append-file-2.js

var vertx = require("vertx");
var console = require("vertx/console");
var eb = require('vertx/event_bus');
var fs = vertx.fileSystem;

var path = "data.log";

registerAppend = function() {
  var unwrittenBytes = 0;
  fs.open(path, fs.OPEN_WRITE | fs.CREATE_NEW, true, function(err, asyncFile) {
    if (!err) {
      eb.registerHandler(
      "append", 
      function(msg) {
        var buff = new vertx.Buffer(java.util.Calendar.getInstance().getTimeInMillis() + "\n");
        fs.props(path, function(err, props) {
          if (!err) {
            asyncFile.write(buff, props.size + unwrittenBytes, function(err) {
              if (!err) {
                unwrittenBytes -= buff.length();
              } else {
                console.log("Failed to write file: " + err);
              }
            });
            unwrittenBytes += buff.length();
          } else {
            console.log("Failed to retrieve file props: " + err);
          }
        });
      }, 
      function() {
        for (var i = 0; i < 1000; i++) {
          eb.publish("append");
        }
      });
    } else {
      console.error("Failed to open file: " + path, err);
    }
  });
};

fs.exists(path, function(err, exists) {
  if (!err) {
    if (exists) {
      registerAppend();
    } else {
      fs.createFile(path, function(err) {
        if (!err) {
          registerAppend();
        } else {
          console.log("Failed to create file: " + err);
        }
      });
    }
  } else {
    console.log("Failed to check file existence: " + err);
  }
});