ZeroMQ-Octave

This section will use ZeroMQ in Octave for simple message passing, including examples of Request/Reply and Publish/Subscribe patterns.

Installing ZeroMQ

If Octave is installed on a Windows system, the zeromq package should generally be installed as well. You can confirm this by using the following command in Octave:

>> pkg list

Check the list to see if zeromq is included. If not, consider reinstalling Octave.

For Ubuntu users, you can follow these steps to install:

1. Install libzmq-dev

apt install libzmq-dev

2. Install the ZeroMQ package in Octave:

pkg install -forge zeromq

Using ZeroMQ

Before using ZeroMQ in Octave, you need to load it first:

pkg load zeromq

You can use the help zeromq command to see available functions and usage instructions.

Basic Request/Reply Pattern

Server-Side Code

pkg load zeromq % Load the zeromq library
more off % Turn off paging of output
printf("Creating hello world server...\n");
sock = zmq_socket(ZMQ_REP); % Create Reply port
zmq_bind(sock, "tcp://*:5555"); % Listen on port 5555 on all network interfaces
printf("Waiting for clients ...\n");

while (true)
  recievedata = zmq_recv(sock, 10); % Receive messages of up to ten bytes
  printf("Received %s\n", recievedata); % Print the received message
  zmq_send(sock, "World", 5); % Respond with World
endwhile

zmq_close(sock);

Client-Side Code

pkg load zeromq % Load the zeromq library
more off % Turn off paging of output
printf("Connecting to hello world server...\n");
sock = zmq_socket(ZMQ_REQ); % Create Request port
zmq_connect(sock, "tcp://localhost:5555"); % Connect to port 5555 on localhost

for request_nbr = 1:10
  printf("Sending Hello %d...\n", request_nbr);
  zmq_send(sock, uint8("Hello"), 5); % Send Hello
  printf("Waiting for server response %d... (Ctrl-C to exit)\n", request_nbr);
  recieved = zmq_recv(sock, 10); % Receive messages of up to ten bytes
  printf("Received %d = %s\n", request_nbr, recieved);
endfor

zmq_close(sock);

Basic Publish/Subscribe Pattern

Server-Side Code

pkg load zeromq % Load the zeromq library
more off % Turn off paging of output
publisher = zmq_socket(ZMQ_PUB); % Create Publish port
zmq_bind(publisher, "tcp://*:5556"); % Listen on port 5556 on localhost

while (true)
  dice_number = randi(6); % Select a random integer between 1 and 6
  data = sprintf("Dice %d", dice_number); % Prepare data to send
  zmq_send(publisher, data); % Publish the dice number message
  data = sprintf("Score %d", randi(100)); % Prepare data to send
  zmq_send(publisher, data); % Publish the score message
endwhile

zmq_close(publisher);

Client-Side Code

pkg load zeromq % Load the zeromq library
more off % Turn off paging of output
subscriber = zmq_socket(ZMQ_SUB); % Create Subscribe port
zmq_connect(subscriber, "tcp://localhost:5556"); % Connect to port 5556 on localhost
msgfilter = "Dice"; % Message prefix filter
zmq_setsockopt(subscriber, ZMQ_SUBSCRIBE, msgfilter); % Set the filter

total = 0;
printf("Receiving 100 dice numbers...\n");
for update_nbr = 1:100
  string = char(zmq_recv(subscriber, 128)); % Convert received message to string
  [prefix, number] = sscanf (string, "%s %d", "C"); % Read the prefix string and number using C format
  printf(" %d", number); % Print the number
  total += number; % Calculate the total
endfor
printf("\n\nAverage = %.2f\n", total/100.0); % Print the average dice number

%fprintf("Average temperature for zipcode '%s' was %dF\n", zipfilter, (total_temp / update_nbr));
zmq_close(subscriber);

The above demonstrates how to perform basic message passing using ZeroMQ in Octave.

Exercise 1

1. Implement the sample programs in Octave.
2. In the second example, publish several different types of messages and try subscribing to different types of messages in the client, then process the received messages.
3. Modify the connection to allow communication between different computers.