Question

I hope someone can help me get jsonrpc-cpp to compile. (http://jsonrpc-cpp.sourceforge.net/)

When I type scons as per the documentation, I get:

eamorr@Compaq6000:~/Desktop/jsonrpc-cpp$ scons
scons: Reading SConscript files ...
scons: done reading SConscript files.
scons: Building targets ...
g++ -o src/jsonrpc_handler.os -c -std=c++98 -Wall -Wextra -pedantic -Wredundant-decls -Wshadow -Werror -O2 -fPIC src/jsonrpc_handler.cpp
src/jsonrpc_handler.cpp: In member function ‘bool Json::Rpc::Handler::Process(const std::string&, Json::Value&)’:
src/jsonrpc_handler.cpp:208:25: error: ambiguous overload for ‘operator[]’ in ‘root[i]’
/usr/local/include/json/value.h:322:14: note: candidates are: Json::Value& Json::Value::operator[](Json::Value::ArrayIndex)
/usr/local/include/json/value.h:329:14: note:                 Json::Value& Json::Value::operator[](int)
/usr/local/include/json/value.h:334:20: note:                 const Json::Value& Json::Value::operator[](Json::Value::ArrayIndex) const
/usr/local/include/json/value.h:339:20: note:                 const Json::Value& Json::Value::operator[](int) const
src/jsonrpc_handler.cpp:213:23: error: ambiguous overload for ‘operator[]’ in ‘response[j]’
/usr/local/include/json/value.h:322:14: note: candidates are: Json::Value& Json::Value::operator[](Json::Value::ArrayIndex)
/usr/local/include/json/value.h:329:14: note:                 Json::Value& Json::Value::operator[](int)
/usr/local/include/json/value.h:334:20: note:                 const Json::Value& Json::Value::operator[](Json::Value::ArrayIndex) const
/usr/local/include/json/value.h:339:20: note:                 const Json::Value& Json::Value::operator[](int) const
scons: *** [src/jsonrpc_handler.os] Error 1
scons: building terminated because of errors.

Here is src/jsonrpc_handler.cpp (I’ve marked lines 208 and 213):

/*
 *  JsonRpc-Cpp - JSON-RPC implementation.
 *  Copyright (C) 2008-2011 Sebastien Vincent <[e-mail]>
 *
 *  This program is free software: you can redistribute it and/or modify
 *  it under the terms of the GNU Lesser General Public License as published by
 *  the Free Software Foundation, either version 3 of the License, or
 *  (at your option) any later version.
 *
 *  This program is distributed in the hope that it will be useful,
 *  but WITHOUT ANY WARRANTY; without even the implied warranty of
 *  MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
 *  GNU Lesser General Public License for more details.
 *
 *  You should have received a copy of the GNU Lesser General Public License
 *  along with this program.  If not, see <http://www.gnu.org/licenses/>.
 */

/**
 * \file jsonrpc_handler.cpp
 * \brief JSON-RPC server processor engine.
 * \author Sebastien Vincent
 */

#include "jsonrpc_handler.h"

namespace Json
{

  namespace Rpc
  {

    CallbackMethod::~CallbackMethod()
    {
    }

    Handler::Handler()
    {
      /* add a RPC method that list the actual RPC methods contained in the Handler */
      Json::Value root;

      root["description"] = "List the RPC methods available";
      root["parameters"] = Json::Value::null;
      root["returns"] = "Object that contains description of all methods registered";

      AddMethod(new RpcMethod<Handler>(*this, &Handler::SystemDescribe, std::string("system.describe"), root));
    }

    Handler::~Handler()
    {
      /* delete all objects from the list */
      for(std::list<CallbackMethod*>::const_iterator it = m_methods.begin() ; it != m_methods.end() ; it++)
      {
        delete (*it);
      }
      m_methods.clear();
    }

    void Handler::AddMethod(CallbackMethod* method)
    {
      m_methods.push_back(method);
    }

    void Handler::DeleteMethod(const std::string& name)
    {
      /* do not delete system defined method */
      if(name == "system.describe")
      {
        return;
      }

      for(std::list<CallbackMethod*>::iterator it = m_methods.begin() ; it != m_methods.end() ; it++)
      {
        if((*it)->GetName() == name)
        {
          delete (*it);
          m_methods.erase(it);
          break;
        }
      }
    }

    bool Handler::SystemDescribe(const Json::Value& msg, Json::Value& response)
    {
      Json::Value methods;
      response["jsonrpc"] = "2.0";
      response["id"] = msg["id"];

      for(std::list<CallbackMethod*>::iterator it = m_methods.begin() ; it != m_methods.end() ; it++)
      {
        methods[(*it)->GetName()] = (*it)->GetDescription();
      }

      response["result"] = methods;
      return true;
    }

    std::string Handler::GetString(Json::Value value)
    {
      return m_writer.write(value);
    }

    bool Handler::Check(const Json::Value& root, Json::Value& error)
    {
      Json::Value err;

