xmlrpc_helpers.h

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#ifndef XMLRPCHELPERS_H
#define XMLRPCHELPERS_H

#include <sstream>
#include <ros/ros.h>

namespace xh
{

  class XmlrpcHelperException : public ros::Exception
  {
  public:
    XmlrpcHelperException(const std::string& what)
      : ros::Exception(what) {}
  };

  typedef XmlRpc::XmlRpcValue Struct;
  typedef XmlRpc::XmlRpcValue Array;

  template <class T>
  void perform_cast(XmlRpc::XmlRpcValue val, T& output)
  {
    output = static_cast<T>(val);
    return;
  }

  // this is to allow integers to be silently converted to doubles
  template <>
  inline void perform_cast<double>(XmlRpc::XmlRpcValue val, double& output)
  {
    if (val.getType() == XmlRpc::XmlRpcValue::TypeInt)
    {
      output = static_cast<double>(static_cast<int>(val));
    }
    else
    {
      output = static_cast<double>(val);
    }
  }

  template <class T>
  void fetchParam(ros::NodeHandle nh, const std::string& param_name, T& output)
  {
    XmlRpc::XmlRpcValue val;
    bool ok = false;
    try
    {
      ok = nh.getParamCached(param_name, val);
    }
    catch(const ros::InvalidNameException& e) {}

    if (!ok)
    {
      std::ostringstream err_msg;
      err_msg << "could not load parameter '" << param_name << "'. (namespace: "
              << nh.getNamespace() << ")";
      throw XmlrpcHelperException(err_msg.str());
    }

    perform_cast(val, output);
  }

  inline void checkArrayItem(const Array& col, int index)
  {
    if (col.getType() != XmlRpc::XmlRpcValue::TypeArray)
      throw XmlrpcHelperException("not an array");
    if(index >= col.size())
    {
      std::ostringstream err_msg;
      err_msg << "index '" << index << "' is over array capacity";
      throw XmlrpcHelperException(err_msg.str());
    }
  }

  inline void checkStructMember(const Struct& col, const std::string& member)
  {
    if (col.getType() != XmlRpc::XmlRpcValue::TypeStruct)
      throw XmlrpcHelperException("not a struct");
    if (!col.hasMember(member))
    {
      std::ostringstream err_msg;
      err_msg << "could not find member '" << member << "'";
      throw XmlrpcHelperException(err_msg.str());
    }
  }

  template <class T>
  void getArrayItem(Array& col, int index, T& output) // XXX: XmlRpcValue::operator[] is not const
  {
    checkArrayItem(col, index);
    perform_cast(col[index], output);
  }

  template <class T>
  void getStructMember(Struct& col, const std::string& member, T& output)
  {
    checkStructMember(col, member);
    perform_cast(col[member], output);
  }

}

#endif