Zeromq package

The zeromq package is part of the Octave Forge project and provides Octave bindings to the ZeroMQ library.

Installation

package requirements

The zeromq package requires the ZeroMQ libraries and include files to be installed in order to compile.

for fedora: yum install zeromq-devel

for ubuntu: apt install libzmq-dev

octave installation

With the ZeroMQ library installed, from octave commmand line:

>> pkg install -forge zeromq

Using it

Load it before any usage:

>> pkg load zeromq

Look at the quick reference for the package:

 >> help zeromq

Differences between C and Octave bindings

The Octave binding is a subset of the C binding of the ZeroMQ library.

Major differences are:

1. The octave binding creates a single zeromq context that is used for all zeromq sockets. In the C bindings, the programmer must create a context and use it during socket creation.

2. only limited zmq_getsockopt and zmq_setsockopt is currently implemented.

3. functions mostly return true or false for whether they succeeded or failed. In the C binding, 0 signified success.

The functions

zmq_bind
         Bind a zeromq socket to a endpoint.

zmq_close
         Close a zeromq socket.

zmq_connect
         Connect a zeromq socket to a endpoint

zmq_errno
         Get system errno value.

zmq_getsockopt
         Get current value of a zeromq socket option.

zmq_poll
         Poll a socket or sockets for a timeout or incoming data
         available.

zmq_recv
         Attempt to read data from a zeromq socket.

zmq_send
         Attempt to send data from a zeromq socket.

zmq_setsockopt
         Set a zeromq socket option.

zmq_strerror
         Get the last zmq error string.

zmq_unbind
         Unbind a previously bound zeromq socket.

zmq_version
         Get the zeromq library version numbers.

Examples

The zeromq package comes with a number of examples included in it. They can be opened in octave using:

 >> edit examples/zmq_example1.m

basic request/reply pattern

Example based on client/server example from http://zguide.zeromq.org/page:all#Ask-and-Ye-Shall-Receive

The client sends a "Hello" to the server which responds back "World". No error checking or data validation is done in the example.

Code: Server code

% zeromq package must be installed and loaded to work pkg load zeromq % dont buffer output more off printf ("Creating hello world server...\n"); % create reply socket, and bind it to port 5555 sock = zmq_socket (ZMQ_REP); zmq_bind (sock, "tcp://*:5555"); printf ("Waiting for clients ...\n"); % loop forever, waiting for client requests and responding back while (true) recievedata = zmq_recv (sock, 10, 0); printf ("Received Hello\n"); zmq_send (sock, "World", 5, 0); endwhile

Code: Client code

% zeromq package must be installed and loaded to work pkg load zeromq % dont buffer output more off printf ("Connecting to hello world server...\n"); % Create socket and connect to server sock = zmq_socket (ZMQ_REQ); zmq_connect (sock, "tcp://localhost:5555"); for request_nbr = [1:10] printf ("Sending Hello %d...\n", request_nbr); zmq_send (sock, uint8("Hello"), 5, 0); % try to read up to 10 bytes of reply data. printf ("Waiting for server response %d... (Ctrl-C to exit)\n", request_nbr); recieved = zmq_recv (sock, 10, 0); printf ("Received World %d\n", request_nbr); endfor zmq_close (sock);

basic publish/subscribe pattern

Example based on client/server example from http://zguide.zeromq.org/page:all#Getting-the-Message-Out

The server pushes 'weather updates' for random zipcodes. The client subscribes to the server just for zipcode 10001.

Code: Server code

% zeromq package must be installed and loaded to work pkg load zeromq % dont buffer output more off publisher = zmq_socket (ZMQ_PUB); rc = zmq_bind (publisher, "tcp://*:5556"); assert (rc); while (true) % Get values that will fool the boss zipcode = 10000 + randi (20); temperature = randi (215) - 80; relhumidity = randi (50) + 10; % Send message to all subscribers update = sprintf ("%05d %d %d", zipcode, temperature, relhumidity); zmq_send (publisher, update); endwhile zmq_close (publisher);

Code: Client code

% zeromq package must be installed and loaded to work pkg load zeromq % dont buffer output more off subscriber = zmq_socket (ZMQ_SUB); rc = zmq_connect (subscriber, "tcp://localhost:5556"); assert (rc); % Subscribe to zipcode, default is NYC, 10001 zipfilter = "10001 "; rc = zmq_setsockopt (subscriber, ZMQ_SUBSCRIBE, zipfilter); assert (rc); % Process 100 updates update_nbr = 0; total_temp = 0; for update_nbr = 1:100 string = char( zmq_recv(subscriber, 128) ); [zipcode, temperature, relhumidity, count, errmsg] = sscanf (string, "%d %d %d", "C"); fprintf ("recieved a temp for zipcode '%s' of %dF\n", ... zipfilter, temperature); total_temp += temperature; endfor fprintf ("Average temperature for zipcode '%s' was %dF\n", ... zipfilter, (total_temp / update_nbr)); zmq_close (subscriber);