ZMQ C++ Req to Router issues - c++

Question

I am using ZeroMQ for my network layer and so far everything works except when it comes to ROUTER sockets. In particular I receive the expected message on the ROUTER but when I try send an answer back to my REQ socket the message is never received.
Here is a relatively simple test I wrote which tries to send a "HELLO" message to the ROUTER and expects a message to come back.
here the client code :
try
{
zmq::context_t myContext;
zmq::socket_t reqSocket(myContext, ZMQ_REQ);
reqSocket.setsockopt(ZMQ_IDENTITY, "REQ", 3);
reqSocket.connect(gpRouterAddress);
//request delimiter
zmq::message_t zmqMsgReqDelimiter(1);
memcpy ((void *) zmqMsgReqDelimiter.data(), "\0", 1);
reqSocket.send(zmqMsgReqDelimiter, ZMQ_SNDMORE);
//some message
zmq::message_t reqMsg(5);
memcpy ((void *) reqMsg.data(), "HELLO", 5);
reqSocket.send(reqMsg, 0);
int rcvMore = 0;
size_t sizeInt = sizeof(int);
bool bRcvMore = true;
std::vector<std::string> history;
while(bRcvMore)
{
zmq::message_t zmqMsg;
reqSocket.recv(&zmqMsg, rcvMore);
const char* pMsgStr = static_cast<char*>(zmqMsg.data());
history.push_back(pMsgStr);
reqSocket.getsockopt(ZMQ_RCVMORE, &rcvMore, &sizeInt);
bRcvMore = (rcvMore == 1);
}
}
catch (zmq::error_t error)
{
std::string errorStr = error.what();
}
and here is my Router code (can run in a different thread , in which case theContext would be the same as "myContext" from the code above) or a entirely different application :
try
{
zmq::context_t theContext;
zmq::socket_t router (theContext, ZMQ_ROUTER);
int value = 1;
router.setsockopt(ZMQ_ROUTER_MANDATORY, &value, sizeof(int));
router.setsockopt(ZMQ_IDENTITY, "ROUT", 4);
router.bind(gpRouterAddress);
zmq::message_t zmqMsgInternalAddress;
router.recv(&zmqMsgInternalAddress, 0);
const char* pAddressStr = static_cast<char*>(zmqMsgInternalAddress.data());
zmq::message_t zmqMsgDelimiter;
router.recv(&zmqMsgDelimiter, ZMQ_RCVMORE);
const char* pDelimiterStr = static_cast<char*>(zmqMsgDelimiter.data());
int rcvMore = 0;
size_t sizeInt = sizeof(int);
bool bRcvMore = true;
router.getsockopt(ZMQ_RCVMORE, &rcvMore, &sizeInt);
bRcvMore = (rcvMore == 1);
std::vector<std::string> history;
while(bRcvMore)
{
zmq::message_t zmqMsg;
router.recv(&zmqMsg, rcvMore);
const char* pMsgStr = static_cast<char*>(zmqMsg.data());
history.push_back(pMsgStr);
router.getsockopt(ZMQ_RCVMORE, &rcvMore, &sizeInt);
bRcvMore = (rcvMore == 1);
}
//reply address
size_t len = strlen(pAddressStr) - 1; //if I don't subtract 1 char here, an exception will be raised
zmq::message_t replyAddress(len);
memcpy ((void *) replyAddress.data(), pAddressStr, len);
router.send(replyAddress, ZMQ_SNDMORE);
//reply delimiter
zmq::message_t zmqMsgReplyDelimiter(1);
memcpy ((void *) zmqMsgReplyDelimiter.data(), "\0", 1);
router.send(zmqMsgReplyDelimiter, ZMQ_SNDMORE);
//some message
zmq::message_t replyMsg(5);
memcpy ((void *) replyMsg.data(), "WORLD", 5);
router.send(replyMsg, 0);
}
catch (zmq::error_t error)
{
std::string errorStr = error.what();
}
I receive the "HELLO" message on the router and I can step through the ROUTER send and everything seems to be sent okay (i.e. no exception is being raised) but I never receive a message on the REQ socket which will keep waiting indefinitely.
According to the ZeroMQ Guide I should expect the ROUTER to receive the following messages :
The REQ socket sends
empty
HELLO
the ROUTER receives
REQ
empty
HELLO
but I receive
REQ
some binary message
empty
HELLO
and I send
REQ
empty
WORLD
which I would expect to arrive at REQ as
empty
WORLD
If I connect to a REP socket instead (using a simple REQ-REP topology everything works fine).
Can anyone see what I am missing/doing wrong?

Answer 1

I found the issue.
Basically the error was in how I sent the delimiter
zmq::message_t zmqMsgReplyDelimiter(1);
memcpy ((void *) zmqMsgReplyDelimiter.data(), "\0", 1);
router.send(zmqMsgReplyDelimiter, ZMQ_SNDMORE);
it should just be
zmq::message_t zmqMsgReplyDelimiter(0);
router.send(zmqMsgReplyDelimiter, ZMQ_SNDMORE);