      /* check the JSON-RPC version => 2.0 */
      if(!root.isObject() || !root.isMember("jsonrpc") || root["jsonrpc"] != "2.0") 
      {
        error["id"] = Json::Value::null;
        error["jsonrpc"] = "2.0";

        err["code"] = INVALID_REQUEST;
        err["message"] = "Invalid JSON-RPC request.";
        error["error"] = err;
        return false;
      }

      if(root.isMember("id") && (root["id"].isArray() || root["id"].isObject()))
      {
        error["id"] = Json::Value::null;
        error["jsonrpc"] = "2.0";

        err["code"] = INVALID_REQUEST;
        err["message"] = "Invalid JSON-RPC request.";
        error["error"] = err;
        return false;
      }

      /* extract "method" attribute */
      if(!root.isMember("method") || !root["method"].isString())
      {
        error["id"] = Json::Value::null;
        error["jsonrpc"] = "2.0";

        err["code"] = INVALID_REQUEST;
        err["message"] = "Invalid JSON-RPC request.";
        error["error"] = err;
        return false;
      }

      return true;
    }

    bool Handler::Process(const Json::Value& root, Json::Value& response)
    {
      Json::Value error;
      std::string method;

      if(!Check(root, error))
      {
        response = error;
        return false;
      }

      method = root["method"].asString();

      if(method != "")
      {
        CallbackMethod* rpc = Lookup(method);
        if(rpc)
        {
          return rpc->Call(root, response);
        }
      }

      /* forge an error response */
      response["id"] = root.isMember("id") ? root["id"] : Json::Value::null;
      response["jsonrpc"] = "2.0";

      error["code"] = METHOD_NOT_FOUND;
      error["message"] = "Method not found.";
      response["error"] = error;

      return false;
    }

    bool Handler::Process(const std::string& msg, Json::Value& response)
    {
      Json::Value root;
      Json::Value error;
      bool parsing = false;

      /* parsing */
      parsing = m_reader.parse(msg, root);

      if(!parsing)
      {
        /* request or batched call is not in JSON format */
        response["id"] = Json::Value::null;
        response["jsonrpc"] = "2.0";

        error["code"] = PARSING_ERROR;
        error["message"] = "Parse error.";
        response["error"] = error; 
        return false;
      }

      if(root.isArray())
      {
        /* batched call */
        size_t i = 0;
        size_t j = 0;

        for(i = 0 ; i < root.size() ; i++)
        {
          Json::Value ret;
          Process(root[i], ret);   //line 208!

          if(ret != Json::Value::null)
          {
            /* it is not a notification, add to array of responses */
            response[j] = ret;   //line 213!
            j++;
          }
        }
        return true;
      }
      else
      {
        return Process(root, response);
      }
    }

    bool Handler::Process(const char* msg, Json::Value& response)
    {
      std::string str(msg);

      return Process(str, response);
    }

    CallbackMethod* Handler::Lookup(const std::string& name) const
    {
      for(std::list<CallbackMethod*>::const_iterator it = m_methods.begin() ; it != m_methods.end() ; it++)
      {
        if((*it)->GetName() == name)
        {
          return (*it);
        }
      }

      return 0;
    }

  } /* namespace Rpc */

} /* namespace Json */

I’m really hoping someone might be able to point me in the right direction.

Many thanks in advance,

---

Edit: Here’s what I did on lines 208 and 213:

Process(root[(Json::Value::ArrayIndex)i], ret); //line 208

response[(Json::Value::ArrayIndex)j] = ret; //line 213

Answer 1

As the operator[] expects either int or Json::Value::ArrayIndex, you should pass one of those instead of a size_t. I guess that ArrayIndex is a signed type, too, or sizeof(size_t)>sizeof(ArrayIndex), so there is no good conversion of size_t to either int or ArrayIndex, therefore it is ambiguous.

Maybe post a suggestion to the developers or find out about the motivation for not using the more idiomatic size_t.