How to get a count of the current open sockets in Node?

Question

I am using the request module to crawl a list of URLs and would like to limit the number of open sockets to 2:

var req = request.defaults({
   forever: true,
   pool: {maxSockets: 1}
});

req(options, function(error, response, body) {

 ... code ...

 done();

however, when looping over an array of URLs and issuing a new request to each - that does not seem to work.

is there a way to get the current number of open sockets to test it?

Answer 1

I believe that maxSockets maps to http.Agent.maxSockets, which limits the number of concurrent requests to the same origin (host:port).

This comment, from the developer of request, suggests the same:

actually, pooling controls the agent passed to core. each agent holds all hosts and throttles the maxSockets per host

In other words, you can't use it to limit the number of concurrent requests in general. For that, you need to use an external solution, for instance using limiter or async.queue.