[zeromq-dev] Communication between C++ zmq client and Python zmq Server
Luca Boccassi
luca.boccassi at gmail.com
Sat Jan 27 16:07:19 CET 2018
Yes you can just send unstructured binary data or strings - Python has
native helpers for strings, and CZMQ as well
On Fri, 2018-01-26 at 21:27 -0500, Bernardo Augusto García Loaiza
wrote:
> Thomas, I understand perfectly your explanation. But I want share
> with you
> another similar case, just for curiosity or to receive some
> additional
> orientation about it.
>
> I have a script client C++ ZEROMQ as a documentation, and I have
> script
> server python, together based in the documentation zeromq website.
> This mean, together are scripts basics
>
> From C++ client I am sending the string message
> <https://github.com/bgarcial/zeroMQ_Client/blob/master/client.cpp#L27
> > and
> I have a python server which receive this string message client
> <https://github.com/bgarcial/zeroMQ_Client/blob/master/Python/server.
> py#L20>
> of a direct way and show me their content
>
> In this basic sample (documentation zmq based) I am not
> using structures
> data members. Is for this reason that in this case I receive and I
> can see
> the content of the client message in the zmq server side without have
> use
> something like Google Protocol Buffer, This mean, is because in this
> case I
> am not sending any structures data members?
>
> I appreciate one more your orientation
>
>
> Bernardo Augusto García Loaiza
> Ingeniero de Sistemas
> Estudiante de Maestría en Ingeniería Informática - Universidad EAFIT
> http://about.me/bgarcial
>
>
> On Fri, Jan 26, 2018 at 7:44 AM, Thomas Rodgers <rodgert at twrodgers.co
> m>
> wrote:
>
> > Short answer yes, it’s related to different languages. TCP and
> > ZeroMQ only
> > deal with transport and framing of messages (respectively) Python
> > has no
> > idea that that 10 bytes corresponds to a C/C++ struct of a given
> > layout
> > until you tell it. Different platforms (CPU architectures) have
> > potentially
> > different representations of fundamental types.
> >
> > On Thu, Jan 25, 2018 at 4:37 PM Bernardo Augusto García Loaiza <
> > botibagl at gmail.com> wrote:
> >
> > > One more question. Why is necessary the serialization process? It
> > > is
> > > assumed that zeromq works via TCP and in the TCP protocol, the
> > > data does
> > > not undergo any transformation? This is related with the fact of
> > > that I
> > > have different platform/languages?
> > >
> > > On Thu, Jan 25, 2018 at 4:45 PM Bernardo Augusto García Loaiza <
> > > botibagl at gmail.com> wrote:
> > >
> > > > 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 twrodge
> > > > rs.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
> > > > > >
> > > > > >
> > > > > >
> > > > > >
> > > > > > _______________________________________________
> > > > > > zeromq-dev mailing list
> > > > > > zeromq-dev at lists.zeromq.org
> > > > > > https://lists.zeromq.org/mailman/listinfo/zeromq-dev
> > > > > >
> > > > >
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> > > > >
> > > >
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> > >
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> > >
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--
Kind regards,
Luca Boccassi
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