Today, after a long wait is part 4 of the node.js and ZeroMQ series. This part is about XRequest and XReply sockets also called XREQ and XREP sockets.

There isn't a lot of documentation about this. As I understand it, these socket types allow you to asynchronously implement the request response pattern. Pretty much like REQ/REP actually, but I've found XREQ/XREP to be more stable.

Without further ado, here's xrequestxreplyclient.js:

var zeromq = require("zeromq");

var counter = 0;
var socket = zeromq.createSocket('xrequest');
socket.identity = "client";

socket.connect("tcp://127.0.0.1:5502");
console.log("Connected to port 5502!");

setInterval(function(){
  var value = Math.floor(Math.random()*100);
  socket.send('', ''+value);
}, 10);

socket.on('message', function(data) {
  console.log("Answer data: "+data);
  counter += 1;
});

socket.on('error', function(error) {
  console.log("Error: "+error);
});

Here's xrequestxreplyserver.js:

var zeromq = require("zeromq");

var socket = zeromq.createSocket('xreply');
socket.identity = "server";

socket.bind("tcp://127.0.0.1:5502", function(err) {
  if (err) throw err;
  console.log("bound!");

  socket.on('message', function(envelope, blank, data) {
    console.log("Received: "+envelope+" - "+data.toString('utf8'));
    socket.send(envelope, ''+data*2);
  });

  socket.on('error', function(err) {
    console.log("Error: "+err);
  });
});

Here again the server part is actually a value duplication service (times two service).