jv.kind() )

{

case kind::null:

out.push_back( 224 + 22 );

break;

case kind::bool_:

out.push_back( 224 + 20 + jv.get_bool() );

break;

case kind::int64:

{

std::int64_t n = jv.get_int64();

if( n >= 0 )

serialize_cbor_number( 0, n, out );

else

serialize_cbor_number( 1, ~n, out );

}

break;

case kind::uint64:

serialize_cbor_number( 0, jv.get_uint64(), out );

break;

case kind::double_:

{

unsigned char data[ 9 ];

data[ 0 ] = 224 + 27;

boost::endian::endian_store<double, 8, boost::endian::order::big>( data + 1, jv.get_double() );

out.insert( out.end(), std::begin(data), std::end(data) );

}

break;

case kind::string:

serialize_cbor_string( jv.get_string(), out );

break;

case kind::array:

{

const array& ja = jv.get_array();

std::size_t n = ja.size();

out.reserve( out.size() + n + 1 );

serialize_cbor_number( 4, n, out );

for( std::size_t i = 0; i < n; ++i )

serialize_cbor_value( ja[i], out );

}

break;

case kind::object:

{

const object& jo = jv.get_object();

std::size_t n = jo.size();

out.reserve( out.size() + 3 * n + 1 );

serialize_cbor_number( 5, n, out );

for( const key_value_pair& kv: jo )

{

serialize_cbor_string( kv.key(), out );

serialize_cbor_value( kv.value(), out );

}

break;

}

BOOST_NORETURN

void

throw_eof_error()

{

throw std::runtime_error( "Unexpected end of input" );

}

BOOST_NORETURN

void

throw_format_error( char const * err )

{

throw std::runtime_error( err );

}

void

ensure( std::size_t n, const unsigned char* first, const unsigned char* last )

{

if( static_cast<std::size_t>(last - first) < n )

throw_eof_error();

}

const unsigned char*

parse_cbor_value(

const unsigned char* first, const unsigned char* last, value& v );

const unsigned char*

parse_cbor_number(

const unsigned char* first, const unsigned char* last, unsigned char ch, std::uint64_t& n )

{

unsigned char cv = ch & 31;

if( cv < 24 )

{

n = cv;

}

else if( cv == 24 )

{

ensure( 1, first, last );

n = *first++;

}

else if( cv == 25 )

{

ensure( 2, first, last );

n = boost::endian::load_big_u16( first );

first += 2;

}

else if( cv == 26 )

{

ensure( 4, first, last );

n = boost::endian::load_big_u32( first );

first += 4;

}

else if( cv == 27 )

{

ensure( 8, first, last );

n = boost::endian::load_big_u64( first );

first += 8;

}

else if( cv == 31 )

{

// infinite array/object

throw_format_error( "Infinite sequences aren't supported" );

}

else

{

throw_format_error( "Invalid minor type" );

}

return first;

}

const unsigned char*

parse_cbor_string(

const unsigned char* first, const unsigned char* last, unsigned char ch, value& v )

{

std::uint64_t n;

first = parse_cbor_number( first, last, ch, n );

ensure( n, first, last );

string_view sv( reinterpret_cast<char const*>( first ), n );

first += n;

v = sv;

return first;

}

const unsigned char*

parse_cbor_array(

const unsigned char* first, const unsigned char* last, unsigned char ch, value& v )

{

std::uint64_t n;

first = parse_cbor_number( first, last, ch, n );

array & a = v.emplace_array();

a.resize( n );

std::size_t i = 0;

for( ; i < n; ++i ) // double[] fast path

{

ensure( 1, first, last );

unsigned char ch2 = *first;

if( ch2 != 0xFB ) break;

++first;

ensure( 8, first, last );

double w = boost::endian::endian_load<double, 8, boost::endian::order::big>( first );

first += 8;

a[ i ] = w;

}

for( ; i < n; ++i ) // int[] fast path

{

ensure( 1, first, last );

unsigned char ch2 = *first;

if( ch2 >= 0x40 ) break;

