CODEWITHSUNDEEP
javascriptnode.jssocketstcp
flosse
flosse

Reputation: 3

Node.js is unable to handle multiple tcp messages

Here is a simple TCP-Server stress test. As long as we send only one message per client everything works as expected. But when two messages per client are send, the server suddenly stops without an exception or error. So is this a bug or a feature?

var net = require("net");
var async = require("async");
var cluster = require("cluster");

// `ulimit -n` tells us that we can open max. 1024 files per process.
//  Creating a socket means opening a file so we are limited.
var CLIENTS = 1000;

// Here is the weird part:
// - sending one message per client works fine
// - sending multiple message per client sucks
var MESSAGES = 2;

var TOTAL = CLIENTS * MESSAGES;
var PORT = 1234;
var HOST = "127.0.0.1";

if (cluster.isMaster) {
  var count = 0;
  var start = new Date;

  var server = net.createServer(function(socket) {
    socket.on("data", function(data) {
      var t;
      count++;
      console.log("server received " + count + " messages");
      socket.write(data, function(err) { if (err) console.error(err); });
      if (count === TOTAL) {
        t = (new Date) - start;
        console.log("server received and sent " + count + " messages within " + t + "ms");
      }
    });
  });

  server.listen(PORT, HOST, function() { cluster.fork(); });

} else {

  var run = function(i) {
    var c = net.connect({ port: PORT, host: HOST }, function() {
      var tasks = (function() {
        var results = [];
        for (var x = 1; x <= MESSAGES; ++x) {
          results.push((function(x) {
            return function(next) { c.write("Hello server!", next); };
          })(x));
        }
        return results;
      })();

      async.series(tasks, function(err) {
        if (err) { console.error(err); }
      });

    });
  };
  for (var i = 1; i <= CLIENTS; ++i) { run(i); }
}

Tested on Linux 3.11, Node.js 0.10.21

Upvotes: 0

Views: 1306

Answers (1)

robertklep
robertklep

Reputation: 203304

You're assuming that calling .write twice from a client triggers the data event twice on the server, not taking into account any buffering that might be going on which will coalecse multiple writes.

When the callback to .write is called, it doesn't mean the message it actually sent, it means that the message is put in some kernel buffer (which might contain more than one message when it's sent to the server).

Upvotes: 2

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