Custom JSON Parsers Not Detected

[freesurfer-rge]

I seem to be unable to successfully use methods whose arguments are types such as enum classes, where I have used nlohmann::json to provide serialisation and deserialisation routines. The method successfully binds, but when I invoke it using curl, there is an error response of invalid parameter: must be object, but is string for parameter \"e\"

The attached zip file contains a repro case. The enum itself is:

 enum class MyEnum { Zero, One, Two };

with serialisation provided by NLOHMANN_JSON_SERIALIZE_ENUM. There are then two methods which I'm attempting to call:

  int MyService::OptionOne( MyEnum e ) {
    std::cout << __FUNCTION__ << std::endl;
    return static_cast<int>(e);
  }

  int MyService::OptionTwo( std::string s ) {
    std::cout << __FUNCTION__ << std::endl;
    nlohmann::json j(s);

    MyEnum e = j.get<MyEnum>();

    return static_cast<int>(e);
  }

I can invoke the second via:

curl http://localhost:8483/jsonrpc -H "Content-Type application/json" --data '{ "method":"OptionTwo", "params":{"s":"One"}, "id":10, "jsonrpc": "2.0" }'

However, when I try to call the first:

curl http://localhost:8483/jsonrpc -H "Content-Type application/json" --data '{ "method":"OptionOne", "params":{"e":"One"}, "id":10, "jsonrpc": "2.0" }'

I see the error noted above.

jsonrpccxxissue.zip

[cinemast]

Thank you for reporting this. I did not think of this scenario. The typemapper fallsback to object if it does not find a specified typemapping.

Adding the following lines to your code should work:

constexpr nlohmann::json::value_t GetType(jsonrpccxx::type<MyEnum>) {
  return nlohmann::json::value_t::string;
}

I will try to provide a macro for this.

[cinemast]

To match your exact example:

#pragma once
#include <nlohmann/json.hpp>
#include <jsonrpccxx/typemapper.hpp>

namespace SimpleService {
  enum class MyEnum { Zero, One, Two };

  NLOHMANN_JSON_SERIALIZE_ENUM(MyEnum,
			       {
				{MyEnum::Zero, "Zero"},
				{MyEnum::One, "One"},
				{MyEnum::Two, "Two"}
			       })

	constexpr nlohmann::json::value_t GetType(jsonrpccxx::type<MyEnum>) {
  		return nlohmann::json::value_t::string;
	}
}

[cinemast]

Nevermind my comments above, it should now work out of the box.

[freesurfer-rge]

Thanks. After also updating the example to pull in the version 3.9.1 of nlohmann's json library, the example code started to work.

I did also find I needed to add a type mapper:

 constexpr nlohmann::json::value_t GetType(jsonrpccxx::type<ItemId>) {
    return nlohmann::json::value_t::string;
  }

into my rpcserver.hpp file (where ItemId is my custom type). Is this expected? I don't see anything like that for Product in the example code.

[cinemast]

I could not find anything like a ItemId in your provided example (zip-file). However I assume you have something like

typedef std::string ItemId

in your code, which would require a custom typemapping, yes (At least I cant think of anything how to resolve this automatically).

If you take a look at typemapper.h these are the types that are automatically resolved, all other types fallback to value_t::object.

[freesurfer-rge]

Sorry, I didn't explain myself well. The attached is an update which shows the problem.

jsonrpccxxissue.zip

The appropriate CURL command is:

curl http://localhost:8483/jsonrpc -H "Content-Type application/json" --data '{ "method":"EchoId", "params":{"id":"00:00:00:10"}, "id":10, "jsonrpc": "2.0" }'

To fix the error, enable the #if 0 block in rpcserver.hpp.

Basically the ItemId type is a wrapper for an unsigned 32 bit number, which takes care of pretty-printing it to a string, and parsing it back afterwards.

[cinemast]

In this case it is definitely required. How else should the json deserializer know how to decode the custom class?

[freesurfer-rge]

Thanks for letting me know.