++first;

std::uint64_t m;

first = parse_cbor_number( first, last, ch2, m );

if( ch2 < 0x20 )

{

a[ i ] = m;

}

else

{

a[ i ] = static_cast<std::int64_t>( ~m );

}

for( ; i < n; ++i )

first = parse_cbor_value( first, last, a[ i ] );

return first;

}

const unsigned char*

parse_cbor_object(

const unsigned char* first, const unsigned char* last, unsigned char ch, value& v )

{

std::uint64_t n;

first = parse_cbor_number( first, last, ch, n );

object & o = v.emplace_object();

o.reserve( n );

for( std::size_t i = 0; i < n; ++i )

{

// key string

ensure( 1, first, last );

unsigned char ch2 = *first++;

if( ( ch2 >> 5 ) != 3 )

throw_format_error( "Object keys must be strings" );

std::uint64_t m;

first = parse_cbor_number( first, last, ch2, m );

ensure( m, first, last );

string_view sv( reinterpret_cast<char const*>( first ), m );

first += m;

// value

first = parse_cbor_value( first, last, o[ sv ] );

}

return first;

}

const unsigned char*

parse_cbor_unsigned(

const unsigned char* first, const unsigned char* last, unsigned char ch, value& v )

{

std::uint64_t n;

first = parse_cbor_number( first, last, ch, n );

v = n;

return first;

}

const unsigned char*

parse_cbor_signed(

const unsigned char* first, const unsigned char* last, unsigned char ch, value& v )

{

std::uint64_t n;

first = parse_cbor_number( first, last, ch, n );

v = static_cast<std::int64_t>( ~n );

return first;

}

const unsigned char*

parse_cbor_semantic_tag(

const unsigned char* first, const unsigned char* last, unsigned char ch, value& v )

{

std::uint64_t n;

first = parse_cbor_number( first, last, ch, n );

// ignore semantic tags

return parse_cbor_value( first, last, v );

}

const unsigned char*

parse_cbor_type7(

const unsigned char* first, const unsigned char* last, unsigned char ch, value& v )

{

switch( ch & 31 )

{

case 20:

v = false;

return first;

case 21:

v = true;

return first;

case 22:

v = nullptr;

return first;

case 26: // float

{

ensure( 4, first, last );

float w = boost::endian::endian_load<float, 4, boost::endian::order::big>( first );

first += 4;

v = w;

return first;

}

case 27: // double

{

ensure( 8, first, last );

double w = boost::endian::endian_load<double, 8, boost::endian::order::big>( first );

first += 8;

v = w;

return first;

}

default:

throw_format_error( "Invalid minor type for major type 7" );

}

const unsigned char*

parse_cbor_value( const unsigned char* first, const unsigned char* last, value& v )

{

ensure( 1, first, last );

const unsigned char ch = *first++;

switch( ch >> 5 )

{

case 0:

return parse_cbor_unsigned( first, last, ch, v );

case 1:

return parse_cbor_signed( first, last, ch, v );

case 2:

throw_format_error( "Binary strings aren't supported" );

case 3:

return parse_cbor_string( first, last, ch, v );

case 4:

return parse_cbor_array( first, last, ch, v );

case 5:

return parse_cbor_object( first, last, ch, v );

case 6:

return parse_cbor_semantic_tag( first, last, ch, v );

case 7:

return parse_cbor_type7( first, last, ch, v );

default:

BOOST_JSON_UNREACHABLE();

}

int

main(int argc, const char** argv)

{

if( argc != 2 )

{

std::cerr << "Usage: cbor FILE_NAME\n";

return EXIT_FAILURE;

}

std::ifstream is(argv[1]);

is.exceptions(std::ios::badbit);

const value jv = parse(is);

std::vector<unsigned char> out;

serialize_cbor_value( jv, out );

value jv2;

parse_cbor_value( out.data(), out.data() + out.size(), jv2 );

if( jv != jv2 )

{

std::cerr << "Roundtrip check failed\n";

return EXIT_FAILURE;

}

return EXIT_SUCCESS;

}

// end::example_cbor[]

json/example/cbor.cpp at develop · boostorg/json · GitHub

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