"Re-chunking" Stream object in node.js

Question

Pretty simple node.js question. I want to extend the stream object to re-chunk the data that is coming in from a remote connection. I'm doing multiple telnets and sending commands to other servers, and they send back responses. It looks something like this.

> Hello, this is a command

This is the response to the command.
Sometimes it pauses here (which triggers the 'data' event prematurely).

But the message isn't over until you see the semicolon
;

What I'd like to do is instead of triggering the 'data' event at the pause, is wait for the ; and trigger a custom 'message' event.

I've read and reread this question, but I don't quite get it yet (partially because it's about a writable stream, and partially because I don't yet grok CoffeeScript).

EDIT: I guess I'm asking two things here:

How do I extend/inherit the stream object that net.CreateConnection uses?
Can I just extend the prototype.write to do a 'split' and re-'emit' each part?

Here's a snip of what I'm doing so far, but the chunking should be part of the stream, not part of the 'data' listener:

var net = require('net');

var nodes = [
        //list of ip addresses
];

function connectToServer(ip) {
        var conn = net.createConnection(3083, ip);
        conn.on('connect', function() {
                conn.write ("login command;");
        });
        conn.on('data', function(data) {
                var read =  data.toString();

        var message_list = read.split(/^;/m);

        message_list.forEach (function(message) {
                    console.log("Atonomous message from " + ip + ':' + message);
            //I need to extend the stream object to emit these instead of handling it here
            //Also, sometimes the data chunking breaks the messages in two,
                        //but it should really wait for a line beginning with a ; before it emits.
        });

        });
        conn.on('end', function() {
                console.log("Lost conncection to " + ip + "!!");
        });
        conn.on('error', function(err) {
                console.log("Connection error: " + err + " for ip " + ip);
        });
}

nodes.forEach(function(node) {
        connectToServer(node);
});

If I was using a raw stream, I guess it would be something like this (based on code I found elsewhere)?

var messageChunk = function () {
  this.readable = true;
  this.writable = true;
};

require("util").inherits(messageChunk, require("stream"));

messageChunk.prototype._transform = function (data) {

  var regex = /^;/m;
  var cold_storage = '';

  if (regex.test(data))
  {
    var message_list = read.split(/^;/m);

    message_list.forEach (function(message) {
      this.emit("data", message);
    });
  }
  else
  {
    //somehow store the data until data with a /^;/ comes in.
  }
}

messageChunk.prototype.write = function () {
  this._transform.apply(this, arguments);
};

But I'm not using a raw stream, I'm using the stream object in the net.createConnection object returns.

Can you post your code here, maybe? That'll make it much easier to help. — mzedeler
– mzedeler, Commented Mar 23, 2013 at 18:54
How's that? Anyone? I could be going about this the wrong way... — coding_hero
– coding_hero, Commented Apr 2, 2013 at 18:59

Nathan Tuggy · Accepted Answer · 2015-03-18 01:06:36Z

0

Don't use the _transform,_read,_write,or _flush functions you implement directly, those are for the internals of node to use.

Emit a custom event when you see the character ";" in your stream:

var msg = "";
conn.on("data",function(data)  {
  var chunk = data.toString();
  msg += chunk;
  if(chunk.search(";") != -1)  {
    conn.emit("customEvent",msg);
    msg = "";
  }
});
conn.on("customEvent",function(msg)  {
  //do something with your message
});

edited Mar 18, 2015 at 1:06

Nathan Tuggy

2,23727 gold badges33 silver badges38 bronze badges

answered Mar 18, 2015 at 0:44

riatzukiza

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