json_escape.cpp

namespace sanitization {

inline char to_hex_char( unsigned int c )
{
    assert( c <= 0xF );

    const char ch = static_cast< char >( c );

    if( ch < 10 ) return '0' + ch;

    return 'A' - 10 + ch;
}

template< class String_type >
String_type non_printable_to_string( unsigned int c )
{
    // Silence the warning: typedef ‘Char_type’ locally defined but not used [-Wunused-local-typedefs]
    // typedef typename String_type::value_type Char_type;

    String_type result( 6, '\\' );

    result[1] = 'u';

    result[ 5 ] = to_hex_char( c & 0x000F ); c >>= 4;
    result[ 4 ] = to_hex_char( c & 0x000F ); c >>= 4;
    result[ 3 ] = to_hex_char( c & 0x000F ); c >>= 4;
    result[ 2 ] = to_hex_char( c & 0x000F );

    return result;
}

template< class String_type >
String_type add_esc_chars( const String_type& s )
{
    typedef typename String_type::const_iterator Iter_type;
    typedef typename String_type::value_type     Char_type;

    String_type result;

    const Iter_type end( s.end() );

    for( Iter_type i = s.begin(); i != end; ++i )
    {
        const Char_type c( *i );

        const wint_t unsigned_c( ( c >= 0 ) ? c : 256 + c );

        if( iswprint( unsigned_c ) )
        {
            result += c;
        }
        else
        {
            result += non_printable_to_string< String_type >( unsigned_c );
        }
    }

    return result;
}

}