Question

I just started playing with node.js and the zeromq bindings today and am seeing some behavior that I don’t quite understand.

Here’s my sample code which calls to another ruby based zeromq REP process on port 9000 on the same machine:

var zeromq = require("zmq");
var http = require('http');

var counter = 0;

var availabilityResponse = function(counter, data, request, response) {
    var str = data.toString('utf-8');
    console.log(str);
    response.writeHead(200, {'Content-Type': 'text/plain'});
    response.write(str);
    response.end();                 
}

var zmqSocket = zeromq.createSocket('request');
zmqSocket.connect("tcp://127.0.0.1:9000");


var server = http.createServer()
server.on('request', function(request, response) {
    counter += 1;
    zmqSocket.send("Hola! - This is call # " + counter);
    zmqSocket.on('message', function(data) {
        availabilityResponse(counter, data, request, response);
    });

});
server.listen(8888);
console.log("Starting HTTP server on port 8888");

I’m hitting the node server using my browser and waiting for a response. What is strange is that the output I get in the console is coming across in an additive manner which I’m not grokking:

Request received: Hola! - This is call # 1 - Now going to sleep for 1.0

Request received: Hola! - This is call # 2 - Now going to sleep for 3.0
Request received: Hola! - This is call # 2 - Now going to sleep for 3.0

Request received: Hola! - This is call # 3 - Now going to sleep for 3.0
Request received: Hola! - This is call # 3 - Now going to sleep for 3.0
Request received: Hola! - This is call # 3 - Now going to sleep for 3.0

Request received: Hola! - This is call # 4 - Now going to sleep for 2.0
Request received: Hola! - This is call # 4 - Now going to sleep for 2.0
Request received: Hola! - This is call # 4 - Now going to sleep for 2.0
Request received: Hola! - This is call # 4 - Now going to sleep for 2.0

I tried moving the zmqSocket.on() call outside of the http request block which removes the additive behavior but it also doesn’t then include the request/response objects that I need.

The point of this exercise is to have the browser wait until the response comes back from the long running zeromq server process on port 9000 (currently just a faked up sleep response).

I’m pretty sure I’m just misunderstanding the callback here but can’t find much in the way of documentation on this scenario.

Thanks for any help.

Answer 1

You are rebinding your zmqSocket.on(‘message’, function(data) { event everytime an incoming request comes in. This is causing multiple event binds, move that block of code outside your request handler.