ZMQ messages not being received - c++

Question

Please forgive me if I'm missing something simple, this is my first time doing anything with messaging and I inherited this codebase from someone else.
I am trying to send a message from a windows machine with an IP of 10.10.10.200 to an Ubuntu machine with an IP of 10.10.10.15.
I got the following result when running TCPView from the Windows machine, which makes me suspect that the problem lies in the Ubuntu machine. If I'm reading that right, then my app on the windows machine has created a connection on port 5556 which is what it is supposed to do. In case I'm wrong, I'll include the windows code too.
my_app.exe 5436 TCP MY_COMPUTER 5556 MY_COMPUTER 0 LISTENING
Windows app code:
void
NetworkManager::initializePublisher()
{
globalContext = zmq_ctx_new();
globalPublisher = zmq_socket(globalContext, ZMQ_PUB);
string protocol = "tcp://*:";
string portNumber = PUBLISHING_PORT; //5556
string address = protocol + portNumber;
char *address_ptr = new char[address.size() + 1];
strncpy_s(address_ptr, address.size() + 1, address.c_str(), address.size());
int bind_res = zmq_bind(globalPublisher, address_ptr);
if (bind_res != 0)
{
cerr << "FATAL: couldn't bind to port[" << portNumber << "] and protocol [" << protocol << "]" << endl;
}
cout << " Connection: " << address << endl;
}
void
NetworkManager::publishMessage(MESSAGE msgToSend)
{
// Get the size of the message to be sent
int sizeOfMessageToSend = MSG_MAX_SIZE;//sizeof(msgToSend);
// Copy IDVS message to buffer
char buffToSend[MSG_MAX_SIZE] = "";
// Pack the message id
size_t indexOfId = MSG_ID_SIZE + 1;
size_t indexOfName = MSG_NAME_SIZE + 1;
size_t indexOfdata = MSG_DATABUFFER_SIZE + 1;
memcpy(buffToSend, msgToSend.get_msg_id(), indexOfId - 1);
// Pack the message name
memcpy(buffToSend + indexOfId, msgToSend.get_msg_name(), indexOfName - 1);
// Pack the data buffer
memcpy(buffToSend + indexOfId + indexOfName, msgToSend.get_msg_data(), indexOfdata - 1);
// Send message
int sizeOfSentMessage = zmq_send(globalPublisher, buffToSend, MSG_MAX_SIZE, ZMQ_DONTWAIT);
getSubscriptionConnectionError();
// If message size doesn't match, we have an issue, otherwise, we are good
if (sizeOfSentMessage != sizeOfMessageToSend)
{
int errorCode = zmq_errno();
cerr << "FATAL: couldn't not send message." << endl;
cerr << "ERROR: " << errorCode << endl;
}
}
I can include more of this side's code if you think it's needed, but the error is popping up on the Ubuntu side, so I'm going to focus there.
The problem is when I call zmq_recv it returns -1 and when I check zmq_errno I get EAGAIN (Non-blocking mode was requested and no messages are available at the moment.) I also checked with netstat and I didn't see anything on port 5556
First is the function to connect to the publisher, then the function to get data, followed by main.
Ubuntu side code:
void
*connectoToPublisher()
{
void *context = zmq_ctx_new();
void *subscriber = zmq_socket(context, ZMQ_SUB);
string protocol = "tcp://";
string ipAddress = PUB_IP; //10.10.10.15
string portNumber = PUB_PORT; // 5556
string address = protocol + ipAddress + ":" + portNumber;
cout << "Address: " << address << endl;
char *address_ptr = new char[address.size() + 1];
strcpy(address_ptr, address.c_str());
// ------ Connect to Publisher ------
bool isConnectionEstablished = false;
int connectionStatus;
while (isConnectionEstablished == false)
{
connectionStatus = zmq_connect(subscriber, address_ptr);
switch (connectionStatus)
{
case 0: //we are good.
cout << "Connection Established!" << endl;
isConnectionEstablished = true;
break;
case -1:
isConnectionEstablished = false;
cout << "Connection Failed!" << endl;
getSubscriptionConnectionError();
cout << "Trying again in 5 seconds..." << endl;
break;
default:
cout << "Hit default connecting to publisher!" << endl;
break;
}
if (isConnectionEstablished == true)
{
break;
}
sleep(5); // Try again
}
// by the time we get here we should have connected to the pub
return subscriber;
}
static void *
getData(void *subscriber)
{
const char *filter = ""; // Get all messages
int subFilterResult = zmq_setsockopt(subscriber, ZMQ_SUBSCRIBE, filter, strlen(filter));
// ------ Get in main loop ------
while (1)
{
//get messages from publisher
char bufferReceived[MSG_MAX_SIZE] = "";
size_t expected_messageSize = sizeof(bufferReceived);
int actual_messageSize = zmq_recv(subscriber, bufferReceived, MSG_MAX_SIZE, ZMQ_DONTWAIT);
if (expected_messageSize == actual_messageSize)
{
MESSAGE msg = getMessage(bufferReceived); //Uses memcpy to copy id, name, and data strutct data from buffer into struct of MESSAGE
if (strcmp(msg.get_msg_id(), "IDXY_00000") == 0)
{
DATA = getData(msg); //Uses memcpy to copy data from buffer into struct of DATA
}
} else
{
// Something went wrong
getReceivedError(); //This just calls zmq_errno and cout the error
}
usleep(1);
}
}
int main (int argc, char*argv[])
{
//Doing some stuff...
void *subscriber_socket = connectoToHeadTrackerPublisher();
// Initialize Mux Lock
pthread_mutex_init(&receiverMutex, NULL);
// Initializing some variables...
// Launch Thread to get updates from windows machine
pthread_t publisherThread;
pthread_create(&publisherThread,
NULL, getData, subscriber_socket);
// UI stuff
zmq_close(subscriber_socket);
return 0;
}
If you cannot provide a solution, then I will accept identifying the problem as a solution. My main issue is that I don't have the knowledge or experience with messaging or networking to correctly identify the issue. Typically if I know what is wrong, I can fix it.

Answer 1

Ok, this has nothing to do with signalling / messaging framework
Your Ubuntu code instructs the ZeroMQ Context()-instance engine to create a new SUB-socket instance and next the code insist this socket to try to _connect() ( to setup a tcp:// transport-class connection towards the peering counterparty ) to "opposite" access-point, sitting on an address of the Ubuntu localhost:port# that was setup as 10.10.10.15:5556, while the intended PUB-side archetype access-point actually lives not on this Ubuntu machine, but on another, Windows host, IP:port# of which is 10.10.10.200:5556
This seems to be the root-cause of the problem, so change it accordingly to match the physical layout and you may get the toys work.