[zeromq-dev] Communication between C++ zmq client and Python zmq Server

Bernardo Augusto García Loaiza botibagl at gmail.com
Thu Jan 25 00:26:28 CET 2018

Hi, ZMQ people.

I have a  C++ zeromq client process in which I am sending some data members

*ZMQComponent.h* file

#include <zmq.hpp>
#include <sofa/defaulttype/VecTypes.h>

// To Quat datatype
#include <sofa/defaulttype/Quat.h>
using sofa::defaulttype::Quat;

using std::string;

namespace sofa

namespace component

namespace controller

/* data structure which I want send data to python zmq server */
struct instrumentData
typedef sofa::defaulttype::Vec3d Vec3d;
Vec3d pos;
Quat quat;
int btnState;
float openInst;
bool blnDataReady;

class ZMQComponent : public sofa::core::behavior::BaseController
SOFA_CLASS(ZMQComponent, sofa::core::behavior::BaseController);

virtual ~ZMQComponent();
/* Conect to ZMQ external python Server */
void setupConnection();

/* Send some data memeber instrumentData structure to ZMQ external Server */
void instrumentDataSend(instrumentData a);

/* initialize function */
void init();


} // namespace sofa

} // namespace component

} // namespace controller

The *ZMQComponent.cpp* is:

#include <sofa/core/ObjectFactory.h>
#include <zmq.hpp>
#include <iostream>
#include <string>
#include "ZMQComponent.h"

using namespace std;

namespace sofa

namespace component

namespace controller

/* ZMQ Internal Client context and socket */
zmq::context_t context(1);
zmq::socket_t socket(context, ZMQ_REQ);


void ZMQComponent::setupConnection()
cout << "Connecting to python zeroMQ server ..." << endl;

void ZMQComponent::instrumentDataSend(instrumentData a)
/* Initialize the data members structure instrumentData */
a.pos = sofa::defaulttype::Vec3d(1.0f, 1.0f, 1.0f);
a.quat = defaulttype::Quat(1.0f, 1.0f, 4.0f, 1.0f);
a.btnState = 5671;
a.openInst = 1.0f;
a.blnDataReady = false;

/* We send the btnState data */
zmq::message_t request(10);
cout << "The data are: " << a.btnState;

/* We ask for the memory address to ge the btnState content and send it. */
memcpy(request.data(), &a.btnState, 10);

/* In the init function we create the objects to setup connection and send
data */
void ZMQComponent::init()
std::cout << "ZeroMQCommunication::init()" << std::endl;
ZMQComponent z;

instrumentData itemp;

/* Other code related .... */

// int ZeroMqComponentClass = sofa::core::RegisterObject("This component
does nothing.").add<ZeroMqComponent>();

int ZMQServerComponentClass = sofa::core::RegisterObject("This component
create a Socket.").add< ZMQServerComponent >();
} // namespace controller

} // namespace component

} // namespace sofa

Then , my python zmq server  which receive the *btnState*  int variable is:

import time
import zmq

context = zmq.Context()
socket = context.socket(zmq.REP)
print('ZMQ Server listening ... ')

while True:
# Wait for next request from client
message = socket.recv()
print("Received message from Sofa: {}".format(message))
# print("Received message from c++ %s" % message)

# Do some 'work'

# Send reply back to client
# socket.send(b"Hola cliente, muy bien y tu ?")
# print('Response sent')

The output or the message which arrive to python zmq server is the symbols
characters of the btnState:

(cnvss_test) ➜  Python git:(ZMQCommunication) ✗ python server.py
ZMQ Server listening ...
*Received message from Sofa: b"\x00'\x84)\xff\x7f\x00\x00\x98&*"

Likely, As I in my python server I am representing like  a string message
arrived and I am sending from my c++ client a int btnState data,
then I try convert int to string in  the python server side:

And I replace this line

print("Received message from Sofa: {}".format(message))

by thiis line

print("Received message from c++ %s" % str(message))

But my output is:

(cnvss_test) ➜  Python git:(ZMQCommunication) ✗ python server.py
ZMQ Server listening ...
*Received message from c++ b'\x00^n&\xff\x7f\x00\x00\xd8\\'*
Traceback (most recent call last):
  File "server.py", line 19, in <module>
    message = socket.recv()
  File "zmq/backend/cython/socket.pyx", line 693, in
  File "zmq/backend/cython/socket.pyx", line 727, in
  File "zmq/backend/cython/socket.pyx", line 150, in
  File "zmq/backend/cython/socket.pyx", line 145, in
  File "zmq/backend/cython/checkrc.pxd", line 25, in
zmq.error.ZMQError: Operation cannot be accomplished in current state
(cnvss_test) ➜  Python git:(ZMQCommunication) ✗

I follow getting the characters symbolss.
My question is: How to can I represent the arrived message in my python zmq
server to show their content ?
According to this behavior, can I assume that the btnState data is sent to
python server of anyway?

Any support or orientation will be highly appreciated
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