msg_lookup.cpp

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#include "rosserial_server/msg_lookup.h"
#include "Python.h"

namespace rosserial_server
{

const MsgInfo lookupMessage(const std::string& message_type, const std::string submodule)
{
  MsgInfo msginfo;
  size_t slash_pos = message_type.find('/');
  if (slash_pos == std::string::npos)
  {
    throw std::runtime_error("Passed message type string does not include a slash character.");
  }
  std::string module_name = message_type.substr(0, slash_pos);
  std::string class_name = message_type.substr(slash_pos + 1, std::string::npos);

  // For now we initialize and finalize for each message. It's quick to do and avoids
  // an initialized Python interpreter hanging around for the duration of the execution.
  Py_Initialize();
  PyObject* module = PyImport_ImportModule((module_name + "." + submodule).c_str());
  if (!module)
  {
    Py_Finalize();
    throw std::runtime_error("Unable to import message module " + module_name + ".");
  }
  PyObject* msg_class = PyObject_GetAttrString(module, class_name.c_str());
  if (!msg_class)
  {
    Py_Finalize();
    throw std::runtime_error("Unable to find message class " + class_name +
                             " in module " + module_name + ".");
  }
  Py_XDECREF(module);

  PyObject* full_text = PyObject_GetAttrString(msg_class, "_full_text");
  PyObject* md5sum = PyObject_GetAttrString(msg_class, "_md5sum");
  if (!md5sum)
  {
    Py_Finalize();
    throw std::runtime_error("Class for message " + message_type + " did not contain" +
                             "expected _md5sum attribute.");
  }
  Py_XDECREF(msg_class);

#if PY_VERSION_HEX > 0x03000000
  if (full_text)
  {
    msginfo.full_text.assign(PyUnicode_AsUTF8(full_text));
  }
  msginfo.md5sum.assign(PyUnicode_AsUTF8(md5sum));
#else
  if (full_text)
  {
    msginfo.full_text.assign(PyString_AsString(full_text));
  }
  msginfo.md5sum.assign(PyString_AsString(md5sum));
#endif

  // See https://github.com/ros/ros_comm/issues/344
  // and https://github.com/ros/gencpp/pull/14
  // Valid full_text returned, but it is empty, so insert single line
  if (full_text && msginfo.full_text.empty())
  {
    msginfo.full_text = "\n";
  }

  Py_XDECREF(full_text);
  Py_XDECREF(md5sum);
  Py_Finalize();

  return msginfo;
}

}  // namespace rosserial_server