to/from_json Failing To Convert String

[cliffburdick]

Trying to convert a simple JSON type into a class using the instructions provided in the README.

What is the issue you have?

When the from_json code is called, it seems to successfully run the function, but segfaults in a string copy assignment/operator.

Please describe the steps to reproduce the issue.

Here is the class and the code to convert:

class ExampleJsonConvert
{
    public: 
        std::string a;
        int b;
        float c;
};

void from_json(const nlohmann::json& j, ExampleJsonConvert& p) {
    j.at("a").get_to(p.a);
    j.at("b").get_to(p.b);
    j.at("c").get_to(p.c);
}   

The callback is invoked with the following template:

template <typename T>
int GenericJsonConverter(std::string json_str, void *output)
{
    try {
        T *conv = reinterpret_cast<T*>(output);
        nlohmann::json json_obj = nlohmann::json::parse(json_str);
        *conv = json_obj;
    }
    catch (const nlohmann::json::parse_error &e) {
        printf("Failed to parse payload from PubSub message: %s, exception:%s", json_str.c_str(), e.what());   
        return -1;         
    }     
    catch (const nlohmann::detail::type_error &e) {
        printf("Failed to parse type from PubSub message: %s, exception: %s", json_str.c_str(), e.what());
        return -1;              
    }       

    return 0;
}

GenericJsonConverter<ExampleJsonConvert>(j["payload"].dump(), mybuffer);

The JSON being passed in is as follows:

{
   "hdr" : {"module": "_ANY_", "core": 0, "name": "none"},
   "payload" : {"a": "test", "b":1, "c":2.0}
}

When hitting the callback, I put a print statement after the j.at("c").get_to(p.c); line, and it succeeds, but the stack trace shows:

#0  0x00007fffe0597b6a in ?? ()
#1  0x0000555556553a9b in std::char_traits<char>::copy (__n=4, __s2=<optimized out>, __s1=<optimized out>) at /usr/include/c++/7/bits/char_traits.h:350
#2  std::__cxx11::basic_string<char, std::char_traits<char>, std::allocator<char> >::_S_copy (__n=4, __s=<optimized out>, __d=<optimized out>) at /usr/include/c++/7/bits/basic_string.h:340
#3  std::__cxx11::basic_string<char, std::char_traits<char>, std::allocator<char> >::_M_assign (this=this@entry=0x1996f2510, __str=...) at /usr/include/c++/7/bits/basic_string.tcc:272
#4  0x00005555567c1afb in std::__cxx11::basic_string<char, std::char_traits<char>, std::allocator<char> >::assign (__str=..., this=0x1996f2510) at /usr/include/c++/7/bits/basic_string.h:1347
#5  std::__cxx11::basic_string<char, std::char_traits<char>, std::allocator<char> >::operator= (__str=..., this=0x1996f2510) at /usr/include/c++/7/bits/basic_string.h:766
#6  TestBed::ExampleJsonConvert::operator= (this=0x1996f2510) at ./src/RPC/interfaces/json_converters/CommonConverters.h:8
#7  TestBed::GenericJsonConverter<TestBed::ExampleJsonConvert> (json_str=..., output=0x1996f2510) at ./src/RPC/interfaces/json_converters/ConverterUtilities.h:16

Can you provide a small but working code example?

See above

What is the expected behavior?

No crash

And what is the actual behavior instead?

Crash

Which compiler and operating system are you using?

• Compiler: ___
• Operating system: ___

Which version of the library did you use?

• [ X ] latest release version 3.8.0
  Ubuntu 18.04
  gcc 7.3.0

[cliffburdick]

Nevermind, issue with std::string allocating heap memory.