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Zeromq package

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

Contents

InstallationEdit

package requirementsEdit

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 installationEdit

With the ZeroMQ library installed, from octave commmand line:

>> pkg install -forge zeromq

Using itEdit

Load it before any usage:

>> pkg load zeromq

Look at the quick reference for the package:

 >> help zeromq

Differences between C and Octave bindingsEdit

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 functionsEdit

iszmq
         Determine whether H is a zeromq socket object.
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_curve_keypair
         Generate a random private/public keypair
zmq_curve_public
         Derive the public key from a private key
zmq_disconnect
         Disconnect a zeromq socket from an endpoint.
zmq_errno
         Get system errno value.
zmq_getsockopt
         Get current value of a zeromq socket option.
zmq_has
         Check if the zmq library supports a given feature.
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_socket
         Create a zeromq socket.
zmq_strerror
         Get the last zmq error string.
zmq_unbind
         Unbind a previously bound zeromq socket.
zmq_version
         Get the zeromq library version numbers.
zmq_z85_decode
         Decode a z85 encoded string to a binary key.
zmq_z85_encode
         Encode a binary key as Z85 printable text.

ExamplesEdit

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 patternEdit

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 patternEdit

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);