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

[Bernardo Augusto García Loaiza]

Hi Thomas,
Thanks for your illustrative response

I'll look Google Protocol Buffers. My sender is from C++ language and my
reception is Python. What sort of installation recommend me you? Binaries
or build protocol buffer along my C++ runtime? or o build protoc binary
from source?

On Wed, Jan 24, 2018 at 8:36 PM Thomas Rodgers <rodgert at twrodgers.com>
wrote:

> You can have a look at Python’s ctypes module, which will let you define a
> ‘struct’ from Python with the same layout as your C++ struct.
>
> You can also investigate any number of serialization libraries that have
> C++ and Python support, eg ProtoBufs or Thrift, or MagPack or whatever.
>
> On Wed, Jan 24, 2018 at 5:26 PM Bernardo Augusto García Loaiza <
> botibagl at gmail.com> wrote:
>
>> Hi, ZMQ people.
>> Greetings.
>>
>>
>> I have a  C++ zeromq client process in which I am sending some data
>> members structures
>>
>> *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
>> {
>> public:
>> SOFA_CLASS(ZMQComponent, sofa::core::behavior::BaseController);
>>
>> ZMQComponent();
>> 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);
>>
>> ZMQComponent::ZMQComponent(){}
>>
>> void ZMQComponent::setupConnection()
>> {
>> cout << "Connecting to python zeroMQ server ..." << endl;
>> socket.connect("tcp://localhost:5555");
>> }
>>
>> 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);
>> socket.send(request);
>> }
>>
>>
>> /* 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;
>> z.setupConnection();
>>
>> instrumentData itemp;
>> z.instrumentDataSend(itemp);
>> }
>>
>> /* Other code related .... */
>> ZMQComponent::~ZMQComponent(){}
>>
>> // int ZeroMqComponentClass = sofa::core::RegisterObject("This component
>> does nothing.").add<ZeroMqComponent>();
>> SOFA_DECL_CLASS(ZMQServerComponent)
>>
>> 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)
>> socket.bind("tcp://*:5555")
>> 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'
>> time.sleep(1)
>>
>> # 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
>> zmq.backend.cython.socket.Socket.recv
>>   File "zmq/backend/cython/socket.pyx", line 727, in
>> zmq.backend.cython.socket.Socket.recv
>>   File "zmq/backend/cython/socket.pyx", line 150, in
>> zmq.backend.cython.socket._recv_copy
>>   File "zmq/backend/cython/socket.pyx", line 145, in
>> zmq.backend.cython.socket._recv_copy
>>   File "zmq/backend/cython/checkrc.pxd", line 25, in
>> zmq.backend.cython.checkrc._check_rc
>> 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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>> zeromq-dev at lists.zeromq.org
>> https://lists.zeromq.org/mailman/listinfo/zeromq-dev
>>
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